Mustansiriyah University College of science Biology Dept Zoology
Mustansiriyah University College of science Biology Dept. Zoology th 4 class Embryology LAB. (5) NAME : 1
• As a useful generalization, • 1. The ectoderm (the outer skin) forms the covering of the body (the epidermis) as well as the nervous system. • 2. The endoderm (the inner skin) forms the lining of the gastrointestinal and respiratory systems. • 3. The mesoderm (the middle skin) forms the skeletal, connective and muscle tissues of the body.
The integumentary, skeletal and muscular systems • The skin • The integumentary system includes the skin and its specialized derivatives, including the hairs, nails, sweat and sebaceous glands. The mammary glands and teeth are also considered as components of the integumentary system. • The system develops from surface ectoderm, mesoderm and neural crest cells.
• By the end of the first month the single layer of ectodermal cells divide, forming a superficial layer of cells known as the periderm and a basal layer. • The basal layer becomes the stratum germinativum (1 st layer of epidermis) which produces all the definitive layers of the epidermis. • The cells of the periderm become keratinized, and Later in fetal life, the peridermal cells are replaced by the stratum corneum(5 th layer of epidermis) and the melanocytes derived from the neural crest migrate into the epidermis.
The hairs and glands of the skin • Hairs develop during the fetal period as proliferations of the stratum germinativum. • The epidermal cells in the center of the hair bud become keratinized to form the hair shaft, and the surrounding mesenchymal cells differentiate into the dermal root sheath.
• Most sebaceous glands develop as buds from the side of the epithelial root sheath growing into the dermis. • these glands produce an oily secretion that lubricates the hair and skin. • The sweat glands develop as epidermal buds into the underlying dermis which become coiled to form the secretory part of the glands.
The skeletal system • The origin of mesenchymal cells forming the skeletal tissues varies in different regions of the body. Mesenchymal cells forming the axial skeleton arise from the mesodermal somites. • The axial skeleton is composed of the • 1. skull. • composed of the neurocranium, which surrounds the brain, and the viscerocranium, which surrounds the mouth, pharynx and larynx • 2. vertebral column. • 3. sternum. develops from a pair of cartilaginous bars that form in the ventral body wall • 4. ribs.
Clinical info. • 1. Most skull deformities result from abnormal development of the brain, Babies born with acrania fail to survive because most of the brain is absent. • 2. In microcephaly, the size of the brain is very small, and consequently the skull fails to grow
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