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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