Pituitary Gland Flashcards
What are the 2 principal organisers of the endocrine system?
Hypothalamus and pituitary
What is the hypothalamus?
Part of the brain and is directly connected to the pituitary gland via stalk called infundibulum
How would you describe communication between hypothalamus and pituitary?
NEUROENDOCRINE (neural - post; endo - ant)
What are tropic hormones?
Hormones which govern the release of another hormone (tropic and non-tropic released form H + P)
What type of hormones are released by hypothalamus?
Neurohormones
What type of hormones are released by the posterior pituitary?
Neurohormones
What type of hormones are released by the anterior pituitary?
Classic endocrine hormones
What part of the pituitary do hormones travel from hypothalamus to?
Posterior
Where are hormones released from in the posterior pituitary?
Vesicles
Are tropic or non-tropic hormones secreted into capillaries travelling to anterior pituitary?
TROPIC (govern release of anterior pituitary hormones)
Are tropic or non-tropic hormones produced in hypothalamus and travel to posterior pituitary?
NON-TROPIC (travel via axons of hypothalamic neurons where they are released into blood)
What is a property of all tropic hormones?
Bind to receptors on anterior pituitary and stimulate/inhibit release of AP hormones
Name 5 hypothalamic ‘releasing hormones’
Thyrotropin Releasing Hormone (TRH) Corticotropin Releasing Hormone (CRH) Growth Hormone Releasing Hormone (GHRH) Gonadotropin Releasing Hormone (GnRH) Prolactin Releasing Hormone (PRH)
Name 2 hypothalamic ‘inhibiting hormones’
Growth Hormone Inhibiting Hormone (GHIH) aka somatostatin
Dopamine aka Prolactin Inhibiting Hormone (PIH)
Are all hypothalamic tropic hormones peptide or amine hormones?
They are all peptides, except dopamine which is amine
What is the hypothalamo-hypophyseal portal system?
Network of tiny vessels which transfer trophic hormones from hypothalamus to ant pituitary
Do we need small or large numbers of neurosecretory neurons for control?
Small numbers are sufficient as ant pituitary is hypersensitive to minute amounts (like any other endocrine cell)
Where are hormones released from hypothalamo-hypophyseal portal system?
From neurosecretory neurons at the median eminence
What type of tissue is the anterior pituitary?
True endocrine tissue
What type of tissue is the posterior pituitary?
Neuroendocrine tissue
What is the origin of ant pituitary tissue?
Epithelial origin
What is the origin of post pituitary tissue?
Neural tissue origin
How is ant pituitary connected to hypothalamus?
Via hypothalamic-hypophyseal portal system (2 capillary beds connected in series)
How is post pituitary connected to hypothalamus?
Neural connection
What is another name for ant pituitary?
Adenohypophysis
What is another name for post pituitary?
Neurohypophysis
What part of the pituitary gland makes up 2/3rds?
Anterior (posterior is 1/3rd)
What is the production of anterior pituitary hormones controlled by?
Hypothalamus
How does the hypothalamus control the production of anterior pituitary hormones?
Producing ‘releasing’ or ‘inhibiting’ trophic hormones (aka factors) that stimulate or inhibit hormone production from AP
Give an example of a ‘releasing’ hormone produced by the hypothalamus to the AP
Thyrotropin Releasing Hormone (TRH) stimulates AP to secrete Thyroid Stimulating Hormone (TSH)
What type of hormones are released from the AP gland?
Peptides; 5 are also tropic
Name the 6 anterior pituitary hormones
- Thyroid Stimulating Hormone (TSH) aka thyrotropin
- Adrenocorticotrophic Hormone (ACTH) aka corticotrophin
- Follicle Stimulating Hormone (FSH) aka a gonadatrophin
- Luteinising Hormone (LH) aka a gonadatrophin
- Growth Hormone (GH)
- Prolactin
What is the function of the 5 tropic AP hormones?
Control secretion of other endocrine glands and have direct/indirect effects in promoting growth
What is the function of prolactin (only non-tropic AP hormone)?
