Hypothalamic & Pituitary Hormones Flashcards
Where is the hypothalamus located?
Below the thalamus, just above the brain stem.
What is the hypothalamus important for?
The control of basic functions, such as hunger, thirst and sleep. It senses internal and external environments and gives out signals to the rest of the body in order to adapt
What is the pituitary gland?
An endocrine gland that sits in a small bone cavity below the hypothalamus. It connects to hypothalamus via the ifundibulum
What 2 lobes does the pituitary gland have?
Anterior and posterior. These link to the hypothalamus in very different ways
How does the Anterior lobe link to the hypothalamus?
Parvicellular neurons in the hypothalamus secrete regulatory hormones into the bloodstream which travel through the portal system to the anterior pituitary lobe triggering secretion of other hormones (CIRCULATORY SYSTEM LINK)
How does the posterior lobe link to the hypothalamus?
Large magnocellular neurons in the hypothalamus have long axons which extend down into the posterior pituitary lobe (DIRECT NEURO-ENDOCRINE LINK).
Carried to the nerve terminals
How do hormones secreted by the hypothalamus reach the target cells of the anterior pituitary?
Via the hypothalamic-pituitary portal system
What function does the Prolactin releasing hormone have?
It’s a hypothetical hormone as the effect is not proven, but it has a positive tropic effect, causing the anterior pituitary to produce prolactin and that has an effect on the mammary develo-ment and lactation
What does the Prolactin inhibiting hormone do?
Released from the hypothalamus, has no tropic effect, inhibits the secretion of prolactin. This is the normal response, only during pregnancy that the dopamine negative effect is stopped in order to produce milk
What does the Thyrotropin Releasing Hormone (TRH) do?
TRH signals the production of TSH in the anterior pituitary which then acts on the thyroid glands to secrete thyroid hormones
What does the Corticotropin Releasing Hormone do?
Released from hypothalamus, causes the production of Adrenocorticotropic hormone (ACTH) in the anterior pituitary which causes the release of cortisol from the adrenal cortex
What does the Growth Hormone Releasing Hormone do?
Signals the release of Growth Hormone from the anterior pituitary, having an effect on the growth and secretion of insulin-like growth factors from liver
What does the Gonadotropin releasing hormone do?
Stimulates the release of FSH and LH from the anterior pituitary which has an effect on the gonads for production of sex hormones
What is somatostatin?
Growth Hormone Inhibiting Hormone
What does tropic mean?
means hormone will act on an endocrine gland (i.e. pituitary) to cause the release of another hormone
Where are hypothalamic regulatory hormones secreted directly into?
the portal system = hypothalamic-pituitary portal vein (no dilution or degradation) to cause cells in the anterior pituitary lobe to secrete other hormones
What hormones are tropic?
TSH, ACTH, LH, FSH
What does FLATPiG stand for?
All the anterior pituitary hormones: Follicle Stimulating hormone (FSH) Luteinising Hormone (LH) Adrenocorticotropic hormone (ACTH) Thyroid Stimulating Hormone (TSH) Prolactin (PRL) Growth Hormone (GH)
FLAT = tropic hormones PiG = non-tropic
Where are FSH and LH secreted from?
Gonadotropes
What does FSH do?
stimulates ovaries to produce oestrogen and testes to produce testosterone
What does LH do?
LH has a role in ovulation and the growth of the corpus luteum.
LH stimulates androgen secretion by interstitial cells in testes
Where is ACTH secreted from?
The corticotropes
Where is TSH secreted from?
Thyrotropes
How would the hypothalamus react to a lowering of the body temperature?
Hypothalamus detects low temperature and secretes TRH – goes on to cause the secretion of TSH from anterior pituitary, goes on the cause endocrine gland to increase secretion of T3 and T4
Increase in metabolism increases temperature
What feedback loops does T3 have?
Has a short negative feedback loop where it reduces the secretion of TSH and a long negative feedback loop where it jumps 2 levels back and inhibits the hypothalamus from releasing TRH
What are the feedback loops for CRH and ACTH?
Cortisol has a short negative feedback on ACTH and a long negative feedback on CRH.
CRH also has an ultra short negative feedback loop where it inhibits itself
Where do non-tropic hormones act?
Directly on the tissue (prolactin and Growth Hormone)
Where is prolactin secreted?
By lactotropes - acts on breast tissue for lactation
What problems can dysregulation of prolactin cause?
Prolactinoma - tumour of pituitary, treated using dopamine receptor agonists e.g. bromocriptine, cabergoline
Where is GH secreted?
By somatotropes - GH stimulates growth, cell reproduction and regeneration of specific cells
What can hypersecretion of GH cause in children?
Gigantism in children (before long bones have fused )
What can hypersecretion of GH cause in adults?
Acromegaly - after long bones have fused. Can cause:
enlargement of the head, hands, feet, lower jaw, tongue and lips
excessive sweating, headaches and visual field loss, due to pressure on optic nerve
What is used in the treatment of Acromegaly?
Somatostatin (growth hormone inhibiting hormone). Regulates production of growth hormone (GH) and affects cell proliferation and growth via somatostatin receptors. has a longer half life
What is Growth hormone deficiency caused by?
tumour pressing on ifendibula stalk that connects glands and prevents signals getting from pituitary from hypothalamus
Can be a genetic condition – problems in growth hormone binding proteins or growth hormone receptors on the tissues
What neurons synthesise and secrete oxytocin and vasopressin (ADH)?
Magnocellular neurons
Where are oxytocin and ADH released?
At the axon terminals, where they diffuse into the capillary network of the posterior lobe (THEY DO NOT GO THROUGH THE PORTAL SYSTEM)
What are the functions of Oxytocin
1) stimulation of milk ejection
2) stimulation of uterine smooth muscle contraction at birth
3) Establishment of maternal behaviour: positive feedback regulation – pressure of babies head stimulates release of oxytocin – reacts with receptors on uterus causing contraction activating sensory nerves again
When is oxytocin given?
Used if labour isn’t progressing – Pitocin speeds up contractions – HOWEVER if too quick and too strong it reduces blood supply to baby (can cause cerebral palsy) – have to be closely monitored
What are the functions of ADH?
Water regulation, binds to receptors in cells of collecting ducts of kidney and distal convoluted tubule. when it binds , it causes synthesis of aquaporin 2 - responsible for transport of water from filtrate back into the blood (RE-ABSORPTION)
What happens in the absence of ADH?
the collecting ducts are virtually impermeable to water, which therefore flows out as urine
What is hypothalamic (central) diabetes insipidus?
Deficiency in vasopressin secretion
Caused by: head trauma, infections or tumors involving the hypothalamus
Treat using exogenous vasopressin
What is Nephrogenic diabetes insipidus?
Kidney is insensitive to vasopressin
Caused by: renal disease, mutations in the vasopressin receptor gene or in the gene encoding aquaporin-2
Treat by increasing water consumption
What is melatonin secreted by?
Pinealocytes (pineal gland).
Melatonin helps regulate circadian rhythm
What inhibits the production of melatonin
light to the retina (permitted by darkness)
What disorder has melatonin been shown to be effective in?
Seasonal affective disorder (SAD) and insomnia
