Physiology -- Intestinal Absorptive and Secretory Processes Flashcards
4 enzymes that break down proteins to small peptides
- Pepsin
- Trypsin
- Chymotrypsin
- Carboxypeptidase
Location of Brunner’s glands
Duodenum submucosa
Contents of Brunner’s glands
- No digestive enzymes
- Lots of HCO3-
- Mucin
Location of goblet cells
Throughout the small intestine
Secretions of goblet cells
Mucin
Characterization of intestinal mucosa
Crypts and villi
Location of complete digestion and absorption in terms of the small intestine
Villi
Location of secretion in terms of small intestine
Crypt
Rate of cell shedding at the tip of the villus
100 x 106 cells/min
Location of villus enzymatic activity
Brush border
Secretions from crypt cells and volume produced
No digestive enzymes
Succus entericus (3L per day)
Ionic composition of succus entericus
Isotonic:
- Na+
- K+
- Cl-
- HCO3-
pH of succus entericus secretions
~7.5 - 9
What is located in the lumen of the SI crypts?
Cotransporter protein transporting Na+ and Cl-
Describe the function of the cotransporter of the crypts
- Na+ brought out of cell by Na+-K+-ATPase
- Na+ cotransported with Cl- into cell
- Cl - secreted out of the other end of the cell through Ca++ dependent cAMP
- Na+ also flows between cells
- Water follows osmotic gradient
Effect of vibrio cholerae bacterium
Enterotoxic effect: bind to receptors on apical membrane –> stimulate adenylate cyclase –> increase cAMP = maximally stimulates intestinal secretion
Net result = overwhelms the absorptive capacity of SI and colon (need rapid rehydration)
Also, cAMP decreases absorption of neutral NaCl in villi
Describe the regulation of succus entericus secretions
Poorly understood interactions of ENS, ANS, gut peptides (gastrin, VIP) acting in paracrine/endocrine fashion
Effect of prostaglandins and histamine on succus entericus secretion
Increase secretion
Effect on somatostatin on succus entericus secretion
Inhibition of secretion
Function of villi
- Synthesize enzymes (retained in brush border)
- Absorb nutrients and fluids
6 enzyme types synthesized by the intestinal villi
- Enterokinase
- Amylase
- Lipase
- Aminopeptidases
- Dipeptidases
- Disaccharases
4 disaccharases synthesized by the intestinal villi
- Sucrase
- Maltase
- Isomaltase
- Lactase
Location of paneth cells
Base of crypts
2 substances secreted by paneth cells
Lysozymes
Defensins
Function of paneth cell secretions
Possible importance in protecting mucosa against bacteria
Contents of SI lamina propria
Lymphocytes and plasma cells
Role of SI lamina propria contents
Secretion of Ig = important in mucosal immune system
Volume of colonic secretions
Small
pH of colonic secretions
Alkaline
Composition of colonic secretions
- [HCO3-] = 100 - 150 mEq/L
- [K+] = 100 - 150 mEq/L
Protein included in colonic secretions
Mucin
Characteristic feature of colonic secretions
Bacterial activity
NO DIGESTIVE ENZYMES
Approximate daily input and output of solids
Input = 500 g
Output = 50 g
Approximate daily water input and output
Input = 2000 mL
Output = 200 mL
Approximate composition of solid output
- 30% bacteria
- 30% undigested fiber
- 10 - 20% lipids
- 10 - 20% inorganic matter
Volume of fluid produced by salivary glands
1500 mL
Sources of fluids input to the GI
- Oral intake
- Salivary glands
- Stomach
- Bile
- Pancreas
- Intestine
Volume of stomach fluids produced daily
2500 mL
Volume of bile produced daily
500 mL
Volume of pancreatic fluid produced daily
1500 mL
Volume of intestinal fluids produced daily
1000 mL
Approximate volume of fluid that must be absorbed daily
9000 mL