CHAPTER 23 - DIGESTIVE SYSTEM

Regulation of bile secretion

* bile secretion stimulated by 1. bile salts in enterohepatic circulation 2. secretin from intestinal cells exposed to HCl and fatty chyme -hepatopancreatic sphincter closed unless digestion active-> bile stored in gallbladder --released to small intestine ~ only with contraction

The liver & Gallbladder

*accessory organs LIVER: many functions- only digestive function- bile production, bile= fat emulsifier GALLBLADDER: chief function-bile storage

Bacterial flora

*consists of 1000+ different types of bacteria, outnumber own cells 10 to 1 -center from small intestine or anus to colonize colon

Regulation of bile secretion (gallbladder contraction)

*gallbladder contraction stimulated by 1. cholecystokinin (CCK) from intestinal cells exposed to acidic, fatty chyme 2. vagal stimulation (minor stimulus)-parasympathetic -secretin causes secretion of bicarbonate-rich pancreatic juice by duct cells -vagal stimulation also causes release of pancreatic juice (minor stimulus)

Bacterial flora: gut bacteria and health

*gut bacteria and health -mounting evidence supports findings that the kinds and proportions of gut bacteria can influence: 1. body weight 2. susceptibility to various diseases (including diabetes, atherosclerosis, fatty liver disease) 3. our moods -manipulating gut bacteria may become a routine health-care strategy in future

Structural modifications of small intestine

*increase SA of proximal part for nutrient absorption 1. circular folds 2. villi 3. microvilli (brush border)

Hepatocytes

*increased rough & smooth ER, golgi, peroxisomes, mitchondria function: process bloodborne nutrients, store fat-soluble vitamins, perform detoxification, produce ~900 ml bile / day

Bacteria floria: pathogenic bacteria

*keeping pathogenic bacteria in check -beneficial bacteria outnumber and suppress pathogenic bacteria -immune system destroys any bacteria that try to breach mucosal barrier --epithelial cells recruit dendritic cells to mucosa to sample microbial antigens and present to T cells of MALT, triggering production of IgA that restricts microbes

Bacterial flora functions

*metabolic functions 1. fermentation: ferment indigestible carbohydrates and mucin, release irritating acids and gases(~500 ml/day) 2. vitamin synthesis: synthesize B complex and some vitamin K needed by liver to produce clotting factors

Pancreatic Juice: protease activation

*protease activation in duodenum -trypsinogen activated to trypsin by brush border enzyme enteropeptidase -procarboxypeptidase and chymotrypsinogen activated by trypsin

Bile

*yellow-green, alkaline(basic) solution containing 1. bile salts: cholesterol derivatives that function in fat emulsification and absorption 2. bilirubin: pigment formed from heme, bacteria break down in intestine to stercobilin (brown color of feces) 3. cholesterol, triglycerides, phospholipids, and electrolytes -enterohepatic circulation: recycles bile salts, bile salts-> duodenum-> reabsorbed from ileum->hepatic portal blood-> liver-> secreted into bile

Motility of small intestine (neurons)

-local enteric neurons coordinate intestinal motility -cholinergic sensory neurons may activate myenteric plexus --causes contraction of circular muscle proximally and of longitudinal muscle distally -forces chyme along tract

Pancreatic Juice

-1200-1500 ml/day -watery alkaline (pH8) neutralizes acidic chyme -electrolytes (primarily HCO3-) -enzymes: amylase, lipases, nucleases secreted in active form but require ions or bile for optimal activity, proteases secreted in inactive form

Control of salivation

-1500 ml/day -intrinsic glands continously keep mouth moist -major salivary galnds activated by parasympathetic NS (R&D) when --ingested food stimulates chemoreceptors and mechanoreceptors in mouth-> --salivatory nuclei in brain stem send impulses along parasympathetic fibers in cranial nerves VII and IX -strong sympathetic stimulation inhibits salivation and results in dry mouth (xerostomia)

