Chapter 23 Digestive System

feedback mechanisms regulating chyme entry

enterogastric refelx and enterogastrones; the same as those that decrease gastric secretion

fructose

enters the cells by facilitated diffusion

brush border enzymes

enzymes associated with the microvilli of the SI mucosal cells; perform the final digestion of food into the simple components that can be absorbed by intestinal cells; are not secreted; they remain bound to the brush border plasma membranes

one organ of the alimentary canal found in the thorax

esophagus

functional significance of the epithelial change seen at the esophagus-stomach junction?

esophagus is a mere chute for food passage and is subjected to good deal of abrasion, so stratified squamous epithelium is good; the stomach mucosa is a secretory mucosa served well by a simple columnar epithelium

the splanchnic circulation

includes those arteries that branch off the abdominal aorta to serve the digestive organs and the hepatic portal circulation; the arterial supply -- the branches of the celiac trunk that serve the spleen, liver and stomach, and the mesenteric arteries that serve the small and large intestines -- normally receives one-quarter of the cardiac output; percentage increases after a meal

mucosa

innermost layer of the alimentary canal; a moist epithelial membrane that lines the canal lumen from mouth to anus; consists of three sublayers: a lining epithelium, a lamina propria, and a muscularis mucosae; in the stomach and small intestine, it also contains both enzyme-synthesizing and hormone-secreting cells; in such sites, the mucosa is a diffuse endocrine organ as well as pat of the digestive organ

the submucosal and myenteric nerve plexuses

interconnect like chicken wire all along the GI tract and regulated digestive activity throughout its length; enteric neurons of both provide the major nerve supply to the GI tract wall and control GI tract motility (motion);

metabolic functions of bacterial flora

fermentation: ferment some of the indigestible carbs and mucin in gut mucus; resulting in short-chain fatty acids that can be absorbed and used for fuel by the body's cells; unfortunately, fermentation also produces a mix of gases, which are quite odorous vitamin synthesis: B complex vitamins and some of the vitamin K the liver needs to produce several clotting proteins are synthesized by them

pepsin and protein digestion

functions optimally in the acidic pH range found in the stomach. it preferentially cleaves bonds involving the amino acids tyrosine and phenylalanine, breaking the proteins down into poly peptides and free amino acids; hydrolyzes 10-15% of ingested protein, is inactivated by the high pH in the duodenum, so its proteolytic activity is restricted to the stomach

three monosaccharides common in the diet

glucose, fructose, and galactose

Non-alcoholic fatty liver disease (NAFLD)

has become the most common liver disease in NA; obesity and increased insulin resistance are associated with abnormal lipid metabolism and liver inflammation, which cause this; usually no symptoms associated with it; predisposes the patient to develop full-blown cirrhosis or liver cancer

mechanical breakdown

has only changed the appearance of food

colon

has several distinct regions; ascending colon; right colic (hepatic flexure; transvers; left colic (splenic) flexure; descending colon; inferiorly, it enters the pelvic, where it becomes the S-shaped sigmoid; in the pelvic at the lvl of the third sacral vertebra, the sigmoid colon joins the rectum, which runs posterioinferiorly just infront of the sacrum

rectum

has three lateral curves or bends, represented internally as three transverse folds called rectal valves; these valves stop feces from being passed along with gas

buccal glands

have approximately equal numbers of serous and mucous cells

bile salts role in lipid digestion

have both nonpolar and polar regions, their nonpolar(hydrophobic) parts cling to the fat molecules and their polar (ionized hydrophilic) parts allow them to repel each other and interact with water; as a result, fatty droplets are pulled off the large fat globules, forming a stable emulsion- an aqueous suspension of fatty droplets, emulsification does not break chemical bonds, it just reduces the attraction between fat molecules so they can be more widely dispersed, just as dish detergent breaks up a pool of fat drippings

premolars (bicuspids) and molars

have broad crown with rounded cusps (tips) best suited for grinding or crushing

hepatocytes

have large amounts of rough and smooth ER, gogli apparatus, peroxisomes and mitochondria; they can secrete 900 ml of bile daily; process bloodborne nutrients in various ways; store fat-soluble vitamines; play important role sin detoxification, such as ridding the blood of ammonia by converting it to urea

the lips and the cheeks

help keep food between the teeth when we chew, are composed of a core of skeletal muscle covered externally by skin

name given to the venous portion of the splanchnic circulation

hepatic portal circulation

inhibition of gastric secretion

highly acidic pH below 2 gastric contents; a situation that commonly occurs between meals; stress, fear, anxiety or anything that triggers the fight-or-flight response because the sympathetic division overrides parasympathetic controls of digestion

pectinate line

horizontal, tooth-shaped line that parallels the inferior margins of the anal sinuses; superior to this line, visceral sensory fibers innervate the mucosa, which is relatively insensative to pain; area inferior to this is very sensitive to pain, a reflection of the somatic sensory fibers serving it

bile canaliculi

in which secreted bile flows through; tiny canal; run between adjacent hepatocytes toward the bile duct branches in the portal triads; their walls are formed by the apical membranes of adjoining hepatocytes

the submucosa

just external to the mucosa, is areolar connective tissue containing a rich supply of blood and lymphatic vessels, lymphoid follciles, and nerve fibers which supply the surrounding tissues of the GI tract wall; its abundant elastic fibers enable the stomach, for example, to regain its normal shape after temporarily storing a large meal

rectum and anal canal

lack teniae coli and haustra; the rectum's muscularis muscle layer are complete and well developed, consistent with its role in generating strong contractions to expel feces

layer and sublayer of the alimentary canal wall that houses the capillaries into which nutrients are absorbed

lamina propria of the mucosa of the small intestine

composition of saliva

largerly water - 97 to 99.5 %- therefor is hypo-osmotic; osmolarity depends on the specific glands that are active and the stimulus for salivation; slightly acidic (6.75 to 7); solute include: electroyltes (Na+, K+, Cl-, PO4 3-, and HCO3-), digestive enzymes saolivary amylase and lingual lipas (makes only a minor contribution to overall fat digestion), proteins mucin, lysozyme and IgA, and metabolic wastes (urea and uric acid)

by the time food reaches the small intestine

it is unrecognizable, but still far from being digested; carbs and proteins are partially degraded, but fat digestion has only begun; the process of digestion accelerates during the chyme's tortuous 3-6 hour journey through the small intestine, and it is here that most of the water and virtually all nutrients are absorbed

nucleosidases and phosphatases

intestinal brush border enzymes; break the nucleotides apart to release their nitrogenous bases, pentose sugars, and phosphate

absorption of iron and calcium

intimately related to the body's need for them at the time unlike every other nutrient that will be absorbed not matter what

long reflexes

involve CNS integration centers and extrinsic autonomic nerves; the enteric NS sends info to the CNS via afferent visceral fibers; receives sympathetic and parasympathetic branches (motor fibers) of the autonomic NS that enter the intestinal wall to synapse with neurons in the intrinsic plexuses; can be initiated by stimuli arising inside or outside GI tract; in these type of reflexes, the enteric NS acts as a way station for the autonomic nervous system, allowing extrinsic controls to influence digestive activity

extrinsic controls

involve long reflexes that control digestive activity

intrinsic controls

involve short reflexes entirely within the enteric NS that controls digestive activity

receptors involved in controlling GI tract activity

located in the walls of the tract's organs; they respond to several stimuli, most importantly stretching of the organ by food in the lumen, changes in osmolarity (solute concentration) and pH of the contents, and the presence of substrates and end products of digestions

pleatlike foliate papillae

located on the lateral aspects of the posterior tongue

mass movements

long, slowing-moving, but powerful contractile waves that move over large areas of the colon 3 of 4 times daily and force the contents toward the rectum; typically occur during or just after eating

three antimicrobal substances found in saliva

lysozyme, defensins, and IgA antibodies

halitosis (bad breath)

mainly caused by the metabolic activity of anaerobic protein-digesting bacteria at the back of the tongue that yields hydrogen sulfide (rotten egg smell), methyl mercaptan (also in feces), cadaverine (associated with rotting corpses), and other smelly chemicals

tongue

occupies the floor of the mouth; composed of interlacing bundles of skeletal muscle fibers, and during chewing, it grips the food and constantly repositions it between the teeth; mixes food with saliva, forming it into compact mass called a bolus, and then initiates swallowing by pushing the bolus posteriorly into the pharynx; also helps form consonants when we speak; has both intrinsic and extrinsic skeletal muscle fibers

submucosal nerve plexus

occupies the submucosa

as motilin blood levels rise

peristaltic waves are initiated in the proximal duodenum every 90-120 minutes and sweep slowly along the intestine, moving 50-70 cm before dying out; each successive wave begins a bit more distally, a pattern of peristaltic activity called the migrating motor complex (MMC)

haustra

pocketlike sacs in result of the teniae coli's tone which puckers the wall of the large intestine

root of a tooth

portion of the tooth embedded in the jawbone

factors that inhibit gastric emptying

presence of fatty, hypertonic, acidic chyme in duodenum which cause duodenal enteroendocrine cells to secrete enderogastrones (secretin, cholecystokinin) and chemo and stretchreceptors to trigger the enterogastric reflex (short reflex via enteric nuerons and long reflexed via CNS centers ) that both decrease contractile force of the stomach.

salivary amylase

present in saliva, splits starch into oligosaccharides, smaller fragments of two to eight linked glucose molecules starting in the mouth; continues until salivary amylase is inactivated by stomach acid and broken apart by the stomach's protein-digesting enzymes; longer the meal the longer it works in the stomach because foodstuffs in its relatively immobile fundus are poorly mixed with gastric juices

bile duct blockage

prevents both bile salts and bile pigments from entering the intestine; as a result, yellow bile pigments accumulate in blood and eventually are deposited in the skin, causing it to become yellow; jaundice caused by blocked ducts is called obstructive jaundice, but jaundice may also reflect liver disease (in which the liver is unable to carry out its normal metabolic duties)

control of salivation

primarily by the paraysmpathetic division of the autonomic nervous system

peyer's patches

primarily located in the lamina propria but occasionally protrude into the submucosa below; their increasing abundance toward the distal end of the small intestine reflects the fact that this region contains huge numbers of bacteria that must be prevented from entering the blood stream;

bile salts

primarily salts of cholic and chendeoxygcholic acids are cholesterol derivatives; play a crucial role in both the digestion and absorption of fats; the substance in bile that doesn't leave the body in feces; they go through a recycling mechanism called the enterohepatic circulation.

