D236 Notes on Homeostasis & Cellular Responses
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Western Governors University
D236 Pathophysiology
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SECTION 2: Musculoskeletal Disorders and Related Conditions
What is Degenerative Disc Disease (DDD)?
Degenerative Disc Disease (DDD) is a prevalent musculoskeletal disorder characterized by the progressive breakdown of intervertebral discs. These discs function as cushions and provide flexibility between the vertebrae. With aging or repetitive stress, these discs gradually lose their hydration and elasticity, impairing their ability to absorb shocks effectively. As a result, vertebral misalignment can occur, which increases the risk of spinal nerve compression and leads to radiculopathy, a condition marked by nerve root pain.
When DDD affects the lower spine, particularly the lumbar or sacral regions, it may compress the sciatic nerve. This compression can cause sciatica, a painful condition where discomfort radiates along one or both legs (Huether & McCance, 2020).
What is Paget’s Disease of Bone?
Paget’s Disease of Bone is a chronic disorder involving abnormal and accelerated bone remodeling. In this condition, bone resorption and formation become unbalanced, leading to the creation of structurally unsound, weak, and brittle bone tissue. Many affected individuals show no symptoms until the disease is incidentally detected through imaging.
During active disease phases, increased osteoclastic activity releases excessive calcium into the bloodstream, possibly resulting in hypercalcemia. Clinical symptoms can include localized bone pain, deformities, and neurological issues caused by bone enlargement compressing adjacent nerves (Porter et al., 2021).
How do Stress Fractures Develop and Where Are They Commonly Located?
Stress fractures occur when bone breakdown surpasses bone repair due to repetitive mechanical loading without sufficient recovery. This injury is frequent in athletes and military recruits. Patients often report localized pain that intensifies with activity and subsides during rest.
| Causes | Risk Factors | Common Sites |
|---|---|---|
| Repetitive impact activities | Vitamin D deficiency, overtraining, poor nutrition | Tibia, metatarsals, femur |
What Are Rickets and Osteomalacia?
Rickets (in children) is a bone disorder caused by defective mineralization of the developing skeleton, leading to soft, fragile bones and deformities. Vitamin D deficiency is the primary cause, but other contributors include malabsorption syndromes, liver or kidney dysfunction, and insufficient sunlight exposure. Clinical signs of rickets include bone pain, delayed growth, softening of the skull bones (craniotabes), bowing of the legs, and a protruding abdomen.
Osteomalacia (in adults) is characterized by inadequate mineralization of mature bone, resulting in soft and fragile bones prone to fractures. Symptoms include widespread bone and joint pain, muscle weakness, and an increased risk of fractures even with minor trauma (McCance & Huether, 2020).
What is Compartment Syndrome and How is it Diagnosed?
Compartment Syndrome develops when pressure rises within a closed muscle compartment, compromising blood circulation and nerve function. If untreated, it can cause tissue death and permanent disability.
Clinical Signs (6 P’s):
- Pain disproportionate to injury
- Paresthesia (tingling)
- Pallor (paleness)
- Pulselessness (absent pulse)
- Poikilothermia (cool temperature)
- Paralysis (a late sign)
| Causes | Complications | Diagnostic Criteria |
|---|---|---|
| Crush injuries, fractures, burns, tight casts or dressings | Tissue necrosis, gangrene, rhabdomyolysis, nerve injury | Compartment pressure >30 mmHg, CT, MRI, CBC |
Emergency fasciotomy or removal of constrictive dressings is crucial. In severe cases, amputation may be necessary.
What is Rhabdomyolysis and Its Classic Presentation?
Rhabdomyolysis involves the destruction of skeletal muscle fibers, releasing intracellular contents like myoglobin and creatine kinase into the bloodstream. Excess myoglobin can obstruct renal tubules, resulting in acute kidney injury.
Classic Triad of Symptoms:
- Muscle pain (myalgia)
- Muscle weakness
- Dark, tea-colored urine (myoglobinuria)
Prompt intravenous hydration and correction of electrolyte imbalances are vital to prevent renal damage.
What is a Sequestrum?
A sequestrum refers to a segment of dead bone separated from living bone, typically following infection or trauma. Surgical removal (debridement) of this necrotic bone is essential to promote healing and prevent chronic osteomyelitis (Smeltzer et al., 2020).
