Ch. 24 - The Digestive System

pulp cavity (dentes)

The dentin of a tooth encloses a enlarged space within the crown filled with *pulp*, a connective tissue containing blood vessels, nerves, and lymphatic vessels.

layers of the GI tract

The four layers of the tract, from deep to superficial, are the: *mucosa* - epithelium, enteroendocrine cells - lamina propria, MALT - muscularis mucosae *submucosa* - submucosal plexus *muscularis * *serosa* - visceral peritoneum - adventitia

fundus, body, neck (gallbladder)

The functions of the gallbladder are to store and concentrate the bile produced by the liver (up to tenfold) until it is needed in the small intestine. Parts: - broad fundus, which projects inferiorly beyond the inferior border of the liver - the body, the central portion, projects superiorly - the neck, the tapered portion, projects superiorly - inner: mucosa - simple columnar epithelium (rugae like stomach), stores water and ions - no submucosa - middle: muscular smooth muscle fibers (contraction ejects bile into cystic duct) - outer: visceral peritoneum

intestinal juice (small intestine)

a clear yellow fluid that contains water and mucus and is slightly alkaline (pH 7.6). The alkaline pH of intestinal juice is due to its high concentration of bicarbonate ions (HCO3-).

mass peristalsis (large intestine mech. digestion)

a final type of movement in mechanical digestion of the large intestine is a strong peristaltic wave that begins at about the middle of the transverse colon and quickly drives the contents of the colon into the rectum

lingual frenulum (tongue)

a fold of mucous membrane in the midline of the undersurface of the tongue; attached to the floor of the mouth function aids in limiting the movement of the tongue posteriorly

pharynx

a funnel-shaped tube that extends from the internal nares to the esophagus posteriorly and to the larynx anteriorly structure: skeletal muscle lined by mucous membrane 3 parts: *nasopharynx* - respiration *oropharynx and laryngopharynx* - respiratory and digestive function - where food from the mmouth passes - muscular contractions of these areas help propel food into the esophagus and then into the stomach.

salivary glands (buccal cavity)

a gland that releases saliva into the oral cavity for salivation function: moisten the mucous membranes of the mouth and pharynx; cleanse the mouth and teeth; lubricates, dissolves, and begins the chemical breakdown of the food glands: *submandibular (A)* *sublingual (B)* *parotid (C)*

small intestine

a long tube, after stomach, where most digestion and absorption of nutrients occur length provides large surface area which is further increased by circular folds, villi, and microvilli begins at the pyloric sphincter and coils through the central and inferior part of the abdominal cavity; eventually opens to the large intestine

uvula (buccal cavity)

hanging from the free border of the soft palate is a fingerlike muscular structure During swallowing, the soft palate and uvula are drawn superiorly, closing off the nasopharynx and preventing swallowed foods and liquids from entering the nasal cavity.

gastrointestinal (GI) tract or alimentary canal (digestive system)

is a continuous tube that extends from the mouth to the anus through the thoracic and abdominopelvic cavities. mouth, most of the pharynx, esophagus, stomach, small intestine, and large intestine.

functions of the liver

In addition to secreting bile, which is needed for absorption of dietary fats, the liver performs many other vital functions: (1) *Carbohydrate metabolism.* The liver is especially important in maintaining a normal blood glucose level. When blood glucose is low, the liver can break down glycogen to glucose and release the glucose into the bloodstream. The liver can also convert certain amino acids and lactic acid to glucose, and it can convert other sugars, such as fructose and galactose, into glucose. When blood glucose is high, as occurs just after eating a meal, the liver converts glucose to glycogen and triglycerides for storage. (2) *Lipid metabolism.* Hepatocytes store some triglycerides; break down fatty acids to generate ATP; synthesize lipoproteins, which transport fatty acids, triglycerides, and cholesterol to and from body cells; synthesize cholesterol; and use cholesterol to make bile salts. (3) *Protein metabolism.* Hepatocytes deaminate amino acids so that the amino acids can be used for ATP production or converted to carbohydrates or fats. The resulting toxic ammonia (NH3) is then converted into the much less toxic urea, which is excreted in urine. Hepatocytes also synthesize most plasma proteins, such as alpha and beta globulins, albumin, prothrombin, and fibrinogen. (4) *Processing of drugs and hormones.* The liver can detoxify substances such as alcohol and excrete drugs such as penicillin, erythromycin, and sulfonamides into bile. It can also chemically alter or excrete thyroid hormones and steroid hormones such as estrogens and aldosterone. (5) *Excretion of bilirubin.* As previously noted, bilirubin, derived from the heme of aged RBC, is absorbed by the liver from the blood and secreted into bile. Most of the bilirubin in bile is metabolized in the small intestine by bacteria and eliminated in feces. (6) *Synthesis of bile salts.* Bile salts are used in the small intestine for the emulsification and absorption of lipids. (7) *Storage.* In addition to glycogen, the liver is a prime storage site for certain vitamins (A, B12, D, E, and K) and minerals (iron and copper), which are released from the liver when needed elsewhere in the body. (8) *Phagocytosis.* The stellate reticuloendothelial (Kupffer) cells of the liver phagocytize aged RBC, WBC, and some bacteria. (9) *Activation of vitamin D.* The skin, liver, and kidneys participate in synthesizing the active form of vitamin D. tldr: - carb, lipid, protein metabolism - drug and hormone processing - bilirubin excretion - bile salt synthesis - storage - phagocytosis - VitD activation

retroperitoneal (periotoneum)

'behind' term for some organs that lie on the posterior abdominal wall and are covered by peritoneum only on their anterior surfaces = not in the peritoneal cavity. I.e. the kidneys, ascending and descending colons of the large intestine, duodenum of the small intestine, and pancreas

6 basic processes of the digestive system

(1) *ingestion* This process involves taking foods and liquids into the mouth (eating). (2) *secretion* Each day, cells within the walls of the GI tract and accessory digestive organs secrete a total of about 7 liters of water, acid, buffers, and enzymes into the lumen (interior space) of the tract. (3) *mixing and propulsion* Alternating contractions and relaxations of smooth muscle in the walls of the GI tract mix food and secretions and move them toward the anus. This capability of the GI tract to mix and move material along its length is called *motility* (4a) *mechanical digestion* The teeth cut and grind food before it is swallowed, and then smooth muscles of the stomach and small intestine churn the food to further assist the process. As a result, food molecules become dissolved and thoroughly mixed with digestive enzymes. (4b) *chemical digestion* The large carbohydrate, lipid, protein, and nucleic acid molecules in food are split into smaller molecules by hydrolysis Digestive enzymes produced by the salivary glands, tongue, stomach, pancreas, and small intestine catalyze these catabolic reactions. few substances in food can be absorbed without chemical digestion. These include vitamins, ions, cholesterol, and water. (5) *absorption* The entrance of ingested and secreted fluids, ions, and the products of digestion into the epithelial cells lining the lumen of the GI tract is called absorption. The absorbed substances pass into blood or lymph and circulate to cells throughout the body. (6) *defecation* Wastes, indigestible substances, bacteria, cells sloughed from the lining of the GI tract, and digested materials that were not absorbed in their journey through the digestive tract leave the body as *feces/stools* through the anus in a process called defecation

lobules (hepatic and portal); hepatic acinus (liver)

*Hepatic lobule* - hexagon-shaped - center: central vein - radiating out: rows of hepatocytes and hepatic sinusoids - 3 corners: portal triad - based on pig-models, hard to find in humans due to thick connective tissues *Portal lobule* - triangle-shaped - defined by imaginary straight lines that connect 3 central veins that are closes to the portal triad - center: bile duct of portal triad - model has not gained widespread acceptance *hepatic acinus* - oval-shaped - short axis: branches of the portal triad—branches of the hepatic artery, vein, and bile ducts— that run along the border of the hepatic lobules - long axis: two imaginary curved lines, which connect the two central veins closest to the short axis - hepatocytes arranged in 3 zones around short axis with no sharp boundaries Zone 1 - cells closest to portal triad - first to receive incoming O2, nutrients, and toxins from blood - first to take up glucose or breakdown glycogen after a meal or during fasting - first to show morphological changes following bile duct obstruction or exposure to toxic substances - cells are last to die if circulation is impaired and the first ones to regenerate Zone 2 - cells have structural and functional characteristics intermediate between the cells in zones 1 and 3. Zone 3 - cells farthest from portal triad - opposite of zone 1 in effects - also first to show evidence of fat accumulation - most preferred model for structural and function units in recent years - provides a logical description and interpretation of (1) patterns of glycogen storage and release and (2) toxic effects, degeneration, and regeneration relative to the proximity of the acinar zones to branches of the portal triad

pancreas histology

*acini* - 99% small clusters of glandular epithelial cells - exocrine portion of the organ - secrete a mixture of fluid and digestive enzymes called pancreatic juice *pancreatic islets (Langerhans)* - 1% of small clusters of glandular epithlial cells - endocrine portion of the pancreas. - secretes glucagon, insulin, somatostatin, pancreatic polypeptide.

enzymes that digest carbohydrates (small intestine)

*dextrinase* - acts on resulting a-dextrins (i.e. cellulose, an indigestible plant fiber) from smaller starch fragments 3 brush-border enzymes: - digest di- to monosaccharides, which is then absorbable *sucrase* sucrose -> glucose + fructose *lactase lactose -> glucose + galatose *maltase* maltose and maltriose -> 2-3 glucose

mucosa (large intestine)

*epithelium* - simple columnar - absorptive cells (water absorption) - goblet cells (secrete mucus that lubricates the passage of the colonic content) - both cells located in *intestinal glands or crypts of Lieberkunh* that extend the full thickness of the mucosa *lamina propria* - areolar connective tissue - *solitary lymphatic nodules*, may extend through the muscularis mucosae into the submucosa. *muscularis mucosae* - smooth muscles large intestine does not have as many structural adaptations no circular folds or villi, only microvilli are present on the absorptive cells.