Microscopic anatomy of stomach

-4 tunics 1. muscularis/mucosa modified 2. serosa 3. submucosa 4. mucosa

Absorption of water

-9 L water, most from GI tract secretions, enter small intestine --95% absorbed in the small intestine by osmosis --most of rest absorbed in large intestine -net osmosis occurs if concentration gradient established by active transport of solutes -water uptake coupled with solute uptake

Composition of saliva

-97-99% water, slightly acidic -electrolytes: Na+, K+, Cl-, PO4 2-, HCO 3- -salivary amylase and lingual lipase -mucin -metabolic wastes: urea and uric acid -lysozyme, IgA, defnesins, and a cyanide compound protect against microorganisms

Absorption of lipids

-absorption of monoglycerides and fatty acids --cluster with bile salts and lecithin to form micelles --released by micelles to diffuse into epithelial cells --combined with lecithin, phospholipids, cholesterol, & coated with proteins to form chylomicrons --enter lacteals; transported to systemic circulation --hydrolyzed to free fatty acids and glycerol by lipoprotein lipase of capillary endothelium ---cells can use for energy or stored fat -absorption of short chain fatty acids --diffuse into portal blood for distribution

Absorption of protein

-amino acids transported by several types of carriers, most coupled to active transport of Na+ (co-transport) -dipeptides and tripeptides actively absorbed by H+-dependent cotransport; digested to amino acids within epithelial cells -enter capillary blood by diffusion

Parotid Gland

-anterior to ear; external to masseter muscle -parotid duct opens into oral vestibule next to upper molar -mumps is inflammation of parotid glands -mostly serous cells

Sublingual gland

-anterior to submandibular gland under tongue -open via 10-12 ducts into floor of mouth -mostly mucous cells

Submucosa

-areolar CT -blood and lymphatic vessels, lymphoid follices, and submucosal nerve plexus

Serosa/visceral peritoneum

-areolar CT covered with mesothelium in most organs -replaced by fibrous adventitia in esophagus -retroperitoneal organs have both an adventitia and serosa

Regulation of gastric emptying

-as chyme enters duodenum --receptors respond to stretch and chemical signals --enterogastric reflex and enterogastrones inhibit gastric secretion and duodenal filling -carbohydrate-rich chyme moves quickly through duodenum -fatty chyme remains in duodenum 6 hours or more

Regeneration in Liver

-can restore full size in 6-12 months after 80% removal -injury->hepatocytes->growth factors->endothelial cell proliferation

Mastication

-cheeks and closed lips hold food between teeth -tongue mixes food with saliva; compacts food into bolus -teeth cut and grind -partly voluntary -partly reflexive/involuntary --stretch reflexes; pressure receptors in cheeks, gums and tongue

Digestion in small intestine

-chyme from stomach contains 1. partially digested carbohydrates and proteins 2. undigested fats -3-6 hours in small intestine 1. most of water absorbed 2. ~ all nutrients absorbed -small intestine, like stomach, no role in ingestion or defacation -requirements for digestion and absorption in small intestine include: slow delivery of acidic, hypertonic chyme, delivery of bile, enzymes, bicarbonate ions from liver and pancreas, mixing

Summary of ATP production

-complete oxidation of 1 glucose molecule -glycolysis + Krebs cycle + ETC -> CO2 + H20 -> 32 molecules of ATP --by both substrate level+ oxidative phosphorylation -but, energy required to move NADH + H+ generated in glycolysis into mitochondria ~30 molecules ATP --still uncertainty on final total

Athletes & carbohydrates

-complex carbs -> more glycogen storage in muscle; more effective than high-protein meal for intense muscle activity -carb loading: --carbohydrate rich diet for 3-4 days; decreased activity-> muscles store more glycogen -> improved performance and endurance

Enteric NS

-enteric neurons make up bulk of two main interconnecting intrinsic nerve plexuses 1. submucosal nerve plexus: regulates glands and smooth muscle in mucosa 2. myenteric nerve plexus: controls GI tract motility

Histology of Esophagus

-esophageal mucosa contains stratified squamous epithelium-> changes to simple columnar at stomach -esophageal glands in submuscosa secrete mucus to aid in bolus movement -muscularis externa made of skeletal superiorly, mixed in middle, smooth muscle inferiorly -adventitia instead of serosa