What are Deep Vein Thrombosis (DVT) and Pulmonary Embolism (PE), and How Are They Diagnosed?
Orthopedic procedures and immobilization predispose patients to DVT and PE through venous stasis and vessel injury.
| Condition | Key Features | Diagnostic Tests |
|---|---|---|
| DVT | Swelling, tenderness, warmth, palpable cord | D-dimer test, Doppler ultrasound, coagulation profile |
| PE | Shortness of breath, chest pain, cyanosis, rapid breathing, coughing blood | CT pulmonary angiogram, ventilation/perfusion (V/Q) scan |
Preventive measures include early mobilization, compression stockings, and anticoagulation therapy.
What is Fat Embolism Syndrome (FES), and How is It Diagnosed?
FES occurs when fat droplets released from bone marrow after fractures enter the bloodstream and obstruct pulmonary or cerebral vessels, causing respiratory distress and neurological signs.
| Diagnostic Criteria for FES | Major Criteria | Minor Criteria |
|---|---|---|
| Requires 1 major + ≥4 minor criteria + fat macroglobulinemia | Respiratory failure, cerebral symptoms, petechial rash | Tachycardia, fever, retinal petechiae, renal dysfunction, jaundice, anemia, thrombocytopenia, elevated ESR |
Immediate fluid resuscitation with normal saline or lactated Ringer’s solution is critical to maintain circulation and facilitate emboli clearance.
What is Avascular Necrosis (AVN)?
AVN results from the interruption of blood flow to bone tissue, leading to bone death, structural collapse, and joint dysfunction. Commonly affected sites include the femoral head, scaphoid, and talus. Patients often report pain, weakness, and limited joint mobility. Diagnosis is confirmed through MRI or bone scans, and treatment options include core decompression or surgical removal of dead bone tissue.
How Are Delayed Healing Fractures Classified?
| Term | Definition | Clinical Implications |
|---|---|---|
| Delayed Union | Prolonged bone healing time | Persistent pain and reduced function |
| Malunion | Healing in an improper alignment | Bone deformity and impaired function |
| Nonunion | Failure of bone ends to unite | Requires surgical repair |
What Are the Consequences of Prolonged Immobility?
Extended immobilization can affect multiple body systems, causing:
| System | Possible Complications |
|---|---|
| Skin | Pressure ulcers, infections |
| Gastrointestinal | Constipation due to slowed motility |
| Muscular | Atrophy and weakness |
| Skeletal | Osteoporosis, decreased bone density |
| Cardiovascular | Venous stasis, thrombosis |
| Urinary | Urinary stasis, kidney stones |
| Respiratory | Pneumonia, atelectasis |
| Psychological | Depression, social isolation |
SECTION 3: The Nervous System (Overview)
What Are the Types of Stroke and Their Characteristics?
Strokes are classified by the underlying cause of cerebral ischemia:
| Type | Pathophysiology | Clinical Note |
|---|---|---|
| Ischemic Stroke | Artery blocked by thrombus or embolus | Most common (~85% of strokes) |
| Thrombotic Stroke | Local clot from atherosclerosis | Develops gradually |
| Embolic Stroke | Clot from heart or artery travels to brain | Sudden onset |
| Hemorrhagic Stroke | Arterial rupture causing bleeding inside brain | High mortality (~15%) |
The ischemic penumbra is the surrounding salvageable brain tissue; prompt reperfusion is vital to limit damage (Grossman & Porth, 2021).
What are Neuropathies and Related Disorders?
Peripheral Neuropathy involves damage to peripheral nerves causing sensory loss, weakness, and pain.
| Type | Mechanism | Examples/Causes |
|---|---|---|
| Demyelinating | Myelin sheath destruction | Guillain-Barré Syndrome |
| Axonal Degeneration | Axon damage | Diabetes mellitus, toxins |
Common causes include diabetes, chronic alcohol use, and neurotoxic medications.
Myasthenia Gravis is an autoimmune disease targeting acetylcholine receptors at the neuromuscular junction, resulting in fluctuating muscle weakness. Symptoms include eyelid drooping (ptosis), double vision (diplopia), and worsening weakness with activity.
Meniere’s Disease is an inner ear disorder caused by fluid imbalance, producing vertigo, tinnitus, and progressive hearing loss.
