REPRODUCTION IN ANIMALS

Gametes refers to the sperm and the egg. During sexual reproduction, the sperm and the egg unite to form the zygote.
                           Zygote = sperm + egg

Each gamete has half the normal complement of chromosomes, that is, 23 chromosomes in each gamete. The gametes are said to be monoploids (haploid). Fusion results in the full number of chromosomes, 46 (23 pairs). The zygote is referred to as diploid.

In the male, the external reproductive organs are the penis and scrotum.
The internal organs consist of:

• The testis which contains the seminiferous tubules, where the sperms are produced.
• The interstitial cells produce testoterone, the male sex hormones.
• The sperm travels in the epididymis, the coiled tubules, into the vas deferens to the ejaculatory duct to the urethra.
• Seminal vesicles produce seminal fluid that carries the sperms.
• Prostate produces prostatic fluid that also carries the sperms.

In the female, the primary reproductive organs are the ovaries, fallopian tubes and uterus.

• Ovaries produce the eggs and the hormones, estrogen and progesterone.
• Immature egg is called oocyte.
• Matured egg is released during ovulation.
• The egg travels in the fallopian tubes, where it can be fertilized by the sperm. Note that the fertilized egg begins to divide within the tubes within few hours of conception.
• The lining of the uterus is called the endometrium.
• The fertilized egg implants in the endometrium.
• The fetus obtains nourishment via the placenta. Note that, the fetal and maternal blood do not have direct connections. Exchange of nutrients and oxygen is by diffusion.
• The fetus is connected to the placenta via the umbilical cord.
• The fetus is covered by the following membranes: amnion and chorion.
• If there is no fertilization, the uterus sheds its, endometrium. This is referred to as menstruation.