Jejunum

-extends from duodenum to ileum -about 2.5 m long

Esophagus

-flat muscular tube from laryngopharynx to stomach -pierces diaphragm at esophageal hiatus -joins stomach at cardial orifice

Pharynx and Espohagus

-food passes from mouth -> oropharynx-> laryngopharynx -> esophagus --stratified squamous epithelium lining, mucus-producing glands -skeletal muscle layers: inner longitudinal, outer pharyngeal constrictors

Absorption of carbohydrates

-glucose and galactose: secondary active transport (cotransport) with Na+ epithelial cells, apical side, move out of epithelial cells by facilitated diffusion capillary beds in villi -fructose: facilitated diffusion to enter and exit cells, basal side

Process of carbohydrate metabolism

-glucose enters cells by facilitated diffusion 1. glycolysis, in the cytosol, breaks down each glucose molecule into two molecules of pyruvic acid. 2. the pyruvic acid then enters the mitochondrial matrix, where the Krebs cycle decomposes it to CO2. 3. energy-rich electrons picked up by coenzymes are transferred to the electron transport chain, built into the cristae membrane.

Carbohydrate metabolism

-glucose is used in oxidative (ATP producing) pathways -oxidation of glycose: C6H12O6 + 6O2 6H2O + 6CO2 + 32 ATP + heat -glucose catabolism requires 3 pathways: 1. glycolysis 2. krebs cycle 3. ETC and oxidative phosphorylation

Glycogenolysis

-glycogen breakdown via glycogen phosphorylase in response to low blood glucose -only by hepatocytes, some kidney + intestinal cells

Glycogenesis

-glycogen formation via glycogen synthase when glucose supplies exceed need for ATP synthesis -mostly in liver and skeletal muscle

Lipid metabolism

-greater energy yield than from glucose or protein catabolism --fat catabolism: ~9 kcal/gram --carb/protein catabolism ~ 4 kcal/gram -most products of fat digestion transported in lymph as chylomicrons -hydrolyzed by endothelial enzymes into fatty acids and glycerol -two building blocks oxidized separately --glycerol OR fatty acid pathway

Mucosal barrier

-harsh digestive conditions in stomach -has mucosal barrier to protect --thick layer of bicarbonate-rich mucus --tight junctions between epithelial cells (prevent juice seeping underneath tissue) --damaged epithelial cells quickly replaced by division of stem cells (surface cells replaced every 3-6 days)

Gallstones

-high cholesterol, too few bile salts --obstruct flow of bile from gallbladder (may cause obstructive jaundice) --gallbladder contracts against sharp crystals-> pain --treated with drugs, ultrasound vibrations(lithotripsy), laser vaporization, surgery

Motility of small intestine (sphincter)

-ileocecal sphincter relaxes, admits chyme into large intestine when 1. gastroileal reflex enhances force of segmentation in ileum 2. gastrin increases motility of ileum -ileocecal valve flaps close when chyme exerts backward pressure --prevents regurgitation into ileum

Digestive processes: mouth

-ingestion -mechanical breakdown(chewing/mastication) -propulsion (deglutition-swallowing) -digestion (salivary amylase and lingual lipase -no absorptions, except for a few drugs

Motility of small intestine: peristalsis

-initiated by rise in hormone motilin in late intestinal phase; every 90-120 minutes (occasional) -each wave starts distal to previous(migrating motor complex) -meal remnants, bacteria, and debris to large intestine -from duodenum->ileum, ~2 hours

Deglutition (swallowing)

-involves tongue, soft palate, pharynx, esophagus -requires coordination of 22 muscle groups -buccal phase: voluntary contraction of tongue -pharyngeal-esophageal phase: involuntary(primarily vagus nerve), control center in the medulla and lower pons

Ileum

-joins large intestine at ileocecal valve -about 3.6 m long -recycles bile salts

Liver

-largest gland in body -four lobes: right, left, caudate, quadrate -falciform ligament: separates larger right and smaller left lobes, posterior aspect, suspends liver from diaphragm and anterior abdominal wall -round ligament: remnant of fetal umbilical vein along free edge of falciform ligament