large intestine mechanical digestion

*gastroileal reflex* *haustral churning* *mass peristalsis* *gastrocolic reflex*

mucosa, submucosa and muscularis (esophagus)

*mucosa:* - nonkeratinized stratified squamous epithelium (protection against abrasion, wear, and tear) - lamina propria (areolar connective tissue), - muscularis mucosae (smooth muscle) - near the stomach, it also contains mucous glands. *submucosa* - areolar connective tissue - blood vessels, glands *muscularis:* - superior third: skeletal - intermediate third: skeletal and smooth - inferior third: smooth circular layer longitudinal layer

pyloric parts (stomach)

*pyloric antrum* - first region, connects to the stomach body *pyloric canal* - second region, leads to next *pylorus* - third region, connects to duodenum (A in picture)

rectum, anal canal, anus

*rectum*: lies anterior to the sacrum and coccyx. *anal canal*: terminal part of the large intestine *anal columns*: mucous membrane arranged in longitudinal folds, contain a network of arteries and veins. *anus*: opening of the anal canal to the exterior *internal anal sphincter*: smooth muscles (involuntary), guards anus *external anal sphincter*: skeletal muscles (voluntary), guards anus

enzymes of chemical digestion in mouth

*salivary amylase* - secreted by salivary glands - initiates breakdown of starch (i.e. monosaccharide, disaccharide, polysaccharides) - acts on the food for about 1 hr. until stomach acid inactivates it *lingual lipase* - secreted by lingual glands - activated by stomach acid - breaks down dietary triglycerides (fats and oils) into fatty acids and diglycerides

histology of liver and gallbladder

- hepatocytes - bile canaliculi ducts - right, left, common hepatic ducts - cystic duct, common bile duct - sinusoids, central vein - lobules (hepatic, portal) - hepatic acinus

cementum (dentes)

covers the root dentin, another bonelike substance, which attaches the root to the periodontal ligament.

mechanical digestion (small intestine)

2 types of movements governed mainly by the myenteric plexus. *segmentation* and *migrating motility complex (MMC)*

muscularis (stomach)

3 additional smooth muscle layers that lie deep to the mucosa (rather than the two found in the esophagus and small and large intestines) outer longitudinal layer middle circular layer inner oblique layer the oblique layer is limited primarily to the body of the stomach.

histology of large intestine

4 layers found in the rest of GI tract: *mucosa* epithelium - simple columnar - absorptive and goblet cells lamina propria - areolar connective tissue muscularis mucosae - smooth muscle *submucosa* - areolar connective tissue *muscularis* - outer longitudinal smooth muscles - inner circular smooth muscle - teniae coli - haustra *serosa*

mesentery (periotoneum)

A fan-shaped fold of the peritoneum binds the jejunum and ileum of the small intestine to the posterior abdominal wall Components: typically laden with fat Location: extends from the posterior abdominal wall to wrap around the small intestine and then returns to its origin, forming a double-layered structure. Between the two layers are blood and lymphatic vessels and lymph nodes.

migrating motility complex (MMC) (small intestine)

After most of a meal has been absorbed, which lessens distension of the wall of the small intestine, segmentation stops and peristalsis begins This is a type of peristalsis that begins in the lower portion of the stomach and pushes chyme forward along a short stretch of small intestine before dying out. The MMC slowly migrates down the small intestine, reaching the end of the ileum in 90-120 minutes. Then another MMC begins in the stomach. Altogether, chyme remains in the small intestine for 3-5 hours.

enterohepatic circulation

After participating in the emulsification and absorption of lipids, most of the bile salts are reabsorbed by active transport in the final segment of the small intestine (ileum) and returned by the blood to the liver through the hepatic portal system for recycling. This cycle of bile salt secretion by hepatocytes into bile, reabsorpion by the ileum, and resecretion into bile is called the enterohepatic circulation.

absorption of monosaccharides

All carbohydrates are absorbed as monosaccharides. The capacity of the small intestine to absorb monosaccharides is huge as all dietary carbohydrates that are digested normally are absorbed, leaving only indigestible cellulose and fibers in the feces. *Monosaccharides* pass from the lumen through the apical membrane via *facilitated diffusion or active transport.* Monosaccharides then move out of the absorptive cells through their basolateral surfaces via *facilitated diffusion* and enter the capillaries of the villi *Fructose*, a monosaccharide found in fruits, is transported via *facilitated diffusion* *Glucose and galactose* are transported into absorptive cells of the villi via *secondary active transport* that is coupled to the active transport of Na+. - transporter has binding sites for 1 Glucose and 2 Na+; unless all three sites are filled, neither substance is transported. - galactose competes with glucose to ride the same transporter. (Because both Na+ and glucose or galactose move in the same direction, this is a symporter.)

absorption of lipids and bile salts

All dietary lipids (small short-chain, large short-chain, long-chain, monoglycerides) are absorbed via *simple diffusion*. Adults absorb about 95% of the lipids present in the small intestine; due to their lower production of bile, newborn infants absorb only about 85% of lipids. *small short-chain FA* - dissolve in chyme - pass absorptive cell via simple diffusion and same into blood capillary of villus *large short-chain, long-chain, or monoglycerides FA* - surrounded by bile salts, forming a *micelles* - FA diffuse out of micelles (left in chyme) into absorptive cells - FA recombines to form triglycerides which aggregate with phospholipids and cholesterol, and coated with protein (helps suspend in blood and prevent sticking), into masses called *chylomicrons* - chylomicrons leave cells via exocytosis and enter lacteals which have larger pores than capillaries - transported via lymphatic vessels and enter blood at left internal jaguar and left subclavian vein junction - *lipoprotein lipase* attached to apical surface of capillary epithelial cells breakdown triglycerides to other lipoproteins (i..e FA and glycerol) Micelles - hydrophobic region interact with FA and hydrophilic region interact with watery chyme - move from interior of small intestinal lumen to brush border of absorptive cells - micelles also solubilize other large hydrophobic molecules such as fat-soluble vitamins (A, D, E, and K) and cholesterol that may be present in intestinal chyme, and aid in their absorption.

retropulsion (stomach)

Because most food particles in the stomach initially are too large to fit through the narrow pyloric sphincter, they are forced back into the body of the stomach in a process call this. pyloric sphincter normally remains almost, but not completely, closed. If the food particles are still too large to pass through the pyloric sphincter, retropulsion occurs again as the particles are squeezed back into the body of the stomach. Then yet another round of propulsion occurs and the cycle continues to repeat.

absorption in the small intestine

All of the chemical and mechanical phases of digestion from the mouth through the small intestine are directed toward changing food into forms that can pass through the absorptive epithelial cells lining the mucosa and into the underlying blood and lymphatic vessels. These forms are monosaccharides (glucose, fructose, and galactose) from carbohydrates; single amino acids, dipeptides, and tripeptides from proteins; and fatty acids, glycerol, and monoglycerides from triglycerides. Passage of these digested nutrients from the GI tract into the blood or lymph is called absorption. Absorption of materials occurs via diffusion, facilitated diffusion, osmosis, and active transport. About 90% of all absorption of nutrients occurs in the small intestine; the other 10% occurs in the stomach and large intestine. Any undigested or unabsorbed material left in the small intestine passes on to the large intestine.

appendix or vermiform appendix

Attached to the cecum is a twisted, coiled tube which is attached to the inferior part of the mesentery of the ileum by the mesoappendix

absorption and feces formation

By the time chyme has remained in the large intestine 3-10 hours, it has become solid or semisolid because of water absorption and is now called feces. Chemically, feces consist of water, inorganic salts, sloughed-off epithelial cells from the mucosa of the gastrointestinal tract, bacteria, products of bacterial decomposition, unabsorbed digested materials, and indigestible parts of food. The large intestine absorbs enough to make it an important organ in maintaining the body's water balance and also absorbs ions, including sodium and chloride, and some vitamins.

histology of the esophagus

From deep to superficial: *lumen of esophagus* *mucosa:* nonkeratinized stratified squamous epithelium lamina propria (areolar connective tissue), muscularis mucosae (smooth muscle) *submucosa* areolar connective tissue *muscularis:* circular layer longitudinal layer *adventitia* -> see detail notes

phases of digestion

Digestive activities occur in 3 overlapping phases: *cephalic phase* *gastric phase* - neuronal and hormonal regulation *intestinal phase* - neuronal and hormonal regulation

autonomic nervous system (GI tract neural innervation)

ENS can function independently but they are subject to regulation by ANS neurons *Parasympathetic NS* - speeds up GI activity (increase secretion and motility via activating ENS neurons) - supplied by vagus (X) nerves (except last half of large intestine, supplied by fibers from sacral SC) - PNS nerves form neural connections with ENS *Sympathetic NS* - slows down GI activity (decrease secretion and motility via inhibiting ENS neurons) - supplied by thoracic and lumbar nerves of SC - postganglionic neurons synapse neurons in myenteric and submucosal plexus. - emotions such as anger, fear, and anxiety may stimulate these nerves that supply the GI (slows digestion)

composition and functions of pancreatic juice

Each day the pancreas produces 1200-1500 mL (about 1.2-1.5 qt) of pancreatic juice. A clear, colorless liquid consisting mostly of water, some salts, sodium bicarbonate, and several enzymes. The sodium bicarbonate gives pancreatic juice a slightly alkaline pH (7.1-8.2) that buffers acidic gastric juice in chyme, stops the action of pepsin from the stomach, and creates the proper pH for the action of digestive enzymes in the small intestine.

