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An ovum or an ova is a single female reproductive cell that is released from the female sex organs called ovaries. They are capable of developing new organisms if fertilised by a sperm cell. Once the sperm and egg fuse during fertilization, a diploid cell, the zygote, is formed that rapidly grows into a new organism. If the ovum doesn’t get fertilised within 24 hours of its eruption, they begin to degenerate and are released out of the body in the form of blood and other components in the form of the Menstrual Cycle. The process by which the ovum is released from the ovaries is known as ovulation and it occurs as soon as the follicle is fully grown and reaches its appropriate size by the accumulation of liquid within it.
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Key Takeaways: Ovum, ovulation, gestation, mammals, ovaries, estrogen, progesterone, gamete, menstrual cycle, sperm
Human Female Reproductive System
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The female reproductive system comprises of:
Ovaries
Overies are the primary sex organs that produce the ovum and several steroid hormones. Located on either side of the abdomen in the pelvic region, each ovary measures 2 -4 cm in length connecting the uterus and pelvic wall with ligaments. The ovaries are surrounded by a thin epithelium that encloses the ovarian stroma and is divided into – the outer peripheral cortex and the inner medulla.
The process by which the egg cell (ovum) is released is called ovulation, after which they pass along the fallopian tubes.
Fallopian tubes
The released ovum travels down the fallopian tube to the uterus, to be fertilised. In the presence of sperms, the ovum releases certain chemicals that are essential to guide the sperm, allowing the surface of the egg to attach to the sperm's surface. The ovum then absorbs the sperm and fertilization begins. The fallopian tubes are lined with cilia that carry the ovum to the uterus.
Uterus
Also called the womb, the uterus is a muscular, inverted pear-shaped organ of the female reproductive system. The walls of the uterus consist of the inner glandular layer, the middle thick layer, and the outer thin layer that is attached to the pelvic wall with ligaments.
Its major function of the uterus is to accept a fertilised ovum that becomes implanted into the endometrium and derives nourishment from blood vessels that develop exclusively for this purpose. It also provides mechanical protection, nutritional support, and waste removal for the developing embryo. The fertilised ovum then becomes an embryo, develops into a fetus, and gestates until childbirth. The muscular wall of the uterus contracts to push out the fetus at the time of birth.
Cervix, Vagina, and External Genitalia
A cylindrical-shaped muscle, the cervix joins the lower part of the uterus with the upper part of the vagina. A part of it is visible from the outside.
The vagina is a muscular elastic tube that connects the cervix to the external body. It acts as the path for the sperms to enter during sexual intercourse. It is also the birth canal to allow delivery of the baby during childbirth.
The external genitalia includes the mons pubis, labia majora, labia minora, hymen, and clitoris.
Mammary Glands
The pair of mammary glands ( breasts ) contain glandular tissue and fat which is divided into 15- 20 mammary lobes containing cells called alveoli which secrete milk that is stored in the cavities of alveoli. The tubules join to form mammary ducts which in turn join to form a mammary ampulla that connects it to the lactiferous duct through which milk is sucked out.
Mammary glands
Also Read: Female Hormones
What is an Ovum?
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The term ovum was first defined in 1672 with the literal meaning of it being ‘an egg ‘ in Latin. A young ovum is described as an ovule and is produced in all female mammals. A number of ova are produced at birth and they gradually mature by a process called Oogenesis. Each ovum develops from germ cells that are embedded in the ovaries that divide repeatedly and ultimately form blastocysts. Studies have claimed that a female mammal has a finite number of eggs at birth that is depleted throughout life and finally exhausted at menopause.
Ovum
Structure of Human Ovum
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- The ovum is one of the largest cells in the human body, visible to the naked eye without the aid of a microscope or other magnification device, measuring approximately 120 μm (0.0047 in) in diameter.
- Ovum is microlecithal. It contains a large amount of cytoplasm which is differentiated into outer, smaller and transparent exoplasm or egg cortex and inner, larger and unique endoplasm or ooplasm.
- The egg cortex has cytoskeletal structures like microtubules and microfilaments, pigment granules and cortical granules of mucopolysacchirides.
- The endoplasm has cell organelles, informosomes, tRNA, histones, and enzymes.
- Each ovum has a nucleus which is large, with nucleoplasm and is called germinal vesicle.
- The ucleus is excentric in position. The egg is surrounded by a number of egg envelopes - vitelline membrane, zona pellucida, corona radiata.
- Secreted by the ovum, the vitelline membrane is inner, thin, and transparent.
- The zona pellucida is the middle, thin, transparent, and non-cellular that are partly secreted by the follicular cells and partly by the oocytes.
- The outer layer is the corona radiata.
Functions of Human Ovum
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- The main function of an ovum is to carry the set of chromosomes contributed by the female gamete.