Mucosa

-lines lumen -functions: secretes mucus, digestive enzymes, and hormones; absorbs end products of digestion; protects against infectious disease -three layers: a. epithelium- simple columnar/mucus-secreting cells b. lamina propia- loose areolar CT; capillaires for nourishment and absorption; lymphoid follices; defend against microorganisms c. muscularis mucosae- smooth muscle-> local movements of mucosa

Pancreas

-location: mostly retroperitoneal, deep to greater curvature of stomach, head encircled by duodenum, tail abuts spleen -endocrine function: pancreatic islets secrete insulin and glucagon -exocrine function: acini(clusters of secretory cells)-secrete pancreatic juice --to duodenum via main pancreatic duct --zymogen granules of acini cells contain inactive proenzymes

Homeostatic imbalance of large intestine

-low fiber diet narrowed colon -> strong contractions -> increased pressure on walls -> 1. diverticula (herniations of mucosa) 2. iverticulosis commonly in sigmoid colon --affects ½ people > 70 years 3. diverticulitis --inflamed diverticula; may rupture and leak into peritoneal cavity; may be life threatening 4. irritable bowel syndrome --functional GI disorder, recurring abdominal pain, stool changes, bloating, flatulence, nausea, depression, stress common precipitating factor--stress management important in treatment

Small Intestine: gross anatomy

-major organ of chemical digestion and absorption -2-4 m long, from pyloric sphincter to ilocecal valve -subdivisions: 1. duodenum 2. jejunum 3. ileum

Defecation

-mass movements force feces toward rectum -distension initiates spinal defecation reflex -parasympathetic signals --stimulate contraction of sigmoid colon and rectum --relax internal anal sphincter -conscious control allows relaxation of external anal sphincter

Digestive processes in stomach

-mechanical breakdown -denaturation of proteins by HCl -enzymatic digestion of proteins by pepsin (and milk protein by rennin in infants) -delivers chyme to small intestine -lipid soluble alcohol and aspirin absorbed into blood -only stomach function essential to life: secrete intrinsic factor for B12 absorption --B12 needed-> mature RBC's, lack of intrinsic factor causes pernicious anemia, treated with B12 injections

Submandibular gland

-medial to body of mandible -duct opens at base of lingual fenulum -mostly serous cells

Histology of small intestine wall

-modifications of mucosa and submucosa of small intestine reflect its function in digestion -intestinal crypts: tubular glands scattered between villi

Motility of small intestine: segmentation

-most common motion of small intestine -initiated by intrinsic pacemaker cells -mixes/moves contents toward ileocecal valve -intensity altered by long & short reflexes; hormones --parasympathetic increases, sympathetic decreases -wanes in late intestinal(fasting) phase

Absorption of electrolytes

-most ions actively along length of small intestine -iron and calcium are absorbed in duodenum -Na+ coupled with active absorption of glucose and amino acids -Cl- transported actively -K+ diffuses in response to osmotic gradients; lost if poor water absorption -usually amount in intestine is amount absorbed -iron and calcium absorption related to need --ionic iron stored in mucosal cells with ferritin --when needed, transported in blood by transferrin -Ca2+ absorption regulated by vitamin D and parathyroid hormone (PTH)

Alimentary Canal

-mouth to anus -digests food and absorbs fragments -mouth, pharynx, esophagus, stomach, small intestine and large intestine

Tissue of small intestine wall

-mucosa associated lymphoid tissue (MALT) protects against microorganisms and includes: individual lymphoid follicles, Peyer's patches (aggregated lymphoid nodules)-located in lamina propria- found in great #'s in distal part of small intestine, where bacterial #s increase, lamina propria also contains large #s of plasma cells that secrete IgA -submucosa consists of areolar tissue: duodenal glands of duodenum secrete alkaline mucus to neutralize acidic chyme

Defecation (muscles)

-muscles of rectum contract to expel feces -assisted by Valsalva's maneuver --closing of glottis, contraction of diaphragm and abdominal wall muscles increased intra-abdominal pressure --levator ani muscle contracts anal canal lifted superiorly feces leave body