parotid duct (buccal cavity)

Each parotid gland secretes saliva into the oral cavity via a parotid duct that pierces the buccinator muscle to open into the vestibule opposite the second maxillary (upper) molar tooth.

apical foramen tooth

Each root canal has an opening at its base, through which blood vessels, lymphatic vessels, and nerves enter a tooth. The blood vessels bring nourishment, the lymphatic vessels offer protection, and the nerves provide sensation.

defecation reflex

Eliminates feces through the anus by contractions in sigmoid colon and rectum. peristaltic movements push fecal material from the sigmoid colon into the rectum. The resulting distension of the rectal wall stimulates stretch receptors, which initiates a defecation reflex that results in defecation 1.) In response to distension of the rectal wall, the receptors send sensory nerve impulses to the sacral spinal cord. 2.) Motor impulses from the cord travel along parasympathetic nerves back to the descending colon, sigmoid colon, rectum, and anus. 3.) The resulting contraction of the longitudinal rectal muscles shortens the rectum, thereby increasing the pressure within it. 4.) This pressure, along with voluntary contractions of the diaphragm and abdominal muscles, plus parasympathetic stimulation, opens the internal anal sphincter. 5.) The external anal sphincter is voluntarily controlled. If it is voluntarily relaxed, defecation occurs and the feces are expelled through the anus; if it is voluntarily constricted, defecation can be postponed.

root(s) (dentes)

Embedded in the socket are one to three roots.

enzymes that digest lipids (small intestine)

Enzymes that split triglycerides (most abundant) and phospholipids are called *lipases* - i.e. lingual lipase, gastric lipase, and pancreatic lipase Before a large lipid globule containing triglycerides can be digested in the small intestine, it must first undergo emulsification—large lipid globule is broken down into several small lipid globules. *pancreatic lipase* - digest most fats in the small intestine - tiglycerides -> fatty acids + monoglycerides

blood supply of the liver (liver)

From central veins the blood flows into the hepatic veins, which drain into the inferior vena cava in contrast to blood, which flows toward a central vein, bile flows in the opposite direction. Liver receives blood from 2 sources: 1.) *hepatic artery* for oxygenated blood, 2.) *hepatic portal vein* for deoxygenated blood containing newly absorbed nutrients, drugs, and possibly microbes and toxins from the gastrointestinal tract Branches of both the hepatic artery and the hepatic portal vein carry blood into hepatic sinusoids, where oxygen, most of the nutrients, and certain toxic substances are taken up by the hepatocytes. Products manufactured by the hepatocytes and nutrients needed by other cells are secreted back into the blood, which then drains into the central vein and eventually passes into a hepatic vein. Because blood from the gastrointestinal tract passes through the liver as part of the hepatic portal circulation, the liver is often a site for metastasis of cancer that originates in the GI tract.

central vein (liver)

Hepatic sinusoids converge and deliver blood into a central vein.

stomach

J-shaped enlargement of the GI tract directly inferior to the diaphragm in the abdomen. The stomach connects the esophagus to the duodenum, the first part of the small intestine serve as a mixing chamber and holding reservoir. At appropriate intervals after food is ingested, the stomach forces a small quantity of material into the first portion of the small intestine.

absorption of electrolytes

Many of the electrolytes absorbed by the small intestine come from gastrointestinal secretions, and some are part of ingested foods and liquids. Na+ in GI secretions are reclaimed and not lost in the feces. Ca2+ ions also are absorbed actively in a process stimulated by calcitriol. Negatively charged bicarbonate, Cl-, I- and nitrate ions can passively follow Na+ or be actively transported. Other electrolytes such as iron, potassium, magnesium, and phosphate ions also are absorbed via active transport mechanisms.

absorption of amino acids, dipeptides and tripeptides

Most proteins are absorbed (>95% of the proteins present) as amino acids via *active transport processes* that occur mainly in the duodenum and jejunum. About half of the absorbed amino acids are present in food; the other half come from the body itself as proteins in digestive juices and dead cells that slough off the mucosal surface! Some amino acids enter absorptive cells of the villi via *Na+-dependent secondary active transport processes* that are similar to the glucose transporter; other amino acids are *actively transported* by themselves. At least one symporter brings in dipeptides and tripeptides together with H+; the peptides then are hydrolyzed to single amino acids inside the absorptive cells. Amino acids move out of the absorptive cells via *diffusion* and enter capillaries of the villus Both monosaccharides and amino acids are transported in the blood to the liver by way of the hepatic portal system. If not removed by hepatocytes, they enter the general circulation.

cuspids or canines

Nnxt to the incisors, moving posteriorly; pointed surface called a cusp and are used to tear and shred food; only have 1 root/tooth canine (16-24 mo.)

enzymes that digest nucleic acids (small intestine)

Pancreatic juice contains two nucleases: *ribonuclease* which digests RNA, *deoxyribonuclease* which digests DNA. The nucleotides that result from the action of the two nucleases are further digested into pentoses, phosphates, and nitrogenous bases by brush-border enzymes: *nucleosidases* and *phosphatases* These products are absorbed via active transport.

propulsion (stomach)

Several minutes after food enters the stomach, waves of peristalsis pass over the stomach every 15 to 25 seconds. Few peristaltic waves are observed in the fundus, which primarily has a storage function. Instead, most waves begin at the body of the stomach and intensify as they reach the antrum. Each peristaltic wave moves gastric contents from the body of the stomach down into the antrum, a process known as *propulsion*.

voluntary stage (deglutition)

Swallowing starts when the bolus is forced to the back of the oral cavity and into the oropharynx by the movement of the tongue upward and backward against the palate;

cystic duct (liver)

The common hepatic duct joins the cystic duct from the gallbladder to form the *common bile duct*. From here, bile enters the duodenum of the small intestine to participate in digestion.

Major digestion hormones

Table 24.8. Gastrin, Secretin, CCK *Gastrin* Stimulus: stomach distension, partially digested proteins and caffeines, high stomach chyme pH Site: enteroendocrine G cells in mucosa of pyloric antrum of stomach Major effect: promotes gastric juice secretion, increase gastric juice motility, promotes growth of gastric mucosa Minor effect: contricts lower esophageal sphincter, relaxes pyloric spincter *Secretin* Stimulus: acidic chyme that enters small intestine Site: enteroendocrine S cells in mucosa of duodenum Major effect: stimulates secretion of pancreatic juice and bile that are rich in HCO3- Minor effect: inhibits secretion of gastric juice, promotes normal growth and maintenance of pancreas, enhances CCK effects *CCK* Stimulus: partially digested proteins (a.a.), triglycerides, and fatty acids that enter small intestine Site: enteroendocrine CCK cells in mucosa of small intestine, CCK also released in brain Major effect: stimulates secretion of pancreatic juice rich in digestive enzymes, ejection of bile from gallbladder and opening of sphincter of the hepatopancreatic ampulla (Oddi), induces satiety Minor effect: inhibits gastric emptying, promotes normal growth and maintenance of pancreas, enhances effects of secretin

right and left hepatic ducts (liver)

The bile ducts merge and eventually form the larger right and left hepatic ducts,

deglutition

The movement of food from the mouth into the stomach is achieved by the act of swallowing; facilitated by the secretion of saliva and mucus and involves the mouth, pharynx, and esophagus. Swallowing occurs in three stages: (1) *voluntary stage* - bolus is passed into the oropharynx (2) *pharyngeal stage* - involuntary passage of the bolus through the pharynx into the esophagus (3) *esophageal stage* - involuntary passage of the bolus through the esophagus into the stomach. mouth to the stomach takes 4 to 8 seconds; very soft foods and liquids pass through in about 1 second.

enteric nervous system (ENS)

The neurons of the ENS extends from the esophagus to the anus and are arranged into 2 plexuses: *myenteric (Auerbach) plexus* *submucosal (Meissner) plexus* - the plexuses consist of motor neurons, interneurons, and sensory neurons - interneurons interconnect the neurons of the 2 plexus - the sensory neurons supply the mucosal epithelium and contain receptors that detect stimuli in the lumen of the GI tract The wall of the GI tract contains two major types of sensory receptors: (1) *chemoreceptors* - respond to certain chemicals in the food present in the lumen, (2) *mechanoreceptors* - i.e. stretch receptors that are activated when food distends (stretches) the wall of a GI organ.

colon

The open end of the cecum merges with a long tube called the colon (= food passage) Both the ascending and descending colon are retroperitoneal; the transverse and sigmoid colon are not. *ascending colon* ascends on the right side of the abdomen, reaches the inferior surface of the liver, and turns abruptly to the left to form the right colic (hepatic) flexure. *transverse colon* The colon continues across the abdomen to the left side as the transverse colon. *descending colon* It curves beneath the inferior end of the spleen on the left side as the left colic (splenic) flexure and passes inferiorly to the level of the iliac crest as the descending colon. *sigmoid colon* begins near the left iliac crest, projects medially to the midline, and terminates as the rectum at about the level of the third sacral vertebra.

cecum (large intestine)

The opening from the ileum into the large intestine is guarded by a fold of mucous membrane called the ileocecal sphincter (valve), which allows materials from the small intestine to pass into the large intestine.

sphincter of the hepatopancreatic ampulla or sphincter of Oddi (pancreas)

The passage of pancreatic juice and bile through the hepatopancreatic ampulla into the duodenum of the small intestine is regulated by a mass of smooth muscle surrounding the ampulla known as this H in picture

permanent first molars, second molars and third molars (or wisdom teeth) (dentes)

The permanent molars, which erupt into the mouth posterior to the premolars, do not replace any deciduous teeth and erupt as the jaw grows to accommodate the First molar (6-7 yr.) Second molar (12-13 yr.) Third molar or wisdom tooth (17-21 yr. or not at all)

fundus (stomach)