cells in the glands of the cardia and pylorus of the stomach

primarily secrete mucus

digestive system activity that moves nutrients from the outside to the inside of the body

process of absorption

absorption

process of moving substances from the lumen of the gut into the body; material enter an epithelial cell through its apical membrane from the lumen of the gut and exit through the basolateral membrane into the interstitial fluid on the other side of the cell; once there, substance diffuse into the blood capillaries; from the capillary blood in the villus, they are transported in the hepatic portal vein to the liver; the exception is some lipid digestion products, which enter the lacteal in the villus to be carried via lymphatic fluid to the blood; although this happens all along the length of the SI; most of it is completed by the time chyme reaches the ileum

serous cells

produce a water secretion containing enzymes, ions, and a tiny bit of mucin; the parotid and submandibular glands contain mostly this type of secretory cells

cells of the gastric glands of the pyloric antrum

produce mucus and several hormones including most of the stimulatory hormone called gastrin

mucous cells

produce mucus, a stringy, viscous solution; sublingual glands contain mostly this type of secretory cell

intestinal gastrin

produced by duodenal mucosa; stimulated by acidic and partially digested food in duodenum; stimulates gastric glands and motility

secretin

produced by duodenal mucosa; stimulated by acidic chyme and also partially digested proteins and fats; inhibits gastric gland secretion and gastric motility ; increases output of pancreatic juice rich in bicarbonate ions, potentiates CCK's action; increases bile out from the liver

motilin

produced by duodenal mucosa; stimulated by fasting; periodic release every 1.5-2 hours by neural stimuli; stimulates migrating motor complex

vasoactive intestinal peptide

produced by enteric neurons; stimulated by chyme containing partially digested foods; stimulated buffer secretion; dilates intestinal capillaries and relaxes intestinal smooth muscle; increases pancreas secretion; and inhibits acid secretion from stomach

somatostatin

produced by stomach mucosa and duodenal mucosa; stimulated by food in stomach and by sympathetic nerve fibers; inhibits gastric secretion of all products; inhibits secretion; inhibits GI blood flow; thus inhibits intestinal absorption; inhibits contraction and bile release

histamine

produced by stomach mucosa; stimulated by food in stomach; activates parietal cells to release HCl

serotonin

produced by stomach mucosa; stimulated by food in stomach; causes contraction of stomach muscle

most saliva

produced by the major or extrinsic salivary glands that lie outside the oral cavity and empty their secretions into it

glucose-dependent insuilinotropic peptid (GIP)

produced in duodenal mucosa; stimulated by fatty chyme; inhibits HCl production and stimulates insulin release

cholecystokinin (CCK)

produced in the duodenal mucosa; stimulated by fatty chyme; inhibits stomach's secretory activity; potentiates secretin's actions on these organs; increases output to contract and expel stored biled; relaxes hepatopancreatic sphincter to allow entry of bile and pancreatic juice into duodenum

pancreatic juice

produced in the exocrine parts of the pancreas; 1200-1500 ml produced daily; consists mainly of water and contains enzymes and electrolytes (primarily bicarbonate); high pH helps neutralize acidic chyme entering the duodenum and provides the optimal environment for intestinal and pancreatic enzymes;

gastrin

produced in the stomach mucosa; stimulated by food in stomach and acetylcholine released by nerve fibers; increases HCl secretion from parietal cells; stimulates gastric emptying; stimulates conraction of intestinal muscle; relaxes ileocecal valve; stimulates mass movements

friendly bacteria that live on the back of the tongue

promote the conversion of food-derived nitrates in saliva into nitric oxide in an acidic environment; this transformation occurs around the gums, where acid-producing bacteria tend to cluster, and in the hydrochloric acid-rich secretions of the stomach; the highly toxic NO is believed to be bactericidal in these location

segmenting movements in the descending and sigmoid colon

promote the final drying out of the feces; this part of the colon also stores feces until mass movements propel the feces into the rectum

peristaltic waves in the stomach

propulsion; move from the fundus toward the pylorus; grinding: the most vigorous peristalsis and mixing action occur close to the pylorus; the pyloric end of the stomach act as a pump that delivers small amounts of chyme into the duodenum; retropulsion: the wave closes the pyloric valve, forcing most of the contents of the pylorus backward into the stomach where it is mixed further which effectively breaks up solids; rate is constant around 3 per minute set by enteric pacemaker cells

Major function of the LI

propulsive activities that force fecal material toward the anus and eliminate if from the body (defecation)

pancreatic enzymes

proteases (for proteins); amylase (for starch); lipases (for fats); nucleases (for nucleic acids)

proteases of the pancreas

protein-digesting enzyme; like pepsin of the stomach, are produced and released in inactive forms that are activated in the duodenum, where they do their work; protects the pancreas from digesting itself

liver

largest gland in the body; entirely enclosed by the visceral peritoneum; hepatic artery proper and hepatic portal vein enter it at the porta hepatis, and the common hepatic duct, which runs inferiorly from it, all travel through the lesser omentum to reach their destinations ; composed of functional units called liver lobules; main function is to process the nutrient-rich blood delivered to it; at each of the 6 corners of a lobule is a portal triad

intestinal phase

last part of gastric secretion; begins with a brief stimulatory component followed by inhibition; stimulated as partially digested food fills the first part (duodenum) of the small intestine; this stimulates intestinal mucosal cells to release intestinal (enteric) gastrin, a hormone that encourages the gastric glands to continue their secretory activity; this stimulatory effect is brief because it is overriden by inhibitory stimuli as the intestine fills

muscularis mucosae

layer of the mucosa of the alimentary canal; external to the lamina propria; a scant layer of smooth muscle cells that produces local movements of the mucosa that can enhance absorption and secretion

gastric pits

lead into tubular gastric glands that produce gastric juice; the cells forming the walls of these are primarily mucous cells, but those composing the gastric glands vary in different stomach regions

myenteric nerve plexus

lies between the circular and longitudinal muscle layers of the muscularis externa

parietal peritoneum

lines the body wall; separated from the visceral layer by the peritoneal cavity

accessory organs associated with the small intestine

liver, gallbladder, and pancreas

eight to twelve large vallate papillae

located in a V-shaped row at the back of the tongue; they resemble the fungiform papillae but have an additional surrounding furrow

hepatopancreatic ampulla

where the bile duct, delivering bile from the liver and the main pancreatic duct, carrying pancreatic juice from the pancreas, unite in the wall of the duodenum; fuse together at this bulblike structure; opens into the duodenum via the volcano-shaped major duodenal papilla; a smooth muscle valve called the hepatopancreatic sphincter controls the entry of bile and pancreatic juice

cardial orifice

where the esophagus joins the stomach within the abdominal cavity; surrounded by gastroesophageal or cardial sphincter.

molars

with four or five cusps, are the best grinders; during chewing, the upper and lower ones repeatedly lock together, an action that generates tremendous crushing forces

enteropeptidase

within the duodenum; an enzyme bound to the plasma membrane of the duodenal epithelial cells; acitvates trypsinogen to trypsin; trypsin in turn, activates more trypsinogen and two other pancreatic proteases (procarboxypeptidase and chymotrypsinogen) to their active forms: carboxypeptidase and chymotrypsin respectively

histology of the pharyngeal wall

resembles that of the oral cavity; mucosa contains a friction-resistant stratified squamous epithelium well supplied with mucus-producing glands; the external muscle layer consists of two skeletal muscle layers; the cells of the inner layer run longitudinally; those of the outer layer, the constrictor muscles, encircle the wall like three stacked fists; contractions of these muscles propel food into the esophagus below

dental caries or cavities

result from bacterial action that gradually demineralizes enamel and underlying dentin; decay begins when dental plaque (a film of sugar, bacteria, and other mouth debris) adheres to the teeth; bacterial metabolism of the trapped sugars produces acids, which dissolve the calcium salts of the teeth; once the salts are leached out, enzymes released by the bacteria readily digest the remaining organic matrix of the tooth

major functions of the mucosa

secrete mucus, digestive enzymes, and hormones absorb the end products of digestion into the blood protect against infectious disease in particular regions the GI tract may perform one or all three of these functions

what stimulates CCK release and what are its effects on the digestive process

secreted in response to the entry into the duodenum of chyme rich in protein and fat; causes the pancratic acini to secrete digestive enzymes, stimulates the gallbladder to contract, and relaxes the hepatopancreatic sphincter

increased gastric motility and emptying

stimulus which acts via the gastroileal reflex (long neural reflex) and gastrin; causes increased motility in ileum and relaxaion of ileocecal valve

three organs located in the abdominal cavity

stomach, small intestine

mucosa of the anal canal

stratified squamous epithelium, merges with the true skin surrounding the anus; reflecting the greater abrasion that this region receives; superiorly, it hangs in long ridges or folds called anal columns; anal sinuses, recesses between the colunms, exude mucus when compressed by feces, which aids in emptying this structure.

fiber in the diet

strengthens colon contractions and softens the feces, allowing the colon to act like a well-oiled machine

more complex carbs our digestive system can break down

sucrose, lactose, maltose, glycogen and starch

blood vessels that serve the teeth

superior and inferior alveolar nerves, branches of the trigeminal nerve; the superior and inferior alveolar arteries, branches of the maxillary artery, supply blood

pancreas

supplies most of the enzymes that digest chyme as well as bicarbonate that neutralizes stomach acid; contains exocrine parts (produces pancreatic juice) and endocrine parts.

hepatits C

the most important infectious liver disease in the US because it produces persistent or chronic liver infections (opposed to acute ones)

pepsin

the most important protein-digesting enzyme produced by the gastric mucosa

intestinal crypts

tubular glands in the small intestine mucosa; they decrease in number along the length of the small intestine

omenta

two mesenteries that extend from the curvatures of the stomach; help tether the stomach to other digestive organs and the body wall

ordinarily by age 21

two sets of teeth, the primary and permanent dentitions have formed

hemorrhoidal veins

two superficial venous plexues associated with the anal canal; if they become dilated and inflamed, itchy, varicosities called hemorrhoids result

enteroendocrine cells

typically located deep in the gastric glands; release a variety of chem messengers directly into the interstital fluid of the lamina propria; chem messengers like histamin and serotonin, act locally as paracrines, somatostatin, act both as paracrines locally and as hormones that diffuse into the blood capillaries to influences several digestive system target organs; gastrin, a hormone, plays essential roles in regulating stomach secretions and motility.

