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
Describe the structure of the testes
Are male gonads which are paired, ovoid structures– produce spermatozoa and male hormones– are suspended in the scrotum by the spermatic cords
Describe the tunica vaginalis
Have two layer of tunica vaginalis which cover the surface– visceral layer attaches everywhere except the epididymis and where the spermatic cord attaches to the testes– parietal layer lines the internal spermatic fascia and it extends onto the distal part of the spermatic cord. – have fluid between the two layers allowing for movement of the testes in the scrotum
Describe the outer layer of the testes
Is tough and fibrousIs known as the tunica albuginea– thickens into a ridge on posterior lateral side known as the mediastinum of the testis– fibrous septums extend form this ridge in between the seminiferous tubules
What are sertoli cells?
Are found in the seminiferous tubules and this is where spermatozoa development takes place.
What are Leydig/interstitial cells?
Cells which are found in the interstitial tissue which secrete testosterone.
Describe the vas deferens
Is a continuation of the epididymis and it has quite thick muscular walls and a small lumen. These muscles in the wall contract during copulation which forces sperm along the tube, mixing it with the other components of ejaculate.
Describe seminal vesicles
Secrete the thick alkaline fluid which is rich in fructose and a coagulating agent. It makes up 60% of the volume of semen. The duct of the seminal gland joins the ductus deferens to form the ejaculatory duct.
What are the bulbourethral glands?
Two pea sized glands which lie posterior and laterally to the intermediate part of the urethra. They are mostly embedded in the external urethral sphincter. The ducts of these glands open into the proximal part of the spongy urethra in the bulb of the penis.
What do the bulbourethral glands secrete?
They secrete a mucus like substance which enter the urethra during sexual arousal.
