Digestive
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| stages of digestion | ingestion, digestion, absorption, compaction, defecation
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| ingestion | intake of food
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| digestion | mechanical & chemical breakdown of food
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| absorption | uptake of macromolecules into epithelial cells of the digestive tract and then into the blood or lymph
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| compaction | absorbing water and consolidating indigestibles into feces
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| defecation | elimination of feces
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| accessory organs | structures not part of digestive canal (teeth, tongue, salivary glands, liver, gallbladder, pancreas)
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| 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
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| layers of digestive tract= | serosa, muscularis externa, submucosa, mucosa
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| 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
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| submucosa | • Connective tissue w/ capillaries & blood vessels, lymph vessels
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| 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
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| serosa | • In visceral peritoneum
• Secrete serous fluids
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| enteric nervous system's components: | 1. myenteric plexus (PERISTALSIS, contractions of muscularis externa), 2. submucosal plexus (GLANDULAR secretions of mucosa, movements of muscularis mucosae)
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| GI tract stimuli= | mechanical & chemical
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| GI responses mediated by | long (VAGOVAGAL) reflexes, short (MYENTERIC) reflexes, hormones
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| GI tract effects= | secretion, motility
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| 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
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| Intrinsic salivary glands | dispersed oral mucosa, All live within MUCOSA,
Constantly secreting saliva
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| extrinsic salivary glands | three pair connected to oral cavity by ducts; -Parotid, submandibular, and sublingual glands, Secrete primarily when eating
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| mucus: secrete....stimulated by.... | secrete mucus, stimulated by sympathetic NS
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| serous cells | secrete thin fluid rich in amylase and electrolytes, Stimulated by parasympathetic NS
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| pharynx | muscular tube extending from nasal cavity --> oral cavity --> esophagus; Swallowing (deglutition) begins here; muscles around bolus CONSTRICTS --> cause food to slip down
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| deglutition | =swallowing
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| esophagus | muscular tube extending from pharynx --> stomach,
Contains only 3 layers (no serosa);
Responsible for PERISTALSIS
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| peristalsis | movement of a bolus by successive wave of contraction starting at one place of mouth, moving down
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| stomach | primarily functions as a food storage organ, mechanical digestion
liquefies the bolus --> producing CHYME, chemical digestion of protein & fat
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| pyloric sphincter | regulates passage of chyme into duodenum; opens @ end of stomach-intestine junction
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| gastric glands (of stomach) secretes... | HCl (very acidic stomach), intrinsic factor (for B12 absorption) --> pernicious anemia= deficiency
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| why secrete HCl | activates enzymes, denatures proteins, converts Fe3+ to Fe2+, destroys most pathogens
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| regenerative (stem cells) | found throughout gastric glands, high turnover of cells
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| gastric glands: types of cells | parietal, regenerative, enteroendocrine, mucous, chief cells
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| enteroendocrine cells | secrete paracrine factors and hormone GASTRIN (G-cells); secretions= HORMONES (gastrin= most important hormone)
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| chief cells | secrete pepsinogen (to break down proteins) & lipase (break down fat)
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| 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
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| phases in regulation of gastric function | cephalic phase, gastric phase, intestinal phase
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| cephalic phase | Vagus nerve stimulates gastric secretion even before food is swallowed; originates from head --> no food in stomach required, PREPARES stomach for food
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| gastric phase | Food stretches the stomach and activates MYENTERIC and VAGOVAGAL reflexes, gastric secretion is stimulated. HORMONES: Histamine & gastrin also stimulate acid and enzyme
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| 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.
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| main cell type of liver | hepatocytes
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| hepatocytes absorb from blood... | glucose, amino acids, iron, vitamins, and other nutrients for metabolism or storage
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| hepatocytes degrade from blood... | hormones, toxins, bile pigments, drugs
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| hepatocytes secrete into blood.... | glucose, albumin, lipoproteins, clotting factors, angiotensinogen
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| hepatocytes excrete bile: | bile pigments, bile salts
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| gallbladder main functions | stores & concentrates BILE
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| 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)
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| gallstones | formed if bile is too concentrated; 80% bile acids reabsorbed in small intestine --> liver; 20% excreted in feces
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| pancreatic zymogens (proenzymes) converted to these active enzymes | proteases (trypsinogen, carboxypeptidase), amylase, lipase, ribonuclease and deoxyribonuclease
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| pancreatic juice rich in ________ | HCO3 ions (bicarbonate)
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| pancreas: hormones regulating secretion | acetylcholine (ACh), cholecystokinin (CCK), secretin
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| acetylcholine | from VAGUS & enteric nerves --> stimulate acini to secrete enzymes
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| CCK | secreted by duodenum in response to FATS; stimulate acini to secrete enzymes, stimulate gallbladder CONTRACTION
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| secretin | stimulate by high acidity (low pH), secreted from duodenum in response to ACIDIC CHYME arriving from stomach; stimulates BICARBONATE release
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| duodenum | Receives and MIXES chyme, pancreatic juice, and bile, Emulsify fats (via bile acids), neutralize acids, pancreatic enzymes take over job of chemical digestion
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| jejunum | first 40% of small intestine beyond duodenum; lots of ABSORPTION, thick & muscular walls, large tall circular folds= PLICA
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| ileum | last 60% of small intestine, thinner less muscular & vascular; lots of LYMPHATIC NODULES (=PEYER PATCHES), contains villi & microvilli; lacteal, absorption of LIPIDS
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| VILLI | multicellular projection, blood capillaries of villus absorb most of the nutrients, LACTEAL absorbs most lipids
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| 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
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| peristalsis | gradual movement of contents towards colon
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| segmentation | pinching off of a segment, followed by churning within the segment
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| carb digestion: starch is digested to.... | oligosaccharides, maltose (disaccharide), glucose (monosaccharide)
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| carb absorption | transmembrane transporters move monosaccarides across cells
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| 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
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| absorption of proteins | Na+ dependent amino acid cotransporters move amino acids into epithelial cells
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| 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
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| large intestine functions | does not chemically change the residue,
reabsorbs water and electrolytes
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| feces made of.... | 75% water, 25% solids (bacteria, undigested fiber, fat); also lots of BACTERIA
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| bacterial flora | populate large intestine: 800 species of bacteria; ferment undigested carbohydrates, help in synthesis of vitamin B and K
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| 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
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