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Uterus is a female secondary sex organ also known as the womb. It is inverted pear-shaped and located between the bladder and the rectum. It is a muscular organ that stretches and contracts to support a developing foetus during pregnancy and pushes a baby out during delivery. The primary function of the uterus is to provide a suitable environment for the fertilised egg and sustain it until the foetus (offspring) is ready to be delivered. Fertility of the woman and the whole process of menstruation is managed by the uterus.
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Key Terms: Perimetrium, Myometrium, Endometrium, Fundus, Corpus, Isthmus, Cervix, Function of Uterus, Female Reproductive System, Secondary sex organ, Primary sex organs
Secondary Sex Organ
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Organs that are not taking part in reproduction are called secondary sex organs. Male secondary sex organs are Epididymes, vasa deferentia, penis, etc. Breast, oviducts, uterus, etc are examples of secondary sex organs in females.
Secondary Sex Organs
Read Also: Sexual Reproduction
Difference Between Primary Sex Organs and Secondary Sex Organs
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| Primary Sex Organs | Secondary Sex Organs |
|---|---|
| Primary sex organs produce gametes for reproduction. | Secondary sex organs do not produce gametes. They are responsible for maturation and conduction. |
| Primary sex organs secrete sex hormones | Secondary sex organs do not secrete sex hormones. |
| Examples of primary sex organs: Testes in males Ovaries in females | Examples of secondary sex organs: Epididymis, vasa deferentia, penis, etc are secondary sex organs in males, Breast, oviducts, uterus, etc are examples of secondary sex organs in females. |
Read Also: Human Development
Anatomy of Uterus
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The uterus comprises three distinct layers of tissue:
- Perimetrium: The outer serosal layer of tissue made of epithelial cells. The main function of this layer is to secrete a lubricating fluid that aids in friction reduction. It also covers the parts of the pelvic organs.
- Myometrium: The middle layer is made of smooth muscle tissue (uterine myocytes). The main function is to stimulate uterine contractions.
- Endometrium: The inner lining of the uterus builds up over the course of a month and is shed if pregnancy does not occur. It changes size every month throughout the reproductive years.
Muscle fibres extend longitudinally, circularly, and obliquely, intertwined with connective tissue from blood vessels, elastic fibres, and collagen fibres. As the foetus grows inside the uterus, the muscular wall of the uterus starts expanding and becomes thin.
Anatomy of Uterus
The uterus is inverted pear-shaped, and its location is behind the bladder and in front of the rectum. It has four main regions:
- Fundus: The broad curved area at the top portion and widest portion that connects to the fallopian tubes of the female reproductive system. In pregnancy, fundal height (measured from the top of the pubic bone) is routinely monitored to estimate growth rates.
- Corpus: The upper â portion of the uterus is the corpus. This is another important part of the uterus which initiates from below the level of fallopian tubes and continues downward, becoming increasingly narrower.
- Isthmus: This refers to the lower narrow part of the uterus which is about 2cm. This joins the ampulla and infundibulum to the uterus.
- Cervix: The lowest two inches of the womb. The cervix serves as a passage into the uterus via which sperm can enter and fertilise eggs. The shape of the cervix is tubular and it opens into the vagina and dilates (widens) to allow. It permits menstrual blood and a foetus (baby) to move from the womb into the vagina.
The diaphragm, perineal body, and a group of ligaments, including the round ligaments, support the uterus in the pelvis.
When a woman reaches menopause and is no longer able to bear children, her uterus shrinks get more fibrous and paled. Among the disorders that can affect the uterus are infections, benign and malignant tumours, abnormalities such as a double uterus, and prolapse, in which part of the uterus becomes displaced and protrudes from the vaginal opening.
Functions of Uterus
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- The uterus plays several important roles in the reproductive cycle, fertility, and childbirth.
- The endometrium is the source of the blood and tissue lost each month during menstruation. Endometrial lining is where implantation occurs. During the menstrual cycle, the lining thickens, becoming thickest during the period of egg release from the ovaries, known as ovulation.
- If the egg is fertilised, it connects with the uterus' thick endometrial wall and continues to develop. If the egg is not fertilised, the endometrial wall sheds its outer layer of cells, and the egg and surplus tissue are expelled from the body during menstruation.
- If fertilisation succeeds, the fertilised egg (the embryo) penetrates into the endometrium, where the decidua basalis, the maternal component of the placenta, develops.
- As pregnancy proceeds, the uterus grows and the muscular walls of the uterus become thinner day by day, like an inflated balloon, to support the developing foetus. The protecting amniotic fluid is secreted initially by the woman and then by the baby's urine and lung secretions.
- The muscular layer of the uterus begins to contract on and off throughout pregnancy in preparation for birthing. These "practise" contractions, known as Braxton-Hicks contractions, mimic period symptoms, and some women are unaware of them. They are not the increasingly intense and regular contractions that are strong enough to force the baby out of the uterus and into the vagina.
