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.
Glands
- 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.