The pituitary gland Flashcards
What are the 2 principal organisers of the endocrine system?
hypothalamus
pituitary
What are chemicals called that are released into the blood by the hypothalamus?
neurohormones as the hypothalamus is made up of neural tissue
What is the stalk called that connect the hypothalamus to the pituitary?
Infundibulum
Where do hypothalamic axons and nerve terminals project to and from?
The posterior pituitary
Connection between the anterior pituitary and the hypothalamus is via what?
neurohormones via capillary portal system
What type of tissue is the anterior pituitary made up of
Endocrine tissue of epithelial origin
What type of tissue is the posterior pituitary made up of
it is an extension of the neural tissue
What lies between the anterior and posterior pituitary releasing melanin?
Pars intermedia
What sorts of stimuli does the hypothalamus respond to? (11)
cold stress metabolic demand hydration status exercise day/night menstrual cycle sleep breastfeeding pregnancy puberty
What types of hormones do the hypothalamus and the anterior pituitary release?
tropic and non-tropic hormones
What is a tropic hormone?
One that governs the release of another hormone - so the tropic hormone travels elsewhere and turns another hormone on/off
What is a non-tropic hormone
A hormone that travels straight to target tissue to elicit a response - there is no intermediate hormone
What types of hormones does the anterior pituitary release?
Classic endocrine hormones
Hypothalamus: tropic and non-tropic hormone functions
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 release of anterior pituitary hormones
What are magnocellular neurons?
Neurons that have their cell bodies in the hypothalamus.
They are within the posterior pituitary however - once the hormones are synthesised in the hypothalamus they are transported to nerve terminal in post. pituitary where they are stored until needed
the terminals end directly on capillaries
Which peptide neurohormones do magnocellular neurons release
Vasopressin i.e ADH
Oxytocin
different subsets of neurons make either vasopressin or oxytocin
What is the function of vasopressin?
maintains water balance
What is the function of Oxytocin? (2)
Stimulates uterine contraction at birth
Aids expression of milk in lactating breast
All hypothalamic neurohormones acting on anterior pituitary cells are of what type?
tropic hormones, i.e. stimulate/inhibit release of AP hormones
What are the 5 hypothalamic ‘releasing hormones’ ie when they reach anterior pituitary they stimulate the release of another hormone
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’ in the anterior pituitary
ie when they reach anterior pituitary they inhibit the release of another hormone
Growth Hormone Inhibiting Hormone (GHIH) aka somatostatin
Dopamine aka Prolactin Inhibiting Hormone (PIH) (amine not peptide)
What is the median eminence?
1st capillary bed that collects the trophic hormone from the hypothalamus
Where is the 2nd capillary bed?
within the anterior pituitary
What is the hypothalamo-hypophyseal portal system?
Network of tiny vessels which transfer trophic hormones from hypothalamus to anterior pituitary - 2 capillary beds connected in series
What is the production of anterior pituitary hormones controlled by?
the hypothalamic “releasing” or “inhibiting” trophic hormones
What are the 6 hormones released from the anterior pituitary if stimulated?
Thyroid Stimulating Hormone (TSH) aka thyrotropin
Adrenocorticotrophic Hormone (ACTH) aka corticotropin
Follicle Stimulating Hormone (FSH)
Luteinising Hormone (LH)
Growth Hormone (GH)
Prolactin
All but prolactin are tropic hormones (targets are in distal areas) Prolactin directly stimulates milk production from the breast during lactation.
Why is growth hormone produced throughout life even after we have stopped growing?
For the general repair of tissue
In anterior pituitary feedback control what are the 3 integration centres
hypothalamus
anterior pituitary
target endocrine cell
What act as the negative feedback signal?
hormones themselves
Describe a long-loop feedback
feedback from endocrine target
end endocrine target hormone feeds back and inhibits activity in hypothalamus and anterior pituitary
Describe a short-loop feedback
feedback from anterior pituitary to hypothalamus
Result of hormone disorders (4)
hyposecretion: too little hormone secreted
hypersecretion: too much hormone secreted
Hyporesponsiveness relates 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 and adrenaline. Thyroid hormone causes increase in response of our tissues to adrenaline.
Primary disorders
those in which the defect is in the cells that secrete the hormone (e.g end endocrine gland – generally most common)
Secondary disorders
those in which there is too little or too much tropic hormone from pituitary
Tertiary disorders
relate to hypothalamic defects - much less common
What homeostatic responses are initiated to reduce impact on end function when normal plasma hormone concentration is disrupted?
Prolonged exposure to low [hormone] in plasma often leads to up-regulation of receptor number (increases tissue sensitivity/response to hormone).
Conversely, prolonged exposure to high [hormone] in plasma typically leads a decrease in the number of receptors on the surface of target cells (decreases tissue sensitivity/response to that hormone).
Define the term permissive effects
the presence of one hormone enhances the effect of another
best example is adrenaline and thyroid hormone - thyroid hormone increases expression of adrenaline (epinephrine) receptors on adipocytes. Thyroid itself has no effect on lypolysis but affects adrenaline which affects lypolysis
Give an example of antagonistic effects
growth hormone impairs glucose uptake in response to insulin by decreasing the number of insulin receptors on muscle and adipose tissue