epithelial cells at the tips of the villi in the SI

undergo apoptosis and are shed, renewing the villus epithelium every three to five days

how is the muscularis externa of the esophagus unique in the body

undergoes a transformation along its length from skeletal muscle superiorly to smooth muscle near the stomach

the hard palate

underlain by the palatine bones and the palatine processes of the maxillae, and it forms a rigid surface against which the tongue forces food during chewing; the mucosa on either side of its raphe, midline ridge, is slightly corrugated, which helps create friction

nuclei acid digestion

units enter intestinal cells by active transport via membrane carriers; units are absorbed into cap blood in the villi and transported to the liver via the hepatic portal vein

regulation of bile and pancreatic juice

via hormones and neural stimuli; hormones include two enterogastrones (secretin and cholecystokinin).

digestive processes in the LI

what is finally delivered to it contains few nutrients but still have 12-24 hours to spend there; except for a small amount of digestion of that residue by the enteric bacteria, no further food breakdown occurs; harvests vitamines made by the bacterial flora and reclaims most of the remaining water and some of the electrolytes

mucin

when dissolved in water, the glycoprotein forms thick mucus that lubricates the oral cavity and hydrates foodstuffs

glands of the stomach fundus and the body

where most digestion occurs; they are substantially larger and produce the majority of the stomach secretions; contain variety of secretory cells, including mucous neck, parietal, chief, and enteroendocrine cells

mechanism of HCl secretion by parietal cells

H+ and HCO3- are generated from the dissociation of carbonic acid produced from CO2 and H20 by carbonic anhydrase; H+-K+ ATPase pumps H+ into the lumen and K+ into the cell. K+ returns to the lumen through membrane channels; Cl- in the interstitial fluid is exchanged for intracellular HCO3-; Cl- diffuses through membrane channels into the lumen

when parietal cells are appropriately stimulated

H+ is actively pumped into the stomach lumen by H+-K+ ATPases (proton pumps); as acid is pumped into the stomach, base bicarbonate is exported into the blood; this flow of base is called the alkaline tide

fat soluble vitamins

A D E K dissolve in dietary fats, become incorporated into micelles, and move across the villus epithelium passively; it follows that gulping pills containing fat-soluble vitamins without simultaneously eating some fat-containing food results in little or no absorption of these vitamins

digestive system function of the liver

to produce bile for export to the duodenum

major absorptive role of the ileum

to reclaim bile salts to by recycled back to the liver for resecretion

intraperitoneal parts of the LI

transverse and sigmoid colon; anchored to the posterior abdominal wall by mesentary sheets called mesocolons

tongue role in swallowing

mixes the chewed food with saliva, compacts the food into a bolus, and initiates swallowing

role of gastrin in ileocecal valve control

released by the stomach, increases the motility of the ileum and relaxes the valve

intrinsic factor

required for intestinal absorption of vitamin b12, needed to produce mature erythrocytes; it its absence, pernicious anemia results.

distension of small intestine

stimulus that causes increased strength of segmentation via long and short neural reflexes

reduced intestinal volume; fasting

stimulus that initiates migrating motor complex (peristalsis); repeats until next meal via motilin (initiates long and short neural reflexes)

mechanisms promoting secretion and release of bile and pancreatic juice

1. CCK and secretin are secreted by duodenal enteroendocrine cells: CCK release is stimulated by proteins and fats in chyme; secretin stimulated by acidic chyme; both enter circulation and cause the following 4 events 2. pancreatic secretion: CCK induces secretion by acinar cells of enzyme-rich pancreatic juice; secretin causes secretion by duct cells of HCO3- rich pancreatic juice; vagus nerve weakly stimulates during cephalic and gastric phases 3. Bile secretion by liver: Bile salts returning from enterohepatic circulation are the most powerful stimulus for bile secretion; secretion is a minor stimulus 4. Gallbladder contraction: CCK causes gallbladder contraction; vagus nerve stimulates weak gallbladdr contraction durning cephalic and gastric phases 5. hepatopancreatic sphincter relaxation: CCK causes sphincter to relax; bile and pancreatic juice enter duodenum

carbohydrate digestion and absorption in the SI

1. pancreatic amylase breaks down starch and glycogen into oligosaccharides and disaccharides 2. brush border enzymes break oligosaccharides and disaccharides into monosaccharides 3. monosaccharides are cotransported across the apical membrane of the absorptive epithelial cell; this active transport uses the Na+ concentration gradient established by the Na+-K+ ATPase pump in the basolateral membrane 4. monosaccharides exit across the basolateral membrane by facilitated diffusion and enter the capillary via intercellular clefts

primary dentition dental formula

2I, 1C, 2M/ 2I, 1C, 2M x 2 = 20 teeth

permanent dentition dental formula

2I, 1C, 2PM, 3M/ 2I, 1C, 2PM, 3M x 2 (32 teeth)

jejunum

2nd part of the small intestine

water soluble vitamins

B and C; absorbed via specific active or passive transporters; except for B12; intrinsic factor produced by the stomach binds to vitamin B12 which then binds to specific mucosal receptor sites in the terminal ileum which trigger its active uptake by endocytosis

regulation of chyme entry

feedback via enterogastic reflex and enterogastrones to the stomach pylorous carefully controls food movement into the small intestine to prevent the duodenum from being overwhelmed

passage of short-chain fatty acids

don't depend on the presence of bile salts or micelles; not recombined to form triglycerides within the intestinal cells; they simply diffuse into the portal blood for distribution

greater omentum

drapes inferiorly from the greater curvature of the stomach to cover the coils of the small intestine. It then runs dorsally and superiorly, wrapping the spleen and the transverse portion of the large intestine before blending with the mesocolon, a dorsal mesentary that secures the large intestine to the parietal peritoneum of the posterior abdominal wall

subdivisions of of the small intestine

duodenum (mostly retroperitoneal) and the jejunum and ileum (both intraperitoneal)

duodenal glands

elaborate mucus-secreting glands in the submucosa of the duodenum produce an alkalin (bicarbonate-rich) mucus that helps neutralize acidic chyme moving in from the stomach

a smaller accessory pancreatic duct

empty directly into the duodenum just proximal to the hepatopancreatic ampulla main duct

lipid digestion in the SI

emulsification: bc triglycerides and their breakdown products are insoluble in water, fats need special pretreatment with bile salts to be digested in the watery environment of the small intestine; in aqeuous solution, they aggregate to form large fat globules and only the triglyceride molecules at the surfaces of such fatty masses are accessible to the water-solulbe lipase enzymes; but bile salts vastly increase the SA exposed to pancreatic lipases by breaking large fat globuls into many smaller droplets; without bile lipids could not be completely digested during the time food spends in the SI digestion: pancreatic lipases catalyze the breakdown of fats by splitting off two of the fatty acid chains, yielding free fatty acids and monoglycerides micelle formation: just as bile salts accelerated lipid digestion, they are also essential for the absorption of its end products; as the water-insoluble produces of fat digestion, the monoglycerides and free fatty acids-- are liberated by lipase acitivty, they quickly become associated with bile salts and lecithin (phospholipid found in bile) to form micelles diffusion: upon reach the epithelial cells, the various lipid substances leave the micelles and move through the lipid phase of the PM by simple diffusion chylomicron formation: once the free fatty acids and monoglycerides enter the epithelial cells, the smooth ER converts them back into triglycerides; then they are combine with lecithin and other phospholipids and cholesterol and coated with a "skin" of proteins to form water-soluble lipoprotein droplets called chylomcirons; this series of evens is quite different from the absorption of amino acids and simple sugars, which pass through the epithelial cells unchanged chylomicron transport: the milk-white molecule are too large to pass through either the PM of the epithelial cell or the basement membrane of a blood cap; instead, the chylomicron-containing vesicles migrate to the basolateral membrane and are extruded by exocytosis; then enter the more permeable lacteal; thus, must fat enters the lymphatic stream for distribution in the lymph; eventually the chylomicrons are emptied into the venous blood via the thoracic duct, which drains the lymphatics of the digestive viscera

role of bile salts

emulsify fats so that they can be acted on efficiently by lipase enzymes and form micelles that aid fat absorption

tooth substance that is harder than bone

enamel

enamel

a brittle ceramic-like material thick as a dime, directly bears the force of chewing; the hardest substance in the body; heavily mineralized with calcium salts, and its densely packed hydroxyapatite (mineral) crystals are oriented in force-resisting columns perpendicular to the tooth's surface; cells that produce it degenerate when the tooth erupts, so decayed or cracked areas of it will not heal and must be artificially filled

cement

a calcified connective tissue, covers the outer surfaces of the root and attaches the tooth to the thin periodontal ligament

bile

a fat emulsifier that breaks fats into tiny particles to make them more readily digestible; leaves the liver lobes through the right and left hepatic ducts; these fuse to form the large common hepatic duct, which travels downward toward the duodenum; along its course, the duct fuses with the cystic duct draining the gallbladder to form the bile duct; flows the opposite direction of blood in the liver; a yellow-green, alkaline solution containing bile salts, bile pigments, cholesterol, triglycerides, phospholipids, and a variety of electrolytes; of these, only bile salts and phospholipids aid the digestive process

lingual frenulum

a fold of mucosa that secures the tongue to the floor of the mouth and limits its posterior movements

intrinsic facto

a glycoprotein required for vitamin B12 absorption in the small intestine

gastroileal reflex

a long neural reflex triggered by stomach activity, increases the force of segmentation in the ileum and relaxes the ileocecal valve

falciform ligament

a mesentary, separates the right and left lobs anteriorly and suspends the liver from the diaphragm and anterior abdominal wall.

