Gamete formation Flashcards
Where are germ cells found in the male?
They colonise the sex cords in the primordial gonad – will develop into the testes
What will the sex cords become?
They will hollow out at puberty to form the seminiferous tubules which the spermatagonia clustering around the periphery of the lumen
Where do you find the seminiferous tubules?
The tubules are found circling the outer edge of the testes, with the open end of the blind ended tube draining into the rete testes. There are about 250-750 tubules per testis.
What do the seminiferous tubules drain into?
The rete testis which then drain into the ducti efferentes, to the epididymis and then to the vas deferens
How do the numbers of spermatagonia remain the same?
They are maintained by mitosis which produces a population of self-regenerating stem cells. After each division, two identical daughter cells are produced.
What are the two types of stem cells which are produced from spermatogenesis?
Type A and Type B cells
What are the difference between Type A and Type B cells?
Type A cells will replace the stem cells and Type B cells will go on to produce spermatozoa.
What does a single type B spermatozoa produce?
It undergoes a series of mitotic divisions to produce (usually 64) primary spermatocytes which are linked together by cytoplasmic bridges
What happens to the connected spermatocytes?
They move in from the periphery of the tubules towards the lumen and being the meiotic process, initially producing two haploid secondary spermatocytes and then four spermatids.
What happens once the spermatozoa have been produced?
The cytoplasmic bridges break down and the sperm are released into the lumen to be washed down to the rete testis and onwards, by the fluid secreted from sertoli cells.
What is spermatogenesis?
The remodelling process of spermatagonia to from spermatozoa.
How long does spermatogenesis take?
70 days in total. – new groups of A1 apermatagonia arise every 16 days, so there are four processes occuring at once.
Why are there multiple stages of spermatogenesis occuring at once?
The process begins at different times in different parts of the tubules.
When are sperm fully matured?
As they pass through the epididymis– it is also the main storage area for sperm
What happens during copulation?
The vas deferns contracts and causes sperm to be mixed with the other components of semen. This is known as emission.
What are the components of semen?
– secretions of seminal vesicles (60% of volume)– secretions of prostate (20% of volume)– sperm– secretions of bulbo-urethral glands
What is the spermatogenic cycle?
The development of a A1 Spermatogonia through to 256 sperms. The amount of time it takes for reappearance of the same stage of the cycle within a given segment of the tube.
What is the spermatogenic wave?
Different parts of the tube begin the spermatogenic cycle at different times, in a ‘wave’, so the production of sperm is constant. The distance on the tube between parts that are in the same stage is the spermatogenic wave.
What reproductive hormones are produced by the hypothalamus?
– Gonadotrophin Releasing Hormone (GnRH)– Prolactin Releasing Hormone (PRH)– Prolactin Inhibiting Hormone (PIH)
What reproductive hormones are produced by the posterior pituitary gland?
Oxytocin
What reproductive hormones are produced by the anterior pituitary gland?
– Follicle Stimulating Hormone (FSH)– Luteinising Hormone (LH)– Prolactin
What reproductive hormones are produced by the testes?
– Testosterone– Inhibin– Mullerian Inhibiting Hormone (MIH)
What reproductive hormones are produced by the ovaries?
– Oestrogen– Progesterone– Inhibin
What reproductive hormones are produced by the placenta?
– Human Chorionic Gonadotrophin (hCG)– Human Placental Lactogen (hPL)– Oestrogen– Progesterone
