Absorbing the Nutrients from the Small Intestine

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Absorbing the Nutrients from the Small Intestine
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Movement of food through digestive system

• Outline movement of food from ingestions to
  egestion

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Absorption of Nutrients

• As intestinal fluids move from the duodenum,
  micronutrients are released from the food.
• These must be absorbed and distributed to all all
  cells in the body

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Absorption takes place by diffusion and
endocytosis 

• How does diffusion work?
• How does endocytosis work?

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Diffusion
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Encocytosis
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Most absorption takes place by diffusion

• Diffusion is passive transport
• Ions or molecules move down concentration
  gradients set up between solutions separated by
  biological membranes.

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Absorption rate

• Rate of diffusion/absorption determined by
• Surface area
• gt surface (epithelial cells) area gt likelihood
  that particles will hit the surface
• Concentration gradient across the epithelial cell
  membranes

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How the intestine has evolved to maximize both
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Microvilli
Epithelium
Lacteal
Capilary
vein
Artery
Lymphatic system
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Microvilli

• Increases surface area
• Increases absorption of nutrients
• Nutrients are removed from epithelial cells of
  the microvilli as fast as they are absorbed by
  capillary and lacteal system
• This prevents nutrient saturation levels inside
  the epithelial cells which would stop diffusion

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Route of nutrients

• The anterior mesenteric artery brings blood from
  heart to small intestine
• Blood coming to microvilli is low in nutrients
  (sets up concentration gradient)
• Tiny arterioles branch into each villus.
  Nutrients are absorbed by epithelial cells and
  quickly diffuse into capillaries

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• The capillaries form a tiny venule that leaves
  the villus.
• The venules join veins, eventually forming
  hepatic portal vein.
• The hepatic portal drains all blood from
  intestines moving it to liver.

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Maintenance of ConcentrationGradient

• The constant flow of blood ensures that
• blood rich in nutrients is always being removed
  and replaced with blood low in nutrients

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Why is nutrient rich blood sent to liver?

• Liver serves two functions
• Controls level of blood sugar (Glucose)
• Screen/detoxify toxins

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Blood Glucose Regulation by Liver

• Blood from the gut is very high in nutrients,
  such as glucose.
• High levels are dangerous for other organs,
  particularly the brain.
• The liver
• Removes excess glucose from blood
• Stores excess glucose until they its needed
  (i.e. between meals)

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Screening for toxins.

• Poisonous may enter the body by ingestion and
  enter blood by diffusion
• The liver detoxifies poisons before they reach
  vulnerable or sensitive organs.
• Alcohol is one such example.

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Lacteals and Endocytosisof Lipids (fats)

• Digested lipids enter epithelial cells by
  endocytosis (active transport).
• Lipids are passed directly to small vessels
  called lacteals
• Lacteals connect to lymphatic system, which
  carries lipids to veins near heart.
• Lipid does not get screened by the liver before
  it is distributed to the body.

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Task

• Read pages 50 53, 56, 57 and answer questions 1
  6 on page 57