esophagus

a muscular tube about 25 cm long and is collapsed when not involved in food propulsion; as food move through the laryngopharynx, it is routed into this structure posteriorly because the epiglottis closes off the larynx to incoming food; pierces the diaphragm at the esophageal hiatus to enter the abdomen; joins the stomach at the cardial orifice within the abdominal cavity

dentin

a protein-rich bonelike material, underlies the enamel cap and forms the bulk of a tooth; more resilient than enamel; acts as a shock absorber during biting and chewing; surround a central pulp cavity containing a number of soft tissue structures collectively called pulp; contains unique radial striations called dentinal tubules; each tuble contains an elongated process of an odontoblast (the cell type that secretes and maintains dentin); forms throughout adult life and gradually encroaches on the pulp cavity; can be laid down fairly rapidly to compensate for tooth damage or decay

endocrine part of the pancreas

a scattering of mini-endocrine glands called pancreatic islets; these islets release insulin and glucagon, hormones that play an important role in carbohydrate metabolism

stomach

a temporary "storage tank" where chemical breakdown of proteins begins and food is converted to a paste called chyme; lies in the upper left quadrant of the peritoneal cavity, nearly hidden by the liver and diaphragm

crown of the tooth

enamil-covered; exposed part of the tooth above the gingiva, or gum, which surrounds the tooth like a tight collar

parasympathetic inputs

enhance digestive activity

submandibular gland

about the size of a walnut; lies along the medial aspect of the mandibular body; its duct runs beneath the mucosa of the oral cavity floor and opens at the base of the lingual frenulum

functional difference between pancreatic acini and islets

acini produce the exocrine products of the pancreas (digestive enzymes and bicarbonate-rich juice) and the islets are the endocrine part of the pancreas that produce the hormone (insulin and glucagon)

pancreatic amylase in SI

act on digestible carbs and starchy foods that escaped salivary amylase; after 10 minutes after entering the SI, starch is entirly converted to various oligosaccharides, mostly maltose brush border enzymes break oligo and disaccharides into monosaccharides

distension of the stomach wall by food

activates stretch receptors and gastrin-secreting cels, both of which ultimately stimulate gastric smooth muscle and increase gastric motility

stomach distension

activates stretch receptors and initiates both short and long reflexes; in the long reflexes, impulses travel to the medulla and then back to the stomach via vagal fibers

presence of food in the stomach

activates the gastroileal reflex in the small intestine and the propulsive gastrocolic reflex in the colon

factors that increase salivation

activation of chemoreceptors and mechanoreceptors in the mouth; the sight or smell of food; irritation of the lower GI tract by bacterial toxins, spicy food, or hyperacidity which may help wash away or neutralize the irritants

factors that inhibit salivation

activation of the sympathetic division; dehydration because low blood volume reduces filtration pressure at capillary beds; promotes tooth decay and makes it difficult to talk and eat; decomposing food particles accumulate and bacteria flourish, resulting in halitosis (bad breath)

ionic iron

actively transported into the mucosal cells, where it binds to the protein ferritin; intracellular iron-ferritin complexes then serve as local storehouses for iron; when body reserves of iron are adequate, only 10-20% is allowed to pass into the portal blood and most of the stored iron is lost as the epithelial cells later slough off but when iron is depleted; iron uptake from the intestine and its release to the blood accelerate in the blood it binds to transferrin, a plasma protein that transports it in the circulation (women have more iron transport proteins in intestinal epithelial cells)

hydrolysis

adding a water molecule to each molecular bond to be broken; what enzymatic breakdown of any food molecule is

enamel, dentin, and cement

all calcified and resemble bone, but they differ from it because they are avascular; enamel differs from the other two because it lacks collagen and is almost entirely mineral

common advantage of circular folds, villi, and microvilli provide to the digestive process

all increase the SA of the SI

serous fluid in the peritoneal cavity

allows the mobile digestive organs to glide easily across one another and along the body wall as they carry out their activities

alimentary canal

also called the gastrointestinal (GI) tract or gut; continuous muscular tube that winds through the body from the mouth to the anus; it digests food, breaks it down into smaller fragments and absorbs the digest fragments through its lining into the blood

the mouth

also called the oral (or buccal) cavity; anterior opening is the oral orifice; posteriorly, it is continuous with the oropharynx; walls lined with a thick stratified squamous epithelium which withstand considerable friction

protein digestion

amino acids are absorbed via cotransport with Na+; some dipeptides and tripeptides are absorbed via cotransport with H+ and hydrolyzed to amino acids within the cells; infrequenlty, transcytosis of small peptides occurs; amino acids leave the epithelial cells by facilitated diffusion, enter the capillary blood in the villi, and are transported to the liver via the hepatic portal vein

oblique layer

an additional layer of smooth muscle in the stomach that allows it to pummel food in addition to making its peristaltic movements

rennin

an enzyme that acts on milk protein (casein), converting it to a curdy substance that looks like soured milk; secreted by the stomach glands of infants

peristalsis

an involuntary process; the major means of propulsion; involves alternating waves of contraction and relaxation of muscles in the organ walls; main effect is to squeeze food along the tract, but some mixing occurs as well; its waves are so powerful that, once swallowed, food and fluids will reach your stomach even if you stand on your head; adjacent segments of alimentary canal organs alternately contract and relax; food is moved distally along the tract; primarily propulsive

periodontal ligament

anchors the tooth in the bony socket (alveolus) of the jaw, forming a fibrous joint called a gomphosis

mechanoreceptors in the mouth

are activated by virtually any mechanical stimulus, even chewing rubber bands

chemoreceptors in the mouth

are activated most strongly by acidic substances

intrinsic muscles of the tongue

are confined and not attached to bone; their muscle fibers, which run in several different planes, allow the tongue to change its shape (but not its position), becoming thicker, thinner, longer, or shorter as needed for speech and swallowing

monosaccharides

are cotransported across the apical membrane of the absorptive epithelial cell; glucose and galactose, liberated by the breakdown of starch and disaccharides, are shuttled by secondary active transport with Na+ into the epithelial cells ; exit across the basolateral membrane by facilitated diffusion and pass into the capillaries via interceullar clefts

while in the blood stream, the triglycerides of the chylomicrons

are hydrolyzed to free fatty acids and glycerol by lipoprotein lipase, an enzyme associated with capillary endothelium; the fatty acids and glycerol can then pass through the capillary walls to be used by tissue cells for energy or stored as fats in adipose tissue; liver cells then endocytose and process the residual chylomicron material

proteins that transport monosaccharides into the cells

are located very close to the disaccharidase enzymes on the brush border; they combine the monosaccharides as soon as the disaccharides are broken down

microvilli

are long, densely packed cytoplasmic extensions of the absorptive cells of the mucosa that give the mucosal surface a fuzzy appearance called the brush border; the plasma membrane of them bear enzymes referred to as brush border enzymes, which complete the digestion of carbohydrates and proteins in the small intestine

major or extrinsic salivary glands

are paired compound tubuloalaveolar glands that develop from the oral mucosa and remain connected to it by ducts; the large parotid gland lies anterior to the air between the masseter muscle and the skin; its prominent duct parallels the zygomatic arch, pierces the buccinator muscles, and opens into the vestibule next to the second upper molar; activated when food enters the mouth and large amounts of saliva pour out; average output of saliva is about 1500 ml per day

the mushroom-shaped fungiform papillae

are scattered widely over the tongue surface; each has a vascular core that gives it a reddish hue

enteroendocrine cells in the SI

are the source of the enterogastrones; secretin and cholecystokini; they are mostly found scattered in the crypts but some are also found in the villi

retroperitoneal organs

aren't suspended by a mesentery; some regions of the small intestine adhere to the dorsal abdominal wall; they lose their mesentery and come lie posterior to the peritoneum; include most of the pancreas and duodenum and parts of the large intestine; have bothh an adventita (on the side facing the dorsal body wall) and a serosa (on the side facing the peritoneal cavity)

the stomach and duodenum act in tandem

as chyme enters the duodenum, receptors in its wall respond to chemical signals and to stretch, initiating the enterogastric reflex and the hormonal (enterogastrone) mechanisms that inhibit acid and pepsin secretion; these mechanisms also prevent further duodenal filling by reducing the force of pyloric contractions

permanent teeth

as the enlarge and develop, the roots of the milk teeth are resorbed from below, causing them to loosen and fall out between ages 6 and 12; generally all of them but the third molars have erupted by the end of adolescence; the third molars also called wisdom teeth, emerge between ages 17-25; usually 32 teeth in this set; but sometimes the wisdom teeth never erupt or are completely absent

portal triad

at the 6 corners of each liver lobule; contains a branch of the hepatic artery proper (supplying oxygen-rich arterial blood); a branch of the hepatic portal vein (carrying venous blood laden with nutrient from the digestive viscera); and a bile duct

apical foramen

at the proximal end of each root canal; allows blood vessels, nerves, and other structures to enter the pulp cavity

appendix

attached to the posteromedial surface of the cecum; contains masses of lymphoid tissue and as part of MALT it plays an important role in body immunity; it serves as a storehouse of bacteria and recolonizes the gut when needed ; its twisted structure makes it susceptible to blockage

why saliva protects against microorganisms

because it contains IgA antibodies; lysozyme, a bacterial enzyme that inhibits bacterial growth in the mouth and may help prevent tooth decay; and defensins, besides acting as a local antibiotic, defensins function as cytokines to call defensive cells (lymphocytes, neutrophil) into the mouth for battle

protein digestion

begins in the stomach and is the main type of enzymatic breakdown that occurs theres ; HCl produced by stomach glands denatures dietary proteins in preparation for enzymatic digestion because the unfolded amino acid chain is more accessible to the enzymes

potentially harmful bacteria in our LI are kept in check in two ways

beneficial bacteria out compete and actively suppress harmful ones and as a result normally vastly outnumber them; our immune system prevents bacteria from entering the body through the gut epithelium: dendritic cells sample the microbial antigens in the lumen. they then migrate to the nearby lymphoid follicles within the gut mucosa (MALT) and trigger an IgA antibody-mediated response restricted to the gut lumen; this prevents the bacteria from straying into tissues deep to the mucosa where they might elicit a much more widespread systemic response

muscularis externa of the stomach

besides the usual circular and longitudinal layers of smooth muscle, it has an incomplete innermost layer of smooth muscle fibrils that run obliquely; this arrangement allows the stomach not only to mix, churn, and move food along the tract, but also to pummel the food, physically breaking it down into smaller fragments and ramming it into the small intestine

liver sinusoids

between the hepatocyte plates; enlarged and heavily fenestrated; blood from both the hepatic portal vein and hepatic artery proper percolates from the triad regions through these and empties into the central vein; star-shaped stellate macrophages, also called hepatic macrophages form part of its wall, they remove debris such as bacteria and worn-out blood cells from the blood as it flows past

major stimulus for enhanced bile secretion

bile salts; after a fatty meal, when the enterohepatic circulation is returning large amounts of bile slats to the liver, its output of bile rises dramatically; secretin, released by intestinal cells exposed to fatty chyme, also stimulates liver cells to secrete it.