The rounded portion superior to and to the left of the cardia, food storage function before chemical digestion

peritoneal cavity (periotoneum)

The slim space containing lubricating serous fluid that is between the parietal and visceral portions of the peritoneum

absorption of water

The total volume of fluid that enters the small intestine each day—about 9.3 liters The small intestine absorbs about 8.3 liters of the fluid; the remainder passes into the large intestine, where most of the rest of it—about 0.9 liter— is also absorbed. Only 0.1 liter (100 mL) of water is excreted in the feces each day. All water absorption in the GI tract occurs via *osmosis* from the lumen of the intestines through absorptive cells and into blood capillaries. Because water can move across the intestinal mucosa in both directions, the absorption of water from the small intestine depends on the absorption of electrolytes and nutrients to maintain an osmotic balance with the blood. The absorbed electrolytes, monosaccharides, and amino acids establish a concentration gradient for water that promotes water absorption via osmosis.

mesocolon (periotoneum)

Two separate folds of peritoneum, binds the transverse colon (transverse mesocolon) and sigmoid colon (sigmoid mesocolon) of the large intestine to the posterior abdominal wall It also carries blood and lymphatic vessels to the intestines. Together, the mesentery and mesocolon hold the intestines loosely in place, allowing movement as muscular contractions mix and move the luminal contents along the GI tract.

rugae (stomach)

When the stomach is empty, the mucosa lies in large folds, or wrinkles, that can be seen with the unaided eye.

peristalsis (deglutition)

a progression of coordinated contractions and relaxations of the circular and longitudinal layers of the muscularis, pushes the bolus onward (1) In the section of the esophagus just superior to the bolus, the *circular muscle fibers* contract, constricting the esophageal wall and squeezing the bolus toward the stomach. (2) *Longitudinal fibers* inferior to the bolus also contract, which shortens this inferior section and pushes its walls outward so it can receive the bolus contractions are repeated in waves that push the food toward the stomach. Steps 1 and 2 repeat until the bolus reaches the lower esophageal sphincter muscles. (3) The lower esophageal sphincter relaxes and the bolus moves into the stomach.

pancreas

a retroperitoneal gland; thick, lies posterior to the greater curvature of the stomach. anatomy: - *head, a body, and a tail* - *pancreatic duct (Wirsung)* - *heptopancreatic ampulla (Vater)* - *majorduodenal papilla* - *spincter of hepatopancreatic ampulla (Oddi) * - *accessory duct (Santorini)* histology: - acini - pancreatic islets (Langerhans) related: - pancreatic amylase - trypsin, chymotrypsin - carboxypeptidase - elastase - pancreatic lipase - ribonuclease and deoxyribonuclease - trypsinogen - enterokinase

brush border enzymes (small intestine)

absorptive cells of the small intestine synthesize several digestive enzymes, called brush-border enzymes, and insert them in the plasma membrane of the microvilli. thus, some enzymatic digestion occurs at the surface of the absorptive cells that line the villi, rather than in the lumen exclusively, as occurs in other parts of the GI tract. Also, as absorptive cells slough off into the lumen of the small intestine, they break apart and release enzymes that help digest nutrients in the chyme *carbohydrate-digesting enzymes* dextrinase, maltase, sucrase, lactase, *protein-digesting enzymes* peptidases (amino- and di-) *nucleotide-digesting enzymes* nucleosidases and phosphatases

tongue

accessory digestive organ composed of skeletal muscle covered with mucous membrane, forms the floor of the oral cavity. divided into symmetrical lateral halves by a median septum that extends its entire length, and it is attached inferiorly to the hyoid bone, styloid process of the temporal bone, and mandible. Each half of the tongue consists of an identical complement of *extrinsic and intrinsic muscles*. Other components: - lingual frenulum - papillae - lingual glands - lingual lipase

tooth or dentis (plural is dentes)

accessory digestive organs located in sockets of the alveolar processes of the mandible and maxillae. gingivae peridontal ligament/membrane crown, root, neck enamel, dentin, pulp cavity, pulp cementum root canals apical foramen dentitions deciduous/primary/milk/baby teeth central and lateral incisos cuspids or canines first and second molars permanent/secondary teeth incisors or cuspids first and second premolars or bicuspids first, second, and third molar or wisdom teeth mechanical and chemical digestion mastication bolus salivary amylase lingual lipase

enterokinase

activating brush-border enzyme at the small intestine lumen, activates trypsinogen -> trypsin In turn, trypsin acts on the inactive precursors (called chymotrypsinogen, procarboxypeptidase, and proelastase) to produce chymotrypsin, carboxypeptidase, and elastase, respectively.

permanent teeth or secondary teeth

all of the deciduous teeth are lost—generally between ages 6 and 12 years—and are replaced by 32 permanent (secondary) teeth (between 6 and adulthood) central incisor (7-8yr.) lateral incisor (8-9yr.) canine or cuspids (11-12yr.) first premolar or bicuspid (9-10 yr.) second premolar or bicupsid (10-12 yr.) first molar (6-7yr.) second molar (12-13yr.) third molar or wisdom tooth (17-21yr.)

gingivae (dentes)

alveolar processes, containing the tooth, are covered by this which extend slightly into each socket

diarrhea

an increase in the frequency, volume, and fluid content of the feces caused by increased motility of and decreased absorption by the intestines. When chyme passes too quickly through the small intestine and feces pass too quickly through the large intestine, there is not enough time for absorption. Frequent diarrhea can result in dehydration and electrolyte imbalances. Excessive motility may be caused by lactose intolerance, stress, and microbes that irritate the gastrointestinal mucosa.

mastication

another term for chewing or mechanical digestion of food in the mouth where it is manipulated by the tongue, grounded by the teeth, and mixed with saliva result: *bolus* - soft, flexible, easily swallowed mass of food

sublingual glands (buccal cavity)

are beneath the tongue and superior to the submandibular glands. contain mostly mucous cells, so they secrete a much thicker fluid that contributes only a small amount of salivary amylase.

lesser omentum (periotoneum)

arises as an anterior fold in the serosa of the stomach and duodenum, and it connects the stomach and duodenum to the liver Components: It is the pathway for blood vessels entering the liver and contains the hepatic portal vein, common hepatic artery, and common bile duct, along with some lymph nodes.

lower esophageal (cardiac) sphincter

at each end of esophagus, muscularis becomes more prominent and forms 2 sphincters smooth muscle and is near the heart; regulates the movement of food from the esophagus into the stomach.

upper esophageal sphincter

at each end of esophagus, muscularis becomes more prominent and forms 2 sphincters skeletal muscle, regulates the movement of food from the pharynx into the esophagus;

falciform ligament (periotoneum)

attaches the liver to the anterior abdominal wall and diaphragm The liver is the only digestive organ that is attached to the anterior abdominal wall.

ileocecal sphincter (small intestine)

band of muscle that encircles the junction of ileum and *cecum* (large intestine)

deciduous teeth or primary teeth or milk teeth or baby teeth (dentes)

begin: 6 months of age - approx. 2 teeth/month after until all 20 are present central incisor (8-12 mo.) lateral incisor (12-24 mo.) canine (16-24 mo.) first molar (12-16 mo.) second molar (24-32 mo.)

esophageal stage (deglutition)

begins once the bolus enters the esophagus; peristalsis is used to push it towards the stomach

role and composition of bile

bile is partially an excretory product and digestive secretion - pH of 7.6-8.6 - consists mostly of water, bile salts, cholesterol, a phospholipid called lecithin, bile pigments (*bilirubin*), and several ions.

pharyngeal stage (deglutition)

bolus stimulates receptors in the oropharynx, which send impulses to the *deglutition center* in the medulla oblongata and lower pons of the brain stem. returning impulses cause the soft palate and uvula to move upward to close off the nasopharynx, which prevents swallowed foods and liquids from entering the nasal cavity. the epiglottis closes off the opening to the larynx, which prevents the bolus from entering the rest of the respiratory tract bolus moves through the oropharynx and the laryngopharynx. Once the upper esophageal sphincter relaxes, the bolus moves into the esophagus. tldr: the tongue rises against the palate, the nasopharynx is closed off, the larynx rises, the epiglottis seals off the larynx, and the bolus is passed into the esophagus when upper esophageal spincter relaxes

salivary amylase (buccal cavity)

chloride ions in the saliva activate this enzyme that starts the breakdown of starch in the mouth into maltose, maltotriose, and a-dextrin. Bicarbonate and phosphate ions buffer acidic foods that enter the mouth, saliva is only slightly acidic (pH 6.35-6.85)

esophagus

collapsible muscular tube, that lies posterior to the trachea; begins at the inferior end of the laryngopharynx, passes through the inferior aspect of the neck, and enters the mediastinum anterior to the vertebral column. Then it pierces the diaphragm through an opening called the *esophageal hiatus* and ends in the superior portion of the stomach

periodontal disease

collective term for a variety of conditions characterized by inflammation and degeneration of the gingivae, alveolar bone, periodontal ligament, and cementum. causes: poor oral hygiene; by local irritants, such as bacteria, impacted food, and cigarette smoke; or by a poor "bite." Pyorrhea initial symptoms: enlargement and inflammation of the soft tissue and bleeding of the gums. consequences: the soft tissue may deteriorate and the alveolar bone may be resorbed, causing loosening of the teeth and recession of the gums.

