Small Intestine Structure and Function Flashcards
How long is the small intestine?
Roughly 6m
What are the 3 components of the small intestine and their lengths?
- Duodenum 25cm
- Jejunum 2.5m
- Ileum 3.5m
What takes place in the duodenum?
- Gastric acid neutralisation
- Digestion
- Iron absorption
What takes place in the jejunum?
95% of nutrient absorption
What takes place in the ileum?
NaCL and H2O absorption leading to chime dehydration
How is the absorptive area of the small intestine enhanced?
- Folds
- Villi
- Microvilli
What does a villus cell absorb?
- NaCl
- Monosaccharides
- Amino acids
- Peptides
- Fats
- Vitamins
- Minerals
- Water
What do crypt cells secrete?
- Cl
- H2O
Describe the Na coupled secondary active transport that takes place at the villi.
- Cooperative transport means that Na enters alongside glucose/galactose/amino acids/nucleosides
- Na is then pumped into the blood while K is pumped in.
- Another transporter pumps K into the blood
- Meanwhile a transporter pumps glucose/glactose/amino acids/nucleoside into the blood
How much water does the small intestine secrete each day?
1500ml
Where does H2O secretion come from?
Epithelial cells lining crypts of Lieberkuhm
How is H2O secreted?
Passively as a consequence of active secretion of chloride into intestinal lumen
Why is H2O important for normal digestion?
- Maintains luminal contents in liquid state
- Promotes mixing of nutrients with digestive enzymes
- Aids nutrient presentation to absorbing surface
- Dilutes and washes away potentially injurious substances
What normally happens to H2O secreted by crypts?
Reabsorbed by villi
Slide 9
Slide 9
What are the 2 distinct types of movement within the intestine?
- Segmentation
- Peristalsis
When is segmentation most common?
During a meal
What is segmentation?
Contraction and relaxation of short intestinal segments
Describe the process of segmentation.
- Contraction moves chyme into adjacent areas of relaxation
- Relaxed areas then contract and push chyme back
- Provides thorough mixing of contents with digestive enzymes
- Brings chyme into contact with absorbing surface
How is segmentation generated?
-Initiated by depolarisation generated by pacemaker cells in longitudinal muscle layer
What does the intestinal basic electrical rhythm produce?
- Oscillations in the membrane potential
- Meets threshold
- Initiates action potential
- Leads to contraction
What determines the strength of contraction?
Action potential frequency
What is the frequency of segmentation determined by?
BER
What happens to BER as it moves down the intestine to the rectum?
Decreases
