SECONDARY SEXUAL CHARACTERISTICS

Male Sexual Characteristics

Testerone is the main androgen that stimulates the development of secondary sexual characteristics. Broadening of the shoulders. Deepening of the voice due to enlargement of larynx.

Hair at the pubic area, armpit and chin regions. Penis and testis enlarge and produce sperms. Body becomes more masculine. Female Enlargement of mammary glands.

Hair grows around pubic and armpit regions. Widening of the hips. Ovaries mature and start producing ova. Menstruation starts. Oestrogen triggers the onset of secondary sexual characteristics.

Menstrual Cycle

This is characterized by discharge of blood and tissue debris (menses) from the uterus every 28 days. This is due to the breakdown of the endometrium which occurs when the level of progesterone falls and the girl starts to menstruate.

The follicle stimulating hormone (FSH) causes the Graafian follicle to develop and also stimulate the ovary to release oestrogen. Oestrogen hormone triggers the onset of secondary sexual characteristics.

Luteinising hormone (L.H) causes the mature ovum to be released from the Graafian follicle – a process called ovulation. After ovulation progesterone hormone is produced.

After menstruation, the anterior lobe of the pituitary gland starts secreting the follicle stimulating hormone (FS.H) which causes the Graafian follicle to develop in the ovary. It also stimulates the ovary tissues to secrete oestrogen.

Oestrogen brings about the repair and healing of the inner lining of the uterus (endometrium) which had been destroyed during menstruation. Oestrogen level stimulates the pituitary gland to produce (Luteinising Hormone (L.H).

This hormone makes the mature Graafian follicle to release the ovum into the funnel of oviduct, a process called ovulation. After releasing the ovum, the Graafian follicle changes into a yellow body called corpus luteum.

The luteinising hormone stimulates the corpus luteum to secrete a hormone called progesterone which stimulates the thickening and vascularisation of endometrium.

This prepares the uterine wall for implantation of the blastocyst. If fertilization takes place, the level of progesterone increases and thus inhibits FSH from stimulating the maturation of another Graafian follicle.

If fertilization does not occur, the corpus luteum disintegrates and the level of progesterone goes down. The endometrium, sloughs off and menstruation occurs.

Advantages of Reproduction Asexual

Good qualities from parents are retained in the offspring without variation. New individuals produced asexually mature faster. Process does not depend on external factors which may fail such as pollination.

New individuals obtain nourishment from parent and so are able to survive temporarily under unsuitable conditions. No indiscriminate spreading of individuals which can result in wastage of offspring. Takes a shorter time and leads to rapid colonization.

Disadvantages of asexual reproduction

New offspring may carry undesirable qualities from parents. Offspring may be unable to withstand changing environmental conditions. Faster maturity can cause overcrowding and stiff competition. Reduced strength and vigour of successive generations.

Advantages of sexual reproduction

Leads to variations. Variations which are desirable often show hybrid vigour. High adaptability of individuals to changing environmental conditions. Variations provide a basis for evolutionary changes.

Disadvantages of sexual reproduction

Fusion is difficult if two individuals are isolated. Some variations may have undesirable qualities. Population growth is slow.

Evaluation

1. What are male secondary characteristics?
2. What are the secondary characteristics of male and female?
3. What are the characteristics of male and female?
4. What are the secondary female characteristics?
5. What are male characteristics?
6. What are 5 characteristics of a man?
7. What are feminine traits?