1. GI Part 3

Question 1

describe the small intestine mucosa

Answer 1

the small intestine mucosa has a large surface area

there are three levels of surface convolutions that serve to expand the surface area

Question 2

what are the three levels of surface convolutions in the small intestine

Answer 2

1. plicae circulares – in some species
2. villi – finger like epithelial projections
3. microvilli

Question 3

what are at the base of the villi in the small intestine

Answer 3

gland like structures called crypts of Lieberkühn

Question 4

list the cells of the small intestine and their secretions (4)

Answer 4

1. mature enterocytes/absorptive cells
   absorption of nutrients,
   secretion of digestive enzymes, water, Cl, HCO3
2. goblet cells
   secretion of mucus
3. Paneth cells
   antimicrobial enzymes and peptides
4. enteroendocrine cells
   hormones such as CCK, secretin, GIP

Question 5

what are Brunner’s glands and what is the function

Answer 5

tubulo alveolar glands in the submucosa of the small intestine

secretion of mucus through exocytosis

secrete glycoproteins and bicarbonate ions

protection of small intestine mucosa by neutralizing acid-containing chyme delivered from the stomach

pH of Brunner’s gland secretion – 8.1-9.3

Question 6

how is the small intestine involved in the immune system

Answer 6

interplay intestinal barrier and immune system

Question 7

in the small intestine division and replication of enterocytes occurs where

Answer 7

occurs in cells of the crypts only

Question 8

describe the regeneration of intestinal crypt cells

Answer 8

intestinal crypt cells are among the most rapidly regenerating cells of the body

as crypt cells multiply they migrate upward the villi

Question 9

what determines the length of the intestinal villi

Answer 9

the rate at which cells are lost at the tips and the rate at which they are replaced

an increase in cell loss at villi tips (relative to crypt cell replication) results in shortening of the villi

Question 10

what is the turnover time of enterocytes

Answer 10

4 to 7 days

Question 11

where do progenitor cells arise from

Answer 11

the stem cell compartment of the crypts

Question 12

what do progenitor cells differentiate into

Answer 12

absorptive enterocytes or secretory goblet, enteroendocrine cells, or Paneth cells

Question 13

where do differentiated progenitor cells migrate, where do Paneth cells migrate

Answer 13

most of the differentiated cells migrate up the villi

Paneth cells move downward into the crypt and reside between the crypt base columnar cells

Question 14

what mediates water secretion in the large intestine

Answer 14

osmosis

Question 15

when do different types of food become hyperosmotic

Answer 15

salty foods and foods with high sugar content – hyperosmotic when they enter the intestines

starchy meal – becomes hyperosmotic after digestion

Question 16

what do osmotically active substances do in the large intestine

Answer 16

draw water from the lateral spaces into the intestinal lumen

Question 17

what happens as solutes are absorbed in the large intestine

Answer 17

water follows them osmotically back through the epithelium and into the vascular system reaching the blood stream

Question 18

what direction does water move in in the large intestine

Answer 18

water moves in whatever direction to keep the ingesta isosmotic (maintain osmotic pressure)

Question 19

in what species is microbial metabolism in the large intestine important

Answer 19

horses and rabbits

Question 20

microbial metabolism in the large intestine

Answer 20

one layer cylindric epithelium (crypts are also present)

water absorption, vitamins

goblet cells –> mucus

secretion: small volume, isotone to plasma, mucin, bicarbonate and potassium rich (alkaline)

Question 21

how is the large intestine involved in the immune system

Answer 21

the cecum and colon are very similar in their microscopic structure

the mucosa in composed of crypts but not villi lined by goblet cells (mucus) and some absorptive epithelial cells (absorption of some electrolytes and water)

at the base of each crypt there are some stem cells

Question 22

nutrient movement - where do water and nutrients enter first

Answer 22

water and nutrients first enter the extracellular fluid before entering the vascular system

Question 23

nutrient movement -

forces driving movement of solutes and water?

Answer 23

forces driving movement of solutes and water between intravascular and extravascular fluids are the same as in other tissues

osmotic and hydrostatic forces

Question 24

nutrient movement - how do absorbed nutrients enter capillaries

Answer 24

absorbed nutrients then enter capillaries by diffusion from the interstitium (this drives water to the capillaries too)

Question 25

nutrient movement - where is blood from the GI system collected and what is the exception

Answer 25

all venous blood from the GI tract is collected into the hepatic portal vein and passes through the liver before entering the vena cava and returning to the heart

the exception is – venous blood from the terminal colon and rectum

Question 26

nutrient movement - what does lymphatic drainage bypass and how does it enter the blood stream

Answer 26

lymphatic drainage from the gut bypasses the liver

it enters the bloodstream through the thoracic duct

Question 27

nutrient movement - chylomicrons

Answer 27

chylomicrons move via lymphatics and therefore bypass the liver