Tissues

Four Primary Tissue Classes and Their Subclasses

The human body is composed of four primary tissue types, each with distinct subclasses and functions:

• Epithelial Tissue: Covers body surfaces and lines cavities. Subclasses include simple and stratified epithelium, squamous, cuboidal, and columnar types.

• Connective Tissue: Supports, protects, and binds other tissues. Subclasses include loose connective tissue (areolar, adipose), dense connective tissue, cartilage, bone, and blood.

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

• Nervous Tissue: Initiates and transmits electrical impulses. Subclasses include neurons and neuroglia.

Characteristics, Functions, and Cell Types of Each Tissue Class

• Epithelial Tissue

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

  • Functions: Protection, absorption, filtration, secretion.

  • Cell Types: Squamous, cuboidal, columnar cells.

• Connective Tissue

  • Characteristics: Extracellular matrix, varying vascularity.

  • Functions: Support, protection, transport, insulation.

  • Cell Types: Fibroblasts, chondrocytes, osteocytes, adipocytes, blood cells.

• Muscle Tissue

  • Characteristics: Elongated cells (fibers), contractility.

  • Functions: Movement, posture, heat production.

  • Cell Types: Skeletal muscle fibers, cardiac muscle cells, smooth muscle cells.

• Nervous Tissue

  • Characteristics: Excitable, specialized for communication.

  • Functions: Sensory input, integration, motor output.

  • Cell Types: Neurons, glial cells.

Differences Between Tissue Types

Tissues differ in cell shape, arrangement, function, and regenerative capacity. For example, epithelial tissue is highly regenerative, while nervous tissue has limited regeneration.

Inflammation and Tissue Repair

• Causes of Inflammation: Physical injury, infection, chemical exposure, autoimmune reactions.

• Regenerative Capacity: Epithelial and connective tissues regenerate well; muscle tissue regenerates moderately; nervous tissue regenerates poorly.

• Healing Processes:

  1. Inflammation: Initial response to injury, characterized by redness, heat, swelling, and pain.

  2. Organization: Restoration of blood supply and formation of granulation tissue.

  3. Regeneration/Fibrosis: Replacement of damaged tissue with new cells or scar tissue.

• Factors Affecting Tissue Repair: Nutrition, blood supply, age, infection, and overall health.

Skin (Integumentary System)

Functions of Skin

• Protection against mechanical, chemical, and biological threats

• Regulation of body temperature

• Sensory reception

• Excretion of wastes

• Synthesis of vitamin D

Layers of Skin and Their Components

• Epidermis: Stratified squamous epithelium; contains keratinocytes, melanocytes, Langerhans cells, and Merkel cells.

• Dermis: Connective tissue; contains fibroblasts, blood vessels, nerve endings, glands, and hair follicles.

• Hypodermis (Subcutaneous layer): Adipose and areolar tissue; provides insulation and energy storage.

Thermoregulation by Skin

• Vasodilation and vasoconstriction of dermal blood vessels

• Sweat production for evaporative cooling

Skin Changes with Aging

• Thinning of epidermis and dermis

• Reduced collagen and elastin production

• Decreased sweat and oil gland activity

• Slower wound healing

Types of Burns and Associated Complications

• First-degree: Affects only the epidermis; redness and pain.

• Second-degree: Affects epidermis and part of dermis; blisters, pain.

• Third-degree: Destroys epidermis and dermis; may affect deeper tissues; risk of infection, fluid loss.

Rule of Nines

The "Rule of Nines" is used to estimate the percentage of body surface area affected by burns:

Blister Formation

A blister forms when fluid accumulates between the epidermis and dermis due to friction or burns.

Skin Diseases

• Examples include eczema, psoriasis, acne, and skin cancer.

Functions of Epidermal Derivatives

• Glands: Sweat glands regulate temperature; sebaceous glands lubricate skin.

• Hair: Provides protection and sensory input.

• Nails: Protect fingertips and enhance fine touch.

Skin Color and Health

• Skin color can indicate health conditions: pallor (anemia), cyanosis (hypoxia), jaundice (liver disease).

Skeletal System

Functions of the Skeletal System

• Support

• Protection of internal organs

• Movement (leverage for muscles)

• Mineral storage (calcium, phosphate)

• Blood cell production (hematopoiesis)

• Triglyceride storage

Bone Classification by Shape

• Long bones: e.g., femur, humerus

• Short bones: e.g., carpals, tarsals

• Flat bones: e.g., skull, sternum

• Irregular bones: e.g., vertebrae, pelvis

General Features of a Long Bone

• Diaphysis (shaft)

• Epiphyses (ends)

• Metaphysis (growth region)

• Medullary cavity (contains marrow)

• Periosteum (outer covering)

• Endosteum (lining internal surfaces)

Principal Cell Types in Osseous Tissue

• Osteoblasts: Bone-forming cells

• Osteocytes: Mature bone cells

• Osteoclasts: Bone-resorbing cells

• Osteogenic cells: Stem cells for bone

Spongy vs. Compact Bone

• Spongy bone: Trabecular structure, found in epiphyses, supports marrow.

• Compact bone: Dense, organized in osteons, provides strength.

Hematopoiesis

Hematopoiesis is the formation of blood cells, occurring in the red bone marrow of certain bones (e.g., pelvis, sternum).

Bone Formation

• Intramembranous ossification: Direct formation from mesenchyme (e.g., flat bones).

• Endochondral ossification: Bone forms from cartilage model (e.g., long bones).

Bone Maintenance

• Bone remodeling: Continuous process of bone resorption and formation.

• Influenced by mechanical stress, hormones, and nutrition.

Nutrition and Bone Maintenance

• Calcium, vitamin D, and protein are essential for bone health.

Hormonal Regulation of Bone

• Parathyroid hormone (PTH): Increases blood calcium by stimulating osteoclasts.

• Calcitonin: Lowers blood calcium by inhibiting osteoclasts.

• Growth hormone, sex hormones: Stimulate bone growth.

Bone Disorders

• Osteoporosis, osteomalacia, Paget's disease, and others.

Fracture Types

• Simple (closed), compound (open), comminuted, greenstick, spiral, and others.

Fracture Repair Steps

1. Hematoma formation

2. Fibrocartilaginous callus formation

3. Bony callus formation

4. Bone remodeling

Example: A femur fracture undergoes hematoma formation, followed by callus formation and remodeling to restore bone integrity.

Additional info: Academic context was added to expand brief points into full explanations and to provide examples and definitions for clarity.