Lecture 20- Digestion 3 Flashcards
What are the segmentation contractions?
-segmentation contractions occur in the large intestine and small intestine. While peristalsis involves one-way motion in the caudal direction, segmentation contractions move chyme in both directions, which allows greater mixing with the secretions of the intestines. Segmentation involves contractions of the circular muscles in the digestive tract, while peristalsis involves rhythmic contractions of the longitudinal muscles in the GI tract. Unlike peristalsis, segmentation actually can slow progression of chyme through the system.
- vigorous post meal
- Ileum: increase = by gastrin (gastro-ileal reflex)
What is the gastro-ileal reflex?
-Gastroileal reflex is one of the ways in which gastric motility influences intestinal motility
When there is vigorous gastric peristalsis of increased secretion, it stimulates peristalsis in the ileum
This causes the ileal contents to be pushed into the colon, in turn stimulating colonic peristalsis and an urge to defecate
What is the small intestine for?
- it is really long, small diameter most 10-12meters long
- main ingerdients mixed already so get more breakdown and absorption
- as it moves so it has finite time in which to absorb it- wasteful if gets to large intestine (in case of hindgut fermenters= horses, if too much carbohydrates then can’t break it all down and get interference with fermentation= bad)
What is motilin?
- hormone
- The main function of motilin is to increase the migrating motility complex component of gastrointestinal motility and stimulate the production of pepsin. Motilin is also called “housekeeper of the gut” because it improves peristalsis in the small intestine and clears out the gut to prepare for the next meal
What is the migrating motility complex?
- waves of activity that sweep through the intestines in a regular cycle during fasting state
- help trigger peristaltic waves, which facilitate transportation of indigestible substances such as bone, fiber, and foreign bodies from the stomach, through the small intestine, past the ileocecal sphincter, and into the colon
- Carries undigested material, mucosal debris, bacteria
- Weak peristaltic waves progressively move from stomach to colon
- this activity is increased by the secretion of motilin
What is the ileocecal juncture?
- a sphincter or valve connecting the end of the small intesting (the ileum) with the beginning of the large intestine (the cecum)
- much larger and more pronounced in herbivores.
- regulates passage of material from ileum to the caecum(large intestine)
What is the structure of the small intestine epithelium?
villi-microvilli= increase surface are 600x
- encased in “jelly-like” glycoprotein & mucous secreted by epithelial goblet cells
- also circular folds of the intestine make it possible to fit more into the body
What is the lumenal phase of digestion?
- the stage of the digestion of fats that goes on in the lumen of the intestine
- pancreatic digestive enzyme
- pepsin
- salivary amylase
What is the membraneous phase of digestion?
- Boundary layer of water; Unstirred by movement of luminal contents
- happens at the membrane by membrane bound proteins
When are enzymes released in the small intestine and why?
- enzymes just before absorptions so the things are broken down to their contituents just before it
- there are tight junctions but it is more leaky than the stomach
How do the tight junction in the small intestine differ to those in the stomach?
-the ones in the small intestine are much more leaky
How are carbohydrates digested and absorbed?
- absorbed in the small intestine must be hydrolyzed to monosaccharides prior to absorption
- begins (starch) in mouth with amylase eventually broken down to maltose
- maltose= broken down by maltase into two glucose molecules
- absorption of most digested food occurs in the small intestine through the brush border of the epithelium covering the villi(small hair-like structure). It is not a simple diffusion of substances, but is active and requires energy use by the epithelial cells.
How is lactose, maltose and sucrose digested and absorbed?
-start with quite simple sugars but has to be broken down further
also has Na co transport channel= actively transported into cells and creates gradient so these sugars will enter circulation
- lactose= broken into galactose and glucose by lactase then with help of Na+ co-transport channel absorbed
- maltose= broken into two glucose molecules and also Na+ co-transport channel for absorption
- sucrose= the same only it’s broken down to glucose and fructose
What is the Na+ glucose co-transport system?
- transport the glucose from the lumen into epithelial cells from which it can reach the blood
- it is an active process driven by the concentration gradient of Na+
- glucose and Na+ are actively transported down the Na+ gradient into the epithelial cells= no energy is required
- via glucose carrier the glucose enters blood
How is glucose absorbed into the blood?
-most of it is done by facilitated diffusion
-only when very low level of glucose does the co-transport system come into play
=these three things are at play
- Active transport of sodium into blood (Na+ K+ pump)
- Cotransport of glucose and sodium from lumen into ileum epithelial cells(passive= no energy)
- Facilitated diffusion of glucose into blood
-the sodium is high in the lumen and low in epithelial cells, glucose is low in lumen and high in epithelial cells
=cotransport of sodium and glucose = passive
cotrasport= involves more than one type of particle being transported in the same direction at the same time by the same mechanism
-Occurs from the lumen into the epithelial cell, absorbing a sodium ion and glucose molecule together : COTRANSPORT down a concentration gradient for SODIUM… but AGAINST for glucose
