- •Importance of the reproductive function:
- •The reproductive capacities among livings.
- •Methods of reproduction in livings.
- •1. Binary fission:
- •2. Budding:
- •In unicellular organisms:
- •In multicellular organisms:
- •3. Regeneration:
- •4. Sporogony:
- •5. Parthenogenesis:
- •In some other cases, the eggs may result from mitotic division, where they develop to diploid (2n) individuals from the beginning as in case of the Aphid insect.
- •6. Tissue culture:
- •Reproduction in Flowering Plants.
- •2. Formation of fruits and seeds:
- •Reproduction in Human Being
- •Stages of Spermatogenesis
- •The Human Female Genital System
- •Breeding cycle
- •Phase of menstruation:
- •If the ovum is not fertilized:
- •If the ovum is fertilized:
- •Fertilization
Stages of Spermatogenesis
The structure of a sperm:
1. The head:
It contains the nucleus with 23 chromosomes. There is an acrosome in the forehead which secretes the Hyaluronic enzyme that dissolves a part of the ovum membrane, to facilitate its penetration process.
2. The neck:
It contains two centrioles which play an important role in the division of the fertilized ovum.
3. The midpiece:
It contains mitochondria which supply energy for sperm movement.
4. The tail:
It consists of an axis which ends with caudal piece. It helps the sperm to move.
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The Human Female Genital System
It consists of two ovaries, two oviducts, the uterus, and the vagina. This system produces the ova and the female sex hormones, besides providing a safe place for completion of fertilization, and embryonic development till birth.
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The organs of this system lie behind the urinary bladder in the pelvic region. They are firmly connected in this position with elastic ligaments which allows its expansion during pregnancy.
1. The two ovaries:
They lie on the sides of the pelvic cavity. Each ovary has an oval shape. It equals in size a peeled almond. During childhood, each ovary contains several thousands of ova in various stages of development. After maturity, about 400 of these ova only, will mature during the thirty years of active reproductive life (fecundity years). From each ovary, one mature ovum is discharged alternately with the other ovary per month. It secretes the maturation hormones for regulating menstrual cycle and embryo development.
2. The two fallopian tubes:
Each oviduct (fallopian tubes) has a funnel shaped opening. It lies just opposite the ovary to insure the fall of ovum in it; besides, it is provided with finger like processes to receive the ovum. It is lined with cilia to direct the ovum towards the uterus.
3. The uterus:
It is an elastic muscular sac-like organ. It lies in the pelvic cavity. It has a thick muscular strong wall, lined with a glandular membrane. The uterus is ended with the cervix which opens in the vagina. The embryo develops inside the uterus for 9 months.
4. The vagina:
It is a muscular tube, its length is about 7 cm that starts with the cervix and ends with the genital opening. This tube is lined with a membrane that secretes mucus fluid to moisten the vagina. Vagina has folds to allow its expansion during delivery.
N.B.:
1. As a female approaches maturity (at the age of 12 up to 15 years), a monthly rhythmic changes take place in the female reproductive system according to the ovarian and the uterine activities. Such activities may correlated with fertilization and pregnancy or non-pregnancy, and the monthly bleeding which is termed as menstruation.
2. At the age of 45 up to 50 years, the ovaries become inactive i.e. the hormonal secretion is decreased, and the uterine lining is wrinkled. This is known as menopause.
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Study of a T.S. in the ovary:
The ovary contains a group of cells in different stages, and ovum inside the Graafian follicle. This follicle is transformed into the Corpus luteum after the release of the ovum.
Stages of Oogenesis:
1. Multiplication phase:
In which, the Primary germ cells (2N) divide mitotically forming the Oogonia (2N). This phase occurs during the development of the female embryo.
2. The growth phase:
The Oogonia (2N) store an amount of food, increase in size, and are transformed into Primary Oocytes (2N). This phase occurs during the development of the female embryo.
3. Maturation phase:
Each Primary Oocyte (2N) divides 1st. meiotic division to give two haploid cells Secondary Oocyte (N) and 1st. polar body (N). (the Oocyte is larger than the polar body). Then 2nd. meiotic division takes places in which the Secondary Oocyte (N) divides giving an ovum and 2nd. polar body, while the 1st. polar body divides giving 2 polar bodies. So the resultants are 3 polar bodies.
The ovum contains cytoplasm and a nucleus. It is enveloped with a thin cellular coat, its cells are held together by Hyaluronic acid, the enzymes secreted by the acrosomes of sperms dissolved this coat at the penetration position. Therefore millions of sperms are required to penetrate the ovum.
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