Unit 1 Skin Notes

Life Functions
- Maintain Boundaries: Skin and mucus membranes separate internal and external environments.
- Movement: Enabled by muscles, bones, and joints.
- Responsiveness: Function of the nervous and endocrine systems.
- Digestion: Breakdown of nutrients, occurs in the gastrointestinal (GI) tract.
- Metabolism: Chemical processes in tissues, primarily in the liver.
- Excretion: Removal of waste products through various systems (cutaneous, GI).
- Reproduction: Involves the genital systems.
- Growth: Increase in size and number of cells.
Organization of Tissues:
- Lining epithelia provide interfaces with the basal lamina.
- Made up of connective tissue for support (fascia).
- Types of muscle: smooth, cardiac, and skeletal.
- Formation of tubes/layers and organs, including cavities:
  - Cranial, Dorsal, Mediastinal, Thoracic, Pericardial, Ventral, Pleural, Abdominal, Pelvic.
Homeostasis:
- Maintenance of stable internal conditions.
- Involves a receptor, control center, and effectors.
- Feedback mechanisms:
  - Negative feedback (reduces output) vs. positive feedback (enhances output).
Cellular Components:
- Plasma membrane structure includes proteins (receptors, enzymes, transport proteins).
- Functions: Cell signaling, transport, recognition, and adhesion.

Intercellular Junctions:
- Tight Junctions:
  - Zipper-like structure at the apical edge, prevents paracellular diffusion.
- Gap Junctions:
  - Channel-forming junctions facilitating ion movement between cells via transmembrane proteins.
- Desmosomes:
  - Snap-like connections allowing slight movement; facilitates diffusion between cells.
- Hemidesmosomes:
  - Attach cells to the basal lamina.
Cytoskeleton Components:
- Microfilaments:
  - Composed of actin; provide support and shape, especially in microvilli.
- Intermediate Filaments:
  - Composed of actin tetramers; enhance cell strength.
- Microtubules:
  - Composed of tubulin; involved in organelle movement and cell division.
Membrane Transport:
- Diffusion: Movement along concentration/electrical gradients.
- Passive Transport: Spontaneous movement through channels.
- Active Transport: Requires ATP for transporters.

Histology:
- Sectioning Techniques: Longitudinal, sagittal, transverse, and oblique planes.
Epithelia Functions:
- Protection, secretion, absorption.
- Classifications:
  - Simple: One layer thick; found in areas requiring absorption and secretion.
  - Stratified: Multiple layers; offer additional protection.
Characteristics of Epithelia:
- Avascular: Rely on diffusion for nutrient and gas exchange.
- Types:
  - Pseudostratified Columnar:
    - Ciliated; found in the respiratory tract.
  - Simple Squamous:
    - Thin and flat; ideal for diffusion (e.g., blood vessels).
  - Simple Cuboidal:
    - Secretion and absorption; kidneys, glandular epithelium.
  - Stratified Cuboidal:
    - Found in sweat, salivary, and mammary glands.
  - Transitional Epithelium:
    - Allows expansion, found in the urinary bladder.
  - Stratified Squamous (Keratinized and Non-Keratinized):
    - Protective layers; found in the skin (keratinized) and oral cavity (non-keratinized).

Gland Classification:
- Exocrine Glands: Secrete products outside the body (e.g., sweat, gastric).
- Endocrine Glands: Release hormones into the bloodstream.
- Types of Secretions:
  - Serous: Thin, watery secretions.
  - Mucous: Thick, viscous secretions.
  - Holocrine: Whole cells disintegrate to release secretion.
  - Merocrine: Releases products via exocytosis.
  - Apocrine: Modified merocrine (e.g., sweat, mammary glands).
Connective Tissue Components:
- Ground Substance: Adhesive proteins linking different tissue types.
  - Laminin, proteoglycans, fibrillin, glycosaminoglycans (GAGs).
Types of Connective Tissues:
- Loose Connective Tissue: Areolar (underlies epithelia and between muscles).
- Dense Connective Tissue: Regular (tendons, ligaments) and irregular (dermis).
- Cartilage:
  - Chondroblasts produce hyaline (trachea), elastic (pinna), and fibrocartilage (symphysis).
- Bone Tissue: Produces compact and spongy bone.
- Hematopoietic Stem Cells: Give rise to all formed elements of blood (red cells, white cells, platelets).

Wound Healing Process:
- Inflammation: Characterized by swelling, redness, pain, and heat due to vasodilation and increased blood flow to the area.
- Edema: Fluid accumulation containing pathogens that stabilizes the injury site.
- Pain: Signals the need for protective measures and promotes healing responses.
Healing Stages:
- Epithelium regeneration (cells divide and migrate).
- Granulation Tissue Formation: Restores vascular supply and involves
  - Fibroblast migration to deposit collagen and develop budding capillaries.
- Maturation: Fibrosed area matures, contracts over time, can take months.
- Scarring:
  - Erythematous (red), hypertrophic (overgrowth), atrophic (indentation).
Nerve and Muscle Tissue:
- Nerve cells (neurons) consist of cell bodies and long projections (axons, dendrites).
- Neurons cannot divide, but peripheral nerves may regenerate if the cell body remains intact.
- Muscle tissues: Smooth, cardiac (contains intercalated discs), skeletal (striated).
- Tissue Growth Mechanisms:
  - Hypertrophy: Increase in cell size without increasing number of cells.
  - Atrophy: Decrease in cell size or number.

Skin Layers:
- Epidermis: Outermost layer with varied thickness across body.
  - Stratum Lucidum: Found only in thick skin.
  - Stratum Corneum: Dead keratinized cells.
  - Stratum Granulosum: Keratinizing cells.
  - Stratum Spinosum: Connects cells for strength (keratinocytes).
  - Stratum Basale: Stem cells for keratinocytes and melanocytes.
Dermis:
- Includes dense irregular connective tissue, blood vessels, nerves, and hair follicles.
Hypodermis:
- Contains larger blood vessels and connects the skin to underlying tissues.
Hair Characteristics:
- Shape:
  - Circular = straight; oval = curly (more oval = tighter curls).
- Pigmentation:
  - Eumelanin (brown/black) and pheomelanin (yellow) dictate hair color.
- Growth Phases:
  - Anagen (growth), Catagen (transition), Telogen (resting).
- Importance of Hair Papilla: Must be intact for proper hair growth; blocked follicles can hinder growth.
Nails:
- Formed by keratinized cells; nail bed provides sensitivity and support.