Sun21November0437PM 20

True / False

Secretion increases during fasting Correct

Is a polypeptide containing two chains of amino acids linked bydisulfide bridges Correct

Causes potassium to enter cells Correct

Is necessary for glucose uptake in the brain Correct

Deficiency is characterised by reduced glucose entry into cells Correct

Explanation

The passage of glucose into cells is achieved with the help of glucose transporters. These glucose transporters (GLUT) are proteins located in cell membranes which promote glucose uptake into the cytoplasm by facilitated diffusion or active transport.

There are four glucose transport proteins:

GLUT1: universally distributed

GLUT2: present in gut, liver, and pancreatic islets

GLUT3: present in the central nervous system and brain

GLUT4: present in insulin-responsive tissues, skeletal muscle, adipose tissue, and heart.

GLUT3 is not dependent on insulin.

Insulin is composed of two polypeptide chains (A and B) linked by two disulfide bridges. The A chain typically contains 21 amino acids and the B chain 30 amino acids.

The hyperglycaemia from insulin resistance or lack of insulin is characterised by reduced entry of glucose into the cells.

One physiological action of insulin is to increase the permeability of cell membranes to potassium, magnesium and phosphate ions. This forms the basis of treating life threatening hyperkalaemia with a glucose/insulin infusion.

During fasting, serum insulin and glucose levels fall whilst lipolysis increases.

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