Small Intestine Structure and Function

Question 1

How long is the small intestine?

Answer 1

~6m

Question 2

What are the parts of the small intestine and their lengths?

Answer 2

Duodenum - 25cm
Jejunum - 2.5m
Illeum - 3.5m

Question 3

Functions of duodenum?

Answer 3

Gastric acid neutralization
Digestion
Iron absorption

Question 4

Functions of the jejunum

Answer 4

Absorbs 95% of nutrients

NaCl absorption for chyme dehydration

Question 5

Why does the jejunum appear pink?

Answer 5

Highly vascular

Question 6

What increases the small intestines surface area?

Answer 6

Folds
Villi
Microvilli

Question 7

What is the plicae circularis?

Answer 7

Folds in small bowel that make chyme flow in a spiral patter to maximise absorption and mixing

Question 8

What is the myenteric plexus?

Answer 8

Major nerve supply to GI tract that controls motility

Question 9

What do crypt of lieberkuhn cells secrete?

Answer 9

Cl and H2O

Question 10

Why do crypt cells secrete water?

Answer 10

Water gives an aq environment for digestion to take place

Question 11

How does chlorine enter the lumen?

Answer 11

Brought into cell by Na-K-cl transporter (Na and K taken right back out to maintain gradient)

Cl- ion is pumped into lumen by CFTR

CFTR is opened via cAMP to adenosine cyclase conversion

Question 12

What happens if CFTR doesn’t work?

Answer 12

This is seen in disease - Cystic fibrosis

Question 13

What do goblet cells do?

Answer 13

Create a diffusion barrier to increase diffusion and secrete mucous

Question 14

What are lacteals?

Answer 14

Lymphatic capillaries that absorb dietary fats

Question 15

What does Na+ coupled active transport actually transport in the small bowel?

Answer 15

Glucose
Galactose
Amino Acids
Nucleosides

Question 16

What 2 types of motility is seen in the small bowel?

Answer 16

Segmentation

Peristalisis

Question 17

Describe segmentation

Answer 17

The following is the tube:

Relaxed-CONTRACTED-Relaxed-CONTRACTED-Relaxed

In the relaxed areas the chyme moves up and down and mixes further

The relaxed areas then become contracted and vice versa = slower movement towards colon

Question 18

When does segmentation occur?

Answer 18

During a meal

Question 19

What makes segmentation?

Answer 19

Pacemaker cells in the longitudinal muscle layer

Question 20

What does parasympa and sympa activity do for segmentation?

Answer 20

PS via vagal nerve = increased contractions

S - decreased contractions

Question 21

What determines the freq. of segmentation

Answer 21

frequency of the basic electrical rhythm

Question 22

What determines strength of contractions?

Answer 22

AP freq.

Question 23

What is peristalsis?

Answer 23

A strong contraction behind the bolus moving food forward

Question 24

What generages peristaltic waves?

Answer 24

The migrating motility complex

Question 25

Describe the MMC.

Answer 25

It starts in the stomach antrum and travels all the way to the ileum

Once at illeum a new one is generated

Question 26

What initiates the migrating motility complex?

Answer 26

Motilin hormone

Question 27

What stops the MMC?

Answer 27

Arrival of food in stomach - stops MMC and initiates segmentation

Question 28

Describe the ENS

Answer 28

PS - vagal nerve - stimulatory
S - splanchnic nerve - inhibitory

Salivation has different effects and PS supplies

Question 29

What is the law of the intestine?

Answer 29

If intestinal smooth muscle is distended by a bolus of chyme, the mouth side of intestine contracts and anus side relaxes to move the bolus

This is mediated by neurones in the myenteric plexus

Question 30

What is the gastroileal reflex?

Answer 30

When the ileocaecal sphincter opens to let chyme into colon there is a reflex contraction of the ileocaecal sphincter to prevent backflow