BSI 2 Lecture 65-66: Lower GI Tract Flashcards
Where does most digestion and absorption occur?
Small intestine
What is responsible for digestion in the small intestine?
enzymes on the intestinal wall or brush border, pancreatic juice, and bile
What do the crevices between the villi form?
crypts of lieberkuhn
What do the crypts of lieberkuhn do?
secrete digestive juices
What is contained in the submucosa of the small intestine?
Brunner’s glands
What do Brunner’s glands do?
Secrete alkaline mucus with NaHCO3 that helps neutralize gastric acid in the chyme
What cells are in the small intestine?
- absorptive cells
- goblet cells
- S cells
- CCK cells
- K cells
- L cells
- Paneth cells
What do absorptive cells contain?
Brush border enzymes
What are the brush border enzymes?
- maltase
- sucrase
- lactase
- alpha-dextrinase
- aminopeptidase
- dipeptidase
- nucleosidases
- phosphatases
- enterokinase
What does maltase do?
digests maltose into glucose + glucose
What does sucrase do?
digests sucrose into glucose+ fructose
What does lactase do?
digests lactose into glucose + galactose
What does alpha-dextrinase do?
breaks down dextrins into glucose
What does aminopeptidase do?
digests proteins
What does dipeptidase do?
Breaks down dipeptides into amino acids
What do nucleosidases do?
digest nucleic acids
What do enterokinases do?
activate trypsinogen into trypsin which digests proteins
What do goblet cells do?
secrete mucous
What do S cells secrete?
secretin
What do CCK cells secrete?
CCK
What do K cells secrete?
Glucose-dependent insulinotrophic peptide
What do L cells secrete?
GLP-1
What do paneth cells do?
secrete lysozyme and bactericidal enzyme
What is the pancreas made of?
small clusters of glandular epithelial cells
How much pancreatic juice is secreted per day?
1500 mL
What does pancreatic juice consist of?
- water
- salts
- sodium bicarbonate
- digestive enzymes
What digestive enzymes are included in pancreatic juice?
- pancreatic amylase
- pancreatic lipase
- trypsin
- chemotrypsin
- carboxypeptidase
- elastase
- ribonuclease
- deoxyribonuclease
How do the protein digesting enzymes in the pancreas get activated?
Enterokinase cleaves trypsinogen into trypsin, in the duodenum, and trypsin activates everything else
During which phases is pancreatic juice secreted?
the cephalic, gastric, and intestinal phases
What solid organ can regenerate itself?
Liver
Where is the gallbladder located?
In the posterior surface of the liver
What does the liver do?
Produces and secretes bile
What does the gallbladder do?
stores and concentrates bile
What makes up the liver?
lobes made of lobules
What does the liver have instead of capillaries?
sinusoids
What are sinusoids?
endothelial-lined spaces that contain Kupffer cells
Where does the liver receive oxygenated blood from?
Branch of the hepatic artery
Where does the liver receive blood that is deoxygenated and needs filtering?
Branch of the hepatic portal vein
What makes up bile?
water, bile salts/acids, cholesterol, lecithin, bile pigments, ions and other things
What are the functions of bile?
- breakdown of large lipid globules
- formation of micelles which bind lipids to wall of GI tract for absorption
- excretion of cholesterol, calcium, bilirubin, and drugs
How does bile get stored in the gallbladder?
The sphincter of Oddi has to be closed so bile can enter the cystic duct
What is the pathway of bile secretion?
Bile is secreted by hepatocytes, caniliculi, bile ductules, bile duct, right and left hepatic ducts, exits liver via common hepatic duct
What is the large intestine composed of?
simple columnar epithelium, long tubular intestinal glands, and lymphatic nodules
What cells make up the large intestine?
goblet cells and absorptive cells
Does digestion macromolecules occur in the large intestine?
No
What happens in the final stages of digestion?
- ferment remaining carbohydrates
- break down AA into smaller components
- synthesize short chain fatty acids
Where is 90% of water reabsorbed?
small intestine
Where does mass paristalsis occur?
transverse colon
What initiates the gastrocolic reflex?
Food in the stomach
Steps of the defecation reflex
stretch receptors, sacral spinal cord, PNS, sigmoid colon, rectum, anus, contraction of longitudinal rectal muscles, increase pressure, opening of internal anal sphincter, defecation if external sphincter is relaxed
