A 45-year-old male reports several years of asbestos exposure while working in the construction industry. He reports smoking 2 packs of cigarettes per day for over 20 years. Smoking and asbestos exposure increase the incidence of which of the following diseases?

Malignant pulmonary mesothelioma

A 44-year-old man is brought to the emergency department after sustaining high-voltage electrical burns over his left upper limb. On examination, the tip of his left middle finger is charred, and there are 2nd-degree burns involving the whole of the left upper limb. Radial and ulnar pulses are strong, and there are no signs of compartment syndrome. An exit wound is present over the sole of his right foot. His temperature is 37.7°C (99.8°F), the blood pressure is 110/70 mm Hg, the pulse is 105/min, and the respiratory rate is 26/min. His urine is reddish-brown, and urine output is 0.3 mL/kg/h. Laboratory studies show: Hemoglobin 13.9 g/dL Hematocrit 33% Leukocyte count 11,111/mm3 Serum Creatinine 4.6 mg/dL Creatine phosphokinase 15,230 U/L K+ 7.7 mEq/L Na+ 143 mEq/L What is the most likely mechanism for this patient's renal failure?

Rhabdomyolysis, myoglobinuria, and renal injury

Septicemia leading to acute pyelonephritis

Direct visceral electrical injury to the kidneys

Fluid and electrolyte loss and hypovolemia

Volume overload because of excessive intravenous fluid resuscitation

A 65-year-old man presents to the emergency department for shortness of breath. He was at home working on his car when he suddenly felt very short of breath, which failed to improve with rest. He states he was working with various chemicals and inhalants while trying to replace a broken piece in the engine. The patient was brought in by paramedics and is currently on 100% O2 via nasal cannula. The patient has a 52 pack-year smoking history and drinks 2 to 3 alcoholic drinks every night. He has a past medical history of asthma but admits to not having seen a physician since high school. His temperature is 98.2°F (36.8°C), blood pressure is 157/108 mmHg, pulse is 120/min, respirations are 29/min, and oxygen saturation is 77%. Physical exam demonstrates tachycardia with a systolic murmur heard best along the right upper sternal border. Breath sounds are diminished over the right upper lobe. Bilateral lower extremity pitting edema is noted. Which of the following best describes the most likely diagnosis?

Rupture of an emphysematous bleb

Fe3+ hemoglobin in circulating red blood cells

Pulmonary edema secondary to decreased cardiac output

A 46-year-old man comes to the physician because of a 6-week history of fatigue and cramping abdominal pain. He works at a gun range. Examination shows pale conjunctivae and gingival hyperpigmentation. There is weakness when extending the left wrist against resistance. Further evaluation of this patient is most likely to show which of the following?

Basophilic stippling of erythrocytes

Beta‑2 microglobulin in urine

Septal thickening on chest x-ray

Increased total iron binding capacity

A 33-year-old pilot is transported to the emergency department after she was involved in a cargo plane crash during a military training exercise in South Korea. She is conscious but confused. She has no history of serious illness and takes no medications. Physical examination shows numerous lacerations and ecchymoses over the face, trunk, and upper extremities. The lower extremities are cool to the touch. There is continued bleeding despite the application of firm pressure to the sites of injury. The first physiologic response to develop in this patient was most likely which of the following?

Increased capillary refill time

Decreased systolic blood pressure

A 7-month old boy, born to immigrant parents from Greece, presents to the hospital with pallor and abdominal distention. His parents note that they recently moved into an old apartment building and have been concerned about their son's exposure to chipped paint from the walls. On physical exam, the patient is found to have hepatosplenomegaly and frontal skull bossing. Hemoglobin electrophoresis reveals markedly increased HbF and HbA2 levels. What would be the most likely findings on a peripheral blood smear?

Microcytosis and hypochromasia of erythrocytes

Basophilic stippling of erythrocytes

Macrocytosis of erythrocytes with hypersegmented neutrophils

Schistocytes and normocytic erythrocytes

A 61-year-old man presents with gradually increasing shortness of breath. For the last 2 years, he has had a productive cough on most days. Past medical history is significant for hypertension and a recent admission to the hospital for pneumonia. He uses a triamcinolone inhaler and uses an albuterol inhaler as a rescue inhaler. He also takes lisinopril and a multivitamin daily. He has smoked a pack a day for the last 32 years and has no intention to quit now. Today, his blood pressure is 142/97 mm Hg, heart rate is 97/min, respiratory rate is 22/min, and temperature is 37.4°C (99.3°F). On physical exam, he has tachypnea and has some difficulty finishing his sentences. His heart has a regular rate and rhythm. Auscultation of his lungs reveals wheezing and rhonchi that improves after a deep cough. Fremitus is absent. Pulmonary function tests show FEV1/FVC of 55% with no change in FEV1 after albuterol treatment. Which of the following is the most likely pathology associated with this patient's disease?

