Lower GI Histology II Flashcards
Where does the digestion of carbohydrates begin?
in the mouth
Amylase ______ starch to form ______.
hydrolyzes, sugars
What is starch hydrolyzed to?
disaccharides
What also secretes amylase?
the pancreas
What are disaccharides are broken down to?
monosaccharides
Where does the degradation of disacchrides occur?
in brush border of small intestine
What absorbs monosaccharides?
enterocytes
What does the absorption of monosaccharides entail?
- Involves energy-dependent mediator-specific carriers:
* Na+-dependent sugar glucose transporter-1 (SGLT-1)
Where does the digestion of proteins begin?
in the stomach
What are proteins hydrolyzed to?
peptides
True or false the digestion of proteins in the stomach occurs through action of pepsin.
True
Where does the breakdown of polypeptides occur and what does it break down into?
in the small intestine, peptides
What enzymes does the breakdown of polypeptides involve?
Trypsin, chymotrypsin, elastase, carboxypeptidase
True or false, activation of pancreatic proteolytic enzymes is initiated by enteropeptidase (enterokinase) which are secreted by duodenal enterocytes.
true
Where does further breakdown of oligopeptides to amino acids occur?
in intestinal brush border
Transport of amino acids into enterocytes is via a ________ process.
carrier-mediated
Where does the digestion of lipids begin?
in the small intestine
Lipids enter the small intestine as _______ ________.
triglyceride droplets
Pancreatic _______ emulsifies these large droplets into smaller droplets and releases ____ _____ and which _____ then combine with bile salts to form _______.
lipase, fatty acids, glycerol, micelles
What do micelles transport?
- Fatty acids, monoglycerides, glycerol, phospholipids, cholesterol, and vitamins A and K.
- Pancreatic lipid esterase splits cholesterol esters into cholesterol and fatty acids.
True or false, micelles are passively absorbed across enterocyte apical plasma membrane.
true
How are micelles passively absorbed across enterocyte apical plasma membrane?
through fatty acid binding proteins (FABPs) in apical membrane
How are monoglycerides and glycerol reesterified in the enterocyte SER to form triglyceride?
Requires acyl-CoA synthetase and acyltransferase:
• Found in membranes of enterocyte SER
Describe chylomicrons
Chylomicrons are enclosed within membranes in Golgi apparatus.
• These membranes fuse to the plasma membrane and allow exocytosis.
__________ recombine with _______ (from RER) to form _______.
Triglycerides, proteins, chylomicrons
Chylomicrons will later enter the blood via what?
the lymph ducts that enter the subclavian veins
Chylomicrons enter intercellular spaces and are taken up by what?
central lacteals
What are central lacteals?
These are blind endings of lymphatic vessels within lamina propria that forms the content of the intercellular spaces within the villi.
What do the lacteals dump into?
the large lymphatic network (cisterna chyli) that carry lymph from the gut tract
Proteins and carbohydrates enter the blood vessels __ ___ ____ and are transported to the ____ via the ______ ______ ________.
in the villi, liver, hepatic portal system
True or false, secretory activities of the GI tract are largely controlled by various hormones that, in turn, are under the influence of the contents of the GI tract.
true
Describe the site of secretion for cholecystokinin.
- Upper intestinal mucosa (duodenum)
* Secreted in response to gastric contents
What does cholecystokinin target and effect?
- Acts on pyloric sphincter to slow down emptying of stomach.
- Stimulates bile release from gallbladder
- Stimulates secretion of pancreatic enzymes
- Competitive inhibitor of gastrins
Describe the site of secretion for gastrin.
Pyloric-antral portion of stomach
What does gastrin target and effect?
- Stimulates HCl production by gastric parietal cells
- Promotes growth of gastric mucosa
- Stimulates gastric motility
- Stimulates release of insulin by pancreatic β cells
Describe the site of secretion for secretin.
- Epithelial cells of duodenum
* Stimulated by acid contents of stomach
What does secretin target and effect?
- Enhances release of insulin by pancreatic β cells
* Stimulates bicarbonate secretion by pancreas
What is the epithelium of the anal canal?
stratified squamous epithelium
What type of muscle is the external anal sphincter?
skeletal
