Histology: Tissue Types and Cell Junctions

• Four major tissue types: epithelial, connective, muscle, and nervous.

Cell Junctions

• Tight junctions: prevent substances from passing between cells.
• Adherens junctions: provide strong mechanical attachments between cells.
• Desmosomes: act like rivets, anchoring cells together tightly.
• Hemidesmosomes: connect cells to the extracellular matrix.
• Gap junctions: allow direct communication between cells via channels.

Epithelial Tissue Types

• Simple squamous epithelium: single layer of flattened cells; found in air sacs of lungs and lining blood vessels; allows for diffusion and filtration.
• Simple cuboidal epithelium: single layer of cube-shaped cells; found in kidney tubules and glands; involved in secretion and absorption.
• Simple columnar epithelium: single layer of column-shaped cells; lines the gastrointestinal tract; functions in absorption and secretion.
• Pseudostratified columnar epithelium: single layer of cells of varying heights; lines the trachea; involved in secretion and movement of mucus.
• Stratified squamous epithelium: multiple layers of flattened cells; epidermis of skin; protects against abrasion.
• Transitional epithelium: many layers of cells that can change shape; lines the urinary bladder; allows for stretching.

Connective Tissue Types

• Connective tissue proper:
  • Loose connective tissue (areolar, adipose, reticular):
    • Areolar: widely distributed; wraps and cushions organs.
    • Adipose: stores fat; provides insulation and support.
    • Reticular: forms a supportive network in lymphoid organs
  • Dense connective tissue (regular, irregular, elastic):
    • Regular: tendons and ligaments; provides strong attachment
    • Irregular: dermis of the skin; provides strength in multiple directions
    • Elastic: walls of large arteries; allows recoil after stretching
• Cartilage (hyaline, elastic, fibrocartilage):
  • Hyaline: ends of long bones; reduces friction
  • Elastic: external ear; maintains shape while allowing flexibility
  • Fibrocartilage: intervertebral discs; provides cushioning and resists compression
• Bone: supports and protects; stores calcium
• Blood: transports oxygen and nutrients

Muscle Tissue Types

• Skeletal muscle: striated, voluntary; attached to bones; responsible for movement.
• Cardiac muscle: striated, involuntary; forms the heart; pumps blood.
• Smooth muscle: non-striated, involuntary; walls of hollow organs; involved in movement of substances within the body.

Nervous Tissue

• Nervous tissue: consists of neurons and glial cells; found in the brain, spinal cord, and nerves; conducts electrical signals and supports neurons.

Glandular Epithelium

• Glandular epithelium: specialized epithelial tissue that secretes substances.
• Endocrine glands: secrete hormones directly into the bloodstream.
• Exocrine glands: secrete substances through ducts onto a surface.
  • Merocrine: secrete products by exocytosis (e.g., sweat glands).
  • Apocrine: accumulate products at the apical surface, then pinch off (e.g., mammary glands).
  • Holocrine: accumulate products within, then rupture (e.g., sebaceous glands).

Membranes

• Mucous membranes: line cavities that open to the exterior; secrete mucus.
• Serous membranes: line closed cavities; secrete serous fluid.
• Cutaneous membrane: the skin; protects the body from the external environment.

Integumentary System: Gross Anatomy

• Epidermis: outermost layer; provides protection.
• Dermis: middle layer; contains blood vessels, nerves, and accessory structures.
• Hypodermis: innermost layer; stores fat and anchors skin.
• Accessory structures: hair follicles, sweat glands, sebaceous glands, and nails.

Integumentary System: Microscopic Anatomy

• Epidermis layers: stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, stratum corneum.
• Keratinocytes: produce keratin; most abundant cell type in the epidermis.
• Melanocytes: produce melanin; protect against UV radiation.
• Langerhans cells: immune cells; involved in defense.
• Merkel cells: touch receptors.

Pigments of the Skin

• Melanin: provides brown to black color; protects against UV radiation.
• Carotene: provides yellow to orange color.
• Hemoglobin: provides pinkish hue in fair skin.
• Tanning: UV radiation stimulates melanin production.

