9.4 - Assimilation

The Role of the Circulatory System

Assimilation refers to the process of forming complex compounds or structural components. Some of the products of digestion are directly taken to the liver via the hepatic portal vein for processing and used for metabolic processes or assimilation. Lacteals carry lipids and fat-soluble vitamins which are drained into the right lymphatic duct and thoracic duct and eventually into the subclavian veins.

Functions of Liver in the Assimilation of Digested Food

Liver is the checkpoint which regulates the amount of nutrients released into the blood circulatory system. There are 3 important functions carried out by the liver.

• Food metabolism

  • Glucose is needed for cellular respiration.
  • Amino acids are used to make proteins and enzymes needed by the body.

• Detoxification

  • Blood is detoxified to remove toxic substances.
  • Toxins, pesticides, carcinogens and poisons are dangerous substances which need to be remove from the body.

• Storage of nutrients

  • Excess glucose is turned into fat in the liver and stored in other parts of the body.
  • The liver stores fat-soluble vitamins (A, D, E, K), vitamin B12 and ferum from the hemoglobin.

Figure 5 - Transport of nutrients and assimilation in the liver and body cells.

Assimilation in the Liver

Amino acids

• The liver uses amino acids to make plasma proteins and enzymes.
• Excess amino acids cannot be stored. They are broken down through deamination.
• If glucose is deficient, liver converts amino acids to glucose.

Glucose

• Essential for cellular respiration.
• Excess is stored as glycogen in the liver.
• When glycogen storage is full, glucose will be converted into fats.
• When blood glucose level drops, the liver converts glycogen to glucose.

Assimilation in the Cells

Amino acids

• Used to make new protoplasm.
• Used to repair damaged tissues.
• Basic components for the synthesis of hormones and enzymes.

Glucose

• Main substrate for cellular respiration.
• Energy is used by cells for other living processes.
• Excess glucose is stored as glycogen in the muscles.

Lipids

• Phospholipids and cholesterol are the main components of plasma membrane.
• Excess fats are stored in the adipose as reserve energy.
• When glucose is deficient, fats are oxidized to release energy.