Detailed Notes Chapter 2-Human Reproduction

Chapter 2-Human Reproduction

Introduction

Male Reproductive System:

1. Testes:
   • Primary male reproductive organs.
   • Produce sperm and testosterone.
2. Epididymis:
   • Coiled tube behind each testicle.
   • Stores and matures sperm.
3. Vas Deferens:
   • Muscular tube transporting mature sperm from the epididymis to the urethra during ejaculation.
4. Seminal Vesicles, Prostate Gland, and Bulbourethral Gland:
   • Produce fluids that mix with sperm to form semen.
   • Semen is ejaculated during sexual intercourse.
5. Urethra:
   • Tube carrying urine and semen out of the body.
   • Functions separately for each fluid.

Female Reproductive System:

1. Ovaries:

   • Primary female reproductive organs.
   • Produce eggs and hormones (estrogen, progesterone).

2. Fallopian Tubes (Oviducts):

   • Tubes connecting ovaries to uterus.
   • Site of fertilization between egg and sperm.

3. Uterus (Womb):

   • Organ where fertilized egg implants and fetus develops during pregnancy.
   • Inner lining (endometrium) thickens monthly in preparation for pregnancy.

4. Cervix:

   • Lower part of the uterus connecting to the vagina.
   • Produces mucus to assist or prevent sperm from entering the uterus.

5. Vagina:

   • Muscular tube connecting uterus to outside of the body.
   • Functions as birth canal during childbirth and receives sperm during intercourse.

Throughout a woman’s reproductive years:

• Ovaries release an egg monthly during ovulation.
• If fertilized, the egg implants in the uterus and develops into a fetus.
• Reproductive years typically span from puberty to menopause (around ages 45-55).
• Sperm production continues throughout a man’s life, while ovum production ceases around menopause in women.

2.1 THE MALE REPRODUCTIVE SYSTEM

1. Location and Structure:

   • Located in the pelvis region.
   • Consists of testes, accessory ducts, glands, and external genitalia.
   • Testes are situated outside the abdominal cavity within the scrotum, aiding in maintaining a lower temperature necessary for spermatogenesis.
   • Each testis is oval-shaped, about 4 to 5 cm in length and 2 to 3 cm in width, covered by a dense covering and contains about 250 compartments called testicular lobules.

2. Spermatogenesis:

   • Spermatogenesis occurs within highly coiled seminiferous tubules found in each testicular lobule.
   • Seminiferous tubules lined by two types of cells: male germ cells (spermatogonia) and Sertoli cells.
   • Male germ cells undergo meiotic divisions, leading to sperm formation, while Sertoli cells provide nutrition to germ cells.
   • Interstitial spaces outside seminiferous tubules contain Leydig cells, which synthesize and secrete androgens (testicular hormones).

3. Accessory Ducts:

   • Include rete testis, vasa efferentia, epididymis, and vas deferens.
   • Seminiferous tubules open into vasa efferentia through rete testis, which then lead to epididymis located along the posterior surface of each testis.
   • Epididymis leads to vas deferens, which ascends to the abdomen and loops over the urinary bladder, eventually opening into the urethra as the ejaculatory duct.
   • These ducts store and transport sperm from the testis to the outside through the urethra.

4. External Genitalia:

   • The penis is the male external genitalia, made up of special tissue facilitating erection for insemination.
   • Glans penis, the enlarged end of the penis, is covered by a loose fold of skin called foreskin.

5. Accessory Glands:

   • Paired seminal vesicles, prostate, and paired bulbourethral glands constitute the male accessory glands.
   • Secretions from these glands form seminal plasma, rich in fructose, calcium, and certain enzymes.
   • Secretions from bulbourethral glands also aid in lubrication of the penis.

2.2 THE FEMALE REPRODUCTIVE SYSTEM

1. Components and Location:

   • Consists of ovaries, oviducts (fallopian tubes), uterus, cervix, vagina, and external genitalia.
   • Located in the pelvic region, integrated structurally and functionally to support ovulation, fertilization, pregnancy, birth, and child care.
   • Mammary glands are also part of the system, contributing to child care.