substance required for digestion

bile, digestive enzymes (except for the brush border enzymes), and bicarbonate ions (to provide pH for enzymatic catalysis); are imported from the liver and pancreas; therefore anything that impairs liver or pancreatic function or delivery of their juices to the small intestine severly hinders our ability to digest food and absorb nutrients

antihistamines like cimetidine

bind to and block the histamine receptors of parietal cells; used to treat gastric ulcers caused by hyperacidity

from the central veins of the liver

blood eventually enters the hepatic veins, which drain the liver, and empties into the inferior vena cava

regulation of gastric secretion

both neural and hormonal mechanisms; stimuli acting at three distinct sites -- the head, stomach, and small intestine -- provoke or inhibit secretion

pancreatic enzymes

break large chemicals (usually polymers) into smaller pieces that are broken down into individual components by the intestinal (brush border) enzymes; alkaline pancreatic juice neutralizes that acidic chyme that enters the small intestine from the stomach; this provides the proper environment for operation of the enzymes; both pancreatic juice (main source of lipases) and bile are necessary for fat breakdown

digestion

breaks down ingested foods into their chem building blocks, which are very different molecules chemically; only these molecules are small enough to be absorbed across the wall of the small intestine; catabolic process that breaks down large food molecules to monomers; accomplished by enzymes secreted into the lumen of the alimentary canal by intrinsic and accessory glands

minor or intrinsic salivary glands

buccal glands and others; scattered through the oral cavity mucosa augment the output slightly; secrete saliva continuously in amounts just sufficient to keep the mouth moist

calculus

calcfied dental plaques or tartar; these stony-hard deposits disrupts the seal between gingivae and teeth, deepening the sulcus and putting the gums at risk for infection by pathogenic anaerobic bacteria

carboxypeptidases and aminopeptidases

can independently dismantle a protein, but the teamwork between these enzymes and between trypsin and chymotrypsin, which attack the more internal parts of the protein speeds up the process tremendously

sympathetic division activation

causes release of thick, mucin-rich saliva; constricts blood vessels serving the salivary glands and almost completely inhibits saliva release, causing a dry mouth

retroperitoneal parts of the LI

cecum, appendix, colon (except for its transver and sigmoid parts) , and rectum

LI subdivisions

cecum, appendix, colon, rectum, and anal canal

odontoblast

cell type that secretes and maintains the dentin; like the pulp cavity just deep to the dentin;

three phases of gastric secretion

cephalic, gastric and intestinal

five major types of cells found in the mucosal epithelium of the villi and crypts

enterocytes; goblet cells; enterendocrine cells; paneth cells; stem cells

when we ingest food

chemoreceptors and mechanoreceptors in the mouth send signals to the salivatory nuclei in the brain stem (pons and medulla) ; as a result, parasympathethic NS activity increases; impulses sent via motor fibers in the facial (VII) and glossopharyngeal (IX) nerves dramatically increase the output of water (serous), enzyme-rich saliva

bilirubin

chief bile pigment; a yellow waste produce of the heme of hemoglobin formed during the breakdown of worn-out erythrocytes; absorbed from the blood by liver cells, excreted into bile, and metabolized in the small intestine by resident bacteria; one of its breakdown produces (stercobilin) gives feces a brown color; in the absence of bile, feces are gray-white and have fatty streaks because essentialy no fats are digested or absorbed.

gallbladder

chiefly a storage organ for bile not immediately needed for digestion and concentrates it by absorbing some its water and ions; muscular wall contracts to expel bile into the cystic duct; from there bile flows into the bile duct; covered by visceral peritoneum

incisors

chisel-shaped adapted for cutting or nipping off pieces of food

three structural modifications of the small intestine

circular folds, villi, and microvilli; amplify its absorptive surface enormously (by a factor of more than 600 times)

saliva functions

cleanses the mouth; dissolves food chemicals so they can be tasted; moistens food and helps compact it into a bolus; contains the enzyme amylase that begins the digestion of starchy foods

calcium absorption

closely related to blood levels of ionic calcium; the active form of vitaman D promotes active calcium absorption; decreased blood levels of ionic calcium prompt parathyroid hormone release; beside facilitating the release of Ca ions from bone matrix and enhancing the reabsorption of Ca by the kidneys, PTH stimulates activation of vitamin D to calcitriol by the kidneys, which in turn accelerates calcium ion absorption in the SI

acini

clusters of secretory acinar cells that produce the enzyme-rich component of pancreatic juice; acinar cells are full of RER and exhibit deeply staining zymogen granules which contain inactive digestive enzymes (proenzymes)

micelles

collections of fatty elements clustered together with bile salts in such a way that the polar ends of the molecules face the water and the nonpolar portions form the core; also nestled in the hydrophobic core are cholesterol molecules and fat-soluble vitamins; although they are similar to emulsion droplets, they are about 500 times smaller and easily diffused between microvilli to come into close contact with the apical cell surface; without the, the lipids would simply float on the surface of the chyme, inaccessible to the absorptive surfaces of the epithelial cells

the hepatic portal circulation

collects nutrient-rich venous blood draining from the digestive viscera and delivers it to the liver

absorbed electrolytes

come from both ingested foods and gastrointestinal secretions; most ions are actively absorbed along the entire length of the SI; but absorption of iron and calcium is largely limited to the duodenum for the most part, anions passively follow the electrical potential established by Na transport; Na+ is actively pumped out of the epithelial cells by Na+-K+ pump after entering those cells; usually Cl- passively follow Na+. in the terminus of the SI, HCO3- is actively secreted into the lumen in exchange for Cl- K+ ions move across the intestinal mucosa passively by facilitated diffusion; as water is absorbed from the lumen, rising potassium levels in chyme create a concentration gradient for its absorption; anything that interferes with water absorption not only reduces potassium absorption but also pulls K+ from the interstitial spaces into the intestinal lumen

fat absorption

completed in the ileum generally; but in the absence of bile it happens so slowly that most of the fat passes into the large intestine and is lost in feces

exocrine part of the pancreas

consists of acini and ducts; produces pancreatic juice

neural controls of gastric secretion

consists of both long (vagus nerve-mediated) and short (local enteric) nerve reflexes; in each case, acetylcholine is released, stimulating the output of gastric juice; when the stomach is stimulated by the vagus nerves, secretory activity of virtually all of its glands increases

the primary dentition

consists of the deciduous teeth, also called milk or baby teeth; first appear at about 6 months of age, are the lower central incisors; additional pairs of teeth erupt at one-to-two month intervals until about 24 months, when all 20 milk teeth have emerged

neck of a tooth

constricted region that connects the crown and root

lamina propria of the SI mucosa

contains large numbers of immunoglobulin A (Ig-A)-secreting plasma cells that help protect against intestinal pathogens

stem cells

continuously divide in the depths of the crypts; their daughter cells differentiate to become all of the other cell types; most of these daughter cells (except paneth cells) differentiate as they gradually migrate up the villi;

essentially all digestive tract regulatory mechanisms

control luminal conditions so that food breakdown and absorption can occur there as effectively as possible; in order to accomplish this, the GI tract has its own enteric nervous system (sometimes called the gut brain)

absorption of sodium ions in the SI

coupled to active absorption of glucose and amino acids

visceral peritoneum

covers the external surfaces of most digestive organs and is continuous with the parietal peritoneum

circular folds

deep, permanent folds of the mucosa and submucosa; force chyme to spiral through the lumen, slowing its movement and allowing time for full nutrient absorption

semisolid feces

delivered to the rectum contain undigested food residues, mucus, sloughed-off epithelial cells, millions of bacteria and just enough water to allow their smooth passage; of the 500 mll or so of food residue entering the cecum daily, approximately 150 ml becomes this.

rate of gastric emptying

depends on type of contents, how large of a meal was taken in; on the contents of the duodenum as on what is happening in the stomach.

most important brush border enzymes

dextrinase and glucoamylase; which act on oligosaccharies composed of more than three simple sugars and maltase, sucrase, and lactase, which hydrolyze maltose, sucrose, and lactose respectively into their constituent monosaccharides; because the intestine can absorb only monosaccharides, all dietary carbs must be digested to this to be absorbed

three key concepts that govern regulation of digestive activity

digestive activity is provoked by a range of mechanical and chemical stimuli; effectors of digestive activity are smooth muscle and glands; neurons (intrinsic and extrinsic) and hormone control digestive activity

involuntary or automatic defecation

fecal incontinence; occurs in infants because they have not yet gained control of their external anal sphincter; it also occurs in those with spinal cord transections

most important secretory stimuli

distension, peptides, and low acidity

indigestible polysaccharides

do not nourish us, but they do help move food along the GI tract by providing fiber

epithelium of the mucosa

except for that of the mouth, esophagus, and anus, where it is stratifed squamous; it is a simple columnar epithelium rich in mucus-secreting cells; the slippery mucus it produces protects certain digestive organs from being digested by enzymes working within their cavities and eases food passage along the tract

teniae coli

except for the LI's terminal end, the longitudinal muscle layer of its muscularis is mostly reduced to three bands of smooth muscle called this

the extrinsic muscles of the tongue

extend from the tongue from their points of origin on bones of the skull or the soft palate; alter the tongue's position; they protrude it, retract it, and move it from side to side

fat digestion

fatty acids and monoglycerides enter the intestinal cells via diffusion; fatty acids and monoglycerides are recombined with other lipids and proteins within the cells. the resulting chylomicrons are extruded by exocytosis; the chylomicrons enter the lacteals of the villi and are transported to the systemic circulation via the lymph in the thoracic duct; some short-chain fatty acids are absorbed, move into the cap blood in the villi by diffusion and are transported to the liver via the hepatic portal vein

villi

fingerlike projections of the mucosa; over 1 mm high, that give it a velvety texture, much like the soft nap of a towel; are large and leaflike in the duodenum (the intestinal site of most active absorption) and gradully narrow and shorten along the length of the SI; in the core of each one is a dense capillary bed and wide lymphatic capillary called a lacteal; digested foodstuffs are absorbed through the epithelial cells into both the capillary blood and the lacteal

cephalic (reflex) phase

first part of gastric secretion; occurs before food enters the stomach; only a few minutes long, it is triggered by the aroma, taste, sight, or thought of food; these triggers act via the vagus nerve to stimulate gastric glands, getting the the stomach ready for its digestive chore

buccal phase

first step of deglutition (swallowing); the upper esophageal sphincter is contracted (closed); the tongue presses against the hard palate, forcing the food bolus into the oropharynx

carbohydrate digestion

foods like starch and disaccharides; glucose and galactose are absorbed via cotransport with Na+; fructose passes via facilitate diffusion; all monosaccharides leave the epithelial cells via facillitated diffusion, enter the capillary blood in the villi, and are transported to the liver via the heaptic portal vein

