COMPOUND EPITHELIA (MULTILAYERED EPITHELIA) -
- These are made up of more than one layer of cells.
- The compound epithelia may be stratified and transitinal.
1. STRATIFIED EPITHELIUM -
- It has many layers of epithelial cells, however, the deepest layer is made up of columnar or cuboidal cells.
- On the basis of the shape of the cells present in the surperficial layers.
It is of four types :-
(i) Stratified Squamous Epithelium -
- The cells in the deepest (= basal) layer are columnar or cuboidal with oval nuclei.
- It is called germinative layer (= stratum germinativum).
- The cells of this layer divide by mitosis to form new cells.
- The new cells gradually shift outward.
- In the middle layers the cells become polyhedral with rounded nuclei.
- These are called intermediate layers.
- The superficial layers are flat with transversely elongated nuclei.
- These layes are called squamous layers.
- It is of two types : (a) Keratinized Stratified Squamous Epithelium.
(b) Nonkeratinized Stratified Squamous Epithelium.
(ii) Stratified Cuboidal Epithelium -
- It has outer layer of cuboidal cells and basal layer of columnar cells.
- It forms the epidermis of fishes and many urodels (tailed amphibians such as salamanders). e.g. ® It also lines the sweat gland ducts and larger salivary and pancreatic ducts.
(iii) Stratified Columnar Epithelium -
- It has columnar cells in both superficial and basal layers.
- e.g. It covers the epiglottis and lines mammary gland ducts and parts of urethra.
(iv) Stratified Ciliated Columnar Epithelium -
- Its outer layer consists of ciliated columnar cells and basal layer of columnar cells. e.g. ® It lines the larynx and upper part of the soft palate.
2. TRANSITIONAL EPITHELIUM (= UROTHELIUM) -
- This epithelium consists of 4 to 6 layers of cells.
- The cells of deepest (= basal) layer are columnar or cuboidal.
- The cells of middle layer are polyhedral or pear shaped.
- The cells of the surface layer are large and globular or umbrella shaped.
- There is no germinative layer or basement membrane but shows mitosis.
- e.g. renal calyces, renal pelvis, ureters, urinary bladder and part of the urethra.