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07 STRUCTURAL ORGANIZATION IN ANIMALS
STRUCTURAL ORGANIZATION IN ANIMALS 0 142 SCAN CODE Structural Organization in Animals Chapter 07 Structural Organization in Animals  In the animal kingdom, there are a variety of organisms. Some of them are unicellular while some are multicellular.  In unicellular organisms, all functions like digestion, respiration and reproduction are performed by a single cell.  In the complex body of multicellular animals, the same basic functions are carried out by different groups of cells in a well- organized manner. Such an organization is called a tissue.  A tissue is a group of one or more types of cells and their intercellular substance that perform a particular function.  The word “tissue” was given by Bichat. In the animal kingdom, tissues evolved for the first time in Cnidarians.  The study of tissue is called histology. The term histology was given by Mayer.  The human body is composed of billions of cells to perform various functions. These cells are organized in the following manner: Cells Tissues Organs Organ system Organism. Fig. 7.1: Level of organization in humans Types of Tissues Based on embryonic development, structural organization, and functional properties. Name Origin Main Functions 1. Epithelial Tissues Ectoderm, Mesoderm, Endoderm Protection, secretion, absorption, excretion, reproduction 2. Connective Tissues Mesoderm Attachment, support, protection, storage, transport 3. Muscular Tissues Mesoderm Movement of body parts and locomotion 4. Nervous Tissues Ectoderm Control and coordination by nerve impulse conduction.
STRUCTURAL ORGANIZATION IN ANIMALS 143 SCAN CODE Structural organization in Animals 1. Epithelial Tissues (Epi= Above, Thelium= Layer)  Word epithelium was introduced by Ruysch.  It was the first tissue to be formed in animals.  This tissue has a free surface, which faces either a body fluid or the outside environment and thus provides a covering or a lining for some part of the body.  Features:  Cells are closely packed with very little intercellular spaces.  It is avascular i.e., it has no blood supply. However, it has great capacity for regeneration.  It is derived from all the three germ layers such as  Ectoderm: Skin epidermis  Mesoderm: Coelomic epithelium  Endoderm: Lining of alimentary canal  Epithelial tissue that lies on the interior of the body is called endothelium.
STRUCTURAL ORGANIZATION IN ANIMALS 0 144 SCAN CODE Structural Organization in Animals Fig. 7.2: Epithelial tissue with basement membrane  Only tissue with an underlying acellular basement membrane.  It consists of two layers:  Basal Lamina: It is an outer thin layer made up of mucopolysaccharides and glycoproteins secreted by epithelial cells.  Fibrous or reticular lamina: It is an inner thick layer composed of collagen or reticular fibers of underlying connective tissue.  The basement membrane provides elastic support. It also allows selective chemical exchange between epithelial tissues and surrounding blood vessels. 1.1 Specialization of Plasma Membrane of Epithelium  In some cases, the plasma membrane of epithelial cells has certain specialization. They can be as follows: Cilia Stereocilia Microvilli 1. Arise from basal granules Basal granules absent Basal granules absent 2. Motile Non-motile Non-motile 3. 9+2 structure Absent Absent 4. Taper distally Cylindrical Extremely thin and short structured 5. Cells of respiratory and reproductive tracts Epididymis and vas deferens of male reproductive system Intestinal absorption and secretion are the major activity