Male reproduction system Flashcards
What are male’s primordial germ cells? Where can they be found? How do they differentiate?
Primordial germ cells are undifferentiated cells that, by undergoing further division, they become gametes (spermatozoa).
Spermatogonia remain dormant from the 6th week of embryonic development until puberty, when sexual maturation is reached: these cells are stored in the seminiferous tubules.
After a first mitosis, the two daughter cells will take different paths:
- Type A: one cell will remain spermatogonia, by keep dividing via mitosis, to maintain spermatogonia population. (Symmetric division)
- Type B: the other cell will undergo meiosis and it will be destined to develop into sperm. (Asymmetric division). All four daughter cells will become spermatozoa.
What is spermatogenesis?
Spermatogenesis is the production of spermatozoa, with the differentiation and specialisation of spermatogonia into spermatozoa:
- Mitosis: spermatogonia divide by mitosis to produce two diploid daughter cells:
- one remain spermatogonium (Type A)
- one differentiates into primary spermatocyte
- Meiosis I: the primary spermatocyte begin meiosis I, forming two secondary spermatocytes.
- Meiosis II: the secondary spermatocytes will differentiate into four spermatids, which are haploid, immature gametes.
- Spermiogenesis: the spermatids differentiate into spermatozoa.
- Maturation: the spermatozoa lose contact with the wall of the seminiferous tubules, entering the lumen and is transported to the penis via cilia, since it is structurally mature but still functionally immature. The ability of self-propulsion will be gained after capacitation.
What is spermiogenesis?
Spermiogenesis is the maturation of spermatids into spermatozoa: this process is called “cytodifferentiation”, since from an immature, general cell mature, specialised cell is produced.
Spermiogenesis is assisted by nurse/sustencular/sertoli cells, which have a supportive role.
Mature spermatozoa lacks of all organelles, due to its reduced size and its need to absorb fructose from the environment. In addition, the only goal of the spermatozoa is to fertilise an oocyte, thus organelles are useless.
What is capacitation and why is it necessary?
Capacitation is the process that spermatozoa have to undergo to, to obtain motility and the ability of fertilisation:
- Spermatozoa is mixed with secretions of seminal vesicles and it becomes motile.
- Spermatozoa is exposed to the female reproductive tract and it becomes capable of fertilisation and more motile. This is because the female tract is rich of lipoproteins, that cause the loss of cholesterol and inhibitors of sperm-egg binding.
Capacitation is regulated by the internal calcium concentration [Ca2+].
- Low calcium concentration cause sperm to remain attached to isthmus, to maintain longevity and function.
- High calcium concentration cause the sperm to detach, enabling more vigorous motility.
Why are accessory glands so important?
The accessory glands are glands that allow complete formation of the seminal fluid.
95% of the seminal fluid volume is secretion of accessory glands, while only 5% of it is secretions of seminiferous tubules and epydidymis.
The glands are:
- Seminal gland/vesicle
- Prostate gland
- Bulbourethral glands/Cowper’s glands
Their main functions are:
- Activation of spermatozoa
- Provision of nutrients needed for motility to spermatozoa
- Propulsion of spermatozoa and fluids along the reproductive tract, mainly by peristaltic contraction of the smooth muscles but also by cilia
- Production of buffers, needed to maintain a neutral environment an counteract the acidity of urethral and vaginal environment
Which hormones are released? From which organs? Why are they essential?
The hormones that are released in the reproductive tract are:
- GnRH (gonadotropin-releasing hormone)
- LH (luteinizing hormone)
- FSH (follicle-stimulating hormone)
- Testosterone
- Inhibin
The organ that release this hormones are:
- Hypothalamus
- Pituitary gland
- Testes
The hypothalamus release GnRH that stimulate the pituitary gland to secrete LH, responsible for the secretion of androgens, and FSH, responsible for the promotion of spermatogenesis and secretion of ABP and inhibin; this two hormones stimulate respectfully interstitial cells and seminiferous tubules: interstitial cells are responsible for the secretion of Testosterone, the most important androgen, which stimulate a variety of effects, but inhibit via negative feedback the GnRH; seminiferous tubules stimulate the sustencular cells that, other that stimulate spermatogenesis and spermiogeensis, they synthesise ABP (Androgen Binding protein), responsible for the high concentration of testosterone in spermatogenic cells, and secrete inhibin, responsible for the inhibition of FSH, suppression of GnRH secretion and acceleration of sperm development.
Give an overview of the testes.
The testes are the organs responsible for the secretion of testosterone. They support blood and lymphatic vessels and sperm.
The testes are covered by the tunica albuginea, a layer of connective tissue, that form the septa testis, a fibrous partition. These septa testis subdivide the testis into lobules with each contain 800 seminiferous tubules, responsible for the production of sperm. These tubules are connective tissues and interstitial endocrine cells (Leydig cells).
Does hormones affect only spermatogenesis?
Testosterone not only affect spermatogenesis, but also:
- has effects on the CNS
- stimulate bone and muscle growth
- establish and maintain male secondary sex characteristics
- maintain accessory glands and organs
Why sustentacular cells are so important?
- maintain blood testis barrier to isolate seminiferous tubules from general circulation, to preserve the differences between luminal and interstitial fluid and to prevent that the immune system attack the new spermatozoa.
- support mitosis and meiosis.
- support spermiogenesis.
- secretion of various hormones, such as inhibitin and androgen-binding proteins.
