Human Reproduction Practice Flashcards

Introduction and Reproductive Events

  • Nature of Human Reproduction:

    • Humans are sexually reproducing and viviparous organisms.
    • Reproduction is defined as the ability to produce individuals of the same species.

  • Sequence of Reproductive Events:

    1. Gametogenesis: The formation of gametes. Male gametes are called sperms, and female gametes are called egg or ovum. The formation of sperm is termed spermatogenesis, while the formation of an egg is termed oogenesis.
    2. Insemination: The transfer of sperms into the female genital tract.
    3. Fertilisation: The fusion of male and female gametes, resulting in the formation of a zygote.
    4. Implantation: The attachment of the Blastocyst to the inner wall of the uterus (the endometrium).
    5. Gestation: The period of embryonic development within the mother's uterus. In humans, the gestation period is approximately 99 months.
    6. Parturition (Delivery): The process of delivering the baby.

  • Puberty and Timing:

    • All reproductive events occur only after the onset of puberty.
    • There are significant differences between male and female reproductive processes. For example, sperm formation (spermatogenesis) continues even in old men, whereas the formation of the ovum (oogenesis) typically ceases in women around the age of 5050 years.

The Male Reproductive System

  • Location: The male reproductive system is situated in the pelvis region.

  • Components:

    • A pair of testes.
    • Accessory ducts.
    • Accessory glands.
    • External genitalia.

  • The Testes:

    • Position: Situated outside the abdominal cavity within a pouch called the scrotum.
    • Thermoregulation: The scrotum helps maintain a low temperature for the testes, approximately 2 to 2.5 ∘C2 \text{ to } 2.5\,^{\circ}\text{C} lower than the normal internal body temperature. This low temperature is essential for the process of spermatogenesis.
    • Shape and Size: Each testis is oval in shape, with a length of 4 to 5 cm4 \text{ to } 5\,cm and a width of 2 to 3 cm2 \text{ to } 3\,cm.
    • Structure: Each testis is covered by a dense covering and contains about 250250 compartments known as testicular lobules.
    • Seminiferous Tubules: Each testicular lobule contains one to three highly coiled seminiferous tubules. These are the sites of sperm production.

  • Cellular Composition of Seminiferous Tubules:

    • Male Germ Cells (Spermatogonia): Also known as sperm mother cells, these undergo meiotic divisions leading to the formation of sperms.
    • Sertoli Cells (Nursing Cells): These cells provide nutrition to the developing germ cells.
    • Interstitial Spaces: The regions outside the seminiferous tubules contain small blood vessels and interstitial cells, also called Leydig cells, which produce androgens (testicular hormones).

Male Accessory Ducts and Glands

  • Accessory Ducts:

    • The ducts include the Rete testis, Vasa efferentia, Epididymis, and Vas deferens.
    • Pathway of Sperm Transport: Seminiferous tubules $\rightarrow$ Rete testis (irregular cavities in the testes) $\rightarrow$ Vasa efferentia $\rightarrow$ Epididymis $\rightarrow$ Vas deferens (ascends to the abdomen and loops over the urinary bladder).
    • Ejaculatory Duct: Formed when the Vas deferens receives a duct from the seminal vesicle. It opens into the urethra.
    • Urethra: Originates from the urinary bladder and extends through the penis to its external opening called the urethral meatus. These ducts are responsible for storing and transporting sperm.

  • External Genitalia:

    • The penis is the male external genitalia.
    • It is composed of special spongy erectile tissue that facilitates erection for insemination.
    • Glans Penis: The enlarged end of the penis, covered by a loose fold of skin called the foreskin.

  • Accessory Glands:

    • Includes paired Seminal vesicles, a single Prostate gland, and paired Bulbourethral glands (also known as Cowper's glands).
    • Seminal Plasma: The collective secretions of these glands. It is rich in fructose, calcium, and specific enzymes.
    • Functions of Secretions:
      • Bulbourethral gland secretions help in the lubrication of the penis.
      • Secretions from the epididymis, vas deferens, seminal vesicle, and prostate are essential for sperm maturation and motility.
    • Semen: The combination of seminal plasma and sperm: Seminal Plasma+Sperm=Semen\text{Seminal Plasma} + \text{Sperm} = \text{Semen}.

The Female Reproductive System

  • Location and Integration: Located in the pelvic region. It includes ovaries, accessory ducts, and external genitalia. These parts, along with the mammary glands, are integrated to support ovulation, fertilisation, pregnancy, birth, and childcare.

