SECONDARY SEXUAL CHARACTERISTICS

Biology

SECONDARY SEXUAL CHARACTERISTICS

What are secondary sexual characteristics?

Male

  • 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.
See also  THEORIES OF EVOLUTION

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.
See also  RECEPTION, RESPONSE AND CO-ORDINATION IN PLANTS

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.
See also  JOINTS AND MOVEMENT

Disadvantages of sexual reproduction

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

See also

FERTILIZATION IN ANIMALS

REPRODUCTION IN ANIMALS

METHODS OF FRUIT AND SEED DISPERSAL

POLLINATION

SEXUAL REPRODUCTION IN PLANTS

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