Directly stimulates milk production from breast during lactation
If u can, name the destinations of the 6 AP hormones
GH = adipose tissue, liver TSH = thyroid gland ACTH = adrenal cortex LH + FSH (gonadatrophins) = gonads Prolactin = mammary glands
Describe the 3 broad stages of hypothalamus to AP to hormone release
- NEURONS synthesizing trophic hormones release them into capillaries of the portal system
- PORTAL VESSELS carry the trophic hormones directly to the AP
- ENDOCRINE CELLS release their hormones into the 2nd set of capillaries for distribution to rest of body
Describe the mechanism of the hypothalamic-hypophyseal portal system
Hypothalamic neurohormone released from stimulated hypothalamic neuron
Hormone moves from capillary bed 1 through portal system + binds to receptor on surface of AP endocrine cell in capillary bed 2
AP cell releases hormone that diffuses into capillary system + into circulation
If u can, describe the effect of AP hormones on their target tissues
Prolactin = lactation
TSH = TH release
ACTH = cortisol release
GH = IGF-1 release (tropic) + tissue metabolism (direct)
FSH + LH = regulation of repro function (direct) + sex hormone release (tropic)
What type of control is involved in the anterior pituitary?
Feedback control
What are the 3 integration centres in anterior pituitary?
1) hypothalamus
2) anterior pituitary
3) target endocrine cell
What acts as a negative feedback signal in the AP?
The hormones themselves
How does each hormone feed back to inhibit hormone secretion?
By integrating centres earlier in the reflex
Feedback from endocrine target cell =
long-loop feedback
Feedback from anterior pituitary to hypothalamus =
short-loop feedback
What do the feedback signals link?
Links levels of sequential hormones together and tightly maintains plasma levels within the correct range
What 2 neurohormones does the posterior pituitary store and release?
VASOPRESSIN (aka ADH)
OXYTOCIN
Where are the PP hormones synthesised?
Magnocellular neurons; diff subsets make either vasopressin or oxytocin
Where are the cell bodies of magnocellular neurons?
In specific areas of the hypothalamus
Where do axons project down to from the hypothalamus?
Down the infundibulum to the posterior pituitary
Do the axons from the hypothalamus synapse with other neurons?
No, their terminals end directly on capillaries
How are the PP hormones released at the PP?
Directly into the blood stream
Describe the steps of the pathways of vasopressin and oxytocin from hypothalamus to PP to bloodstream
1: hormone is made and packaged in cell body of neuron
2: vesicles are transported down the cell
3: vesicles containing hormone are stored in posterior pituitary
4: hormones are released into blood
What type of hormone do oxytocin and vasopressin behave as?
Typical peptide hormones i.e. synthesis and storage in vesicles, cell surface receptors etc
What is the main function of vasopressin (ADH)?
Regulates water balance
What is the main function of oxytocin?
Milk ejection and uterine contraction
What is the release of vasopressin triggered by?
Increased plasma osmolarity
Decreased plasma volume/blood pressure
What is the release of oxytocin triggered by?
Labout (baby’s head against cervix)
Suckling
What is the site/mode of action of vasopressin?
Kidney collecting ducts
- Increased water reabsorption
Vascular smooth muscle
- Increase BP
What is the site/mode of action of oxytocin?
Milk duct smooth muscle
- Contracts muscle, ejecting milk
Uterine smooth muscle
- Child birth
Walk us through the neurohormone release from posterior pituitary gland
Integration of stimuli triggers action potential in neurons e.g. suckling
Hormone is released from either oxytocin or ADH specific magnocellular neuron in the hypothalamus
Action potential travels down axon to terminals in posterior pituitary
Mature hormones are stored within terminals in posterior pituitary
Hormone is released directly into blood stream for effect
What are the 2 types of secretion disorders
Hypo
Hyper
What are the 2 types of responsiveness disorders
Hypo
Hyper
(response of target cell)
What is a primary disorder?
Those in which the defect is in the cells that secrete the hormone
What are secondary disorders?
Those in which there is too little or too much trophic hormone from pituitary
What are tertiary disorders?
Relate to hypothalamic defects
Give an example of 1, 2, 3 disorders using thyroid
Primary hyperthyroidism = thyroid gland making too much
Secondary = anterior pituitary producing too much TSH
Tertiary (least common) = hypothalamus releasing too much TRH
What could hyporesponsiveness be caused by?
Alterations in receptor for hormone, disordered post-receptor events or failure of metabolic activation of hormone
What could hyperresponsiveness be cause by?
Permissive effects e.g. thyroid hormone ++ adrenaline mediated lipolysis
