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Digestive
| Question | Answer |
|---|---|
| stages of digestion | ingestion, digestion, absorption, compaction, defecation |
| ingestion | intake of food |
| digestion | mechanical & chemical breakdown of food |
| absorption | uptake of macromolecules into epithelial cells of the digestive tract and then into the blood or lymph |
| compaction | absorbing water and consolidating indigestibles into feces |
| defecation | elimination of feces |
| accessory organs | structures not part of digestive canal (teeth, tongue, salivary glands, liver, gallbladder, pancreas) |
| peritoneum | =where guts are; Within the abdominal cavity, Contains most of the GI tract, SEROSA (secretes fluid into cavity) define the cavity’s boundaries, MESENTERIES connect & transmit vessels and nerves |
| layers of digestive tract= | serosa, muscularis externa, submucosa, mucosa |
| mucosa | Layer of epithelium in digestive tract= continuous •Layer beneath= LAMINA PROPRIA oBind epithelium to layer of muscle= MUSCULARIS MUCOSA •LYMPHATIC TISSUE: lies beneath barrier oContain macrophages; b-cells, t-cells |
| submucosa | • Connective tissue w/ capillaries & blood vessels, lymph vessels |
| muscularis externa | • 2 layers: inner circular layer (makes lumen SMALLER at that place) • outer longitudinal layers (runs top to bottom along length) o when contracts, tube gets SHORTER but WIDER • propel food from visceral tract |
| serosa | • In visceral peritoneum • Secrete serous fluids |
| enteric nervous system's components: | 1. myenteric plexus (PERISTALSIS, contractions of muscularis externa), 2. submucosal plexus (GLANDULAR secretions of mucosa, movements of muscularis mucosae) |
| GI tract stimuli= | mechanical & chemical |
| GI responses mediated by | long (VAGOVAGAL) reflexes, short (MYENTERIC) reflexes, hormones |
| GI tract effects= | secretion, motility |
| saliva/ salivary gland functions | moistens mouth: MUCUS, starch (AMYLASE) and fat (LIPASE) digestion, cleanse teeth: HCO3-, inhibits bacterial growth: LYSOZYME, IgA, dissolves molecules so they can stimulate the taste buds, moistens & binds food into BOLUS to aid in swallowing |
| Intrinsic salivary glands | dispersed oral mucosa, All live within MUCOSA, Constantly secreting saliva |
| extrinsic salivary glands | three pair connected to oral cavity by ducts; -Parotid, submandibular, and sublingual glands, Secrete primarily when eating |
| mucus: secrete....stimulated by.... | secrete mucus, stimulated by sympathetic NS |
| serous cells | secrete thin fluid rich in amylase and electrolytes, Stimulated by parasympathetic NS |
| pharynx | muscular tube extending from nasal cavity --> oral cavity --> esophagus; Swallowing (deglutition) begins here; muscles around bolus CONSTRICTS --> cause food to slip down |
| deglutition | =swallowing |
| esophagus | muscular tube extending from pharynx --> stomach, Contains only 3 layers (no serosa); Responsible for PERISTALSIS |
| peristalsis | movement of a bolus by successive wave of contraction starting at one place of mouth, moving down |
| stomach | primarily functions as a food storage organ, mechanical digestion liquefies the bolus --> producing CHYME, chemical digestion of protein & fat |
| pyloric sphincter | regulates passage of chyme into duodenum; opens @ end of stomach-intestine junction |
| gastric glands (of stomach) secretes... | HCl (very acidic stomach), intrinsic factor (for B12 absorption) --> pernicious anemia= deficiency |
| why secrete HCl | activates enzymes, denatures proteins, converts Fe3+ to Fe2+, destroys most pathogens |
| regenerative (stem cells) | found throughout gastric glands, high turnover of cells |
| gastric glands: types of cells | parietal, regenerative, enteroendocrine, mucous, chief cells |
| enteroendocrine cells | secrete paracrine factors and hormone GASTRIN (G-cells); secretions= HORMONES (gastrin= most important hormone) |
| chief cells | secrete pepsinogen (to break down proteins) & lipase (break down fat) |
| emesis | =vomiting; in response to: overstretching of the stomach or duodenum, chemical irritants (alcohol, bacterial toxins), visceral trauma, intense pain or psychological and sensory stimuli |
| phases in regulation of gastric function | cephalic phase, gastric phase, intestinal phase |
