Hypothalamus and Pituitary System Flashcards
What is the Hypothalamic-Pituitary axis
- a unit found in the brain aligned with the bridge of the nose
- made of hypothalamus and pituitary gland
what connects the hypothalamus and pituitary gland
infundibulum ( aka : pituitary stalk ) which contains nerves and blood vessels
Where is the pituitary gland located
- hypophyseal fossa , small bony cavity
What could a pituitary tumour impinge on
- the optic chiasma , where optic nerves of both eyes cross over
- could lead to bitemporal hemianopia : loss of peripheral vision
Where do surgeons enter to operate on pituitary gland
- access from nostril or top of lip and go through sphenoidal sinus
Describe vascular and neuronal connections between hypothalamus and pituitary
- posterior lobe connected neurologically to hypothalamus
- anterior lope connected vascularly to hypothalamus
What are the pituitary lobes and what are they connected to ( and how )
- posterior and anterior pituitary lobes
- posterior ( neurohypophysis) is connected to hypothalamus by neural pathway
- anterior ( adenohypophysis ) is connected to hypothalamus by vascular pathway
Why are the pituitary lobes named neurohypophysis and adenohypophysis
- neurohypophysis is made from brain tissue
- adenohypophysis is made from glandular tissue derived from mouth
Is there any connections between the anterior and posterior pituitary
none
List the main pituitary hormones ( COME BACK TO )
- hypothalamus and posterior pituitary form neuroendocrine system that secreted ADH and oxytocin
- anterior pituitary secretes mainly tropic hormones
What are the nuclei for the axons connecting the hypothalamus and posterior pituitary called and what is their function and location.
- the paraventricular nucleus and supra-optic nucleus
- both located in the hypothalamus
- Contain cell bodies that produce ADH and oxytocin are manufactured
- neurohormones are packaged and stored in the axon terminal in the posterior pituitary lobe
Most neurons that secrete ADH are located where
supra-optic neurons
Most neurons that secrete oxytocin are located where
paraventricular neurons
Does the posterior pituitary manufacture ADH and oxytocin ?
no, just stores them
What are the actions of oxytocin
- stimulates uterine contraction and milk ejection
- given to women to start birthing process if they’re overdue
- love hormone: important for bonding and building connection
What are the actions of Antidiuretic hormone
- increases water permeability and absorption in renal collecting ducts by inserting water channels ( aquaporons) into walls of collecting ducts to enable absorption
- vasoconstrictor , increase BP
Give alternate name for ADH
vasopressin
What are tropic hormones , how many are there
- hormones that influence the secretion of another endocrine gland
- stimulate and maintain endocrine target tissue
- 5 released from anterior pituitary gland
What are the 7 anterior pituitary hormones and their function
1- growth hormone : stimulate secretion of insulin like growth factor in liver which affects bone and muscle( GH )
2- thyroid stimulating hormone : stimulate thyroid (TSH)
3- adrenocorticotrophic hormone : stimulate adrenal gland to secrete corticosteroids (ACTH)
4- Prolactin : produces milk in mamMary glands and regulating reproductive function (PRL)
5- Follicle stimulating hormone : act on gonads , ovaries , testes (FSH)
6- Leuteinising hormone : act on gonads, ovaries , testes (LH)
7- Melanocyte stimulating hormone : stimulate melanocyte in skin to produce melanin (MSH)
Is prolactin and melanocyte stimulating hormone a tropic hormone
no
What are the gonadotrophin
Follicle stimulating hormone and leuteinising hormone
Which brain region regulates hormone secretion from pituitary gland
Hypothalamus
Which hormones are secreted by neurohypophysis
- ADH and oxytocin
How are levels of tropic hormones modulated by feedback from target hormones
- by hypothalamic hormones and feedback by target gland hormones
What are the hypothalamic hypophysiotropic hormones
- hormones released by hypothalamus
- aka releasing hormones
- cause release and inhibition of anterior pituitary hormones
List the hypophysiotropic hormones
1- growth hormone releasing hormone
2- growth hormone inhibiting hormone ( somatostatin )
3- thyroid releasing hormone
4- corticotrophin releasing hormone
5- prolactin releasing hormone
6- prolactin inhibiting hormone ( dopamine )
7- gonadotrophin releasing hormone
Which hormone is being secreted more often, PRH or PIH
prolactin inhibiting hormone , why we are not lactating all the time
What stimulated the secretion of the anterior pituitary hormones
- the hypothalamic hypophysiotropic hormones
-
How are hypothalamic hypophysiotropic hormones secreted and where are they released
- from neurosecretory neurons
- released into portal system ( capillary network from hypothalamus to anterior pituitary )
What is the hypothalamic hypophyseal portal system
- venous blood flowing from one capillary network (hypothalamus ) to another capillary network ( anterior pituitary )
Why is it important for the hormones to travel via the hypothalamic hypophyseal portal system and not enter the systemic circulation
- minimizes dilution of hormones as it moves from hypothalamus to pituitary
- allows rapid response since they travel directly between hypothalamus & pituitary
Decreased secretion of which hormone results from damage to hypothalamic hypophyseal portal system
a: ADH b: prolactin c: oxytocin d: PTH e: TSH
- e
Describe the 3 hormone sequence
1- hypophysiotropic hormone
2- anterior pituitary tropic hormone
3- peripheral target-endocrine gland hormone
What does the peripheral target-endocrine gland hormone do
- suppress secretion of tropic hormone driving
- aka long-loop negative feedback
what is the short loop negative feedback mechanism
- hormone produced by pituitary gland can feedback negatively to hypothalamus and stop the hypohysiotropic hormone releasing
why are diurnal or circadian rhythms important to keep in mind
- when giving someone hormones it’s important to know that during different times of the day there are different hormone levels
Endocrine disorders are attributable to what ( 3)
- hormonal deficiency , hormonal excess or decreased responsiveness of target cells
What is primary hyposecretion and give examples of causes
- too little hormones are being secreted due to abnormality with gland ( adrenal, liver , etc)
- ex: genetic , dietary or cancer, iatrogenic surgery, immunological or toxic causes
What is secondary hyposecretion and give examples of causes
- gland is normal but too little hormone is secreted due to deficiency in tropic hormone
- disorders of anterior pituitary
What is tertiary hyposecretion and give examples of causes
- gland is normal but too little hormone is secreted due to deficiency of the hypothalamic releasing hormone
- disorder of hypothalamus
What is panhypopituitarism
- ## a condition in which the production and secretion of all hormones by the pituitary gland is reduced. ( anterior and posterior )
What is primary hypersecretion
- tumours that ignore normal regulatory input and secrete excess hormones
- abnormality within gland itself
What is secondary/tertiary hypersecretion
- tumours that ignore normal regulatory input and secrete excess hormones
- excessive secretion from pituitary or hypothalamus
What are some consequences of hyper secretion
1- excess ACTH ( Cushing’s disease )
2- excess prolactin ( impaired reproductive function )
3- excess ADH ( fluid retention & low plasma osmolarity )
4- excess TSH ( grave’s disease )
5- excess hGH in children ( giantism )
6- excess hGH in adults ( acromegaly )
