Overview
This lecture introduces the four main tissue types in the human body—epithelial, connective, muscle, and nervous tissue—covering their structures, functions, and key cell types.
Introduction to Cells and Tissues
- The human body contains over 32 trillion cells and about 200 different cell types.
- All cells function together to maintain homeostasis (internal stability).
- Similar cells group to form tissues, the basic fabric and structure of the body.
Four Major Tissue Types
- The four primary tissue types are epithelial, connective, muscle, and nervous tissue.
Epithelial Tissue
- Epithelial tissue lines body surfaces and organs or forms glands.
- Two main types: covering (lining) epithelia and glandular (secretory) epithelia.
- Classified by cell shape (cuboidal, squamous, columnar) and layers (simple, stratified).
- Examples:
- Simple cuboidal: ducts/kidney tubules (secretion/absorption).
- Stratified squamous: skin, esophagus (protection).
- Simple columnar: GI tract (absorption/secretion).
- Pseudostratified: respiratory tract.
- Transitional: urinary bladder/ureter (stretching).
- Specialized structures include microvilli, stereocilia, and cilia for absorption/movement.
- Epithelia are avascular and rest on a basement membrane for support.
Connective Tissue
- Most abundant and diverse tissue, derived from mesenchyme (embryonic tissue).
- Consists of cells in an extracellular matrix (fluid, semi-solid, or solid).
- Functions: support, protection, binding, insulation, energy storage, and transport.
- Immature ("-blast") cells build tissue; mature ("-cyte") cells maintain tissue.
- Types include:
- Liquid matrix: blood (erythrocytes, leukocytes, plasma, platelets).
- Semi-solid matrix: loose (areolar, reticular, adipose) and dense (regular, irregular, elastic).
- Solid matrix: cartilage (hyaline, elastic, fibrocartilage) and bone (compact, spongy).
- Connective tissue also contains immune cells for defense.
Muscle Tissue
- Responsible for movement by converting chemical to mechanical energy.
- Types:
- Skeletal muscle: striated, multinucleated, voluntary movement.
- Cardiac muscle: striated, branched, single nucleus, involuntary, found in heart.
- Smooth muscle: spindle-shaped, non-striated, single nucleus, involuntary, found in organs.
Nervous Tissue
- Composed of neurons (signal transmission) and glial cells (support/protection).
- Divided into central (brain/spinal cord) and peripheral (nerves) nervous systems.
- Neurons have a cell body, dendrites (input), and axon (output).
- Glial cells include Schwann cells (PNS), oligodendrocytes, and astrocytes (CNS).
Key Terms & Definitions
- Homeostasis — Maintenance of stable internal conditions.
- Epithelial tissue — Layers of cells covering external/internal surfaces or forming glands.
- Connective tissue — Tissue supporting, binding, and protecting body parts.
- Extracellular matrix — Non-cellular material surrounding connective tissue cells.
- Basement membrane — Supportive layer under epithelial tissue.
- Muscle tissue — Tissue enabling movement via contraction.
- Neuron — Nerve cell transmitting electrical impulses.
- Glial cell — Supporting cell for neurons in nervous tissue.
Action Items / Next Steps
- Review notes on the structure, types, and functions of the four major tissue types.
- Prepare to identify examples of each tissue type in histological images.
- Study the definitions and functions of all key terms listed.