Transcript Chapter 24
Chapter 24 The Digestive System Structures and functions, fig 24.1 Digestive System Organs Alimentary Canal Accessory Digestive Organs Digestive Processes Ingestion Secretion Propulsion Digestion Absorption Defecation Anatomy of the Digestive System ________________ Mouth, Pharynx, and Esophagus Stomach Small Intestine Large Intestine ___________ Digestive Organs Teeth, Tongue, Salivary Glands Liver and Gallbladder Pancreas Functions 1. _______________ taking food into the mouth 2. _______________ release of water, acid, buffers, & enzymes into lumen of GI tract 3. ___________ and __________ churning & propulsion of food thru GI tract 4. ______________ mechanical & chemical breakdown of food 5. _________________ passage of digested products from the GI tract into blood & lymph 6. ___________ elimination of feces from GI tract Mouth, Pharynx, & Esophagus Anatomy Mouth Lips and Cheeks Palate Tongue Salivary Glands Teeth Pharynx Esophagus Digestive Processes Mastication Deglutition Mouth (oral or buccal cavity) fig 24.5 Formed by cheeks, hard & soft palate, tongue Where mechanical AND chemical digestion begin _____________ - chewing Bolus- soft, flexible mass ______________ – enzyme, initiates breakdown of starch ______________ – enzyme in saliva, works in stomach to breakdown dietary triglycerides Tongue accessory organ skeletal muscles covered w/ mucous membrane Attached to hyoid, styloid process, mandible Extrinsic muscles manuever food -chewing, form bolus, force back for swallowing Intrinsic muscles alter shape and size during speech & swallowing Dorsal & lateral surfaces covered w/_____________ which are projections of lamina propria Many contain taste buds - ______________ Lacking taste buds - touch, increase friction ____________ – secrete mucus, & serous fluid that contains lingual lipase Teeth figure 24.7 Accessory digestive organs in _________ __________ Crown, neck, root – major external regions _______________ - calcifed CT, gives shape and rigidity, harder than bone, majority of tooth ________________- covers dentin on crown, hardest substance in body, protects tooth from wear & tear of chewing, and acids ________________ - CT containing bv, nerves, lymphatic vessels Dentitions figure 24.8 ______________ teeth = primary, milk, or baby teeth – begin to erupt @ 6 months 20 in full set All are lost between age 6 to 12 ______________ or secondary teeth 32 teeth 8 incisors – chisel shaped for cutting 4 canine or cuspid – pointed to tear and shred 8 premolars or bicuspid – crush and grind 4 first molars (age 6) – crush and grind 4 second molars (age 12)- crush and grind 4 third molars or wisdom teeth (age 17)- crush and grind Oral mucosa Non-keratinized stratified squamous ______________ – membrane that lines a body cavity that opens to the exterior Of mouth and tongue- contain small salivary glands that open into oral cavity Labial, buccal, palatal, and lingual Make small contribution to saliva Salivary glands figure 24.6 Keep mouth & pharynx mucous membranes moist Cleanse mouth & teeth When food enters mouth, secretion Lubricates, dissolves, begins chemical digestion 3 major glands (in pairs)- parotid, submandibular, sublingual glands Control of salivation ______________ stim= continuous secretion ______________ stim= dominates during stress resulting in dryness of mouth If body dehydrated, saliva not secreted dry mouth sensation of thirst Feel & taste of food stimulate receptors in taste buds nuclei in brain stem parasymp impulse via facial & glossopharyngeal nerves to stimulate salivation Smell, sight, sound or thought of food may also stim. 4 basic layers of GI tract fig 24.2 Variations, but same basic organization in esophagus, stomach, small & large intestines From inner to outermost (starting inside the __________) Mucosa Submucosa Muscularis Serosa Layers of GI tract 1. ____________ - lines lumen, has 3 layers: ______________ mouth, pharynx, esophagus, & anal canal= non-keratinized stratified squamous for protective function stomach & intestines = simple columnar, w/ tight junctions for secretion & absorption Cells renew every 5-7 days (rapid reproduction) Some epithelium = exocrine - mucus secreting cells Enteroendocrine cells secrete hormones into bloodstream ________________ –areolar CT, many bv & lymphatic vessels, nutrients tissues of body Supports epithelium & binds to muscularis mucosa Contains most mucosa-associated lymphoid tissue (MALT) – lymphatic nodules containing immune cells • Also found in tonsils, s.i., appendix and l.i. ________________- thin layer