The pituitary gland Flashcards by Anna Coull

What are the 2 principal organisers of the endocrine system?

hypothalamus

pituitary

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What are chemicals called that are released into the blood by the hypothalamus?

neurohormones as the hypothalamus is made up of neural tissue

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What is the stalk called that connect the hypothalamus to the pituitary?

Infundibulum

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Where do hypothalamic axons and nerve terminals project to and from?

The posterior pituitary

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Connection between the anterior pituitary and the hypothalamus is via what?

neurohormones via capillary portal system

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What type of tissue is the anterior pituitary made up of

Endocrine tissue of epithelial origin

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What type of tissue is the posterior pituitary made up of

it is an extension of the neural tissue

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What lies between the anterior and posterior pituitary releasing melanin?

Pars intermedia

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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

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What types of hormones do the hypothalamus and the anterior pituitary release?

tropic and non-tropic hormones

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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

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What is a non-tropic hormone

A hormone that travels straight to target tissue to elicit a response - there is no intermediate hormone

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What types of hormones does the anterior pituitary release?

Classic endocrine hormones

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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

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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

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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