Histology
Ass. lec.
Dentistry College
Wafaa H. M. Alhashimy
Second Stage
The different types of cells composing the human body are arranged and coorperatively organized into four tissues .
Groups of these tissues are assembled in various organizational and functional arrangements into organs which vary out functions of the body . the four basic tissue types are epithelium , connective , muscle and nervous tissue ,
Consist of sheets of cells that cover the external surfaces of the body , have numerous functions : protection , transport , secretion , absorption , control of movement of materials body compartments via selective permeability of intercellular junctions between epithelial cells , and detection of sensations .
Types of epithelial :
- Simple epithelium , is composed of asingle layer of cells with basement membrane .
Simple epithelium classification into four types and they are :
1- Simple Sequamous epithelium that covers the external surface of the digestive organs lungs and heart called mesothelium , also covers the lumina of the heart , blood vessles and lymphatic vessles is called endothelium .
2- Simple cuboidal epithelium lines small excretory ducts in different organs such as in the proximal convoluted tubules of the kidney .
3- Simple columanar epithelium covers the digestive organs such as stomach , small and large intestines.
columnar cells are Ciliatedon free surfaces that covers the lumina of the trachea .
4- Pseudostratified columnar epithelium lines the respiratory passages such as trachea .
1

-Stratified epithelium : is composed of more than one layer ofcells with basement membrane . .
1- StratifiedSequamous epithelium there are two types keratinized epithelium is found exposed surface of the body such as the skin . Non keratinized epithelium covers moist cavities such as oral cavity and esophagus .
2- Stratifiedcuboidal epithelium and Stratified columnar epithelium lines the larger excretory ducts of salivery glands .
3- transitional epithelium lines the bladder .
Consists of cells and extracellular material called matrix , the matrix consists of connective tissue fibers , ground substance and tissue fluid . the connective tissue binds , anchors and supports various cells , tissues and organs in the body
Table – 1 – Function of connective tissue cells
Cell Typ
Fibroblast , Chondroblast , Osteoblast
Plasma cell
Lymphocyte ( several types)
Eosinophilic leukocyte
Neutrophilic leukocyte (phagocyte)
Macrophage
Mast cell and basophilic leukocyte
Adipose ( fat ) cell
Function
Production of fibers and ground substance
Production of antibodies
Production of immunocompetent cells
Participation in allergic and vasoactive reaction , modulation of inflammatory process
Phagocytosis of foreign substances , bacteria
Secretion of cytokines and other molecules , Phagocytosis of foreign substances , bacteria
Liberation of pharmacologically active molecules (eg.histamine)
Storage of neutral fats
2

FiGURE 1: Cells of the connective tissue
1- Collagen fibers
2- Elastic fibers
3- Reticular fibers
Classification of connective tissues: this tissue is classified into loose and dense connective tissue depending on the amount , type ,arrangement and abundance of cells , fibers and ground substance.
Loosconnective tissue: abundant ground substance and thin and relatively sparse fibres. It has a viscous gel-like consistency and is important for the diffusion of oxygen and nutrients from small vessels, and the diffusion of metabolites back to the vessels. The primary location of loose connective tissue is beneath epithelia that line the internal surfaces of the body .
Dence connective tissue:
- Dence regular connective tissue is found in tendons and ligaments .
- Dence Irregular connective tissue is present in the dermis of skin .
3