Small intestine: structure and function

Question 1

What are the 3 parts of the small intestine called?

Answer 1

duodenum
jejunum
ileum

Question 2

what happens in the duodenum? (3)

Answer 2

gastric acid neutralisation
digestion
iron absorption

takes in semi-digested food from your stomach through the pylorus and continues the digestion process

uses bile from your gallbladder, liver, and pancreas to help digest food

Question 3

Function of Jejunum

Answer 3

carries food through rapidly, with wave-like muscle contractions, towards the ileum

nutrient absorption 95%

Question 4

what is it about the small intestine that enhances it’s absorptive ability? (3)

Answer 4

folds in the surface
villi
microvilli

Question 5

What things can a villus cell absorb? (8)

Answer 5

NaCl
monosaccharides
amino acids
peptides
fats
vitamins
minerals 
water

Question 6

What are crypt cells and what is their purpose?

Answer 6

invaginations of the epithelium around the villi

they have stem cells that divide and specialise to become villi (mature epithelial cells) when they get to the tip of the villus they die and shed off into the contents of your gut (on av. = 5 day process)

secrete Cl and H20

Question 7

how much H20 does the small intestine secrete per day?

Answer 7

1500 ml

Question 8

In the small intestine, where does H20 secretion come from? and what usually reabsorbs it?

Answer 8

epithelial cells lining crypts of Lieberkuhn

villi

Question 9

Is H20 secretion an passive or active process?

Answer 9

passive

Question 10

why is H20 secretion important for normal digestive process?

Answer 10

Maintains lumenal contents in liquid state - need solution to get nutrients up to absorbing surface

Promotes mixing of nutrients with digestive enzymes

Aids nutrient presentation to absorbing surface

Dilutes and washes away damaging injurious substances

Question 11

what are the 2 distinct types of movement in the intestine

Answer 11

segmentation

peristalsis

Question 12

Describe movement by segmentation

Answer 12

most common during meal

contraction and relaxtion of short intestinal segments

contraction moves chyme (up+down) into adjacent areas of relaxation

think toothpaste tube - contract tube and contents push to both sides + mix. Relaxed areas then contract and push chyme back

provides thorough mixing of contents with digestive enzymes but chyme doesn’t move that far forward - slow process to allow time for absorption

brings chyme into contact with absorbing surface

Question 13

what is chyme?

Answer 13

the pulpy acidic fluid which passes from the stomach to the small intestine, consisting of gastric juices and partly digested food

Question 14

how are segmentation contractions generated?

Answer 14

Initiated by depolarisation generated by pacemaker cells in longitudinal muscle layer

Intestinal basic electrical rhythm (BER) produces oscillations in membrane potential - threshold - action potential - contraction
A.P freq. determines strength of contraction

freq. of segmentation determined by BER

as you move down intestine BER decreases

Question 15

Parasympathetic NS has what effect on segmentation contractions

Answer 15

increases contraction - increase speed of chyme through intestine

Question 16

sympathetic NS has what effect on segmentation contractions

Answer 16

decreases contraction

Question 17

is there an effect of autonomic nervous system (sympathetic or para-sympathetic) on BER?

Answer 17

no

Question 18

what is peristalsis?

Answer 18

After nutrients have been absorbed/ you get all the nutrients required from food - segmentation stops and peristalsis STARTS

Question 19

what is the migrating motility complex?

Answer 19

pattern of peristaltic activity travelling down SMALL intestine - ie contraction behind chyme/bolus, relaxation in front moving it along

Starts in antrum (tail end) of stomach as one MMC ends (terminal ileum) another begins at the stomach.

If food arrives in the stomach this is put on hold and segmentation occurs to process it then peristalsis starts again once this is done to clear it out.

Question 20

when does migrating motility complex finish?

Answer 20

when food arrives in stomach - MMC immediately stops and segmentation starts again to get nutrients and it will continue until you process that food and then peristalsis starts again to clear it out

Question 21

purpose of migrating motility complex?

Answer 21

Move undigested material into large intestine

Limit bacterial colonisation of small intestine

Question 22

what is the ‘law of the intestine’

Answer 22

if intestinal smooth muscle is distended (e.g bolus filling it) then the muscle on the oral (mouth) side of bolus contracts and muscle on anal side relaxes. Bolus moves into area of relaxation towards colon

Question 23

Myenteric plexus mediates what?

Answer 23

the movement of bolus through the intestine

Question 24

primary role of the ileum

Answer 24

to get salt and H2O back as 8/9 litres of H20 go into gut but only have 200ml by the end so ileum ensures more salt absorption and water follows suit

Question 25

where does the myenteric plexus lie?

Answer 25

between the longitudinal and circular muscle

Question 26

what are goblet cells, what is their role and where are they located?

Answer 26

goblet cells contain mucus and secrete it out into the apical membrane
They also:-
- help to create the acid microclimate
- control diffusion up to the surface
- protect the surface of cells from excessive damage

they lie interspersed with epithelial cells

Question 27

villi ____ and cyrpts ____

Answer 27

villi absorb

crypts secrete

Question 28

Name the transport method that things like glucose, galactose, amino acids and nucleosides follow

Answer 28

Na+ coupled secondary active transport

2 transporters, Na+/K+ pump, osmotic gradient created by Na+ pulls H20 across from lumen into the cell

Question 29

Overview/summary of normal digestive process in small intestine?

Answer 29

secretory pathway

Regulatory control on the by cyclic AMP – adenylate cyclase makes cAMP
cAMP which goes on to phosphorylate PKA

PKA then activates the CFTR channel which in turn opens and Cl- moves out

Question 30

Describe the basic electrical rhythm in the small intestine

Answer 30

BER at top is a bit higher than at the bottom – decline is happening very gradually between cells down the gut tube

Material is very gradually moving forward (always downwards due to the BER being slightly higher higher up – can’t move against this ie things can’t go backwards up the tube)

Question 31

How does the body prevent chyme moving back from the L intestine into the small intestine?

Answer 31

At the ileocaecal valve – junction between small and large intestine – when the chyme reaches it it opens and the chyme moves into large intestine

The large intestine then becomes distended and causes a reflex contraction that goes back and closes the ileocaecal valve

this prevents material from going back into the small intestine

Question 32

Name of the hormone that is released/required to generate migrating motility complex in small intestine

Answer 32

motilin

when motilin levels in plasma are high, peristalsis takes place