The Pituitary Gland and the Hypothalamus Flashcards
What is the hypothalamus and the pituitary gland known as?
Principle organisers of the endocrine system
How is the hypothalamus and pituitary connected?
Via the pituitary stalk called the infundibulum
Is hypothalamic communication to the Pit. Gland neural or endocrine?
Both - neural to posterior gland and endocrine to anterior gland = neuroendocrine function
Where is the Pit gland?
In a pocket in the sphenoid bone directly below the hypothalamus
What types of hormone do the hypothalamus and pit gland release?
Trophic and non-trophic
What is a trophic hormone? Give an example of when oit is used?
A hormone that governs the release of another hormone
Neurohormones secreted into capillaries and traveling to the anterior pit. gland governing release of AP hormones
Give an example of non-trophic hormones.
Neurohormones made in hypothalamus and travel via hypothalamic axons to the posterior Pit. gland
All hormones released by the posterior pit. gland are…
Neurohormones from hypothalamus
All hormones released by the AP gland are…
Classic endocrine hormones
What do all hypothalamic trophic hormons bind to? What does this binding do?
Receptors on the AP gland which inhibit or stimulate hormone release
Name the 5 hypothalamic releasing hormones and what they do.
Stimulate AP to release hormones
Thyrotropin releasing hormone - TRH
Corticotropin releasing hormone - CRH
Growth Hormone Releasing Hormone - GHRH
Gonadotropin Releasing Hormone - GnRH
Prolactin Releasing Hormone - PRH
Name the hypothalamic inhibiting hormones.
Growth hormone inhibiting hormone - GHIH
Prolacting inhibiting hormone - PIH
What is growth hormone inhibiting hormone also known as?
Somatostatin
What is prolactin inhibiting hormone?
Dopamine
What type of hormone class are all the hypothalamic hormones?
All are peptide BESIDES dopamin/prolactin inhibiting hormone which is an amine
What is the hypothalamo-hypophyseal portal system?
A network of vessels which transfer trophic hormones from hypothalamus to the AP
What is needed to maintain control of the hypothalamo-hypophyseal portal system?
Small numbers of neurosectretory neurons
How does the H-H portal system work?
Hormones are released from the neurosecretory neurons at the median eminence and travel via capillaries to the AP gland
Does the H-H portal system encompass a short or long system - what significance does this have?
Short - leads to a rapid and dynamic response
What is a hypophysiotropic hormone?
Hormones made by endocrine cells in the hypothamalus and released at the capillary bed called the median eminence and transported to the AP gland
What type of tissue is the AP and the PP glands?
AP - true endocrine
PP - neuroendocrine
What is the origin of both glands
AP - epithelial
PP - neural tissue
How are both glands connected to the hypothalamus?
AP - via capillary portal system called the hypothalamo-hypophyseal system
PP - neural connection
What is the AP gland also called?
Adenohypophysis
What does the PP gland secrete?
Neuro hormones made in the hypothalamus
What is the PP gland also called?
Neurohypophysis
How much of the pituitary does each gland make up?
AP - 2/3s
PP- 1/3
What are the 6 hormones released from the AP gland?
Thyroid stimulating hormone - TSH
Adrenocorticotrophic hormone - ACTH
Follicle stimulating hormone - FSH
Luteinising Hormone - LH
Growth Hormone - GH
Prolactin
5 of the 6 hormones released by the AP gland have trophic functions- which one is not trophic and what does it do?
Prolactin - direct stimulation of milk production during lactation
What is another name for Thyroid stimulation hormone? And what does it do?
Thyrotrophin - Leads to thyroid hormone release
What is another name for adrenocotricotrophic hormone and what does it do?
Corticotrophin - Acts on adrenal cortex to stimulate cortisol release
What is another name for follicle stimulating hormone and luteinising hormone?
Gonadotrophins - act on gonads leading to regulation of reproductive function (non-trophic action of the hormone) and sex hormone release (trophic)
What does growth hormone do?
Acts on liver to release IGF-1* (trophic action)
Directly stimulates tissue metabolism (non-trophic)
What does 3 integration centers does feedback control involve?
Hypothalamus
AP gland
Target endocrine cell
What acts as the neg. feedback signal?
The hormone itself
How does the neg. feedback work?
The hormone fees back to inhibit hormone secretion
What is a long-loop feedback?
When the hormone feeds back from the endocrine target
What is a short-loop feedback?
When the feedback is from the AP to the hypothalamus
Purpose of feedback systems?
Link levels of sequential hormones together and maintains plasma conc within correct range
What hormones does the PP gland store and release?
Vasopressin
Oxytocin
What is another name for vasopressin?
ADH - Anti-diuretic hormone
Where are ADH and oxytocin synthesised?
In magnocellular neurons which have their cell bodies in specific areas of the hypothalamus
How do these hormones get from the hypothalamus to the PP gland?
Axons project down the infundibulum to the PP gland, they don’t synspase but their terminals end on capilaries -
The hormones travel down this route and are stored in the terminals until the nerve is stimulated and they are released directly into blood stream into PP gland
ADH and oxytocin behave as what type of hormones?
Peptide
Function of ADH?
Regulate water balance
What triggers ADH release?
Increased plasma osmolarity
Decreased plasma volume/BP
What is the site of action for ADH and what is its mode of action?
Site - kidney collecting ducts
Mode - increase water re absorption and increase BP
Function of oxytocin?
Milk ejection and uterine contraction
What triggers oxytocin release?
Labour - babies head against cervix
Suckling
Site and mode of action for oxytocin for milk production?
Site - milk duct, smooth muscle
Mode - contracts muscle which ejects milk
Site and mode of action for oxytocin for labour
Site - uterine smooth muscle
Mode - Child birth
What is hyposecretion?
Too little
Hypersecretion?
Too much
Hyper/Hypo-responsiveness means?
Reduced or increased response of target cell
1* disorders are what…?
Those in which the defect is in the cells that secrete the hormone
2* disorders?
Where there is too little or too much trophic hormone from pituitary causing hormone to be too high or too low
3* disorders?
Relate to hypothalamic defects
What can cause hyporesponsiveness?
Alterations in receptors for the hormone
Disordered post-receptor events
Failure of metabolic activation of hormone (Still a prehormone/prepro)
What can cause hyper-responsiveness
Permissive effects
