Human Reproduction

Key Concepts

The Male Reproductive System

The male reproductive system is located in the pelvis region and includes a pair of testes, accessory ducts, glands, and external genitalia.

Testes: Situated outside the abdominal cavity in the scrotum, which maintains a temperature 2-2.5°C lower than the internal body temperature, essential for spermatogenesis.

Scrotum Temperature The scrotum maintains the testes at a temperature 2-2.5°C lower than the normal internal body temperature. This cooler environment is essential for the production of viable sperm (spermatogenesis).

Testicular Lobules: Each testis has about 250 compartments. Each lobule contains 1-3 highly coiled seminiferous tubules.
Cells in Seminiferous Tubules:
- Male Germ Cells (Spermatogonia): Undergo meiotic divisions to form sperms.
- Sertoli Cells: Provide nutrition to the germ cells.
- Leydig Cells (Interstitial Cells): Located outside tubules; synthesize and secrete testicular hormones called androgens.
Accessory Ducts: Include rete testis, vasa efferentia, epididymis, and vas deferens.
Accessory Glands: Include paired seminal vesicles, a prostate, and paired bulbourethral glands. Their secretions form seminal plasma (rich in fructose, calcium, and enzymes).

The Female Reproductive System

Located in the pelvic region, it consists of a pair of ovaries, oviducts, uterus, cervix, vagina, and external genitalia, along with mammary glands.

Ovaries: Primary female sex organs. Produce the ovum and steroid hormones (estrogen and progesterone).
Accessory Ducts:
- Oviducts (Fallopian Tubes): 10-12 cm long. Parts include the infundibulum (with finger-like fimbriae), ampulla, and isthmus.
- Uterus (Womb): Supported by ligaments. The wall has three layers: perimetrium (outer), myometrium (middle smooth muscle), and endometrium (inner glandular layer).
External Genitalia: Includes mons pubis, labia majora, labia minora, hymen, and clitoris.
Mammary Glands: Paired structures containing glandular tissue and fat. Divided into 15-20 mammary lobes containing alveoli, which secrete milk.

Gametogenesis

The process of gamete formation.

Spermatogenesis:
- Starts at puberty due to increase in GnRH.
- GnRH stimulates LH (acts on Leydig cells for androgens) and FSH (acts on Sertoli cells).
- Spermiogenesis: Transformation of spermatids into spermatozoa (sperms).
- Spermiation: Release of sperms from seminiferous tubules.
Structure of Sperm: Composed of a head (with a haploid nucleus and an acrosome filled with enzymes), neck, middle piece (with mitochondria for energy), and a tail.
Oogenesis:
- Initiated during embryonic development.
- Primary oocytes are arrested at Prophase-I.
- At puberty, only 60,000-80,000 primary follicles remain in each ovary.
- Ovulation: Rupture of the Graafian follicle to release the secondary oocyte (ovum).

Menstrual Cycle

The reproductive cycle in female primates (e.g., humans).

Menstrual Phase (Days 1-5): Breakdown of endometrial lining; occurs if the ovum is not fertilized.
Follicular Phase: Primary follicles grow into Graafian follicles; endometrium regenerates. Induced by LH and FSH.
Ovulatory Phase (Mid-cycle): LH surge induces rupture of Graafian follicle and release of ovum.

LH Surge A rapid increase in LH (Luteinizing Hormone) level, known as the LH surge, occurs at the middle of the menstrual cycle (day 14). This surge is the primary trigger for the rupture of the Graafian follicle and the subsequent release of the ovum (ovulation).

Luteal Phase: Remaining Graafian follicle transforms into corpus luteum, which secretes progesterone to maintain the endometrium.

Fertilisation and Implantation

Fertilisation: Fusion of sperm and ovum in the ampullary region of the fallopian tube.
Sex Determination: The sex of the baby is determined by the father. Sperms carry either X or Y chromosomes, while ova only carry X. XX = Female, XY = Male.
Cleavage: Mitotic division of the zygote to form 2, 4, 8, 16 daughter cells called blastomeres.
Implantation: The blastocyst (with trophoblast and inner cell mass) embeds into the endometrium.

Pregnancy and Embryonic Development

Placenta: A structural and functional unit between the foetus and maternal body. Facilitates nutrient/oxygen supply and waste removal.
Hormones: Placenta produces hCG, hPL, estrogens, and progestogens. Relaxin is secreted by the ovary in the later phase.
Germ Layers: Inner cell mass differentiates into ectoderm, endoderm, and mesoderm.
Developmental Milestones:
- 1 Month: Heart formed.
- 2 Months: Limbs and digits develop.
- 12 Weeks (First Trimester): Major organ systems formed.
- 5 Months: First movements and head hair.
- 24 Weeks: Body hair, eyelids separate, eyelashes form.

Parturition and Lactation

Parturition: The process of delivery of the foetus (childbirth). Induced by a neuroendocrine mechanism involving oxytocin.
Lactation: Production of milk by mammary glands.
Colostrum: The milk produced during the initial few days; rich in antibodies (IgA) essential for the newborn’s resistance.

