Human Female Reproductive System

(1) Ovaries: The ovaries are the primary sex organs of the female that lie in the lower part of the abdomen. The ovaries like the testes have both exocrine function that is production of ova and endocrine role that is secretion of female sex hormone, estrogen and progesterone. When a girl child is born, the ovaries already contain thousands of immature eggs. On reaching puberty, some of these starts maturing. One egg is produced every month by one of the ovaries.

(2) Fallopian tube (oviducts): A fallopian tube is a long tube. It conveys the egg from the ovary to the uterus and also provides the appropriate environment for its fertilization. Oviducts are the sites of fertilization of male and female gametes.

(3) Uterus: The uterus is a large, highly elastic sac specialized for the development of the embryo. The two oviducts unite to open into uterus. The uterus opens into the vagina through the cervix.

(4) Vagina: It is a large, elastic, muscular tube. It is adapted for receiving the semen during copulation, allowing menstrual flow and serving as birth canal during parturition.

1.0Menstrual Cycle In Females

Sexual cycle in human females starts at puberty (sexual maturity at the age of about 10 to 12 years). This is called menarche. The menstrual cycle starts and continues upto the age of 45 to 50 years. After this age menstruation stops and females become inactive as regards to reproduction. This is called menopause. Menstruation is a cyclic phenomenon that occurs regularly in every 28 days or month, in a female after attaining puberty. Menstrual or sexual cycle in women is a regular cyclic change that may be regarded as periodic preparation for fertilisation and pregnancy.

During menstrual cycle the ovaries and uterus undergo many changes under the influence of some hormones.

These Changes are Divided Into Four Main Phases

(1) Menstrual phase (2) Follicular phase or Proliferation phase 

(3) Ovulatory phase (4) Luteal phase or secretory phase

(1) Menstrual phase: If the fertilization of ovum does not take place, the lining of the uterus degenerates. It leads to menstruation which lasts for 3-5 days during which blood is discharged. The bleeding is caused due to the shedding of uterine lining and rupturing of the blood vessels.

(2) Follicular phase: In this phase, the anterior pituitary begins the secretion of follicle stimulating hormone that stimulates the development of an ovarian follicle in the ovary. As the follicle grows, hormone estrogen is produced by it. Estrogen reactivates the wall of uterus to become thickened and to be supplied with lots of blood. In order to prepare the uterus to receive the fertilized egg and to help in the development of the future embryo.

(3) Ovulatory phase: On 13^th or the 14^th day of menstrual cycle, the follicle ruptures and releases the egg (ovulation) under the influence of hormone LH.

(4) Luteal phase: This phase lasts from 15^th to 28^th day. The Graafian follicle after ovulation changes into corpus luteum. It starts secreting a hormone progesterone that makes the uterine lining thick. If there is no fertilisation, the egg disintegrates and endometrium restarts shedding on the 28^th day. The corpus luteum degenerates.

2.0Fertilization

(i) For sexual reproduction to occur, a male gamete should fuse with a female gamete. 

(ii) The fusion of male gamete and female gamete to form a zygote during sexual reproduction is called fertilization. 

(iii) When sperms come in contact with egg, one of the sperm may fuse with the egg.

(iv) This results in the formation of zygote or fertilized ovum.

(v) So new individual inherits some characters from father and some from mother.

Embryo Development and Nourishment

Zygote formed after fertilization begins to develop into an embryo. It starts dividing repeatedly to produce a hollow ball of cell. The cell begins to form a group that develops into different tissues and organs of the body. This developing structure is termed as embryo. The developing embryo gets attached to the lining endometrium of uterus, this is known as implantation. Inside the womb the umbilical cord connects the baby with mother’s placenta which provides nutrition to the foetus. Here it develops over the nine months. The developing embryo gradually differentiates into different body parts such as hands, legs, head, eyes, ears etc. The stage of the embryo in which all the body parts can be identified is called as foetus.

The development of the child inside the mother’s body takes approximately nine months that is 280 days known as gestation period. The child is born as a result of forceful muscular contractions in the uterus, called labour pain.

The mother’s body is designed to undertake the development of the child. Hence, the uterus prepares itself every month to receive and nurture growing embryo. The lining thickens and is richly supplied with blood to nourish the growing embryo.

Advantages of Sexual Reproduction 

(i) More genetic variations within a species. Genetic variations can lead to evolutionary advancement.

(ii) More variations assist with survival. It increases the chance that atleast some offsprings of a parent survive.

Note: The type of fertilization which occurs inside the body of female is called internal fertilization and fertilization which occurs outside the body of female is called external fertilization. External fertilization takes place in many invertebrates, fish and amphibians and internal fertilization takes place in all reptiles, birds and mammals.

Hermaphrodite:- The animals having both male and female reproductive organs are called hermaphrodite animals. e.g. Earthworms.