BIOLOGY REPRODUCTION

Different mammals have different patterns of reproduction
mammals, rats and mice can breed all year round, whereas others have distinct breeding seasons. This is to ensure that the young are born when food is abundant. The timing of the breeding season is regulated by a biological clock, which is probably adjusted by seasonal changes in day length.
In mammals the gametes (sex cells) are:
• small motile male gametes (sperm) whish is produced in large quantities
• larger, non-motile food storing female gamete (ovum) which is produced in much smaller numbers
Gametogenesis is the formation of gametes
• sperm production is called spermatogenesis
• where the eggs are formed (matured) is called oogenesis
In the females of all mammals, there is a cycle known as:
• Oestrous cycle 􀃆 ovulation, when the female is most fertile
• Menstruation cycle 􀃆 the uterus lining in all mammals undergoes a similar pattern of thickening during a reproductive cycle. However if fertilisation does not occur, the uterine lining of primates breaks down and it is discharged with blood through the vagina, whereas the uterine lining of non-menstruating mammals is reabsorbed and there is no excessive bleeding. The discharge of blood is called menstruation.


Hormonal Control of the Female Menstrual Cycle
• Lasts approximately 28 days in Humans.
• It is controlled by the interaction of several hormones. The action of one hormone is used to stimulate or inhibit the production of another. Hormones are chemical messengers, produced and secreted by organs, which travel via the blood, and exerts some influence upon a target tissue.
• Events are divided into three phases: follicular phase, ovulatory phase, and the leutal phase
o The follicular phase is the first part of the menstrual cycle, where one or more follicles start to develop into a mature female gamete. The follicle cells surround the oocyte (developing egg cell), and produce hormones that trigger other responses
o The Ovulatory phase is when the oocyte is released (follicle cells remain in the ovary) from the ovary and passes down the fallopian tube and towards the uterus
o The Luteal phase most of the follicle cells remain in the ovary after ovulation. They continue to develop and form a structure called the corpus luteum, as a result more hormones are produced
The ovaries are organs that are responsible for the development of female gametes. At birth around 400 000 cells have reached prophase of the first meiotic division and are called primary oocytes (often called follicles). Each month after puberty, one of these cells completes its development into an ovum.