Small Intestine Structure and Function

Question 1

What is the average total length of the GI tract?

Answer 1

6m (Range of 4.5-9m)

Question 2

How long is the duodenum?

Answer 2

25cm

Question 3

What are the functions of the duodenum?

Answer 3

Gastric acid neutralisation, beginning of digestion and absorption of iron

Question 4

How long is the jejunum?

Answer 4

2.5m long (approx. 2/5 total length of GIT)

Question 5

What is the role of the jejunum?

Answer 5

Nutrient absorption

Question 6

How long is the ileum?

Answer 6

3.5m long

Question 7

What is the role of the ileum?

Answer 7

NaCl/H2O absorption (dehydration of chyme)

Question 8

What three structures enhance the absorptive process?

Answer 8

Folds, villi and microvilli

Question 9

What are villi?

Answer 9

Finger like projections specialised for absorption of nutrients

Question 10

What do villi absorb?

Answer 10

NaCl
Monosaccharides
Amino Acid
Peptides
Fats
Vitamins
Minerals
Water

Question 11

What is the function of crypt cells?

Answer 11

Secretes Cl and water

Question 12

What central tubular structure runs up each vilus? What is its function?

Answer 12

Lacteal - lymphatic vessel used to transport fats

Question 13

Where are crypt cells found?

Answer 13

In the crypts of Liederkuhn

Question 14

What are the four reasons water may be secreted into the lumen of the small intestine?

Answer 14

1. Maintains lumenal contents in liquid state
2. Promotes mixing with enzymes
3. Helps present nutrients to absorptive surface
4. Dilutes and washes away potentially harmful substances

Question 15

What is usually the fate of water secreted by crypt cells?

Answer 15

Reabsorbed in the large intestine

Question 16

What are the two types of intestinal motive processes?

Answer 16

Segmentation and peristalsis

Question 17

What is segmentation?

Answer 17

Contraction and relaxation of short intestinal segements

Question 18

When is segmentation most likely to occur?

Answer 18

During a meal

Question 19

How does segmentation move a bolus?

Answer 19

Contraction of lumen wall causes bolus to move to areas of relaxation - moves forwards and back for a few hours, slowly towards the caeca.

Pushes bolus in contact with absorptive wall

Question 20

What is responsible for initiating depolarisation ?

Answer 20

Pacemaker cells in longitudinal muscle

Question 21

What rhythm is maintained in the small intestine?

Answer 21

Intestinal basic electrical rhythm

Question 22

What determines strength of contraction?

Answer 22

Action potential frequency

Question 23

How does BER change the further through the gut system?

Answer 23

Decreases as it passes through the intestine

Question 24

What is peristalsis?

Answer 24

Pattern of motility migrating complex (MMC) in waves along the length of the small intestine. As one MMC ends, another begins.

Question 25

What stimulus causes the end of peristalsis and the beginning of segmentation?

Answer 25

Arrival of food in the stomach

Question 26

What hormone is closely associated with the initiation of an MMC?

Answer 26

Motiline

Question 27

What is the gastroilieal reflex?

Answer 27

Gastric emptying leading to increased segmentation activity in the ileum

Question 28

How does a bolus leave the ileum?

Answer 28

• Opening of ileocaecal sphincter
• Entry of chyme into large intestine
• Distention of colon
• Reflex contraction of sphincter to prevent back flux

Question 29

What is the law of the intestine?

Answer 29

If intestinal muscle is distended:

Muscle on oral side contract and relaxes on anal side

Question 30

What neural structure mediates the law of the intestine?

Answer 30

Myenteric plexus