Animal Tissues and Organization Notes

Animal Tissues

  • Tissues: Groups of cells sharing structure and function.
  • Held together by extracellular matrix.

Types of Tissues

  • Epithelial tissue
  • Connective/supporting tissue (including blood)
  • Muscular tissue
  • Nervous tissue

Epithelial Tissues

  • Covers body's exterior, lines organs/cavities.
  • Cells tightly joined, minimal material in between.
  • Tight junctions act as barriers against injury, microbes, fluid loss.
  • Free surface exposed to air or fluid; base attached to basement membrane (extracellular matrix).
  • Classification:
    • Cell layer number: simple (single), stratified (multiple)
    • Cell shape: cuboidal (cube-like), columnar (column-like), squamous (flat)
  • Function:
    • Lining epithelia
    • Glandular epithelia: absorb/secrete solutions (e.g., thyroid hormone secretion)

Specific Epithelial Tissues

  • Simple squamous: single layer, flattened cells; lines cavities/systems, lung/kidney surfaces; for diffusion/filtration.
  • Simple cuboidal: single layer, square cells; lines ducts/tubules (e.g., kidney); for secretion/absorption.
  • Simple columnar: single layer, taller cells; lines stomach/intestines; for secretion/absorption; may have cilia/microvilli.

Epithelial Tissue Review

  • Cells arranged in sheets.
  • Classified by cell shape and layer number.
  • Functions: protection, absorption, secretion.
  • Covers internal/external surfaces.
  • Endothelium: lines blood/lymph vessels.

Connective/Supporting Tissue

  • Cells in an extracellular matrix.
  • Functions: structural support (bones), connections (ligaments/tendons), protection (fat pads), includes blood.
  • Cells:
    • Fibroblasts: secrete matrix proteins (collagen, elastin).
    • Adipocytes
    • Macrophages: engulf bacteria/debris via phagocytosis.
    • Mast cells: prevent clotting, increase capillary permeability.
    • Plasma cells
  • Extracellular matrix:
    • Ground substance: organic materials for nutrient diffusion.
    • Structural glycoproteins.
  • Fibers:
    • Collagenous: collagen (most abundant protein).
    • Elastic: elastin protein threads.
    • Reticular: thin, branched; join connective to adjacent tissue.

Types of Connective Tissues

  • Loose: cells, ground substance, few fibers.
  • Dense: more fibers, fewer cells, less ground substance.
    • Dense regular (fibrous): tendons (muscle to bone), ligaments (bone to bone).
    • Dense irregular: dermis of skin, tendon/nerve sheaths.

Specific Connective Tissues

  • Loose connective tissue: abundant cells/ground substance, few fibers; packing material.
  • Adipose tissue: loose connective with adipocytes; honeycomb appearance.
  • Dense connective tissue: more fibers, fewer cells, less ground substance than loose.
  • Fibrous connective tissue: dense regular; tendons (muscle to bone); collagen fibers and fibroblasts.
  • Cartilage: Firmer than dense connective tissue, network of fibers, gel-like intercellular material
    • Chrondrocytes: produce collagen and chondroitin sulfate
    • No blood vessels, nutrient and oxygen depends on diffusion
    • Hyaline: amorphous matrix of ground substance reinforced by collagen
    • Elastic: flexible and returns to normal position.
    • Fibrocartilage: intervertebral disks; with dense fibrous tissue.
  • Bone
    • Mineralized connective tissue = Hydroxyapatite
    • Osteoblasts: bone-forming cells deposited in a matrix of collagen.
    • Osteocytes: osteoblasts trapped in their secretion
    • Compact bone: consists of repeating unit called osteon or Haversian system
  • Blood: matrix = plasma (water, salts, proteins); cells: erythrocytes, leukocytes, platelets.

Connective Tissue Review

  • Made of cells, extracellular fibers, and ground substance.
  • Functions: structural support, connections, elasticity, and protection.
  • Blood cells and platelets are connective tissue.

Muscle Tissue

  • Contractile cells; specialized proteins shorten cells for movement.
  • Types: skeletal, cardiac, smooth.
  • Controlled by nerves, hormones, chemicals, or itself.

Muscle Types

  • Skeletal:
    • Voluntary control; attached to bones.
    • Long, multinucleated myofibers in parallel bundles.
    • Innervated by a neuron.
    • Striated.
  • Cardiac:
    • Involuntary, striated.
    • Heart muscle.
    • Single, central nucleus; joined end-to-end via intercalated discs.
  • Smooth:
    • Involuntary; walls of viscera/vessels.
    • One central nucleus.
    • Not individually innervated; excitation spreads via junctions.

Muscle Tissue Review

  • Contains actin and myosin.
  • Skeletal: voluntary, striated, multinucleate.
  • Cardiac: involuntary, striated, single nucleate, intercalated discs.
  • Smooth: involuntary, non-striated, single nucleate, junctions.

Nervous Tissue

  • Two cell types: neurons, glial (support) cells.
  • Neurons: transmit electrical impulses.
  • Glial cells (neuroglia): support, nourish neurons.

Cells

  • Astrocytes: support neurons, clear debris, blood-brain barrier.
  • Oligodendrocytes: myelin sheaths around CNS axons.
  • Schwann cells: myelin sheaths around PNS axons.

Structure

  • Cell body: nucleus, metabolic machinery, synthesizes proteins/neurotransmitters.

Nervous Tissue Review

  • Neurons: dendrites (receive signals), cell body (maintenance), axon (transmit signals), terminals (synapses).
  • Cell bodies in PNS are in ganglia.
  • Glial cells: support, nourish neurons.
  • Nerves: bundles of axons, glial cells, connective tissue; sensory/motor function.