Colostrum The milk produced during the first few days of lactation is called colostrum. It is exceptionally rich in antibodies (especially IgA), which provide passive immunity to the newborn infant.

Key Concepts

The male reproductive system is located in the pelvis region and includes a pair of testes, accessory ducts, glands, and external genitalia.

Testes: Situated outside the abdominal cavity in the scrotum, which maintains a temperature 2-2.5°C lower than the internal body temperature, essential for spermatogenesis.

Testicular Lobules: Each testis has about 250 compartments. Each lobule contains 1-3 highly coiled seminiferous tubules.

Cells in Seminiferous Tubules:

Male Germ Cells (Spermatogonia): Undergo meiotic divisions to form sperms.
Sertoli Cells: Provide nutrition to the germ cells.
Leydig Cells (Interstitial Cells): Located outside tubules; synthesize and secrete testicular hormones called androgens.

Accessory Ducts: Include rete testis, vasa efferentia, epididymis, and vas deferens.

Accessory Glands: Include paired seminal vesicles, a prostate, and paired bulbourethral glands. Their secretions form seminal plasma (rich in fructose, calcium, and enzymes).

Located in the pelvic region, it consists of a pair of ovaries, oviducts, uterus, cervix, vagina, and external genitalia, along with mammary glands.

Ovaries: Primary female sex organs. Produce the ovum and steroid hormones (estrogen and progesterone).

Accessory Ducts:

Oviducts (Fallopian Tubes): 10-12 cm long. Parts include the infundibulum (with finger-like fimbriae), ampulla, and isthmus.
Uterus (Womb): Supported by ligaments. The wall has three layers: perimetrium (outer), myometrium (middle smooth muscle), and endometrium (inner glandular layer).

External Genitalia: Includes mons pubis, labia majora, labia minora, hymen, and clitoris.

Mammary Glands: Paired structures containing glandular tissue and fat. Divided into 15-20 mammary lobes containing alveoli, which secrete milk.

The process of gamete formation.

Spermatogenesis:

Starts at puberty due to increase in GnRH.
GnRH stimulates LH (acts on Leydig cells for androgens) and FSH (acts on Sertoli cells).
Spermiogenesis: Transformation of spermatids into spermatozoa (sperms).
Spermiation: Release of sperms from seminiferous tubules.

Structure of Sperm: Composed of a head (with a haploid nucleus and an acrosome filled with enzymes), neck, middle piece (with mitochondria for energy), and a tail.

Oogenesis:

Initiated during embryonic development.
Primary oocytes are arrested at Prophase-I.
At puberty, only 60,000-80,000 primary follicles remain in each ovary.
Ovulation: Rupture of the Graafian follicle to release the secondary oocyte (ovum).

The reproductive cycle in female primates (e.g., humans).

Menstrual Phase (Days 1-5): Breakdown of endometrial lining; occurs if the ovum is not fertilized.

Follicular Phase: Primary follicles grow into Graafian follicles; endometrium regenerates. Induced by LH and FSH.

Ovulatory Phase (Mid-cycle): LH surge induces rupture of Graafian follicle and release of ovum.

Luteal Phase: Remaining Graafian follicle transforms into corpus luteum, which secretes progesterone to maintain the endometrium.

Fertilisation: Fusion of sperm and ovum in the ampullary region of the fallopian tube.

Sex Determination: The sex of the baby is determined by the father. Sperms carry either X or Y chromosomes, while ova only carry X. XX = Female, XY = Male.

Cleavage: Mitotic division of the zygote to form 2, 4, 8, 16 daughter cells called blastomeres.

Implantation: The blastocyst (with trophoblast and inner cell mass) embeds into the endometrium.

Placenta: A structural and functional unit between the foetus and maternal body. Facilitates nutrient/oxygen supply and waste removal.

Hormones: Placenta produces hCG, hPL, estrogens, and progestogens. Relaxin is secreted by the ovary in the later phase.

Germ Layers: Inner cell mass differentiates into ectoderm, endoderm, and mesoderm.

Developmental Milestones:

1 Month: Heart formed.
2 Months: Limbs and digits develop.
12 Weeks (First Trimester): Major organ systems formed.
5 Months: First movements and head hair.
24 Weeks: Body hair, eyelids separate, eyelashes form.

Parturition: The process of delivery of the foetus (childbirth). Induced by a neuroendocrine mechanism involving oxytocin.

Lactation: Production of milk by mammary glands.

Colostrum: The milk produced during the initial few days; rich in antibodies (IgA) essential for the newborn’s resistance.

Human Reproduction

Human Reproduction

Key Concepts

The Male Reproductive System

The Female Reproductive System

Gametogenesis

Menstrual Cycle

Fertilisation and Implantation

Pregnancy and Embryonic Development

Parturition and Lactation

On this page

Human Reproduction

Human Reproduction

Key Concepts

The Male Reproductive System

The Female Reproductive System

Gametogenesis

Menstrual Cycle

Fertilisation and Implantation

Pregnancy and Embryonic Development

Parturition and Lactation

On this page