3. Assimilation

Figure above shows a model of liver as well as its associated blood vessels. The hepatic portal vein transports blood rich in digested food materials (simple sugars, amino acids and fats) from the small intestines to the liver.

1. Fate of absorbed carbohydrates

• Glucose is sent to the various parts of the body. Glucose is used to release energy via respiration.

• Liver regulates blood glucose concentration. Normal blood glucose is 110mg/dl. Above this level, a hormone known as insulin is secreted by pancreas.

• Insulin stimulates the liver cells to convert excess glucose to glycogen which is stored in the liver. Liver can store a maximum of 100g of glycogen.

• During events like starvation or fasting, blood glucose level falls below the normal level. Glucagon is secreted by pancreas.

• Glucagon stimulates the liver cells to convert glycogen to glucose.

2. Fate of amino acids

• Amino acids is sent to various cells of the body where they are used for synthesis of enzymes, hormones and protoplasm.

• Excess amino acid cannot be stored in the body and they are deaminated .

• During deamination, the amino group is removed and converted into ammonia (highly toxic) and subsequently converted into urea (less toxic substance). Urea is eventually excreted out of the body as urine.

• Remaining acid group is converted into glucose in the liver.

• Excess glucose will be converted into glycogen and stored in the liver.

3. Fate of fats

• Fats are needed for formation of protoplasm and hormones.

Excess fats are stored in the adipose tissue under the skin, around the heart and kidneys.

Other Functions of Liver

(i) Store for fat-soluble vitamins, Vitamins A & D.

(ii) Breakdown of red blood cells – (1) Storage of iron and (2) Production of bile

- Red blood cells generally have a lifespan of 3 months.

- After 3 months, red blood cells will breakdown at the spleen, a gland near the liver. The haemoglobin, red pigment present in red blood cells are sent to the liver. The liver breaks down haemoglobin and stores the iron that is released.

- Remaining haemoglobin that is not recycled is converted into bile pigment, bilirubin which is later stored in the gall bladder.

(iii) Breakdown alcohol

- Detoxification involves the conversion of harmful substances into harmless ones.

- Liver contains alcohol dehydrogenase that breaks down alcohol into acetaldehyde.

- Acetyladehyde can be further broken down into compounds that can be used in respiration to provide energy for cell activities.