The Pituitary Gland Flashcards
The hypothalamus is part of the brain (_____) and is connected to the pituitary gland (_____). Part of it’s function is to released chemicals into the blood that act at distal sites, hence it has _____________ function
The hypothalamus is part of the brain (above) and is connected to the pituitary gland (below). Part of it’s function is to released chemicals into the blood that act at distal sites, hence it has neuroendocrine function
As the hypothalamus is made up of neural (brain) tissue any chemicals released into the blood from the hypothalamus must be ___________
neurohormones
WHat are the secretions of the the hyopthalamus?
Everything out of the hypothalamus is an neuroendocrine hormone
Neural in origin but is releasing its secretions into the blood
the hypothalamus is an integration centre for what?
Integration centre for endocrine systems
How is the hypothalamus connected to the pituitary?
Connected to the pituitary via a stalk (infundibulum)
How is the hpyothalamus connected to the posterior pituitary?
Hypothalamic axons and nerve terminals project to, and form, the posterior pituitary
How is the hypothalamus connected to the anterior pituitary?
Connection with anterior pituitary is via neurohormones
Describe the anatomy of the pituitary gland
Bean-shaped and bean-sized endocrine gland (~14 mm diameter)
Located in a pocket in the sphenoid bone, directly below the hypothalamus
Contains 2 distinct types of tissue – anterior and posterior pituitary
how are the anterior and posterior pituitary connected to the hypothalamus?
A - connected to hypothalamus via capillary portal system
P - is a continuation of the hypothalmus
what are alternative names for the anterior and posterior pituitary glands?
A - also called adenohypophysis
P - also called neurohypophysis
How much of each of the anterior and posterior pituitary make up of the gland?
A - makes up 2/3rds of the gland
P - makes up 1/3rd of the gland
Is the anterior and posterior pituitary endocrine or neuroendocrine?
A - true endocrine tissue
P - is neuroendocrine
what is the origin of the anterior and posterior pituitary?
A - epithelial origin
P - is neural in origin
What does the posterior pituitary secrete?
secretes neurohormones made in hypothalamus
what does the posterior pituitary consist of?
consists of axons and nerve terminals of hypothalamic neurons
What is the bit inbetween the anterior and posterior pituitary and what is its function?
Pars intermedia (MSH) – melanocyte stimulating hormone is released form there and is the hormone that’s influences the production of melanin in your skin and determines the colour of your skin and weather you get freckles or moles
This is the bit between the anterior and posterior pituitary gland
Hypothalamus and pituitary serve key integrative functions
what are some examples?
Both the hypothalamus and the anterior pituitary release _____ ____ _________ hormones (tropic hormones govern the release of another hormone)
tropic and non-tropic
All hormones released by the hypothalamus are _____________
All hormones released by the posterior pituitary are _____________ (from the hypothalamus)
All hormones released by the anterior pituitary are classic ________________
All hormones released by the hypothalamus are neurohormones
All hormones released by the posterior pituitary are neurohormones (from the hypothalamus)
All hormones released by the anterior pituitary are classic endocrine hormones
What are the 2 forms of Hypothalamic Neurohormones?
non-tropic
tropic
what are non-tropic neurohormones?
neurohormones produced in the hypothalamus and travel to posterior pituitary (via axons of hypothalamic neurons) where they are released into blood
what are tropic neurohormones?
neurohormones secreted into capillaries travelling to anterior pituitary
Govern release of anterior pituitary hormones
the posterior pituitary contains what type of neurones?
magnocellular neurons which have their cell bodies in the hypothalamus
their axons form the posterior pituitary along with nerve terminal
the posterior pituitary contains magnocellular neurons which have their cell bodies in the hypothalamus. These neurons store and releases 2 peptide neurohormones:
what are they?
- vasopressin (aka anti-diuretic hormone; ADH) = maintains water balance
- Oxytocin = stimulates uterine contraction at parturition, and aids expression of milk in lactating breast
different subsets of neurons make either vasopressin or oxytocin
What is the process of hormones made in the hypothlamus getting to the blood stream?
hormones are synthesised in the hypothalamus and transported to the nerve terminal in posterior pituitary ready for release. Their terminals end directly on capillaries
activity in these neurons results in release of the neurohormone directly into the blood stream at the posterior pituitary
What type of hormones are the hormones that are released from the posterior pituitary?
oxytocin and vasopressin behave as typical peptide hormones
i.e. synthesis and storage in vesicles, cell surface receptors etc
All hypothalamic neurohormones acting on anterior pituitary cells are ______ hormones, i.e. stimulate/inhibit release of AP hormones
tropic
How many hypothalamic “releasing hormones” and hypothalamic “inhibiting hormones” are released and act on the anterior pituitary?
