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Histology : It is the science which deals with the microstructures of tissues and organs.

Histology : It is the science which deals with the microstructures of tissues and organs. The tissues A basic tissue type is a group of similar cell and able to perform a common function. Our body is composed of only four basic tissue types:.

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Histology : It is the science which deals with the microstructures of tissues and organs.

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  1. Histology: It is the science which deals with the microstructures of tissues and organs. • The tissues • A basic tissue type is a group of similar cell and able to perform a common function. • Our body is composed of only four basic tissue types:

  2. In most animals, combinations of various tissues make up functional units called organs, and groups of organs that work together form systems. • For example, the human digestive (system )consists of a stomach (organ) small intestine, large intestine, and several other organs, each a composite of different tissues (epithelium- connective-muscles-nervous) .

  3. 1-Epithelial Tissue • means covering body surface and lining body cavity. General characters of epithelial tissues : • The cells are closely aggregated with very little intercellular substance (matrix) of acid mucopolysaccharides . • The cells are regular in shape .They are held tightly together byjunctional complex • Epithelial cells are firmly bound to the underlying CT by a thin membrane called basement membrane. • Blood vessels do not penetrate the epithelium (avascular). • Epithelium can be derived from all three embryonic germ layer : ectoderm ------------- epidermis of the skin endoderm-------------epithelium of alimentary canal mesoderm-------------kidney • Epithelium is in a continuous process of degeneration and regeneration. It has a high mitotic activity .It has a high renewal rate.

  4. General Functions of epithelium

  5. Classification of the epithelia Classification of epithelia according to A-number of layers B-Shape of cells 1-Simple epithelium (one layer) 1-Squamous(flat) 2-Cuboidal (Height = width) 2-Stratified epithelium ((more than one layer 3-Columnar (Hight is 2-5 greater than width)

  6. Based on the last two criteria we classify the epithelium:

  7. II-glandular epithelium Glands can be classified according to:

  8. 1-number of cells • a-unicellular glands consists of one cell (goblet cell of small intestine) • b-multicellular glands composed of cluster of cells

  9. 2-The presence or absence of a duct system : • a- Exocrine(in which secretion is released through ducts (salivary glands) • b-Endocrine glands (secretion released directly to the blood) thyroid glands. • c- Mixed glands (endocine and exocrine)----pancrease

  10. 3-According to the mode of secretion (mechanism) • a-Merocrineglands (no loss of its cellular material) pancreas (exocytosis) • b-Holocrineglands (complete destruction of the cell)---sebaceous gland • c- Apocrine glands ( secretory product is discharged with apical parts of the cytoplasm) ----mammary glands

  11. II-glandular epithelium Glands can be classified according to:

  12. 2-Muscular tissue ( skeletal, smooth, cardiac muscles) - Muscular tissue is composed of long cells called muscle fibers that are capable of contracting when stimulated by nerve impulses. -It has large numbers of myofibrils made of the contractile proteins actin and myosin. -The sliding filament is accepted as the mechanism that accounts for muscular contraction.

  13. There are three types of muscle tissue in the vertebrate body: 1- Skeletal muscles connected to the skeleton and is concerned with body movements. 2- Cardiac muscles forms the contractile portion of the heart . 3-Smooth muscles does not exhibit striations. It is found as part of the walls of the viscera.

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