- Both FSH and LH hormones are produced by the Pituitary Gland, whereas estrogen and progesterone hormones are produced by the ovaries.
- This along with the sperm determines the characteristics of the child.
- It also provides nutrition to the growing embryo.
Also Read:
| Related Articles | ||
|---|---|---|
| Difference Between Sperm and Ovum | Fertilization | Difference Between Spermatogenesis and Oogenesis |
Things to Remember
- Ovum is the name given to the haploid female reproductive gamete.
- The largest egg is of ostrich and is about 170 x 135 mm while that of a human is 0.15mm.
- Hormones estrogen and progesterone are produced by the ovaries that help in the development of reproductive organs by maintaining the proper uterine cycle and by developing female secondary sex characteristics.
- GnRH, FSH, and LH are other hormones secreted by the brain that help in controlling the female reproductive system.
- The menstrual cycle of a woman repeats every 28 days when they are not pregnant. Each cycle lasts for a period of 2- 7 days.
Symptoms of ovolution
Sample Questions
Ques: Name the steps of fertilization (3 Marks)
Ans: The female gamete ovum comes in contact with the male gamete, fertilization occurs. This takes place in the fallopian tube that connects the uterus to the ovaries. The steps of fertilization are:
- Sperm capitation
- Sperm zona pellucida binding
- The acrosome reaction
- Penetration of the zona pellucida
- Sperm oocyte binding
- Egg activation and cortical reaction
- Zona reaction.
Ques: Why does menstruation occur? Name the stages. (4 Marks)
Ans: When a female reaches adolescence, ovaries start discharging a mature egg every month. If the egg is not fertilised in the uterus, the lining in the uterine sheds away, and a new cycle begins. A menstrual cycle lasts for 28 days, in some cases, these cycles may either last for 21 days or as long as 35 days in some individuals. The stages of a menstruation cycle are:
- During the secretory phase, the thickened lining called the endometrium is released through the vagina.
- The follicular phase is the phase between the first day of the period and ovulation.
- The proliferative phase is the phase after the follicular phase where the uterus starts forming again.
- The luteal phase lasts between ovulation and the start of menstruation.
Ques: What are the constituents of the ooplasm of an ovum? (2 Marks)
Ans: An ovum is a non-motile cell that is produced by all female mammals. The largest ovum is that of an ostrich. A human ovum is round in shape having a cytoplasm called the ooplasm which is filled with lipoproteins, water, pigment granules, and cytoplasmic organelles which helps in providing nourishment to the developing egg.
Ques: Write two major functions of the ovary? (3 Marks)
Ans: The main function of the ovaries is to shelter and protect the eggs a female is born with until they are ready for use. Women are known to be born with a lifetime supply of eggs. It has been recently found that chemotherapy sparks the development of new eggs.
The second function is that ovaries produce female reproductive hormones called estrogen and progesterone which are used by the body to develop adult female characteristics, breasts, and larger hips, and to aid in the reproduction cycle. Progesterone helps mainly in reproduction. A lesser hormone secreted, relaxin helps loosen the pelvic ligaments so they can stretch during childbirth.
Ques: Where does fertilization take place? What is the fusion of male and female gametes called? (2 Marks)
Ans: The ovaries produce egg cells called oocytes which then travel to the fallopian tubes wherein the presence of sperms, fertilization may occur. If fertilised, the egg travels down the fallopian tube and moves to the uterus, and implants there where the uterus lining has thickened due to the action of the hormones and the embryo starts growing. The fusion of male and female gametes ( ovum and sperm) at the fallopian tube, is known as fertilization.
Ques: Name the components of the female reproductive system. (3 Marks)
Ans: Following are the components of the female reproductive system.
- A pair of ovaries: are oval-shaped glands located on each side of the body that produces ovum and hormones.
- The uterus: is a hollow-shaped vessel that houses the developing fetus.
- A pair of fallopian tubes: Narrow tubes that are attached to the upper part of the uterus and the ovaries and allow the eggs to travel to the uterus.
- Cervix, vagina, and external genitalia: which includes the labia majora, labia minora, Bartholin’s gland, and clitoris.
- Mammary glands: are a pair of glands that secrete milk due to the action of female hormones and are sucked out by the newborn.
Ques: What are the common methods of birth control? (3 Marks)
Ans: The most common methods for birth control are as follows:
- Male condoms are used by males to prevent the discharge of sperms into the vagina during ejaculation.
- Female intrauterine device is a T-shaped device inserted surgically into the uterus to prevent conceiving.
- Contraceptive pills are usually taken by females the day after sexual intercourse to prevent unwanted pregnancy.
- Birth control pills are a long-term medication usually taken under a doctor's guidance.
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