Flashcards in Small Intestine Structure and Function Deck (25):
What are the three parts of the small intestine and their roles?
Duodenum - Gastric acid neutralisation, digestion * iron absorption (25cm)
Jejunum - Nutrient absorption (2.5m)
Ileum - NaCl/H2O absorption leading to chyme dehydration (3.5m)
How is the absorptive surface increased?
Microvilli found on top of the epithelial cells of the villi
Where are crypts found, what are they lined with and what is found at the bottom of them?
At the bottom of villi
Younger epithelial cells which are primarily involved in secretion
Where are hydrogen ions held?
Within the mucus layer
What does the villous cell absorb?
What do crypt cells secrete?
Where does water secretion come from and how does it occur?
Epithelial cells lining the crypts of Lieberkuhn
Secreted passively as consequence of the active secretion of chloride from the intestinal lumen
Why is water important in digestion?
Maintains luminal contents in liquid state
Promotes nutrient mixing
Aids nutrient presentation
Dilutes/washes away potential harmful substances
What happens to water after it is secreted?
Usually reabsorbed by the villi
What are the two types of movement in the GI tract?
When is segmentation most common and what is it the contraction of?
During a meal
The short circular intestinal segments
*Longitudinal segments remain relaxed the whole time*
What area contracts?
That which was relaxed as the other part was contracted to provide a thorough mixing of contents with digestive enzymes
What does segmentation bring the chyme into contact with and where does it propel it?
The absorbing surface
Towards the large intestine
How is the generation of contractions initiated?
Depolarisation of pacemaker cells in the longitudinal muscle layer causing the BER to produce oscillation in the membrane potential
Does the BER increase or decreased as it moves down the intestine towards the rectum?
How do sympathetic and parasympathetic signals affect contraction?
Sympathetic decreases contraction
Parasympathetic increases contraction
How does the autonomic nervous system affect the BER?
It has no effect
Following the absorption of nutrients what stops and what starts?
Segmentation stops and peristalsis starts
What is the Migrating Motility Complex (MMC)?
Pattern of peristaltic activity travelling down the small intestine and as one MMC ends, another begins
What is the aim of MMC?
To move undigested material into the large intestine
Limit bacterial colonisation of of small intestine
What will happen if cellulose remains in your gut for too long?
Bacteria will colonise there
*No bacteria wanted in the small intestine*
What area of the lumen does the bolus always move into?
The relaxed muscle on the anal side
What does gastric emptying lead to with respect to the ileum?
An increase in segmentation activity
What sphincter allows the entry of the chyme into the large intestine causing distension?