LECTURER: DR. ADELEKE O.S
THE EMBRYONIC PERIOD
The embryonic period is a crucial stage in prenatal development that occurs from the third to the eight
weeks after fertilization. It marks the initial stages of organogenesis, during which the basic structure
of the body and its major organs begins to form.
Key events during the embryonic period are:
1. Gastrulation: During gastrulation, cells within the blastocyst start to differentiate into three
primary germ layers: ectoderm, mesoderm, and endoderm. These layers will give rise to various
tissues and organs in the body.
2. Neurulation: A critical event in early embryonic development, neurulation is the process by which
the neural plate folds and forms the neural tube. The neural tube ultimately gives rise to the central
nervous system, including the brain and spinal cord.
3. Organogenesis: This is the phase where the major organ systems begin to develop. Differentiation
of the germ layers leads to the formation of structures such as the heart, lungs, liver, kidneys, and
limbs.
4. Somite Formation: Somites are segmented blocks of mesodermal cells that give rise to important
structures such as the vertebrae, skeletal muscles, and dermis of the skin. Somite formation is a
critical process during the embryonic period.
5. Placenta Development: The placenta, a vital organ for nutrient and waste exchange between the
mother and the developing embryo, undergoes development during this period. The placenta plays a
crucial role in providing oxygen and nutrients to the developing fetus and removing waste products.
DERIVATIVES OF THE GERM LAYERS
The three primary germ layers—ectoderm, mesoderm, and endoderm—give rise to various tissues
and organs during embryonic development. These derivatives highlight the remarkable differentiation
and specialization that occur during embryonic development. The interactions between cells, guided
by genetic and environmental factors, lead to the formation of a highly organized and complex
organism. Understanding the derivatives of germ layers is essential for comprehending the
subsequent development of specific organs and systems in the human body.
Derivatives of each germ layer are:
1. Ectoderm:
- Epidermis: The outermost layer of the skin.
- Central Nervous System: Brain and spinal cord.
- Peripheral Nervous System: Nerves and ganglia.
THE EMBRYONIC PERIOD
The embryonic period is a crucial stage in prenatal development that occurs from the third to the eight
weeks after fertilization. It marks the initial stages of organogenesis, during which the basic structure
of the body and its major organs begins to form.
Key events during the embryonic period are:
1. Gastrulation: During gastrulation, cells within the blastocyst start to differentiate into three
primary germ layers: ectoderm, mesoderm, and endoderm. These layers will give rise to various
tissues and organs in the body.
2. Neurulation: A critical event in early embryonic development, neurulation is the process by which
the neural plate folds and forms the neural tube. The neural tube ultimately gives rise to the central
nervous system, including the brain and spinal cord.
3. Organogenesis: This is the phase where the major organ systems begin to develop. Differentiation
of the germ layers leads to the formation of structures such as the heart, lungs, liver, kidneys, and
limbs.
4. Somite Formation: Somites are segmented blocks of mesodermal cells that give rise to important
structures such as the vertebrae, skeletal muscles, and dermis of the skin. Somite formation is a
critical process during the embryonic period.
5. Placenta Development: The placenta, a vital organ for nutrient and waste exchange between the
mother and the developing embryo, undergoes development during this period. The placenta plays a
crucial role in providing oxygen and nutrients to the developing fetus and removing waste products.
DERIVATIVES OF THE GERM LAYERS
The three primary germ layers—ectoderm, mesoderm, and endoderm—give rise to various tissues
and organs during embryonic development. These derivatives highlight the remarkable differentiation
and specialization that occur during embryonic development. The interactions between cells, guided
by genetic and environmental factors, lead to the formation of a highly organized and complex
organism. Understanding the derivatives of germ layers is essential for comprehending the
subsequent development of specific organs and systems in the human body.
Derivatives of each germ layer are:
1. Ectoderm:
- Epidermis: The outermost layer of the skin.
- Central Nervous System: Brain and spinal cord.
- Peripheral Nervous System: Nerves and ganglia.
