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Notes Class 11 Chapter 10 Biology Maharashtra Board

Animal Tissue

Introduction

  • Tissue: A group of cells with similar embryonic origin, structure, and function.
  • Histology: The study of the structure and arrangement of tissues.
  • Organization: Cells → Tissues → Organs → Organ Systems → Body.
  • Cell Types:
    • Somatic Cells: Body cells excluding sperm and ova (from Greek “soma” meaning body).
    • Germ Cells: Sperm and ova, part of the reproductive system.
  • Animal Tissues: Classified into four types:
    1. Epithelial Tissue
    2. Connective Tissue
    3. Muscular Tissue
    4. Nervous Tissue

10.2 Epithelial Tissue

  • Definition: Forms covering on inner and outer surfaces of the body and organs.
  • Characteristics:
    • Cells are compactly arranged with little intercellular matrix.
    • Rest on a non-cellular basement membrane.
    • Cells are polygonal, cuboidal, or columnar with a single nucleus (central or basal).
    • Avascular (no blood vessels), but has good regeneration capacity.
  • Functions: Protection, absorption, transport, filtration, secretion.
  • Classification:
    • Simple Epithelium: Single layer of cells.
    • Compound Epithelium: Two or more layers of cells, lowermost layer on basement membrane.

A. Simple Epithelium

  1. Squamous Epithelium:
    • Structure: Flat, thin, polygonal cells with serrated margins, fitting like tiles (pavement epithelium). Central spherical/oval nucleus.
    • Functions: Protection, absorption, transport, filtration, secretion.
    • Locations: Blood vessels, alveoli, coelom.
  2. Cuboidal Epithelium:
    • Structure: Cuboidal cells with a central spherical nucleus.
    • Functions: Absorption, secretion.
    • Locations: Lining of pancreatic duct, salivary duct, proximal/distal convoluted tubules of nephron.
  3. Columnar Epithelium:
    • Structure: Tall, pillar-like cells; narrow inner ends, broad flat free ends with microvilli. Oval nucleus in lower half.
    • Functions: Secretion, absorption.
    • Locations: Inner lining of intestine, gall bladder, gastric glands, intestinal glands.
  4. Ciliated Epithelium:
    • Structure: Cuboidal or columnar cells with hair-like cilia on free ends, oval nucleus at basal end.
    • Functions: Moves materials in a specific direction, prevents entry of foreign particles.
    • Locations: Buccal cavity (frog), nasal cavity, trachea, oviduct.
  5. Glandular Epithelium:
    • Structure: Columnar, cuboidal, or pyramidal cells with large basal nucleus and secretory granules.
    • Types:
      • Unicellular: E.g., goblet cells in intestine.
      • Multicellular: E.g., salivary gland.
    • Classification by Secretion:
      • Exocrine Glands: Have ducts, secrete at specific sites (e.g., salivary, sweat glands).
      • Endocrine Glands: Ductless, release secretions into bloodstream (e.g., thyroid, pituitary).
    • Functions: Secretes mucus, enzymes, hormones; lubricates respiratory/digestive tracts.
  6. Sensory Epithelium:
    • Structure: Modified columnar cells with elongated neurosensory cells and sensory hairs.
    • Function: Perceives external/internal stimuli.
    • Locations: Nose (olfactory), ear (auditory hair cells), eye (photoreceptors).
  7. Germinal Epithelium:
    • Structure: Cells divide meiotically to produce haploid gametes.
    • Locations: Lining of seminiferous tubules, inner lining of ovary.

B. Compound Epithelium

  1. Stratified Epithelium:
    • Structure: Nucleus in stratum germinativum; cells at free surface flatten (stratum corneum, lack nucleus).
    • Function: Protection.
    • Locations: Epidermis of skin, esophagus, cornea, vagina, rectum.
  2. Transitional Epithelium:
    • Structure: Similar to stratified epithelium; cells change shape based on organ stretch.
    • Function: Distension of organ.
    • Location: Urinary bladder.

