A group of cells which have same origin, same structure and function called tissue.
Study of tissue is called Histology.
Nervous system and Endocrynic systems co-ordinated and intigrated the different tissues, organs and systems of multi cellular animals.
Tisues are classified into:
4. Nervous tissues
I. Epithelial tissues:
1. Epithelial tissues may be originated from any of the three germinal layers.
2. Cells are arrenged in continuous sheets.
3. Cells are aggregated with very little extracellular substance.
4. Cells are joined by intercellular junctions.
5. Epithelial tissue is avascular(with out blood supply).
6. Cells contain nucleus and rests on a basement membrane.
7. The free or apical urface of many types of epithelial cells contains microvilli or stericelia or celia
Epithelial tisues are of two types based on their function. They are:
1. Covering and lining Epithelia
2. Glandular Epithelia
1.Covering and Lining Epithelia:
• They cover the surface of organs and line the cavities.
• According to the number of cell layers they can be classified into three types. They are
1. Simple Epitheliaum
2. Stratified Epithelium
3. Psuedo Stratified Epithelium.
1. Simple Epithelium:
1.It consists of a single layer of cell.
2. All the cells rest on the basal lamina
3. It helps for diffusion, secretion, and absorption.
4.Cells contain nucleus and the form of the nucleus corresponds to the cell shape.
5. Cells are joined by inter cellular junctions.
6. This tissues cover the surface of organs and cavities.
7. This tissue may be derived from any of the three germ layers.
8. Based on cell shape, simple epithelium is off different kinds. They are:
a) Simple squamous epithelium- Lines blood vessels,heart, cavities, bowman’s capsule, alveoli of lungs.
b) Simple cuboidal epithelium- Lines ovary, thyroid vessels, convoluted tubules of nephron.
c) Simple columnar epithelium- Mucosa of stomach, interstine lining of fallopian tubes, uterus, canal of spinal aord and ventricles of brain.
a) Simple squamous epithelium :
1. The endothelium that lines blood vessels and heart.
2. The mesothelium that lines body caviteis. i.e. pleura, peritonium, pericardium.
3. Wall of Bowman’s capsule of nephron
4. Lining of alveoli of lungs.
b) Simple cuboidal epithelium:
1. Cells are cube shaped.
2. Nucleus is spherical and centrally located.
1. Generally epithelium covering the ovary.
2. Lining of thyroid vesicles, salivary gland and sweat glands.
3. Lining of proximal and distal convoluted tubules of nephron.
c) Simple columnar epithelium:
1. The cells are pillar like taller than broad.
2. Nucleus is oval and located near the base.
3. This is of two types: Non ciliated and ciliated
I. Non Ciliated:
1. Columnar cells with ut Cilia.
2. Cell surface may bear microvilli.
3. Mucus –secreting goblet cells may be present .
Mucosa of stomach and intestine.
II. Ciliated :
1. Columnar cells bear cilia. Goblet cells occur in same cases.
Lining of fallopian tubes,uterus, central canal f spinal cord, ventricles of brain.