Chapter 4: Tissue – The Living Fabric

Organization and Types of Tissues

Tissues are groups of cells with similar structure and function. The human body contains four primary tissue types, each with distinct characteristics and roles.

• Epithelial Tissue: Covers body surfaces, lines cavities, and forms glands. Functions include protection, absorption, filtration, excretion, secretion, and sensory reception.

• Connective Tissue: Supports, protects, and binds other tissues. Includes bone, cartilage, blood, and adipose tissue.

• Muscle Tissue: Responsible for movement. Types include skeletal, cardiac, and smooth muscle.

• Nervous Tissue: Initiates and transmits electrical impulses, coordinating body activities.

Locations: Each tissue type is found in specific body regions (e.g., epithelial in skin and lining of organs, connective in bones and blood, muscle in heart and limbs, nervous in brain and nerves).

Characteristics and Functions of Tissues

• Epithelial: Tightly packed cells, avascular, high regenerative capacity.

• Connective: Fewer cells, abundant extracellular matrix, varying vascularity.

• Muscle: Elongated cells (fibers), contractile proteins, excitable.

• Nervous: Neurons and supporting glial cells, excitable, transmit signals.

Tissue fibers (in connective tissue): Collagen (strength), elastic (flexibility), reticular (support).

Tissue Repair

Tissue repair involves restoring tissue integrity after injury. The process includes:

1. Inflammation: Damaged cells release chemicals, increasing blood flow and permeability.

2. Organization: Blood clot replaced by granulation tissue; new capillaries form.

3. Regeneration and/or Fibrosis: Epithelial cells regenerate; connective tissue may form scar (fibrosis).

Chapter 6: Bones and Bone Tissue

Skeletal Cartilages

Cartilage is a resilient, semi-rigid connective tissue found in various parts of the skeleton.

• Types of Cartilage:

  • Hyaline: Most abundant; provides support and flexibility (e.g., nose, trachea, articular surfaces).

  • Elastic: Contains elastic fibers; maintains shape (e.g., ear, epiglottis).

  • Fibrocartilage: Strongest; resists compression (e.g., intervertebral discs, menisci).

• Major Cartilages in Adults: Articular, costal, respiratory, nasal, and intervertebral cartilages.

• Cartilage Growth: Appositional (from perichondrium) and interstitial (within cartilage).

Classification and Structure of Bones

• Bone Classes:

  • Long Bones: Longer than wide (e.g., femur, humerus).

  • Short Bones: Cube-shaped (e.g., carpals, tarsals).

  • Flat Bones: Thin, flat, often curved (e.g., sternum, skull).

  • Irregular Bones: Complex shapes (e.g., vertebrae, hip bones).

• Major Skeletal Regions: Axial (skull, vertebral column, rib cage) and appendicular (limbs, girdles).

• Functions of Bones: Support, protection, movement, mineral storage, blood cell formation (hematopoiesis), triglyceride storage, hormone production.

Bone Structure and Histology

• Long Bone Anatomy: Diaphysis (shaft), epiphyses (ends), metaphysis, medullary cavity, articular cartilage, periosteum (outer covering), endosteum (inner lining).

• Marrow: Red marrow (hematopoiesis), yellow marrow (fat storage).

• Bone Markings: Projections (muscle/ligament attachment), surfaces (joint formation), depressions/openings (passage for vessels/nerves).

• Histology:

  • Compact Bone: Dense, organized in osteons (Haversian systems).

  • Spongy Bone: Trabeculae, spaces filled with marrow.

• Chemical Composition: Organic (cells, collagen fibers) for flexibility; inorganic (hydroxyapatite crystals) for hardness.

Bone Development and Growth

• Ossification:

  • Intramembranous: Bone develops from fibrous membrane (e.g., flat bones of skull).

  • Endochondral: Bone replaces hyaline cartilage (e.g., long bones).

• Long Bone Growth: Occurs at epiphyseal plates via interstitial growth; appositional growth increases thickness.

Bone Remodeling and Repair

• Cells: Osteoblasts (build bone), osteocytes (maintain bone), osteoclasts (resorb bone).

• Regulation: Hormones (parathyroid hormone, calcitonin), physical stress (Wolff's law).

• Fracture Repair Steps:

  1. Hematoma formation

  2. Fibrocartilaginous callus formation

  3. Bony callus formation

  4. Bone remodeling

Homeostatic Imbalances and Developmental Aspects

• Osteoporosis: Decreased bone mass, increased fracture risk.

• Osteomalacia: Soft bones due to vitamin D/calcium deficiency.

• Paget’s Disease: Disorganized bone remodeling.

• Developmental Changes: Bone mass increases during childhood, peaks in early adulthood, declines with age.

Chapter 10: Muscle Tissue and Physiology

Characteristics and Types of Muscle Tissue

Muscle tissue is specialized for contraction and movement. There are three types:

• Skeletal Muscle: Voluntary, striated, attached to bones, responsible for body movement.

• Cardiac Muscle: Involuntary, striated, found in heart, pumps blood.

• Smooth Muscle: Involuntary, non-striated, found in walls of hollow organs (e.g., intestines, blood vessels).

Functions of Muscle Tissue

• Movement of body parts and substances

• Maintaining posture

• Stabilizing joints

• Heat generation

Muscle Cell Anatomy and Sliding Filament Theory

• Muscle Fiber: Long, cylindrical cell with multiple nuclei; contains myofibrils (actin and myosin filaments).

• Sliding Filament Theory: Muscle contraction occurs as myosin heads bind to actin, pulling filaments past each other, shortening the sarcomere.

Role of Calcium and Acetylcholine (ACh) in Contraction

• Calcium: Released from sarcoplasmic reticulum, binds to troponin, exposes binding sites on actin.

• Acetylcholine (ACh): Neurotransmitter released at neuromuscular junction, initiates action potential in muscle fiber.

Muscle Contraction and Relaxation

• Three Types of Activity:

  1. Excitation (nerve impulse and ACh release)

  2. Contraction (cross-bridge cycling)

  3. Relaxation (removal of calcium, breakdown of ACh)

• Types of Contraction: Isotonic (muscle changes length), isometric (muscle length unchanged).

• Examples: Lifting a weight (isotonic), holding a posture (isometric).

Motor Units, Recruitment, Force, and Tone

• Motor Unit: A motor neuron and all muscle fibers it innervates.

• Recruitment: Increasing number of active motor units to generate more force.

• Muscle Tone: Continuous, partial contraction of muscles for posture.

Twitch vs Graded Response

• Twitch: Single, brief contraction in response to a single stimulus.

• Graded Response: Varying strength of contraction by changing frequency or number of stimuli.

Smooth Muscle Characteristics

• Spindle-shaped cells, single nucleus, no striations.

• Involuntary control, slow and sustained contractions.

• Found in walls of hollow organs (e.g., digestive tract, blood vessels).

Muscle Fatigue

• Caused by depletion of ATP, accumulation of lactic acid, ionic imbalances.

• Results in reduced ability to contract.

Example Table: Comparison of Muscle Tissue Types

Key Equations

• Force of Muscle Contraction: Where F = force, m = mass, a = acceleration

• Calcium Homeostasis (Bone): Parathyroid hormone increases blood calcium by stimulating osteoclasts.

Additional info: Locations and specific examples of tissues, as well as detailed lab-based identification, are typically covered in laboratory sessions and may require reference to lab manuals or atlases.