Cell Junctions

  • Definition: Junctional complexes connecting epithelial cells laterally and to the basement membrane.
  • Types:
    1. Tight Junctions (TJs): Maintain cell polarity, prevent lateral diffusion of proteins/ions.
    2. Gap Junctions (GJs): Allow passage of ions, small molecules, and chemical messages.
    3. Hemidesmosomes (HDs): Anchor cells to basement membrane via integrins, maintain tissue homeostasis.
    4. Desmosomes (Ds): Provide mechanical strength to epithelial tissue, cardiac muscles, meninges.
    5. Adherens Junctions (AJs): Involved in signaling and transcriptional regulation.

10.3 Connective Tissue

  • Definition: Most widely spread tissue; binds, supports, and strengthens other tissues/organs.
  • Characteristics:
    • Contains variety of cells and fibres in abundant intercellular matrix.
    • Highly vascular (except cartilage).
    • Protects vital organs, acts as packing material, aids healing.
  • Classification:
    1. Connective Tissue Proper: Loose and dense.
    2. Supporting Connective Tissue: Cartilage and bone.
    3. Fluid Connective Tissue: Blood and lymph.

A. Connective Tissue Proper

  1. Loose Connective Tissue:
    • Matrix: Semisolid, jelly-like, gelatinous.
    • Types:
      • Areolar Tissue:
        • Fibres: White (collagen, tensile strength), yellow (elastin, elastic).
        • Cells:
          • Fibroblasts: Large, flat, branching; produce fibres and matrix.
          • Mast Cells: Oval, secrete heparin/histamine.
          • Macrophages: Amoeboid, phagocytic.
          • Adipocytes: Fat cells with eccentric nucleus.
        • Functions: Packing material, connects organs/tissues, aids healing.
        • Locations: Under skin, between muscles, bones, around organs, blood vessels, peritoneum.
      • Adipose Tissue:
        • Structure: Many adipocytes (round/polygonal, peripheral nucleus due to fat droplets), less matrix, few fibres/vessels.
        • Types:
          • White Adipose: Opaque, common in adults.
          • Brown Adipose: Reddish-brown, many blood vessels.
        • Functions: Insulation, shock absorber, energy storage.
        • Locations: Sole, palm, around kidneys.
  2. Dense Connective Tissue:
    • Structure: Fibres and fibroblasts compactly arranged.
    • Types:
      • Dense Regular: Parallel collagen fibres.
        • Tendons: Connect muscles to bones, contain white fibres (e.g., Achilles tendon).
        • Ligaments: Connect bones at joints, elastic due to yellow fibres.
      • Dense Irregular: Fibres/fibroblasts not orderly, found in dermis of skin.

B. Supporting Connective Tissue

  1. Cartilage:
    • Characteristics: Pliable, tough; forms endoskeleton in cartilaginous fishes (e.g., shark).
    • Structure: Matrix (chondrin) enclosed by perichondrium (collagenous fibres). Chondroblasts (immature cells) mature into chondrocytes in lacunae (2-8 per lacuna).
    • Types:
      • Hyaline Cartilage: Perichondrium present, bluish-white gel-like matrix, fine collagen fibres, elastic, compressible. Found in ends of long bones, epiglottis, trachea, ribs, larynx, hyoid.
      • Elastic Cartilage: Perichondrium present, matrix with elastic fibres, few chondrocytes. Found in ear lobe, nose tip.
      • Fibrocartilage: No perichondrium, matrix with collagen bundles, few chondrocytes. Most rigid, found in intervertebral discs, pubic symphysis.
      • Calcified Cartilage: Rigid due to salt deposition, reduces joint flexibility in old age (e.g., head of long bones).
    • Functions: Shock absorption, flexibility, reduces friction.
  2. Bone:
    • Characteristics: Hard matrix (ossein) with hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂).
    • Structure:
      • Enclosed by periosteum (tough membrane); blood vessels/nerves pierce it.
      • Matrix in concentric lamellae with fluid-filled lacunae connected by canaliculi.
      • Cells: Osteoblasts (active), osteocytes (inactive), osteoclasts.
      • Haversian System: In compact bones, central canal with artery/vein/nerves.
    • Types:
      • Spongy Bone: No haversian system, reticular matrix with trabeculae, contains red bone marrow.
      • Compact Bone: Haversian system, no spaces between lamellae.
    • Functions: Support, protection, movement.

