Small Intestine Structure and Function

Question 1

How long is the small intestine?

Answer 1

Roughly 6m

Question 2

What are the 3 components of the small intestine and their lengths?

Answer 2

• Duodenum 25cm
• Jejunum 2.5m
• Ileum 3.5m

Question 3

What takes place in the duodenum?

Answer 3

• Gastric acid neutralisation
• Digestion
• Iron absorption

Question 4

What takes place in the jejunum?

Answer 4

95% of nutrient absorption

Question 5

What takes place in the ileum?

Answer 5

NaCL and H2O absorption leading to chime dehydration

Question 6

How is the absorptive area of the small intestine enhanced?

Answer 6

• Folds
• Villi
• Microvilli

Question 7

What does a villus cell absorb?

Answer 7

• NaCl
• Monosaccharides
• Amino acids
• Peptides
• Fats
• Vitamins
• Minerals
• Water

Question 8

What do crypt cells secrete?

Answer 8

• Cl

- H2O

Question 9

Describe the Na coupled secondary active transport that takes place at the villi.

Answer 9

• Cooperative transport means that Na enters alongside glucose/galactose/amino acids/nucleosides
• Na is then pumped into the blood while K is pumped in.
• Another transporter pumps K into the blood
• Meanwhile a transporter pumps glucose/glactose/amino acids/nucleoside into the blood

Question 10

How much water does the small intestine secrete each day?

Answer 10

1500ml

Question 11

Where does H2O secretion come from?

Answer 11

Epithelial cells lining crypts of Lieberkuhm

Question 12

How is H2O secreted?

Answer 12

Passively as a consequence of active secretion of chloride into intestinal lumen

Question 13

Why is H2O important for normal digestion?

Answer 13

• 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 14

What normally happens to H2O secreted by crypts?

Answer 14

Reabsorbed by villi

Question 15

Slide 9

Answer 15

Slide 9

Question 16

What are the 2 distinct types of movement within the intestine?

Answer 16

• Segmentation

- Peristalsis

Question 17

When is segmentation most common?

Answer 17

During a meal

Question 18

What is segmentation?

Answer 18

Contraction and relaxation of short intestinal segments

Question 19

Describe the process of segmentation.

Answer 19

• Contraction moves chyme into adjacent areas of relaxation
• Relaxed areas then contract and push chyme back
• Provides thorough mixing of contents with digestive enzymes
• Brings chyme into contact with absorbing surface

Question 20

How is segmentation generated?

Answer 20

-Initiated by depolarisation generated by pacemaker cells in longitudinal muscle layer

Question 21

What does the intestinal basic electrical rhythm produce?

Answer 21

• Oscillations in the membrane potential
• Meets threshold
• Initiates action potential
• Leads to contraction

Question 22

What determines the strength of contraction?

Answer 22

Action potential frequency

Question 23

What is the frequency of segmentation determined by?

Answer 23

BER

Question 24

What happens to BER as it moves down the intestine to the rectum?

Answer 24

Decreases

Question 25

What does segmentation produce?

Answer 25

Slow migration of chyme towards large intestine (more chyme pushed down that up)

Question 26

How does the parasympathetic system affect segmentation?

Answer 26

Via the vagus increases contraction

Question 27

How does the sympathetic system affect segmentation?

Answer 27

Decreases contraction

Question 28

How does the autonomic nervous system affect BER?

Answer 28

No effect

Question 29

When does peristalsis occur?

Answer 29

Following absorption of nutrients, segmentation stops and peristalsis starts

Question 30

What is the migrating motility complex?

Answer 30

Pattern of peristaltic activity travelling down small intestine ( starts in gastric antum) -As one MMC enda another begins

Question 31

What causes cessation of MMC?

Answer 31

Food arriving in the stomach which causes initiation of segmentation

Question 32

What does MMC act to do?

Answer 32

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

Question 33

What is involved in the initiation of MMC?

Answer 33

Hormone motilin

Question 34

Law of Intestine | If intestinal smooth muscle is distended:

Answer 34

- Muscle on oral side of bolus contracts - Muscle on anal side of bolus relaxes - Bolus is moved into area of relaxation towards colon - Mediated by neurones in myenteric plexus