3. Types of tissues Epithelial tissue Connective tissue Muscular tissue
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:
Types of tissues
Epithelial tissue
Connective tissue
Muscular tissue
Nervous tissue

4. 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) .

5. 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 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.

6. General Functions of epithelium
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 ovary
4-Reproduction:
myoepithelial cells are contractile in function.
5-Contraction:
is specialized in perception of external stimuli ex. (taste buds of tongue)).
6-Neuroepithelium:

7. Classification of epithelia according to
Classification of the epithelia
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

8. Based on the last two criteria we classify the epithelium:
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)

9. 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

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

11. 1-number of cells
a-unicellular glands consists of one cell (goblet cell of small intestine)
b-multicellular glands composed of cluster of cells

12. 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

13. 3-According to the mode of secretion (mechanism)
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

15. 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 the mode of secretion (mechanism)

16. ( skeletal, smooth, cardiac muscles)
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.

17. 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.