of smooth muscle Puts mucous membrane of stomach & s. i. into many small folds ↑ SA for digestion & absorption movements insure absorptive cells fully exposed 2. _________________- areolar CT binds mucosa to muscularis Highly vascular __________________- portion of ENS- regulates movements of mucosa & bv vasoconstriction Sensory – act as chemoreceptors & stretch receptors Interneurons – connect myentric & submucosal Motor - innervates secretory cells of epithelium May contain glands and lymphatic tissue 3. _____________- mouth, pharynx, & superiormid esophagus = skeletal muscle- swallow Skeletal muscle forms external anal sphincter Thru rest of tract: smooth muscle- generally found in 2 sheets (exception- stomach has 3): Inner = circular layer outer = longitudinal layer Involuntary contractions breakdown food Mix food w/ secretions & propel it along tract Between 2 sheets: ________________ (ENS)- mostly controls GI tract motility- freq & strength of contraction 4. __________- found in portions of GI tract suspended in abdominopelvic cavity serous membrane: areolar CT & simple squamous epithelium AKA- visceral peritoneum Esophagus lacks this layer, has adventitia instead- single layer of areolar CT & no simple squamous Peritoneum figure 24.4 largest serous membrane of body consists of a layer of simple squamous (mesothelium) w/ supporting areolar CT __________________- lines abdominopelvic cavity wall __________________- covers some organs in cavity, is serosa peritoneal cavity- slim space between these layers • contains serous fluid Peritoneum (2) ___________________- organs lie on posterior abdominal wall covered by peritoneum on their anterior surface kidneys and pancreas Bind organs to each other & walls of abdominal cavity Contain bv, lv, & nerves -supply organs Contains large folds between viscera: 1. ___________________ outward fold of serous coat of small intestine; binds to posterior ab wall 2. ___________________ binds large intestine to posterior ab wall; carries bv & lv to intestines *both hold intestines loosely in place Peritoneum (3) 3. ________________- attaches liver to anterior ab wall & diaphragm, (liver = only digestive organ attached to anterior wall) 4. ________________- 2 folds in serosa, suspends stomach & duodenum from liver, contains some lymph nodes 5. _______________- largest part of peritoneum Hangs loosely like a “fatty apron” over transverse colon & coils of small intestine Contains considerable adipose & many lymph nodes, contributes macrophages & plasma cells to combat infection & prevent spread of infection Esophagus figure 24.10 Extends from laryngopharynx esophageal hiatus (surrounded by diaphragm) stomach Stratified squamous epithelium Muscularis: superior 1/3 = skeletal Intermediate 1/3 = skeletal & smooth Inferior 1/3 = smooth At each end is sphincter ____________ – skeletal, regulate pharynx esophagus ____________ – smooth, regulate esophagus stomach Adventitia- not serosa (no simple squamous cells) Secretes mucus, transport food No production of enzymes, no absorption Deglutition (swallowing) - 3 phases Movement of food from mouth to stomach ________________ stage- bolus forced back into oropharynx by movement of tongue _______________ stage- bolus stimulates receptors in oropharynx deglutition center in medulla & pons Soft palate & uvula close off nasal cavity Epiglottis closes off opening to larynx Bolus moves thru oro & laryngopharynx ________________ stage- bolus enters esophagus Peristalsis- progression of coordinated contractions & relaxations of circular & longitudinal layers of muscularis Mucus to lubricate & reduce friction Stomach Functions Anatomy Surface Epithelium Gastric Glands Secretory Cells Digestive Processes Regulation of Gastric Secretion Gastric Motility and Emptying Stomach functions figure 24.11 Mixes saliva, food & gastric juices to form __________ – semifluid mixture of partially digested food reservoir for holding before release into s.i. secretes ___________ (2-3L/day), contains: HCl - kills bacteria & denatures proteins Pepsin begins the digestion of proteins Intrinsic factor- aids absorption of vitamin B12 Gastric lipase - aids digestion of triglycerides Secretes ___________ into blood when stomach is distended or pH is too high Stomach anatomy figure 24.11 4 main regions: Cardia Fundus Body Pylorus Pyloric sphincter Lesser curvature Greater curvature ____________ – large folds of mucosa when stomach is empty Histology of stomach fig 24.12, 13 Mucosa – simple columnar = surface mucous cells that extend into lamina propria forming