9.4 - Assimilation

• During assimilation, nutrients are used by cells to form complex compounds or structural components.

The Role of the Circulatory System

• The blood circulation and lymphatic systems transport nutrients for assimilation.
• Blood capillaries in the small intestine combine to form the hepatic portal vein, which transports blood to the liver.
• Lacteals combine into larger lymph vessels.
• Lymph enters the thoracic duct, which flows into the left subclavian vein.
• Lipid is then transported throughout the body by blood.

Functions of the Liver in Assimilation

• The liver regulates the quantity of nutrients entering the blood circulation.

Metabolism of Digested Food

• Glucose is used for cellular respiration.
• Amino acids synthesise plasma proteins and enzymes.
• Deamination converts excess amino acids into urea for excretion in urine.

Detoxification

• Liver cells remove toxic substances from the blood.
• Toxic substances are expelled through urine.

Storage of Nutrients

• Excess glucose is converted to glycogen and stored.

Assimilation Process in the Liver

Amino Acids

• Synthesise plasma proteins and enzymes.
• Excess amino acids undergo deamination to form urea for excretion.
• When glucose is insufficient, amino acids are converted into glucose.

Glucose

• Used for cellular respiration when required.
• Excess is converted to glycogen and stored in the liver.
• Glycogen is converted to glucose when blood glucose decreases and energy is needed.
• Excess glucose is converted to fats when glycogen storage reaches its maximum.

Assimilation Process in Cells

Amino Acids

• Synthesise new protoplasm and repair damaged tissues.
• Synthesise hormones and enzymes.

Glucose

• Oxidised in cellular respiration to release energy, water and carbon dioxide.
• Excess is stored as glycogen in muscles.
• Released energy supports cell processes such as protein synthesis.

Lipids

• Phospholipids and cholesterol build plasma membranes.
• Excess fats are stored as energy in adipose tissues beneath the skin.
• Fats are oxidised to release energy when glucose is insufficient.