Lecture #35: Lower GI Histology II

Question 1

Where does carbohydrate digestion begin?

Answer 1

Digestion of carbohydrates begins in the mouth.

• amylase hydrolyzes starch to form sugars
  
  • starch is hydrolyzed to disaccharides
• amylase is also secreted by the pancreas

Question 2

What is the role of amylase?

Answer 2

• Amylase hydrolyzes starch to form sugars, beginning in the mouth.
  
  • starch is hydrolyzed to disaccharides
• Amylase is also secreted by the pancreas

Question 3

Where are disaccharides broken down to monosaccharides?

Answer 3

Occurs in brush border of small intestine.

Question 4

What cell type absorbs monosaccharides after they are broken down from disaccharides in the brush border of the small intestine?

Answer 4

monosaccharides are absorbed by enterocytes

• involves energy-dependent mediator-specific carriers:
  
  • Na+-dependent sugar glucose transporter-1 (SGLT-1)

Question 5

Describe the sequential breakdown of proteins into amino acids; where do each of the steps occur?

Answer 5

• Digestion of proteins begins in the stomach.
  
  • proteins are hydrolyzed to peptides
  • occurs through action of pepsin (activated from pepsiongen)
  • requires acidic environment of stomach
• Polypeptide breakdown to peptides also occurs in the small intestine:
  
  • involves enzymes secreted by the pancreas:
    
    • trypsin
    • chymotrypsin
    • elastase
    • carboxypeptidase
  • activation of pancreatic proteolytic enzymes is initiated by enteropeptidase (enterokinase) secreted by duodenal enterocytes
• Further breakdown of oligopeptides to amino acids occurs in intestinal brush border
• Transport of amino acids into enterocytes is via a carrier mediated process

Question 6

Where does lipid digestion begin?

Answer 6

Digestion of lipids begins in the small intestine.

Question 7

What enzymes are involved in lipid digestion?

Answer 7

• pancreatic lipase

Question 8

What role does micelles and chylomicrons play in lipid digestion?

Answer 8

• pancreatic lipase emulsifies large droplets into smalle droplets and releases fatty acids and glycerol.
  
  • these combine with bile salts to form micelles
• Micelles can transport:
  
  • fatty acids, monoglycerides, glycerol, phospholipids, cholesterol, and viatmains A and K
  • pancreatic lipid esterase splits cholesterol esters into cholesterol and fatty acids
• Micelles are passively absorbed across enterocyte apical plasma membrane.
  
  • requires fatty acid binding proteins (FABPs) in apical membrane
• Chylomicrons are formed by triglycerides that recombine with proteins (from RER).
  
  • chylomicrons are enclosed within membranes in Golgi apparatus.
  • these membranes fuse to the plasma membrane and allow exocytosis
• Chylomicrons enter intercellular spaces and are taken up by central lacteals.
  
  • these are blind endings of lymphatic vessels within lamina propria that forms the content of the intercellular spaces within the villi.
  • lacteals dump into the large lymphatic network (cisterna chyli) that carry lymph from the gut tract
  • chylomicrons will later enter the blood via the lymph ducts that enter the subclavian veins

Question 9

What is the site of secretion, target, and effect of cholecystokinin?

Answer 9

• Site or Secretion:
  
  • upper intestinal mucosa (duodenum)
  • secreted in response to gastric contents
• Targets and Effects:
  
  • acts on pyloric sphincter to slow down emptying of stomach
  • stimulates bile release from gallbladder
  • stimulates secretion of pancreatic enzymes
  • competitive inhibitor of gastrins

Question 10

What is the site of secretion, target, and effect of gastrin?

Answer 10

• Site of Secretion:
  
  • pyloric-antral portion of stomach
• Targets and Effects:
  
  • stimulates HCl production by gastric parietal cells
  • promotes growth of gastric mucosa
  • stimulates gastric motility
  • stimulates release of insulin by pancreatic beta cells

Question 11

What is the site of secretion, target, and effect of secretin?

Answer 11

• Site of Secretion:
  
  • epithelial cells of duodenum
  • stimulated by acid contents of stomach
• Targets and Effects:
  
  • enhances release of insulin by pancreatic beta cells
  • stimulates bicarbonate secretion by pancreas

Question 12

Which hormone stimulates bicarbonate secretion by the pancreas?

Answer 12

Secretin

Question 13

Which hormone enhances the release of insulin by pancreatic beta cells?

