TISSUES
• There are 4 main types, each of which has subdivisions.
• They are:
1. epithelial tissue or epithelium
2. connective tissue
3.muscle tissue
3. nervous tissue.
EPITHELIAL CELLS
• Are found:
– covering the body
– lining cavities, hollow organs and tubes.
– In glands.
• Functions:
– protection of underlying structures from, for example, dehydration, chemical and
mechanical damage
– secretion
– absorption.
• The cells are very closely packed and the intercellular substance,(the matrix) is minimal.
The cells usually lie on a basement membrane, which is an inert connective tissue.
• Epithelial tissue may be:
, a)simple: a single layer of cells
b)stratified: several layers of cells
SIMPLE EPITHELIUM
• Consists of a single layer of identical cells
• Usually found on absorptive or secretory surfaces, where the single layer enhances these
processes, and not usually on surfaces subject to stress.
• Types:
– Squamous epithelium
– Cuboidal epithelium
– Columnar epithelium
The types are named according to the shape of the cells, which differs according to their
functions.
The more active the tissue, the taller are the cells
A) Squamous (pavement) epithelium
• Composed of a single layer of flattened cells.
• The cells fit closely together like flat stones, forming a thin and very smooth membrane.
• Diffusion takes place freely through this thin, smooth, inactive lining of the following
structures:
– Heart (endocardium)
– blood vessels endothelium
– lymph vessels
– alveoli of the lungs.
, – Lining of collecting ducts of nephrons
b) Cuboidal (cubical) epithelium
• Consists of cube-shaped cells fitting closely together lying on a basement membrane.
• Forms the tubules of the kidneys & found in some glands.
• Actively involved in secretion, absorption and excretion.
c) Columnar epithelium
• Formed by a single layer of cells, rectangular in shape, on a basement membrane.
• Found lining the many organs and often has adaptations suited to its functions e.g:
– Stomach has simple columnar epithelium
– Columnar epithelium in the small intestaines are lined with microvilli which
increases surface area for absorption.
– Those in the trachea are ciliated and also have goblet cells. This produce
mucus that traps dust and then the cilia removes it
• There are 4 main types, each of which has subdivisions.
• They are:
1. epithelial tissue or epithelium
2. connective tissue
3.muscle tissue
3. nervous tissue.
EPITHELIAL CELLS
• Are found:
– covering the body
– lining cavities, hollow organs and tubes.
– In glands.
• Functions:
– protection of underlying structures from, for example, dehydration, chemical and
mechanical damage
– secretion
– absorption.
• The cells are very closely packed and the intercellular substance,(the matrix) is minimal.
The cells usually lie on a basement membrane, which is an inert connective tissue.
• Epithelial tissue may be:
, a)simple: a single layer of cells
b)stratified: several layers of cells
SIMPLE EPITHELIUM
• Consists of a single layer of identical cells
• Usually found on absorptive or secretory surfaces, where the single layer enhances these
processes, and not usually on surfaces subject to stress.
• Types:
– Squamous epithelium
– Cuboidal epithelium
– Columnar epithelium
The types are named according to the shape of the cells, which differs according to their
functions.
The more active the tissue, the taller are the cells
A) Squamous (pavement) epithelium
• Composed of a single layer of flattened cells.
• The cells fit closely together like flat stones, forming a thin and very smooth membrane.
• Diffusion takes place freely through this thin, smooth, inactive lining of the following
structures:
– Heart (endocardium)
– blood vessels endothelium
– lymph vessels
– alveoli of the lungs.
, – Lining of collecting ducts of nephrons
b) Cuboidal (cubical) epithelium
• Consists of cube-shaped cells fitting closely together lying on a basement membrane.
• Forms the tubules of the kidneys & found in some glands.
• Actively involved in secretion, absorption and excretion.
c) Columnar epithelium
• Formed by a single layer of cells, rectangular in shape, on a basement membrane.
• Found lining the many organs and often has adaptations suited to its functions e.g:
– Stomach has simple columnar epithelium
– Columnar epithelium in the small intestaines are lined with microvilli which
increases surface area for absorption.
– Those in the trachea are ciliated and also have goblet cells. This produce
mucus that traps dust and then the cilia removes it
