Introduction to the hypothalamic pituitary axis

Question 1

Area of the brain directly above the pituitary gland

Answer 1

The hypothalamus

Question 2

Pituitary gland connected to the brain by

Answer 2

The infundibulum

Question 3

Posterior pituitary gland

Answer 3

A down growth from the brain

Sometimes called the neurohypophysis

Question 4

Hormones secreted by the posterior pituitary fland

Answer 4

ADH

Oxytocin

Question 5

ADH and oxytocin

Answer 5

Peptide hormones, 9 amino acids each with seven identical

Not synthesis within the gland, but by neurones of the hypothalamus

Synthesised as inactive precursors and converted to active hormones within the posterior pituitary

Question 6

Neurones of the hypothalamus that synthesis ADH and oxytocin

Answer 6

Supraoptic nuclei

Paraventricular nucleus

Question 7

Route of inactive ADH and oxytocin

Answer 7

Transported from supraoptic and paraventricular nuclei along the hypothalamico-neurohypophyseal tract

Stored within the posterior pituitary

Question 8

ADH

Answer 8

Secretion is influenced by plasma osmolarity

Stimulation of V2 receptors causes translocation of aquaporins to the membrane of the kidney tubule

Allows water reabsorption

Stimulation of V1 receptors causes vasoconstriction (does not occur at physiological concentrations)

Question 9

Oxytocin

Answer 9

Acts via IP3 to cause contraction of smooth muscles in genital tract and breast

Secretion of oxytocin stimulated by stimulation of the genitals and nipples

Most important at parturition and during lactation

Question 10

Oxytocin during pregnancy

Answer 10

Synthesis increases

Parallel increase in oxytocinase activity

Question 11

Oxytocin during parturition

Answer 11

Causes contraction of the smooth muscle of the uterus to aid expulsion of the infant

Continued stimulation of the cervix causes continued secretion

Question 12

Oxytocin after parturition

Answer 12

Responsible for milk expulsion

Stimulus is suckling, but there is a delay between the start of suckling and milk let down

Question 13

Anterior pituitary gland

Answer 13

Up growth from the palate

Question 14

Hormones secreted by the anterior pituitary gland

Answer 14

Growth hormone

Prolactin

Thyroid stimulating hormone

Adrenocorticotrophic hormone

Follicle stimulating hormone

Luteinising hormone

Question 15

Route of releasing hormones

Answer 15

Secreted by the hypothalamus

Go to the hypothalamico-adenohypophyseal portal vessel

Carries them to the anterior pituitary

(do not enter the systemic circulation)

Question 16

Clinical investigations

Answer 16

Signs and symptoms

Biochemical tests

Imaging

Visual field tests

Question 17

Bilateral hemianopsia

Answer 17

Due to compression of the optic chiasm

Question 18

Prolactin

Answer 18

199 amino acid peptide

Synthesised in the lactotrophe cells of the anterior pituitary

Secretion controlled by prolactin release inhibiting factor (dopamine)

TRH stimulates prolactin synthesis

Question 19

Prolactin secretion stimulated by

Answer 19

Mild stress
Nipple stimulation

Coitus

Question 20

Primary role of prolactin

Answer 20

To promote lactation and development of breast tissue

Most important in females after puberty and during and after pregnancy

Question 21

Growth hormone

Answer 21

Synthesised in the somatotrophe cells of the anterior pituitary gland

Question 22

Secretion of growth hormone controlled by

Answer 22

Hypothalamus via

• growth hormone releasing hormone
• growth hormone release inhibiting hormone (somatostatin)

Question 23

Secretion of growth hormone stimulated by

Answer 23

Decreased carbohydrates and fatty acids and increased amino acids

Question 24

Primary effect of GH

Answer 24

Promote the linear growth of adolescence by increasing protein synthesis and collagen deposition

Mediated via the nucleus

Foetal growth is relatively independent of GH