explain the testes
- testes are located outside of the abdominal cavity and within the scrotal sac
- in most males, the testes will descend into the scrotum int he last months of fetal life
explain the descension of the testes
- for the majority of premature male babies, the testes will descend in early childhood
- in some cases, the testes remain within the body cavity
- should they remain undescended into adulthood, this condition is called cryptorchidism and results in sterility
what is the significance of the location of the testes
- important to the primary role of the testes, spermatogenesis
- the temperature within the scrotum averages several degrees celcius less than normal body (core) temp
- descent of the testes into the cooler environment is essential, because spermatogenesis is temperature sensitive and cannot occur at normal body temp
- an individual with cryptorchidism is unable to produce viable sperm
what happens when the testes are too hot/cold
- when they are too cold for spermatogenesis, the scrotal muscles (cremaster muscle and the dartos muscle) contract to bring the testes closer to the body to gain heat
- when they are too hot for spermatogenesis, the scrotal muscles relax to move the testes away from the body
- the majority of the testes consists of coiled seminiferous tubules in which sperm are produced
explain testosterone in the testes
- within the connective tissues between the seminiferous tubules are Leydig cells
- once secreted by these cells, some testosterone enters the bloodstream and circulated to distant target cells
- most of the testosterone enters the lumen of the seminiferous tubules where it supports sperm production
what are the effects of testosterone before birth
causes the masculinization of the reproductive tract and external genitalia as well as the descent of the testes into the scrotum
what are the effects of testosterone on sex-specific tissues after birth
it maintains the reproductive tract throughout adulthood, promotes spermatogenesis, and promotes maturation of the reproductive system at puberty
what are the effects of testosterone on other reproductive effects
develops sex drive at puberty and controls the secretion of gonadotropin hormone
what is the effect of testosterone on secondary sexual characteristics
causes voice to deepen, development of male pattern of body hair, and promotion of muscle growth (protein anabolism)
what is the effect of testosterone on non-reproductive actions
- promotes bone growth at puberty and plays a role in the closing of the epiphyseal plates
- can also induce aggressive behaviour
explain the seminiferous tubules
- within the testes are the highly coiled seminiferous tubules which are the location of spermatogenesis
- the majority of the seminiferous tubules are composed of two cell types: germ cells and sertoli cells
what is spermatogenesis
the process in which diploid (46 chromosomes) primordial germ cells are converted into motile sperm cells with a haploid (23 chromosomes) set of chromosomes
explain the first step of spermatogenesis - mitotic proliferation
- the primordial germ cells are called spermatogonia and they are located in the outermost layer of the seminiferous tubule
- these cells continuously undergo mitotic division to create a constant supply of new germ cells
- following each division, one of the daughter cells remains at the outer edge while the other starts to migrate towards the lumen of the tubule
- this sperm-forming daughter cell will undergo mitotic divisions twice more to produce 4 identical primary spermatocytes that enter a resting phase in preparation for meiosis I
explain the second step of spermatogenesis - meiosis
- each primary spermatocyte forms two secondary spermatocytes, each with 23 double stranded chromosomes
- during meiosis II, each secondary spermatocyte results in 2 spermatids, each with 23 single stranded chromosomes
- at this point there are no further divisions
- for each spermatogonia, 16 spermatids can be produced
explain the third step of spermatogenesis - packaging
- the final maturation of spermatids into spermatozoa is the process of packaging
- during this phase, the cells are stripped down of all non-essentials such as the cytosol and most organelles
what are the 4 parts of a mature spermatozoa
- Head: consists of the nucleus
- Acrosome: enzyme-packed vesicle at the tip of the head that is needed to penetrate the ovum
- Midpiece: packed full of mitochondria to provide energy for locomotion
- Tail(Flagellum): movement of this provides propulsion (a process that requires lots of ATP)
what are sertoli cells
- a single layer of sertoli cells makes up the walls of the seminiferous tubules
- they are connected to their neighbours by tight junctions, but during the process of spermatogenesis, developing sperm cells pass between them as they migrate towards the lumen
- developing sperm cells are essentially engulfed in the sertoli cells as they migrate towards the lumen when the sperm head remains embedded until it is mature
what are the 6 functions of sertoli cells for spermatogenesis
- the tight junctions which exist between sertoli cells form the blood testes barrier. for a substance to reach the intratubular fluid it must pass through the sertoli cells. this allows sertoli cells to control the intratubular environment optimal for developing spermatozoa
- nourish sperm cells
- absorb developing sperm cytoplasm and remove any defective germ cells
- secrete siminferous tubule fluid into the lumen to flush released sperm into the epididymis for storage
- secrete androgen-binding protein that helps to concentrate testosterone in lumen
- site of action for testosterone and FSH to regulate spermatogenesis
explain the hormonal regulation of testosterone and spermatogenesis
- the testes are under the control of LH and FSH
- in males, LH stimulates the Leydig cells to secrete testosterone and FSH acts on Sertoli cells to stimulate spermatogenesis and secrete inhibin
- testosterone has a direct negative-feedback pathway at the level of both hypothalamus to decrease GnRH release and at the antierior pituitary to decrease LH and FSH release
- the inhibin released by Sertoli cells feeds back to anterior pituitary to decrease FSH release
what are the 2 components of the male reproductive tract
- epididymis and ductus deferens
- male accessory sex glands
explain the epididymis and ductus deferens
- after sperm are produced in the seminiferous tubules, they are swept into the epididymis, which is a tightly coiled tube around 5m in length
- when sperm enter the epididymis they are not motile, mainly due to low pH in this region
- the epididymal ducts from each testis converge to form the ductus deferens of each testis empties into the urethra
- sperm can be stored for months in the epididymis
explain male accessory sex glands
there are 3 primary accessory sex glands whose secretions make up the bulk of semen and they function to provide support for the continuing viability of sperm inside the female reproductive tract
what are the 3 accessory glands in males
- seminal vesicles
- prostate gland
- bulbourethral glands
explain seminal vesicles
- there are 2 seminal vesicles, one that empties into each of the ductus deferens just before the urethra
- their purpose is to provide the bulk of the semen, supply fructose as an energy source for ejaculated sperm, secrete prostaglandins to cause smooth muscle contractions in both the male and female reproductive tracts, and to secrete fibrinogen
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