How to Differentiate Cerebrovascular and Neurological Conditions?
| Condition | Definition | Key Differentiator |
|---|---|---|
| Aneurysm | Dilation of a cerebral artery | Risk of rupture causing hemorrhage |
| Hemorrhage | Active bleeding in brain tissue | Often due to hypertension |
| Hematoma | Localized blood collection | Can cause compression symptoms |
| Epidural Hematoma | Bleeding between skull and dura mater | Linked to temporal bone fracture and arterial rupture |
SECTION 4: Cardiovascular and Hematologic Disorders
What is the Role of the Cardiovascular System?
The cardiovascular system is a closed circuit transporting oxygen, nutrients, hormones, and waste. It depends on coordinated cardiac electrical activity, vascular integrity, and adequate blood volume. Dysfunction in any component can cause diseases such as hypertension, atherosclerosis, or heart failure (Huether & McCance, 2020).
How is Hypertension Classified and What Are Its Risk Factors?
Hypertension is a chronic condition marked by persistently high blood pressure, often asymptomatic but with severe long-term effects.
| Classification | Systolic (mmHg) | Diastolic (mmHg) |
|---|---|---|
| Normal | <120 | <80 |
| Elevated | 120–129 | <80 |
| Stage 1 HTN | 130–139 | 80–89 |
| Stage 2 HTN | ≥140 | ≥90 |
| Hypertensive Crisis | ≥180 | ≥120 |
Risk factors include genetics, obesity, excessive salt/alcohol intake, chronic stress, diabetes, and hyperlipidemia.
What Are the Pathophysiology and Complications of Hypertension?
Persistent hypertension damages the endothelium, increases arterial stiffness, and raises peripheral resistance. These changes may cause left ventricular hypertrophy (LVH) and increase the risk of stroke, myocardial infarction, kidney disease, and hypertensive retinopathy.
What Is Atherosclerosis and Its Risk Factors?
Atherosclerosis involves lipid plaque buildup inside arteries, narrowing vessels and impairing blood flow. Plaque rupture can cause thrombosis or embolism.
| Pathogenesis Steps |
|---|
| Endothelial injury (due to hypertension, smoking, diabetes) → LDL infiltration → inflammation and foam cell formation → fibrous cap and calcification → plaque rupture → thrombus |
Risk factors: dyslipidemia, hypertension, diabetes, smoking, obesity, and sedentary lifestyle.
| Plaque Type | Characteristics | Clinical Presentation |
|---|---|---|
| Stable Plaque | Thick fibrous cap, gradual narrowing | Predictable angina |
| Unstable Plaque | Thin cap, prone to rupture | Myocardial infarction, stroke |
What is Coronary Artery Disease (CAD) and How Does Angina Present?
CAD is caused by atherosclerotic narrowing of coronary arteries, reducing oxygen supply to the heart.
| Type of Angina | Description | Trigger | Relief |
|---|---|---|---|
| Stable Angina | Predictable chest pain with exertion | Physical/emotional stress | Rest or nitroglycerin |
| Unstable Angina | Chest pain at rest or minimal exertion | Plaque rupture, thrombosis | Emergency treatment required |
| Prinzmetal (Variant) | Vasospasm of coronary arteries | Cold, stress, drugs | Calcium channel blockers |
What Are the Clinical Features and Management of Myocardial Infarction (MI)?
MI results from complete blockage of coronary blood flow causing heart muscle death.
Clinical Features:
- Severe chest pain (may radiate to jaw, shoulder, arm)
- Diaphoresis, shortness of breath, nausea, anxiety
- ECG changes (ST elevation/depression, Q waves)
- Elevated cardiac enzymes (troponin, CK-MB)
Complications:
- Heart failure, arrhythmias, cardiogenic shock, pericarditis
Treatment:
- MONA (Morphine, Oxygen, Nitrates, Aspirin)
- Reperfusion therapy (thrombolytics, PCI)
- Long-term medications (beta-blockers, ACE inhibitors, statins)
What Are the Types of Heart Failure and Their Symptoms?
| Type | Pathophysiology | Key Symptoms |
|---|---|---|
| Left-Sided HF | LV fails to eject blood → pulmonary congestion | Dyspnea, orthopnea, crackles, cough |
| Right-Sided HF | RV failure due to pulmonary hypertension or LV failure | Peripheral edema, ascites, hepatomegaly |
| Systolic HF | Decreased ejection fraction (<40%) | Fatigue, poor contractility |
| Diastolic HF | Impaired ventricular relaxation | Preserved EF, pulmonary congestion |
What Are Peripheral Arterial Disease (PAD) and Its Management?
