Ravela Da Cruz

CBSE Class 12 Biology Chapter 3 Revision Notes

Humans are sexually reproducing organisms and viviparous (give birth to young ones).

Chapter 3: Human Reproduction

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The Male Reproductive System

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

Gametogenesis Oogenesis: 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. Embryonic Development
  • 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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