Lecture notes
Reproductive endocrinology
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- Aston University, Birmingham (Aston)
In depth cell signalling and physiology notes, created using synchronous and asynchronous material.
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Reproductive endocrinology.Male reproductive physiology.
In order to produce functional sperm, there needs to be a site for the production and
storage of sperm, a route by which the sperm can exit the male body and reach the
egg as well as mechanisms to nourish those sperms, so that they are healthy and in a
good state for fertilisation.
The site of sperm production is the testes. This is where the sperm will develop and
it is also the major site of testosterone production, in the male reproductive system.
The sperm then mature in the epididymis, and they are stored here before exiting via
the ductus deferens.
As the sperm pass through the ductus deferens, they encounter the seminal vesicle,
this organ will secrete seminal fluid. The seminal fluid will contain fructose, to keep
the sperm well nourished, and prostaglandins, which will stimulate sperm motility.
The seminal vesicle will also introduce clotting factors into the seminal fluid, and
these are important to increase the viscosity of the sperm deposits once it has been
left within the female reproductive tract.
The prostate gland also contributes important molecules to the seminal fluid, so it
will release factors that are responsible for making the vaginal environment more
alkaline and the change in PH within the vagina will trigger those clotting factors that
have been provided via the seminal vesicle.
Cells of the testes.
Sertoli cells
These are a group of cells that form the blood testes barrier. They form this barrier
because they are very closely associated with one another, and tight junctions form
between the cells.
They provide the main source of nourishment for the developing cell.
They are also phagocytic so they will engulf any potential pathogens.
They are also responsible for secreting fluid to flush the developing sperm into the
epididymis for storage.
In terms of hormonal regulation, they are important because they secrete androgen
binding protein (ABP). The secretion of ABP by the Sertoli cells is important to
maintain high testosterone levels, within the testes.
Sertoli cells within the testes are the main site of action of testosterone within the
male gonad.
Sertoli cells are arranged into seminiferous tubules.
Leydig cells
These are interstitial endocrine cells, that sit within the connective tissue that lies
between adjacent seminiferous tubules.
These cells within the testes synthesis and secrete the male sex hormone
testosterone.
They are very well supplied with blood, through lots of capillaries that lie adjacent to
them.
Spermatogenesis
, This is a continuous process that takes 2 months for a single sperm to mature.
200 million sperms present at any one time.
Female reproductive anatomy.
We have ovaries, this is the site at which the egg develops.
Once the egg is released from the ovary, it will travel along the oviduct towards the
uterus.
Within the oviduct fertilisation will occur and the uterus is where any fertilised eggs
will implant, this will occur within the endometrial lining.
Phases of the female reproductive cycle.
Female reproductive cycle is cyclical in nature.
There are 3 distinct phases within the cycle.
Phase 1: follicular phase:
This is the stage at which the primary follicles start to grow, into mature follicles.
Once the egg and the follicle have matured, the egg will be released from the ovary
during ovulation (phase 2).
Once ovulation has occurred, the ruptured follicle will then develop into a
specialised endocrine organ called the corpus luteum (phase 3). This endocrine
organ will secrete the hormone progesterone.
If the egg is not fertilised, then the cycle will progress. The corpus luteum will
degenerate, and the cycle will start again.
If the egg is fertilised, so if pregnancy occurs, then the corpus luteum will be
maintained, and it will continue to secrete progesterone.
The continued secretion of progesterone will halt the cycle at this stage.
Hypothalamic-pituitary-gonadotrophin (HPG) axis.
Gonadal function, in both male and female is regulated by the same hypothalamic
pituitary gonadotrophin or HPG axis.
We start with a stimulus which is puberty, this signal will be received by the
hypothalamus, and stimulate cells within the hypothalamus to release gonadotropin
releasing hormone (GnRH).
The hypothalamic nuclei which is responsible for the release of GnRH is the arcuate
nucleus.
Once GnRH is secreted, it will then travel from the hypothalamus to the anterior
pituitary, where it will stimulate gonadotrophs within the anterior pituitary to
release two hormones: luteinising hormone (LH) and follicle stimulating hormone
(FSH). These are the gonadotrophic hormones; they are released in both males and
females.
These two hormones will be released into the circulation, they will then travel to the
gonad, either the testes or the ovaries.
In the testes they will stimulate the release of testosterone and in the ovary they will
stimulate the release of oestradiol and progesterone.
All endocrine axis have feedback to regulate the release of these upstream hormonal
signals.
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