Identify the type of interaction, Gland Y, and the associated disorder.

*a) The diagram illustrates a regulatory mechanism where the product (thyroxin) inhibits its own production, which is characteristic of a negative feedback mechanism.

*b) Gland Y is stimulated by TSH (Thyroid Stimulating Hormone) from the pituitary gland to produce thyroxin. This identifies Gland Y as the thyroid gland.

*c) The enlargement of the thyroid gland (Gland Y) is known as goitre.

Thyroxin is a hormone that plays a crucial role in regulating the body's metabolic rate.

At point X, the diagram indicates "Less TSH" as a response to the "Level of thyroxin (Z)". This means that when the level of thyroxin in the blood is high, it sends a signal to the pituitary gland. The pituitary gland then reduces its secretion of TSH (Thyroid Stimulating Hormone). This decrease in TSH subsequently causes Gland Y (the thyroid gland) to reduce its production of thyroxin, thereby bringing the thyroxin level back down to the normal range.

Thyroxin is responsible for regulating the body's metabolic rate. A continuous undersecretion of thyroxin leads to a decreased metabolic rate. This means that the body burns less energy, and consequently, excess energy from food intake is stored as fat, resulting in an increase in body mass.

a) The type of interaction represented by the diagram:

• Negative feedback

b) Gland Y:

• Thyroid gland

c) The disorder that is characterised by the enlargement of gland Y:

• Goitre

One function of thyroxin:

• Regulates the metabolic rate of the body.

The role of the pituitary gland in correcting the level of thyroxin at X:

• When the level of thyroxin is high, it inhibits the pituitary gland. The pituitary gland then secretes less TSH, which reduces thyroxin production by the thyroid gland, lowering the thyroxin level back to normal.

Explanation why a continuous undersecretion of thyroxin may lead to an increase in body mass:

• Thyroxin regulates the metabolic rate. Undersecretion of thyroxin leads to a lower metabolic rate, causing the body to burn less energy. This results in excess energy being stored as fat, leading to an increase in body mass.