Tiêu đề Med-RM_Zoo_SP-1_Ch-1_Structural Organisation in Animals (Animal Tissues).pdf ✅

Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Chapter Contents ANIMAL TISSUES Life evolved on Earth in the form of single-celled (unicellular) organisms. They were able to perform all the functions necessary for life such as digestion, respiration and reproduction. Multicellular organisms came into existence later and they consist of several types of cells where each type is specialised to perform different functions. Group of structurally similar cells sharing same origin that are specialized to perform a specific function form a tissue. The body of a multicellular organism exhibits division of labour and contributes to the survival of the organism as a whole. The first phylum to exhibit tissue level of organisation is Cnidaria. Animal Tissues Epithelial Tissue Connective Tissue Muscular Tissue Nervous Tissue Simple Epithelium (Single layered) Compound Epithelium (Multi layered) Skeletal Visceral Cardiac Squamous Cuboidal Columnar Ciliated Loose Connective Tissue Areolar Adipose Dense Connective Tissue Specialized Connective Tissue Bone Cartilage Blood Lymph Pseudostratified Classification of Animal Tissues All these tissues occur in the vertebrates and also in most invertebrates. Note: The branch of science dealing with study of tissues is called histology. EPITHELIAL TISSUE Cells of the epithelium are set very close to each other, separated by very thin films of extracellular material. Neighbouring cells are held together by cell junctions. The epithelial tissue rests on a noncellular basement membrane, which separates it from the underlying connective tissue. Chapter 1 Structural Organisation in Animals (Animal Tissues) Animal Tissues Epithelial Tissue Connective Tissue Muscular Tissue Nervous (Neural) Tissue
2 Structural Organisation in Animals (Animal Tissues) NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph.011-47623456 The basement membrane is a non-cellular membrane made up of two layers: (i) Upper thin layer called basal lamina made up of glycoproteins and mucopolysaccharides secreted by epithelial cells. (ii) Lower thick fibrous layer called reticular lamina, made up of reticular fibres and collagen fibres which are the part of underlying connective tissue. Blood vessels are absent in epithelial tissue. Materials are exchanged between epithelial cells and blood vessels of the connective tissue by diffusion across the basement membrane. Classification of Epithelial Tissue Squamous Cubical Ciliated Columnar Pseudostratified Transitional Stratified Stratified squamous Stratified cubical Keratinised Non-Keratinised Epithelial Tissues Simple Compound 1. Simple Epithelium It is formed of a single layer of cells, resting on the basement membrane. Simple epithelium occurs mainly on secretory and absorptive surfaces. (i) Squamous epithelium consists of a layer of thin, flat, scale-like cells with prominent nuclei. The cells have irregular boundaries that fit closely into those of neighbouring cells like the tiles in a floor hence also called pavement epithelium. It is also known as Tessellated epithelium. It forms the inner lining of lung alveoli and blood vessels. (ii) Cubical epithelium has cells which are polygonal in outline, but appear cuboidal in vertical section. It lines small salivary and pancreatic ducts and thyroid follicles. The cells participate in secretion, excretion and absorption. The cells of cubical epithelium in absorptive surfaces often bear microvilli on their free ends. This gives a brush-like appearance to their free border. They are, therefore, called brush-bordered cubical epithelial cells e.g, in proximal tubules of kidneys. Microvilli greatly increase the area of the free surface of the cell and thereby enhance reabsorption. (a) Flattened cell Cube-like cell Tall cell (b) (d) (c) Fig.: Types of simple epithelium : (a) Squamous, (b) Cuboidal, (c) Columnar, (d) Columnar cells bearing cilia
NEET Structural Organisation in Animals (Animal Tissues) 3 Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph.011-47623456 (iii) Columnar epithelium is characterised by the presence of tall cells shaped like polygonal columns. The nucleus is usually located at the base of the cell. Columnar epithelium covers the inner surface of the intestine, stomach and gall bladder. It also occurs in gastric and intestinal glands. Its function is secretion or absorption. The intestinal mucosa is lined by brush-bordered columnar epithelium which is highly absorptive. (iv) Ciliated epithelium consists of columnar or cubical cells bearing cilia on their free surfaces. The function of the cilia is to move particles, or mucus in a specific direction over the epithelial surface. Ciliated epithelium lines the inner surfaces of some hollow organs such as fallopian tubes, bronchioles and small bronchi. Ciliated columnar epithelium lining the ventricles of brain and spinal canal is called ependyma and it shows presence of both microvilli and cilia. (v) Pseudostratified epithelium covers the inner lining of trachea and large bronchi. Although made up of a single layer of columnar cells, it appears two-layered, because some cells are shorter than the others and have their nuclei at a different level. The shorter cells lack cilia and secrete mucus which traps particles on the epithelial surface. The longer cells can be ciliated. The ciliary movement propels the mucus and the particles towards the larynx. Goblet cell Mucus Long cell Short cell Basement membrane (Oval Nucleus) (Round Nucleus) Fig.: Pseudostratified epithelium (vi) Glandular Epithelium The cells of glandular epithelia are generally columnar or cuboidal. The glandular epithelium can be classified into two types : unicellular, consisting of isolated glandular cells (e.g. goblet cell of alimentary canal) and multicellular, consisting of cluster of cells. A gland with a single unbranched duct is called simple gland. The secretory part of the gland consists of epithelial cells arranged in the form of tubes (tubules) or sacs (acini, alveoli) or a combination of both. The duct is also made up of epithelial cells. Tubular glands found in the human intestine, are example of simple gland. A gland with a branched system of ducts is called compound gland. In these glands, the secretory tubule or acinus may be coiled or branched and opens into the single duct of the gland. Compound glands are present in the pancreas and salivary glands. Unicellular gland Multicellular gland (a) (b) Fig: Glandular epithelium: (a) Unicellular, (b) Multicellular