Anatomy, Physiology and Disease · 9 min read
Integumentary, Skeletal and Muscular Systems
This chapter covers the skin, bones and muscles: their structures, functions and the common disorders that bring patients to dermatology, orthopedic and family practice offices. Expect exam questions on skin layers, burn classification, melanoma warning signs, arthritis types, fracture types and repetitive-strain injuries.
The Integumentary System
The integumentary system includes the skin, hair, nails, sweat glands and sebaceous (oil) glands. The skin is the largest organ of the body.
| Layer | Description | Key Features |
|---|---|---|
| Epidermis | Outer layer, no blood vessels | Keratin for waterproofing; melanocytes make melanin pigment |
| Dermis | Middle layer of connective tissue | Blood vessels, nerves, hair follicles, sweat and oil glands |
| Subcutaneous (hypodermis) | Deepest layer, mainly fat | Insulation, cushioning, energy storage; site of subcut injections |
Functions of the skin include protection against microorganisms and injury, temperature regulation through sweating and blood vessel changes, sensation (touch, pain, pressure, heat and cold), vitamin D production when exposed to sunlight, and prevention of fluid loss.
Sudoriferous glands are sweat glands. Sebaceous glands secrete sebum, an oily substance that keeps skin and hair soft. Nails are made of hard keratin; pale or bluish nail beds may suggest poor oxygenation, which is why the capillary refill check uses the nail bed.
Common Skin Disorders
| Disorder | Key Signs | Typical Office Care |
|---|---|---|
| Psoriasis | Thick red plaques with silvery scales, often on elbows, knees, scalp; chronic autoimmune | Topical steroids, light therapy, biologic drugs |
| Eczema (atopic dermatitis) | Dry, itchy, red patches; common in skin folds; linked to allergies and asthma | Moisturizers, avoid triggers, topical steroids |
| Impetigo | Honey-colored crusted sores, often around nose and mouth; contagious bacterial infection | Topical or oral antibiotics; keep child home until treated |
| Cellulitis | Red, warm, swollen, tender skin that spreads; may have fever | Oral or IV antibiotics; mark the border to track spread |
| Herpes zoster (shingles) | Painful blistering rash in a band on one side of the body | Antiviral drugs; shingles vaccine for adults 50 and older |
| Tinea (ringworm) | Ring-shaped scaly rash; fungal (tinea pedis is athlete's foot) | Antifungal creams or oral antifungals |
| Acne vulgaris | Blackheads, whiteheads, pimples from blocked oil glands | Topical retinoids, benzoyl peroxide, antibiotics |
| Basal cell carcinoma | Pearly bump or nonhealing sore; most common, rarely spreads | Biopsy and excision |
| Squamous cell carcinoma | Scaly red patch or crusted sore on sun-exposed skin | Biopsy and excision |
| Malignant melanoma | Changing mole; most dangerous skin cancer, spreads early | Excisional biopsy, staging, referral |
The ABCDE rule helps patients and staff recognize a mole that may be melanoma:
Burns and the Rule of Nines
Burns are classified by depth.
| Depth | Old Term | Layers Involved | Appearance |
|---|---|---|---|
| Superficial | First degree | Epidermis only | Red, painful, no blisters (sunburn) |
| Partial-thickness | Second degree | Epidermis and part of dermis | Blisters, red, moist, very painful |
| Full-thickness | Third degree | All skin layers, may reach fat or deeper | White, leathery or charred; little pain because nerves are destroyed |
The rule of nines estimates the percentage of total body surface area (TBSA) burned in an adult. The head and neck equal 9%, each arm equals 9%, the front of the trunk equals 18%, the back of the trunk equals 18%, each leg equals 18%, and the genital area (perineum) equals 1%, for a total of 100%.
Worked example: An adult burns the entire front of the right arm and the entire front of the trunk. The front of one arm is half of 9%, which is 4.5%. The front of the trunk is 18%. Add them: 4.5% + 18% = 22.5% TBSA. Burns over about 20% TBSA in adults are generally treated as major burns needing hospital care.
The Skeletal System
The adult skeleton has 206 bones. The axial skeleton includes the skull, vertebral column, ribs and sternum. The appendicular skeleton includes the shoulder girdle, arms, pelvic girdle and legs.
Functions of the skeletal system include support, protection of organs (the skull protects the brain, the ribs protect the heart and lungs), movement with muscles as levers, mineral storage (mainly calcium and phosphorus) and hematopoiesis, the production of blood cells in red bone marrow.
| Term | Meaning | Example |
|---|---|---|
| Long bone | Longer than wide | Femur, humerus |
| Flat bone | Thin and flat | Skull bones, sternum, ribs |
| Diaphysis | Shaft of a long bone | Middle of the femur |
| Epiphysis | End of a long bone | Head of the femur |
| Epiphyseal plate | Growth plate in children | Fractures here can affect growth |
The vertebral column has 7 cervical, 12 thoracic and 5 lumbar vertebrae, plus the sacrum and coccyx. A joint (articulation) is where two bones meet. Synovial joints, such as the knee and shoulder, move freely and contain synovial fluid. Ligaments connect bone to bone; tendons connect muscle to bone; cartilage cushions joint surfaces.