Digestion of carbohydrates

-only monosaccharides can be absorbed -monosaccharides absorbed as ingested--glucose, fructose, galactose -digestive enzymes --salivary amylase, pancreatic amylase, and brush border enzymes (dextrinase, glucoamylase, lactase, maltase, and sucrase) --break down disaccharides sucrose, lactose, maltose; polysaccharides glycogen and starch

Gastric contractile activity

-peristaltic waves move upward toward pylorus at rate of 3/minute --basic electrical rhythm (BER) set by enteric pacemaker cells --pacemaker cells linked by gap junctions -> entire muscularis contracts -distention and gastrin increase force of contraction -most vigorous near pylorus -chyme is either: delivered in ~3 ml spurts to duodenum OR forced backward into stomach

Microscopic anatomy of liver

-portal triad at each corner of lobule --branch of hepatic artery supplies oxygen --branch of hepatic portal vein brings nutrient-rich blood -bile duct receives bile from bile canaliculi -liver sinusoids: leaky capillaries between hepatic plates, leak blood -stellate macrophages (hepatic macrophages/Kupffer cells) in liver sinusoids remove debris & old RBC's *blood moves toward central vein, bile moves away from central vein

Digestion of lipids

-pretreatment: emulsification by bile salts (does not break bonds) -enzymes: pancreatic lipases (fatty acids and monoglycerides)

Digestive processes in large intestine

-residue remains in large intestine 12-24 hours -no food breakdown except by enteric bacteria -vitamins (made by bacterial flora), water, and electrolytes (especially Na+ and Cl-) reclaimed -major functions - propulsion of feces to anus; defecation -colon not essential for life

Muscularis Externa

-responsible for segmentation and peristalsis -inner circular and outer longitudinal layers: a. circular layer thickens in some layers-> sphincters b. myenteric nerve plexus between two muscle layers

Colon

-retroperitoneal except for transverse and sigmoid regions -ascending colons-> right colic (hepatic) flexure-> transverse colon-> left colic (splenic) flexure-> descending colon -> sigmoid colon in pelvis-> rectum

Starch digestion

-salivary amylase (saliva) ->oligosaccharides at pH 6.75 - 7.00 -pancreatic amylase (small intestine) -> breaks down any that escaped salivary amylase -> oligosaccharides -brush border enzymes (dextrinase, glucoamylase, lactase, maltase, sucrase) -> oligosaccharides -> monosaccharides

Stomach: mucosa

-simple columnar epithelium composed of mucous cells --secrete two-layer coat of alkaline mucus -dotted with gastric pits-> gastric glands --gastric glands produce gastric juice

Tongue

-skeletal muscle -functions include: 1. repositioning and mixing food during chewing 2. formation of bolus 3. initiation of swallowing, speech, and taste -surface bears papillae: filiform, fungiform, vallate, foliate -lingual frenulum: attachment to floor of mouth (mandible)

Digestion of proteins

-source is dietary, digestive enzymes, mucosal cells; digested to amino acid monomers -begins with pepsin in stomach at pH 1.5 - 2.5, inactive in high pH of duodenum -pancreatic proteases: trypsin, chymotrypsin, and carboxypeptidase -brush border enzymes: aminopeptidases, carboxypeptidases, and dipeptidases *-peptidase signals enzymes for protein digestion

Response of the stomach to filling

-stretches to accomodate incoming food --pressure constant until 1.5 L food ingested ---reflex mediated receptive relaxation (coordinated by swallowing center of brain stem) ---gastric accommodation (plasticity of smooth muscle)

Teeth

-tear and grind food for digestion -primary and permanent dentitions formed by age 21 -20 deciduous teeth erupt (6-24 months of age) --roots resorbed, teeth fall out (6-12 years of age) as permanent teeth develop -32 permanent teeth --all by third molars in by end of adolescence ---third molars at 17-25, or may not erupt

Accessory digestive organs

-teeth, tongue, gallbladder -digestive glands: salivary glands, liver, pancreas

Large intestine: microscopic anatomy

-thicker mucosa of simple columnar epithelium except in anal canal (stratified squamous to withstand abrasion) -no circular folds, villi, digestive secretions -abundant deep crypts with goblet cells -superficial venous plexuses of anal canal form hemorrhoids if inflamed