roles of the tongue besides preparing food for swallowing

for taste and speech, particularly for uttering consonants

fats

form an oily layer at the top of the chyme and are digested more slowly by enzymes acting in the intestine. for this reason, when chyme entering the duodenum is fatty, reflexes slow stomach emptying, and food may remain in the stomach 6 hours or more

enterocytes

form the bulk of the SI mucosal epithelium of the villi and crypts; they are simple columnar absorptive cells bound by tight junctions and richly endowed with microvilli; these cells bear the primary responsibility for absorbing nutrients and electrolytes in the villi; in the crypts they are primairly secretory cells that secrete intestinal juice, a watery mixture that contains mucus and serve as a carrier fluid for absorbing nutrients from chyme

chylomicron

formed when lecithin combines triglycerides and other phospholipids and cholesterol; coated with a "skin" of proteins to form water-soluble lipoprotein droplets

the palate

forming the roof of the mouth; has two distinct parts: the hard part anteriorly and the soft part posteriorly

paneth cells

found deep in the crypts of the SI, specialized secretory cells that fortify the small intestine's defenses by releasing antimicrobial agents such as defensins and lysozyme; these secretions destroy certain bacteria and help to determine which bacteria colonize the intestinal lumen; migrate to the very bottom of the crypts

parietal cells

found mainly in the more apical region of the gastric glands scattered among the chief cells; secrete HCl and intrinsic factor; although they appear oval when viewed; they actually have three prongs that bear dense microvilli; this structure provides a huge SA for secreting H+ and Cl- into the stomach lumen

inhibition of the intestinal phase of gastric secretion

four main factors in the duodenum; distension or the presence of acidic, fatty, or hypertonic chyme all trigger both neuronal and hormonal signals to tell the stomach enough already; these "brakes" protect the small intestine from excessive acidity and prevent a massive influx of chyme from overwhelming the digestive and absorptive capacities of the duodenum by matching the amount of entering chyme to the processing abilities of the small intestine. achieved in two ways- enterogastric reflex: the duodenum inhibits acid secretion in the stomach by short reflexes through the enteric NS and by long reflexed involving symp and vagus nerves enterogastrones: enterogastrone hormones are released by a scattering of enterendocrine cells in the duodenal mucosal epithelium; the two most important ones are secretin and cholecystokinin (CCK); they inhibit gastric secretion and also play other roles

large intestine

frames the small intestine on three sides and extends from the ileocecal valve to the anus; greater diameter but shorter than SI; major digestive functions are to absorb most of the remaining water from indigestible food residues, store the residue temporarily and then eliminate the from the body as semisolid feces, also called stool; also absorbs metabolites produced by resident bacteria as they ferment carbs not absorbed in the SI

mucosal barrier

how the stomach protects itself from its acidic condition; a thick coating of bicarbonate-rich mucus builds up on the stomach wall; the epithelial cells of the mucosa re joined together by tight junctions that prevent gastric juice from leaking into underlying tissue layers; damaged epithelial mucosal cells are shed and quickly replaced by division of undifferentiated stem cells that reside where the gastric pits join the gastric glands; the stomach surface epithelium of mucous cells is completely renewed every three to 6 days but the more sheltered glandular cells deep within the gastric glands have a much longer life span

terminal sulcus

immediately posterior to the vallate papillae; a groove that distinguishes the portion of the tongue that lies in the oral cavity (its body) from its posterior portion in the oropharynx (its root); the mucosa covering the root of the tongue lacks papillae, but it is still bumpy because of the nodular lingual tonsil, which lies just deep to its mucosa

malabsorption

impaired nutrient absorption; can result from anything that interferes with the delivery of bile or pancreatic juice to the small intestine; factors that damage the intestinal mucosa (bacterial infections and some antibiotics) or reduce its absorptive SA are also common causes

pancreatic nucleases

in pancreatic juice; hydroyze the nucleic acids to their nucleotide monomers;

emetic center

in the medulla, where bloodborne molecules and sensory impulses stream from the irritated sites of the stomach where they initiate a number of motor responses: a deep inspiration directly precedes vomiting; the diaphragm and abdominal wall muscles contract, increasing intra-abdominal pressure, the gastroesophageal sphincter relaxes, and the soft palate rises to close off the nasal passages; as a result the stomach contents are forced upward through the esophagus and pharynx and out the mouth

hormone-producing cells

in the stomach and small intestine; when stimulated, they release their products to the interstitial fluid in the extracellular space; blood and interstitial fluid distribute these products to their target cells in the same or different digestive tract organs, where they affect secretion or contraction

different effects of distension of the stomach and duodenal walls

in the stomach it enhances stomach secretory activity; in the walls of the SI it reduces stomach secretory activity (to give the small intestine time to carry out its digestive and absorptive activities)

hepatits

inflammation of the liver; often due to viral infection; hepatitis-causing viruses named A-F

processing of food by the digestive system involves 6 essential activities

ingestion- taking food into the digestive tract (eating) propulsion- which moves food through the alimentary canal, includes swallowing, which is initiated voluntarily, and peristalsis an involuntary process mechanical breakdown- increases the surfaces are of ingested food, physically preparing it for digestion by enzymes; mechanical processes include chewing, mixing food with saliva by the tongue, churning food in the stomach, and segmentation (rhythmic local contractions of the small intestine) digestion- involves a series of catabolic steps in which enzymes secreted into the lumen (cavity) of the alimentary canal break down complex food molecules to their chemical building blocks absorption- is the passage of digested end products (plus vitamins, minerals and water) from the lumen of the GI tract through the mucosal cells by active or passive transport into the blood or lymph defecation- eliminates indigestible substances from the body via the anus in the form of feces

digestive functions associated with the mouth

ingestion; mostly reflect the activity of the related accessory organs, such as teeth, salivary gland, and tongue; we chew food and mix it with saliva containing enzymes that begin the process of digestion; also begins the propulsive process of swallowing, which carries food through the pharynx and esophagus to the stomach

sympathetic inputs

inhibit digestive activity

stimulated receptors in the GI tract

initiate reflexes that stimulate smooth muscle of the tract walls to mix lumen contents and move them along the tract; reflexes can also activate or inhibit glands that secrete digestive juices into the lumen or hormones into the blood

defecation reflex

initiated by stretching of the rectal wall when mass movements force feces into the rectum; parasympathetic spinal reflex causes the sigmoid colon and the rectum to contract, and the internal anal sphincter to relax; as feces are forced into the anal canal, messages reach the brain allowing us to decide whether the external anal sphincter should open or remain constricted to stop passage of feces temporarily.

result of stimulation of stretch receptors in the rectal walls

initiates the defecation reflex

mesentery

is a double layer of peritoneum-- a sheet of two serous membranes fused back to back -- that extends to the digestive organs from the body wall; provide routes for blood vessels, lymphatics, and nerves to reach the digestive viscera; hold organs in place; and store fat; in most places it is dorsal and attaches to the posterior abdominal wall, but there are ventral ones too such as the one that extends from the liver to the anterior abdominal wall

the soft palate

is a mobile fold formed mostly of skeletal muscles that rises reflexively to cost off the nasopharynx when we swallow; laterally it is anchored to the tongue by the palatoglossal arches and to the wall of the oropharynx by the more posterior palatopharyngeal arches; these two pared folds form the boundaries of the fauces, the arched area of the oropharynx that contains the palatine tonsils; projecting downward from the free edge is the fingerlike uvula

regenerative capacity of a healthy liver

is exceptional; can regenerate to its former size in 6-12 months even after surgical removal or loss of 80% of its mass; parts of a living donor's liver can be removed for transplant without long-term harm to the donor

hormonal controls of gastric secretion

is largely the province of gastrin; it stimulates secretion of enzymes and HCl by the stomach, and of hormone (mostly gastrin anatagonists) by the small intestine

the only stomach function essential to life

is secretion of intrinsic factor

epithelium on the gums, hard palate, and dorsum of the tongue

is slightly keratinized for extra protection against abrasion during eating

segmentation in the SI

is the principal form of motility after a meal; this motor pattern ensures that chyme is throughly mixed with bile and pancreatic and intestinal juices; also ensures that the absorbable products of digestion come in contact with the mucosa for absorption; intrinsic pacemaker cells (in the circular smooth muscle layer) initiate these segmenting movements; the intensity of it is altered by long and short reflexes, which parasympathetic activity enhances and sympathetic activity decreases, and by hormones; the more intense the contractions, the greater the mixing; think of it as a purely mixing movement

when the stomach is empty

it collapses inward, throwing it mucosa and submucosa into large, longitudinal folds called rugae

once chyme as pass through the ileocecal valve

it exerts backward pressure that closes the valve's flaps, preventing regurgitation into the ileum; this reflex sweeps the contents of the previous meal completely out of the stomach and small intestine as the next meal is eaten.

to send food on its way from the mouth

it is first compacted by the tongue into a bolus and is then swallowed

intestinal juice

major stimulus for its production come from hypertonic or acidic chyme; normally it is slightly alkaline and isotonic with blood plasma; is largely water but also contains some mucus, which is secreted both by the duodenal glands and by goblet cells of the mucosa

HCl

makes the stomach contents extremely acidic (1.5-3.5), a condition necessary for activation and optimal activity of the protein-digesting enzyme pepsin; the acidity also helps digest food by denaturing proteins and breaking down cell walls of plant foods, and is harsh enough to kill many of the bacteria ingested with food.

