Small Intestine Structure and Function Flashcards
Describe the section’s of the small intestine
Duodenum 25cm, gastric acid neutralisation, digestion and iron absorption.
Jejunum 2.5m long, 95% of nutrient absorption. Mostly empty and flat as it absorbs almost everything that goes into it.
Illeum -3.5m long
NaCl/H2O absorption causing chyme dehydration.
Describe Peyer’s Patches
egg-shaped lymphatic tissue nodules found through the ileum
Describe Plica
Folds of the mucosal intestinal membrane that increase surface area for absorption
Describe the Brush Border
The micro-villi of the small intestine.
Epithelia of the Small intestine
simple columnar intestinal epithelial cells.
Goblet Cells
Mucous secretory cells scattered between the simple columnar epithelial
Crypt of Liberkuhn
The epithelia of the villi extend down to the lamina propria where they form crypts.
They secrete Cl (CFTR) and water
Crypts of liberkuhn contain:
- Paneth Cells (base of crypt, defensive)
- Enteroendocrine cells (secrete secretin, CCK, GIP and motilin)
Stem Cells
What do Villus Cells absorb?
NaCl Monosaccarides Amino Acids Peptides Fats Vitamins Minerals Water
Describe Water secretion into the small intestine
Chloride ions enter the epithelial cell from circulation by co-transport of Na, K, and Cl through a basal membrane trasporter.
Sodium is pumped back via Na/K pump and K+ exits via other channels.
This activates adenyly cyclase, which generates cAMP from ATP
Elevated cAMP activate CFTR resulting in secretion of Cl into the lumen of the gut.
Negatively charged Cl ions attact Na+ to the intestinal lumen.
Net Result –> Secretion of NaCl ad water is drawn into the lumen.
How is secreted water reabsorbed?
Water secreted by crypts is reabsorbed by the intestinal villi
Peristalsis
Forward movement of food through the GI tract
Segmentation
Contraction & Relaxation of short intestinal segments. Mixes and Churns.
Generation of Segemental Contraction
- Initiated by depolarisation of pacemaker cells in the longitudinal muscle layer.
- Basic electrical rhythm determines frequency of contraction
- Stimulus triggers AP, as BER subthreshold. Number of AP’s triggered determines force of contraction.
Neural Input to Contraction & BER
Vagus - Increases contraction.
Sympathetic - Decreases contraction.
Neural input does not affect BER
When does peristalsis take place
Peristalsis takes place after segmentation.
