1. GI Part 3 Flashcards
describe the small intestine mucosa
the small intestine mucosa has a large surface area
there are three levels of surface convolutions that serve to expand the surface area
what are the three levels of surface convolutions in the small intestine
- plicae circulares – in some species
- villi – finger like epithelial projections
- microvilli
what are at the base of the villi in the small intestine
gland like structures called crypts of Lieberkühn
list the cells of the small intestine and their secretions (4)
- mature enterocytes/absorptive cells
absorption of nutrients,
secretion of digestive enzymes, water, Cl, HCO3 - goblet cells
secretion of mucus - Paneth cells
antimicrobial enzymes and peptides - enteroendocrine cells
hormones such as CCK, secretin, GIP
what are Brunner’s glands and what is the function
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
how is the small intestine involved in the immune system
interplay intestinal barrier and immune system
in the small intestine division and replication of enterocytes occurs where
occurs in cells of the crypts only
describe the regeneration of intestinal crypt cells
intestinal crypt cells are among the most rapidly regenerating cells of the body
as crypt cells multiply they migrate upward the villi
what determines the length of the intestinal villi
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
what is the turnover time of enterocytes
4 to 7 days
where do progenitor cells arise from
the stem cell compartment of the crypts
what do progenitor cells differentiate into
absorptive enterocytes or secretory goblet, enteroendocrine cells, or Paneth cells
where do differentiated progenitor cells migrate, where do Paneth cells migrate
most of the differentiated cells migrate up the villi
Paneth cells move downward into the crypt and reside between the crypt base columnar cells
what mediates water secretion in the large intestine
osmosis
when do different types of food become hyperosmotic
salty foods and foods with high sugar content – hyperosmotic when they enter the intestines
starchy meal – becomes hyperosmotic after digestion
what do osmotically active substances do in the large intestine
draw water from the lateral spaces into the intestinal lumen
what happens as solutes are absorbed in the large intestine
water follows them osmotically back through the epithelium and into the vascular system reaching the blood stream
what direction does water move in in the large intestine
water moves in whatever direction to keep the ingesta isosmotic (maintain osmotic pressure)
in what species is microbial metabolism in the large intestine important
horses and rabbits
microbial metabolism in the large intestine
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)
how is the large intestine involved in the immune system
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
nutrient movement - where do water and nutrients enter first
water and nutrients first enter the extracellular fluid before entering the vascular system
nutrient movement -
forces driving movement of solutes and water?
forces driving movement of solutes and water between intravascular and extravascular fluids are the same as in other tissues
osmotic and hydrostatic forces
nutrient movement - how do absorbed nutrients enter capillaries
absorbed nutrients then enter capillaries by diffusion from the interstitium (this drives water to the capillaries too)
nutrient movement - where is blood from the GI system collected and what is the exception
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
nutrient movement - what does lymphatic drainage bypass and how does it enter the blood stream
lymphatic drainage from the gut bypasses the liver
it enters the bloodstream through the thoracic duct
nutrient movement - chylomicrons
chylomicrons move via lymphatics and therefore bypass the liver