The Gallbladder

-thin walled muscular sac on ventral surface of liver -stores and concentrates bile by absorbing water and ions -muscular contractions release bile via cystic duct, which flows into bile duct

Stomach: muscularis externa

-three layers of smooth muscle -inner oblique layer allows stomach to churn, mix, move and physically break down food

Homeostatic imbalance of Stomach

-vomiting (emesis) cause by: 1. extreme stretching 2. intestinal irritants eg. bacterial toxins, excessive alcohol, spicy food, certain drugs -chemical/sensory impulses-> emetic center of medulla -excessive vomiting-> dehydration, electrolyte and acid-base imbalances (alkalosis)

Homeostatic imbalance of protein absorption

-whole proteins not usually absorbed -can be taken up by endocytosis/exocytosis --most common in newborns-> food allergies, usually disappear with mucosa maturation --allows IgA antibodies in breast milk to reach infant's bloodstream -> passive immunity

Absorption

-~all food; 80% electrolytes; most water absorbed in small intestine (most prior to ileum-ileum reclaims bile salts) -most absorbed by active transport->blood (exceptions-lipids)

Deglutition phase 1

1. Buccal phase: upper esophageal sphincter is contracted(closed), tongue presses against the hard palate, forcing food bolus into oropharynx (VOLUNTARY)

3 Phases of gastric secretion

1. Cephalic (reflex) phase: conditioned reflex triggered by aroma, taste, sight, thought 2. Gastric phase: lastes 3-4 hours, 2/3 gastric juice release, stimulated by distention, peptides, low acidity, gastrin (major stimulus), enteroendocrine G cells stimulated by caffeine, peptides, rising pH->gastrin 3. Intestinal phase: stimulatory component-- partially digested food enters small intestine-> brief intestinal gastrin release; inhibitory effects (enterogastric reflex and enterogastrones)-- chyme with H+ (acidic), fats, peptides, irritating substances-> inhibition

Digestion of lipids process

1. Emulsification: bile salts in the duodenum break large fat globules into smaller fat droplets, increasing the surface area available to lipase enzymes. 2. Digestion: pancreatic lipases hydrolyze triglycerides, yielding monoglycerides and free fatty acids. 3. Micelle formation: Micelles (consisting of fatty acids, monoglycerides, and bile salts) ferry their contents to epithelial cells. 4. Diffusion: Fatty acids and monoglycerides diffuse from micelles into epithelial cells. 5. Chylomicron formation: Fatty acids and monoglycerides are recombined and packaged with other fatty substances and proteins to form chylomicrons. 6. Chylomicron transport: Chylomicrons are extruded from the epithelial cells by exocytosis, enter lacteals, and are carried away from the intestine in lymph.

GI Tract Regulatory Mechanisms

1. Mechanoreceptors and chemoreceptors: respond to stretch, changes in osmolarity and pH, and the presence of substrate and end products of digestion 2. Intrinsic and extrinsic controls: a. short reflexes-enteric nerve plexuses (gut brain) respond to stimuli in GI tract b. long reflexes-respond to stimuli inside or outside GI tract; involve CNS centers and autonomic nerves

Two groups of digestive organs

1. alimentary canal(GI tract) 2. accessory digestive organs

Two types of metabolic reactions

1. anabolism: synthesis of large molecules from small ones, ex. amino acids-> proteins 2. catabolism: hydrolysis of complex structures to simpler ones, ex. proteins-> amino acids

Subdivisions of large intestine(cecum & appendix)

1. cecum: first part of large intestine 2. appendix: masses of lymphoid tissue, part of MALT of immune system, bacterial storehouse-> recolonizes gut when necessary, twisted-> tenteric bacteria accumulate and multiply

Functions of saliva

1. cleanses mouth 2. dissolves food chemicals for taste 3. moistens food; compacts into bolus (mechanical breakdown) 4. begins breakdown of starch with enzymes

Digestion

1. digestion: catabolic; macromolecules-> monomers small enough for absorption 2. enzymes: intrinsic and accessory gland enzymes break down food 3. hydrolysis: water is added to break bonds

