Tuesday, July 14, 2009

[Science Form 3] Course Of Nature

Menstruation is the blood discharge from the uterus through the vagina of a female every month. A menstrual cycle takes an average of 28 days, and begins 14 days following ovulation.

Ovulation is the release of a mature ovum from the ovary. The ovum travels into the uterus and is ready for fertilisation. Usually, ovaries take turns to release the ovum.

The fertile phase is the period in which ovulation occurs.

Changes in the males during puberty

When a baby boy is born, he has all the parts of his reproductive system in place, but it is only when he reaches puberty that he is able to reproduce.

Puberty usually begins when one is nearing the ages of between 10 and 14. The pituitary gland, which is located in the central part of the brain, secretes hormones that stimulate the testicles to produce testosterone.

The production of testosterone brings about several physical changes. During the first stage of male puberty, the scrotum and testes grow larger.

Then, the penis becomes longer, and the seminal vesicles and prostate gland start to grow. Hair begins to appear in the pubic are and later, on the face and underarms.

During this time, the voice also deepens. A male who has reached puberty produces millions of sperm cells every day.

Changes in the females during puberty

When a baby girl is born, her ovaries contain hundreds of thousands of eggs, which remain inactive until puberty begins.

At puberty, the pituitary gland starts making hormones that stimulate the ovaries to produce female sex hormones like estrogen.

The secretion of these hormones causes a girl to develop into a sexually mature woman. The hormones also stimulate physical development, such as growth and breast development.

Usually, a girl gets her first menstrual period about 2 to 2.5 years after her breasts begin to develop.

Menstrual cycle

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