Embryology and Fetal Development

Stages of Human Development

• Development progresses through distinct stages, from conception to adulthood and aging.
• Each stage is characterized by specific physical, cognitive, and social changes.

Fertilization and Zygote Formation

• Fertilization is the fusion of a sperm and an egg to form a zygote.
• Steps in zygote formation involve: sperm penetration of the egg's outer layers, fusion of the male and female pronuclei, and the activation of the egg’s developmental program.
• Fertilization marks the start of a new organism.

Cleavage, Growth, and Morphogenesis

• Cleavage involves rapid cell divisions, increasing the number of embryonic cells without increasing overall size.
• Growth is the increase in the size and mass of the developing embryo through cell division and differentiation.
• Morphogenesis is the process of shaping the developing embryo into its particular body form, involving the migration and organization of cells.

Primary Germ Layers and Tissue Formation

• Three primary germ layers—ectoderm, mesoderm, and endoderm—derive all the tissues and organs of the body.
• Ectoderm gives rise to the nervous system and epidermis.
• Mesoderm forms the skeletal, muscular, circulatory, and urogenital systems.
• Endoderm forms the linings of the digestive tract and respiratory systems.

Extraembryonic Membranes

• Extraembryonic membranes (chorion, amnion, yolk sac) support the developing embryo.
• The chorion contributes to the placenta.
• The amnion encloses the embryo in fluid for protection.
• The yolk sac plays a role in early blood cell formation.

Fetal Circulation

• Fetal circulation differs from adult circulation based on the presence of the placenta and the umbilical cord.
• Specialized structures (e.g., foramen ovale, ductus arteriosus) allow blood to bypass the lungs.

Changes During Birth

• Circulatory and respiratory systems undergo significant changes as the baby transitions from a dependence on the placenta to breathing and circulating oxygen independently.

Abnormalities in Sex Organ Development

• Genetic or environmental factors can lead to variations in sex organ development.
• Examples include chromosomal disorders influencing sexual differentiation.

Hormonal Regulation of Pregnancy

• Progesterone and estrogen play crucial roles in maintaining pregnancy.

Stages of Childbirth

• Childbirth is a three-stage process.
• First stage: dilation of the cervix.
• Second stage: expulsion of the baby.
• Third stage: expulsion of the placenta.

Aging and the Body Systems

• Aging affects various body systems, including the cardiovascular, immune, musculoskeletal, integumentary, sensory, and nervous systems.
• Changes may result in loss of function or increased susceptibility to disease.

Signs of Aging in the Integumentary System

• Skin loses elasticity, becomes thinner, wrinkles, and may display age spots.

Sensory System Changes with Aging

• Vision and hearing can decline, resulting in difficulty with tasks requiring visual acuity or auditory perception.

Osteoporosis

• Osteoporosis is a bone disorder characterized by reduced bone density, increasing fracture risk, especially in postmenopausal women.

Aging and the Nervous System

• The brain undergoes changes, including a decrease in brain volume and changes in neurotransmitter function.
• Cognitive functions may be affected, though this does not universally occur.

Zygote, Morula, and Blastocyst

• A zygote is the fertilized egg.
• A morula is a solid ball of cells resulting from early cleavage.
• A blastocyst is a hollow sphere of cells with an inner cell mass, which forms the embryo.

Implantation

• Implantation is the process by which the blastocyst embeds itself in the uterine wall.
• Implantation marks the beginning of pregnancy.

Key Milestones in Embryonic Development

• Specific developments typically occur, such as the formation of organs and body parts by specific time periods.

Fetal Development Changes by Month

• Fetus grows and develops progressively in a complex series of changes across the trimesters.

Placenta and Umbilical Cord Function

• The placenta facilitates nutrient and gas exchange between mother and fetus.
• The umbilical cord connects the fetus to the placenta.

Stages of Labor

• Labor progresses through distinct stages characterized by various physiological changes.

Positive Feedback in Childbirth

• Positive feedback mechanisms amplify the uterine contractions during childbirth.

This quiz explores key concepts in embryonic development, including the primary germ layers and their derivatives. It covers morphogenesis in early development, differences between fetal and adult circulation, the hormones that regulate pregnancy, and the stages of childbirth.