Accessory Structures of the Skin

• Sweat glands: regulate body temperature.
• Sebaceous glands: secrete sebum; lubricate skin and hair.
• Hair follicles: produce hair; provide insulation and protection.
• Capillary beds: supply blood to the skin; regulate temperature.
• Cutaneous receptors: detect touch, pressure, temperature, and pain.

Skin Barrier Functions

• Chemical barrier: sebum, sweat, and antimicrobial peptides.
• Physical barrier: keratinized epidermis.
• Biological barrier: Langerhans cells and macrophages.

Metabolic and Excretory Functions of the Skin

• Metabolic functions: synthesis of vitamin D.
• Excretory functions: excretion of salts, water, and organic wastes.

Skin Cancers and Burns

• Skin cancers: basal cell carcinoma, squamous cell carcinoma, melanoma.
• Burns: first-degree (epidermis), second-degree (epidermis and dermis), third-degree (full thickness).

Bone Classification

• Long bones: longer than wide (e.g., femur).
• Short bones: cube-shaped (e.g., carpals).
• Flat bones: thin and flat (e.g., skull bones).
• Irregular bones: complex shapes (e.g., vertebrae).

Functions of Bone and Skeletal Tissues

• Support, protection, movement, mineral storage, blood cell formation.

Bone Histology and Structure

• Compact bone: dense outer layer; provides strength and support.
• Spongy bone: inner network of bone; contains red marrow.
• Long bone: diaphysis (shaft), epiphyses (ends), epiphyseal plate (growth plate).
• Flat bone: periosteum-covered compact bone sandwiching endosteum-covered spongy bone

Bone Cells

• Osteoblasts: bone-forming cells.
• Osteocytes: mature bone cells; maintain bone matrix.
• Osteoclasts: bone-resorbing cells.

Bone Formation, Growth, Remodeling, and Repair

• Endochondral ossification: bone formation from cartilage.
• Intramembranous ossification: bone formation from mesenchyme.
• Longitudinal growth: occurs at the epiphyseal plate.
  • Zones of epiphyseal plate: reserve cartilage, proliferation, hypertrophy, calcification, ossification.
• Bone remodeling: ongoing replacement of old bone tissue with new.
• Fracture repair: hematoma formation, callus formation, bone remodeling.

Hormones Regulating Bone Growth

• Growth hormone, thyroid hormone, sex hormones.

Vitamin and Mineral Requirements for Bone Growth

• Calcium, phosphorus, vitamin D.

Blood Calcium Homeostasis

• Hypercalcemia: high blood calcium; stimulates calcitonin release.
• Hypocalcemia: low blood calcium; stimulates parathyroid hormone (PTH) release.

Bone Disorders

• Osteoporosis, rickets, osteomalacia.

Regional Anatomy Terms

• Anterior, posterior, superior, inferior, medial, lateral, proximal, distal

Abdominopelvic Regions

• Right hypochondriac, epigastric, left hypochondriac, right lumbar, umbilical, left lumbar, right iliac, hypogastric, left iliac

Serous Membranes

• Parietal layer: lines the body cavity.
• Visceral layer: covers the organs.

Carbonic Acid/Bicarbonate Buffer System

• CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-; maintains blood pH.

States of Matter

• Solids, liquids, gases.

Subatomic Particle Composition

• Protons (atomic #), neutrons (mass #), electrons (charge)

Ionic Compounds

• Acids: release H+ ions.
• Bases: accept H+ ions.
• Salts: formed from the reaction of an acid and a base.

Anabolic and Catabolic Reactions

• Anabolic: build complex molecules.
• Catabolic: break down complex molecules.

Monosaccharides

• Glucose, fructose, galactose, ribose, deoxyribose

Protein Structure

• Primary, secondary, tertiary, quaternary.

Secondary Active Transport

• Uses Na+ gradient to transport other substances.

Mitosis Phases

• Prophase, metaphase, anaphase, telophase.

Protein Synthesis

• mRNA codons pair with tRNA anticodons.

Osmosis

• Water movement across a semipermeable membrane based on tonicity.