Reproduction Flashcards
What is the male reproductive tract?
The male reproductive tract is external and consists of a penis and a pair of testes enclosed within the scrotum.
What are the testes?
The testes are gonads i.e. the structures responsible for the production of sperm - a process called spermatogenesis.
They are also the primary source of the male sex hormones known collectively as androgens.
The best known example of an androgen is testosterone.
The testes are composed of a series of coiled tubes called what?
Seminiferous tubules
What are the 2 important cell types in the seminiferous tubules?
- Sertoli cells which are responsible for sperm production
- Leydig cells which are responsible for testosterone production and release
Leydig cells are sometimes called interstitial cells.
Where do individual seminiferous tubules drain into?
Structures called the rete testes
What do the rete testes drain into?
The rete testes drain into a highly coiled tube called the epididymis, which in turn drains into the vas deferens.
The vas deferens from each testicle dilates and forms a structure called the ampulla of the vas deferens.
The ampulla merges with the outflow from the seminal vesicle to form a structure called the ejaculatory duct.
What is the general organisation of the male reproductive tract?
Figure 9.1 PG 133
What is the cross section through a testicle?
Figure 9.2 PG 134
What is the process of ejaculation?
The ejaculatory ducts enter the prostate gland, merge together, and enter the urethra which allows sperm and the secretions of various glands to be released from the penis.
What is ejaculated from the penis?
Whilst sperm are produced in the testes and mature as they move through to the epididymis, it is semen which is ejaculated.
What is semen?
Semen is a mixture of sperm and secretions of the seminal vesicle and prostate gland.
These secretions provide nutrients for the sperm cells, are alkaline ( to buffer the acidic secretions of the female reproductive tract) and contain anticoagulants.
What is a typical ejaculatory volume?
2 - 5 ml, 80% of which is made up from glandular secretions.
What is the production of functional sperm known as?
It is known as spermatogenesis.
This begins at puberty and continues, although at a reduced efficiency, until death
Once spermatogenesis is initiated how much sperm does a male produce each day?
Once spermatogenesis is initiated a male may produce 200 -250 million sperm a day.
What is the first step of spermatogenesis?
It is the production from diploid germ cells of cells called spermatogonia.
Diploid means that the cells have a full complement of chromosomes, i.e. 23 pairs comprising 22 pairs of autosomes and one each of the X and Y chromosomes (the so called sex chromosomes)
What does haploid mean?
Haploid
A cell that contains a single set of chromosomes. For example, human egg and sperm cells are haploid, containing 23 chromosomes.
What does diploid mean?
Diploid
A cell that contains two complete sets of chromosomes. For example, most cells in humans are diploid, containing 46 chromosomes in total.
How are primary and secondary spermatocytes formed?
Spermatogonia undertake 2 further mitotic cell divisions to form primary spermatocytes which are still diploid.
They then begin to undergo meiotic cell divisions to form structures called secondary spermatocytes.
How are spermatids formed?
Secondary spermatocytes undergo a further meiotic cell division to form spermatids. These are now haploid cells.
They contain one of each pair of autosomes and one of the sex chromosomes - making 23 chromosomes in total
What are autosomes?
any chromosome that is not a sex chromosome.
What is the final stage in the production of sperm?
Maturation and formation of sperm cells from the spermatids - a process called spermiogenesis
What is the cross section through a seminiferous tubule?
Figure 9.3 PG 135
What happens as the development from spermatogonia to sperm occurs?
As the development from spermatogonia to sperm occurs, the cells move through the Sertoli cells towards the lumen of the seminiferous tubules.
How long does it take to produce sperm cells from spermatagonia?
about 70 days
What is the structure of a typical sperm cell?
Figure 9.4 PG 136
What are the 3 regions of sperm?
- Head
- Mid-piece
- Tail
What does the head of the sperm cell contain?
The head contains the nucleus (which contains half the full chromosome number.)
Within the head is the acrosome. This contains hydrolytic enzymes whose function is to allow the sperm to penetrate the egg at fertilization.
How is the mid piece of the sperm characterized?
The mid piece is characterized by spirally arranged mitochondria
What is the tail of the sperm?
The tail of the sperm is motile, powered by the ATP produced in the mitochondria of the mid-piece.
The tail is a single flagellum and is identical to the 9 + 2 flagella seen in other organisms.
What do sperm cells lack?
Other intracellular organelles.
What is one of the roles of the testes?
Produce the male sex hormones (androgens) - primarily testosterone.
What are the multiple functions of testosterone?
Testosterone has a number of important functions:
- It stimulates sperm production
- It promotes the development of male secondary sexual characteristics at puberty
- Its anabolic effects include increased protein synthesis and muscle growth hence its use as a banned substance in sport
- Via its effect on the CNS, it increases libido.
What produces testosterone?
Leydig cells in the testes.
Where does the vast majority of testosterone go?
The vast majority enters the plasma however some enters the seminiferous tubules where it binds to androgen-binding protein and stimulates sperm production.
Why is it important that the levels of testosterone are regulated?
To ensure the male reproductive function is optimized
How is hormonal control of testicular function achieved?
By the hypothalamo - pituitary axis
Where is Gonadotrophin releasing hormone (GnRH) released from?
Gonadotrophin releasing hormone (GnRH) is synthesized and released from neurons in the hypothalamus.
What does Gonadotrophin releasing hormone promote?
It enters the portal blood vessels and travels to the anterior pituitary gland where it promotes the release of follicle stimulating hormone (FSH) and luteinizing hormone (LH)
What does LH do?
LH targets Leydig cells, where it promotes the release of testosterone.
What does FSH do?
FSH targets Sertoli cells, where it promotes the release of androgen-binding protein.
It also promotes the release of inhibin and the enzyme aromatase, which promotes the conversion of testosterone to the female sex hormone oestradiol (oestrogen.)
How does the released testosterone inhibit the release of further LH?
By reducing activity in both the hypothalamus and the anterior pituitary gland.
What does increased levels of inhibin and aromatase result in?
They inhibit activity in the hypothalamus and anterior pituitary gland and reduce FSH secretion.
What is the female reproductive tract responsible for?
The production of ova and the development of the foetus.
Following birth there is a variable period when the mother is the sole source of nutrients for the baby.
Is the female reproductive system internal or external?
The female reproductive system is internal in contrast with the male reproductive system.
What is the general organisation of the female reproductive tract?
Fig 9.5 PG 138
What are the paired ovaries?
The paired ovaries lie within the pelvis these are the gonads of the female reproductive tract.
They are responsible for ensuring that on a cyclical basis, an ovum (egg) is prepared for fertilisation.
Where do the fallopian tubes originate from?
Functioning with the ovaries are a pair of fallopian tubes, which originate from the uterus.
Where does sperm deposited in the vagina travel to?
The distal regions of the fallopian tubes where fertilization of the ovum occurs.
They then allow the fertilized egg to travel back to the uterus where it will initially implant in the uterus prior to the formation of the placenta.
What does distal mean?
Distal refers to sites located away from a specific area, most often the centre of the body
What are the 2 important regions of the uterus?
- The innermost lining called the endometrium which undergoes cyclical changes to ensure that a fertilized egg has an initial location for development to proceed prior to the formation of the placenta.
- The uterus also contains smooth muscle the myometrium. Activity in this muscle expels the foetus at the end of pregnancy.