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Short Notes on Structural Organisation in Animals

Notes on Structural Organisation in Animals

Epithelial Tissues

An epithelium is a tissue composed of one or more layers of cells that cover the body surface and lines its various cavities.

It serves for protection, secretion and excretion.

The word ‘epithelium’ was introduced by Ruysch.

Epithelial tissue evolved first in animal kingdom.

It originates from all the three primary germ layers. e.g. Epidermis arises from ectoderm, Coelomic epithelium from the mesoderm and epithelial lining of alimentary canal from the endoderm.


Multicellular exocrine glands are classified by structure, using the shape of their ducts and the complexity (branching) of their ducts system as distinguishing characteristics.

Shape include tubular and alveolar (Sac like).

Simple exocrine glands e.g. intestinal glands, mammalian sweat glands, cutaneous glands of frog etc. have only one duct leading to surface.

Compound exocrine glands have two or more ducts e.g. liver, salivary glands etc.

Muscle Tissues

Muscle cells are highly contractile (contracting to 1/3 or 1/2 the resting length).

Muscle cells lose capacity to divide, multiply and regenerate to a great extent. Study of muscle is called myology.

About 40% to 50% of our body mass is of muscles.

The muscle cells are always elongated, slender and spindle-shaped, fibre-like cells, These are, therefore called muscle fibres.

These possess large numbers of myofibrils formed of actin and myosin.

Connective Tissues

It connects and supports all the other tissues, the intercellular element predominating.

The cellular element is usually scanty. In function this tissue may be mechanical, nutritive and defensive.

It is a tissue made up of matrix (abundant intercellular substance or ground substance) and living cells that connects and support different tissues.

Connective tissue was called mesenchyme by Hertwig (1893).

Important Points

Argentaffin cells which produce a precursor of serotonin, a potent vasoconstrictor hormone, occurs in intestinal cells.

The brown adipose tissue in human is restricted till third month of post natal life.

White fibres yield gelatin on boiling and are digestible with enzyme pepsin but yellow (elastic) fibres are not digestible by enzyme trypsin.

The fat in the globules is stored in the form of triglycerides.

The Cytoplasmic granules basophils contain histamine.

Sprain – Excessive pulling of ligaments.

Plasma cells are also called as “Cart wheel cells”.

Collagen constitutes about 33% of total body protein.