histology of small intestine

composed of the same 4 layers that make up most of the GI tract: *muscosa* epithelium (simply columnar with cells) - absorptive cells - goblet cells - intestinal glands or crypts or Lieberkuhn - Paneth cells - S cells (secretin) - CCK cells (cholecystokinin (CCK)) - K cells (glucose dependent insulinotropic peptide (GIP)) lamina propria - solitary lymphatic nodules - aggregated lymphatic follicle or Peyer's patches musclaris mucosae - smooth muscles *submucosa* - duodenal or Brunner glands *muscularis* - circular layer - longitudinal layer *serosa* related terms: - circular folds - villus - lacteal - microvillus - brush border - brush border enzymes (dextrinase, maltase, sucrase, lactase, peptidases (amino and di-), nucleosidases, phosphatases) - intestinal juice

lesser curvature (stomach)

concave medial border of the stomach

greater curvature (stomach)

convex lateral border

visceral peritoneum (periotoneum)

covers some of the organs in the cavity and is their serosa

peptic ulcer disease (PUD)

craterlike lesion that develop in areas of the GI tract exposed to acidic gastric juice causes - stressors: cigarette smoke, alcohol, caffeine, and NSAIDs should be avoided because they can impair mucosal defensive mechanisms, which increases mucosal susceptibility to the damaging effects of HCl. (1) Helicobacter pylori bacterium Helicobacter pylori is the most frequent cause of PUD. The bacterium produces an enzyme called urease, which splits urea into ammonia and carbon dioxide. While shielding the bacterium from the acidity of the stomach, the ammonia also damages the protective mucous layer of the stomach and the underlying gastric cells. The microbe also produces catalase, an enzyme that may protect H. pylori from phagocytosis by neutrophils, plus several adhesion proteins that allow the bacterium to attach itself to gastric cells. treatment: - with H. pylori, treatment with an antibiotic drug often resolves the problem. (2) nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin (3) hypersecretion of HCl (i.e. in Zollinger-Ellison syndrome, gastrin-producing tumor in pancreas) treatment: - H2 blockers (such as Tagamet®) or proton pump inhibitors such as omeprazole (Prilosec®), which block secretion of H from parietal cells, may be used. - Oral antacids such as Tums® or Maalox® can help temporarily by buffering gastric acid. consequences: bleeding (lead to anemia), shock and death.

permanent first and second premolars or bicuspids (dentes)

deciduous molars are replaced by the first and second premolars (bicuspids), which have 2 cusps and 1 root and are used for crushing and grinding. First premolar or bicuspid (9-10 yr.) Second premolar or bicuspid (10-12 yr

hepatopancreatic ampulla or ampulla of Vater (pancreas)

dilated common duct that enters the duodenum from where the pancreatic duct joins the bile duct of the liver and gallbladder B in picture

lingual lipase (tongue)

enzyme that is activated by stomach acid and digests fat into simpler fatty acids and diglycerides after the food is swallowed

gastric lipase

enzyme to digest fat which splits triglycerides (fats and oils) in fat molecules (such as those found in milk) into fatty acids and monoglycerides. has a limited role in the adult stomach, operates best at a pH of 5-6.

pancreatic amylase

enzymes in pancreatic juice include a starch-digesting enzyme

trypsin, chymotrypsin, carboxypeptidase, elastase (pancreas)

enzymes that digest proteins into peptides

lamina propria (stomach)

epithelial cells of mucosa layer extends into this region of areolar connective tissue forms *gastric glands* = columns of secretory cells

G cells (stomach)

gastric glands include a type of enteroendocrine cell, which is located mainly in the pyloric antrum and secretes the hormone gastrin into the bloodstream. *gastrin* - stimulates sustained secretion of gastric juice from the stomach - increases acid secretion by parietal cells

absorption of vitamins

fat-soluble vitamins A, D, E, and K are included with ingested dietary lipids in micelles and are absorbed via simple diffusion. Most water-soluble vitamins, such as most B vitamins and vitamin C, also are absorbed via simple diffusion. Vitamin B12, however, combines with intrinsic factor produced by the stomach (parietal cells), and the combination is absorbed in the ileum via an active transport mechanism.

ileum (small intestine)

final and longest region of the small intestine, measures about 2 m (6 ft) joins the large intestine at a smooth muscle sphincter called the ileocecal sphincter (valve)

large intestine chemical digestion

final stage of digestion occurs in the colon through the activity of bacteria that inhabit the lumen. Mucus is secreted by the glands of the large intestine, but no enzymes are secreted. (1) bacteria ferment any remaining carbohydrates in chyme and release hydrogen, carbon dioxide, and methane gases. these gases contribute to flatus (gas) in the colon, termed flatulence when it is excessive. (2) bacteria convert any remaining proteins to amino acids and break down the amino acids into simpler substances: indole, skatole, hydrogen sulfide, and fatty acids. Some of the indole and skatole is eliminated in the feces and contributes to their odor; the rest is absorbed and transported to the liver, where these compounds are converted to less toxic compounds and excreted in the urine. (3) Bacteria decompose bilirubin to simpler pigments, including stercobilin, which gives feces their brown color. (4) Bacterial products that are absorbed in the colon include several vitamins needed for normal metabolism, among them some B vitamins and vitamin K.

villus (plural is villi) (small intestine)

fingerlike projections of the mucosa function: increases the surface area of the epithelium available for absorption and digestion gives the intestinal mucosa a velvety appearance

duodenum (small intestine)

first part of the small intestine shortest region, and is retroperitoneal. It starts at the pyloric sphincter of the stomach and is in the form of a C-shaped tube that extends and merges with the jejunum. Duodenum means "12"; it is so named because it is about as long as the width of 12 fingers.

lip or labium (buccal cavity)

fleshy folds surrounding the opening of the mouth structure: covered externally by skin and internally by a mucous membrane components: contain the orbicularis oris muscle function: during chewing, contraction of the buccinator muscles in the cheeks and orbicularis oris muscle in the lips helps keep food between the upper and lower teeth; muscles also assist in speech.

circular folds (small intestine)

folds of the mucosa and submucosa; permanent ridges that begin near the proximal portion of the duodenum and end at about the midportion of the ileum. Some extend all the way around the circumference of the intestine; others extend only part of the way around. Function: enhance absorption by increasing surface area and causing the chyme to spiral, rather than move in a straight line, as it passes through the small intestine.

gastric emptying (stomach)

food particles in chyme are small enough, they can pass through the pyloric sphincter, a phenomenon known as gastric emptying. Gastric emptying is a slow process: only about 3 mL of chyme moves through the pyloric sphincter at a time.

cheeks (buccal cavity)

form the lateral walls of the oral cavity. structure: covered externally by skin and internally by a mucous membrane (non-keratinized stratified squamous epithelium) components: buccinator muscles and connective tissue lie between the skin and mucous membranes of the cheeks. function: during chewing, contraction of the buccinator muscles in the cheeks and orbicularis oris muscle in the lips helps keep food between the upper and lower teeth; muscles also assist in speech.

mouth or oral cavity or buccal cavity

formed by the cheeks, hard and soft palates, and tongue; other components: cheeks lip or labium labial frenulum vestibule oral cavity proper fauces hard and soft palate uvual salivary glands parotid ducts and glands submandibular ducts and glands sublingual glands lesser sublingual duct saliva salivary amylase salivation tongue (see detail slides) tooth/dentis (see detail slides)

dentin (dentes)

forms the majority of the tooth; consist of calcified connective tissue that gives the tooth its basic shape and rigidity. It is harder than bone because of its higher content of hydroxyapatite (70% versus 55% of dry weight).

soft palate (buccal cavity)

forms the posterior portion of the roof of the mouth, is an arch-shaped muscular partition between the oropharynx and nasopharynx that is lined with mucous membrane During swallowing, the soft palate and uvula are drawn superiorly, closing off the nasopharynx and preventing swallowed foods and liquids from entering the nasal cavity

sinusoids (liver)

highly permeable blood capillaries between rows of hepatocytes that receive oxygenated blood from branches of the hepatic artery and nutrient-rich deoxygenated blood from branches of the hepatic portal vein. Recall that the hepatic portal vein brings venous blood from the gastrointestinal organs and spleen into the liver. Also present are fixed phagocytes called stellate reticuloendothelial cells or hepatic macrophages, which destroy worn-out RBC, WBC, bacteria, and other foreign matter in the venous blood draining from the gastrointestinal tract.

gastroileal reflex (large intestine mech. digestion)

immediately after a meal, this reflex intensifies peristalsis in the ileum and forces any chyme into the cecum of the large intestine through the ileocecal sphincter which normally remains partially closed so that there is slow passage The hormone gastrin also relaxes the sphincter. Whenever the cecum is distended, the degree of contraction of the ileocecal sphincter intensifies.

ligamentum teres (liver)

in the free border of the falciform ligament is this round ligament a remnant of the umbilical vein of the fetus this fibrous cord extends from the liver to the umbilicus.

lingual glands (tongue)

in the lamina propria of the tongue secrete both mucus and a watery serous fluid fluid contains the enzyme *lingual lipase* which acts on as much as 30% of dietary triglycerides (fats and oils) and converts them to simpler fatty acids and diglycerides.

trypsinogen (pancreas)

inactive form of trypsin The protein-digesting enzymes of the pancreas are produced in an inactive form just as pepsin is produced in the stomach as pepsinogen. Because they are inactive, the enzymes do not digest cells of the pancreas itself. Pancreatic acinar cells also secrete a protein called trypsin inhibitor that combines with any trypsin formed accidentally in the pancreas or in pancreatic juice and blocks its enzymatic activity.

