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12.2.5

Human reproduction is the process are equipped with a tail which When the dominant follicle has for producing new life. It is the propels them along and helps them reached maturity (about cycle day process through which genetic to be carried by fluid movement up 12) it signals the brain to release a material is passed from generation to the reproductive tract (i.e. the burst of the luteinizing generation, and maintains the , , and fallopian tubes) to hormone (green line on diagram). continuation of the human species. In reach and penetrate the ovum. The This hormone starts a process called , the new sperm pass out of the testes into the that leads to the bursting of individual results from the coming male reproductive ducts where they the follicle within the next 40-48 together of two cells (): an are suspended in secretions which hours. On rupture the contents of the ovum produced by the female, and a form . The average volume of follicle including the single mature sperm produced by the male. The semen for each is 2.5 to pour into the . fusing of the two gametes is called 6 mls, and the average number of , and the resulting sperm ejaculated is 40-100 million which will grow into the new per ml. If intercourse occurrs within 48 hours individual is called a . Each of ovulation, then the sperm need to contributes half the genetic complete the long arduous swim material present in the zygote and, The reproductive cycle in female from the vagina, through the hence,in the new individual, half the is known as the menstrual and into the fallopian tube. Of the genetic material is provided by the cycle. The cycle is normally 28 days many millions (up to 200 million) that and half by the father. in length but can vary considerably started the journey only several between individuals. thousand survive to be in the

fallopian tube when the egg arrives.

Sperm are produced in the testes, One single sperm detects the egg the male reproductive organs. The Under the action of FSH (a hormone and with its last reserve of energy testes are located outside the main secreted by the brain) follicles (cyst penetrates the outer egg membrane body cavity in the scrotum, a pouch like structures on the ovary surface) and is engulfed by the egg of loose skin below the abdomen. are stimulated to grow (red line on cytoplasm. This is the process of The testes also produce the male diagram). Each follicle contains an fertilisation and within 24 hours cell hormone testosterone. Boys start egg, and there may be as many as 6 division occurs. The journey down producing sperm at follicles stimulated to grow. The the Fallopian tube takes 6 days in (approximately 15 years of age), and steroid hormone oestradiol is which time the fertilised egg has most men have mature sperm well secreted within the follicle and become a 130-160 cell structure into old age. Sperm are made at the provides a nurturing environment for known as a . rate of about 300 million per day, and the developing egg. (blue line on live about 48 hours after being diagram). The remains of the original ovulated deposited in the 's vagina. follicle becomes the corpus luteum

As development proceeds the and secretes a steroid hormone biggest follicle is able to scavenge all called (pink line on the FSH "starving" the other sister the diagram). Progesterone helps follicles which subsequently die. This prepare the uterus for when the leads to the development of a single blastocyst arrives, 6-8 days after dominant follicle. This process is fertilisation. complete by Day 10 of the .

Version 3 June 2015 Authorised by Peter Burton Page 1 of 2 Page 2 of 2

The blastocyst finds a suitable area, Males continuously produce sex In summary, for fertilisation to occur: hatches out of it's shell (zona and sperm but, in ,  sufficient numbers of sperm pellucida) and buries itself into the the production of sex hormones and must be deposited into the uterine lining. This is the process of the release of an ovum is vagina at the appropriate time in implantation. The blastocyst secretes intermittent, or cyclic, and is known the woman's menstrual cycle a hormone (chorionic gonadotrophin) as the menstrual cycle. A period of  an ovum has to be released and that signals the mother that the egg , lasting from two to enter the fallopian tube is implanted and is growing. This eight days, marks the beginning of a  the fallopian tube must not be hormone stimulates the corpus new cycle. The average length of a luteum to continue to secrete menstrual cycle is 28 days but it can blocked, in order for sperm to progesterone. vary from 21 days to 36 days, or even travel up, and so the fertilised ovum can move down and longer. Ovulation occurs at implant into the lining of the approximately Day 14 in a 28 day uterus. If the blastocyst does not implant or cycle, but occurs earlier in a short is not viable this stimulation does not cycle and later in longer cycles. (Note occur. The corpus luteum starts to that some women menstruate but do is an important regress (shrivel and die) by day 21 or not ovulate, i.e. no ovum is released component of human sexual 22 and progesterone levels fall (pink from the ovary.) When an ovum is behaviour. It is usually accompanied line on the diagram). present , there is a relatively short by much pleasure for both people, period of approximately 24 to 48 which forms the basis of the strong hours when the woman is fertile. bond which develops between Soon after, the process of During this fertile period, sperm must sexual partners. Sexual intercourse menstruation (shedding of the be present in the fallopian tube and may result in and is a uterine lining) occurs and the cycle be able to reach the egg. Only one component of reproduction. starts again. On average only one in sperm is required to fertilise the five cycles in which fertilisation has ovum but in order for this to occur occurred will result in implantation there must be a minimum of 40 and ongoing pregnancy. million sperm per ml in the semen deposited in the woman's vagina. If Contact Us the ovum is not fertilised, it dies. 218 Nicholson Road Subiaco WA 6008

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