Small Intestine Function Flashcards
How long is the duodenum?
~25cm
What is the function of the duodenum?
Neutralise acid
Digestion
Absorption of Fe
What is the function of the jejunum?
~95% of nutrient absorption?
What is the function of the ileum?
Absorption of NaCl to dehydrate Chyme
What structures increase the surface area of the small intestine?
Folds
Villi
Microvilli
What structure lies at the bottom of Villi?
Crypts
What is the function of small intestinal crypts?
Growth of villi endothelial cells
What are plicae circularis?
Circular folds inside the small intestine
How tall are microvilli?
1um
What types of cells are found on the surface mucosa of villus?
Simple columnar epithelium
Goblet cells
What vessels are found within a villus?
Capillary networks
Lacteals
What is the function of crypt cells of the small intestine?
Secretion of Cl and Water
Why is Cl secreted by Crypt cells?
So water will follow the osmotic gradient and keep the mucus watery
Villus cells absorb what?
Everything
How is Sodium absorbed into the cell in the small intestine?
Coupled with:
Glucose/Galactose
AAs
Nucleosides
How is Na taken from the small intestinal epithelial cells to the blood?
Na-K ATPase
How much water is secreted by the small intestine each day?
1500ml
What is the purpose of of secreting water into the small intestine?
Lumenal contents liquidity
Mixing of nutrients and enzymes
Dilutes injurious surface
How is chloride taken from the blood into small intestinal epithelial cells?
2 Cl- ions coupled with 1 K+ and 1 Na+
How does Cl- enter the lumen of the small intestine?
CFTR channel protein triggered by cAMP –> PKA
What is the purpose of pumping Cl- into the small intestinal lumen?
Passive diffusion of water
What types of movements occur in the intestines?
Segmentation
Peristalsis
What is segmentation?
Contraction and relaxation lengthways up intestinal surface
What is the purpose of segmentation?
Move chyme back and forwards, mixing contents with enzymes
Bringing chyme into contact with BBM
How are segmentation contractions triggered?
Depolarisation generated by pacemaker cells (longitudinal muscle layer)
Action potential frequency in the longitudinal muscle layer determines what?
Strength of contraction
What determines the strength of segmentation?
Basic electrical rhythm
Distance down intestine (–> rectum)
Is segmentation fast or slow?
Slow
What is the effect of the Parasympathetic NS on segmentation?
Increased contractility
What is the effect of the Sympathetic NS on segmentation?
Decreased contractility
When does peristalsis begin?
When nutrients are absorbed (segmentation stops)
What is the Migrating Motility Complex
Pattern of peristaltic activity from antrum to terminal ileum
What causes the Migrating Motility Complex to stop?
Arrival of food into the stomach
What is the purpose of the Migrating Motility complex?
Move undigested material into the large intestine
Limit bacterial colonisation of SI
What is the function of Motilin?
Initiation of MMC
What is the law of the intestine?
Muscle on oral side of bolus contracts
Muscle on anal side of bolus relaxes
The law of the intestine is mediated by what?
Myenteric plexus
What is the gastroileal reflex?
Gastric emptying increases segmentation Ileocaecal valve opens Chyme --> LI Colon distended Reflex contraction of Ileocaecal valve to prevent backflux