motility that occur in the LI

mass movements- long, slow, powerful contractions that move over large area of the colon three or four times a day, forcing the contents toward the rectum; haustral contractions are a special type of segmentation

short reflexes

mediated entirely by enteirc NS plexuses in response to stimuli within the GI tract; control of the patterns of segmentation and peristalsis is largely automatic, involving pacemaker cells and reflex arcs between enteric neurons in the same or different organs

digestive system function of the pharynx and esophagus

merely serve as conduits to pass food from the mouth to the stomach; food propulsion accomplished by deglutition, or swallowing

water

most abundant substance in chyme; and 95% of it is absorbed in the SI by osmosis; most of the res is absorbed in the LI, leaving only about .1L to soften the feces normal rate for absorption is 300-400 ml per hour; moves freely in both directions across the intestinal mucosa, but net osmosis occurs whenever a concentration gradient is established by the active transport of solutes (Na+) into the mucosal cells; in this way water uptake is effectively coupled to solute uptake and in turn effects the absorption of substances that normally pass by diffusion; as water moves into mucosal cells, these substances follow along their concentration gradients

a carb-rich meal

moves through the duodenum rapidly

esophagus wall

mucosa which contains nonkeratinized stratified squamous epithelium; at the esophagus-stomach junction the epithelium changes abruptly to the simple columnar epithelium of the stomach; the submucosa contains mucus-secreting glands: as a bolus moves through it , it compresses these glands, causing them to secrete mucus that "greases" the walls and aids food passage; the muscularis externa is skeletal muscle in its superior third, a mixture of skeletal and smooth muscle in its middle third, and entirely smooth muscle in its inferior third; instead of a serosa, it has a fibrous adventitia composed entirely of CT, which blends with surrounding structures along its route

four basic layers of the walls of the alimentary canal

mucosa, submucosa, muscularis externa, and serosa; each layer contains a predominant tissue type that plays a specific role in food breakdown

name the layers of the alimentary canal from inside out

mucosa; submucosa; muscularis externa; serosa

type of digestive activity put into motion via reflexes stimulated by sensors in the GI tract

muscle contraction and secretion of digestive juices or hormones

enteric pacemaker cells

muscle-like noncontractile cells; located between the smooth muscle layers, they depolarize and depolarize spontaneously three times each minute, establishing the so-called cyclic slow waves of the stomach or its basic electrical rhythm (BER); coupled by gap junctions so their "beat" is transmitted efficiently and quickly to the entire musclaris; the same factors that increase gastric secretion also enhance the strength of stomach contractions

segmentation

nonadjacent of the alimentary canal organs contract and relax; food is moved forward, then backward; primarily mixes food and breaks it down mechanically; some propulsion may occur; mixes food with digestive juices and makes absorption more efficient by repeatedly moving different parts of the food mass over the intestinal wall

stomach contraction

not only accommodate its filling and cause its emptying, but they also compress, knead, and mix the food with gastric juice to produce chyme; the processes of mechanical breakdown and propulsion are inseparable in the stomach due to a unique type of peristalsis

Protein digestion

not only include dietary proteins, but also 15-25 g of enzyme proteins secreted into the GI tract by its various glands and protein derived from sloughed and disintegrating mucosal cells; most healthy people digest much of this protein all the way to its amino acid monomers; begins in the stomach when pepsinogen secreted by the chief cells is activated to pepsin

nucleic acid digestion

nuclei of the cells of ingested foods contain DNA and RNA Pancreatic nucleases in pancreatic juice hydrolyze the nucleic acids to their nucleotide monomers intestinal brush border enzymes (nucleosidases and phosphatases) then break the nucleotides apart to release their nitrogenous bases, pentose sugars, and phosphate ions special carriers in the epithelium of the villi actively transport the breakdown products of nucleic acid digestion across the epithelium these then enter the blood

chief cells

occur mainly in the basal regions of the gastric glands; cuboidal; produce pepsinogen, the inactive form of the pepsin; when these cell are stimulated, the first pepsinogen molecules they release are activated by HCl encountered in the apical region of the gland. But once pepsin is present, it also catalyzes the conversion of pepsinogen to pepsin; the activation process involves removing a small peptide fragment from pepsinogen, causing it to change shape and expose its active site; this positive feedback process is limited only by the amount of pepsinogen present; these cells also secrete lipases (fat-digesting enzymes) that account for about 15% of overally GI lipolysis

ingestion

occurs only at the mouth

fat digestion

occurs primarily in the small intestine, but gastric and lingual lipases acting in the acidic pH of the stomach also contribute

bacterial flora

of the LI consists of over a thousand diff types of bacteria; count for a couple of pounds of your body weight; some colonize the colon via the anus, but others enter from the small intestine after runnning the gauntlet of antimicrobial defenses; depend upon them as much as they depend on us ; help us by recovering energy from otherwise indigestible food and synthesizing some vitamins

gastric accommodation

one of the factors responsible for the rise of pressure during stomach filling; is the intrinsic ability of visceral smooth muscle to exhibit the stress-relaxation response. in other words, the stomach can stretch without greatly increasing its tension and contracting expulsively; this capability is very important in hollow organs like the stomach that must serve as temporary reservoirs

receptive relaxation

one of the factors responsible for the rise of pressure in a filling stomach; of smooth muscle in the stomach fundus and body which occurs both in anticipation of and in response to food moving through the esophagus and into the stomach; the swallowing center of the brain stem coordinates this process, which is mediated by the vagus nerves

mastication

or chewing; as food enters the mouth, its mechanical breakdown begins with this; the cheeks and closed lips hold food between the teeth, the tongue mixes food with saliva to soften it, and the teeth cut and grind solid food into smaller morsels; partly voluntary and partly reflexive; pattern and rhythm of continued jaw movements are controlled mainly by stretch reflexes and in response to pressure inputs from receptors in the cheeks, gums, and tongue, but they can also be voluntary if desired.

intraperitoneal or peritoneal organs

organs like the stomach that keep their mesentery and remain in the peritoneal cavity

of the following organs, which are retroperitoneal; stomach, pancreas, liver?

pancreas

protein digestion in the SI

pancreatic proteases break down proteins and protein fragments into smaller pieces and some individual amino acids: proteolytic enzymes: trypsin and chymotrypsin cleave the proteins into smaller peptides; carboxypeptidases split off one amino acid at a time from the end of the polypeptide chain that bears the carboxyl group brush border enzymes break oligo and dipeptides into amino acids: a variety of brush border peptidases liberate individual amino acids from either end of a peptide chian (carboxypeptidases and aminopeptidase), while dipeptidases break pairs of amino acids aparts; amino acids are cotransported across the apical membrane of the absorptive epithelial cell; coupled to the active transport of sodium; short chains of two or three amino acids are also actively absorbed using H+ dependent cotransport; they are digested to their amino acids within the epithelial cells amino acids exit across the basolateral membrane via facilitated diffusion and enter the cap via intracellular clefts

lamina propria

part of the mucosa of the alimentary canal; underlies the epithelium, is a loose areolar connective tissue; its capillaries nourish the epithelium and absorb digested nutrients; its isolated lymphoid follicles, part of MALT, help defend us against bacteria and other pathogens, which have rather free access to our digestive tract;

two substances secreted by cells of the gastric glands that are needed to produce the active protein-digesting enzyme pepsin.

pepsinogen produced by chief cells which is the inactive enzyme form and parietal cells that secrete HCl needed to activate pesinogen

chemical secretory stimuli

provided by partially digested proteins, caffeine, and rising pH directly activate gastrin-secreting enteroendocrine cells G cells in the stomach antrum; during this phase, gastrin plays a major role in stimulating stomach gland secretion

tooth region that includes nervous tissue and blood vessels

pulp

the relatively unchanging pressure in a filling stomach is due to two factors

receptive relaxation and gastric accommodation

importance of the enterohepatic circulation

recycling mechanism for retaining bile salts needed for fat absorption

enterohepatic circulation

recycling mechanisms of bile salts; they are reabsorbed into the blood by the ileum (the last part of the small intestine), returned to the liver via the hepatic portal blood; resecreted in newly formed bile; about 95% of secreted bile salts are recycled, so only 5% is newly synthesized each time

"gut brain"

refers to the enteric NS, the web of neurons closely associated with the digestive organs

if defecation is delayed

reflex contractions end within a few seconds and the rectal walls relax; the next mass movement initiates the defecation reflex again, and so on, until the person chooses to defecate or the urge becomes irresistible

periodontal disease

results of neglected calculus; bacteria eventually for pockets of infection which becom inflamed; neutrophils and other immune cells attack not only the intruders but also body tissues, carving deep pockets around the teeth, destroying the periodontal ligament, and activating osteoclasts which dissolve the bone; may jeopardize more than just teeth; some contend it increases the risk of heart disease and stroke in at least two ways: the chronic inflammation promotes atherosclerotic plaque and bacteria entering the blood from infected gums stimulate the formation of clots that clog coronary and cerebral arteries; risk factors include smoking, diabetes mellitus, and oral piercings

conical filiform papillae

roughen the tongue surface, helping us lick semisolid foods (such as ice cream) and providing friction for manipulating foods; are the smallest and most numerous type, align in parallel rows in the tongue dorsum; contain keratin, which stiffens them and gives the tongue its whitish appearance

liver lobules

roughly hexagonl structure consisting of plates of liver cells, or hepatocytes, organized like bricks; hepatocyte plates radiate outward from a central vein running in the longitudinal axis of the lobule;

branches of the facial nerve

run through the parotid gland on their way to the muscle of facial expression; for this reason, surgery on this gland can result in facial paralysis

round ligament

running along the inferior edge of the falciform ligament of the liver; a fibrous remnant of the fetal umbilical vein

lesser omentum

runs from the liver to the lesser curvature of the stomach, where it becomes continuous with the visceral peritoneum covering the stomach

cecum

saclike; lies below the ilecocecal valve in the right iliac fossa is the first part of the LI; attached to it is the blind, wormlike appendix

mucous neck cells

scattered in the "neck" and more basal regions of the gastric glands; produce a thin, soluble mucus quite different from that secreted by the mucous cells of the surface epithelium; not yet understood what special function this acidic mucus performs

pharyngeal-esophageal phase

second part of deglutition; the tongue blocks the mouth; the soft palate and its uvula rise, closing off the nasopharynx; the larynx rises so that the epiglottis blocks the trachea; the upper esophageal sphincter relaxes; food enters the esophagus; the constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly; the upper esophageal sphincter contracts after food enters; then peristalsis moves food through the esophagus to the stomach; the gastroesophageal sphincter surrounding the cardial orifice opens; after food enters the stomach, the sphincter closes, preventing regurgitation

gastric phase

second part of gastric secretion; once food reaches the stomach, local neural and hormonal mechanisms initiate this phase; lasts three to four hours and provides about two-thirds of the gastric juice released

two most important enterogastrones that inhibit gastric secretion

secretin and cholecystokinin (CCK)

two motility patters in the SI

segmentation after a mean and migrating motor complex in between meals

after a meal, what is the SI's most common motility pattern? why?

segmentation; it mixes chyme with digestive enzymes and exposes the products of this digestion to the absorptive epithelium where brush border enzymes complete digestion and where absorption occurs

two types of secretory cells that make up the salivary glands

serous and mucous

peritoneum

serous membrane lining the interior of the abdominal cavity and covering the surfaces of abdominal organs

dental formula

shorthand way of indicating the numbers and relative positions of the different types of teeth; written as a ration, uppers over lowers, for one-half of the mouth; since the other side is a mirror image, we obtain total dentition by multiplying the dental formula by 2

