Unit 5 - Digestion Flashcards
How does HCl aid digestion?
- activates pepsinogen to pepsin (in stomach)
Production of HCl by parietal cells:
- CO2 diffuses into cells from blood
- Carbonic anhydrase catalyzes a reaction between CO2 & H2O to form carbonic acid (H2CO3)
- Carbonic acid dissociates into H+ and HCO3- (bicarbonate)
- Bicarbonate is transported back into blood stream & Cl- is brought into cell through the Cl-/HCO3- antiporter (secondary active transport)
- Cl- diffuse into stomach (down its concentration gradient)
- H+ is sent to stomach in exchange for a K+ ion through the H=-K+ ATPase pump (active transport - requires ATP)
- H+ and Cl- combine in stomach to form HCl
3 phases for regulation of gastric secretion in stomach
- cephalic (reflex) phase - prior to food entry
- gastric phase - once food enters the stomach
- intestinal phase - as partially digested food enters duodenum
disaccharides
“two sugar” molecule
sucrose
lactose
monosaccharides
glucose
fructose
galactose
polysaccharide
starch
amylose - unbranched chain of glucose
amylopectin - branched chain of glucose
cellulose - cannot be digested; indigestible fiber
glycogen - highly branched form of glucose storage in muscle
absorbable units of protein
amino acids
small polypeptides
dietary proteins
combinations of amino acids held together by peptide bonds
triglyceride
- glycerol with 3 fatty acid molecules
absorbable units of fat
monoglycerides (glycerol w/one fatty acid)
free fatty acids (that have been freed from triglyceride)
hydrolysis
- breakdown of dietary foodstuffs
- by adding H2O at bond site, enzymes in digestive secretions break them down to absorbable units
4 factors in regulating digestive system function?
- autonomous smooth muscle function
- intrinsic nerve plexuses
- extrinsic nerves
- GI hormones
What are the intrinsic nerve plexuses?
Together called: enteric nervous system - within the system itself
- submucosal plexus
- myenteric plexus
- have motor, excitatory, inhibitory and inter-neurons
autonomous smooth muscle function
- Have pacemaker cells that display slow wave potentials
- Are transmitted via gap junctions
extrinsic neural control
- sympathetic nervous system: inhibits digestion
- parasympathetic: increases smooth muscle motility, promote secretion of digestive enzymes
GI hormones
excitatory or inhibitory effect on smooth muscle & exocrine glands cells
chief cells
in stomach
release pepsinogen
parietal cells
in stomach
secrete HCl- & intrinsic factor
chylomicrons
after the micelles have been absorbed into the cell, the monoglycerides and free fatty acids form triglycerides. They gather into droplets & are coated with a layer of lipoprotein which makes them water soluble (called = chylomicrons).
gastrin (hormone)
- released in stomach
- stimulates pepsinogen production
secretin (hormone)
- released in duodenum
- hormone
- stimulated by ACID
- stimulates pancreatic duct cells to produce NaHCO3 (sodium bicarbonate)
- stimulates liver to secrete bile
cholecystokinin (hormone)
- produced in duodenum
- stimulated by FATS or PROTEINS in duodenum
- stimulates pancreas acini – pancreatic enzymes
- stimulates contraction of gallbladder & relaxation of hepatopancreatic ampulla (sphincter of oddi)
somatostatin
Produced by:
- pancreatic D cells - inhibits digestion of nutrients & absorption
- small intestine epithelial cells - inhibits most digestive processes
- hypothalamus (aka GHIH) - inhibits secretion of GH & TSH
insulin (hormone)
- facilitates glucose transport into most cells
- stimulates GLYCOGENESIS, production of glycogen from glucose (in both skeletal muscle & liver)
- inhibits GLYCOGENOLYSIS, breakdown of glycogen into glucose
- inhibits GLUCONEOGENSIS, conversion of amino acids into glucose in the liver
