Physiology 4: Small intestine

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

Parts:

1) Duodenum

2) Jejunum

3) Ileum

Lengths:

• During life is 3 meters

• After death is 6 meters

What are the functions of the small intestine

• Secretes intestinal juice, GIT hormones

• Digestion as food stuff is completed in small intestine

• Absorption of different food stuffs.

• Motor function

What is the definition and routes of the absorption?

The passage of digested food form the lumen of GIT to the blood stream through GIT mucosa.

Routes:

• Small intestine for: most sub.

• Stomach for: Alcohol, drugs, water

• Large intestine for electrolytes, drugs, and water

What are the factors affecting absorption?

1) Vitality of the mucosa

• Depends on blood flow & O2 supply

2) Lymph flow:

• Necessary for fat absorption

Obstruction of thoracic duct decreases fat absorption.

3) Digestion

• Proper digestion → almost complete absorption

• Maldigestion (in pancreatic insufficiency) → malabsorption

4) Area and time of contact with digested food with mucosa

• Decreased area of contact with mucosa = decreased absorption

• Decreased time of contact with mucosa e.g diarrhea = decreased absorption

5) Intestinal motility:

• Increase absorption by increased blood and lymph flow and intraluminal pressure

6) Other factors:

• Bile salts aid in absorption of fat & fat soluble vitamins.

• Intrinsic factors aid in absorption of B12.

• Parathormone & vit.D aid in absorption of Ca++.

Is the absorption of water an active or passive process?

Always passive as water follows during absorption of electrolytes & nutrients by osmosis.

Describe the process of the absorption of Na

• Na+ is transported form the lumen into the enterocytes:

30% by Na-glucose transporter and Na-AA transporter.

30% by Na-Cl cotransporters

40% by special Na channels

• Then Na is transported from the enterocytes to the intercellular spaces through the basolateral border by Na+, K+ pump

How does the absorption of K occur?

Occurs mainly passively according to concentration gradient from the lumen to the blood.

Describe the process of absorption of Ca

How does the process of iron occur?

Active mechanism, occur in the upper part of the small intestine

Describe the mechanism of iron absorption

Describe the mechanism of carbohydrate absorption

Describe the mechanism of lipid absorption

Describe the mechanism of protein absorption

Describe the mechanism of vitamin absorption