Embryonic-Development-Autosaved

Development of Life

Gametes

  • Types of Gametes: Sperm & Ovum (Egg)

  • Characteristics:

    • Sperm: Microscopic, motile, millions produced at once.

    • Ovum: Microscopic, non-motile, typically only one matures per menstrual cycle.

    • Both crucial for reproduction and survival of the species.

Sperm

Definition and Structure

  • Male reproductive cell produced in the testes.

  • Microscopic, consisting of:

    • Head: Contains genetic material.

    • Midpiece: Provides energy for movement.

    • Tail (flagellum): Allows motility through the female reproductive tract.

Function

  • Main job: To fertilize the ovum during sexual activity, forming a zygote, which develops into a new individual.

Lifespan & Production

  • Lifespan typically lasts from a few hours to a few days after ejaculation.

  • Continuous production occurs from puberty until old age, stimulated by hormones from the hypothalamus and pituitary gland.

Ovum

Definition and Structure

  • Female reproductive cell produced in the ovaries, considerably larger than sperm.

  • Contains maternal genetic material in the nucleus.

Function

  • Main job: To combine with sperm during sexual activity to form a zygote.

  • Contributes half of the genetic material necessary for a new individual.

Lifespan & Production

  • Lifespan: 12 to 24 hours post-ovulation.

  • Production occurs once per menstrual cycle, stimulated by hormonal changes, notably luteinizing hormone (LH).

Stages of Prenatal Development

Germinal Stage (Day 0 – 14)

  • Fertilization: Sperm penetrates the egg and nuclei fuse forming a zygote. Occurs in the fallopian tube.

Timeline Post-Fertilization

  1. Zygote Formation:

    • The initial cell formed from sperm and ovum.

    • Viable for up to 24 hours.

  2. Cleavage (Cell Division):

    • Rapid mitotic divisions forming a morula (solid ball of cells).

    • Progresses to a blastocyst (hollow structure).

Blastocyst Development

  • Consists of:

    • Inner Cell Mass: Develops into the embryo.

    • Trophoblast: Forms the placenta.

Journey to the Uterus

  • The blastocyst moves down the fallopian tube toward the uterus, aided by cilia and contractions.

  • Implantation: Occurs 6-10 days post-fertilization into the uterine wall, critical for nutrient supply.

Differentiation and Staging

Cell Differentiation

  • Cells begin specializing for different functions, forming embryonic, placental, or amniotic structures.

  • Gastrulation: Formation of three primary layers—ectoderm, endoderm, and mesoderm:

    • Ectoderm: Skin, nervous system.

    • Endoderm: Digestive and respiratory systems.

    • Mesoderm: Muscles, bones, blood.

Embryonic Stage (2 – 8 weeks)

  • Developing baby known as an embryo.

  • First organ formation begins in the third week.

Fetal Stage (Final Stage)

  • From the 8th week onwards, the fetus grows and develops in the uterus.

  • Major organ systems form, and by the end of the eighth week, the fetus is recognizable.

Growth and Development

  • Distinct limbs and skeletal structures start to appear during this stage.

  • Maternal antibodies provide immunity, and the fetus uses maternal nutrient intake for growth.