Animal Tissue (NEET 2026)

Cheatsheet Content

### Epithelial Tissue - **Definition:** Covers body surfaces, lines cavities, and forms glands. Cells are tightly packed with little intercellular matrix. - **Functions:** Protection, secretion, absorption, filtration, sensation. - **Classification based on layers:** - **Simple Epithelium:** Single layer of cells. - **Squamous:** Flat, tile-like. Found in blood vessels, air sacs of lungs (diffusion). - **Cuboidal:** Cube-shaped. Found in kidney tubules, ducts of glands (secretion, absorption). - **Columnar:** Tall, pillar-like. Found in stomach, intestine (secretion, absorption). May have microvilli (increase surface area) or cilia (movement). - **Ciliated Epithelium:** Columnar or cuboidal with cilia. Found in bronchioles, fallopian tubes (movement of particles/ova). - **Compound (Stratified) Epithelium:** Two or more layers of cells. - **Functions:** Protective role in skin, buccal cavity, pharynx. - **Glandular Epithelium:** Specialized for secretion. - **Unicellular:** Isolated glandular cells (e.g., goblet cells in alimentary canal). - **Multicellular:** Cluster of cells (e.g., salivary gland). - **Exocrine Glands:** Secrete products through ducts (e.g., salivary, sweat, oil, digestive enzymes). - **Endocrine Glands:** Ductless, secrete hormones directly into blood (e.g., thyroid, pituitary). - **Junctions:** - **Tight Junctions:** Prevent leakage across tissue. - **Adhering Junctions:** Cement neighboring cells together. - **Gap Junctions:** Facilitate communication, rapid transfer of ions/molecules. ### Connective Tissue - **Definition:** Most abundant and widely distributed tissue in animals. Provides support, protection, and binds other tissues together. - **Components:** Cells, fibers (collagen, elastin, reticular), ground substance (matrix). - **Types of Connective Tissue:** - **Loose Connective Tissue:** - **Areolar Tissue:** Beneath skin, supports epithelia. Contains fibroblasts, macrophages, mast cells. - **Adipose Tissue:** Beneath skin, around organs. Stores fat. - **Dense Connective Tissue:** - **Dense Regular:** Fibers arranged in parallel bundles. - **Tendons:** Connect muscle to bone. - **Ligaments:** Connect bone to bone. - **Dense Irregular:** Fibers irregularly arranged. Found in skin (dermis). - **Specialized Connective Tissue:** - **Cartilage:** Solid, pliable, resists compression. - **Hyaline:** Most common (nose tip, larynx, tracheal rings). - **Fibrocartilage:** Strong (intervertebral discs). - **Elastic:** Flexible (ear pinna). - **Bone:** Hard, non-pliable matrix (calcium salts, collagen). Provides structural support. - **Osteocytes:** Bone cells in lacunae. - **Haversian canals:** In compact bone, contain blood vessels and nerves. - **Blood:** Fluid connective tissue. - **Plasma:** Fluid matrix. - **Blood cells:** Erythrocytes (RBCs), Leukocytes (WBCs), Platelets. ### Muscular Tissue - **Definition:** Specialized for contraction and relaxation, responsible for movement. - **Types:** - **Skeletal Muscle (Striated/Voluntary):** - **Structure:** Multinucleated, unbranched fibers with prominent striations. - **Location:** Attached to bones. - **Function:** Body movement, posture. - **Smooth Muscle (Non-striated/Involuntary):** - **Structure:** Uninucleated, spindle-shaped cells, no striations. - **Location:** Walls of internal organs (stomach, intestine, blood vessels, uterus). - **Function:** Involuntary movements (peristalsis, vasoconstriction). - **Cardiac Muscle (Striated/Involuntary):** - **Structure:** Uninucleated (sometimes binucleated), branched fibers with striations. Intercalated discs present for cell communication. - **Location:** Heart wall. - **Function:** Rhythmic contraction and relaxation of heart. ### Neural Tissue - **Definition:** Controls the body's responses to changing conditions. - **Components:** - **Neurons (Nerve Cells):** Structural and functional units. - **Cell Body (Soma):** Contains nucleus and Nissl's granules. - **Dendrites:** Receive signals from other neurons. - **Axon:** Transmits signals away from cell body. - **Synaptic Knob:** Stores neurotransmitters. - **Neuroglia (Glial Cells):** Support and protect neurons. - Make up more than half the volume of neural tissue. - Do not propagate nerve impulses. - **Function:** Transmits electrical impulses (nerve impulses) rapidly throughout the body.