1. Reproductive physiology Flashcards
What are the 2 main functions of the testes?
- Provision of androgens (primarily androgens) to initiate and sustain the male phenotype
- Production of mature sperm
Are the names of LH and FSH related to their biological action in males?
No
Where is sperm stored prior to ejaculation?
Epididymis
What happens to sperm at ejaculation?
- Pass through Vas Deferens (contractile)
- Mixed with fluid from the seminal vesicles
- Passes into urethra and mixes with secretions from the prostate gland
Where are the Leydig cells and what do they do?
- Outside the seminiferous tubules
- Primary source of androgens in all male mammals
- LH acts here
Where are the sertoli cells and what do they do?
- In the seminiferous tubules
- Support spermatogenesis
- Driven by FSH and testosterone
What does androgen binding protein (ABP) do?
Protein that binds to testosterone, to mediate its effects into the Sertoli cells
Describe the negative feedback to constrain the production of GnRH
- Testosterone from the Leydig cells feeds back to the hypothalamus and pituitary gland (also direct on LH and FSH)
- Inhibin from the Sertoli cells feeds back to the hypothalamus
Pulsatile manner
What makes up the majority of the tissue of the testes?
Seminiferous tubules (where sperm are made)
Which cells does the beginning of the production of all gametes start with?
Primordial germ cells
Can men produce sperm after the age of 70?
Yes, even though quality and quantity declines
What stimulates some development of ovarian follicles and 17β-oestradiol synthesis?
FSH
What stimulates progesterone production?
LH
What produces LHRH and what does it do?
- Produced by hypothalamus (pulsatile)
- Drives the pulsatile release of LH and FSH from the pituitary gland
(like GnRH)
Which cells are responsible for the production of oestrogens?
Thecal cells of the developing follicles
Which cells produce oestrogens/progesterone during the second half of the ovarian cycle?
Granulosa-luteal cells
When does oestradiol change from a negative to a positive feedback effect on the hypothalamus and pituitary?
- 17β-oestradiol rises before mid-cycle
- This drives a peak of LH (and FSH) in the MID-CYCLE - change to positive feedback
- LH drives ovulation
When does the cycle go back from a positive to negative feedback mechanism?
Luteal phase - but progesterone is mainly being produced from the ovary instead of oestrogen
(LH, FSH and oestrogen fall)
Why does the hypothalamic-pituitary axis switch off in pregnancy?
Continuous rising progesterone levels - negative feedback
Would a change in menstrual cycle length be due to the follicular or luteal phase length?
Luteal phase, as follicular phase is relatively constant
What is the range of the menstrual cycle?
21-35 days
can be up to 45 days in younger teenagers
What number of eggs will be turned into ova during a normal reproductive lifespan in a female?
450
What stage of development are eggs at just before puberty, and after?
Early stage of meiosis (that has been halted) - prophase I
• then resume at puberty
• go through final stages of folliculogenesis
• the longer they are held, the poorer the organisation of DNA
What does the dominant follicle become when it enters the second part of development, and what does this give rise to?
- Antral follicle
* Gives rise to the egg that is released
How long does it take for the growth of a follicle?
3 months
What division is linked to the LH surge?
First meiotic division, completed during the formation of the secondary follicle (Graafian follicle)
When does meiosis I start in a female?
During embryonic development
For the follicles that become secondary follicles, what stage do they pause at before fertilisation?
Metaphase of meiosis II
When does an egg need to be fertilised?
Within 24 hours of release
What happens when the nucleus of a sperm is released into the cytoplasm of the egg?
- Nucleus expands rapidly in size
- Converts itself into the male pro-nucleus (haploid)
- The egg completes meiosis and switches from 2n to n (haploid - 23 chromatids) - female pro-nucleus
- The pro-nuclei merge to form 2n
- DNA mixes and is duplicated (4n) - there are enough chromosomes for this
- Cell divides - first mitotic division
Which nerve/system is involved in the stimulation of the penis?
- Tactile - pudendeal nerve - afferent system
* Limbic system from brain (mesolimbic dopaminergic system)
What changes occur during an erection?
- Initiated by increased parasympathetic activity to the smooth muscle of the pudendal artery
- Increased activity of nitric oxide synthase => nitric oxide => increased cGMP
- Dilatation of arterial smooth muscle
- Counteracts with sympathetic-maintained myogenic tone
- Increased blood flow to corpus cavernosum
- This compresses the dorsal vein, restricting outflow
(similar reason for increased blood flow and growth of clitoris in a female)
What tissue protects the urethra during an erection?
Surrounding corpus spongiosum
What de-activates cGMP during an erection?
Phosphodiesterase
How does viagra work?
Inhibits phosphodiesterase from de-activating cGMP
Describe the process from the deposition of sperm to fertilisation
- Deposited near cervix
- Cervical mucus changes at mid-cycle to permit sperm to enter
- Passage through the uterus into the fallopian tube and ampulla, moving at 2mm/min
- Sperm meets the egg - acrosome reaction allowing penetration of Zona Pellucida and Coronal cells
How many chromosomes in sperm and oocyte (before fusion)?
Sperm - 23
Oocyte - 46 (then 23 after sperm fuses as it can carry on from metaphase II)
