Tissues are group of associated, similarly structured
cells that perform specialized functions for the
survival of the organism.
Animal tissues are classified into four main groups.
• I. EPITHELIAL TISSUES
• II. CONNECTIVE TISSUES
• III. MUSCLE TISSUES
• IV. NERVOUS TISSUES
• Connective tissues support and hold parts of
the body together, comprise the:
fibrous and elastic connective tissues,
the adipose (fatty) tissues,
cartilage and bone.
• Connective tissues are the most abundant
tissues in the body.
Cells of the connective tissue
• Fibroblast – secrete Collagen, Elastin, reticulin
• Fat cells – Adipose cells
i. Monocytes – blood
ii. Phagocytes – alveoli
iii. Kupfer cells – Liver
iv. Fibroblasts – lymph node and spleen
v. Microglial cells – brain
There are three types of regeneration
1. Labile Cells with continuous replication Eg.
Skin, mucous membrane, secretory gland etc
2. Stable cells – retain the ability to replicate
but do so infrequently eg. Liver, kidney,
3. Permanent cells – unable to replicate after
normal growth is complete. Eg. Nerve cells,
cardiac cells, skeletal cells
Covering and protecting type of tissue
Epithelial tissue may be:
simple: a single layer of cells
stratified: several layers of cells.
• Simple epithelium consists of a single layer of
identical cells and is divided into four types.
• It is usually found on absorptive or secretory
surfaces, where the single layer enhances
these processes, and not usually on surfaces
subject to stress.
• The types are named according to the shape
of the cells, which differs according to their
The squamous is made of
a single thin layer of
flattened cells with
They are found in the
walls of blood vessels
and air sacs of lungs and
are involved in a
functions like forming a
The cuboidal epithelium
The cuboidal epithelium is
composed of a single layer
of cube-like cells.
This is commonly found in
ducts of glands and tubular
parts of nephrons in
kidneys and its main
functions are secretion and
The epithelium of proximal
convoluted tubule (PCT) of
nephron in the kidney has
The columnar epithelium
Composed of a single layer of
tall and slender cells.
Their nuclei are located at the
base. Free surface may have
They are found in the lining of
stomach and intestine and
help in secretion and
If the columnar or cuboidal
cells bear cilia on their free
surface they are called
Compound epithelium is made of more
than one layer (multi-layered) of cells and thus
has a limited role in secretion and absorption .
Their main function is to provide
protection against chemical and mechanical
stresses. They cover the dry surface of the skin,
the moist surface of buccal cavity, pharynx,
inner lining of ducts of salivary glands and of
Stratified squamous epithelium
• This is composed of a number of layers of
cells of different shapes representing newly
formed and mature cells.
• In the deepest layers the cells are mainly
columnar and, as they grow towards the
surface, they become flattened and are then
Non-keratinised stratified epithelium.
• This is found on wet surfaces subjected to
wear and tear but are protected from drying,
e.g. the conjunctiva of the eyes, the lining of
the mouth, the pharynx, the oesophagus and
Keratinised stratified epithelium
• . This is found on dry surfaces subjected to
wear and tear, i.e. skin, hair and nails.
• The surface layer consists of dead epithelial
cells that contain the protein keratin.
• This forms a tough relatively waterproof
protective layer that prevent drying of the
live cells underneath.
This is composed of several layers of pearshaped cells It is found lining the urinary
bladder and allow for stretching as the
1. Mucous membrane Eg,
2. Serous membrane Eg.
Pleura, pericardium and
Lines the cavities of movable
joints and surrounds the
Produces synovial fluid
Any structure of animals that produces chemical
secretions or excretions.
Glands are classified by shape, such as tubular
and saccular, or saclike
By structure, such as simple and compound.
Types of the simple tubular eg. The sweat glands
the simple saccular glands Eg. The sebaceous
• Glands are of two types
1. Endocrine : ductlessproduces hormone
*branched tubularbulbouretral gland
Neural tissue exerts the greatest control over
the body’s responsiveness to changing conditions.
Neurons, the unit of neural system are excitable
The neuroglial cell which constitute the rest of
the neural system protect and support neurons.
Neuroglia make up more than one half the volume
of neural tissue in our body.
STRUCTURE OF NEURON
Principle cells of Nervous Tissue
Consist of 3 parts :
– CELL BODY (perikaryon/soma)
– A single AXON
– Multiple DENDRITES
ø 5-150 µm
• Describe the various types of
human tissues with diagrams.
Mention the functions of
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