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ANIMAL TISSUES
A group of cells having same origin, structure and function
are called the tissues. Animal tissues are 4 types:
(i) Epithelial (ii) Connective (iii) Muscular (iv) Neural
I. EPITHELIAL TISSUE (EPITHELIUM)
• It has a free surface that faces body fluid or outside
environment.
• Covers or lines body or body parts.
• Compactly packed cells with little intercellular matrix. (a) Unicellular (b) Multicellular
• Epithelial tissues are 2 types: Simple and Compound. Based on mode of pouring of secretions, glands are 2 types:
Exocrine glands: Here, secretions are released through
1. Simple epithelium
ducts (tubes). Exocrine glands secrete mucus, saliva,
It is composed of a single layer of cells. It lines body cavities, earwax, oil, milk, digestive enzymes etc.
ducts and tubes. Based on structural modification of cells, Endocrine glands: Ductless. They produce hormones.
simple epithelium is 3 types:
2. Compound epithelium
o Squamous epithelium:
• Made up of more than
- Thin layer of flattened cells with irregular boundaries.
one layer (multi-
- Found in the walls of blood vessels and lung alveoli.
layered) of cells.
- Functions: Form a diffusion boundary.
• Limited role in
o Cuboidal (cubical) epithelium: secretion & absorption.
- Composed of cube-like cells. • They cover dry surface
- Found in ducts of glands and tubular parts of nephrons. of skin, moist surface of buccal cavity, pharynx, inner
- Functions: Secretion and absorption. lining of ducts of salivary glands and pancreatic ducts.
- The epithelium of proximal convoluted tubule (PCT) • Function: Protect against chemical & mechanical stresses.
of nephron in the kidney has microvilli.
Cell junctions: The junctions that provide structural and
o Columnar epithelium:
functional links between adjacent cells. They are found in
- Composed of tall and slender cells. epithelium and other tissues. They are 3 types:
- Their nuclei are located at the base. i. Tight junctions: Help to stop substances from leaking
- Free surface may have microvilli. across a tissue.
- Found in the lining of stomach and intestine. ii. Adhering junctions: Perform cementing to keep
- Functions: Secretion and absorption. neighbouring cells together.
iii. Gap junctions: Facilitate communication b/w adjoining
cells by connecting the cytoplasm for rapid transfer of
ions, small molecules and sometimes big molecules.
II. CONNECTIVE TISSUE
• It links and supports other tissues/organs.
• They are most abundant in complex animals.
• All connective tissues except blood have fibroblast cells.
They secrete structural fibrous proteins called collagen &
Modification of columnar or cuboidal cells elastin. They give strength, elasticity & flexibility to tissue.
• Ciliated epithelium: • The cells also secrete modified polysaccharides (matrix),
which accumulate between cells and fibres.
- Cells bearing cilia on their free surface.
• Types of connective tissues: Loose, Dense & Specialised.
- Present in the inner surface of hollow organs like
bronchioles and fallopian tubes. 1. Loose Connective Tissues
- Functions: To move particles or mucus in a specific In this, cells (fibroblasts, macrophages, mast cells etc.) and
direction over the epithelium. fibres are loosely arranged in a semi-fluid matrix.
• Glandular epithelium: For secretion. They are 2 types: It is 2 types: Areolar & Adipose.
Unicellular: Consists of isolated glandular cells. o Areolar tissue:
E.g. Goblet cells of the alimentary canal. - Present beneath the skin.
Multicellular: Contains cluster of cells. E.g. salivary - It serves as a support framework for epithelium.
glands.
1
, Limb bones serve weight-bearing functions.
Take part in locomotion and movements.
Blood cells are produced in bone marrow.
• Blood:
o A fluid connective tissue containing plasma, red blood
cells (RBC), white blood cells (WBC) and platelets.
o Helps in the circulation of various substances.
o Adipose tissue:
III. MUSCLE TISSUE
- Seen mainly under skin.
- The tissues made of many muscle fibres (muscle cells).
- Its cells (adipocytes) store fats.
- Muscle fibres are composed of numerous fine myofibrils.
- Excess nutrients which are
- Muscle fibres can contract (shorten) and relax (lengthen).
converted into fats are stored in
- Muscles take part in locomotion and movements.
this tissue.
- Muscles are 3 types: skeletal, smooth and cardiac.
2. Dense Connective Tissues
In this, fibres and fibroblasts are compactly packed. 2 types:
o Dense regular connective tissues:
- Show regular pattern of
fibres.
- Collagen fibres are present
in rows between many
parallel bundles of fibres.
- E.g. tendons & ligaments. 1. Skeletal (striated or voluntary) muscle
i. Tendons: Attach
- They are attached to bones. E.g. Biceps.
muscles to bones.
- Striations are present in muscle fibres.
ii. Ligaments: Attach one bone to another.
- Muscle fibres are bundled together in a parallel fashion.
o Dense irregular connective tissues:
- A sheath of tough connective tissue encloses several
bundles of muscle fibres.
Irregular pattern of fibres.
- Fibroblasts & fibres (mostly 2. Smooth (non-striated or visceral) muscle
collagen) are oriented - Involuntary and fusiform (Fibres taper at both ends).
differently. - No striations.
- This tissue is present in skin. - Cell junctions hold them together and they are bundled
together in a connective tissue sheath.
- They are seen in the wall of internal organs such as the
3. Specialized Connective Tissues
blood vessels, stomach and intestine.
• Cartilage:
3. Cardiac muscle
o In this, intercellular material
- Involuntary muscle seen only in the heart.
(matrix) is solid and pliable
- Cell junctions fuse the plasma membranes of cardiac
(due to chondroitin salts)
muscle cells and make them stick together.
and resists compression.
- Communication (gap) junctions (intercalated discs) at
o Cartilage cells (chondrocytes) are enclosed in small
some fusion points allow cells to contract as a unit, i.e., when
cavities within the matrix secreted by them.
a cell receives signal to contract, other cells also contract.
o Most of the cartilages in vertebrate embryos are replaced
by bones in adults. IV. NEURAL TISSUE
o Cartilage is present in the tip of nose, outer ear, joints • Made up of neurons (unit of neural system).
in the vertebral column, limbs and hands in adults. • Responsible for control and co-ordination of the body.
• Bone: • Neurons are excitable cells. They carry impulses.
o It has hard and non-pliable • Neurons are protected and supported by neuroglial cells.
matrix rich in calcium salts • Neuroglia make up more than half the volume of neural tissue.
and collagen fibres which ORGAN AND ORGAN SYSTEM
give bone its strength.
• Cells → tissues → organs → organ systems.
o Bone cells (osteocytes) are seen in spaces called lacunae.
• This organization is essential for better coordinated
o Functions:
It provides structural frame to the body. activities of cells.
Support and protect softer tissues and organs. • An organ is made of one or more type of tissues. E.g. Heart
has epithelial, connective, muscular & neural tissues.
2
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