Epithelial Tissue - Body's Border Patrol
- Core Functions: Protection (skin), absorption (gut), secretion (glands), filtration (kidney), sensation.
- Classification: Based on layers (simple, stratified, pseudostratified) and cell shape (squamous, cuboidal, columnar).
- Polarity:
- Apical surface: Faces lumen/exterior; may have microvilli or cilia.
- Basal surface: Rests on the basement membrane.
- Intercellular Junctions:
- Tight junctions (Zonula Occludens): Prevent paracellular diffusion.
- Adherens junctions (Zonula Adherens): Link actin cytoskeletons.
- Desmosomes (Macula Adherens): Anchor intermediate filaments.
- Gap junctions: Allow direct communication.
⭐ Kartagener Syndrome: A primary ciliary dyskinesia where dynein arm defects impair cilia function. This disrupts mucociliary clearance, causing recurrent sinusitis, bronchiectasis, and situs inversus.
Connective Tissue - The Matrix Masters
- Components: Cells + Extracellular Matrix (ECM).
- ECM: Ground Substance (support) + Fibers (strength).
- Ground Substance: Glycosaminoglycans (GAGs), proteoglycans, glycoproteins.
- Fibers:
- Collagen: Main structural protein. 📌 Cartilage (type II), Bone (type I), Reticulin (type III), Basement membrane (type IV).
- Elastin: Provides stretch/recoil; found in skin, lungs, large arteries.
- Primary Cells:
- Fibroblasts/cytes: Synthesize ECM fibers and ground substance.
- Adipocytes: Store fat.
- Mast Cells: Mediate inflammation (histamine, heparin).
- Macrophages: Phagocytosis.
⭐ Marfan Syndrome: An autosomal dominant genetic disorder caused by a defect in the FBN1 gene, which codes for fibrillin-1. This affects elastic fibers, leading to issues in the aorta, ligaments, and eyes.
Muscle Tissue - The Contraction Crew
A comparative overview of the three muscle types, essential for identifying histological slides.
| Feature | Skeletal Muscle | Cardiac Muscle | Smooth Muscle |
|---|---|---|---|
| Appearance | Striated, ordered | Striated, less ordered | Non-striated |
| Cell Shape | Long, cylindrical fibers | Branched, shorter cells | Fusiform (spindle-shaped) |
| Nuclei | Multinucleated, peripheral | 1-2 nuclei, central | Single nucleus, central |
| Control | Voluntary (somatic) | Involuntary (autonomic) | Involuntary (autonomic) |
| Key Features | Triads (T-tubule & 2 terminal cisternae) | Intercalated discs, gap junctions | Dense bodies, caveolae |
Nervous Tissue - The Command Network
-
Neurons: The primary signaling units.
- Soma (Cell Body): Metabolic core with nucleus.
- Dendrites: Branched extensions that receive incoming signals.
- Axon: Single long process that transmits outgoing signals.
-
Glial Cells: Non-neuronal cells providing crucial support.
- CNS: Astrocytes (support, BBB), Microglia (phagocytes), Oligodendrocytes (myelinate multiple axons), Ependymal cells (line ventricles).
- PNS: Schwann Cells (myelinate single axons), Satellite Cells (support ganglia).
⭐ Nissl bodies (rough ER) are prominent in the soma and dendrites, reflecting high protein synthesis, but are absent from the axon and axon hillock.
High‑Yield Points - ⚡ Biggest Takeaways
- Epithelium lines surfaces and forms glands; it's avascular, rests on a basement membrane, and shows apical-basal polarity.
- Connective tissue is defined by its extracellular matrix (fibers and ground substance) and is derived from mesenchyme.
- Muscle tissue is specialized for contraction; skeletal muscle is voluntary, while cardiac and smooth are involuntary.
- Nervous tissue consists of neurons for signal transmission and glial cells for support.
- Cell junctions are critical: tight junctions create barriers, desmosomes provide strength, and gap junctions allow communication.
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