Hypothalamus and pituitary gland Flashcards
what are the master controllers of the endocrine system?
hypothalamus and pituitary
what is the hypothalamus?
Integration centre for endocrine systems
what is the hypothalamus connected to the pituitary via?
a stalk (infundibulum)
how is the hypothalamus connected to the anterior and posterior pituiary?
Hypothalamic axons and nerve terminals project to the posterior pituitary
Connection with anterior pituitary is via neurohormones
where is the pituitary gland located?
in a pocket in the sphenoid bone, directly below the hypothalamus
what two types of tissue does the pituitary gland contain?
anterior and posterior pituitary
describe the anterior pituitary gland?
connected to hypothalamus via capillary portal system
true endocrine tissue
epithelial origin
also called adenohypophysis
makes up 2/3rds of the gland
describe the posterior pituitary gland?
is a continuation of the hypothalmus
consists of axons and nerve terminals of hypothalamic neurons
secretes neurohormones made in hypothalamus
is neuroendocrine
is neural in origin
also called neurohypophysis
makes up 1/3rd of the gland
what integrative functions do the hypothalamus and pituitary serve?
what is released by both the hypothalamus and the anterior pituitary?
tropic and non-tropic hormones
what are all hormones released by the hypothalamus?
neurohormones
what are all hormones released by the posterior pituitary?
neurohormones (from the hypothalamus)
what are all hormones released by the anterior pituitary?
classic endocrine hormones
define non tropic hormones?
neurohormones produced in the hypothalamus and travel to posterior pituitary (via axons of hypothalamic neurons) where they are released into blood
define tropic hormones?
neurohormones secreted into capillaries travelling to anterior pituitary. Govern release of anterior pituitary hormones
what does the posterior pituitary contain?
magnocellular neurons
where are the cell bodies of magnocellular neurons found?
hypothalamus
what 2 peptide neurohormones do magnocellular neurons release?
vasopressin (aka anti-diuretic hormone; ADH)
Oxytocin
what is the role of vasopressin (aka anti-diuretic hormone; ADH)?
maintains water balance
what is the role of oxytocin?
stimulates uterine contraction at parturition, and aids expression of milk in lactating breast
different subsets of neurons make…
EITHER vasopressin or oxytocin
where are non tropic hormones synthesised?
in the hypothalamus and transported to the nerve terminal in posterior pituitary ready for release. Their terminals end directly on capillaries
what does activity of magnocellular neurons result in?
release of the neurohormone directly into the blood stream at the posterior pituitary
All hypothalamic neurohormones acting on anterior pituitary cells are what?
tropic hormones, i.e. stimulate/inhibit release of AP hormones
what are the 5 different hypothelamix releasing hormones that stimulate release anterior pituitary?
Thyrotropin Releasing Hormone (TRH)
Corticotropin Releasing Hormone (CRH)
Growth Hormone Releasing Hormone (GHRH)
Gonadotropin Releasing Hormone (GnRH)
Prolactin Releasing Hormone (PRH)
what are the 2 hypothalamic “inhibiting hormones” - stimulate posterior pituitary?
Growth Hormone Inhibiting Hormone (GHIH) aka somatostatin
Dopamine aka Prolactin Inhibiting Hormone (PIH)
all hypothelamaic releasing and inhibiting hormones are what?
All are peptides, except dopamine
what is the Hypothalamo-hypophyseal portal system?
Network of tiny vessels which transfer tropic hormones from hypothalamus to anterior pituitary
Hormones released from neurosecretory neurons at the median eminence
Very small amounts of hormones required
Short distance – very rapid and dynamic
what is the production of anterior pituitary hormones controlled by?
hypothalamic “releasing” or “inhibiting” tropic hormones that stimulate or inhibit hormone production from the anterior pituitary e.g. Thyrotropin Releasing Hormone (TRH) from the hypothalamus stimulates the release of Thyroid Stimulating Hormone (TSH) from the anterior pituitary.
6 hormones are released from the anterior pituitary gland, all peptides;
5 of these are also tropic hormones
what are the five anterior pituitary hormones?
Thyroid Stimulating Hormone (TSH) aka thyrotropin
Adrenocorticotropic Hormone (ACTH) aka corticotropin
Follicle Stimulating Hormone (FSH)
Luteinising Hormone (LH)
Growth Hormone (GH)
Prolactin
1-5 above control secretion of other endocrine glands = tropic hormones and also largely have direct or indirect effects in promoting growth = trophic action.
what does prolactin directly stimulate?
directly stimulates milk production from the breast during lactation
what is anterior pituitary feedback control?
complex, multi-tiered pathways involving up to 3 integration centres
what three integration centres make up anterior pituitary feedback control?
hypothalamus
anterior pituitary
target endocrine cell
feedback from endocrine target = long-loop feedback
feedback from anterior pituitary to hypothalamus = short-loop feedback
what is hyposecretion?
too little hormone secreted
what is hypersecretion?
too much hormone secreted
1* disorders?
are those in which the defect is in the cells that secrete the hormone
2* disorders?
are those in which there is too little or too much tropic hormone from pituitary - over or understimylating
3* disorders?
relate to hypothalamic defects - too little much released RARE
hyporesponsiveness?
may be due to alterations in receptor for hormone, disordered post-receptor events, failure of metabolic activation of hormone, (where this is required for function) or antagonistic effects
hyperresponsiveness?
could be due to permissive effects e.g. Thyroid hormone ++ adrenaline mediated lipolysis.
Hypo/hyperresponsiveness origins:
When normal plasma hormone concentration is disrupted homeostatic responses are initiated to reduce impact on end function e.g.
- Prolonged exposure to low [hormone]plasma often leads to up-regulation of receptor number (increases tissue sensitivity/response to hormone). - Conversely, prolonged exposure to high [hormone]plasma typically leads to down-regulation of receptor number (decreases tissue sensitivity/response to hormone).
what are permissive effects?
presence of one hormone enhances the effect of another eg epinephrine causes only modest lipolysis in adipose tissue, but when thyroid hormones are also present, greatly increased lipolysis occurs.
what effect does TH have?
synthesis of receptors for epinephrine on adipocytes. TH itself has no effect on lipolysis but is permissive to epinephrine.
TH also permissive to GH.
The presence of one hormone reduces the effect of another e.g. Growth hormone impairs glucose uptake in response to insulin by decreasing the number of insulin receptors on muscle and adipose tissue.
