Integumentary System

Layers of the Epidermis

The epidermis is the outermost layer of the skin, composed of several distinct strata, each with specialized functions and cell types.

• Stratum Basale: - Mitotically active; responsible for generating new skin cells. - Most nourished layer, attached to the dermis. - Contains melanocytes (produce melanin for UV protection) and Merkel cells (touch receptors).

• Stratum Spinosum: - Metabolically active; hosts several cell layers. - Keratin is produced here. - Desmosomes first appear, providing cell adhesion. - Langerhans cells activate the immune system.

• Stratum Granulosum: - Cells die and become keratinized. - Appear squamous (flattened).

• Stratum Lucidum: - Only present in thick skin (palms, soles). - Provides extra protection against abrasion.

• Stratum Corneum: - All cells are dead, stratified squamous epithelium. - Desmosomes remain, providing a tough layer.

Desmosomes

• Specialized cell junctions that provide strong adhesion between cells, especially in tissues subject to mechanical stress.

• Connect everything in the epidermis.

• Divide tension, preventing tissue separation.

How do blisters occur?

• Fluid accumulation between the dermis and epidermis due to inflammatory response, causing blood vessel leak.

Burns and the Rule of Nines

• Critical: ≥25% of the body is covered in second-degree burns.

• Critical: ≥10% of the body is covered in third-degree burns.

• Third-degree burns are critical if the face, hands, or feet are affected.

• Rule of nines: Helps paramedics estimate fluid volume loss.

Burn Treatment

• Increase fluids and electrolytes.

• Increase calorie intake for metabolic demand.

• Clean and wrap burns; give antibiotics to prevent infection.

• Assist tissue repair (e.g., add collagen or silver).

Skeletal System

Bone Formation: Ossification

Ossification is the process of bone tissue formation, occurring via two main mechanisms during development.

• Intramembranous Ossification (Embryo Stage): - Occurs in membranes because of osteoblasts. - Stem cells differentiate into osteoblasts, which lay down collagen and minerals. - Blood vessels enter, bringing osteoclasts for bone remodeling. - Creates flat bones (skull, sternum, scapula, etc.).

• Endochondral Ossification: - Starts with a cartilage (hyaline) template. - Osteoblasts form a bony collar; cartilage dies. - Chondrocytes secrete calcitonin, causing cartilage growth and eventual death. - Cartilage grows in length; nutrients diffuse in the center. - The periosteal bud invades, bringing osteoblasts and blood vessels. - Epiphyseal growth plate remains for long bone growth at joints. - The process continues after birth.

Long Bone Growth

• Proliferation zone: Mitotically active cartilage cells.

• Hypertrophic zone: Cartilage cells enlarge and secrete calcium.

• Calcification zone: Cartilage cells die.

• Ossification zone: Osteoblasts lay down new bone and remodel.

• Growth ends when epiphyses and diaphysis fuse.

• Regulated by growth hormone and thyroid hormone (requires iodine).

• Resting zone: Cartilage cells undergo mitosis.

Bone Repair

Bone repair after fracture occurs in several stages, restoring bone structure and function.

1. Hematoma forms: Blood clot forms, injured cells die, swelling and pain occur.

2. Fibrocartilaginous Callus: Soft callus forms (2-4 days post-break), fibroblasts and osteoblasts arrive, putting bones together.

3. Bony Callus: Spongy bone connects ends of bones (1 week post-break); osteoclasts kill cartilage, osteoblasts lay new bone.

4. Bone Remodeling: Thicker, scarred bone replaces bony callus.

Bone Resorption and Deposition

Bone tissue is constantly remodeled through deposition and resorption, maintaining strength and mineral balance.

• Deposition: Osteoblasts lay down osteon, deposit minerals (requires vitamin C, D, A).

• Resorption: Osteoclasts break down bone matrix, releasing minerals.

• Regulated by blood calcium levels (9-11 mg/dL), calcitonin (inhibits PTH), and parathyroid hormone (stimulates osteoclasts).

• Bones are mineralized by calcium phosphate.

Pathology of Bone

• Paget's Disease: - Involves abnormal bone remodeling, resulting in imbalance between spongy and compact bone. - Abnormal ratio of spongy bone to compact bone. - Poor mineralization of new bone. - May be viral in origin.

• Osteoporosis: - Characterized by weakened bones due to hormonal changes and loss of bone density. - Common in postmenopausal women and older men with low testosterone. - Lack of vitamin D, calcium, and protein. - Spongy bone (femur, neck, and spine) are most affected. - Hormonal role: HRT (hormone replacement therapy).

• Osteomalacia: - Softening of bones due to vitamin D deficiency. - Pain, deformities, bowlegs.

Hydroxyapatites

• Mineral compounds that provide resistance to compression in bone tissue.

• Essential for bone strength and durability.

Cartilage Types and Characteristics

Hyaline Cartilage

• Shiny, bluish tint

• Flexible, strong, elastic

• Articulate cartilage covers ends of bones (epiphysis)

• Costal cartilage connects ribs to sternum

• Forms skeleton of larynx and reinforces respiratory passages

Elastic Cartilage

• Stretchy, flexible

• Yellow and opaque

• Found in ears and epiglottis

Fibrocartilage

• The strongest type

• Dense collection of hyaline cartilage and collagen fibers

• Found in intervertebral discs, pubic symphysis, meniscus

Cartilage Growth

• Appositional: New chondrocyte and new matrix is added on the outside of the tissue.

• Interstitial: Chondrocyte divides and secretes new matrix expanding cartilage from within the tissue (found during growth periods → puberty).

Chondroblasts

• Cells that produce cartilage matrix.

Bone Structure and Function

• Functions: Support, protection, anchorage, blood cell production, mineral storage.

• Periosteum covers the diaphysis; endosteum lines the medullary cavity.

• Osteons are organized in lamellae for strength.

• Canaliculi allow communication through gap junctions.

• Central canal (Volkmann's canal) provides a passage for blood vessels and nerves.

Glands and Membranes

• Holocrine: Sebaceous glands (release entire cell contents).

• Merocrine: Exocytosis (eccrine sweat glands).

• Apocrine: Found in armpits/genitals; fatty substance in secretion.

• Mucous membrane: Lines closed ventral cavities.

• Serous membrane: Lines closed ventral cavities; contains hyaluronic acid for lubrication.

Table: Comparison of Bone Disorders

Key Formulas

• Blood Calcium Regulation: 9-11 mg/dL

• Bone Growth Equation:

Additional info: Some details inferred from standard Anatomy & Physiology curriculum to clarify fragmented points and ensure completeness.