SECONDARY SEXUAL CHARACTERISTICS
What are secondary 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.
- 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.