Endocrinology 10 - The Gonads I Flashcards
What are the function of the gonads?
- Gametogenesis (production of gametes)
- Males = Spermatogenesis.
- Females = Oogenesis. - Steroidogenesis (production of steroid hormones)
- Males = Androgens (small amounts of oestrogen + progesterone).
- Females = Oestrogen + progesterone (small amounts of androgen).
When are germ cells activated? Where do male and female germ cells derive from?
- They are activated during embryogenesis where germ cells proliferate reaching around 6-7 million.
- Male germ cells are called spermatogonia and female germ cells are called oogonia.
Describe spermatogonia levels in males throughout life.
During childhood, spermatogonia are dormant and are only activated during puberty. Spermatogonia levels remain high throughout life in males.
Describe oogonia levels in females throughout life.
- Oogonia levels reach a maximum at 24 weeks, after this no more oogonia are produced so there are only a finite number of eggs.
- The number of oogonia decrease (atresia) throughout life, rapidly at first.
- At menopause the ovary is depleted of oogonia.
What is Atresia?
When the cells start degenerating and dying off.
Explain the process of spermatogenesis.
- Germ cells in embryogenesis multiply and differentiate into spermatogonia (DIPLOID).
- During puberty = high levels of FSH + testosterone cause spermatogonia to divide by mitosis - either more spermatogonia or primary spermatocytes (DIPLOID).
- Primary spermatocytes enter 1st meiotic division = Secondary spermatocytes (HAPLOID).
- Secondary spermatocytes enter 2nd meiotic division = spermatids.
- Spermatids mature and differentiate into spermatozoa.
Explain the process of oogenesis.
- Germ cells multiply to produce oogonia (DIPLOID).
- Oogonia multiply to produce primary oocytes (DIPLOID).
- Primary oocytes enter 1st meiotic division, however halted at prophase = form primordial follicles.
- Primary oocytes are dormant for 12-50 years - atresia takes place as well.
- When puberty starts, some primary oocytes will be rescued by increased levels of FSH (ovulation) = secondary oocytes + polar body.
- Secondary oocyte enters 2nd meiotic division and will only complete it during fertilization = ovum + polar body.
What is a polar body?
- In female meiosis, there is an unequal distribution of cytoplasm.
- One cell retains all the cytoplasm and the cell resources and the other daughter cell only contains the chromosomes and will die off - this is the polar body.
Describe the journey of spermatozoa.
- Spermatogenesis takes place in the seminiferous tubules.
- Semiferous tubules are lined with layers of spermatogonia and sertoli cells.
- Spermatozoa travel down to Rete testis and they are concentrated and drained by the Vasa efferentia into the epididymis (highly coiled) where they are stored.
- In the epididymis, nutrients are secreted for them and they mature here.
- They are propelled by vas deferens (surrounded by smooth muscle) via the urethra.
Where do the testes develop?
They develop in the abdomen and descend into the scrotum just before birth.
The scrotum is 2-3 degrees cooler than core temperature = critical for spermatogenesis.
Describe the function of sertoli cells. (4)
- Sertoli cells line the seminiferous tubule and form tight junctions that prevent large proteins (e.g. antibodies) getting inside to the spermatozoa. This forms a blood-testis barrier.
- Sertoli cells also provide structural and metabolic support.
- Synthesize FSH and androgen receptors.
- Produce inhibin in response to FSH (negative feedback for FSH).
How do spermatogonia get through the sertoli cell layer?
- They are enclosed in the cytoplasm of the sertoli cells.
- Here they undergo spermatogenesis.
- As they develop, they move towards the lumen and are released into the lumen.
What are Leydig cells? (3)
- Leydig cells are located close to the seminiferous tubule.
- Produce LH receptors.
- They contain enzymes that allow them to synthesize and release testosterone in response to LH.
Where does oogenesis take place?
In the ovaries. The ovaries contain follicles at all stages of development (e.g. some will be undergoing atresia).
What is a graafian follicle?
A follicle which has reached its maximum size and is ready for ovulation.