Animal tissues and their functions pdf
Origin and functions of Animal tissues
|1.||Epithelial||Free surfaces||Ectoderm, endoderm and mesoderm||
secretion, excretion and
|2.||Connective||Below the skin, around organs||Mesoderm||
Attachment, support, protection,
storage and transport
In the body parts involved in movement
and locomotion and also
in visceral organs
Mesoderm (except ciliary body and
iris diaphragm muscles which are ectodermal)
|Movement and locomotion; peristalsis|
|4.||Nervous||Throughout the body organs.||Ectoderm||
Control and coordination,
by nerve impulse conduction
The word ‘epithelium’ was introduced by Ruysch.
It is the most primitive or the first evolved type of tissue.
It consists of cells of different shapes, held together, by a small amount of an intercellular substance called matrix.
The epithelial cells rest on a basement membrane, which serves to bind the epithelial cells and provide nutrition to them. Check our More Biology Doubts
Basement membrane is a delicate, non cellular layer consisting of extracellular substance. It is differentiated into outer basal lamina and inner reticular lamina. Basal lamina (lamina basalis) consists of lamina lucida in contact with the basal surfaces of the epithelial cells and lamina densa just beneath lamina lucida. The former consists of a cell coat or glycocalyx of basal surface of epithelial cells. It has proteoglycans, glycoproteins, adhesive proteins, integrins and hemidesmosomes. In kidney glomerulus, lamina lucida lies on both the sides of basal lamina due to juxtaposition of capillary cells and podocytes and absence of reticular lamina. Lamina densa consists of a delicate network of collagen, heparan sulphate, proteoglycans and laminin protein. Basal lamina is present around Schwann cells and muscle cells. Reticular lamina consists of dense matrix and collagen fibrils which bind the lamina densa to underlying connective tissue. The matrix has abundant proteoglycans.
Diagram exhibiting microvilli, cilia, cell junctions and basement membrane.
Functions of Animal Tisses
Basement membrane anchors epithelial tissue to the underlying connective tissue.
It provides a selectively permeable barrier for glomerular filtration.
It provides a medium for material exchange between epithelial cells and vascular supply underneath.
It determines polarity, metabolism, cell division, repair and movement of other tissues.
It consists of two basic elements: cells and non cellular matrix. Connective tissue cells, unlike epithelial cells, are separated by a considerable amount of matrix. Matrix further consists of ground substance and fibres.
Some interesting facts about connective tissue are as follows:
- Joint cavities are lined by areolar connective tissue.
- Except for cartilage, connective tissue like epithelium has a nerve supply.
- Connective tissue, unlike epithelium, usually is highly vascular. Exceptions include cartilage which is avascular and tendons which are poorly vascular.
- Matrix may be fluid, semifluid, gelatinous, fibrous or calcified and is usually secreted by connective tissue cells and adjacent cells and determines the tissue’s qualities. Exceptionally, blood matrix or fluid plasma is not a derivative of blood cells. Cartilage matrix is firm and pliable. Bone matrix is considerably harder and not pliable.
Connective Tissue Cells
These are derived from mesodermal mesenchymal cells. The immature connective tissue cells include fibroblasts in loose and dense connective tissue, Chondroblasts in cartilage and osteoblasts in bone. These retain the capacity for mitosis and secrete matrix characteristic of the tissue. In cartilage and bone, once the matrix is produced, the immature chondroblasts and osteoblasts differentiate respectively into mature chondrocytes and osteocytes. The latter maintain matrix and have reduced capacity for cell division and matrix formation.
Following is a description of the typical cells found in different types of connective tissues.
- Fibroblasts are large, flat, spindle shaped cells with branching processes. They secrete different components of the matrix.
- Macrophages or histiocytes develop from monocytes, a type of agranular WBCs. They are irregular in shape and have short branching processes. They are phagocytic and hence defensive in function. Wandering macrophages migrate to infected tissues while fixed macrophages remain in certain tissues and organs of the body.
- Plasma cells are small, round or irregular in shape. They develop from B-lymphocytes and secrete antibodies to provide immunity. They are especially abundant in gastrointestinal tract and mammary glands.
- Mast cells are abundant along the blood vessels. They produce histamine, a vasodilator of small blood vessels during inflammation. They also contain heparin which acts as poor anticoagulant. Heparin is in the form of heparin proteoglycan and may serve to bind certain intracellular constituents of mast cells.
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