columns of ____________ secretory cells – gastric glands which line gastric pits Mucous neck cells- secrete mucus Parietal cells- secrete intrinsic factor & HCl Chief cells- secrete pepsinogen & gastric lipase ____________________ cells also part of gastric gland G cells- secretes gastrin, which stimulates gastric acitivity, located mainly at pyloric antrum Muscularis – 3 layers: outer-longitudinal, midcircular, inner-oblique Chemical digestion in stomach food may remain in fundus for hr, salivary amylase works chyme mixes w/gastric juices & lingual lipase activated HCl denatures proteins & stimulates secretion of hormones that promote flow of bile and pancreatic juice Also, acidity kills microbes Enzymatic digestion of proteins begins w/pepsin Gastric lipase breaks down short chain triglycerides (BUT, optimum pH is 5-6) Pancreatic lipase is more important Small amt of nutrients absorbed in stomach Mucous cells absorb some water, ions, some f.a., drugs (such as aspirin) & alcohol What prevents auto-digestion? _____________ secreted in inactive form: pepsinogen cannot digest proteins inside chief cells Pepsinogen pepsin in presence of HCl or other active pepsin Stomach epithelium protected by 1-3 mm of _______________ secreted by surface mucous cells & mucous neck cells 3 Phases of digeston, p 937 _________________ sight, smell, thought or initial taste activates neural centers in cerebral cortex, hypothalamus, & brain stem Facial and glossopharygeal nerves stimulate saliva secretion Vagus nerve stimulates gastric juice secretion (all to prep mouth & stomach for food to be eaten) Phases (2) figure 24.24 _________________ food in stomach, digestion begins Neural regulation- when either of following occur, sets off negative feedback loop submucosal plexus activates parasym & enteric neurons peristalsis & gastric secretion Stretch receptors monitor distention Chemoreceptors monitor pH Hormonal regulation- gastrin regulates gastric secretions, released in response to distension, partially digested proteins, pH (food present), caffeine, or Ach (parasymp) Glands to secrete large amt. gastric juice Strengthens contraction of LES stomach motility Relaxes pyloric sphincter Phases (3) _________________ – food enters small intestine, inhibitory effects to slow exit of chyme from stomach (contrary to cephalic & gastric) Neural regulation: Enterogastric reflex- duodenum distention signals stretch receptors medulla oblongata inhibit parasym & activate symp. contraction of pyloric sphincter gastric emptying Hormonal regulation: (see also table 24.8) Secretin – acidic chyme stimulates release • stimulates secretion of pancreatic juice & bile, rich in HCO3 • Inhibits release of gastric juice • Enhances effects of CCK Cholescystokinin (CCK)- secreted in response to a.a. & f.a. • • • • stimulates secretion of pancreatic juice rich in digestive enzymes causes ejection of bile from gallbladder Causes opening of hepatopancreatic ampulla induces satiety Gastric motility and emptying Several minutes after food enters, peristaltic waves body pylorus every 15-25 sec, create chyme, & forces @ 3mL into duodenum = ________________ During gastric phase, emptying is proportional to volume ingested due to distension & stretching of smooth mus. Extremely large amts of food motility 2-4 hr after meal stomach usually empties carbs take least amt of time, followed by protein-rich meal Lipid rich meals cause slowest emptying f.a. & a.a. in duodenal chyme slows stomach motility Gastrin motility, secretin and CCK emptying Small Intestine & Accessory Organs Small Intestine Duodenum, jejunum, ileum, ileocecal sphincter Villi, Microvilli, plicae circulares Liver Hepatic portal vein & hepatic artery Hepatic vein Bile duct Gallbladder Pancreas Functions of small intestine _________________ mixes chyme w/ digestive juices & brings food into contact w/mucosa for absorption _______________ propels chyme thru s.i. Completes digestion of carbs, proteins & lipids Begins & completes digestion of nucleic acids ____________ about 90% of nutrients and water Other 10% in stomach & large intestine Peristalsis and Segmentation Anatomy of small intestine fig 24.17 3 regions: Duodenum- shortest (10 in), retroperitoneal, pyloric sphincter jejunum Jejunum- 3 ft, extends to the: Ileum- 6 ft, joins w/ l.i. at ileocecal sphincter Differences seen in microanatomy: _______________ in duodenum _______________ in ileum Histology of small intestine fig 24.18, 19 Epithelium– simple columnar, many types: ________________ cells- digest & absorb nutrients in chyme ________________cells- secretes mucus Additional glandular epithelial cells found in intestinal glands- crypts of Lieberkuhn – in mucosa of all s.i. Paneth cells- secrete lysozyme (bacteriocide), are also phagocytic Enteroendocrine cells: S cells- secretes secretin (stim secretion p.j & bile) CCK cells- secretes CCK (stim secretion p.e., release of bile) K cells- secretes (GIP) glucose-dependent insulinotropic peptide Histology (2) In the lamina propria: MALT Solitary lymphatic nodules in ileum Aggregated lymphatic follicles= Peyer’s patches in ileum Submucosa: _____________ or _____________- secrete alkaline mucus to neutralize gastric acid in chyme Lymphatic tissue may extend into Serosa absent in duodenum 3 specializations that absorption in s. i. _________________ (circular folds) – folds in mucosa & submucosa, permanent ridges In duodenum to mid- ileum Enhance absorption by SA & cause chyme to spiral thru ____________- fingerlike projection of mucosa, SA Lacteal- lymph capillary inside villus nutrients absorbed thru epithelial cells pass thru wall of lacteal lymph or blood capillaries blood ___________ - projections of apical surface of absorptive epithelium greatly surface area of plasma membrane form fuzzy line = brush border- contains several digest. enzymes Digestion of carbohydrates ______________- destroyed by pH ________________- in pancreatic juice, acts in small intestine Acts on glycogen and starch but not cellulose -dextrinase- brush border enzyme works on dextrins after amylases work on starch 3 brush border enzymes- ________ _________ ________ work on their respective disaccharides monosaccharides absorbed Digestion of proteins Starts in stomach __________ fragments proteins peptides Pancreatic juice enzymes continue protein peptide, each breaking peptide bonds between different a.a. Trypsin Chymotrypsin Carboxypeptidase Elastase __________ of brush border complete digestion Aminopeptidase- cleaves a.a. at amino end Dipeptidase- splits dipeptides Digestion of lipids Lipase- splits triglycerides & phospholipids Lingual- works in stomach Gastric- works in stomach Pancreatic- works in s.i., where most lipid digestion occurs Triglycerides f.a. and monoglyceride In order to be digested, lipid globules must be ___________ - globule is broken down to several globules, done by _____________ Bile salts- amphipathic molecules that interact with lipid globule and watery intestinal chyme surface area of small globule allows for area on which pancreatic lipase works Absorption figure 24.20 Passage of digested nutrients from ___________ to_______ or _________ Diffusion Facilitated diffusion Osmosis Active transport ___% in _________, 10% in stomach & l.i. Undigested & unabsorbed passes thru l.i. Monosaccharides Form in which all carbs are absorbed Lumen apical surface via facilitated diffusion (fructose) or active transport (glucose & galactose) All 3 monos thru basolateral membrane to capillaries liver via hepatic portal system general circulation (if not removed by hepatocytes) Amino acids, dipeptides, tripeptides Most proteins absorbed via active transport in duodenum & jejunum ½ proteins come from food ½ digestive juices and dead cells ________% of protein in s.i. is absorbed Different transporters for different a.a. a.a. basolateral membrane to capillaries via diffusion liver (like monos) Absorption of lipids Via simple diffusion Bile salts surround f.a. & monoglycerides in chyme making more soluble, form tiny spheres= __________ Micelles can also solubilize vitamins A, E, D, K & cholesterol Micelles ferry f.a. & monoglycerides to brushed border diffuse micelle absorptive cells Inside cell recombine form triglycerides Aggregate w/ phospholipids & cholesterol coated w/protein = _____________ exocytosed lacteals liver & adipose tissue Lipoprotein lipase breaks down triglycerides in chylomicron & f.a. & glycerol diffuse hepatocytes or adipocytes Bile salts reabsorbed in ileum liver for recycling Lipoprotein figure 25.13 Nutrients to blood and lymph Liver functions produces___- lipid emulsifier *main digestive fnc filters blood- destroying worn out RBC, WBC, bacteria & other foreign material in venous blood draining GI tract metabolizes carbs, lipids, protein processes drugs & hormones Excrete _______- byproduct hemoglobin break storage of glycogen, some vitamins & minerals Phagocytosis – ____________ Activation of vitamin D Liver anatomy & histology fig 24.15 Right and left lobe, falciform ligament Lobule = functional unit of liver 6 sided, consists of hepatocytes arranged around a central vein. Blood flows