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.
Patterning of Peristalsis
Migrating Motility Complex, begin in the gastric antrum and continues to the distal ileum, causing another to begin.
Arrival of food in the stomach causes MMC to cease and segmentation to begin.
Motilin involved with MMC intiationMecha
What is the function of MMC
A) Move undigested matieral to the large intestine.
B) Limit bacterial colonisation
Mechanism of Peristalsis
Muscle behind the bolus contracts.
Muscle infront of bolus relaxes.
Bolus is moved down into area of relaxation
Control of Peristaisis
Peristalsis is controlled by the ENS via the myenteric plexus and is independent of CNS control
Name the three extrinsic reflexes that control the movement, digestion and defecation
- Enterogastic Reflex
- Gastocolic Reflex
- Gastoileal reflex
Describe the enterogastric reflex
Reflex is stimulated by acid levels of 3/4 in the duodenum and stomach at 1.5.
This level of pH causes release of gastrin from G-cells in the antrum is inhibited.
This reduces gastric motility and secretion of HCl
Describe the Gastrocolic Reflex
Controls motility of the colon in response to stretch of the stomach. Urge to defecate post meal
Describe the gastroileal reflex
Works with the gastocolic reflex to stimulate the urge to defercate post meal. It is stiumatied by the opening of the ileocecal valve and moevment of digested contents from the ileum to the small intestine into the colon for compaction
https://courses.lumenlearning.com/boundless-ap/chapter/nervous-system-of-the-digestive-system/