There are at least 5 hypothalamic “releasing hormones”
And 2 hypothalamic “inhibiting hormones”
All are peptides, except dopamine
What are 5 hypothalamic “releasing hormones” released acting on the 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 2 hypothalamic “inhibiting hormones” released acting on the anterior pituitary?
Growth Hormone Inhibiting Hormone (GHIH) aka somatostatin
Dopamine aka Prolactin Inhibiting Hormone (PIH)
What is the Hypothalamo-hypophyseal portal system?
Network of tiny vessels which transfer trophic hormones from hypothalamus to anterior pituitary
Small numbers of neurosecretory neurons sufficient for control
Hormones released from neurosecretory neurons at the median eminence
Very small amounts of hormones required
Short distance – very rapid and dynamic
Hormones released from neurosecretory neurons at the __________ ________
Hormones released from neurosecretory neurons at the median eminence
how is the anterior pituitary connected to the hypothalamus?
Connected to hypothalamus via hypothalamic-hypophyseal portal system (two capillary beds connected in series)
What is the control of the anterior pituitary hormones done by?
The production of anterior pituitary hormones is controlled by the hypothalamic “releasing” or “inhibiting” trophic 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 anterior pituitary hormones?
- Thyroid Stimulating Hormone (TSH) aka thyrotropin
- Adrenocorticotrophic Hormone (ACTH) aka corticotropin
- Follicle Stimulating Hormone (FSH) aka gonadotropins
- Luteinising Hormone (LH) aka gonadotropins
- Growth Hormone (GH)
- Prolactin
1-5 above control secretion of other endocrine glands and have direct or indirect effects in promoting growth = tropic hormones
Prolactin directly stimulates milk production from the breast during lactation
What is the anterior pituitary feedback control?
complex, multi-tiered pathways involving up to 3 integration centres:
1) hypothalamus 2) anterior pituitary 3) target endocrine cell
hormones themselves act as negative feedback signal
each hormone feeds back to inhibit hormone secretion by integrating centres earlier in the reflex
links levels of sequential hormones together and tightly maintains plasma levels within the correct range
anterior pituitary feedback control:
feedback from endocrine target = _________ feedback
feedback from anterior pituitary to hypothalamus = __________ feedback
feedback from endocrine target = long-loop feedback
feedback from anterior pituitary to hypothalamus = short-loop feedback
Compare hypothalamic-pituitary hormone-based negative feedback to direct feedback from physiological response e.g. PTH (independent of pituitary control)
Endocrine disorders may be classified as:
what is hyposecretion?
too little hormone secreted
Endocrine disorders may be classified as:
what is hypersecretion?
too much hormone secreted
Endocrine disorders may be classified as:
Hyposecretion or hypersecretion may result from any of the following:
What are 1° disorders?
those in which the defect is in the cells that secrete the hormone
Endocrine disorders may be classified as:
Hyposecretion or hypersecretion may result from any of the following:
What are 2° disorders?
those in which there is too little or too much trophic hormone from pituitary
Endocrine disorders may be classified as:
Hyposecretion or hypersecretion may result from any of the following:
What are 3° disorders?
relate to hypothalamic defects
Anterior pituitary feedback control – sites of disruption to homeostasis
Endocrine disorders may be classified as:
Hyporesponsiveness - What is it?
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
When end tissue is not responding in a way to the hormone as it should. When something is happening at the end tissue meaning it is not responding to the hormone as well as it should e.g receptor broken, intracellular pathway problem, increase or decrease in receptor number
Endocrine disorders may be classified as:
Hyperresponsiveness - what is it?
could be due to permissive effects e.g. Thyroid hormone ++ adrenaline mediated lipolysis
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 ___________
Conversely, prolonged exposure to high [hormone]plasma typically leads to __________
May affect not only the hormone’s own receptors but also receptors for other hormones (permissive or antagonistic effects).
up-regulation of receptor number (increases tissue sensitivity/response to hormone)
down-regulation of receptor number (decreases tissue sensitivity/response to hormone)
what are permissive effects of a hormone?
the 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.
TH leads to increased synthesis of receptors for epinephrine on adipocytes. TH itself has no effect on lipolysis but is permissive to epinephrine.
what are antagonistic effects of a hormone?
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
