Understand the basic structure and function of male and female reproductive systems.
Describe the process of gametogenesis in both males and females.
Explain the phases of the menstrual cycle.
Understand the steps involved in fertilization and implantation.
Discuss the stages of pregnancy, embryonic development, parturition, and lactation.
Humans are sexually reproducing and viviparous organisms. The reproductive processes include gametogenesis (formation of sperms in males and ova in females), insemination (transfer of sperms to the female genital tract), fertilization (fusion of male and female gametes), formation of a zygote, and further development leading to parturition. These events, beginning after puberty, display key differences in the reproductive systems of males and females.
Male Reproductive System
The male reproductive system is located in the pelvic region and includes:
Testes: Positioned outside the abdominal cavity in the scrotum, the testes maintain a temperature 2-2.5°C lower than the body, necessary for spermatogenesis. Each adult testis is about 4-5 cm long and 2-3 cm wide, divided into 250 compartments called testicular lobules. Each lobule contains 1-3 coiled seminiferous tubules where sperms are produced. The seminiferous tubules are lined by two types of cells:
Male germ cells (spermatogonia): Undergo meiosis to produce sperms.
Sertoli cells: Provide nutrition to germ cells.
Leydig cells: Located in the interstitial spaces outside seminiferous tubules, these cells produce testosterone (androgens).
Accessory Ducts: Comprising the rete testis, vasa efferentia, epididymis, and vas deferens, these ducts transport and store sperms. The vas deferens loops over the urinary bladder and joins the urethra via the ejaculatory duct.
Penis: The male external genital organ. Its specialized tissue allows erection for insemination. The glans penis is covered by a loose fold of skin called the foreskin.
Accessory Glands: These include:
Seminal vesicles: Provide fructose-rich fluid to nourish sperms.
Prostate gland: Contributes enzymes to seminal fluid.
Bulbourethral glands: Secrete a lubricating fluid.
Important Note
Spermatogenesis: The production of sperms in males continues throughout their lives, but this process gradually declines with age.
Female Reproductive System
The female reproductive system includes the ovaries, oviducts, uterus, cervix, vagina, and external genitalia. These structures support processes like ovulation, fertilization, pregnancy, and childbirth.
Ovaries: Each ovary, located in the lower abdomen, measures about 2-4 cm in length. They produce ova and secrete ovarian hormones. The ovarian stroma has two regions: the cortex and medulla.
Oviducts (Fallopian tubes): Each is about 10-12 cm long and extends from the ovary to the uterus. The infundibulum (closest to the ovary) has fimbriae that help collect the ovum during ovulation. The oviduct is divided into three regions: the ampulla (wider part), isthmus (narrow lumen), and the uterus.
Uterus: Pear-shaped and muscular, the uterus has three layers:
Perimetrium: Outer thin membrane.
Myometrium: Thick muscular layer that contracts during childbirth.
Endometrium: Inner glandular layer that undergoes cyclical changes during the menstrual cycle.
External Genitalia: Includes the mons pubis, labia majora, labia minora, hymen, and clitoris.
Mammary Glands: Paired structures involved in lactation. Each breast has 15-20 lobes, consisting of alveoli that secrete milk, stored in the mammary ducts.
Important Note
Hymen: Its presence or absence is not a reliable indicator of virginity.
Gametogenesis
Gametogenesis is the process by which sperms and ova are produced.
Spermatogenesis: Occurs in the seminiferous tubules and begins at puberty:
Spermatogonia undergo mitosis and meiosis to form spermatocytes.
Primary spermatocytes (46 chromosomes) undergo meiosis I to form secondary spermatocytes (23 chromosomes).
These secondary spermatocytes undergo meiosis II, producing spermatids, which differentiate into mature sperms.
Sperm Structure: A mature sperm has:
Head: Contains the nucleus and a cap-like acrosome filled with enzymes.
Middle piece: Packed with mitochondria for energy.
Tail: Facilitates sperm movement.
Oogenesis: Unlike spermatogenesis, oogenesis begins during fetal development:
Oogonia multiply and form primary oocytes, which are arrested in prophase I until puberty.
Each primary oocyte is surrounded by granulosa cells, forming a follicle.
Only a few oocytes mature into secondary oocytes, which are released during ovulation.
Hormonal Regulation: Both LH and FSH play crucial roles:
LH: Stimulates Leydig cells to produce testosterone.
FSH: Stimulates Sertoli cells and aids in spermiogenesis.
Spermatogenesis
Oogenesis
Continuous after puberty.
Starts before birth, pauses until puberty.
Produces millions of sperm.
Produces limited ova.
Meiosis produces 4 sperms.
Meiosis produces 1 ovum.
Menstrual Cycle
The menstrual cycle occurs in human females at an average interval of 28-29 days:
Menstrual Phase: Endometrial breakdown occurs if no fertilization takes place, resulting in menstruation (3-5 days).
Follicular Phase: A Graafian follicle matures, and the endometrium regenerates. FSH and LH levels rise.
Ovulation: Around the 14th day, a surge in LH causes the release of the ovum.
Luteal Phase: The ruptured follicle becomes the corpus luteum, secreting progesterone to prepare the endometrium for implantation.
Important Concept
Menarche: The first menstrual cycle marks the beginning of reproductive maturity, while menopause indicates its cessation.
Fertilization and Implantation
Fertilization occurs when a sperm reaches the ampullary region of the fallopian tube, where it fuses with the ovum, forming a zygote. The sperm penetrates the zona pellucida of the ovum, ensuring only one sperm fertilizes the egg.
Implantation: The zygote undergoes mitotic divisions, forming a morula and then a blastocyst. The blastocyst attaches to the uterine wall, marking the onset of pregnancy.
Pregnancy and Embryonic Development
Pregnancy lasts about nine months and begins with the formation of the placenta, a structure facilitating nutrient and oxygen exchange between mother and fetus.
Placenta: The chorionic villi interdigitate with maternal tissues, and the placenta produces hormones like hCG and hPL.
Fetal Development:
After one month, the heart is formed.
By the second month, limbs and digits develop.
By 12 weeks, most organs are formed.
By the fifth month, the fetus shows movements and hair growth.
Stem Cells: The inner cell mass contains pluripotent stem cells, capable of developing into all types of tissues.
Parturition and Lactation
Parturition: The process of childbirth is triggered by oxytocin, causing strong uterine contractions. The fetus is expelled from the uterus, followed by the placenta.
Lactation: After childbirth, the mammary glands secrete colostrum, a nutrient-rich fluid vital for newborn immunity
. Breastfeeding is essential for the infant’s health.
MCQ What hormone induces the rupture of the Graafian follicle during ovulation? Answer: Luteinizing Hormone (LH)