ENDOCRINOLOGY - Hypothalamic-Pituitary-Gonadal Axis

Question 1

What are the components of the Hypothalamic-Pituitary-Gonadal axis?

Answer 1

• Hypothalamus
• Pituitary gland
• Gonads

Question 2

What is the function of the gonadotrophin releasing hormone (GnRH)?

Answer 2

The gonadotrophin releasing hormone is secreted from the hypothalamus and acts on the anterior pituitary gland to stimulate the release of gonadotrophin hormones into the systemic circulation to act on the gonads

Question 3

What are the two gonadotrophin hormones released by the anterior pituitary gland?

Answer 3

• Luteinising hormone (LH)
• Follicle stimulating hormone (FSH)

Question 4

What is the Pars tuberalis?

Answer 4

The region of the base of the hypothalamus that is wrapped around by the anterior pituitary gland

Question 5

What is the median eminence and how is it involved in the transport of the gonadotrophin releasing hormone from the hypothalamus to the anterior pituitary gland?

Answer 5

The median eminence is a neurohaemal organ containing a capillary bed in which the hypothalamic neurosecretory fibres release their hormones into the hypophyseal portal system and into the anterior pituitary gland

Question 6

Why is the gonadotrophin releasing hormone released into the hypophyseal portal system and not into the systemic blood circulation?

Answer 6

Because the gonadotrophin releasing hormone has such a short half life so is broken down very quickly

Question 7

In which area of the brain are the cell bodies of the gonadotrophin releasing hormone neurosecretory neurones located?

Answer 7

Pre-optic region of the brain

Question 8

In which area of the brain are the nerve terminals of the gonadotrophin releasing hormone neurosecretory neurones located?

Answer 8

Within the median eminence located within the Arcuate nucleus (arc region) of the brain

Question 9

What is the releasing pattern for the gonadotrophin releasing hormone and the luteinising hormone?

Answer 9

Pulsitile release pattern

Question 10

What is the relationship between the gonadotrophin releasing hormone and the luteinising hormone?

Answer 10

Every time there is a pulsatile release of the gonadotrophin release hormone, there is a corresponding release of the luteinising hormone

Question 11

What is the relationship between the gonadotrophin releasing hormone and the follicle stimulating hormone?

Answer 11

There is only a corresponding release of the follicle stimulating hormone in response to the release of the gonadotrophin releasing hormone during the follicular phase