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35 Cards in this Set

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Surface of Small Intestine
1) Folds of Kerckring 2) Villus 3) Microvilli 4) Crypt
Fold of Kerckring
Longitudinal fold on surface of small intestine
Villus
1) Projects from folds 2) Lines entire mucosal surface
Microvillus
1) Protrudes from surface of intestinal cells 2) Because of appearance microvillous surface called brush border
Crypt
1) Project down into surface at base of each villus 2) 3 crypts/villus
Cells of Small Intestine
1) Enterocytes 2) Goblet cells 3) Crypt cells
Enterocytes
1) Columnar epithelial cells in villus 2) Microvilli protrude from apical surface 3) Function in digestion, absorption, and secretion 4) Cells near villus tip more capable of digestion and absorption than those at base
Goblet Cells
1) Interspersed with enterocytes in villus 2) Secrete mucus
Crypt Cells
1) Found in crypts at base of villus 2) Proliferative cells in intestine - form: A) Enterocytes B) Goblet cells 3) Secrete: A) Fluids B) Eectrolytes
Small Intestine Motility: Function
1) Mix chyme with digestive juices and bile to facilitate digestion and absorption 2) Reduce size of chyme particles to increase solubility 3) Bring chyme into contact with absorptive surface of microvilli 4) Propel chyme from duodenum to colon
Small Intestine Motility: Types of Contractions
1) Segmentation 2) Peristaltic 3) Migrating Myoelectric complex
Small Intestine Motility: Segmentation
1) Most common type of intestinal contractions 2) Circular smooth muscle of isolated segment of wall contracts 3) Forces chyme towards both stomach and colon 4) When muscle relaxes, chyme returns to original segment 5) Effect is mixing of chyme with digestive juices 6) Because of higher frequency of contractions in proximal intestine than in distal intestine, there is net movement of chyme towards colon
Small Intestine Motility: Peristaltic
1) Serve to propel chyme down small intestine 2) Occur only over short distances
Small Intestine Motility: Migrating Myoelectric Complex
1) Similar to that in stomach 2) Occurs about every 90 min 3) Clears remaining chyme in small intestine
Small Intestine Motility: Control
1) Intestinal slow waves require action potentials for contractions to occur 2) Frequency of slow waves decreases distally 3) Motility of small intestine affected by higher centers of nervous system 4) Reflexes: A) Peristaltic reflex/rush B) Intestinointestinal reflex C) Gastroileal reflex
Peristaltic Reflex/Rush
1) Contraction that moves intestinal contents along small intestine 2) Initiated by chyme in intestine which: A) Distends wall or B) Greatly irritates mucosa 3) Also caused by severe cases of infectious diarrhea
Intestinointestinal Reflex
1) Over-distension of one segment of intestine inhibits contractile activity in rest of intestine 2) Prevents movement of material into already severely distended section of bowel
Gastroileal Reflex
1) Gastric secretion and emptying triggers increased peristalsis in ileum 2) Causes: A) Relaxation of ileocecal sphincter B) Movement of ileal contents into large intestine
Pancreatic Anatomy: Cell Types
1) Acinar cells 2) Ductule cells
Acinar Cells
Produce: 1) Peptidases 2) Lipases 3) Amylases
Ductule Cells
1) Secrete pancreatic juice containing high concentration of HCO3- 2) Function: A) Neutralizes gastric acid in duodenum B) Brings contents within pH range necessary for optimal enzymatic digestion of nutrients
Pancreatic Secretion Components
1) Aqueous component 2) Enzymatic component
Pancreatic Secretion: Aqueous Component
1. at all rates of secretion, juice isotonic with plasma 2. [HCO3-] higher than in plasma; [Cl-] lower than in plasma; [K+] ≈ plasma
3. at lowest flow rates, pancreatic juice primarily Na+ and Cl- 4. at highest flow rates, pancreatic juice primarily Na+ and HCO3-
Changes in Ion Concentrations in Pancreatic Secretion as Flow Rate Increases: Na+
Stays the same
Changes in Ion Concentrations in Pancreatic Secretion as Flow Rate Increases: Cl-
Decreases
Changes in Ion Concentrations in Pancreatic Secretion as Flow Rate Increases: K+
Stays the same
Changes in Ion Concentrations in Pancreatic Secretion as Flow Rate Increases: HCO3-
Increases
Formation of Aqueous Component
1) Acinus produces small volume of initial pancreatic juice, which is primarily Na+ and Cl- 2) Ductule and centroacinar cells modify initial pancreatic juice by secreting
HCO3- and absorbing Cl- A) Cells form HCO3- and H+ from H2O and CO2, using carbonic anhydrase B) H+ transported out of cell into blood in exchange for Na+ by Na+/H+ antiporter i) H+ combines with HCO3- in blood to produce more CO2, which is free to diffuse into cell to form more HCO3- ii) because of secretion of H+, venous blood from actively secreting pancreas has lower pH than blood from nonsecreting gland 3) HCO3- transported across apical membrane of ductal cells into lumen in exchange for Cl-; rate of secretion dependent on Cl- being present in lumen 4) Cl- enters lumen through channel in apical membrane of cell; this channel mutated in cystic fibrosis 5) Na+, which entered cell in exchange for H+, actively transported out of cell by (Na+, K+) ATPase; this keeps intracellular [Na+] low for Na+-H+ exchange 6) Na+ then follows HCO3- into lumen to preserve electrical neutrality 7) Pancreatic ducts permeable to water, so water moves into lumen along osmotic gradient (unlike salivary glands)
Pancreatic Secretion: Enzymatic Component
1) Pancreatic lipase and amylase secreted in active forms 2) Pancreatic proteases (trypsin and chymotrypsins) secreted as inactive precursors, which are activated in small intestine 3) Trypsin inhibitor secreted to protect pancreas from autodigestion
Pancreatic Secretion: Regulation
1) Cephalic and gastric phase 2) Intestinal phase 3) Vagovagal reflexes 4) CCK and ACh
Pancreatic Secretion: Regulation-Cephalic and Gastric Phases
1) ACh acts on acinar and ductule cells 2) Distension of stomach initiates vagovagal reflex, which stimulates secretion 3) Mostly digestive enzymes
Pancreatic Secretion: Regulation-Intestinal Phase
1) Stimulated by: A) Acid B) Fat C) Protein digestion products in duodenum 2) Acid releases secretin from S cells in duodenum 3) Secretin acts on ductule cells to increase HCO3- secretion, which neutralizes acid 4) Fat and protein digestion products release cholecystokinin (CCK) from I cells in duodenum 5) CCK acts on acinar cells to increase enzyme secretion 6) Vagovagal reflexes initiated by acid, fat and protein digestion products also stimulate enzyme secretion
Disorders
1) Pancreatitis 2) Cystic fibrosis
Pancreatitis
1) Most commonly caused by: A) Alcoholism B) Gallstones 2) Two forms – acute and chronic 3) Acute symptoms:
A) Severe abdominal pain B) Swollen and tender abdomen C) Nausea and vomiting D) Diarrhea E) Fever F) High serum amylase and lipase levels 4) Chronic:
A) Due mostly to repeated episodes of acute pancreatitis induced by alcohol abuse B) Symptoms similar to those seen in acute cases
Cystic Fibrosis
1) Defect in Cl- channels 2) Reduces secretion of: A) Aqueous B) Enzymatic components 3) Lack of aqueous secretion leads to concentration of pancreatic juice, which blocks secretion of enzymatic component 4) Leads to: A) Malabsorption B) Steatorrhea