Digestive System: Absorption and Elimination

•I can explain how the structure of the small intestine helps to achieve absorption.

Products of digestion, along with substances such as vitamins, minerals water, are absorbed through the wall of the small intestine into the blood

To increase absorption of nutrients into the blood stream, a large internal surface area of the small intestine is achieved by:

• Long small intestine (6 – 7m)

• Mucosal folds

• Villi

• Microvilli

•I can describe the structure and function of a villus.

Depends on type of molecule. Nutrients absorbed from villi into blood capillaries or lacteals

Blood capillaries

• simple sugars, amino acids, water and water-soluble vitamins → Then, carried via the blood to other cells or further processed in the liver.

Lacteals

• Fatty acids and glycerol recombine in the cells of the villi to form fats, along with the fat-soluble vitamins

• Transported by the lymphatic system

•I can outline the process of elimination.

Defecation is the removal of metabolic wastes that has be produced by metabolic activities, which does not describe the types of wastes in faeces.

•I can describe the composition of faeces.

Large intestine structure and function

Structure: Is shorter than small intestine (length) but the diameter is larger

Made of

• Caecum, small pouch SI join LI.

  • Apendix is attached

• Colon, U-shaped part of LI

• Rectum, last part of LI

• Anus, external opening at end of rectum

Function: Slow movement of material through the large intestine allows water to be absorbed, produces faeces

Bacteria also further break down remaining organic compounds, releasing vitamins and minerals.

What remains after absorption is faeces, which contains:

• water

• Undigested food (eg. Cellulose)

• Bacteria

• bile pigments which give faeces their colour

• remains of cells that have broken away from the internal lining of the alimentary canal.