Hypothalamo-pituitary axis Flashcards
What is the posterior pituitary gland?
Comprises the posterior lobe of the pituitary gland and is part of the endocrine system.
Hormones known as posterior pituitary hormones are synthesized by the hypothalamus, and include oxytocin and antidiuretic hormone.
What is the anterior pituitary gland?
The anterior pituitary is the front lobe of your pituitary gland, which is a small, pea-sized gland located at the base of your brain below your hypothalamus.
The anterior pituitary creates and releases over six different hormones, which regulate various cellular processes including growth.
What are the 3 hypothalamic factors?
Hypothalamo-pituitary-thyroid axis.
Hypothalamo-pituitary-adrenal axis.
Hypothalamo-pituitary control of growth, lactation, reproduction.
What is the pituitary gland?
The pituitary gland is a small, bean-shaped gland situated at the base of your brain, somewhat behind your nose and between your ears.
The hormones it produces help regulate important functions, such as growth, blood pressure and reproduction.
What are the 2 lobes of the pituitary gland?
Anterior lobe: adenohypophysis (non neuronal origin).
Posterior lobe: neurohypophysis (extension of the hypothalamus).
What is important about the posterior lobe (neurohypophysis)?
The posterior lobe is made of nerve endings coming from specific hypothalamic neurones, and glial-like cells.
Upon stimulation from their corresponding hypothalamus neurones, the nerve terminals release two small peptides oxytocin and vasopressin (or ADH), of similar structures.
Oxytocin: very important during and after parturition (child delivery and breast feeding).
ADH (antidiuretic hormone) or vasopressin: crucial role in the control of water content of the body.
What is vasopressin (ADH)?
It is a nonapeptide which has a vital role in the control of water content of the body.
It has selective action on the kidneys, to stimulate water reabsorption (via V2 receptors).
It also causes vasoconstriction (via V1 receptors), platelet aggregation and mobilisation of coagulation factor.
Release is of ADH is stimulated if there is an elevated blood osmolality, low blood volume or pressure, or pain.
What happens to the body if their is a deficiency of vasopressin (ADH)?
Diabetes insipidus.
Patient in a state of permanent dehydration.
How can vasopressin (ADH) be used therapeutically?
Agonists:
Diabetes insipidus and nocturnal enuresis (bed wetting).
As a vasoconstrictor: prevention of bleeding in haemophilia, to potentiate action of local anaesthetics,
also in septic shock when noradrenaline does not help
Antagonists:
To reduce water retention in hyponatremia (post surgical stress), correct hyponatremia (congestive heart failure).
Helps to regulate water retention by absorbing water in the collecting ducts of the nephron. Blocking this receptor will allow water to be excreted more readily.
What is oxytocin?
It is a nonapeptide which stimulates contraction of the uterus during labour and contraction of contractile cells of mammary glands for milk ejection. It also induces constriction of umbilical vessels (to prevent excessive bleeding).
Secretion is triggered by suckling of the nipple or by stimulation of the cervix.
Present in man and woman, often co-secreted with ADH, has certainly a role in osmoregulation.
How can oxytocin be used therapeutically?
To stimulate contraction during delivery (overdose very dangerous).
To assist breast-feeding,
To reduce post-partum or miscarriage bleeding, late therapeutic abortion.
Synthetic analogues like syntocinon (sometimes combined with ergometrine).
Other uses:
Important CNS action, probable role in social recognition, pair bonding, anxiety and maternal behaviours, can improve empathy, may alter memory processing.
What is important about the anterior lobe (adenohypophysis)?
Contains at least five different types of glandular cells which secrete at least 7 hormones (peptides).
There are 4 hormones that stimulate other endocrine glands called tropic hormones.
The other 3 hormones are:
Prolactin (PRL) - initiates milk production and development of mammary gland.
Growth hormone (GH) - somatotropin controls general body growth, increases protein synthesis, cell proliferation and bone growth, metabolic effects, induces the release of IGF (insulin like growth factor) from liver.
Melanocyte-stimulating hormone (a-MSH) - synthesised from the same precursor than ACTH, some effects on skin pigmentation. In the brain MSH neurons regulate appetite.
What are the 4 tropic hormones?
TSH - stimulates thyroid gland and secretion of Thyroid hormones.
ACTH - stimulates adrenal cortex and the secretion of glucocorticoids.
LH and FSH - stimulate secretion of oestrogens by the ovaries and secretion of testosterone by the testes, to regulate menstrual cycle.
How are the adenohypophysis and hypothalamus connected?
The long pituitary portal vein connects the medial eminence of the hypothalamus to the adenohypophysis.
The medial eminence of the hypothalamus is rich in neurone terminals containing dense granules. Some hypothalamic neurons release specific factors in the portal vein, they control the secretion of pituitary cells.
What are the hypothalamus factors?
TRH - Thyrotropin releasing hormone (tripeptide), stimulates the release of TSH from the thyrotroph cells.
GnRH - Gonadotropin releasing hormone, stimulates the release of the gonadotropins LH and FSH from the gonadotroph cells.
GHRH - Growth hormone releasing hormone (GHRH), stimulates the release of growth hormone from the somatotroph cells.
GHIH - Growth hormone inhibitory hormone (GHIH), or somatostatin, inhibits the release of growth hormone.
CRH - Corticotropin releasing hormone, stimulates the release of ACTH from the corticotroph cells.
Dopamine - Catecholamine, inhibits the release of prolactin.
What would happen to the body if there was a deficiency of GH?
Total: Pituitary dwarfism (absolute def., short but proportioned stature, rare).
Partial: Growth retardation (relative deficiency 1/4,000).
Causes: idiopathic, rarely mutation.
Treatment: GH recombinant, like humatrope, protropin (treatment very expensive), also used to treat Turner’ syndrome.
Treatment should start as early as possible.