  • The Ovaries:

    • Primary female sex organs that produce the female gamete (ovum) and steroid hormones (Estrogen and Progesterone).
    • Located on each side of the lower abdomen.
    • Size: Approximately 2 to 4 cm2 \text{ to } 4\,cm in length.
    • Attachment: Connected to the pelvic wall and uterus by ligaments.
    • Structure: Covered by a thin epithelium enclosing the ovarian stroma. The stroma is divided into a peripheral cortex and an inner medulla.

  • Accessory Ducts (Female):

    • Fallopian Tubes (Oviducts): Each tube is 10 to 12 cm10 \text{ to } 12\,cm long.
      • Infundibulum: The funnel-shaped part closest to the ovary. It has finger-like projections called fimbriae that help collect the ovum after ovulation.
      • Ampulla: The wider part of the oviduct following the infundibulum.
      • Isthmus: The last part of the oviduct with a narrow lumen that joins the uterus.
    • Uterus (Womb): Shaped like an inverted pear and supported by ligaments. It opens into the vagina through a narrow cervix.
      • Birth Canal: Formed by the cervical canal plus the vagina: Cervical canal+Vagina=Birth Canal\text{Cervical canal} + \text{Vagina} = \text{Birth Canal}.
    • Uterine Wall Layers:
      1. Perimetrium: The external thin membranous layer.
      2. Myometrium: The middle thick layer of smooth muscle. It exhibits strong contractions during the delivery of the baby.
      3. Endometrium: The innermost glandular layer that undergoes cyclical changes during the menstrual cycle.

Female External Genitalia and Mammary Glands

  • External Genitalia Components:

    • Mons Pubis: A cushion of fatty tissue covered by skin and pubic hair.
    • Labia Majora: Fleshy folds extending from the mons pubis to surround the vaginal opening.
    • Labia Minora: Paired folds of tissue under the labia majora.
    • Hymen: A membrane partially covering the vaginal opening. It can be torn during the first coitus or via sudden falls, tampon insertion, or sports. Its presence/absence is not a reliable indicator of virginity.
    • Clitoris: A tiny finger-like structure at the upper junction of the labia minora above the urethral opening.

  • Mammary Glands (Breasts):

    • Paired structures containing glandular tissue and fat, characteristic of female mammals.
    • Structure: Glandular tissue is divided into 15 to 2015 \text{ to } 20 mammary lobes containing clusters of cells called alveoli.
    • Milk Secretion Path: Alveoli (secrete milk) $\rightarrow$ Mammary tubules $\rightarrow$ Mammary duct $\rightarrow$ Mammary ampulla $\rightarrow$ Lactiferous duct (milk is sucked out).

  • Lactation and Breast-feeding:

    • Lactation is the process of producing milk toward the end of pregnancy.
    • Colostrum: The milk produced during the initial few days. It is high in antibodies (IgA), which are essential for the newborn's resistance.
    • Hormones:
      • Milk synthesizing hormone: Prolactin (PRL).
      • Milk ejecting hormone: Oxytocin (OT).
      • Pregnancy hormone: Progesterone.

Gametogenesis: Spermatogenesis

  • Overview: The process of gamete formation. Male gametes are sperms (Spermatogenesis), and female gametes are eggs/ovum (Oogenesis).

  • Process of Spermatogenesis:

    • Occurs in the seminiferous tubules of the testes starting at puberty.
    • Spermatogonia (2n2n, 4646 chromosomes): Multiply by mitotic division.
    • Primary Spermatocytes (2n2n): Periodically undergo meiosis.
    • Secondary Spermatocytes (nn, 2323 chromosomes): Formed after the first meiotic division (reduction division).
    • Spermatids (nn): Four equal haploid cells produced after the second meiotic division.
    • Spermiogenesis: The transformation of spermatids into spermatozoa (sperms).
    • Spermiation: The release of mature sperms from the seminiferous tubules.

  • Yield Calculations:

    • From a single Primary spermatocyte: 44 sperms are produced.
    • From a single Secondary spermatocyte: 22 sperms are produced.
    • Example: 100100 primary spermatocytes will produce 400400 sperms.

  • Cell Ploidies:

    • Diploid (2n2n): Spermatogonia, Primary spermatocyte.
    • Haploid (nn): Secondary spermatocyte, spermatid, Sperm.

  • Hormonal Control:

    • Initiated by a rise in Gonadotropin Releasing Hormone (GnRH) from the Hypothalamus.
    • GnRH stimulates the anterior pituitary (Adenohypophysis) to secrete Luteinising Hormone (LH) and Follicle Stimulating Hormone (FSH).