Hypothalmic Pituarity Gondal Axis Flashcards
What are some of the characteristics of hypthalmic realeasing hormones?
Secretion in pulses to a biological clock
Act on specific membrane receptors
Transduce signals via second messengers
Stimulate realease of stored pituarity hormones
Stimuate sythensis of pituraty hormones
Stimulates hyperpalais and hypertrophy of target cells
Where would you find the pituarity gland?
Lies immeadatly below the hypthalmus, in a depression in the skull knwon as the pitaurity fossa, and also called the turkish saddle (sella turica)
What are the two lobes of the pituarity gland called?
The anterior lobe/adenohyposis/pars distalis
The posterior lobe/neurohyposis/pars nervosa
What are the emboroynic orgins of the two lobes of the pituarity gland?
Anterior lobe is derivied embroylogically from ectoderm lining the distal pharynx
The posterior portion is derived embryologically from neuroectoderm
What connects the anterior pituarity and the hypothalmus?
The superior hypopheseal atery,
What are the hormones produced by the anterior pituarity?
Produces 6 peptide horomes
Prolactin, growth hormone, thyroid stimulating hromone, adrenocrotiopic hormone, follicle stimulating hormone, and letuinising hormone
Where is GnRH sythesised?
The acurate nucleus of the medial base of the hypothalmus and the peptic areas
What are the two hormones that the pituarity realeases because of GnRH?
Leutisining hormone (LH) and Follicle stimulating hormone (FSH)
How does GnRH reach the pitaruity?
The hypophaseal portal system
In males, what receptors to the pituarity hormones act upon?
Gas PCR and adenylate cylase
What cells does LH have an action on in males and what does this produce?
The leydig cells and they produce testerone
What are the negative feedback properties of testosterone?
Testerone reduces the realease of LH from the anterior Pituarity, and reduced GnRH secretion from the hypothalmus
What are the actions of FSH in the male?
Acts on the sertoli cells of the seminiferous tubules, causing them to grow and secrete spermatogenic substances (which also needs some testosterone) and also produces inhibin
What is the aciton of inhibin in males?
Reduces FSH secretion selectively, if spermatogensis is increased then inhbin is realeased, and if spermatogenesis slows down than inhibin will not be realeased
How do we keep testosterone in the seminiferous tubules?
Protein antigen binding compoun, which binds to the testosterone and therefore keeps some within the tubules
Does the HPG axis in males vary at all?
In the medium to long term the levels are constant but there is a circadian rythum, that is highest in the early morning and there are some effects on environmental stimuli that are driven by the brain
What are the target cells of the hormones in women?
Target cells include the ovarian granulosa cells and then the theca interna
What cells does FSH act upon on in women and what does this cause?
The granulosa cells, and then porjects the oestrogens and progestins
What are the actions of oestrogen and progesterone on GnRH?
Moderate titres of osetrogen reduce GnRH secretion, whereas high tires of oestrogen in the ABSENCE of progesterone promote GnRH secretion and help to create the LH surge
What are the actions of progesterone of the GnRH axis?
Progesterone increases the inhbitroy affects of moderate titres of oestrogen, and prevents the postive feedback of high oestrogen, oestrogen reduces the GnRH per pulse whereas progesterone reduces the frequency of pulses
