Small intestine structure and function Flashcards
What is the total length of the small intestine?
6m
What is the length of the duodenum?
25cm
What is the function of the duodenum?
Gastric acid neutralisation
Digestion
Iron absorption
What is the length of the jejunum?
2.5m
What is the function of the jejunum?
95% of nutrient absorption
What is the length of the ileum?
3.5m
What is the function of the ileum?
NaCl/H2O absorption fo dehydration of chyme
What do the villi absorb?
NaCl Monosaccharides Amino acids Peptides Fats Vitamins Minerals Water
What are crypt cells?
Intestinal gland cell
hat do crypt cells secrete?
Cl
Water
What is the small intestine’s primary secretion?
H2O- 1.3litres
What is H2O secreted from in the small intestine?
Crypt cells
By what mechanism is water secreted into the small intestine?
Passive diffusion due to the active secretion of chloride
What is the purpose of secreting water into the small intestine?
Maintains lumen 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 are the 2 types of intestinal movement?
segmentation
Peristalsis
What is segmentation?
Contration and relaxation of short intestinal segments
Contraction moves chyme to adjacent areas of relaxation
When is segmentation most common?
During a meal
What is the function of segmentation?
Provides thorough mixing of contents with digestive enzymes
Brings chyme into contact with absorbing surface
How is a segmentation contraction initiated?
Initiated by depolarisation generated by pacemaker cells in the longitudinal muscle
Basic electrical rhythm produces oscillations in the membrane potential, which fire action potentials at threshold and cause a contraction
What determines the strength and frequency of segmentation contractions?
Strength- frequency of action potentials
Frequency- basic electrical rhythm
What nervous systems control contractions?
Parasympathetic increases contractions
Sympathetic decreases contractions
When does peristalsis begin?
Following the absorption of nutrients
What is the migrating motility complex?
Pattern of peristaltic activity travelling down the small intestine
What is the pattern of peristaltic contraction?
As one contraction ends in the terminal ileum, another begins
Arrival of food in the stomach causes cessation of peristalsis
What is the function of peristalsis?
Move undigested food into the large intestine
Limit bacterial colonisation of the small intestine
What hormone is involved in initiation of the migrating motility complex?
Motillin
What is the law if the intestine?
If intestinal smooth muscle is distended by a bolus, muscle on oral side contracts an muscle on anal side relaxes
What mediates peristalsis?
Myenteric plexus
What is the gastroileal reflex?
Gastric emptying causes an increase in segmentation activity in the ileum
What does the gastroileal reflex initiate?
Opening of ileocaecal valve
Entry of chyme into large intestine
Distension of colon
Contraction of iliocaecal sphincter to prevent back flux
