CBSE Class 12 Biology Chapter 3 Revision Notes

Chapter 3: Human Reproduction

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The Male Reproductive System

• The male reproductive system consists of a pair of testes and accessory glands, ducts, and external genitalia and is located in the pelvic area.
• The testes are positioned just outside the abdominal cavity and encased in a sac-like structure known as the scrotum.
• The rete testis, vasa differentia, epididymis, and vas deferens are the male sex accessory ducts.
• The urethra connects the urethral meatus to the outside environment.
• The penis, the male external genitalia, is enveloped with foreskin, a loose flap of skin.
• The urethra, which originates in the urine bladder and extends through the penis towards its external entrance, the urethral meatus, stores and transports sperm from the testes to the outside.
• The paired seminal vesicles, prostate, and paired bulbourethral glands are all-male accessory glands.
• The seminal plasma, which includes fructose, calcium, and enzymes, is formed by the secretion of these glands.

The Female Reproductive System

• The female reproductive system’s internal and external sex organs include a pair of ovaries and oviducts, cervix, uterus, vagina, and external genitalia located in the pelvic area.
• Along with the mammary glands, these female reproductive organs are physically and functionally united to support the whole reproductive process, comprising ovulation, fertilization, pregnancy, and childbirth.
• The oviducts(fallopian tube), vagina, and uterus make up the female accessory ducts.
• Mons pubis, labia minora, labia majora, clitoris, and hymen are the parts of the female external genitalia.

Menstrual Cycle

• For females menstruation begins at puberty and is known as menarche.
• It lasts till the female attains the age of 50 and the end of the cycle is called menopause.
• During the follicular stage of this cycle, the primary follicles in the ovary grow and mature into graafian follicles.
• Simultaneously the endometrium (lining of the uterus) regenerates through proliferation.
• The secretion of gonadotropin increases during the follicular phase. This stimulates the follicular development and also the secretion of estrogen.
• LH and FSH attain their peak in the middle of the cycle. (On the 14th day for a female who has a 28 day cycle.)
• The surge in LH induces rapture of the graafian follicle and the ovum is released.
• The endometrium is maintained by progesterone which is secreted in large amounts by the corpus luteum.
• The reproductive phase in a human female extends from menarch to menopause.

Process of Human Reproduction

GametogenesisOogenesis: is the term used to describe the process of formation of mature female gametes.

• The gametes mother cells begin to divide and enter prophase-I of meiotic division, where they are temporarily arrested and referred to as primary oocytes.
• The primary follicle has a layer of granulosa cells that surrounds each primary oocyte.
• The secondary follicle, surrounded by several layers of granulosa cells, transforms into a tertiary follicle with a fluid-filled cavity called the antrum.
• The tertiary follicles then mature into the Graafian follicle, which ruptures to release secondary oocytes (ovum) from the ovary during the ovulation process.Spermatogenesis: spermatogenesis, which begins at puberty, produces sperm in the testes.
• The spermatogonia (immature germ cells) on seminiferous tubules’ inner surface grow and increase in quantity by mitotic division.
• Spermatogonia produces spermatocytes that divide during meiosis to create secondary spermatocytes.
• Spermiogenesis is the process through which spermatids are converted into spermatozoa.
• The sperm heads stay in Sertoli cells and are discharged from seminiferous tubules during the spermiation process.
• Sperm are tiny structures with a head, neck, middle portion, and tail.
• The sperm head has an extended haploid nucleus with a cap-like structure called an acrosome covering the front half.

Fertilization

Fertilization is the process of sperm and ovum fusing.

• Semen is discharged into the vaginal canal during coitus (copulation).
• The motile sperms swim quickly to reach the isthmus and ampulla of the fallopian tube’s junction.
• The ovum also makes its way there, and gametes fuse at the ampullary-isthmic junction.
• The sperm acrosome performs an acrosomal reaction, releasing sperm lysins that break down the egg envelopes locally and open the way for sperm entry.
• These sperm lysins contain hyaluronidase, a lysing enzyme that dissolves the hyaluronic acid polymers in the intercellular spaces that hold the granulosa cells of the corona radiata together.
• It also contains corona penetrating enzyme (which dissolves the corona radiata), and acrosin, a lysing enzyme that dissolves the hyaluronic acid polymers in the intercellular (which dissolves the zona pellucida).
• The zona pellucida is then dissolved.

Embryonic Development

• Chorionic villi are finger-like extensions on the trophoblast after implantation.
• These along with the uterine wall, constitute a functional unit between the growing embryo and the mother body termed the placenta.
• An umbilical cord connects the placenta to the fetus, transporting nourishment and oxygen to the embryo.
• The placenta produces the hormones hCG (human chorionic gonadotropin), hPL (human placental lactogen), and relaxin in women exclusively during pregnancy.
• After implantation, the inner cell mass (embryo) divides into two layers: ectoderm on the outside and endoderm on the inside.
• Between the ectoderm and the endoderm appears a mesoderm.
• These three layers give birth to all tissues (organs) in adults.
• An embryo’s heart in a human is created after one month of pregnancy.
• Legs and fingers are established at the end of the second month.
• In 5 months, the fetus makes its first movement.
• The body is coated with fine hair by the end of 24 weeks, and eyelids and eyeless have developed.
• The fetus is completely formed at 9 months.

Parturition and Lactation

• Parturition refers to the process of delivering a fully formed fetus.
• The fully grown fetus and placenta send out parturition signals, which cause moderate uterine contractions known as the Fetal ejection reflex.
• It causes the maternal pituitary to produce oxytocin.
• Lactation is the process through which a woman’s mammary glands begin producing milk and continue to do so until the pregnancy is over.
• Colostrum is the milk produced during the first few days of breastfeeding and contains many antibodies.

Questions

1. Which of these is a lytic enzyme released by the sperm? ____________
2. A human primary spermatocyte has _____ autosomes.
3. In a human female ovulation normally takes place ________ phase of the menstrual cycle.
4. The ovum receive the sperm at the _______
5. Which part of the sperm penetrates the ovum? ________
6. Which of these is contained in the umbilical cord? _______
7. ______ helps human sperm move.
8. Cryptorchidism is a condition where one or both testes fail to descend into the scrotum. ________
9. Bidder’s canal receives __________.
10. Post ovulation, the mammalian egg is covered by __________.
11. Which of these hormones is released from the testes? _________
12. Another name for Wolffian duct ____________.
13. Acrosome contains _________.
14. Which of these is a temporary organ that connects a mammalian mother to its fetus? _________
15. The sperm is responsible for carrying _______ to the egg.

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