hepatitis

inflammation of the liver that can be caused by viruses, drugs, and chemicals, including alcohol. *Hepatitis A* (infectious hepatitis) - Hep A virus, spread via fecal contamination of objects such as food, clothing, toys, and eating utensils (fecal-oral route). - mild disease of children and young adults characterized by loss of appetite, malaise, nausea, diarrhea, fever, and chills. Eventually, jaundice appears - does not cause lasting liver damage; most people recover in 4 to 6 weeks. *Hepatitis B* - Hep B virus, spread primarily by sexual contact and contaminated syringes and transfusion equipment. It can also be spread via saliva and tears. - present for years or even a lifetime, and it can produce cirrhosis and possibly cancer of the liver. Individuals who harbor the active hepatitis B virus also become carriers. - Vaccines produced through recombinant DNA technology (for example, Recombivax HB®) are available to prevent hepatitis B infection. *Hepatitis C*, - Hep C virus, clinically similar to Hep B. - cause cirrhosis and possibly liver cancer. In developed nations, donated blood is screened for the presence of hepatitis B and C. *Hepatitis D* - Hep D virus, transmitted like hepatitis B, and in fact a person must have been co-infected with hepatitis B before contracting hepatitis D - severe liver damage and has a higher fatality rate than infection with hepatitis B virus alone. *Hepatitis E* - Hep D virus, spread like hepatitis - does not cause chronic liver disease, but has a very high mortality rate among pregnant women

constipation

infrequent or difficult defecation caused by decreased motility of the intestines. Because the feces remain in the colon for prolonged periods, excessive water absorption occurs, and the feces become dry and hard. Constipation may be caused by poor habits (delaying defecation), spasms of the colon, insufficient fiber in the diet, inadequate fluid intake, lack of exercise, emotional stress, and certain drugs.

mucosa (GI tract layer)

inner lining of the GI tract 3 layers (F in picture): (1) *epithelium* - in direct contact with the contents of the GI tract, (2) *lamina propria* - connective tissue (3) *muscularis mucosae* - thin layer of smooth muscle

saliva (buccal cavity)

is 99.5% water and 0.5% solutes. Among the solutes are ions, including sodium, potassium, chloride, bicarbonate, and phosphate. The parotid glands secrete a watery (serous) liquid containing salivary amylase. The submandibular glands contain cells similar to those found in the parotid glands, plus some mucous cells, they secrete a fluid that contains amylase but is thickened with mucus. The sublingual glands contain mostly mucous cells, so they secrete a much thicker fluid that contributes only a small amount of salivary amylase. The water in saliva provides a medium for dissolving foods so that they can be tasted by gustatory receptors and so that digestive reactions can begin. help remove waste molecules from the body, which accounts for the presence of urea and uric acid in saliva. Mucus lubricates food so it can be moved around easily in the mouth, formed into a ball, and swallowed. Immunoglobulin A (IgA) prevents attachment of microbes so they cannot penetrate the epithelium, and the enzyme lysozyme kills bacteria; however, these substances are not present in large enough quantities to eliminate all oral bacteria.

colorectal cancer

is among the deadliest of malignancies, ranking second to lung cancer in males and third after lung cancer and breast cancer in females. causes: - Genetics plays a very important role; an inherited predisposition contributes to more than half of all cases of colorectal cancer. - Intake of alcohol and diets high in animal fat and protein are associated with increased risk of colorectal cancer - precancerous growths on the mucosal surface, called polyps, also increase the risk of developing colorectal cancer. signs and symptoms - diarrhea, constipation, cramping, abdominal pain, and rectal bleeding, either visible or occult (hidden in feces). treatments - dietary fiber, retinoids, calcium, and selenium may be protective - tumors may be removed endoscopically or surgically Screening - testing for blood in the feces, digital rectal examination, sigmoidoscopy, colonoscopy, and barium enema

submucosal plexus (plexus of Meissner)

is found within the submucosa. Function: motor neurons supply the secretory cells of the mucosal epithelium, therefore it controls the secretions of the organs of the GI tract

body (stomach)

is the large central portion of the stomach

pancreatic duct or duct of Wirsung (pancreas)

is the larger of the two ducts (H) joins the common bile duct from the liver and gallbladder E in picture

vestibule (buccal cavity)

is the space between the cheeks, lips, gums, and teeth.

oral cavity proper (buccal cavity)

is the space that extends from the gums and teeth to the fauces

crown (dentes)

is the visible portion above the level of the gums.

peritoneum

largest serous membrane of the body - consists of a simple squamous epithelium (mesothelium) and an underlying supporting layer of areolar connective tissue Divides into 2: *parietal and visceral peritoneum* - peritoneal cavity - retroperitoneal 5 Major folds: - greater omentum - falciform ligament - lesser omentum - mesentery - mesocolon

submucosa (small intestine)

layer deep to mucosa of small intestine *duodenal glands or Brunner's glands* - secrete an alkaline mucus that helps neutralize gastric acid in the chyme. sometimes the lymphatic tissue of the lamina propria extends through the muscularis mucosae into the submucosa.

serosa (small intestine)

layer deep to the muscularis of the small intestine Except for a major portion of the duodenum, which is retroperitoneal, the serosa (or visceral peritoneum) completely surrounds the small intestine.

muscularis (small intestine)

layer deep to the submucosa of the small intestine 2 layers of smooth muscle. - outer, thinner layer contains longitudinal fibers - inner, thicker layer contains circular fibers

mucosa (small intestine)

layer of epithelium, lamina propria, and muscularis mucosae epithelial layer - simple columnar epithelium - *intestinal glands or crypts of Lieberkuhn* (secrete intestinal juices) lamina propria - areolar connective tissue - *solitary lymphatic nodules* (most abundant in distal ileum) - *aggregated lymphatic follicles or Payer's patches* muscularis mucosae - smooth muscles

parietal peritoneum (periotoneum)

lines the wall of the abdominal cavity,

liver and gallbladder

liver: heaviest body gland, second only to the skin in size, inferior to diaphragm anatomy: - right, left, quadrate, caudate lobe - ligamentum teres gallbladder: pear-shaped sac, in depression of posterior surface of liver, typically hangs from anterior inferior margin of liver anatomy: - fundus, body, neck

segmentations (small intestine)

localized, mixing contractions that occur in portions of intestine distended by a large volume of chyme. function: mix chyme with the digestive juices and bring the particles of food into contact with the mucosa for absorption; they do not push the intestinal contents along the tract occur most rapidly in the duodenum (12x/min) and progressively slow (8x/min) in the ileum. steps: (1) contractions of circular muscle fibers in a portion of the small intestine, an action that constricts the intestine into segments. (2) muscle fibers that encircle the middle of each segment also contract, dividing each segment again. (3) fibers that first contracted relax, and each small segment unites with an adjoining small segment so that large segments are formed again. As this sequence of events repeats, the chyme sloshes back and forth. (This movement is similar to alternately squeezing the middle and then the ends of a capped tube of toothpaste.) After most of a meal has been absorbed, which lessens distension of the wall of the small intestine, segmentation stops and peristalsis begins.

myenteric plexus (plexus of Auerbach)

located between the longitudinal and circular smooth muscle layers of the muscularis. Function: motor neurons of this plexus mostly controls GI tract motility (movement), particularly the frequency and strength of contraction of the muscularis

epithelium (mucosa, GI tract layer)

location: mouth, pharynx, esophagus, and anal canal structure: nonkeratinized stratified squamous epithelium function: protective location: stomach and intestines structure: simple columnar epithelium, tight junctions restrict leakage between cells function: secretion and absorption components - exocrine cells: secrete mucus and fluid into the lumen of the tract - endocrine/*enteroendocrin cells*: secrete hormones. The rate of renewal of GI tract epithelial cells is rapid: Every 5 to 7 days they slough off and are replaced by new cells.

serosa (GI tract layer)

location: superficial layer suspended in the abdominal cavity structure: serous membrane composed of areolar connective tissue and simple squamous epithelium (mesothelium) also known as *visceral peritoneum* because it forms a portion of the peritoneum Note: The esophagus lacks a serosa; instead, only a single layer of areolar connective tissue called the *adventitia* forms the superficial layer of this organ.

hepatocytes (liver)

major functional cells of the liver, specialized epiethlial cells; perform a wide array of metabolic, secretory, and endocrine functions. *Hepatic laminae* - cells form complex 3D arrangement - highly branched, irregular structures, grooves in the cell membranes between cells provided spaces for *canaliculi* Hepatic sinusoids* - plates of hepatocytes one cell thick bordered on either side by the endothelial-lined vascular spaces

gastrointestinal reflex pathways (GI tract neural innervation)

many neurons of ENS are components of GI reflex pathways that regulate GI secretion and motility in response to stimuli present in GI tract lumen. Components: Sensory neuron - axons synapse with neurons of ENS, CNS, or ANS - chemoreceptors and stretch receptors Neuron (of ENS, CNS, or ANS) - activate or inhibit GI glands and smooth muscles, altering GI secretion and motility

brush border (small intestine)

microvillus-->When viewed through a light microscope, the microvilli are too small to be seen individually; instead they form a fuzzy line, called this extending into the lumen of the small intestine

chemical digestion (small intestine)

mouth: salivary amylase stomach: pepsin lingual and gastric lipases pancreas: pancreatic juice (trypsin, chymotrypsin, carboxypeptidase, and elastase) small intestine: chyme contains partially digested carbohydrates, proteins, and lipids and the completion of the digestion is a collective effort of pancreatic juice, bile, and intestinal juice in the small intestine

haustral churning (large intestine mech. digestion)

movement characteristic of the large intestine where the haustra remain relaxed and become distended while they fill up and when the distension reaches a certain point, the walls contract and squeeze the contents into the next haustrum. peristalsis also occurs but at a slower rate than in more proximal regions of the tract

stomach histology

mucosa - surface mucosa cells (simple columnar epithelial cell) - lamina propria (areolar connective tissue) - muscularis mucosae (smooth muscle) - gastric glands and pits - mucous neck cells - chief cells (pepsinogen, gastric lipase) - parietal cells (intrinsic factor, HCl acid) - G cell (gastrin) submucosa - areolar connective tissues muscularis - outer longitudinal layer - middle circular layer - inner oblique layer serosa - simple squamous epithelium (mesothelium) - areolar connective tissue

intrinsic muscles (tongue)

muscles which originate in and insert into connective tissue within the tongue. function: alter the shape and size of the tongue for speech and swallowing. include the longitudinalis superior, longitudinalis inferior, transversus linguae, and verticalis linguae muscles.