C. Fluid Connective Tissue

  • Blood and Lymph: Vascular tissues, detailed in Class 12 (Circulation).

10.4 Muscular Tissue

  • Definition: Contractile tissue with elongated cells (muscle fibres) covered by sarcolemma.
  • Characteristics:
    • Cytoplasm (sarcoplasm) contains myofibrils (actin, myosin proteins).
    • Fibres contract on stimulation, highly vascular, innervated, many mitochondria.
  • Types:
    1. Skeletal Muscles:
      • Structure: Attached to bones, fasciculi wrapped by epimysium, each fasciculus by perimysium, myofibres with sarcolemma/sarcoplasm.
      • Myofibrils: Contain sarcomeres (functional units) with:
        • A band: Dark, myosin + actin, H zone (light area) with M line.
        • I band: Light, actin only.
        • Z line: Separates adjacent sarcomeres.
      • Characteristics: Striated, voluntary, quick/strong contractions, multinucleate (peripheral nuclei).
      • Types:
        • Red Muscles: High myoglobin, oxygen from myoglobin/haemoglobin.
        • White Muscles: Low myoglobin.
      • Functions: Voluntary movements.
    2. Smooth Muscles:
      • Structure: Spindle-shaped, unbranched, single central nucleus, myofibrils with more actin, less myosin, no striations.
      • Characteristics: Non-striated, involuntary, slow/sustained contractions, innervated by autonomous nervous system.
      • Locations: Walls of visceral organs, blood vessels (longitudinal/circular arrangement).
      • Functions: Involuntary movements (e.g., peristalsis).
    3. Cardiac Muscles:
      • Structure: Combine striated/non-striated features, indistinct sarcolemma, uni-nucleate (appear multinucleate), branched, connected by intercalated discs.
      • Characteristics: Striated, involuntary, quick stimulus transfer, some self-impulse generating (myogenic heart in mammals, neurogenic in some animals).
      • Location: Myocardium of heart wall.
      • Functions: Heart contractions.

10.5 Nervous Tissue

  • Definition: Composed of neurons (nerve cells) and neuroglia (supporting cells).
  • Characteristics:
    • No intercellular matrix.
    • Neuroglia regenerate/divide; neurons do not (lack centriole).
    • Neurons are excitable (change membrane potential) and conductive经典案例
    • Functions: Impulse generation/conduction for quick communication.

Structure of a Neuron

  • Cyton (Cell Body):
    • Contains neuroplasm (granular cytoplasm) with nucleus, mitochondria, Golgi apparatus, RER, Nissl’s granules (RNA).
  • Processes:
    • Dendrons: Short, branched, carry impulses to cyton via dendrites.
    • Axon: Single, elongated, cylindrical, bounded by axolemma, contains axoplasm (mitochondria, neurofibrils).
      • Myelin Sheath: Fatty layer by Schwann cells, interrupted at Nodes of Ranvier (saltatory conduction).
      • Neurilemma: Outer covering of myelin sheath.
      • Telodendron: Terminal axon branches.
  • Functional Types:
    • Afferent (Sensory) Neuron: Carries impulses from sense organs to CNS (dorsal root of spinal cord).
    • Efferent (Motor) Neuron: Carries impulses from CNS to effector organs (ventral root of spinal cord).
    • Interneuron: Processes/integrates sensory impulses, activates motor neurons.
  • Structural Types:
    • Unipolar Neuron: Single process (axon + dendron from one point), e.g., dorsal root ganglion.
    • Bipolar Neuron: Two processes (dendron + axon from opposite poles), e.g., retina, olfactory epithelium.
    • Multipolar Neuron: Star-shaped cyton, one axon, multiple dendrons, e.g., brain, spinal cord.
  • Myelinated vs. Non-Myelinated Fibres:
    • Myelinated: Fatty myelin sheath, white, fast saltatory conduction, e.g., cranial nerves.
    • Non-Myelinated: No myelin, grey, slower conduction, e.g., autonomous nervous system nerves.
  • Synapse: Functional contact between axonal ends and dendrites (detailed in Class 12).

Key Scientists

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