PAD is arterial narrowing in limbs, mainly from atherosclerosis, causing impaired blood flow.
Clinical Manifestations:
- Intermittent claudication (leg pain on exertion, relieved by rest)
- Pallor, cold limbs, weak pulses
- Ulcers or gangrene in advanced stages
| Diagnostic Tests | Purpose |
|---|---|
| Ankle-Brachial Index (ABI) | <0.9 indicates PAD |
| Doppler Ultrasound | Detects blood flow obstruction |
| Angiography | Visualizes arterial blockages |
Management:
- Smoking cessation, exercise therapy
- Antiplatelet drugs (aspirin, clopidogrel)
- Statins for cholesterol control
- Surgical options (angioplasty, bypass)
What is Deep Vein Thrombosis (DVT), Its Causes, Signs, and Management?
DVT is clot formation in deep veins, often in legs.
Virchow’s Triad of Causes:
- Venous stasis (immobility, long travel)
- Endothelial injury (trauma, surgery)
- Hypercoagulability (cancer, pregnancy)
Signs:
- Swelling, pain, redness, warmth over vein
- Tenderness and positive Homan’s sign (pain on foot dorsiflexion)
Complications: Pulmonary embolism (PE), chronic venous insufficiency
Management:
- Anticoagulants (heparin, warfarin, DOACs)
- Early mobilization
- Compression stockings
- Inferior vena cava filters (in recurrent PE)
What Are Common Hematologic Disorders?
Anemia: Reduced red blood cells or hemoglobin causes decreased oxygen transport.
| Type | Cause | Key Features |
|---|---|---|
| Iron-Deficiency | Blood loss, poor diet | Microcytic, hypochromic RBCs, fatigue |
| Megaloblastic | B12 or folate deficiency | Large RBCs, glossitis, neurologic signs |
| Hemolytic | Premature RBC destruction | Jaundice, splenomegaly |
| Aplastic | Bone marrow failure | Pancytopenia, infections, bleeding |
Treatment depends on cause: supplements, injections, transfusions.
Polycythemia: Excess RBCs cause thick blood and thrombosis risk.
| Type | Mechanism | Example |
|---|---|---|
| Primary | Myeloproliferative (JAK2 mutation) | Polycythemia vera |
| Secondary | Increased erythropoietin | Chronic hypoxia (COPD, high altitude) |
Symptoms: Ruddy complexion, headache, dizziness.
Treatment: Phlebotomy, myelosuppressive drugs.
Disseminated Intravascular Coagulation (DIC): Simultaneous excessive clotting and bleeding caused by sepsis, trauma, or malignancy.
Lab Findings:
- Low platelets and fibrinogen
- Elevated PT, aPTT, D-dimer
- Schistocytes in blood smear
Management: Treat cause, supportive care, blood product replacement.
Key Review Summary
- Differentiate types of strokes and their clinical presentations.
- Recognize musculoskeletal disorders such as DDD, Paget’s disease, and compartment syndrome.
- Understand cardiovascular disorders, including hypertension, atherosclerosis, CAD, and heart failure.
- Identify peripheral vascular diseases like PAD and DVT, and their management.
- Be familiar with common hematologic conditions and their diagnostic features.
References
Huether, S. E., & McCance, K. L. (2020). Understanding Pathophysiology (7th ed.). Elsevier.
Porter, R. S., Kaplan, J. L., & Homeier, B. P. (2021). The Merck Manual of Diagnosis and Therapy (20th ed.). Merck Research Laboratories.
D236 Notes on Homeostasis & Cellular Responses
Smeltzer, S. C., Bare, B. G., Hinkle, J. L., & Cheever, K. H. (2020). Brunner & Suddarth’s Textbook of Medical-Surgical Nursing (15th ed.). Wolters Kluwer.
Grossman, S., & Porth, C. M. (2021). Porth’s Pathophysiology: Concepts of Altered Health States (10th ed.). Wolters Kluwer.