extrinsic muscles (tongue)

muscles which originate outside the tongue (attach to bones in the area) and insert into connective tissues in the tongue, include the hyoglossus, genioglossus, and styloglossus muscles; form the floor of the mouth and hold the tongue in position. function: move the tongue from side to side and in and out to maneuver food for chewing, shape the food into a rounded mass, and force the food to the back of the mouth for swallowing.

root canals (dentes)

narrow extensions of the pulp cavity, run through the root of the tooth.

jejunum (small intestine)

next portion after duodenum and extends to the ileum. Jejunum means "empty," which is how it is found at death.

ribonuclease and deoxyribonuclease (pancreas)

nucleic acid-digesting enzymes that digest ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) into nucleotides.

lesser sublingual duct (buccal cavity)

open into the floor of the mouth in the oral cavity proper. "duct" on left side of photo

enzymes that digest proteins (small intestine)

protein digestion is completed by 2 peptidases in the brush border: 1.) *Aminopeptidase* - cleaves off the amino acid at the amino end of a peptide. 2.) *Dipeptidase* - splits dipeptides into single amino acids.

intestinal glands (small intestine)

or crypts of Lieberkuhn small intestine mucosa contains many deep crevices lined with glandular epithelium which have a variety of cells that secrete intestinal juices: *absorptive cells* - release enzymes and contain microvilli to absorb chyme nutrients *goblet cells* - secrete mucus *paneth cells* - secrete lysozyme, a bactericidal enzyme, and are capable of phagocytosis. - may have a role in regulating the microbial population 3 types of enteroendocrine cells: *S cells* - secretin *CCK cells* - cholecystokinin *K cells* - glucose-dependent insulinotropic peptide (GIP)

dental caries (disorder)

or tooth decay, involves a gradual demineralization (softening) of the enamel and dentin causes: bacteria, acting on sugars, produce acids that demineralize the enamel. Dextran, a sticky polysaccharide produced from sucrose, causes the bacteria to stick to the teeth (forms dental plaque (PLAK)) effects: saliva cannot reach the tooth surface to buffer the acid because the plaque covers the teeth. Brushing the teeth after eating removes the plaque from flat surfaces before the bacteria can produce acids. consequences: microorganisms may invade the pulp, causing inflammation and infection, with subsequent death of the pulp and abscess of the alveolar bone surrounding the root's apex treatment: root canal therapy, dental floss every 24hr to remove plaque between teeth

accessory duct or duct of Santorini

other major duct (smaller of the two) of the pancreas, leads from the pancreas and empties into the duodenum about 2.5 cm (1 in.) superior to the hepatopancreatic ampulla. A in picture

muscularis (large intestine)

outer: longitudinal smooth muscle - thickened portions that form 3 conspicuous bands called *teniae coli* that run most of the length of the large intestin inner: circular smooth muscle.

serosa (large intestine)

part of the visceral peritoneum. Small pouches of visceral peritoneum filled with fat are attached to teniae coli and are called omental (fatty) appendices.

first and second molars

posterior to the canines, which have four cusps used to crush and grind food to prepare it for swallowing Maxillary (upper) molars have 3 roots; Mandibular (lower) molars have 2 roots. first molar (12-16 mo.) second molar (24-32 mo.)

pancreatic lipase

principal triglyceride-digesting enzyme in adults

papillae (tongue)

projections of the lamina propria covered with stratified squamous epithelium; many contain taste buds, the receptors for gustation (taste). Some lack taste buds, but they contain receptors for touch and increase friction between the tongue and food, making it easier for the tongue to move food in the oral cavity.

proton pumps (stomach)

pumps used by parietal cell to secrete H+ into the stomach lumen to create HCl acid the pump is powered by H-K ATPases which actively transport H+ into the lumen while bringing K+ in, Cl- diffuses into the stomach lumen through Cl- channels

pyloric sphincter (stomach)

pylorus communicates with the duodenum of the small intestine via a smooth muscle sphincter

gastrocolic reflex (large intestine mech. digestion)

reflex that is initiated when there is food in the stomach result: mass peristalsis usually takes place 3-4x a day, during or immediately after a meal.

chyme (stomach)

result of repetitive propulsion and retropulsion is that gastric contents are mixed with gastric juice, eventually becoming reduced to a soupy liquid called this

common hepatic duct (liver)

right and left hepatic ducts, which unite and exit the liver as the common hepatic duct

submandibular duct (buccal cavity)

run under the mucosa on either side of the midline of the floor of the mouth and enter the oral cavity proper lateral to the lingual frenulum.

diverticulitis disease

saclike outpouchings of the wall of the colon, termed diverticula, occur in places where the muscularis has weakened and may become inflamed. signs and symptoms: - many have none - diverticulitis (inflammation) - pain, either constipation or increased frequency of defecation, nausea, vomiting, and low-grade fever. treatment: Because diets low in fiber contribute to development of diverticulitis, patients who change to high-fiber diets show marked relief of symptoms. In severe cases, affected portions of the colon may require surgical removal. If diverticula rupture, the release of bacteria into the abdominal cavity can cause peritonitis.

parotid glands (buccal cavity)

salivary gland located inferior and anterior to the ears, between the skin and the masseter muscle secrete a watery (serous) liquid containing salivary amylase.

submandibular glands (buccal cavity)

salivary glands found in the floor of the mouth; they are medial and partly inferior to the body of the mandible secrete a fluid that contains salivary amylase but is thickened with mucus. and contain cells similar to those found in the parotid glands, plus some mucous cells

physiology of the esophagus

secretes mucus and transports food into the stomach. does not produce digestive enzymes and does not carry on absorption.

salivation (buccal cavity)

secretion of saliva, controlled by ANS. *parasympathetic stimulation* - promotes continuous secretion of a moderate amount of saliva, which keeps the mucous membranes moist and lubricates the movements of the tongue and lips during speech. The saliva is then swallowed and helps moisten the esophagus. most components of saliva are reabsorbed, which prevents fluid loss. *Sympathetic stimulation* - dominates during stress, resulting in dryness of the mouth. If the body becomes dehydrated, the salivary glands stop secreting saliva to conserve water; the resulting dryness in the mouth contributes to the sensation of thirst. Drinking not only restores the homeostasis of body water but also moistens the mouth. *Food stimulation* - the feel and taste of food also are potent stimulators of salivary gland secretions. Chemicals in the food stimulate receptors in taste buds on the tongue, and impulses are conveyed from the taste buds to two salivary nuclei in the brain stem (superior and inferior salivatory nuclei). Returning parasympathetic impulses in fibers of the facial (VII) and glossopharyngeal (IX) nerves stimulate the secretion of saliva. Saliva continues to be secreted heavily for some time after food is swallowed; this flow of saliva washes out the mouth and dilutes and buffers the remnants of irritating chemicals such as that tasty (but hot!) salsa. The smell, sight, sound, or thought of food may also stimulate secretion of saliva.

dentitions (dentes)

sets of teeth either deciduous or permanent

pepsin (stomach)

severs certain peptide bonds between amino acids, breaking down a protein chain of many amino acids into smaller peptide fragments most effective in the very acidic environment of the stomach (pH 2); it becomes inactive at a higher pH.

serosa (stomach)

simple squamous epithelium (mesothelium) and areolar connective tissue; the portion of the serosa covering the stomach is part of the visceral peritoneum. At the lesser curvature of the stomach, the visceral peritoneum extends upward to the liver as the lesser omentum. At the greater curvature of the stomach, the visceral peritoneum continues downward as the greater omentum and drapes over the intestines.

bile canaliculi and ducts (liver)

small ducts between hepatocytes that collect bile produced by the hepatocytes; then passes into bile ductules then ducts Bile, a yellow, brownish, or olive-green liquid secreted by hepatocytes, serves as both an excretory product and a digestive secretion.

lacteal (small intestine)

small lymphatic capillary that are found within the villi that absorbs nutrients

periodontal ligament/membrane (dentes)

sockets are lined by the periodontal ligament or periodontal membrane consists of dense fibrous connective tissue that anchors the teeth to the socket walls and acts as a shock absorber during chewing.

stomach anatomy

stomach cardia, fundus, body pyloric antrum, canal, and pylorus pyloric sphincter rugae lesser and greater curvature related terms: mech and chem digestion propulsion retropulsion chyme gastric emptying proton pumps pepsin gastric lipase

submucosa (GI tract layer)

structure: areolar connective tissue function: binds the mucosa to the muscularis components: many blood and lymphatic vessels that receive absorbed food molecules; also *submucosal plexus*, an extensive network of neurons, glands, and lymphatic tissue.

lamina propria (mucosa, GI tract layer)

structure: areolar connective tissue containing many blood and lymphatic vessels, which are the routes by which nutrients absorbed into the GI tract reach the other tissues of the body. function: this layer supports the epithelium and binds it to the muscularis mucosae components: cells of mucosa-associated lymphatic tissue (MALT), prominent lymphatic nodules contain immune system cells that protect against disease. MALT location: all along the GI tract, especially in the tonsils, small intestine, appendix, and large intestine.

