Small intestine structure and function

Question 1

What is the average total length of the small intestine?

Answer 1

6m

Question 2

Why is it advantageous to have a long small intestine?

Answer 2

to prevent material passing through too quickly

Question 3

What is the shortest and longest parts of the small intestine?

Answer 3

duodenum (25cm)
jejunum (2.5m)
ileum (3.5m)

Question 4

What processes occur in the duodenum?

Answer 4

neutralisation, digestion and iron absorption

Question 5

What processes occur in the jejunum?

Answer 5

95% nutrient absorption

Question 6

What processes occur in the ileum?

Answer 6

NaCl/H2O absorption to dehydrate the chyme

Question 7

Name 3 ways in which the surface area of the small intestine is increased

Answer 7

folds (plicae)

villi and microvilli

Question 8

What are plicae?

Answer 8

corkscrew folds of the mucous membranes

Question 9

What are the crypts of Lieberkuhn?

Answer 9

Short gland invaginations between the villi

Question 10

Explain the structure of a villi and the components making it up

Answer 10

simple columnar epithelium
capillaries for exchange and lacteals for fat absorption
Goblet cells present for mucus secretion

Question 11

What is the main difference between the villi and the crypts?

Answer 11

villi absorb and crypts secrete

Question 12

What things does the villi absorb?

Answer 12

amino acids, fat, NaCl, minerals, vitamins, monosaccharides, water

Question 13

What does the crypts secrete?

Answer 13

water and chloride

Question 14

What are some molecules which are sodium coupled for transport?

Answer 14

glucose and galactose

amino acid, nucleotides, water soluble vitamins

Question 15

How much water is secreted a day in the small intestine and from where EXACTLY?

Answer 15

1.5L

epithelial cells of the crypts of Lieberkuhn

Question 16

What is the water secretion in the small intestine due to? (what drives it)

Answer 16

active chloride secretion into the lumen

Question 17

List the 4 things water is important for in the small intestine

Answer 17

wash away toxins
mixing
maintains liquid state of lumen
Aids nutrient presentation to the absorbing surface

Question 18

What is chloride coupled to for movement across the basolateral membrane?

Answer 18

sodium and potassium ie 2 chlorides transported at a time

Question 19

How is chloride expelled from the cell to the apical membrane and through what receptor?

Answer 19

adenylate cyclase catalyses ATP –> cAMP

turns on protein kinase A which turns on CFTR

Question 20

What are the 2 types of intestinal motility?

Answer 20

segmentation

peritalsis

Question 21

When is segmentation most likely to be occurring?

Answer 21

during a meal

Question 22

Briefly explain what segmentation is

Answer 22

the contracting of one part of the intestine and the relaxing of the part before and after the contraction which interchanges to give a mixing of the contents

Question 23

How is segmentation generated?

Answer 23

pacemaker cells depolarise cells in longitudinal muscle layer and the BER produces AP until contraction

Question 24

What determines the strength of contraction?

Answer 24

AP frequency

Question 25

BER decreases or increases from intestine to rectum?

Answer 25

decreases

Question 26

How does the nervous system stimulate the contraction of segmentation?

Answer 26

Para - vagus to increase sympathetic - decrease autonomic - no control

Question 27

When does peristalsis kick in?

Answer 27

After the nutrients have been absorbed

Question 28

What is the MMC?

Answer 28

Pattern of peristaltic activity from the gastric antrum

Question 29

When does another MMC start after the other?

Answer 29

When the one before terminates at the ileum

Question 30

If food enters the stomach what happens to peristalsis?

Answer 30

stops and segmentation begins

Question 31

What are the 2 roles of MMC?

Answer 31

move undigested eg cellulose material to the large intestine prevent bacterial colonisation of the small intestine

Question 32

What is motilin and how is it increased?

Answer 32

A hormone which initiates MMC | nutrient content drops

Question 33

If the smooth muscle in the intestine is distended what are the 3 rules which happen?

Answer 33

muscle on anal side of bolus relax muscle on oral side contract bolus moved into relaxation toward colon

Question 34

What mediates the law of the intestine?

Answer 34

neurons in the myenteric plexus

Question 35

What is the general movement of a bolus in the intestine?

Answer 35

to the anal end

Question 36

What happens to a bolus once it has reached the ileum (gastroileal reflex)

Answer 36

peristalsis starts as the stomach is emptying The ileocaecal sphincter opens and the chime enters the large intestine. This distends the colon and closes the valve behind it to prevent backflux.