Absorption in the Small Intestine

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INGESTION

DIGESTION

ABSORPTION

EGESTION

ASSIMILATION

Food is taken into body

Carbohydrates, proteins and fats are broken down into soluble glucose,

amino acids, fatty acids and glycerol.

Glucose, amino acids, fattyacids and glycerol are absorbed

into body cells

Removal of undigested food e.g. dietary fibre

Absorbed nutrients are transported and utilized by the body

ABSORPTIONMonosaccharides (glucose, fructose and galactose), amino acids, fatty acids, glycerol and water are absorbed in the small intestine.

The absorbed nutrients passesfrom the lumen of the small intestine into the bloodstream.

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lumen

How to ensure that nutrients are quickly absorbed?

Adaptations of the Small Intestine

1. Large surface area: volume ratio1.1 The inner walls of the small intestine have

numerous folds

5http://www.path.cam.ac.uk/Normal/AR_Alimentary/SI_Small_intestine/N_AR_SI_08small.jpg

Adaptations of the Small Intestine

1. Large surface area: volume ratio• Folded inner walls are lined with

numerous minute finger-like projections called villi

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Adaptations of the Small Intestine

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1. Continued...Large surface area: volume ratio•The epithelial cells of the villi have numerous microvilli.

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Adaptations of the Small Intestine

2. The villi wall (epithelial cell layer) is only one cell thick.

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Adaptations of the Small Intestine

3. Presence of numerous capillaries to carry away the absorbed nutrients.

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blood capillaries

Lacteal/lymphatic capillary

Digested food enters villuslumen

epithelial cell layer

Adaptations of the Small Intestine

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Blood capillaries: transport monosaccharides and amino acids.

Lymphatic capillaries (lacteals): transport fats

The continual removal of nutrients maintains a concentration gradient for diffusion.

liver

Adaptations of the Small Intestine

4. Small intestine is long to provide sufficient time for absorption.

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http://blog.lib.umn.edu/trite001/pstl1082anatomy/SmallIntestine.jpg

The small intestine is about 6m long!

How are the nutrients absorbed?

Recall what you have learnt in the topic Movement of Substances!

(Diffusion, osmosis, active transport….)

glucose

amino acids

Fatty Acids

glycerol

How does absorption take place in the villi?

Soluble substance Type of movement into the epithelium

Note:

Monosaccharides(e.g: glucose)

Facilitated DiffusionActive Transport

High conc. in lumenlow conc. in lumen

Amino Acids Facilitated DiffusionActive transport

High conc. In lumenlow conc. In lumen

Fatty acids and glycerol Diffusion Glycerol and fatty combine to form small fat droplets that enter the lacteals.

Water Osmosis Enter the blood capillariesMineral Salts Facilitated Diffusion Enter the blood capillariesWater soluble vitamins (B and C)

Facilitated Diffusion Enter the blood capillaries

Fat –Soluble Vitamins (A, D, E and K)

Diffusion Enter the lacteals14

SUMMARY

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Adaptations of the small intestine:

1. Large SA: Vol. folds, villi and microvilli.

2. Villi epithelial wall is one cell thick rapid diffusion.

3. Blood capillaries and lacteals maintain concentration gradient.

4. Long allows sufficient time for absorption

Movement into villi:

• Glucose and amino acids absorbed by facilitated diffusion or active transport into blood capillaries of the villi.

• Glycerol and fatty acids diffuse into the epithelium combine to form minute fat globules which enter lacteals.

• Water and mineral salts are also absorbed by the small intestine.

Egestion•In the colon, water and mineral salts are absorbed from the undigested food material.

•Bacterial Activity

•Presence of dietary fibre/roughage helps in peristalsis.

•Unabsorbed matter is stored temporarily in the rectum.

•Faeces is discharged through the anus.

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rectum

anus

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