Tissues and the Integumentary System

Strata of the Epidermis

The epidermis is composed of several distinct layers, each with unique characteristics and functions. Understanding these layers is essential for identifying skin structure and pathology.

• Stratum basale: The deepest layer; contains stem cells responsible for generating new keratinocytes.

• Stratum spinosum: Provides strength and flexibility; cells begin to flatten and accumulate keratin.

• Stratum granulosum: Cells undergo apoptosis; keratinization begins.

• Stratum lucidum: Present only in thick skin (palms, soles); provides extra protection.

• Stratum corneum: Outermost layer; consists of dead, keratinized cells that protect underlying tissues.

Connective Tissues and Their Characteristics

Connective tissues support, bind, and protect organs. They are classified based on their structure and function.

• Muscle tissue types:

  • Smooth muscle: Involuntary, non-striated; found in walls of hollow organs.

  • Skeletal muscle: Voluntary, striated; attached to bones for movement.

  • Cardiac muscle: Involuntary, striated; found only in the heart.

• Cartilage types:

  • Hyaline cartilage: Most common; found in nose, trachea, and at ends of long bones.

  • Fibrocartilage: Strongest; found in intervertebral discs and pubic symphysis.

  • Elastic cartilage: Flexible; found in ear and epiglottis.

• Connective tissue types:

  • Adipose: Stores fat; insulates and cushions.

  • Dense regular and irregular: Provides strength; found in tendons (regular) and dermis (irregular).

  • Loose areolar: Most common; supports and binds other tissues.

  • Reticular: Forms supporting framework of lymphoid organs.

Example:

• Cardiac muscle is in the heart.

• Nervous tissue is in the brain.

• Reticular tissue is in the spleen.

Types of Epithelium and Their Identification

Epithelium is classified by cell shape and layering. Each type has specific locations and functions.

• Stratified squamous: Multiple layers; protects against abrasion (e.g., skin, mouth).

• Simple squamous: Single layer; allows diffusion (e.g., alveoli, blood vessels).

• Simple cuboidal: Cube-shaped; secretion and absorption (e.g., kidney tubules).

• Simple columnar: Tall cells; absorption and secretion (e.g., intestines).

• Transitional: Stretches; found in urinary bladder.

• Pseudostratified columnar with cilia: Appears layered but is not; cilia move mucus (e.g., trachea).

Cell Junctions in Epithelial Tissue

Cell junctions maintain tissue integrity and regulate communication between cells.

• Tight junctions: Prevent leakage between cells.

• Desmosomes: Provide mechanical strength.

• Gap junctions: Allow passage of ions and small molecules.

Structural Characteristics of Epithelial Tissue

Epithelial tissue covers surfaces and lines cavities, with distinct features:

• Cells are closely packed with minimal extracellular matrix.

• Polarity: Apical (top) and basal (bottom) surfaces.

• Avascular but innervated.

• High regenerative capacity.

Bone Structure and Function

Regions of Long Bones

Long bones have distinct regions important for growth and function.

• Epiphysis: Ends of the bone; contains spongy bone and red marrow.

• Metaphysis: Region between epiphysis and diaphysis; site of growth plate.

• Diaphysis: Shaft; contains compact bone and medullary cavity.

Bone Susceptibility to Fracture

Certain bones are more prone to fracture due to their location and structure.

• Scaphoid bone: Located in the wrist; susceptible to fracture from falls on outstretched hands.

Bone Cells and Their Functions

Bones contain specialized cells responsible for growth, maintenance, and repair.

• Osteoblast: Builds new bone matrix.

• Osteoclast: Breaks down bone matrix.

• Osteocyte: Maintains bone tissue.

Compact Bone Characteristics

Compact bone is dense and provides strength.

• Canaliculi: Small channels connecting osteocytes.

• Lacunae: Spaces housing osteocytes.

• Volkmann's canals: Transverse channels for blood vessels and nerves.

Ossification Processes

Bone formation occurs via two main processes: intramembranous and endochondral ossification.

• Intramembranous ossification: Mesenchymal stem cells become osteogenic cells, forming flat bones (e.g., skull, clavicle).

• Endochondral ossification: Mesenchymal stem cells become chondroblasts, then osteoblasts; forms most bones, especially long bones.

General differences: Intramembranous forms flat bones directly; endochondral forms bones via cartilage intermediate.

Appendicular vs. Axial Skeleton

The skeleton is divided into two main parts:

• Axial skeleton: Skull, vertebral column, rib cage.

• Appendicular skeleton: Limbs, pelvic and pectoral girdles.

Skin Structure and Function

Skin Layers and Cell Types

The skin consists of multiple layers, each with specialized cells.

• Merkel cells: Touch receptors in the epidermis.

• Melanocytes: Produce melanin, contributing to skin color.

Skin Cancers

Skin cancers are classified by the cell type of origin and their characteristics.

• Basal cell carcinoma: Originates from basal cells; slow-growing, rarely metastasizes.

• Additional info: Other types include squamous cell carcinoma and melanoma.

Burns: Types and Effects

Burns are classified by depth and severity, affecting different skin layers.

• 1st degree burn: Affects only the epidermis; redness, mild pain, heals without scarring.

• 2nd degree burn: Affects epidermis and part of dermis; blisters, more pain, may scar.

• 3rd degree burn: Destroys epidermis and dermis; may affect deeper tissues, requires medical intervention, scarring likely.

Healing outcomes: Deeper burns heal slower and are more likely to scar.

Glands and Secretions

Types of Sweat Glands

Sweat glands differ in location, secretion type, and function.

• Eccrine sweat gland: Widely distributed; secretes watery sweat for thermoregulation.

• Apocrine sweat gland: Found in axillary and genital areas; secretes thicker, odor-producing sweat.

Cellular Structures and Functions

Cell Polarity and Junctions

Cells have distinct regions and specialized junctions for function and communication.

• Apical end: Faces the lumen or external environment.

• Lateral end: Contacts adjacent cells.

• Basal end: Anchors to the basement membrane.

Hormonal Regulation of Bone

Calcium Homeostasis

Blood calcium levels are regulated by hormones released from specific glands.

• Thyroid gland: Releases calcitonin to lower blood calcium.

• Parathyroid gland: Releases parathyroid hormone (PTH) to increase blood calcium.

Hormonal response: Calcitonin inhibits osteoclasts; PTH stimulates osteoclasts and increases calcium reabsorption in kidneys.

Body Positioning and Curvature

Spinal Curvatures

Abnormal spinal curvatures affect posture and movement.

• Scoliosis: Lateral curvature of the spine.

• Kyphosis: Excessive outward curvature (hunchback).

• Lordosis: Excessive inward curvature (swayback).

Additional Info

• Alopecia: Medical term for hair loss.

• Perion region: Area of the skull; clinical significance may relate to trauma or surgical access.