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Human Growth & Development: Prenatal Development


Anatomy of Male Gamete (Sperm)

  • Components: Acrosome, plasma membrane, mitochondria, nucleus, axial filament, centriole, tail, end piece.

  • Spermatogenesis:

    • Starts at puberty.

    • Continuous process with three phases:

    • Mitotic Division: Maintains spermatogonia stem cell population and provides cells destined to become sperm.

    • Meiotic Division: Reduces chromosome number to produce haploid spermatids.

    • Spermiogenesis: Transformation of spermatids into mature spermatozoa (loss of cytoplasm, development of flagella).

Anatomy of Female Gamete (Ovum)

  • Components: Corona radiata, nucleus, cortical granules, zona pellucida, mitochondria.

  • Ova Development: Occurs within ovarian follicles, involving primary oocytes maturing into secondary oocytes (meiosis resumes at ovulation).

Ovarian Cycle

  • 28-day cycle from puberty to menopause divided into:

    1. Follicular Phase (Days 1-13): Development of ovarian follicles; one becomes dominant.

    2. Ovulation (Day 14): Release of secondary oocyte from dominant follicle.

    3. Luteal Phase (Days 15-28): Formation of corpus luteum from ruptured follicle.

Fertilization Process

  • Fusion of male and female gametes; occurs in the ampullary region of the uterine tubes.

  • Phases of Fertilization:

    1. Penetration of the Corona Radiata: Coating surrounding the egg.

    2. Penetration of the Zona Pellucida: Glycoprotein shell around the egg, induces acrosome reaction (release of enzymes).

    3. Fusion of Oocyte and Sperm Cell Membranes: Adhesion mediated by integrins and subsequent fusion of membranes.

Cleavage and Blastulation

  • Post-fertilization, the zygote undergoes cleavage:

    • Series of mitotic divisions producing smaller cells called blastomeres.

    • At 16-cell morula stage, cells form inner cell mass (future embryo) and outer cell mass (trophoblast).

  • Blastulation leads to formation of the blastocyst, characterized by a cavity (blastocele).

Implantation

  • Trophoblasts from the blastocyst penetrate the uterine epithelium around day 6.

  • Three phases of implantation:

    1. Apposition: Initial contact with the endometrium.

    2. Adhesion/Attachment: Strong attachment.

    3. Invasion/Penetration: Trophoblastic cells invade the uterine tissue.

Hormonal Regulation of Menstruation

  • 28-day menstrual cycle:

    1. Menstrual Phase (Days 1-7): Shedding of the endometrium.

    2. Proliferative Phase (Days 7-14): Repair and growth of the endometrium stimulated by estradiol.

    3. Secretory Phase (Days 14-28): Endometrium becomes secretory under progesterone influence.


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Human Growth & Development: Prenatal Development

Anatomy of Male Gamete (Sperm)

  • Components: Acrosome, plasma membrane, mitochondria, nucleus, axial filament, centriole, tail, end piece.

  • Spermatogenesis:

    • Starts at puberty.

    • Continuous process with three phases:

    • Mitotic Division: Maintains spermatogonia stem cell population and provides cells destined to become sperm.

    • Meiotic Division: Reduces chromosome number to produce haploid spermatids.

    • Spermiogenesis: Transformation of spermatids into mature spermatozoa (loss of cytoplasm, development of flagella).

Anatomy of Female Gamete (Ovum)

  • Components: Corona radiata, nucleus, cortical granules, zona pellucida, mitochondria.

  • Ova Development: Occurs within ovarian follicles, involving primary oocytes maturing into secondary oocytes (meiosis resumes at ovulation).

Ovarian Cycle

  • 28-day cycle from puberty to menopause divided into:

    1. Follicular Phase (Days 1-13): Development of ovarian follicles; one becomes dominant.

    2. Ovulation (Day 14): Release of secondary oocyte from dominant follicle.

    3. Luteal Phase (Days 15-28): Formation of corpus luteum from ruptured follicle.

Fertilization Process

  • Fusion of male and female gametes; occurs in the ampullary region of the uterine tubes.

  • Phases of Fertilization:

    1. Penetration of the Corona Radiata: Coating surrounding the egg.

    2. Penetration of the Zona Pellucida: Glycoprotein shell around the egg, induces acrosome reaction (release of enzymes).

    3. Fusion of Oocyte and Sperm Cell Membranes: Adhesion mediated by integrins and subsequent fusion of membranes.

Cleavage and Blastulation

  • Post-fertilization, the zygote undergoes cleavage:

    • Series of mitotic divisions producing smaller cells called blastomeres.

    • At 16-cell morula stage, cells form inner cell mass (future embryo) and outer cell mass (trophoblast).

  • Blastulation leads to formation of the blastocyst, characterized by a cavity (blastocele).

Implantation

  • Trophoblasts from the blastocyst penetrate the uterine epithelium around day 6.

  • Three phases of implantation:

    1. Apposition: Initial contact with the endometrium.

    2. Adhesion/Attachment: Strong attachment.

    3. Invasion/Penetration: Trophoblastic cells invade the uterine tissue.

Hormonal Regulation of Menstruation

  • 28-day menstrual cycle:

    1. Menstrual Phase (Days 1-7): Shedding of the endometrium.

    2. Proliferative Phase (Days 7-14): Repair and growth of the endometrium stimulated by estradiol.

    3. Secretory Phase (Days 14-28): Endometrium becomes secretory under progesterone influence.