Basic Concepts of Regulating Digestive Activity

1. digestive activity is provoked by a range of mechanical and chemical stimuli 2. effectors of digestive activity are smooth muscle and glands 3. neurons (intrinsic and extrinsic) and hormones control digestive activity

5 types of cells found in villi and crypts

1. enterocytes: make up bulk of epithelium, simple columnar absorptive cells bound by tight junctions and contain many microvilli 2. goblet cells: mucus-secreting cells found in epithelia of villi and crypts 3. enteroendocrine cells: source of enterogastrones (examples: CCK and secretin) 4. paneth cells: found depp in crypts, specialized secretory cells that fortify small intestine's defense, secrete antimicrobial agents (defensins and lysozyme) that can destroy bacteria 5. stem cells that continuously divide to produce other cell types- villus epithelium renewed every 2-4 days

Homeostatic imbalance

1. gastritis: inflammation caused by anything that breaches mucosal barrier 2. peptic or gastric ulcers: erosions of stomach wall (can perforate-> peritonitis, hemorrhage), most caused by Helicobacter pylori bacteria, some by NSAIDS

Homeostatic Imbalance

1. heartburn: stomach acid regurgitates into esophagus, likely with excess food/drink, extreme obesity, pregnancy and running -also with hiatal hernia- structural abnormality --part of stomach above diaphragm --can cause esophagitis, esophageal ulcers, esophageal cancer

Homeostatic Imbalance of Liver

1. hepatitis: usually viral infection, drug toxicity, wild mushroom poisoning 2. cirrhosis: progressive, chronic inflammation from chronic hepatitis or alcoholism, liver-> fatty,fibrous-> portal hypertension(obstructs blood flow) *liver transplants are successful but the livers scarce

Classes of teeth

1. incisors: chisel shaped for cutting 2. canines: fang-like teeth that tear or pierce 3. premolars (bicuspids): broad crowns, rounded cusps- grind/crush 4. molars: broad crowns, rounded cusps- best grinder

Digestive processes

1. ingestion 2. propulsion 3. mechanical breakdown 4. digestion 5. absorption 6. defacation

Regulation of gastric secretion

1. neural mechanisms -vagus nerve stimulation-> increase secretion -sympathetic stimulation-> decrease secretion 2. hormonal mechanisms -hormonal control largely gastrin -gastric- increase enzyme and HCl secretion -most small intestine secretions- gastrin antagonists

Protein digestion process

1. proteins and protein fragments are digested into amino acids by pancreatic proteases and by brush border enzymes 2. amino acids are then absorbed by active transport into the absorptive cells, and move to their opposite side 3. amino acids leave the villus epithelial cell by facilitated diffusion and enter the capillary via intercellular clefts

Rectum and anus

1. rectum: three rectal valves stop feces from being passed with gas (flatus) 2. anal canal: last segment of large intestine, opens to body exterior at anus 3. sphincters: internal anal sphincter (smooth muscle), external anal sphincter (skeletal muscle)

Two types of secretory cells in salivary glands

1. serous cells: watery, enzymes, ions, bit of mucin 2. mucous cells: mucus

Deglutition phase 2

2. Pharyngeal-esopheal phase: tongue blocks the mouth, soft palate and its uvula rise, closing of the nasopharynx, larynx rises so that epiglottis blocks trachea, upper esophageal sphincter relaxes, food enters esophagus

Stages of metabolism

3 stages: 1. digestion, absorption, and transport to tissues 2. cellular processing (in cytoplasm) --synthesis of lipids, proteins, and glycogen OR --catabolism (glycolysis) into pyruvic acid and acetyl CoA 3. oxidative (mitochondrial) breakdown of intermediated into CO2, water and ATP

Deglutition phase 3

3. Pharyngeal-esophageal phase continues: constrictor muscles of the pharynx contract, forcing food into esophagus inferiorly, upper esophageal sphincter contracts after food enters