| cephalic phase | Vagus nerve stimulates gastric secretion even before food is swallowed; originates from head --> no food in stomach required, PREPARES stomach for food |
| gastric phase | Food stretches the stomach and activates MYENTERIC and VAGOVAGAL reflexes, gastric secretion is stimulated. HORMONES: Histamine & gastrin also stimulate acid and enzyme |
| intestinal phase | Intestinal gastrin briefly stimulates the stomach, but then SECRETIN, CCK, and the ENTEROGASTRIC (inhibitory signal) reflex INHIBIT gastric secretion and motility while the duodenum processes the chyme. |
| main cell type of liver | hepatocytes |
| hepatocytes absorb from blood... | glucose, amino acids, iron, vitamins, and other nutrients for metabolism or storage |
| hepatocytes degrade from blood... | hormones, toxins, bile pigments, drugs |
| hepatocytes secrete into blood.... | glucose, albumin, lipoproteins, clotting factors, angiotensinogen |
| hepatocytes excrete bile: | bile pigments, bile salts |
| gallbladder main functions | stores & concentrates BILE |
| bile made of... | bilirubin (excretory product), bile salts (bile acids- steroids synthesized from cholesterol), EMULSIFY FATS (dissolve fats in aqueous solutions w/ hydrophillic & hydrophobic side) |
| gallstones | formed if bile is too concentrated; 80% bile acids reabsorbed in small intestine --> liver; 20% excreted in feces |
| pancreatic zymogens (proenzymes) converted to these active enzymes | proteases (trypsinogen, carboxypeptidase), amylase, lipase, ribonuclease and deoxyribonuclease |
| pancreatic juice rich in ________ | HCO3 ions (bicarbonate) |
| pancreas: hormones regulating secretion | acetylcholine (ACh), cholecystokinin (CCK), secretin |
| acetylcholine | from VAGUS & enteric nerves --> stimulate acini to secrete enzymes |
| CCK | secreted by duodenum in response to FATS; stimulate acini to secrete enzymes, stimulate gallbladder CONTRACTION |
| secretin | stimulate by high acidity (low pH), secreted from duodenum in response to ACIDIC CHYME arriving from stomach; stimulates BICARBONATE release |
| duodenum | Receives and MIXES chyme, pancreatic juice, and bile, Emulsify fats (via bile acids), neutralize acids, pancreatic enzymes take over job of chemical digestion |
| jejunum | first 40% of small intestine beyond duodenum; lots of ABSORPTION, thick & muscular walls, large tall circular folds= PLICA |
| ileum | last 60% of small intestine, thinner less muscular & vascular; lots of LYMPHATIC NODULES (=PEYER PATCHES), contains villi & microvilli; lacteal, absorption of LIPIDS |
| VILLI | multicellular projection, blood capillaries of villus absorb most of the nutrients, LACTEAL absorbs most lipids |
| microvilli | fuzzy border on apical surface of each absorptive cell: the “brush border” increases absorptive surface area, brush border enzymes carry out some of the FINAL STAGES of enzymatic digestion |
| peristalsis | gradual movement of contents towards colon |
| segmentation | pinching off of a segment, followed by churning within the segment |
| carb digestion: starch is digested to.... | oligosaccharides, maltose (disaccharide), glucose (monosaccharide) |
| carb absorption | transmembrane transporters move monosaccarides across cells |
| proteases (peptidases) | =enzymes that digest proteins; begin work in stomach @ pH 1.5- 3.5; pepsin digests 10-15% of dietary protein --> shorter peptides and some free amino acids; pancreatic & brush border enzymes reduce oligopeptides --> amino acids |
| absorption of proteins | Na+ dependent amino acid cotransporters move amino acids into epithelial cells |
| micelles | smaller droplets in which fat globules are broken up by lecithin & bile acids; lipids leave micelles --> diffuse into cells --> form chylomicrones secreted/ absorbed by lacteals |
| large intestine functions | does not chemically change the residue, reabsorbs water and electrolytes |
| feces made of.... | 75% water, 25% solids (bacteria, undigested fiber, fat); also lots of BACTERIA |
| bacterial flora | populate large intestine: 800 species of bacteria; ferment undigested carbohydrates, help in synthesis of vitamin B and K |
| defecation reflex | feces stretch rectum --> stimulate stretch receptors --> signal to spinal cord; spinal reflex --> contraction of rectum --> relaxes internal anal sphincter; impulses from brain prevent untimely defecation by keeping external anal sphincter contracted |
Created by:
kpan
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