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:

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).

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 by junctional 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. 1-Epithelial Tissue

of the underlying CT----against injuries, bacteria and chemicals (skin –stomach). 1-Protection : (epithelium is specialized for producing secretion (glandular epithelium) 2-Secretory : (small intestine-kidney)3- Absorption : germinal epithelium of testis and ovary4-Reproduction: myoepithelial cells are contractile in function.5-Contraction: is specialized in perception of external stimuli ex. (taste buds of tongue)).6-Neuroepithelium: General Functions of epithelium

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

1-Simple squamous epithelium: polyhedral in shape and oval nuclei,(thin to allow material transport-filteration (kidney, lung, blood vessel). -Endothelium in blood vessels and lymphatic -mesothelium------in peritoneal 2-Simple cuboidal epithelium: present where ion exchange is required (kidney proximal tubule). 3-Simple columnar epithelium i- non –ciliated columnar(Digestive tract) ii-ciliated columnar (oviducts) Based on the last two criteria we classify the epithelium:

4-Sratified squamous epithelium i-non-keratinized (esophagus) ii-keratinized (skin) 5-Pseudostratified ciliated columnar epitheliun (trachea) 6-Transitional epithelium (urinary bladder). a- full b-empty

1-number of cells 2-The presence or absence of a duct system 3-According to the mode of secretion (mechanism) II-glandular epithelium Glands can be classified according to:

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

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 2-The presence or absence of a duct system :

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

a-unicellular glands consists of one cell (goblet cell of small intestine) b-multicellular glands composed of cluster of cells 1-number of cells 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 2-The presence or absence of a duct system : a-Merocrine glands (no loss of its cellular material) pancreas (exocytosis) b-Holocrine glands (complete destruction of the cell)---sebaceous gland c- Apocrine glands ( secretory product is discharged with apical parts of the cytoplasm) ----mammary glands 3-According to the the mode of secretion (mechanism) II-glandular epithelium Glands can be classified according to:

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

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. There are three types of muscle tissue in the vertebrate body: