Repro 2 Flashcards
What 4 events are needed for successful reproduction?
Fertilisation
Support of conceptus, embryo and foetus
Birth at the correct time
Support of the neonate
What is the HPG axis?
The interaction between the hypothalamus, pituitary gland and the gonads
What does the HPG axis regulate?
Development
Reproduction
Ageing etc.
What does the hypothalamu-pituitary part of the HPG regulate/control?
Hint: 3 glands 4 processes
Thyroid Adrenals Reproductive glands Somatic growth Lactation Milk secretion Water metabolism
Where is the pituitary gland situated?
Base of brain, below hypothalamus but connected by stalk with nerve fibres/blood vessels
In which specific structure is the pituitary located in the skull?
Sella Turcica
What are the other names for the anterior and posterior lobes of the pituitary?
Anterior - pars distalis
Posterior - pars nervosa
What is the visual differentiating feature between the anterior and posterior lobes of the pituitary?
Staining - the anterior is darker
What structural features differentiate the anterior and posterior lobes of the pituitary?
Tissue composition - Anterior is glandular while posterior is nervous
What does the posterior lobe of the pituitary (neurohypophysis) secrete?
ADH & Oxytocin
What is the origin of the posterior pituitary?
Hypothalamus - the lobe is an outgrowth of it, allowing neurons to pass through the stalk (median eminence)
What is the origin of the anterior pituitary gland?
Rathke’s pouch
What connects the anterior lobe of the pituitary to the hypothalamus?
Hypophyseal artery
Which 6 peptide hormones are secreted by the anterior pituitary?
Prolactin GH TSH ACTH FSH LH
How does the hypothalamus control the anterior pituitary?
Hormone releasing hormone -> Hypophyseal-portal circulation -> pituitary releases hormones -> these negatively feedback to hypothalamus
What are the characteristics of hypothalamic releasing hormones?
Hint: 6
Secreted in pules related to “body clock”
Transduced via 2nd messengers
Stimulate release of already stored pituitary hormones
As well as synthesis of these hormones
Stimulate hyperplasia AND hypertrophy of target cells
Regulate their own receptors
Name and action of the hypothalamic releasing hormones please
Hint: 7, most of which do what they say on the tin
CRH - ACTH secretion TRH - TSH and prolactin secretion GHRH - GH secretion Somatostatin - inhibits GH GnRH - LH & FSH secretion PRH - prolactin secretion Dopamine - inhibits prolactin secretion
What are gonadotrophs?
Anterior pituitary cells (5-10% of them) that secrete LH&FSH
How do FSH&LH exert their effect?
Gs-PCReceptors
Briefly describe the secretory mechanisms of GnRH
Hint: 4 main steps
Hypothalamus secretes GnRH -> Anterior pituitary secretes FSH&LH -> Gonads secrete steroids -> Steroids act on reproductive tract or +ly/-ly feedback on pituitary or hypothalamus
Which male gonadal hormone(s) act on GnRH secretion and how?
Testosterone - reduces GnRH secretion
Which female gonadal hormone(s) act on GnRH secretion and how?
Oestrogen - action is different at varying titres
Moderate titres: -ve feedback
High titres: +ve feedback
What is the significance of high levels of oestrogen?
Causes LH surge
On the other hand, what does progesterone do regarding GnRH in females?
Increases inhibitory effect of moderate oestrogen
Prevents +ve feedback of high oestrogen
What, then, is the significance of progesterone?
Prevents the LH surge
Which male gonadal hormone(s) act on the pars distalis and how?
Testosterone - reduces LH&FSH secretion
Which female gonadal hormones act n the pars distalis and how?
Oestrogen - again varying effects as titres change
Moderate titres - reduces LH&FSH secretion
High titres - increases LH&FSH secretion
Which hormone, present in both sexes, also acts on the pars distalis and how?
Inhibin - selectively reduces FSH secretion & is related to developing gametes
Describe the actions of LH in the male
Stimulates Leydig cells in testcles to produce testosterone
Describe the actions of FSH in the male
Stimulates Sertoli cells to produce androgen binding globulin & inhibin
Describe the function of androgen binding globulin in the male
Keeps testosterone bound in seminiferous tubules
Describe the function of inhibin in the male
SUpports spermatogenesis and inhibits the production of LH, FSH and GnRH
What do increased levels of testosterone and inhibin cause in the pituitary and hypothalamus?
Negative feedback
The hormone levels in the male HPG axis must remain constant in the long term, how and why is this?
Spermatogenesis is continuous - the male reproductive system must be ready at all times
It is achieved by negative feedback loops
Briefly describe the negative feedback of inhibin and testosterone
Both from the gonads
Inhibin effects the pars distalis
Testosterone effects the hypothalamus
What do LH&FSH stimulate the production of in the female?
Oestrogen & inhibin
Define Ovarian cycle and Uterine cycle
Ovarian - preparation of the gamete
Uterine - preparation of the endometrium
Briefly describe the hormone profile at the start of the menstrual cycle
Hint: some not present at all, some low and some on the rise
No ovarian hormone production
Low steroid and inhibin levels
FSH on the rise
Decribe the changes to the follicle (and its surroundings) as FSH binds
FSH binds to granulosa cells
Theca interna appears
Follicle can now secrete oestrogen
Inhibin secretion begins
Which two processes are vital to the mid-follicular phase?
Increased LH from +ve feedback of follicular oestrogen
Follicular inhibn rises selectively reducing FSH production at pars distalis
What hormone changes occur in preparation for ovulation?
Hint: 4 hormones
Circulating oestradiol and inhibin rise rapidly (osetradiol production no longer dependent upon FSH)
LH surge
Progesterone production begins
Following progesterone production what change occurs in the granulosa cells?
They become responsive to LH
What does the luteiniesed follicle secrete?
Hint: 3
Inhibin
Oestrogen & progesterone (in large quantities)
What phase is established after the follicle is luteinised and how?
Waiting phase - LH is suppressed by progesterone secretion
What is the luteal phase?
When the corpus luteum develops
What does the corpus luteum produce?
Progsterone, oestrogens and inhibin
What happens to the corpus luteum in the absence of an LH rise?
Spontaneous regression
What follows the regression of the corpus luteum?
Fall in gonadal hormones
relief of negative feedback
Resetting of the cycle
If fertilisation occurs, what maintains the luteinising effect and how?
Syncytiotrophoblast via human chorionic gonadotrophin production
What arte the timelines of the uterine and ovarian cycles?
Ovarian; Follicular - days 0-14, Luteal - days 14-28 (0)
Uterine; Proliferative - days 4-14, Secretory - days 14-28
How long is the menstrual cycle?
21-35 days (+/- 1 week from 4)
WHat causes variation in cycle duration?
Variation in length of follicular phase
List some factors affecting the menstrual cycle
Hint: 4
Pregnancy (obviously)
Lactation
Emotional stress
Low body weight
