Lecture 10 - The Small Intestine Flashcards
(24 cards)
What are the different cells in the villi?
Absorptive cells (transporting epithelia) Goblet cells Enteric endocrine cells Stem/progenitor cells Paneth cells
Briefly describe the structure of the small intestine
It forms circular folds known as the folds of kerckring which are then folded again to form villi.
What do the transporting epithelia cells in the SI do?
They absorb nutrients from the lumen
What do the goblet cells in the small intestine do?
They secrete mucin
What do the enteric endocrine cells do in the small intestine?
They secrete and synthesise hormones
What do the stem cells do in the small intestine?
They replace sloughed cells
What do the paneth cells do in the small intestine?
They are specialised for secretion of antibacterial enzymes such as lysozyme and defensins
What is the purpose of the crypts of leiberkuhn?
They increase the surface area of the small intestine
What are the methods of amplification of the surface area in the small intestine?
Folds of kerckring
Villi
Crypts of leiberkuhn
Microvilli
What are the functions of the small intestine?
Digestion Absorption Secretion Defence Motility
Pancreatic juice and bile are released into the duodenum this includes:
Lipase
Amylase
Trypsin
Protease
What enzymes are expressed on the brush border of the small intestine?
Oligosaccharides
Amino-peptidases
How is glucose absorbed in the small intestine?
By a sodium driven glucose symporter
How are amino acids imported into epithelial cells in the small intestine?
By a sodium symporter
How is water absorbed in the small intestine?
It passively flows down the osmotic gradient generated by secretion and absorption
How is Na absorbed in the small intestine?
Using a Na/H exchanger
How are lipids absorbed in the small intestine?
Stable small micelles form with bile salts, these diffuse amongst the microvilli. Here in the acidic microclimate they release fatty acids which are absorbed by the epithelial cells. Complex fats are then re-synthesises in the endoplasmic reticulum. They are then formed into chylomicrons and leave the basolateral membrane via exocytosis
What are the methods of non-immune defence in the small intestine?
Goblet cells secrete mucin protecting the epithelial cells
Paneth cells secrete defensins (anti-bacterial enzymes)
Tight junctions form a barrier
What are the methods of immune defence in the small intestine?
The lamina propria contains: B cells, T cells, Plasma cells, macrophages, mast cells and easinophilis
Peyer’s patches are distinctive structures with a specialised epithelial lining containing b and T lymphocytes surrounding a lymphoid nodule
What are the methods of motility in the small intestine?
Migrating motor complex
Peristalsis
Segmental movements
Slow waves
What does the migrating motor complex do?
It sweeps remnants into the intestine inbetween meals by rhythmic contractions of the stomach and small intestine in the fasting state
What does peristalsis do in the small intestine?
It is responsible for forward movement of the food bolus. Circular muscles contract whilst longitudinal muscles relax just behind the bolus of food
What do segmental movements do
They are respinsible for mixing and churning in the small intestine. I-5 cm segments alternately contract and relax. This is random
What do slow waves do in the small intestine?
Oscillations in the membrane potential of the GI smooth muscles cells are called slow waves there are several every minute.
