Pituitary Gland and its disorders Flashcards
Where is the pituitary gland located?
Below the brain, encased in a bone cavity of the skull (the sella turcica). It is also known as the ‘master gland’
Where is the hypothalamus located?
Directly above the pituitary gland.
How is the pituitary gland connected to the hypothalamus?
By the infundibulum (pituitary stalk)
What is another word for infundibulum?
Pituitary stalk
Where does the hypothalamus lie?
Directly above the pituitary gland. It lies beneath the thalamus and surrounds the lower portions of the third ventricle.
What is the hypothalamus made up of?
Tuber cinereum, median eminence and several nuclei.
How is the pituitary stalk/ infundibulum formed?
By the continuation of the tuber cinereum and the median eminence. This pituitary stalk joins the hypothalamus with the pituitary.
How is the pituitary gland divided?
Into two separate portions; the anterior and the posterior pituitary glands.
They effectively function independently.
Which gland is a ‘down growth’ form the brain? What is it sometimes called?
Posterior pituitary gland.
Sometimes called the neurohypophysis.
What hormones does the posterior pituitary gland secrete and where do those hormones act?
Antidiuretic hormone (ADH) - kidney tubules
Oxytocin - uterine muscles/ mammary glands.
What type of hormone are ADH and oxytocin? How many amino acids are they composed of?
Peptide hormones - water soluble
Composed of 9 amino acids each; 7 of which are identical
Where is ADH and oxytocin synthesised?
Synthesised by the neurones of the hypothalamus (supraoptic nucleus and paraventricular nucleus)
In what form is ADH and Oxytocin synthesised?
They are formed by the supraoptic nucleus and paraventricular nucleus in the hypothalamus. They are synthesised as inactive precursors and converted to active hormone within the posterior pituitary.
Describe how the inactive hormones are transported.
The inactive hormones are transported from the supraoptic nucleus and paraventricular nucleus alone the hypothalamico-neurohypophyseal tract. They are then stored within the posterior pituitary.
How is ADH released?
ADH secretion is influenced by plasma osmolarity.
Osmoreceptors on the walls of the third ventricle in the brain send impulses to the supraoptic and paraventricular nuclei.
Depolarisation of these nuclei results in an influx of Ca++ at the nerve terminals of the posterior pituitary and releases ADH.
What is the mechanism of action for ADH?
ADH acts on three subtypes of a receptor: V1, V2 and V3.
All are GPCR. V1 and V3 act via IP3 and V2 acts via cAMP.
Which is the most important ADH GPCR?
V2 receptors.
What occurs with V2 stimulation?
Synthesis and translocation of aquaporins (AQP) on the kidney tubule which allows water reabsorption to occur
What occurs with V1 stimulation?
Vasoconstriction. This does not occur at physiological concentrations.
Increased blood osmolarity = ________ ADH secretion
Increased
Increased blood volume = ________ ADH secretion
Decreased
Decreased blood osmolarity = ________ ADH secretion
Decreased
Decreased blood volume = ________ ADH secretion
Increased
Excessive secretion of ADH causes? What are the drug treatments?
Syndrome of inappropriate ADH (SIADH).
Drug treatments: conivaptan, tolvaptan, demeclocycline
Deficient secretion of ADH or decreased responsiveness to ADH causes?
What are the drug treatments?
Diabetes insipidus.
Drug treatments: desmopressin, vasopressin (neurogenic)
Difference between nephrogenic and neurogenic?
Nephrogenic is when enough ADH is secreted but not enough vasopressin receptors present. Can give thiazide?
Neurogenic is when the pituitary gland does not secrete enough ADH.