Answer 13

Secretin

Question 14

Where is secretin secreted from?

Answer 14

epithelial cells of duodenum

Question 15

What stimulates epithelial cells of duodenum to secrete secretin?

Answer 15

stimulated by acid contents of stomach

Question 16

In which portion of the stomach is gastrin secreted?

Answer 16

pyloric-antral portion of stomach

Question 17

Which hormone stimulates gastric motility, release of insulin by pancreatic beta cells, HCl production by gastric parietal cells, and promotes growth of gastric mucosa?

Answer 17

gastrin

Question 18

Where in the duodenum is cholecytokinin secreted from?

Answer 18

upper intestinal mucosa (duodenum)

Question 19

What causes the upper intestinal mucosa to secrete cholecystokinin from the duodenum?

Answer 19

secreted in response to gastric contents

Question 20

Which hormone is a competitive inhibitor of gastrins?

Answer 20

cholecystokinin

Question 21

What does cholecystokinin function to do?

Answer 21

• acts on pyloric sphincter to slow down emptying of stomach
• stimulates bile release form gallbladder
• stimulates secretion of pancreatic enzymes

Question 22

What type of muscle makes up the external and internal anal sphincters?

Answer 22

• Internal Anal Sphincter = Smooth Muscle
• External Anal Sphincter = Skeletal Muscle

Question 23

What type of epithelium is the anus lined by?

Answer 23

stratified squamous epithelium

Question 24

Which of the following best describes the olfactory mucosa?

a) stratified columnar epithelium with goblet cells and a distinct basement membrane.
b) simple ciliated columnar epithelium with goblet cells and a distinct basement membrane.
c) stratified, non-keratinized epithelium lacking goblet cells with thick basement membrane.
d) pseudostratified columnar epithelium lacking goblet cells with no distinct basement membrane.

Answer 24

d) pseudostratified columnar epithelium lacking goblet cells with no distinct basement membrane.

Question 25

Which of the following is not a necessary part of the respiratory membrane ?

a) pneumocyte I
b) basal lamina of pneumocyte I
c) dust cells (pulmonary macrophages)
d) basal lamina of endothelial cell
e) endothelial cell

Answer 25

c) dust cells (pulmonary macrophages)

Question 26

Which of the following is characteristic of an arteriole?

a) thick tunica adventitia and large lumen
b) thick tunica media in relation to size of lumen
c) thin tunica media and relatively large lumen
d) large blood-filled lumen
e) large amounts of elastic fibers in the tunica media

Answer 26

b) thick tunica media in relation to size of lumen

Question 27

Where is the body of a normal, healthy individual would you expect most erythrophagocytosis to be occurring?

a) marginal zone in spleen
b) medulla of thymus
c) hematopoietic cord in bone marrow
d) Cord of Billroth in spleen
e) paratrabecular sinus in lymph node

Answer 27

d) Cord of Billroth in spleen

Question 28

Which of the followingsequences best describes the flow of red blood cells through the spleen?

a) trabecular arteries, central arteries, splenic arteries, penicillus, venous sinuses
b) splenic artery, central arteries, trabecular arteries, venous sinuses, penicillus
c) splenic artery, central arteries, trabecular arteries, venous sinuses, penicillus
d) trabecular arteries, splenic arteries, central arteries, penicillus, venous sinuses
e) splenic artery, trabecular arteries, central arteries, penicillus, venous sinuses

Answer 28

e) splenic artery, trabecular arteries, central arteries, penicillus, venous sinuses

Question 29

The simple cuboidal epithelium of this portion of the kidney tubule is composed of cells in the form of truncated pyramids which are characterized by basal striations that mark the location of mitochondria.

a) proximal convoluted tubule
b) descending thin segment of the loop of Henle
c) ascending thick segment of the loop of Henle
d) distal convoluted tubule
e) collecting duct

Answer 29

a) proximal convoluted tubule

Question 30

Renin is secreted by which of the following?

a) liver
b) macula densa cells
c) atrial cells of the heart
d) mesangial cells
e) juxtaglomerular cells

Answer 30

e) juxtaglomerular cells

Question 31

True or False:

Micelles are passively absorbed across enterocyte apical plasma membranes.

Answer 31

True

Question 32

Which enzyme splits cholesterol esters into cholesterol and fatty acids?

Answer 32

pancreatic lipid esterase