Simple squamous epithelium

GENERAL HISTOLOGY

CONTENTS:

Epithelia....................................................................................3

Connective tissue......................................................................15

Blood...................................................................................... 70

Muscular tissue....................................................................... 90

Nervous tissue....................................................................... 113

Sense organs.......................................................................... 143

EPITHELIUM

Epithelial tissues are formed by closely apposed polygonal cells with little or no intercellular material. The epithelium is normally separated from the underlying connective tissue by a basement membrane. The epithelium is non-vascular; that is, there are no blood vessels within the epithelium itself. As a result, oxygen, nutrients, and metabolites must diffuse from the blood vessels that supply the underlying connective tissue.

Polarization in epithelial cells.

Because the majority of materials entering or leaving the body pass through epithelia, there often is within epithelial cells a specific arrangement or polarization of cytoplasmic organelles. Nuclei tend to be centrally located, often nearer the basal than the apical surface, with the Golgi apparatus and associated secretory material supranuclear or apical in position. The apical surface itself in many simple epithelia shows microvilli and cilia. Basally basal infoldings with many mitochondria lying in the cytoplasmic “pockets” between the infoldings are seen commonly in epithelia, e.g., of kidney tubules, that actively pump ions across the epithelium. Granular endoplasmic reticulum is situated primarily in basal cytoplasm and is present as large masses in those cells concerned with protein secretion. In many types of epithelial cells, there exists a complex network of tonofilaments (10-nanometer filaments) forming a cytoskeleton that is connected to certain types of surface specializations. Apically, fine fiulaments lie in the cytoplasm and extend into the cores of microvilli; many of these are of actin, which suggest that they are concerned with subtle changes in cell shape and, perhaps, with movement of the microvilli.

EPITHELIUM:

- SURFACE

- GLANDULAR

- SENSORY

SURFACE EPITHELIUM:	It lines the outer surface of the body and the luminal surfaces of cavities within the body.
UNILAYERED:	It consists of only one layer of cells.
- Simple:	All the cells are adjacent to the basal membrane and have equal height.
1. squamous	Its cells are flattened, their height being very little as compared to their width.
2. cuboidal	The height and the width of its cells are more or less equal.
3. columnar	The height of its cells is distinctly greater than their width.
- Pseudostratified	All the cells are adjacent to the basal membrane. However, because the cells are of different shapes and heights, not all reach the surface. The cell nuclei lie at different levels.
MULTILAYERED (STRATIFIED):	It consists of several layers of cells.
- Squamous	Superficial cells are squamous in shape.
1. non keratinized	Superficial cells are living and contain nuclei.
2. keratinized	Superficial cells are dead and are devoid of nuclei.
- Transitional	Superficial cells are able to change their form depending upon the degree of distension.

SIMPLE SQUAMOUS EPITHELIUM

Дата добавления: 2015-10-30