- The uterus continues to contract after delivery to evacuate the placenta. It will continue to contract a few weeks after delivery to restore the uterus to normal size and to stop the uterine contraction that happens during delivery.
Read Also: Parturition
Things to Remember
- Uterus is inverted pear-shaped 6 to 8 cm long; its wall thickness is approximately 2 to 3 cm.
- The main function is to provide nourishment to the fertilised eggs.
- Three layers of Uterus: Perimetrium, Myometrium, Endometrium.
- Four regions of Uterus: Corpus, Fundus, Isthmus, Cervix.
- The cervix opens the uterus into the vagina and the cervical canal is the cavity of the cervix which forms the birth canal along with the vagina.
- After pregnancy, the swollen uterus recovers to normal size in around six to eight weeks after delivery. Its dimensions are nearly 1 cm (0.4 inches) bigger in all directions as compared before childbirth.
- The vagina is a muscular tube present at the lower end of the uterus to the outside.
- Water, iron, potassium, salt, chloride, glucose, and proteins are components of the endometrial fluid.
- Menopause: The time that marks the end of your menstrual cycles.
Sample Questions
Ques. Describe the role of the cervix in the female reproductive system. (3 marks)
Ans. It connects the uterus with the vagina and serves as a channel between the vaginal cavity and the uterine cavity. The cervix acts as an entrance in the uterus through which sperm can enter and fertilise eggs. During pregnancy, the cervix assists in keeping the baby in place until it is completely mature.
Ques. What causes the lack of menstrual periods during conception or pregnancy? (3 marks)
Ans. During pregnancy, all menstrual cycle events cease and there is no menstruation. Menstruation happens mainly when the expelled egg is not fertilised. However, during pregnancy, the released egg is fertilised, therefore the uterine lining does not shed and instead feeds the foetus. However, uterine bleeding can occur during pregnancy for a variety of causes.
Ques. Name and explain the role of three different walls of the human uterus. (3 marks)
Ans. Perimetrium, Myometrium, Endometrium are the three layers of the human uterus.
- Role of Perimetrium: Outermost layer, secretes a lubricating fluid that prevents friction.
- Role of Myometrium: made up of a thick layer of smooth muscles and shows strong contractions during delivery of the baby.
- Role of Endometrium: Lines the uterine cavity is glandular in nature and undergoes cyclical changes during the menstrual cycle.
Ques. Explains different regions of the uterus. (4 marks)
Ans.
- Corpus: The wider, upper part of the uterus is called the corpus.
- Fundus: the fundus is the broad curved upper area in which the fallopian tubes connect to the uterus.
- Isthmus: The uterine isthmus is the inferior-posterior part of the uterus, on its cervical end.
- Cervix: The lower part of the uterus connects to the vagina and is called the cervix.
Ques. Explain in detail the functioning of the uterus. (2 marks)
Ans. During the menstrual cycle, the endometrium lining thickens, becoming thickest during the period of egg release from the ovaries, known as ovulation.
If the egg is fertilised, it is attached to the thick endometrial wall and continues to develop.
If the egg is not fertilised, the endometrial wall sheds its outer layer of cells, and the egg and excess tissue are expelled from the body during menstruation.
Ques. Mention the function of Uterus. (3 marks)
Ans. The primary function of the uterus is to provide a suitable environment for the fertilised egg and sustain it until the foetus (offspring) is ready to be delivered.
The uterus is an important part of the female reproductive system because it is the site for the child’s growth. The fertility of the woman and the whole process of menstruation is managed by the uterus.
Ques. Give the functions of Corpus Letum and Endometrium (3 marks)
Ans. Corpus luteum: It secretes progesterone which prepares the endometrium of the uterus for implantation and normal development of the foetus.
Endometrium: It undergoes cyclic changes during the menstrual cycle and prepares itself for implantation of the blastocyst.
Ques. Explain the menstrual cycle with a diagram. (4 marks)
Ans. The menstrual cycle has three phases: menstrual, proliferative, and secretory.
- Menstrual Phase: In females, the menstrual phase lasts for 3-5 days and during this period the endometrial lining of the uterus is cast off and is slowly passed out from the vagina as a mixture of blood.
- Proliferative or Follicular Phase: Between the 6th and 16th day of the cycle, it lasts 11 days. One ovarian follicle is converted to a Graafian follicle during this phase, and the endometrial layer is regenerated, as well as the burst blood vessels are repaired. Oestrogen levels rise. It comes to an end with ovulation.
- Secretory Phase: It exists for 12 days and between 17-28 days. The Graafian follicle gets converted to Corpus Luteum. The endometrium grows and thickens further. Progesterone increases. It ends with the conversion of the corpus luteum to corpus albican.
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