Lecture 2: The Hypothalamus and Pituitary Flashcards
describe the difference between the anterior and posterior pituitary gland
anterior pituitary:
- connected to hypothalamus via capillary portal system
- true endocrine tissue
- epithelial origin
- makes up 2/3 rds of the gland
posterior pituitary:
- is a continuation of the hypothalamus
- consists of axons and nerve terminals of hypothalamic neurons
- secreted neurohomrones made in hypothalamus
- is neuroendocrine and neural in origin
- makes up 1/3rd of the gland
what is the anterior pituitary gland also called?
adenohypophysis
what is the posterior pituitary gland also called?
neurohypophysis
all hormones released the posterior pituitary and hypothalamus are classed as what>
neurohormones
all hormones released by the anterior pituitary are classed as what?
classic endocrine hormones
what are the two forms of hypothalamic neurohormones?
- non-tropic
- tropic
what is the difference between tropic and non-tropic hormones?
- non-tropic: neurohormones produced in the hypothalamus and travel to posterior pituitary (via axons of hypothalamic neurons) where they are released into blood.
- tropic: neurohormones secreted into capillaries travelling to anterior pituitary. Govern the release of anterior pituitary hormones.
posterior pituitary contains magnocellular neurons which have their cell bodies in the?
hypothalamus
magnocellular neurons store and release which two peptide neurohormones?
what are their function?
- vasopressin (aka ADH) = maintains water balance
- oxytocin = stimulates uterine contraction at parturition, and aids expression of milk in lactating breast
do magnocellular hormones secrete tropic or non-tropic hormones?
non-tropic
are vasopressin and oxytocin tropic or non-tropic hormones?
non-tropic
what are the 5 hypothalamic releasing hormones called? (tropic hormones which stimulate release of anterior pituitary hormones)
- thyrotropin releasing hormone (TRH)
- corticotropin releasing hormone (CRH)
- growth hormone releasing hormone (GHRH)
- gonadotropin releasing hormone (GnRH)
- prolactin releasing hormone (PRH)
what are the two hypothalmic ‘inhibiting’ hormones called? (tropic hormones which inhibit the release of anterior pituitary hormones)
- growth hormone inhibiting hormone (GHIH) aka somatostatin
- dopamine aka prolactin inhibiting hormone (PIH)
describe 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 controls the production of anterior pituitary hormones?
controlled by the hypothalamic ‘releasing’ or ‘inhibiting’ tropic hormones that stimulate or inhibit hormone production from the anterior pituitary
what are the 6 hormones released from the anterior pituitary gland classified as?
all peptide hormes, 6 of these are also tropic hormones
what are the 6 anterior pituitary hormones called?
- thyroid stimulating horome (TSH) aka thyrotropin
- adrenocorticotropic hormone (ACTH) aka corticotropin
- follice stimulating hormone (FSH)
- lutenising hormone (LH) aka gonadotropins
- growth hormone (GH)
- prolactin
1-5 are tropic hormones
which of the 6 anterior pituitary hormones is non-tropic?
prolactin > directly stimulates milk production from the breast during lactation.
anterior pituitary feedback control involves complex, multi-tiered pathways involving up to which 3 integration centres:
- hypothalamus
- anterior pituitary
- target endocrinecell
each hormone feeds back to inhibit hormone secretion by integrating centres earlier in the reflex
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what is feedback from the endocrine target called?
anterior pituitary feedback control
long-loop feedback
what is feedback from anterior pituitary to hypothalamus called?
anterior pituitary feedback control
short-loop feedback
what are primary endocrine disorders?
those in which the defect (hyposecretion or hypersecretion) is in the cells that secrete the hormone
what are secondary endocrine disorders?
those in which there is too little or too much tropic hormone from pituitary
what are tertiary endocrine disorders related to?
hypothalamic defects
what may cause hyporesponsiveness?
may be due to alteration in receptor for hormone, disordered post-receptor events, failure of metabolic activation of hormone, or antagonistic effects.
what may cause hyperresponsiveness?
could be due to permissive effects e.g. thyroid hormone ++ adrenaline mediated lipolysis.
prolonged exposure to low [hormone]plasma often leads to….
up-regulation of receptor number (increases tissue sensitivity/response to hormone) > hypersensitivity
prolonged exposure to high [hormone] plasma typically leads to…
down-regulation of receptor number (decreases tissue sensitivity/response to hormone) > hyporesponsiveness
describe permissive effects of hormones
- the presence of one hormone enhances the effect of another e.g. epinephrine causes only modest lipolysis in adipose tissue, but when thyroid hormones are also present, greatly increased lipolysis occurs.
- TH increases synthesis of receptors for epinephrine on adipocytes.
describe antagonstic effects of hormones and give an example
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.
