Small Intestine Function Flashcards
What is the three parts of the small intestine and their sizes
Duodenum - 24cm
Jejnum 2.5m
Illeium 3.5m
What is the three overall functions of the duodenum
Gastric neurtralisation
Digestion
Iron absorption
Where does majority 95% of nutrient absorption occur
Jejnum
Why is the jenjum considered the flat and pink
Flat as mostly empty due to constant detriment absorption
and pink due to well established vascular system present for aximum absorption
What is the main process occurring in the ileum and what is the purpose
NaCl and Water absorption
Necessary for chyme dehydration
also vitamin B 12 absorption,
What enhance the absorptive surface of the small intestine from 0.33m2
Circular fold - Plicae (1m2)
Villi (10m2)
Microvilli (200m2)
What is the cell surface of a Villus
Simple columnar epithelium
What runs up the core of each individual Villi
Lacteal duct surrounded by a capillary network
- takes products of fat digestion to the blood
What is found at the base of villi extending down lamina proper
Crypt of lieberkuhn
What cells are present in villi and what do they produce
Goblet cells producing mucus
What is the purpose of the crypt of lieberkuhn
Produces stem cells that rapidly develop and move up crypt lumen axis shed onto the epithelium and replenishing it
Why is the crpyt of lieberkuhn important
Important due to cell renewal as epithelial cells on the intestine have an average 5 day life span
What is the importance of mucus production from goblet cells in the small intestine
Mucus protects the surface of the small intestine
What do Villi enterocyte cells absorb across the small intestine
NaCl Monosaccharides Amino acids Peptides Fats Vitamins Minerals Water
What is secreted by the crypt cells in the villi
secretes Cl and water
How do most products of digestion enter the intestinal cell
glucose, galactose, amino acids+ nucleotides
Through a NA coupled secondary active transport
How is chloride transported across the intestinal cell and into the lumen
Through the Na-K-Cl cotransporter into intestinal cell then through CFTR channel ono the intestinal villi membrane into the lumen
How does water moves across and into the villi membrane
Water moves passively
As chloride moves into the lumen creates an osmotic gradient so water diffuses through tight junctions following that osmotic gradient
How much water on average does the small intestine secrete and where does this secretion come from
Small intestine secretes ~1500ml H2O per day
H2O secretion comes from epithelial cells lining crypts of Lieberkuhn
How is water important for normal digestive process
Maintains lumenal contents in liquid state
Promotes mixing of nutrients with digestive enzymes
Aids nutrient presentation to absorbing surface
Dilutes and washes away potentially injurious substances
How is water secretion recycled
as is re-asborbed with the villi enterocyte cells
What is the exact pathway that allows CL to leave to intestinal cell and into the lumen
CFTR channels opens to transport CL whenIt is activated by cAMP dependent phosphorylation which is gated by the binding of ATP
What is the two forms of Intestinal movement
Segmentation
Pertalisis
When does the movement of segmentation most likely occur
Whilst eating
How does segmentation occur
Due to the contraction and relaxation of short intestinal segments
What is the purpose of segmentation
Give a thorough mixing of stomach contents with digestive enzymes
Bring chymes into contents with absorbing surface
What is the movement of chyme in segmentation
Contraction lasting a few seconds moves chyme (up & down) into adjacent areas of relaxation
Whilst relaxed areas then contract and push chyme back
(one bit contracts the other relaxes moving chyme around)
How is Segementation contraction initiated
There is a constant depolarisation by the pace makes cells in the longitudinal muscle layer creating a basic electrical rhythm
Contraction occurs when threshold is reached by AP stimuli
What is the frequency of segementation determined by
Basic electrical rhythm
What determines the strength of contractions in segmentation
The frequency of Action potentials
What happens to the basic electrical rhythm as you move down the from the intestine to the rectum,
What is the reason for this
Decreases
Creating a net migration of the material, so there is a slow migration of chyme towards the large bowel
What is the affect of parasympathetic and sympathetic intervention on segmentation
Parasympathetic increases contractions
Sympathetic decreases contraction
What affect does the autonomic NS have on basic electrical rhythm
No effect
When does Pertalisis begin
Following absorption of nutrients: segmentation stops and peristalsis starts
Define the Migrating Motility Complex
Pattern of peristaltic activity travelling down small intestine from gastric antrum to ileum
when one MMC ends in ileum another begins
When food arrives in the stomach what affect does this have on segmentation and peristalsis
cessation of MMC and initiation of segmentation
What is the purpose of the Migrating Motility Complex
Move undigested material into large intestine
Limit bacterial colonisation of small intestine
What hormone is involved in the initiation of Migrating Motility Complx
Moltin
Where is the autonomic control for perstalisis mediates
In the myenteric plexus
Explain how the law of Intestine means that food will forever travel in the direction of mouth to anus
If intestinal smooth muscle is distended (eg by bolus of chyme):
Muscle on oral side of bolus contracts and
Muscle on anal side of bolus relaxes
Therefore Bolus is moved into area of relaxation towards colon
What stimulates the gatroilleal reflex
Gastric emptying increasing the segmentation activity of the ileum
What occurs in the gastroileal reflex
Opening of ileocaecal valve/sphincter
chyme enters into large intestine
Distending colon
Resulting in a Reflex
Causing contraction of ileocaecal sphincter
What is the purpose of the Gastroilleal reflex
prevents backflux into small intestine
