Prenatal Development: Germinal Period and Conception

• Prenatal development is a crucial part of the overall development process, involving the baby's growth inside the mother's womb.
• Prenatal development typically takes about 38 weeks.
• There are three main stages of prenatal development: Germinal Period, Embryonic Period, and Fetal Period.

Germinal Period

• This stage lasts about 14 days, starting at conception when sperm and egg combine to form a Zygote.
• During the germinal stage, the zygote divides to implant into the uterine wall through fertilization, cleavage, blastulation, and implantation.
• Once implantation is complete, the embryonic stage begins.

Types of Cell Division

• Mitosis is the process of making new body cells.
• Meiosis is the cell division that creates egg and sperm cells, and is fundamental for life.

Conception and Zygote

• Conception is the action of conceiving a child.
• A Zygote is a fertilized egg cell, resulting from the union of a female gamete (egg or ovum) with a male gamete (sperm).

Fertilization

• Sperm and egg unite in a fallopian tube, forming a zygote.

Cleavage

• Cleavage includes the early mitotic divisions.
• Multicellular organism development begins from a single-celled zygote, undergoing rapid cell division to form a blastula.
• Rapid, multiple rounds of cell division are termed cleavage.

Blastulation

• This is the process of changing the Morula into a Blastocyst.
• After cleavage produces 100+ cells, the embryo is called a blastula.
• A blastula is typically a spherical cell layer (blastoderm) surrounding a fluid/yolk-filled cavity (blastocoel).

Major Blastocyst Parts:

• Embryoblast is the cell mass at the embryonic pole of the blastocyst that develops into the embryo.
• The trophoblast is a thin cell layer that helps the developing embryo attach to the uterine wall, protects the embryo, and forms part of the placenta.
• The blastocoel is a fluid-filled cavity characteristic of animal embryos at the blastula stage.
• Approximately 60-80% of fertilized eggs do not make it through the blastocyst stage.

Implantation

• The developing embryo, as a blastocyst, moves through the uterus.
• The embryo makes contact with the uterine wall (endometrium) and remains attached until birth.
• The uterine lining (endometrium) prepares for the developing blastocyst to attach via internal changes; without these changes, implantation will not occur and the embryo sloughs off during menstruation.

Details of Germinal Period Development:

• 24-30 hours after fertilization, the male (sperm) and female (egg) chromosomes unite.
• 36 hours after fertilization, the ovum/zygote divides into two cells (cleavage).
• 48 hours (2 days): Two cells divide into four cells.
• 72 hours (3 days): 4 cells become a compact ball of 16-32 cells.
• 96 hours (4 days): The hollow ball (morula) contains 64-128 cells.
• 4-5 days: The blastocyst is still free in the uterus (blastulation).
• 6-7 days: The blastocyst attaches to the uterine wall.
• 11-15 days: The blastocyst invades the uterine wall and becomes implanted (implantation).

Embryonic Period

• Lasts from 2 to 8 weeks after conception, beginning after implantation.
• This period is marked by the early development of internal body structures.
• Cell differentiation intensifies, organs appear, and life support systems for the embryo develop.

Embryonic Mitosis

• Mitosis continues to create more cells for the embryo.
• Late in the second week after fertilization, gastrulation occurs.
• Three germ layers of gastrula give rise to specific organ and organ systems: Endoderm, Mesoderm, and Ectoderm.

Germ Layers

• The Endoderm (inner layer) forms cells of internal glands and organs (lungs, intestines, thyroid, pancreas, and bladder).
• The Mesoderm (middle layer) forms cells of the heart, blood, bones, muscles, and kidneys.
• The Ectoderm (outer layer) forms cells of the epidermis, nervous system, eyes, inner ears, and connective tissues.

Embryo Support System

• Support systems for the embryo develop rapidly as the three layers of the embryo form: placenta, umbilical cord, and amnion.

Fetal Period

• A human embryo becomes a fetus and continues developing until birth, from the ninth week of pregnancy until birth.
• 2-7 months after conception, growth and development continues dramatically.
• 3 months after conception, the baby is fully formed, about 3 inches long, and weighs approximately 1 ounce.
• 4 months after conception, the baby's eyes can blink and the heart and blood vessels are fully formed.
• 5 months after conception, the baby weighs about a pound and is about 12 inches long.
• A mother can usually feel fetal movement at this time, known as "quickening"; ultrasounds are commonly performed for all pregnant women during this period.
• 6 months after conception, the baby can respond to sounds by moving or increasing their pulse
• 7 months after conception, the baby weighs around 3 pounds and is about 16 inches long.
• 8-9 months after conception, the baby grows longer, gains substantial weight (about 4 pounds), and is about to be born.

Hazards in Prenatal Development

• During pregnancy, the mother's body undergoes many changes to nourish and protect the baby.
• Pregnant women and babies are vulnerable due to clusters of hazards to prenatal development.
• Teratology is the study of birth defects and their etiology from the Greek "teratos" or monster.

Groups of Hazards to Prenatal Development

• Prescription and Nonprescription Drugs:
• Nonprescription drugs (over-the-counter/OTC) are considered safe/effective for general public use without professional advice. Examples: acetaminophen, aspirin, antacids, decongestants, antihistamines, and laxatives.
• Prescription drugs require written instruction from an authorized health professional. Examples: blood pressure tablets, cancer medicine, and strong painkillers.
• Psychoactive Drugs: Affect how the brain works and causes changing mood, awareness, thoughts, feelings, or behavior. Examples: alcohol, caffeine, nicotine, marijuana, and certain pain medicines.
• Environmental Hazards: Can affect human health in various ways, from chronic diseases such as cancer to acute illnesses such as heat exhaustion. Examples: water and air pollution, extreme weather, or chemical exposures.
• Maternal Factors: Illnesses such as Rubella (German Measles), Syphilis, Genital Herpes, AIDS, nutrition, high anxiety, and stress. Includes maternal age (too early or too late, beyond 30).