from: _________ at each corner _________ c.v. Bile duct- collect bile flowing thru canaliculi from hepatocytes Hepatic portal vein- blood from GI tract Hepatic artery- oxygenated blood Kupffer cells in sinusoids (large capillaries) Hepatic blood flow figure 24.16 Gallbladder Bile secreted by hepatocytes stored here Mucosa– simple columnar, rugae Smooth muscle causes bile _________ Along w/storage, functions to concentrate bile water & ions absorbed in mucosa Flow of bile figure 24.14 Bile production & release from g.b. Hepatocytes secrete 800-1000mL/day Continuously release bile _____ – neutral pH, water, bile salts, cholesterol, lecithin, bile pigments (biliruben), & ions production & secretion if portal blood contains more bile acids as digestion & absorption continue in s.i. bile release increases When absorption , bile gallbladder _____________________ closed Glucose, glycogen & gluconeogenesis Liver helps maintain normal blood glucose Blood glucose breakdown glycogen & release glucose Convert a.a. & lactic acidglucose=gluconeogenesis Convert galactose & fructose to glucose Blood glucose Convert glucose to glycogen & triglycerides _______________ – glucose formation from non-carbohydrate source When glycogen is depleted, lipids & proteins catabolized Glycogenesis & glycogenolysis 25.11 Gluconeogenesis figure 25.12 Lipid metabolism figure 25.14 Catabolism: __________ - triglyercides glycerol & f.a Done by lipases Necessary for liver, muscle, adipose: f.a. ATP Anabolism: _________ - liver & adipose: glu & a.a.lipids Occurs when consume too many calories Triglyercides can be: • Stored in adipose tissue • More rxns lipoprotein, phospholipids, & cholesterol Plasma proteins & urea production ____________ (removal of NH2 or amine group from a.a.) occurs in hepatocytes a.a. used for: ATP production Converted to carbohydrates and fats Ammonia (NH3) is toxic & converted to urea Hepatocytes synthesize most ________ _________: Globulins & albumin (transport) Prothrombin & fibrinogen (clotting) Pancreas figure 24.15 99% acini- ___________ function Secrete fluid & enzyme mixture = pancreatic juice Pancreatic amylase- carbohydrate-digesting enzyme Trypsin, chymotrypsin, carboxypeptidase, & elastase- protein digesting enz Pancreatic lipase- triglyceride digesting enzymes Ribonuclease & deoxyribonuclease- digest n.a. 1% Islets of Langerhans – __________ function Glucagon Insulin Somatostatin Pancreatic polypeptide Pancreas (2) 2 passageways secretions small intestine: pancreatic duct- joins common bile duct duodenum thru h.p. amp accessory duct = duct of Santorini Pancreatic juice secretion stimulated by: _______________ _________ & ________ (in s.i) CCK also opens hepatopancreatic ampulla Large Intestine Anatomy Digestive Processes Water Electrolytes Vitamins Defecation Functions of the large intestine Haustral churning, peristalsis, & _____________ drive contents of colonrectum Bacteria in large intestine convert proteins to a.a., break down a.a., produce some B vitamins & ____________ Absorbs some water, ions & vitamins Forming feces ______________ emptying the rectum Anatomy of large intestine fig 24.22 cecum ascending transverse descending sigmoid colon rectum anal canal Epithelium mostly simple columnar – absorptive & goblet cells, and are found lining intestinal glands– highly mucus prod. ___________ – 3 longitudinal bands of muscle extending along most l.i., Tonic contractions create pouches - ____________ Digestion in large intestine _______________ – after meal, ileal peristalsis to force all chyme from ileum cecum Gastrin also relaxes ileocecal sphincter Haustral churning- remain relaxed but after distended will contract Peristalsis- slower than other areas of tract Mass peristalsis- strong wave from mid-transverse colon quickly sending contents to rectum Is called a gastrocolic reflex- initiated by food in stomach Usually takes place 3-4 times/ day (immediately after meal) ____________ secreted, just mucus ____________ prepares chyme for elimination Absorption, feces, & defecation Chyme in l.i. 3-10 hr solid or semi-solid due to water absorption = feces Water, inorganic salts, GI mucosal cells, bacteria, products of bacterial decomp, unabsorbed digested & undigested material Water absorption here is crucial 0.5 -1.0 L enters, 100 - 200mL leaves Absorbs ions (Na+, Cl-) & some vitamins Mass peristalsis _____________ – distention impulse parasym motor neuron causes contraction, also external anal sphincter- voluntary Bowel movements depend on diet, health, stress Amt varies: 2-3/day to 3-4/week Daily fluids