Hypothalamic Pituitary Hormones 2 Flashcards
What is the function of FSH and LH in males and females?
males
- FSH stimulates sperm development
- LH stimulates Leydig cell production of testosterone
females
- FSH supports the development of ovarian follicle
- LH stimulates the production of oestrogen and progesterone by the corpus luteum
How is the gonadal axis activated in males?
hypothalamus release gonadotrophin releasing hormone (GnRH)
GnRH stimulates the synthesis and release of FSH and LH from the anterior pituitary
LH binds to leydig cells causing the synthesis and release of androgens
- androgens can undergo peripheral aromatisation via aromatase to convert androgens to oestrogen
- androgens can bind to sertoli cells
FSH binds to sertoli cells
- stimulates the release of androgen binding protein (ABP), inhibin, and growth factor
- stimulates spermatogenesis
- stimulates aromatisation leading oestrogen synthesis
What is the function of growth factors, androgen binding protein (ABP) and inhibin produced by Sertoli cells?
What are the feedback loops in the gonadal axis and what are they controlled by?
growth factors
- can bind to leydig cells activating the synthesis and release of androgens
- supports sperm cells and spermatogenesis
= increases spermatocytes, spermatids and spermatogonia
inhibin
- can activate a negative feedback loop by inhibiting FSH release from the anterior pituitary
androgen binding protein
- binds to testosterone and maintain high local level
What are the feedback loops in the gonadal axis and what are they controlled by?
negative feedback loop
- androgens and inhibins can block FSH and LH release from the anterior pituitary and hypothalamus
How is growth hormone release stimulated?
growth hormone releasing hormone (GHRH) is released from the hypothalamus
GHRH binds to GHRH receptors on somatotrophs in the anterior pituitary causing synthesis and release of growth hormone
- via Gs coupled receptor activation which involves PKA activation via adenylate cyclase cascade activation
Where does the growth hormone act? What are its effects?
adipose
- increases lipolysis
- reduces glucose uptake
muscle
- increases protein synthesis
- reduces glucose uptake
hepatocytes
- increase synthesis of somatomedins
= group of proteins that promote cell growth and division in response to stimulation by growth hormone
somatomedins can either
- bind to its receptors and stimulate cell growth and division
- feedback onto somatotroph and somatostatin inhibiting release
What causes dwarfism? How can it be treated?
dwarfism - childhood deficiency of growth hormone
- disruption of somatorelin secretion by the hypothalamus and release of growth hormone from the pituitary gland
= somatorelin is normally stimulates secretion and GHRH and consequently GH - pituitary tumour
= causes hypopituitarism
it can be treated by administration of somatorelin analogues such as sermorelin (geref)
What causes gigantism and acromegaly?
gigantism and acromegaly - excessive levels of growth hormone
- pituitary tumour
it can be treated with somatostatin analogues such as octreotide (Sandostatin)
How is the prolactin axis activated? How is it inhibited?
prolactin releasing factors (PRF) are released from the hypothalamus
PRF stimulates prolactin synthesis and release from the anterior pituitary
- prolactin acts on the breasts during pregnancy to assist in breathing tissue development and stimulates lactation
prolactin inhibiting factors such as dopamine are released from the hypothalamus to block prolactin synthesis and release from the anterior pituitary
What is hyperprolactinemia? How does it affect female and males?
hyperprolactinemia
- excessive prolactin release due to prolactin secreting tumours and certain drug therapies
females
- amenorrhea (lack of periods), galactorrhea (excessive or spontaneous secretion of milk)
males
- hypogonadism, impotence, reduced libido, reduced sperm production, gynecomastia (breast enlargement)
How can hyperprolactinemia be treated?
dopamine agonist inhibit prolactin release
- bromocriptine
= reduces lactation and treats galactorrhea/pituitary tumours of the lactotrophs
What does the posterior pituitary synthesis and release? How does it do this?
magnocelluar neurons reside in the paraventricular and supraoptic nuclei of the hypothalamus extend axons to the posterios pituitary lobe
- when stimulated via neural depolarisation and calcium influx they induce release of oxytocin and anti-diuretic hormone (ADH) via exocytosis
oxytocin and ADH are released directly into systemic circulation where they act on the kidneys (ADH) or on the mammary glands and uterus (oxytocin)
How is ADH activated? What are the factors affecting its release? What is its functions?
ADH is also known as vasopressin (AVP)
- activated via cleavage to a nonapeptide (9 aa)
factors affecting its release
- increased plasma osmolality
- hypotension
functions
- contraction of arteriolar smooth muscle resulting in vasoconstriction
- enhances water absorption by the kidney decreasing urine volume
What are the different receptors for ADH/AVP? How does it enhance water absorption?
V1 - pressor effect on arterioles and gastrointestinal smooth muscle
V2 - anti-diuretic effect in the kidney
V3 - anterior pituitary minor control in secretion of adrenocorticotrophin (ACTH)
AVP stimulates synthesis of aquaporin 2 (AQP-2) water channel proteins and their transport to the apical surface of collecting duct principle cells
- enhances water absorption
What is oxytocin? What is the function of oxytocin? What stimulates oxytocin release?
oxytocin is a peptide hormone
- it binds to and activates oxytocin receptors that function to mediate uterine contraction and facilitate milk ejection
oxytocin release is stimulated by
- elevated oestrogen levels
- sensory stimuli from stretch receptors in the cervix and vagina at the end of pregnancy
- suckling of the breast which induces contraction of myoepithelial cells during nursing of the infant