Inflamed bronchus with hypertrophy and hyperplasia of mucous glands

Chronic granulomatous inflammation with bilateral hilar lymphadenopathy

Consolidation and red hepatization

Environmental pathology for USMLE Step 2 CK: High-Yield Pathology Lessons

Air Pollution - Breath of Fresh Toxin

Key Pollutants: Ground-level ozone ($O_3$), sulfur dioxide ($SO_2$), nitrogen dioxide ($NO_2$), carbon monoxide (CO), lead (Pb), and particulate matter (PM).
Particulate Matter (PM) Size Effects:
- PM >10 µm: Filtered by the upper airway (nose/pharynx).
- PM <2.5 µm (PM2.5): Reaches alveoli, enters circulation, and triggers systemic inflammation.
Mechanisms of Injury:
- CO: Binds hemoglobin with >200x affinity than $O_2$ → carboxyhemoglobin → systemic hypoxia.
- $O_3$, $SO_2$, $NO_2$: Generate free radicals → damage respiratory epithelium.

⭐ Ultrafine particles (PM2.5) are potent cardiovascular risks. They can translocate into the bloodstream, promoting endothelial dysfunction, atherosclerosis, and thrombosis.

Air pollution particle deposition in the respiratory tract

Heavy Metal Mayhem - Toxic Rock Stars

Lead (Pb)
- Sources: Old paint, batteries, contaminated water.
- Patho: Inhibits ferrochelatase & ALA dehydratase → microcytic anemia with basophilic stippling.
- Clinical: Burton's lines (gums), encephalopathy, abdominal colic, wrist/foot drop.
Mercury (Hg)
- Sources: Contaminated fish (tuna), dental amalgams.
- Clinical: Neuropsychiatric symptoms ("mad as a hatter"), tremors, gingivostomatitis.
Arsenic (As)
- Sources: Contaminated water (wells), pesticides, wood preservatives.
- Clinical: Acute (garlic breath, rice-water stool); Chronic (hyperkeratosis, neuropathy, cancers).
Cadmium (Cd)
- Sources: Cigarettes, batteries.
- Clinical: Obstructive lung disease, kidney damage → Itai-itai disease.

Basophilic stippling in lead poisoning

⭐ Arsenic exposure is strongly associated with squamous cell carcinoma of the skin, lung cancer, and angiosarcoma of the liver.

Chemical & Tobacco Injury - Everyday Exposures

Heavy Metals: Interfere with enzymatic functions by binding to sulfhydryl groups.

Toxin	Common Sources	Key Presentation
Lead	Old paint, batteries	Anemia, wrist/foot drop, lead lines (gums, bones)
Mercury	Fish, dental amalgams	CNS damage, renal toxicity (Minamata disease)
Arsenic	Pesticides, contaminated water	Skin hyperkeratosis, stocking-glove neuropathy
Cadmium	Batteries, contaminated soil	Obstructive lung disease, renal toxicity

-   **Carcinogens:** Polycyclic aromatic hydrocarbons, nitrosamines.
-   **Systemic Effects:** ↑ platelet aggregation, ↓ oxygen transport (CO), direct endothelial injury.

⭐ High-Yield: Tobacco smoke carcinogens (e.g., polycyclic aromatic hydrocarbons) are metabolized by CYP450 enzymes, leading to DNA adducts that are fundamental to carcinogenesis.

Heavy Metals Sources Diagram

Physical Agents - When Physics Hurts

Mechanical Trauma: Abrasion (scrape), contusion (bruise), laceration (tear), incision (cut), puncture.
Thermal Injury:
- Burns: Depth determines severity. Complications: hypovolemic shock, sepsis (📌 Pseudomonas aeruginosa), hypermetabolism.
- Hyperthermia: Heat cramps → exhaustion → stroke (core temp >40°C).
- Hypothermia: Vasoconstriction, ice crystal formation.
Electrical Injury: Severity depends on amperage and path. AC is more dangerous than DC (tetany). Causes burns, v-fib, respiratory arrest.
Radiation Injury: Ionizing radiation damages DNA (direct or free radicals). Affects rapidly dividing cells (GI, bone marrow).

Burn depth by skin layer: 1st, 2nd, 3rd, and 4th degree

⭐ Electrical burns can cause rhabdomyolysis, leading to myoglobinuria and acute kidney injury.

High‑Yield Points - ⚡ Biggest Takeaways

Air pollution, especially PM₂.₅, exacerbates cardiopulmonary diseases; ozone causes free radical lung injury.

Lead poisoning impairs heme synthesis, causing microcytic anemia and neurotoxicity (wrist/foot drop).

Arsenic and mercury are potent neurotoxins; arsenic is also linked to skin and lung cancers.

Asbestos is the only known cause of mesothelioma and leads to pleural plaques and fibrosis.

Ionizing radiation causes DNA damage, with hematopoietic tissue and GI mucosa being highly sensitive.

Cigarette smoke is the leading cause of preventable death, strongly linked to lung cancer and COPD.

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