Basic Tissue Types

Epithelial Tissue - Body's Border Patrol

Covers body surfaces, lines cavities, and forms glands. Avascular; rests on a basement membrane.

• Classification: Based on cell layers and shape.

  Layers	Shape	Key Example & Feature
  Simple (1 layer)	Squamous	Alveoli, endothelium. 📌 Slick & Smooth
  	Cuboidal	Kidney tubules, glands.
  	Columnar	GI tract (often with microvilli).
  Stratified (>1 layer)	Squamous	Skin (keratinized), esophagus.
  Pseudostratified	Columnar	All cells touch basement membrane; Respiratory tract (ciliated).
  Transitional		Lines urinary bladder, ureters (stretchable).

• Key Functions: Protection, secretion, absorption, excretion, filtration, diffusion, sensory reception.
• Surface Specializations:
  • Microvilli: ↑ surface area for absorption (e.g., small intestine brush border).
  • Cilia: Motile, move substances (e.g., trachea).
  • Goblet Cells: Unicellular glands, secrete mucus.
• Glands (derived from epithelia):
  • Exocrine: Secrete products into ducts (e.g., sweat, salivary glands).
  • Endocrine: Ductless; secrete hormones into bloodstream (e.g., thyroid gland).

⭐ Pseudostratified columnar ciliated epithelium is characteristic of the respiratory tract, including the trachea and bronchi.

Connective Tissue - The Grand Unifier

Provides structural/metabolic support, connecting tissues. Components: cells, fibers, ground substance.

• Cells: Fibroblasts (synthesize matrix), adipocytes, chondrocytes, osteocytes, blood cells, immune cells (macrophages, mast cells).
• Fibers:
  • Collagen: Tensile strength. 📌 Be (So Totally) Cool, Read Books.
    • Type I: Bone, Skin, Tendon.
    • Type II: Cartilage.
    • Type III: Reticulin (blood vessels).
    • Type IV: Basement membrane.
  • Elastic: Stretch, recoil (aorta, skin).
  • Reticular: Delicate meshwork (liver, lymph nodes) - Type III collagen.
• Ground Substance: Glycosaminoglycans (GAGs), proteoglycans. Hydrated gel.
• Classification:
  • CT Proper:
    • Loose (Areolar): Abundant ground substance (superficial fascia).
    • Dense Regular: Parallel fibers (tendons).
    • Dense Irregular: Random fibers (dermis).
  • Specialized CT: Adipose, Cartilage, Bone, Blood.

⭐ Type I collagen is the most abundant collagen, providing tensile strength to bone, skin, and tendons.

Muscular Tissue - Motion Makers Inc.

• Enables movement via contraction. Types: Skeletal, Smooth, Cardiac.

• Muscle Fiber Structure:
  • Sarcolemma: Cell membrane.
  • Sarcoplasm: Cytoplasm.
  • Sarcoplasmic Reticulum (SR): Stores $Ca^{2+}$.
  • Myofilaments: Actin (thin), Myosin (thick). Form Sarcomeres (functional unit in striated).
    • 📌 Sarcomere Bands: M-line (Middle), I-band (Isotropic/Light), A-band (Anisotropic/Dark), H-zone (Helle/Bright), Z-disc (Zwischenscheibe/Between).
  • T-tubules: Sarcolemma invaginations; conduct action potentials.

Comparison of Muscle Types:

• Contraction: Sliding filament model (myosin pulls actin).
• Innervation: Skeletal (Somatic motor), Smooth & Cardiac (Autonomic).

Nervous Tissue - Command & Control Central

• For rapid communication, integration, control.
• Cells:
  • Neurons: Functional units. Structure: Soma (cell body), dendrites (input), axon (output, often myelinated by Schwann cells (PNS) or Oligodendrocytes (CNS)).
  • Glial Cells (Neuroglia): Support neurons.

    Glial Cell	Location	Key Function(s)
    Astrocytes	CNS	Support, BBB, repair
    Oligodendrocytes	CNS	Myelination (many axons)
    Microglia	CNS	Phagocytosis
    Ependymal cells	CNS	Line ventricles, CSF production
    Schwann cells	PNS	Myelination (one axon segment), regeneration
    Satellite cells	PNS	Support ganglia neuron bodies
    📌 CNS Glia: Astrocytes Support, Microglia Phagocytose, Ependymal Line, Oligodendrocytes Myelinate.

• Synapse: Neuron communication junction.
• Organization: CNS (brain, spinal cord); PNS (nerves).

⭐ Nissl bodies (RER, free ribosomes) are in neuron soma and dendrites, not axon/axon hillock.

High‑Yield Points - ⚡ Biggest Takeaways

• Epithelium: Covers surfaces, forms glands; avascular; rests on basement membrane; classified by shape/layers.
• Connective Tissue: Supports, connects; abundant extracellular matrix; diverse types: blood, bone, cartilage.
• Muscle Tissue: For contraction. Skeletal (striated, voluntary), smooth (non-striated, involuntary), cardiac (striated, involuntary).
• Nervous Tissue: Transmits nerve impulses; neurons (functional unit) and glial cells (support).
• Cell junctions (tight, desmosomes, gap) are vital for epithelial integrity and intercellular communication.
• Glandular epithelium: Exocrine (ducts, local) vs. Endocrine (ductless, hormones to blood).