Small Intestine Structure and Function

Question 1

What is the length of the small intestine?

Answer 1

About 6m

Question 2

What does the small intestine consist of?

Answer 2

Duodenum

Jejunum

Ileum

Question 3

How long is the duodenum?

Answer 3

25cm long

Question 4

What are some functions of the duodenum?

Answer 4

Gastric acid neutralisation

Digestion

Iron absorption

Question 5

How long is the jejunum?

Answer 5

2.5m long (2/5 of total length)

Question 6

What are some functions of the jejunum?

Answer 6

Nutrient absorption

Question 7

What percentage of nutrient absorption occurs in the jejunum?

Answer 7

95%

Question 8

How long is the ileum?

Answer 8

3.5m (3/5 total length)

Question 9

What is the function of the ileum?

Answer 9

NaCl/H₂O absorption

Question 10

What is the absorptive surface of the small intestine enhanced by?

Answer 10

Folds, villi and microvilli

Question 11

What are the circular folds of the small intestine called?

Answer 11

Plicae

Question 12

What is the relative surface area increase of the small intestine due to plicae?

Answer 12

3

Question 13

What is the relative surface area increase of the small intestine due to villi?

Answer 13

30

Question 14

What is the relative surface area increase of the small intestine due to microvilli?

Answer 14

600

Question 15

What is the classification of the epithelium in the small intestine?

Answer 15

Simple columnar

Question 16

What does villus cells absorb?

Answer 16

NaCl

Monosaccharides

Amino acids

Peptides

Fats

Vitamins

Minerals

Water

Question 17

What are the functions of crypt cells?

Answer 17

Secrete Cl and water

Question 18

How much water does the small intestine secrete everyday?

Answer 18

1500ml

Question 19

Where does the water that the small intestine secretes come from?

Answer 19

Epithelial cells lining the crypts of Lieberkuhn

Question 20

How does the small intestine secrete water passively?

Answer 20

Osmotically as a consequence of secreting Cl into the lumen of the gut

Question 21

Why is H₂O secretion important for normal digestive processes?

Answer 21

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

Question 22

What happens to H₂O secreted by crypts?

Answer 22

Normally reabsorbed by villi

Question 23

What are the 2 distinct kinds of movements that makes up intestinal motility?

Answer 23

Segmentation

Perstalsis

Question 24

What is segmentation?

Answer 24

Contraction of the circular muscles in the digestive tract

Question 25

What is perstalsis?

Answer 25

Contraction of the longitudinal muscles in the digestive tract

Question 26

When is segmentation most common?

Answer 26

During a meal

Question 27

What is the function of segmentation?

Answer 27

Alterations between contraction and relaxation of short intestinal segments moves chyme up and down into adjacent areas of relaxation Provides thorough mixing of contents with digestive enzymes Brings chyme into contact with absorbing surface

Question 28

How long does each cycle of segmentation last?

Answer 28

A few seconds

Question 29

Explain the mechanism of segmentation contractions?

Answer 29

1) Initiated by depolarisation generated by pacemaker cells in longitudinal muscle layer 2) Intestinal basic rhythm (BER) produces oscillations in membrane potential 3) Reaches threshold which generates an action potential 4) Causes contraction

Question 30

What is BER?

Answer 30

Basic electrical rhythm

Question 31

What determins the strength of contraction for segmentation?

Answer 31

Action potential frequency

Question 32

What is frequency of segmentation determined by?

Answer 32

BER

Question 33

How does BER change as chyme moves down the intestine to the rectum?

Answer 33

Decreases

Question 34

What supplies the innervation for segmentation?

Answer 34

Parasympathetic (vagus) increases contraction strength Sympathetic decreases contraction strength

Question 35

Does the autonomic nervous system have an effect on BER?

Answer 35

No

Question 36

What effect does the parasympathetic nervous system have on segmentation?

Answer 36

Increases contraction strength

Question 37

What effect does the sympathetic nervous system have on BER?

Answer 37

Decreases contraction strength

Question 38

What does segmentation cause?

Answer 38

Slow migration of chyme towards large intestine (more chyme is pushed towards it than away from it)

Question 39

What occurs following absorption of nutrients in terms of segmentation and peristalsis?

Answer 39

Segmentation stops and peristalsis begins

Question 40

What are the pattern of contractions that creates peristalsis known as?

Answer 40

Migrating motility complex (MMC)

Question 41

Explain the mechanism of peristalsis?

Answer 41

1) Starts in gastric antrum 2) As one MMC ends at the terminal ileum another begins

Question 42

Where does peristalsis begin and end?

Answer 42

Begins at the antrum of the stomach and ends at the terminal ileum

Question 43

How does the arrival of food into the stomach impact segmentation and peristalsis?

Answer 43

Causes cessation of MMC and initiation of segmentation

Question 44

What is the function of peristalsis?

Answer 44

Move undigested material into large intestine Limit bacterial colonisation of small intestine

Question 45

What is a hormone involved in the initiation of MMC?

Answer 45

Motilin

Question 46

What happens when intestinal smooth muscle is distended such as due to chyme?

Answer 46

Muscle on oral side contracts Muscle on anal side relaxes Bolus is moved into area of relaxation towards colon

Question 47

What is the bolus moving towards the colon mediated by?

Answer 47

Enteric nervous system

Question 48

Explain the mechanism of the gastroileal reflex?

Answer 48

1) Gastric emptying causes increase in segmentation activity in ileum 2) Opening of ileocaecal valve (sphincter) 3) Distention of colon 4) Reflex contraction of ileocaecal sphincter (prevents backflux into small intestine)

Question 49

What reflex controls chyme entering the large intestine?

Answer 49

Gastroileal reflex