Introduction to the hypothalamic pituitary axis Flashcards
Area of the brain directly above the pituitary gland
The hypothalamus
Pituitary gland connected to the brain by
The infundibulum
Posterior pituitary gland
A down growth from the brain
Sometimes called the neurohypophysis
Hormones secreted by the posterior pituitary fland
ADH
Oxytocin
ADH and oxytocin
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
Neurones of the hypothalamus that synthesis ADH and oxytocin
Supraoptic nuclei
Paraventricular nucleus
Route of inactive ADH and oxytocin
Transported from supraoptic and paraventricular nuclei along the hypothalamico-neurohypophyseal tract
Stored within the posterior pituitary
ADH
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)
Oxytocin
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
Oxytocin during pregnancy
Synthesis increases
Parallel increase in oxytocinase activity
Oxytocin during parturition
Causes contraction of the smooth muscle of the uterus to aid expulsion of the infant
Continued stimulation of the cervix causes continued secretion
Oxytocin after parturition
Responsible for milk expulsion
Stimulus is suckling, but there is a delay between the start of suckling and milk let down
Anterior pituitary gland
Up growth from the palate
Hormones secreted by the anterior pituitary gland
Growth hormone
Prolactin
Thyroid stimulating hormone
Adrenocorticotrophic hormone
Follicle stimulating hormone
Luteinising hormone
Route of releasing hormones
Secreted by the hypothalamus
Go to the hypothalamico-adenohypophyseal portal vessel
Carries them to the anterior pituitary
(do not enter the systemic circulation)
Clinical investigations
Signs and symptoms
Biochemical tests
Imaging
Visual field tests
Bilateral hemianopsia
Due to compression of the optic chiasm
Prolactin
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
Prolactin secretion stimulated by
Mild stress
Nipple stimulation
Coitus
Primary role of prolactin
To promote lactation and development of breast tissue
Most important in females after puberty and during and after pregnancy
Growth hormone
Synthesised in the somatotrophe cells of the anterior pituitary gland
Secretion of growth hormone controlled by
Hypothalamus via
- growth hormone releasing hormone
- growth hormone release inhibiting hormone (somatostatin)
Secretion of growth hormone stimulated by
Decreased carbohydrates and fatty acids and increased amino acids
Primary effect of GH
Promote the linear growth of adolescence by increasing protein synthesis and collagen deposition
Mediated via the nucleus
Foetal growth is relatively independent of GH
