Pituitary gland and hypothalamus Flashcards
What is the pituitary gland known as?
The master of all endocrine galnds
What are structural properties of the pituitary gland?
Size of a pea - 0.5g
Sits at the bottom of the brain -> sella turcica
Broad division into the anterior and posterior pituitary
Pituitary and hypothalamus are one unit -> division relates to how it interacts with the hypothalamus
Why are pituitary adenomas often linked to loss of visual acuity?
The pituitary sits adjacet to the branches of the optic nerve
Some of the branches cross over at the levels of the pituitary
Compression of aspects of the optic chiasm if the pituitary expands
What characterises the posterior from the anterior pituitary?
The way they interact with the hypothalamus is different
What is another name for the anterior pituitary?
Adenophysis
How does the hypothalamus communicate to the anterior pituitary?
Anterior pituitary is under the control of hormones (peptides) released by the hypothalamus
Neurosecretory neurons from the hypothalamus secrete the hormones into the venous system that connect the two structures
What is the venous system that joins the adenophysis to the hypothalamus called?
Hypophyseal portal system
How does the hypothalamus communicate to the posterioi pituitary?
Nervous system
The posterior pituitary is innervated by neurones from the hypothalamus
What are the two hormones released from the posterior pituitary?
ADH
Oxytocin
When are hormones released from the posterior pituitary?
In situations of stress
What are 5 hormones released by the anterior pituitary?
Growth hormone Thyroid stimulating hormone Prolactin ACTH LH and FSH
What are hormones released by the hypothalamus that acts on the anterior pituitary?
Growth hormone releasing hormone
Thyroid releasing hormone
CRH
GnRH
What happens in the hypothalamic pituitary thyroid axis?
- TRH is released from the hypothalamus
- Stimulates the anterior pituitary to release TSH
- Acts on the thyroid to release T3 and T4
How is TRH release regulated?
In a dional fashion. High and low concentrations throughout the say. Many nervous stimuli affects its release.
Features of TRH
Thyrotropin releasing hormone
Highly stable
Tripeptide amine
Rapidly degraded by plasma
Where can dysregulation in the thyroid axis happen?
In 3 areas:
Thyroid gland - primary thyroid problem
Pituitary gland - secondary thyroid problem
Hypothalamus - tertiary thyroid problem
Where is GnRH released from?
The hypothalamus
What is released when GnRH stimulates the anterior pituitary?
LH - Leutinizing hormone
FSH - Follicle stimulating hormone
What is LH and FSH involved in?
Development of secondary sexual characteristics
In what pattern is GnRH released?
Pulsatile release
What would happen if GnRH would be released constantly?
Cause the suppression of FSH and LH
Downregulation of receptors to GnRH on the pituitary
Can be used therapeutically to treat:
- Early puberty - constant GnRH to suppress LH and FSH receptors
- Cancer responsive to hormones - testosterone in prostate and oestrogen in breast cancer
What conditions can affect the concentration of hormones released by the pituitary?
Gender
State of developmental activity
How much the pituitary has been stimulated
What happens if GnRH is released under the right conditions and stimuli?
Spermatogenesis in males
Ovulation in females
What hormone is released from the hypothalamus to stimulate GH secretion?
Growth hormone releasing hormone
GHRH
What two ways are there of measuring growth?
Hypertrophy - cells get bigger
Hyperplasia - more cells
What conditions are related to GH dysregulation?
Acromegaly
Pituitary adenoma
Some types of Dwarfism
How do pituitary adenomas dysregulate GH secretion?
Increased GH secretion by the anterior pituitary
Can also release other hormones like prolactin and ACTH
Adenomas are classified by their size
Less than 10 mm -> microadenoma
More than 10mm -> macroadenoma
Pathogenesis of acromegaly
Excess release of GH from the pituitary
Symptoms:
Excess growth of soft tissues
Metabolic abnormalities - diabetes
Linear growth
Galactorrhea - abnormal prolactin signalling
How does a dysregulation of GH from pituitary lead to dwarfism?
GH resistance or receptor to GH is mutated
What hormone acts as a negative regulator of GH release?
Somatostatin
What do cortisol and GH have in common?
They are both stress hormones
Excess GH -> insulin resistance, increased lipolysis and acts downstream through IGF 1 made by hepatocytes
What do prolactin and GH have in common?
Both structurally similar
What roles does prolactin play in the body?
Initiates and maintains lactation
Inhibits GnRH
What makes prolactin different from the other hormones produced by the anterior pituitary?
It is not controlled by a releasing factor
Dopamine produced by the hypothalamus regulates the release of prolactin
Decrease in dopamine production => increase in prolactin secretion
What is prolactinoma?
Increase in prolactin produced
Most common secretory type of pituitary adenoma
What is the difference in presentation of prolactinoma in men and women?
Men present earlier - inhibition of testosterone manifests earlier
What suppresses prolactin release?
Dopamine
What are treatment options for prolactinoma sufferers?
Surgery - hypophysectomy
Dopamine agonists to suppress prolactin secretion
What is another way by which prolcatin can be secreted in excess?
If there is damage to the pituitary stalk
Hypophyseal vein carries dopamine from the hypothalamus to the anterior pituitary
If dopamine doesn’t reach pituitary = increased prolactin secretion
What hormone is released by the hypothalamus to stimulate ACTH release from the anterior pituitary?
CRH
What hormone is released from the anterior pituitary on activation by CRH?
ACTH
What organ does ACTH affect?
Adrenal gland
What does CRH stand for?
Corticotropin releasing hormone
What hormones are released from the adrenal gland upon acrivation with ACTH?
Cortisol - released on psychological and physical stress
Adrenal androgens
Why do conditions where there is dysregulation of ACTH often present with pigmentation problems?
ACTH and MSH (melanocortin stimulating hormone) are both peptides.
They both derive from the same precursor POMC
Increased ACTH = increased POMC
Increased POMC = increased MSH = increased pigmentation
Addison’s disease
Characterised by a decreased production of glucocorticoids and mineralocorticoids
Loss of negative feedback loop means that excess ACTH is produced in response
Damage to the adrenal gland/ mutation to the ACTH receptor or resistance to ACTH