LI mucosa

simple columnar epithelium except in the anal canal; no circular folds, villi, or brush border, however it is thicker, its abundant crypts are deeper, and the crypts contain tremendous numbers of goblet cells; mucus produced by them eases the passage of feces and protects the intestinal wall from irritating acids and gases released by resident bacteria

haustral contractions

sluggish or short-lived compared to the SI; motility of the colon when food enters through the ileocecal valve; slow segmenting movements that last about one minute and occur every 30 minutes or so; occur mainly in the ascending and transverse colon, reflect local controls of smooth muscle within the wall so of the individual haustra; as a haustrum fills with food residue, the distension stimulates its muscle to contract; these movements mix the residue which aids in water absorption

epiploic appendages

small fat-filled pouches of visceral peritoneum that hang from the surface of the LI; significance is not known

sublingual gland

small, almond shaped lies anterior to the submandibular gland under the tongue and opens via 10-20 ducts into the floor of the mouth

pulp

soft tissue structures like connective tissue, blood vessels, and nerve fibers; supplies nutrients to the tooth tissues and provides tooth sensation; where it extends into the root, it becomes the root canal;

how does chyme move along the SI

some very weak, short-distance peristalsis does occur even when full; second the pacemakers in the duodenum depolarize more frequently than those in the ileum; as a result, segmentation also moves intestinal contents slowly and steadily toward the ileocecal valve at a rate that allows ample time to complete digestion and absorption; unlike the strength of contraction, the basic contractile rhythm of each intestinal region is not affected by reflexes or hormones

lacteal

special lymphatic capillaries of the small intestine that take up lipids found in the core of each villus

control of HCl-secreting parietal cells

stimulated by three chemicals: ACh, gastrin, and histamine; when one of the three binds to its receptors, secretion of it is scanty, but when all three bind, HCl pours fourth

how the presence of food in the small intestine inhibit gastric secretion and motility

stimulates enteroendocrine cells to secrete enterogastrones (secretin and CCK) and chemo/stretch receptors trigger enterogastric reflex short and long reflexes

Gastrin

stimulates the release of enzymes, but its main target is the HCl-secreting parietal cells; it prods parietal cells to spew out HCl by acting directly on receptors on these cells, and by stimulating enterendocrine cells to release histamine

the muscularis externa

surrounding the submucosa; also simply called the muscularis; layer is responsible for segmentation and peristalsis; typically has an inner circular layer and an outer longitudinal layer of smooth muscle cells; in several places along the tract, the circular layer thickens, forming sphincters that act as valves to control food passage from one organ to the next and prevent backflow; unitary smooth muscle that has electrically coupled gap junctions an so contracts as a unit, is arranged in longitudinal and circular sheets, and exhibits rhythmic spontaneous action potentials.

cardial sphincter

surrounds the cardial orifice; only structural evidence of this sphincter is a slight thickening of the circular smooth muscle at that point; the muscular diaphragm, which surrounds it helps keep it close when food is not being swallowed; mucous cells on both side of it hep protect the esophagus from reflux of stomach acid

deglutition

swallowing; two major phases involved: the buccal phase: occurs in the mouth and is voluntary. it ends when a food bolus or a "bit of saliva" leaves the mouth and stimulates tactile receptors in the posterior pharynx, initiating the next phase pharyngeal-esophageal phase: involuntary and is controlled by the swallowing center in the brain stem (medulla and lower pons); various cranial nerves, most importantly the vagus nerves, transmit motor impulses from the swallowing center to the muscles of the pharynx and esophagus; once food enter the pharynx, respiration is momentarily inhibitied and all routes except the desired on into the digestive tract are blocked off; solid food pass from the oropharynx to the stomach in about 8 seconds, and fluids, aided by gravity, pass in 1 to 2 seconds

housekeeping function of the motor migrating complex

sweeps the last remnants of a meal plus bacteria, sloughed-off mucosal cells, and other debris into the LI via perstaltic waves

ways enteric bacteria are important to our nutrition

synthesize B vitamins and some K the liver needs to synthesize clotting proteins

ducts of the exocrine parts of the pancreas

system that transports the secretions of the acinar cells; in addition, the epithelial cells of the smallest ones secrete the water that makes up the bulk of the pancreatic juice and the bicarbonate that makes this secretion alkaline (pH 8)

digestive system

takes in food, breaks it down into nutrient molecules, absorbs these molecules into the bloodstream, and then rids the body of the indigestible remains; in other words, system that processes food into absorbable units and eliminates indigestible wastes

conical or fanglike canines

tear and pierce

three unique features of the LI

teniae coli, haustra, and epiploic appendages

primary site of lipid digestion

the SI because the pancreas is the major source of fat-digesting enzymes or lipases

two main groups of the digestive system organs

the alimentary canal and the accessory digestive organs

small intestine

the body's major digestive organ; within its twisted passageway, digestion is completely (with the help of bile and pancreatic enzymes) and virtually all absorption occurs; extends from the pyloric sphincter to the ileocecal valve where it joins the large intestine; longest party of the alimentary canal; highly adapted for absorbing nutrients

major regions of the stomach

the cardial part: surrounds the cardial orifice through which food enters the stomach from the esophagus; the fundus: is the stomachs dome-shaped part, tucked beneath the diaphragm, that bulges superolaterally to the cardia; the body: is continuous inferiorly with funnel-shaped pyloric part; the wider and more superior area of the pyloric part, they pyloric antrum, narrows to form the pyloric canal which terminates at the pylorus; the pylorus is continuous with the duodenum through the pyloric sphincter or valve which controls stomach emptying

two major region of each tooth

the crown and the root

two mechanisms that cause the ileocecal valve to relax and allow food residues to enter the cecum when ileal motility increases

the gastroileal reflex and gastrin

keeping pathogenic bacteria in check

the immune system and the gut flora live in a dynamic equilibrium; IS destroys any bacteria that threaten to breach the mucosal barrier; the gut bacteria instruct the IS not to overreact to their presence in the lumen

enteric nervous system

the in-house nerve supply of the alimentary canal; staffed by enteric neurons that communicate widely with one another to regulate digestive system activity; semiautonomous enteric neurons constitute the bulk of the two major intrinsic nerve plexuses (ganglia interconnected by unmyelinated fiber tracts) found in the walls of the alimentary canal: the submucosal and myenteric nerve plexuses; participates in both short and long reflex arcs

how are the respiratory passages blocked during swallowing

the larynx rises and the epiglottis covers its lumen so that foodstuffs are diverted into the esophagus instead of the trachea

anal canal

the last segment of the LI; lies in the perineum, entirely external to the abdominopelvic cavity; begins where the rectum penetrates the levator ani muscle of the pelvic floor and opens to the body exterior at the anus; has two sphincters, an involuntary internal anal sphincter composed of smooth muscle (part of the muscularis), and a voluntary external anal sphincter composed of skeletal muscle

cirrhosis

the last stage of progressive chronic inflammation of the liver; damaged hepatocytes can regenerate, but the liver's connective (scar) tissue regenerates faster; liver activity is depressed and the liver becomes fibrous with scar tissues which obstructs blood flow throughout the hepatic portal system, causing portal hypertension

stomach mucosa

the lining epithelium is a simple columnar epithelium composed entirely of mucous cells; they produce a cloudy, protective two-layer coat of alkaline mucus in which the surface layer consists of viscous, insoluble mucus that traps a layer of bicrabonate-rich fluid beneath it; dotted with millions of deep gastric pits, which lead into tubular gastric glands that produce the stomach secretion called gastric juice

The mouth and its accessory digestive organs are involved in 4 of the 6 digestive processes

the mouth ingest, begins mechanical breakdown by chewing, initiates propulsion by swallowing, and starts the digestion of polysaccharides ; absorption doesn't occur in the mouth except for a few drugs that are absorbed through the oral mucosa (nitroglycerine used to alleviate the pain of angina); chewing and swallowing are the mechanical processes that promote mechanical breakdown and propulsion, respectively

organs of the alimentary canal

the mouth, pharynx, esophagus, stomach, small intestine, and large intestine which leads to the terminal opening, or anus; food material in this tube is technically outside of the body because the canal is open to the external environment at both ends

during defecation

the muscles of the rectum contract to expel the feces; we aid this process voluntarily by closing the glottis and contracting our diaphragm and abdominal wall muscles to increase the intra-abdominal pressure (Valsalva's maneuver); also contract the levator ani muscle, which lifts the anal canal superiorly; this lifting action leaves the feces below the anus, and outside the body

if large amounts of chyme rushed into the small intestine

the osmotic water loss from the blood into the intestinal lumen would result in dangerously low blood volume because of it's hypertonic properties

the serosa

the outermost layer of the intraperitoneal organs, is the visceral peritoneum; in most alimentary canal organs, it is formed of areolar connective tissue covered with mesothelium, a single layer of squamous epithleial cells

when protein foods are in the stomach

the pH of the gastric content generally rises because proteins act as buffers to tie up H+; the rise in pH stimulates gastrin secretion and subsequently HCl release, which in turn provides the acidic conditions needed to digest them; the more protein in the meal, the greater the amount of gastrin and HCl released; as proteins are digested, the gastric contents gradually become more acidic, which again inhibits the gastrin-secreting cells; this negative feedback mehancism helps maintain optimal pH and working conditions for gastric enzymes

migrating motor complex

the primary motor pattern that is a form of peristalsis that happens in the SI between meals; the peristalsis is largely a housekeeping function that sweeps debris toward the large intestine; peristaltic waves initiated as motilin blood levels rise, each successive wave beings a bit more distally; a complete "trip" from duodenum to ileum takes about two hours; process than repeats itself, sweeping the last remnants of the meal plus bacteria, sloughed-off mucosal cells and other debris into the LI

in the esophagus, which is located in the thoracic instead of the abdominopelvic cavity

the serosa is replaced by an adventita, ordinary dense connective tissue that bind the esophagus to surrounding structures

most digestion is done in

the small intestine

accessory digestive organs

the teeth, tongue, gallbladder, and a number of large digestive glands- the salivary glands, liver, and pancreas which lie outside the GI tract and connect to it by ducts; it's glands produce a variety of secretions that help break down foodstuffs

how the gut bacteria shape our immune system responses

the type of bacteria present influences the balance between subtypes of T cells, and so affects the balance between pro and anti inflammatory responses; the coexistence of enteric bacteria with our immune system does sometimes fail; when that happens, the painful and debilitating condition known as inflammatory bowel disease may result

differences of location of the peritoneum

the visceral part is the outermost layer of the digestive organ; the parietal part is the serous membrane covering the wall of the abdominal cavity