Lecture 2 - Introduction to the HPA Flashcards
What is the potential consequence of a pituitary enlargement or growth?
Compression of optic chiasm and therefore visual disturbances
How many the pituitary be damaged in an RTA?
Infundibulum can be fractured leading to severe endocrine abnormalities
Describe the posterior pituitary gland and the hormones it makes.
It is a down growth from the diencephalon brain
Secretes ADH and oxytocin which are both peptide hormones (They are very similar in structure - contain 9amino acids each, 7 of which are the same, so they have some effect on each other’s receptors)
ADH and oxytocin aren’t synthesized within the gland but are synthesized as inactive precursors by neurons of the hypothalamus (supraoptic and paraventricular nuclei) and then are transported along the hypothalamico-neurohypophyseal tract . They are converted to active hormone in post pituitary
What is ADH? What does It do and how?
Secretion Is influenced by plasma osmolality
It’s function is to decrease urine volume
It stimulates v2 receptors and this causes translocation of aquaporins into the cell membrane of the kidney tubule
Stimulation of v1 receptors causes vasoconstriction but this does not occur at physiological concentrations of ADH only in extreme dehydration or blood loss
Normal urine output is around 750ml per day
What is oxytocin? What does it do and how?
Acts via IP3 to cause smooth muscle contraction of the genital tract(uterus) and breast (milk ducts)
Secretion is stimulated by stimulation of the genital (cervix) and nipples (in breastfeeding)
During parturtion oxytocin acts in a positive feedback loop to expel baby. Oxytocin not necessary for the initiation of labour but can be given to induce labour ( oxytocin facilitates normal delivery although it is not essential it helps)
In breastfeeding it causes milk let down but it is NOT responsible for milk production
Can sex cause labour?
Sex can induce labour because it causes vaginal/cervical stimulation and eventual uterus contraction
What is another effect of oxytocin?
It influences learning and memory
Also oxytocin secretion is believed to increase bonding between mother and baby
What is the anterior pituitary gland and name 6 hormones it makes
It is an up growth from the palate (Rathke’s pouch)
It makes GH, Prolactin, TSH, ACTH, FSH, LH
What are TSH ACTH and FSH synthesised by?
TSH - thyrotrophe cells
ACTH - corticotrophe cells
FSH - gonadotrophe cells
How should you investigate endocrine disorders?
- Signs and symptoms
- Biochemical tests e.g. TSH, ft4, cortisol, LH, FSH, Prolactin, testosterone (for females don’t need to measure oestrogen/progesterone just ask about their menstrual history)(also important to think about what time of day test is done e.g. cortisol)
- Figure out if the issue if primary or secondary
- - to test this you can try to stimulate secretion (e.g. giving ACTH to stimulate cortisol release) or try to suppress secretion (using dexamethasone to suppress ACTH secretion)
If giving ACTH does not cause cortisol to go up then there is an issue with the adrenal cortex
If giving dexamethasone doesn’t suppress ACTH secretion it shows that the pituitary isn’t responding to neg feedback
- Imaging techniques
- Visual fields test e.g. looking for bilateral hemianopia as in optic chiasm compression
What Is prolactin?
199 amino acid peptide
Synthesized in lactotrophe cells of ant pituitary
It causes milk synthesis and it’s main role is to promote lactation and development of breast tissue
It also suppresses ovulation and a high prolactin causes infertility in both men and women
As we age the pituitary gland starts to produce more and more prolactin
What stimulated prolactin and what inhibits it?
TRH stimulates prolactin - it is also stimulatef by mild stress, nipple stimulation and coitus
Secretion is under hypothalamic control by means of Prolactin Release Inhibiting Factor, which is dopamine — dopamine inhibits prolactin secretion.
Therefore also dopamine antagonist e.g. haloperidol and chlorpromazine promote the release or prolactin
What is growth hormone? What does it dp?
It is synthesized in somatotrophe cells of ant pituitary
In some tissues i5 acts via second messengers produced in the liver, these are IGF1 and IGF2. Some growth deficiencies are due to inability to produce enough if these second messengers
The main effect of GH is linear growth of adolescence by increasing protein synthesis and collagen deposition
Foetal growth is relatively independent of GH
GH is also involved in tissue turnover and repair
What controls the secretion of GH?
GH secretion is controlled by the hypothalamus via GHRH and GHRIH (growth hormone release inhibiting hormone). GHRH is more important in this control
GH secretion is stimulated by decreased carbohydrates and fatty acids and increased AAs - poor diet decreases release of GH
