Small intestine structure and function Flashcards
what is the total length of the small intestine
~6m
what is the basic structure of the small intestine
sphincter of Oddi
duodenum
jejunum
ileum
what is the role of the duodenum
gastric acid neutralisation, digestion, IRON absorption
what is the role of the jejunum
nutrient absorption (95%)
what is the appearance of the jejunum
“ribbon like” – usually flat because usually empty (vast bulk of diet absorbed before you leave) – very well established vasculature – pink appearance
what is the role of the ileum
NaCl/H2O absorption = CHYME dehydration
deals with residual capacity - most already absorbed – recouping of salt/water
Lose around 200ml of water feaces - but around 9L pass through everyday - most reabsorbed here
what increases the absorptive area of the small intestine
folds, villi, microvilli
what is the relative surface area increase going from the intestine as a cylinder to the microvilli
intestine as a cylinder = 1
circular folds (plicae) = 3
villi = 30
microvilli = 600
what creates a diffusion barrier for an acid microclimate in the small intestine
goblet cells secreting mucous onto the surface of the villi
what is the basic structure of a villi
in-out:
lacteal
capillary network
simple columnar epithelium
containing goblet cells
what lie bellow the villi
crypts of lieberkuhn (with crypt cells)
what is the role of the crypts
secrete CL and water
Crypts secrete around 1.5L INTO lumen per day from epithelial cells – creates aqueous environment for digestion – once used reabsorbed at villi - recycled
why do people with CF not secrete water
lack of Cl channels
what is the role f the villi
absorption of: NaCl Monosaccharides Amino acids Peptides Fats Vitamins Minerals Water
what use Na+ coupled secondary active transport to be absorbed
glucose
galactose
amino acids
nucleosides
what causes H2O to be secreted from the epithelial cells lining the crypts of lieberkuhn
active secretion of chloride into the intestinal lumen causes water to be secreted passively (OSMOTICALLY)
give 4 reasons why H2O secretion if important for normal digestive processes
- Maintains lumenal contents in liquid state
- Promotes mixing of nutrients with digestive enzymes
- Aids nutrient presentation to absorbing surface
- Dilutes and washes away potentially injurious substances
how is Cl actively transported into the intestinal lumen
to get into cell = by the Na-K-2Cl co-transporter
to get into lumen = by chloride channels
what are the two distinct types of intestinal movement
- segmentation (occurs while actively processing food)
2. peristalsis
how does segmentation work
Contraction and relaxation of short intestinal segments
Contraction (few seconds) moves chyme (up & down) into adjacent areas of relaxation
Relaxed areas then contract and push chyme back
what does segmentation enable
Provides thorough mixing of contents with digestive enzymes
Brings chyme into contact with absorbing surface
what initiates segmentation
initiated by depolarisation generate by pacemaker cells in the longitudinal muscle layer
Intestinal basic electrical rhythm (BER) produces oscillations in membrane potential = threshold = action potential = contraction
what determines the STRENGTH of contraction in segmentation
action potential frequency
what determines the FREQUENCY of segmentation
BER - basic electrical rhythm