2. Ovaries:

   • Primary female sex organs producing ovum and ovarian hormones.
   • Located one on each side of the lower abdomen, about 2 to 4 cm in length, connected to pelvic wall and uterus by ligaments.
   • Covered by a thin epithelium enclosing ovarian stroma divided into cortex and medulla.

3. Oviducts (Fallopian Tubes):

   • Extend from periphery of each ovary to the uterus.
   • Consist of infundibulum (funnel-shaped part with fimbriae for ovum collection), ampulla (wider part), and isthmus (narrow part joining uterus).

4. Uterus (Womb):

   • Single, inverted pear-shaped organ supported by ligaments attached to pelvic wall.
   • Opens into vagina through narrow cervix, forming the birth canal.
   • Uterine wall has three layers: perimetrium (external), myometrium (middle smooth muscle layer), and endometrium (inner glandular layer undergoing cyclical changes during menstrual cycle).

5. Female External Genitalia:

   • Include mons pubis, labia majora, labia minora, hymen, and clitoris.
   • Mons pubis is a cushion of fatty tissue covered by skin and pubic hair.
   • Labia majora are fleshy folds extending down from the mons pubis, surrounding the vaginal opening.
   • Labia minora are paired folds of tissue under the labia majora.
   • Hymen partially covers the vaginal opening and may rupture due to various reasons.
   • Clitoris is a small structure above the urethral opening.

6. Mammary Glands:

   • Paired structures (breasts) containing glandular tissue and fat.
   • Glandular tissue divided into mammary lobes containing alveoli secreting milk.
   • Alveoli open into mammary tubules, joining to form mammary ducts.
   • Mammary ducts connect to lactiferous ducts, through which milk is sucked out.

2.3 GAMETOGENESIS

1. Spermatogenesis:

   • Occurs in the testes, where sperms are produced from spermatogonia.
   • Spermatogonia multiply by mitotic division, becoming diploid cells with 46 chromosomes.
   • Primary spermatocytes undergo meiosis, resulting in two haploid secondary spermatocytes with 23 chromosomes each.
   • Secondary spermatocytes undergo the second meiotic division to produce four equal, haploid spermatids.
   • Spermatids transform into spermatozoa (sperms) through spermiogenesis.
   • Sperm heads contain haploid nucleus covered by acrosome filled with fertilization enzymes, middle piece with mitochondria for energy, and tail for motility.
   • About 200 to 300 million sperms are ejaculated during coitus, with normal fertility requiring at least 60% normal shape and size and 40% vigorous motility.

2. Oogenesis:

   • Occurs in the ovaries, where ovum is produced from oogonia.
   • Oogonia formed during embryonic development; no new oogonia formed after birth.
   • Oogonia undergo division and enter prophase-I of meiotic division, becoming primary oocytes temporarily arrested at that stage.
   • Primary oocytes surrounded by granulosa cells form primary follicles.
   • Majority of follicles degenerate before puberty, leaving about 60,000-80,000 primary follicles in each ovary.
   • Primary follicles develop into secondary follicles, then tertiary follicles characterized by antrum.
   • Tertiary follicles transform into Graafian follicles, where primary oocyte completes first meiotic division, forming secondary oocyte and tiny first polar body.
   • Graafian follicle ruptures during ovulation, releasing secondary oocyte (ovum) from ovary.

Major differences between spermatogenesis and oogenesis include:

• In spermatogenesis, four equal, haploid spermatids are produced from each primary spermatocyte, while in oogenesis, only one functional ovum is produced, along with polar bodies.
• Spermatogenesis begins at puberty and continues throughout life, while oogenesis starts before birth and ends at menopause.
• Sperms are small, mobile, and numerous, while eggs are larger, non-mobile, and fewer in number.