Common Skeletal and Joint Disorders
| Disorder | Key Features | Typical Tests and Care |
|---|---|---|
| Osteoporosis | Loss of bone density; brittle bones; common in postmenopausal women; may cause height loss and hip, wrist or spine fractures | DEXA (bone density) scan, calcium and vitamin D, weight-bearing exercise, medication |
| Osteoarthritis (OA) | "Wear and tear" loss of cartilage; pain worse with use, better with rest; weight-bearing joints; morning stiffness under 30 minutes | X-ray, NSAIDs, weight loss, exercise, joint replacement |
| Rheumatoid arthritis (RA) | Autoimmune; symmetrical swelling of small joints of hands and feet; morning stiffness over 1 hour; fatigue | Rheumatoid factor and anti-CCP blood tests, ESR, CRP, disease-modifying drugs |
| Gout | Uric acid crystals in a joint; sudden, severe pain, often in the big toe; red, hot, swollen joint | Serum uric acid, joint fluid analysis, anti-inflammatory drugs, low-purine diet |
| Scoliosis | Sideways S- or C-shaped curve of the spine; often found in adolescents | Forward-bend screening test, X-ray, bracing |
| Kyphosis | Excessive outward curve of the upper back ("hunchback") | Often linked to osteoporosis |
Fracture Types
A fracture is a break in a bone. Diagnosis is confirmed by X-ray, and treatment includes reduction (realigning the bone) and immobilization with a splint or cast.
| Type | Description |
|---|---|
| Closed (simple) | Bone breaks but skin stays intact |
| Open (compound) | Bone breaks through the skin; high infection risk |
| Greenstick | Incomplete break, bone bends; common in children |
| Comminuted | Bone shatters into several pieces |
| Spiral | Break twists around the bone; can suggest twisting injury or abuse in a child |
| Transverse | Straight break across the bone |
| Compression | Bone is crushed; common in vertebrae with osteoporosis |
| Stress (hairline) | Small crack from repeated force; common in runners |
| Colles | Break of the distal radius from falling on an outstretched hand |
Clinic Scenario: A mother brings in her toddler with a swollen forearm and says he "fell off the couch." The X-ray report later shows a spiral fracture, and the medical assistant notices several bruises in different stages of healing on the child's back. A spiral fracture in a child who cannot yet walk well, with an injury story that does not match, is a red flag for abuse. The MA documents objective observations exactly, reports concerns to the provider, and follows the office's mandatory reporting policy.
The Muscular System
The body has three types of muscle tissue.
| Type | Control | Location | Appearance |
|---|---|---|---|
| Skeletal | Voluntary | Attached to bones | Striated (striped) |
| Smooth | Involuntary | Walls of organs and vessels | Not striated |
| Cardiac | Involuntary | Heart only | Striated, with intercalated discs |
Functions of muscles include movement, posture, joint stability and heat production. Muscles work in pairs: the prime mover (agonist) performs an action, and the antagonist performs the opposite action. For example, the biceps flexes the elbow and the triceps extends it. Muscle contraction needs calcium and energy from ATP.
| Muscle | Location | Clinical Note |
|---|---|---|
| Deltoid | Shoulder | IM injection site for small volumes in adults |
| Vastus lateralis | Outer thigh | Preferred IM site for infants |
| Gluteus medius (ventrogluteal site) | Hip | Preferred IM site for larger volumes |
| Gluteus maximus (dorsogluteal site) | Buttock | Avoided because of the sciatic nerve |
| Diaphragm | Below the lungs | Main muscle of breathing |
Common Muscular and Repetitive-Strain Disorders
| Disorder | Key Features | Typical Tests and Care |
|---|---|---|
| Carpal tunnel syndrome | Median nerve compressed at the wrist; numbness and tingling of thumb, index and middle fingers; worse at night; linked to repetitive wrist motion | Tinel and Phalen tests, nerve conduction study, wrist splint, ergonomic changes, surgery |
| Muscular dystrophy | Inherited group of diseases with progressive muscle weakness; Duchenne type mostly in boys | Genetic testing, CK blood test, physical therapy |
| Strain | Overstretched or torn muscle or tendon | RICE: rest, ice, compression, elevation |
| Sprain | Overstretched or torn ligament | RICE, possible splint |
Key Takeaways
- The skin has three layers: epidermis, dermis and subcutaneous tissue; subcut injections go into the fatty bottom layer.
- Use ABCDE to recognize possible melanoma, and use the rule of nines to estimate adult burn size.
- Osteoarthritis is degenerative and asymmetric; rheumatoid arthritis is autoimmune and symmetric.
- An open (compound) fracture breaks through the skin, and a greenstick fracture is an incomplete break common in children.
- Carpal tunnel syndrome compresses the median nerve; a strain affects muscle or tendon, while a sprain affects ligament.
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