Tissues

Primary Tissue Classes and Subclasses

The human body is composed of four primary tissue classes, each with distinct characteristics and functions. Understanding these tissues is fundamental to anatomy and physiology.

• 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 (areolar, adipose), dense (regular, irregular), cartilage, bone, and blood.

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

• Nervous Tissue: Initiates and transmits electrical impulses. Composed of neurons and supporting glial cells.

Characteristics, Functions, and Cell Types

• Epithelial Tissue: Cells are tightly packed, avascular, high regenerative capacity. Functions include protection, absorption, filtration, secretion. Cell types: squamous, cuboidal, columnar, goblet cells.

• Connective Tissue: Cells are scattered in an extracellular matrix. Functions: support, protection, transport. Cell types: fibroblasts, chondrocytes, osteocytes, adipocytes, blood cells.

• Muscle Tissue: Elongated cells (fibers), contractile proteins. Functions: movement, posture, heat production. Cell types: muscle fibers (skeletal, cardiac, smooth).

• Nervous Tissue: Excitable cells, specialized for communication. Functions: sensory input, integration, motor output. Cell types: neurons, glial cells.

Differences Between Tissue Types

• Structure: Epithelial is tightly packed; connective has matrix; muscle is elongated; nervous is specialized for signaling.

• Function: Protection (epithelial), support (connective), movement (muscle), communication (nervous).

Inflammation and Tissue Repair

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

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

• Healing Processes: Involves inflammation (removal of debris), organization (formation of granulation tissue), regeneration (restoration of original tissue) or fibrosis (scar formation).

• Factors Affecting Repair: Nutrition, blood supply, age, presence of infection.

Example:

Skin wounds heal by inflammation, followed by tissue organization and regeneration. Severe injuries may result in scar tissue (fibrosis).

Skin (Integumentary System)

Functions of Skin

The skin is the largest organ and serves multiple vital functions.

• Protection: Against mechanical injury, pathogens, UV radiation.

• Thermoregulation: Regulates body temperature via sweat and blood flow.

• Sensation: Contains sensory receptors for touch, pain, temperature.

• Metabolic Functions: Synthesizes vitamin D.

• Excretion: Eliminates waste through sweat.

Layers of Skin and Their Components

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

• Dermis: Connective tissue; contains fibroblasts, blood vessels, nerves, glands, hair follicles.

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

Thermoregulation

• Mechanisms: Sweat production, vasodilation/vasoconstriction of dermal blood vessels.

• Example: During exercise, sweat glands increase activity to cool the body.

Aging and Skin

• Changes: Thinning of epidermis, decreased collagen, reduced elasticity, slower healing.

Burns and Complications

• Types: First-degree (epidermis), second-degree (epidermis and dermis), third-degree (full thickness).

• Complications: Fluid loss, infection, scarring.

Rule of Nines

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

Blister Formation

• Mechanism: Separation of epidermis from dermis, fluid accumulates in the space.

Skin Diseases

• Examples: Acne, eczema, psoriasis, skin cancer.

Epidermal Derivatives

• Glands: Sebaceous (oil), sweat glands (eccrine, apocrine).

• Hair: Protection, sensory function.

• Nails: Protection, tool use.

Skin Color and Health

• Indicators: Cyanosis (blue, low oxygen), jaundice (yellow, liver dysfunction), pallor (pale, anemia).

Skeletal System

Functions of the Skeletal System

The skeletal system provides structural support and serves several essential functions.

• Support: Framework for the body.

• Protection: Shields vital organs (e.g., skull, rib cage).

• Movement: Provides attachment for muscles.

• Mineral Storage: Stores calcium and phosphate.

• Hematopoiesis: Blood cell formation in bone marrow.

Bone Classification by Shape

• Long Bones: Femur, humerus.

• Short Bones: Carpals, tarsals.

• Flat Bones: Skull, sternum.

• Irregular Bones: Vertebrae, pelvis.

Features of a Long Bone

• Diaphysis: Shaft, compact bone.

• Epiphyses: Ends, spongy bone.

• Medullary Cavity: Contains marrow.

• Periosteum: Outer covering.

• Endosteum: Inner lining.

Principal Cell Types in Osseous Tissue

• Osteoblasts: Bone-forming cells.

• Osteocytes: Mature bone cells.

• Osteoclasts: Bone-resorbing cells.

Spongy vs. Compact Bone

• Spongy Bone: Trabecular, lighter, found in epiphyses.

• Compact Bone: Dense, strong, forms diaphysis.

Hematopoiesis

• Definition: Formation of blood cells.

• Location: Red bone marrow, especially in flat bones and epiphyses of long bones.

Bone Formation

• Intramembranous Ossification: Forms flat bones from mesenchyme.

• Endochondral Ossification: Forms most bones from cartilage models.

Bone Maintenance

• Remodeling: Continuous process of bone resorption and formation.

• Nutrition: Calcium, vitamin D, protein are essential.

• Hormones: Parathyroid hormone, calcitonin, growth hormone, sex hormones regulate bone metabolism.

Bone Disorders

• Examples: Osteoporosis, osteomalacia, Paget's disease.

Fracture Types

• Simple (Closed): Bone breaks but does not penetrate skin.

• Compound (Open): Bone breaks and penetrates skin.

• Comminuted: Bone fragments into several pieces.

• Greenstick: Incomplete break, common in children.

Fracture Repair Steps

1. Hematoma Formation: Blood clot forms at fracture site.

2. Fibrocartilaginous Callus Formation: Soft callus bridges the gap.

3. Bony Callus Formation: Hard callus replaces soft callus.

4. Bone Remodeling: Bone is reshaped to original form.

Example: After a bone fracture, the body initiates a repair process involving clot formation, callus development, and remodeling to restore bone integrity.