How production and transport of egg takes place in human female
Female gonads
are the paired ovaries which produce eggs and female hormones.
Ovaries:
Ovaries are
located in the pelvic part of the abdomen, one on each side of the uterus. A
cross section of an ovary reveals rounded vesicles called follicles which are
actual centres of egg production (oogenesis). Each follicle contains an
immature egg called primary oocyte and follicles are always present in several
stages of development. After the release of secondary oocyte (an egg) in the
process called ovulation, the lining of follicle grows inward forming corpus
luteum (yellow body) which serves as temporary endocrine tissue and continues
to secrete the female sex hormones estrogen and progesterone.
Uterine tubes:
The paired tubes
that receive the secondary oocyte from the ovary and convey it to the uterus
are called uterine tubes. Feathery fimbriae fringe the part of the uterine tube
that encircles the ovary. Each month as secondary oocyte is released, the
motion of the fimbriae sweeps it across a tiny space between the uterine tube
and the ovary into the tube.
The peristaltic
contractions of the tube and the waving motion of the cilia in the mucous
membrane of the tube carry the secondary oocyte along. Fertilization usually
occurs in the uppermost third of the uterine tube. Zygote continues its journey
toward the uterus where it will implant. The journey takes 4 – 7 days. If
fertilization does not occur the secondary oocyte degenerates in the uterine
tube.
Uterus:
The uterine
tubes terminate in the uterus, a hollow muscular organ in front of rectum and
behind urinary bladder. Uterus has three layers of tissues:
(1) The outer
layer (perimetrium) extends beyond the uterus to form two broad ligaments that
stretch from the uterus to lateral walls of the pelvis.
(2) Middle
muscular layer (myometrium) makes up most of the uterine wall.
(3) Endometrium
is the specialized mucous membrane that contains an abundance of blood vessels
and simple glands. Uterus leads to cervix which leads to the vagina, a muscular
tube 8 to 10 cm long. The wall of vagina is composed of smooth muscle elastic
tissue.
External
genitalia:
They include
monspubis, labia majora, labia minora, vestibular glands, clitoris and vaginal
opening. As a group of these organs are called the vulva.
Hymen:
In most young
women vaginal opening is partially covered by a thin membrane, the hymen, which
may be ruptured during normal strenuous activities or may be stretched or
broken during sexual activity.
Mammary glands:
They are
modified sweat glands that produce and secrete milk. They contain varying
amount of adipose tissue. The amount of adipose tissue determines the size of
the breasts, but the amount of mammary tissue does not vary widely from one
woman to other.
Hormonal control
of female reproductive organs:
The cyclical
production of hormones controls the development of secondary oocyte in a
follicle. Gonadotropin releasing hormone (GnRH) from Hypothalamus acts on the
anterior pituitary gland which releases follicle stimulating hormone (FSH) and
luteinizing hormone (LH) to bring about the oocyte’s maturation and release
from ovary. These hormones regulate
(1) Menstrual
cycle which is the cyclic preparation of uterus to receive a fertilized egg,
and
(2) The ovarian
cycle, during which the oocyte matures and ovulation occurs. This monthly
preparation continues upto age of 45 to 55 years of age, the ovaries lose their
sensitivity to FSH and LH; they stop making normal amount of progesterone and
estrogen. Menstrual cycle takes 28 days to complete one cycle. Hypothalamus
releases on a regular cycle GnRH, which stimulates the anterior pituitary to
secrete FSH and LH. FSH promotes the development of oocyte in one of the
immature ovarian follicles. Follicles produce estrogen causing a build up and
fertilization of endometrium and inhibition of FSH production.
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