animal tissue organ and organ system

ANIMAL TISSUE, ORGAN AND ORGAN SYSTEM

There is only one cell in the body of the animals of the phylum Protozoa. Animals of the Phylum Porifera are simplest multi-cellular animals. Their cells

do not form actual tissue. Though tissues, organs and systems are not formed in
members of the phylum Cnidaria (previously known as Coelenterata), their
body cells are, however, arranged in two layers.
In the animals from phylum Platyhelminthes to Chordata, tissues, organs and organ systems are seen. Members of those phyla are three layered. From there three embryonic cell layers (namely ectoderm, mesoderm and endoderm),
tissues, organs and systems are formed.
Tissue: In the body of multi-cellular animals some cells remain together and
performa particular function. These cells are either formed from the ectoderm,
mesoderm or endoderm of the embryo and remain close together. Inter-cellular
materials or matrix are present between these cells. These cells may be similar
or of different types. Arising from the embryonic cell layer when certain types of cells when remain in a particular place of the animals' body and collectively perform a common function, those cells and the inter-cellular materials or matrix secreted by them are collectively called the Tissue. That is to say, cells
of a particular tissue are similar in its, origin, function and structure. The subject in which the different types of tissue are discussed is called Histology.
Differences between Tissue and Cell:
A. Tissue: Originating from a same place when more than one cell with similar structure and function performs a common function, then those groups of cells are called Tissue. For example, blood is a kind 'of fluid connective tissue. In the liquid matrix or plasma of blood there are red corpuscles, white corpuscles
and platelets. Blood is developed from the mesoderm of the embryo.
B. Cell: Cell is the structural and functional unit of tissue. For example, Red blood corpuscles (Erythrocytes), White blood corpuscles (Leucocytes) and Platelets (Thrombocytes) are various types of blood cells. Of these the red courpuscles transport oxygen and carb.on dioxide, white corpuscles take part in the defense of the body and the platelets take part in blood clotting at the site of injury and stop unwanted blood loss. Blood cells and the plasma together form the blood tissue. Blood generally takes part in the internal transportation of the body.
Types of Tissues :
On the basis of number of cells, characteristic and the presence or absence of
the intercellular materials or matrix secreted by cells, the tissue is mainly divided into four categories.
1. The Epitherlial Tissue.
2. The Connective Tissue.
3. The Muscular Tissue.
4. The Nerve Tissue.
Location, Structural characteristics and Function of different types of Tissue
of the Animal Body :
1. Structural Characteristics, Function and Location of Epithelial Tissue:
Structural Characterisics : The cells of the epithelial tissue lie closely or side by side on a basement membrane. There is no matrix in this tissue. On the basis of cell size, location in the animal body and nature of work, this tissue is of three
types, sch as; a. Squamous Epithelial Tissue: Cells of this tissue are flat like scales; rnucleus is large (Fig- 5.1)
Example: Wall of the Bowman's capsule of Kindey.
Function: Mainly filtration and covering. ~
b. Cuboidal Epithelial Tissue: Cells of this tissue are cuboidal, as the length,
breadth and height of the cells are nearly equal (Fig-5.2).
Example: Collecting tubules of the kidney.
Function: Mainly absorption and covering.

Columnar Epithelial Tissue : Cells of this tissue are narrow and elongated like a column (Fig-5.3)
Example: On the internal wall of intestine.
Function: Mainly secretion, protection and absorption.



i. Simple Epithelial Tissue: On basement membrane the cells are arranged in a single layer.
Example: Bowman's capsule of ki4ney; renal tubules, intestinal wall (Fig-5.1,5.2:5.3).
ii. Stratified Epithelial Tissue: Cells are arranged on the basement membrane
in more than one layer (Fig-5A).
Example: Integument of vertebrate animals.
iii. Pseudo stratified Epithelial Tissue: .Cells, of this tissue are arranged in a
single layer on basement membrane. The cells are not of the same height. So
this tissue appears to be stratified tissue (Fig-5.5).
Example: Trachea. Besides the cells of epithelial tissue. are transformed variously for different functions. As:
1. Ciliated Epithelial Tissue: Found in the wall of the respiratory tube of vertebrate animals.
2. Flagellated Epithelial Tissue: Found in the endoderm of Hydra.
3. Pseudopodia Epithelial Tissue: Found in pseudopodial cells in the
endoderms of Hydra and in the intestine of vertebrate animals.
4. Glandular Epithelial Tissue: This is a kind of epithelial tissue transformed
into gland in the stomach and intestine of vertebrate animals.
5. Germinal Epithelial Tissue: This, is a kind of transformed epithelial tissue.
From this tissue sperms and ovum are formed.
General Functions of Epithelial Tissue:
1. This tissue form, the external and internal- covering of any organ or tube.
2. After transformation this tissue takes part in , protection; secretion,
absorption, diffusion, transportation etc. So, it can be said that epithelial tissue
being transformed into glandular tissue and germinal tissue perform various
important functions.


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