life as a single cell - a fertilized egg cell, or zygote.
The nucleus of each of these cells is packed with
information coded in the form of deoxyribonucleic acid (DNA)
and organized into groups called genes, which are arranged
on thread-like structures known as chromosomes.
A human zygote contains 46 chromosomes arranged in 23 pairs. One of each pair comes from the mother and one from the father.
As well as being packed with information, the DNA of the chromosomes also has the ability to copy itself; without this, the cells could not duplicate, nor could they pass on information from one generation to another.
are the parts of the female reproductive system that produce
and release mature eggs or ova. The female body contains two
ovaries that are located on either side of the uterus. The
ovaries are nodular glands which, following puberty, have a
puckered, uneven surface and resemble a large almond in size
and shape. The surface of the ovaries is covered with
epithelial tissue. Beneath the ovarian epithelium are
thousands of microscopic structures called ovarian
follicles, which are embedded in a connective tissue matrix
known as stroma. The follicles contain the ova, and after
puberty are present in varying stages of development. (The
development of ovarian follicles is described later in this
The ovaries have two primary functions:
|The uterus is
a pear-shaped organ capable of undergoing major changes
during a woman's reproductive life. From puberty to the
menopause, the inner lining of the uterus (the endometrium)
provides a suitable environment for embryo implantation and
development during pregnancy. The endometrial lining
thickens during the proliferative phase (first half) of the
menstrual cycle. It forms secretory glands after ovulation
as it is stimulated by hormones released from the ovaries.
If the egg is not fertilized, or implantation does not occur, the endometrium is shed and excreted from the body via the vagina during menstruation and is slowly replaced in the course of the next menstrual cycle. The uterus also undergoes powerful, rhythmic contractions during labour, resulting in the delivery of the foetus at birth.
The uterus is composed of two main parts:
The upper portion of the uterine body is called the fundus. The fallopian tubes open into the opposite corners of the fundus and the cervix opens into the vagina. The cervix is a cylinder-like structure that leads from the upper end of the vagina into the interior of the uterus. It is about 2.5 cm long and has a fine canal running through it with openings at each end called the internal and external os, respectively. The inner walls of the cervix contain small sacs called crypts that secrete alkaline mucus, which protects sperm from the acidity of the vaginal secretions. The crypts also act as reservoirs for sperm.
The walls of the uterus contain three layers:
The serosa secretes a watery (serous) fluid that prevents friction between the uterus and surrounding organs. A cross-sectional view of the uterine structures is shown below.
|The breasts contain milk-producing glands and provide nourishment to the newborn. After birth, milk production is initiated and maintained by secretion of the hormone prolactin from the pituitary gland. The breasts are not fully developed in the female until well beyond the onset of menstruation. They are present in children and men only in rudimentary form.|
|Summary of female reproductive system|