Hypothalamic Pituitary Hormones II Flashcards
What does the HPG (hypothalamic pituitary gonadal) axis regulate?
It regulates reproduction & fertility via increase/decrease in gonadal sex steroids.
How are gonadotropins (e.g. LH/FSH) released?
Hypothalamus produces GnRH which binds to receptors of gonadotrophs in the anterior pituitary glands. This then releases gonadotropins.
What type of cells produce testosterone, and further into estrogen?
Testicular Leydig cells.
What do testicular sertoli cells do?
They respond to FSH to alter gene transcription of sertoli cells and produce enzymes/proteins
What can binding of LH on Leydig cells cause?
It can increase the gene transcription of testosterone.
What can the binding of FSH on sertoli cells cause?
It can stimulate the transcription of growth hormones, inhibin, and ABP
Why are the activities of LH & FSH different?
Because they both have the same alpha chains, but different beta chains which can differentiate their activities.
What is the process of testosterone formation via Leydig cells?
- LH secreted from pituitary & activates adenylyl cyclase
- cAMP & PKA are activated
- PKA enters the nucleus & alters gene transcription of enzymes
- This converts cholesterol –> testosterone
What is the process of estradiol formation from sertoli cells?
- Testosterone exiting Leydig cells act on sertoli cells
- Sertoli cells convert some of this testosterone into estradiol via aromatase
- Some testosterone also leaves into the lumen
What 4 things can be produced when FSH binds to sertoli cells?
- Androgen inhibiting protein (ABP) - maintains testosterone levels
- Aromatase enzyme - converts testosterone to estradiol
- Growth factors - supports sperm formation
- Inhibins - inhibit FSH secretion
What is the process of the growth hormone axis release?
Hypothalamus releases GHRF –> binds to pituitary & produces cAMP as a secondary messenger –>this stimulates somatotrophs –> growth hormone (GH) is then released
How can GHRF release be inhibited?
By somatostatin induced decrease in cAMP
What causes dwarfism, and gigantism?
Dwarfism: GH deficiency
- Somatotrophs release less GH than normal
- Treated with somatorelin analogues
Gigantism: GH excess
- Bones/hands/feet/face overgrow
- Somatostatin used as treatment to inhibit excess GH
Which cells secrete prolactin, and what does prolactin assist in?
Lactotrophs.
Prolactin assists in breast tissue development, and stimulates lactation in pregnancy
What are the 3 prolactin releasing factors which stimulate prolactin release from lactotrophs?
- VIP
- TRH
- PHM
What happens in hyperprolactinemia?
Prolactin hypersecretion, which can also decrease sexual function.
In females it can cause:
- Lack of menstruation
- Excess milk production
In males:
- Breast enlargement
- Decreased libido/sperm
What can dopamine agonists and antagonists do in terms of prolactin treatment?
DA agonist: increase prolactin
DA antagonist: decrease lactation, and used to treat tumours of lactotrophs
What occurs in the posterior lobe of the pituitary gland?
Oxytocin & ADH production (from depolarisation/Ca2+ influx)
What is anti-diuretic hormone (ADH) also known as?
Vasopressin.
What does ADH do?
- Contracts smooth muscles = vasoconstriction
2. Enhances water reabsorption by kidneys/decreasing urine output
What factors can affect ADH secretion?
- Hypotension
2. Increased plasma osmolarity (being more dilute)
How many receptors are stimulated by ADH/vasopressin and what do they induce?
3 receptors.
V1 - effecting smooth muscle
V2 - anti-diuretic effect on kidneys
V3 - controls ACTH secretion
How does ADH produce an anti-diuretic effect on the kidneys?
- ADH stimulates aquaporin 2 proteins (AQP), also known as water channels
- This increases cAMP & PKA
- PKA can either: increase aquaporin proteins to cells, or promote gene transcription of new aquaporin proteins
- This then promotes the re-uptake of water from the collecting duct
- Water is then removed from the urine
What is the function of oxytocin in the body?
Mediates uterine contractions during birth, and milk ejection.
What can stimulate the release of oxytocin from the posterior pituitary gland?
- Elevated estrogen
- Sensory stimuli of cervix/uterus during birth
- Suckling of breast during breastfeeding
What is the route of administration of oxytocin?
IV or nasally, because it is destroyed in the GI if taken orally
Why would oxytocin be given to a woman?
- To induce further oxytocin release
- Facilitate pregnancy progression
- Lactation assisting
- Controlling post-partum uterine haemorrhage