Histology of Alimentary Canal

4 basic layers 1. mucosa 2. submucosa 3. muscularis externa 4. serosa

Gastric Glands

4 cells types 1. mucous neck cells: thin, acidic mucus of unknown function, toward top of gland 2. parietal cells: secrete HCl, intrinsic factor(vital in absorption of b12) 3. chief cells: secrete pepsinogen - inactive enzyme, lipase 4. enteroendocrine cells: secrete chemical messengers into lamina propria-- PARACRINES: serotonin and histamine, HORMONES: somatostatin and gastrin

Deglutition phase 4

4. Peristalsis: peristalsis moves food through esophagus to the stomach

Deglutition phase 5

5. Gastro-esophageal sphincter: surrounding caridal orifice opens, after food enters the stomach, sphincter closes preventing regurgitation

Control of Digestive System

Enteric Nervous System -GI tract has its own NS, referred to as an enteric NS --also called the gut brain --contains more neurons than spinal cord -gut brain is made up of enteric neurons that communicate extensively with each other --major nerve supply to GI tract wall that controls motility

Salivary Glands

Major salivary glands: produce most saliva, lie outside oral cavity 1. parotid 2. submandibular 3. sublingual

Absorption of vitamins

SMALL INTESTINE: -fat-soluble vitamins (A, D, E, and K) carried by micelles; diffuse into absorptive cells -water-soluble vitamins (vitamin C and B vitamins) absorbed by diffusion or by passive or active transporters. -vitamin B12 (large, charged molecule) binds with intrinsic factor, and is absorbed by endocytosis LARGE INTESTINE: -vitamin K and B vitamins from bacterial metabolism are absorbed

Absorption of nucleic acids

active transport across epithelium -> bloodstream

Peristalsis

adjacent segments of the alimentary canal organs alternately contract and relax -food is moved distally along the tract -primarily propulsive, some mixing may occur

Metabolism

biochemical reactions inside cells involving nutrients

Cholecystokinin (CCK)

causes... 1. secretion of pancreatic juice 2. hepatopancreatic sphincter to relax 3. secretion of enzyme-rich pancreatic juice by acini

Malabsorption of nutrients

causes: 1. anything that interferes with delivery of bile or pancreatic juice 2. damaged intestinal mucosa (e.g., bacterial infection; some antibiotics) gluten-sensitive enteropathy (celiac disease) -immune reaction to gluten -gluten causes immune cell damage to intestinal villi and brush border -treated by eliminating gluten from diet (all grains but rice and corn)

Cell respiration & phosphorylation

cell respiration: catabolism of food fuels-> capture of energy to form ATP in cells -enzymes shift high-energy phosphate groups of ATP to other molecules (phosphorylation) -phosphorylated molecules activated to perform cellular functions

Lipogenesis

dietary glycerol and fatty acids not needed for energy-> stored triglycerides

Digestion of nucleic acids

enzymes: 1. pancreatic ribonuclease and deoxyribonuclease -> nucleotide monomers 2. brush border enzyme nucleosidases and phosphatases -> free bases, pentose sugars, phosphate ions

Mouth: Soft palate

fold formed mostly of skeletal muscle -closes off nasopharynx during swallowing -uvula projects downward from its free edge

Liver: microscopic anatomy

liver lobules: hexagonal structural and functional units, composed of plates of hepatocytes (liver cells): filter & process nutrient-rich blood, central vein in longitudinal axis

Segmentation

nonadjacent segments 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

Functional Anatomy: Mouth

oral (buccal) cavity -bounded by lips, cheeks, palate, and tongue -oral orifice is anterior opening -lined with stratified squamous

Mouth: Hard palate

palatine bones and palatine processes of maxillae -slightly corrugated to help create friction against tongue

Large Intestine

regions 1. cecum 2. appendix 3. colon 4. rectum 5. anal canal * unique features: teniae coli (bands of smooth muscle), haustra, epiploic appendages (fat filled sacs)

Lipolysis

reverse of lipogenesis, stored fat -> glycerol and fatty acids for fuel; preferred by liver, cardiac muscle, resting skeletal muscle

Functions of the Digestive System

take in food-break food stuff down into nutrient molecules-absorb molecules into bloodstream-rid the body of indigestible remains