The small intestine anatomy and structure

Question 1

Why is it called small?

Answer 1

Due to its diameter not length

Actually takes up 6 of 8 meters of intestine

Question 2

What is the function of the duodenum?

Answer 2

gastric acid neutralisation
Digestion
Iron absorption

Question 3

what is the function of the Jejunum?

what is its appearance and why?

Answer 3

absorption- 95%

Appearance: ribbon like- due to high vasculature and high contents of the intestine

Question 4

what is the function of the Ileum?

Answer 4

Nacl and H20 absorption- over 9.5 litres of water that the body produces every day
Dehydrates the chyme

Question 5

Anatomy of the SI

Answer 5

Folded into Plica: cork-screw shape- increases SA and ensures that the contents come into contact with digestive enzymes
Villi- finger-like projections FOR ABSORPTION
Crypts- at the base of villi- feed into them.
Microvilli- present on the surface of villi

Question 6

Crypts

Answer 6

Where all gut cells start off before they differentiate and move into the villi.
They secrete cl and water into the SI

Question 7

The Crypt- Villi pathway

Answer 7

arterialiole supply
venue supply
goblet cells
absorptive cells

Question 8

Increase in SA

Answer 8

standard unit- cylinder of intestine - 0.33 m2
Plica- increase SA X 3 - 1m2
Villi- increase SA X30- 10m2
Microvilli- increase SAX200- 600m2

Question 9

Secretion in the SI

Answer 9

Crypt cells secrete up to 1.5 litres of water a day
Water follows the movement of chloride ions
-2 Cloride ions transported into the cell along with sodium and potassium- ELECTRONEUTRAL PROCESS- IONS BALANCE OUT
-sodium transported back out of cell via Sodium ATPase
-potassium transported back out via transporter molecule
-Clorine moves into lumen via CFTR

Question 10

Control of CFTR protein

Answer 10

adenylate cyclase- when active causes ATP to converted to Camp- activate PKA- activates CFTR.

Question 11

Segmentation

Process

Answer 11

• For absorption of nutrients
• Occurs whilst food is being eaten

Process:

• food in middle gets squished to sides by contractions in middle/relaxation of sides
• contraction of sides- moves food back into middle
• Allows complete action of enzymes

Question 12

How is segmentation controlled?

Answer 12

1-Pacemaker cells in the longitudinal muscle
2-BER- determines RATE of contractions- decreases down the intestine

the frequency of action potentials controls the strength of contraction

Question 13

What affects the BER

Answer 13

Parasympathetic: increases contractions
Sympathetic: decreases contractions
Autonomic: does nothing

Question 14

Peristalsis

Answer 14

After segmentation- stops as soon as any food reaches the stomach

• Migrating motility complexes- where one wave ends a new one begins
• helps moves undigested materials into the LI where bacteria are present

Question 15

what is the law of intestine?

Answer 15

Where food/bolus is present
The smooth muscle of the oral side will contract
The smooth muscle of the anal side will relax

Question 16

Gastroileac reflex

Answer 16

• Increases segmentation in the ileum to increase gastric emptying
• Causes the ileocaecum sphincter to open and chyme to move in
• Distension of LI
• Reflex contraction of ileocaecum sphincter- prevents reflux