muscularis (GI tract layer)

structure: skeletal msucles location: mouth, pharynx, superior and middle parts of the esophagus, external anal sphincter function: voluntary swallowing, forms the external anal sphincter, which permits voluntary control of defecation. structure: smooth muscle (two sheets: an inner sheet of circular fibers and an outer sheet of longitudinal fibers) location: rest of GI tract function: break down food, mix it with digestive secretions, and propel it along the tract. Between the layers of the muscularis is a second plexus of neurons—the myenteric plexus

muscularis mucosae (mucosa, GI tract layer)

structure: thin layer of smooth muscle fibers function: throws the mucous membrane of the stomach and small intestine into many small folds, which increase the surface area for digestion and absorption Movements of the muscularis mucosae ensure that all absorptive cells are fully exposed to the contents of the GI tract.

adventitia (esophagus)

superficial layer of the esophagus; attaches the esophagus to surrounding structures. instead of serosa (stomach and intestines) because not surrounded by mesothelium and because connective tissue merges with connective tissues surrounding structures of the mediastinum (through which it passes)

mucosa (stomach)

surface mucosa cells (simple columnar epithelial cell) contains: - *lamina propria* (areolar connective tissue) - *muscularis mucosae* (smooth muscle) - gastric glands and pits - mucous neck cells - chief cells (pepsinogen, gastric lipase) - parietal cells (intrinsic factor, HCl acid) - G cell (gastrin)

cardia (stomach)

surrounds the opening of the esophagus into the stomach

central and lateral incisors (dentes)

teeth closest to the midline, are chisel-shaped and adapted for cutting into food; only have 1 root/tooth central incisor (8-12 mo.) lateral incisor (12-24 mo.)

accessory digestive organs (digestive system)

teeth, tongue, salivary glands, liver, gallbladder, and pancreas. The other accessory digestive organs never come into direct contact with food. They produce or store secretions that flow into the GI tract through ducts; the secretions aid in the chemical breakdown of food.

large intestine

terminal portion of the GI tract; attached to the posterior abdominal wall by its mesocolon, which is a double layer of peritoneum extends from the ileum to the anus; function: completion of absorption, the production of certain vitamins, the formation and expulsion of feces 4 major regions: *cecum, colon, rectum, and anal canal*

hard palate (buccal cavity)

the anterior portion of the roof of the mouth, forms a bony partition between the oral and nasal cavities. formed by the maxillae and palatine bones and is covered by a mucous membrane

emulsification (liver)

the breakdown of large lipid globules into suspension of small lipid globules Bile salts, which are sodium salts and potassium salts of bile acids (mostly chenodeoxycholic acid and cholic acid), play a role in this process. The small lipid globules present a very large surface area that allows pancreatic lipase to more rapidly accomplish digestion of triglycerides. Bile salts also aid in the absorption of lipids following their digestion.

neck (dentes)

the constricted junction of the crown and root near the gum line.

enamel tooth (dentes)

the dentin of the crown is covered by this, which consists primarily of calcium phosphate and calcium carbonate. Enamel is also harder than bone because of its even higher content of calcium salts (about 95% of dry weight). In fact, enamel is the hardest substance in the body. It serves to protect the tooth from the wear and tear of chewing. It also protects against acids that can easily dissolve dentin.

major duodenal papilla (pancreas)

the hepatopancreatic ampulla (Vater) opens on an elevation of the duodenal mucosa known as the major duodenal papilla, which lies inferior to the pyloric sphincter of the stomach. I in picutre

labial frenulum (buccal cavity)

the inner surface of each lip is attached to its corresponding gum by a midline fold of mucous membrane called this

greater omentum (periotoneum)

the largest peritoneal fold, drapes over the transverse colon and coils of the small intestine like a "fatty apron", double sheet that folds back on itself, giving it a total of four layers. Location: from attachments along the stomach and duodenum, the greater omentum extends downward anterior to the small intestine, then turns and extends upward and attaches to the transverse colon. Component: adipose tissue, many lymph nodes (contribute macrophages and antibody-producing plasma cells that help combat and contain infections of the GI tract)

bilirubin (liver and gallbladder)

the main bile pigment derived from heme, liberated by phagocytosis of aged RBCs secreted into bile and eventually broken down in the small intestine One of its breakdown products—stercobilin —gives feces their normal brown color.

fauces (buccal cavity)

the opening between the oral cavity and the oropharynx (throat).

intestinal phase

this digestion phase begins once food enters the small intestine. In contrast to reflexes initiated during the cephalic and gastric phases, which stimulate stomach secretory activity and motility, those occurring during the intestinal phase have inhibitory effects that slow the exit of chyme from the stomach. This prevents the duodenum from being overloaded with more chyme than it can handle. In addition, responses occurring during the intestinal phase promote the continued digestion of foods that have reached the small intestine. These activities of the intestinal phase of digestion are regulated by neural and hormonal mechanisms. *neural reg.* - *enterogastric reflex* activated when the presence of chyme distends the duodenum - stretch receptors send nerve impulses to the medulla oblongata - inhibits parasympathetic and stimulates sympathetic nerves to the stomach - inhibits gastric motility, increase pyloric sphincter contraction which decreases gastric emptying *hormonal reg* - via *cholecystokinin (CCK)* and *secretin* Cholecystokinin (CCK) - CCK cells of intestinal glands stimulated in response to chyme containing amino acids and fatty acids from partially digested proteins and triglycerides - CCK is secreted which.. (a) stimulates secretion of pancreatic juice that is rich in digestive enzymes (b) causes contraction of the wall of the gallbladder, which squeezes stored bile out of the gallbladder into the cystic duct and through the common bile duct. (c) causes relaxation of the sphincter of the hepatopancreatic ampulla (Oddi), which allows pancreatic juice and bile to flow into the duodenum (d) slows gastric emptying by promoting contraction of the pyloric sphincter (e) produces satiety (a feeling of fullness) by acting on the hypothalamus (f) promotes normal growth and maintenance of the pancreas (g) enhances the effects of secretin. - S cells of intestinal glands stimulated in response to acidic chyme entering the duodenum - secretin is secreted which overall causes buffering of acid in chyme that reaches the duodenum and slows production of acid in the stomach and... (a) stimulates the flow of pancreatic juice that is rich in bicarbonate (HCO3-) ions to buffer the acidic chyme that enters the duodenum from the stomach. (b) inhibits secretion of gastric juice (c) promotes normal growth and maintenance of the pancreas (d) enhances the effects of CCK.

gastric phase (digestion phase)

this digestion phase begins once food reaches the stomach and neural and hormonal regulation promotes gastric secretion and motility *neural reg.* - stretch receptor activated when food distends the stomach - chemoreceptors activated when pH increases (food proteins buffered some stomach acid) - neural regulation feedback loop activated - receptor nerve impulse propagate to submucosal plexus (control center) - activation of parasympathetic and enteric neurons - stimulates peristalsis waves (smooth muscles) and gastric juice flow from gastric glands (i.e. parietal cells) - increase in stomach acidity and mixing of stomach contents - once chyme enters the duodenum, stomach chyme pH decreases and stomach distention lessens therefore suppressing gastric juice secretion *hormonal reg.* stimulations: (a) stomach distention from chyme (b) partially digested chyme proteins (c) high chyme pH (d) caffeine in gastric chyme (e) food in stomach (f) Ach release from parasympathetic neurons - gastrin secretion activated when pH rises - release of *gastrin* by G cells which is controlled by negative feedback loop - negative feedback loops helps provide optimal low pH for pepsin function, killing microbes, and denaturing stomach proteins - gastrin enters blood stream and reaches target organs of digestive system - gastrin secretion inhibited when pH < 2.0 Role of *Gastrin* - stimulates gastric glands to secrete large amounts of gastric juice - strengthens lower esophageal spincter contraction (prevents reflux of acid chyme into esophagus) - increases stomach motility - relaxes pyloric sphincter (promotes gastric emptying)

cephalic phase (digestion phase)

this digestion phase prepares the mouth and stomach for food that is about to be eaten the smell, sight, thought, or initial taste of food activates neural centers in the cerebral cortex, hypothalamus, and brain stem. The brain stem then activates: - *facial (VII)* and *glossopharyngeal (IX)* nerves which stimulates salivary glands to secrete saliva - *vagus (X)* nerves which stimulates gastric glands to secrete gastric juice

haustra (large intestine)

tonic contractions of the bands gather the colon into a series of pouches and give the colon a puckered appearance.

liver lobes

two principal lobes, divided by the falciform ligament, a fold of the mesentery *Right lobe* - larger, considered by many anatomists to include an inferior quadrate lobe and a posterior caudate lobe *Left lobe* - smaller, based on internal morphology (primarily the distribution of blood vessels), the quadrate and caudate lobes more appropriately belong to the left lobe. *Quadrate lobe* - sandwiched between the left lobe and the gallbladder. *Caudate lobe* - smallest lobe of liver, bordered by the IVC and falciform ligament and lesser omentum

microvillus (plural is microvilli) (small intestine)

which are projections of the apical (free) membrane of the absorptive cells. greatly increase the surface area of the plasma membrane

gastric glands (stomach)

within lamina propria, muscosa layer; opens into bottom of narrow channels called *gastric pits* where secretion of each gland flow into then to stomach lumen 3 types of exocrine cells - secretes into stomach lumen (1) *mucosa neck cells* - secrete mucus, protects stomach cells from acid - 2nd line in picture (2) *parietal cells* - produce intrinsic factor for VitB12 absorption) - secretes HCl acid for digestion of food - 3rd line in picture (3) *chief cells* - secrete pepsinogen, breakdown of protein - secrete gastric lipase, breakdown of triglycerides - 4th line in picture (4) *G cells* (enteroendocrine) - secretes gastrin to increase and sustain gastric juice secretion - 5th line in picture