D236 Pathophysiology Final Exam Study Guide

Clinical Case Review and Physiological Interpretations

Acid–Base Imbalance and Respiratory Compensation

Question:
A patient with a viral infection and severe vomiting exhibits an elevated blood CO₂ level, a blood pH of 7.53, and a decreased respiratory rate. What is the most probable diagnosis?

• Respiratory acidosis

• Respiratory alkalosis

• Metabolic acidosis

• Metabolic alkalosis

Answer:
The patient is most likely experiencing metabolic alkalosis.

Explanation:
The blood pH of 7.53 indicates alkalosis. The elevated CO₂ level, in this context, suggests that the respiratory system is compensating rather than causing the imbalance. Vomiting leads to loss of hydrogen ions and chloride, which raises blood pH, resulting in metabolic alkalosis. To compensate, the body slows respiration (hypoventilation), retaining CO₂. This retained CO₂ reacts with water to form carbonic acid, which helps reduce alkalinity and bring pH closer to normal.

Table 1
Summary of Acid–Base Imbalance and Respiratory Compensation

Fluid Balance and Hormonal Response in Dehydration

Question:
What hormonal changes occur in antidiuretic hormone (ADH) levels and the renin-angiotensin-aldosterone system (RAAS) during dehydration?

Answer:
Both ADH secretion and RAAS activation increase in response to dehydration.

Explanation:
When dehydration raises plasma osmolality, hypothalamic osmoreceptors detect this change and stimulate ADH release from the posterior pituitary. ADH enhances water reabsorption in the kidneys, conserving fluid. Simultaneously, decreased renal perfusion activates RAAS, promoting sodium and water retention and vasoconstriction, which collectively help restore blood volume and pressure.

Mechanism of ACE Inhibitors

Question:
How do angiotensin-converting enzyme (ACE) inhibitors reduce blood pressure?

Answer:
ACE inhibitors block the conversion of angiotensin I to angiotensin II, a potent vasoconstrictor. This inhibition results in vasodilation, decreased aldosterone secretion, reduced sodium and water retention, and ultimately lower blood pressure.

Table 2
Effect of ACE Inhibition on Blood Pressure Regulation

Anion Gap in Diabetic Ketoacidosis (DKA)

Question:
What change occurs in the anion gap during diabetic ketoacidosis?

Answer:
The anion gap increases in DKA due to bicarbonate consumption while buffering ketone acids.

Explanation:
During DKA, ketone bodies accumulate and consume bicarbonate ions to maintain pH balance. This lowers bicarbonate levels and raises the anion gap, which is calculated as the difference between measured cations and anions in the blood.

Table 3
Anion Gap Calculation and Changes in DKA

Potassium Regulation in Dialysis

Question:
For patients with end-stage renal disease, what should be the potassium concentration in the dialysate during dialysis?

Answer:
The dialysate potassium concentration should be lower than the patient’s blood potassium level.

Explanation:
Dialysis relies on diffusion to remove excess potassium from the bloodstream. Using a dialysate with lower potassium creates a concentration gradient, encouraging potassium to move from blood into the dialysate. This helps prevent dangerous hyperkalemia and related cardiac complications.

Genetic Probability in Hemophilia

Question:
If a woman is a carrier of hemophilia, what is the probability her male child will inherit the disorder?

Answer:
There is a 50% chance that her son will inherit hemophilia.

Explanation:
Hemophilia is an X-linked recessive disorder. Since males inherit their single X chromosome from their mother, a carrier mother has a 50% chance of passing the affected gene to her son, who will then manifest the disease.

Sickle Cell Disease and Gene Therapy

Question:
What causes sickle cell anemia, and how might gene therapy offer a treatment?

Answer:
Sickle cell anemia is caused by a mutation in the β-globin gene, resulting in abnormal hemoglobin S (HbS) formation. Gene therapy approaches focus on reactivating fetal hemoglobin (HbF) production, which does not sickle, improving oxygen transport and alleviating symptoms.

Effects of Alcohol on Fetal Brain Development

Question:
How does prenatal alcohol exposure affect fetal brain development?

Answer:
Prenatal alcohol exposure reduces brain volume, especially affecting the corpus callosum, cerebellum, and frontal lobes. These changes result in cognitive deficits and behavioral abnormalities characteristic of fetal alcohol spectrum disorders (FASD).

Down Syndrome Etiology

Question:
What genetic abnormality causes Down syndrome?

Answer:
Down syndrome is caused by trisomy 21—having an extra copy of chromosome 21—which leads to characteristic physical features and developmental delays.

Blood Loss and Hormonal Response

Question:
What hormonal response occurs following significant blood loss?

Answer:
ADH secretion increases, promoting renal water reabsorption to restore blood volume and maintain blood pressure.

Respiratory Rate and pH Balance During Exercise

Question:
How does increased respiration during exercise help maintain acid-base balance?

Answer:
Faster breathing eliminates excess CO₂ produced by heightened metabolism. This reduces carbonic acid formation and helps prevent acidosis, stabilizing blood pH.

Arterial Blood Gas Imbalance in ICU Patient

Question:
An ICU patient presents with low pH, low CO₂, and rapid breathing. What is the likely diagnosis?

• Metabolic acidosis

• Metabolic alkalosis

• Respiratory alkalosis

• Respiratory acidosis

Answer:
The patient has metabolic acidosis.

Explanation:
The primary disturbance is metabolic acidosis (low pH). The low CO₂ and increased respiratory rate indicate respiratory compensation via hyperventilation to lower CO₂ and raise pH.

Dialysis and Home-Based Kidney Management

Question:
Which dialysis method allows patients to manage treatment at home?

Answer:
Peritoneal dialysis (PD).

Explanation:
PD uses the peritoneal membrane as a natural filter, facilitating waste removal and electrolyte balance, which patients can perform at home, offering more independence than hemodialysis.

Table 4
Comparison of Dialysis Modalities

Compensation for Pulmonary Edema

Question:
How does the body compensate for increased CO₂ levels caused by pulmonary edema?

Answer:
The kidneys compensate by excreting hydrogen ions and conserving bicarbonate, which helps buffer the blood and correct respiratory acidosis.

Inflammatory Response Mechanisms

Question:
A patient stung by a bee exhibits redness and swelling. Which physiological response is least likely?

• Vasodilation

• Increased capillary permeability

• Vasoconstriction causing fluid buildup

Answer:
Vasoconstriction is unlikely since inflammation typically involves vasodilation.

Explanation:
Histamine release during inflammation causes vasodilation and increased capillary permeability, allowing immune cells and plasma proteins to reach affected tissues, resulting in redness and swelling.

Function of Helper T Cells

Question:
What is the role of helper T cells in the immune response?

Answer:
Helper T cells secrete cytokines that activate B cells to produce antibodies and stimulate cytotoxic T cells to kill infected or malignant cells, coordinating the adaptive immune response.

Genetic Basis of Red–Green Color Blindness

Question:
What genetic disorder causes red–green color blindness?

Answer:
It is an X-linked recessive disorder predominantly affecting males.

Neurobehavioral Congenital Abnormality (ND-PAE)

Question:
What causes neurobehavioral disorder associated with prenatal alcohol exposure (ND-PAE)?

Answer:
Prenatal alcohol exposure leads to ND-PAE, causing cognitive impairments and difficulties with impulse control.

Neural Tube Defect: Spina Bifida

Question:
What developmental defect causes spina bifida?

Answer:
Incomplete closure of the neural tube during embryogenesis causes protrusion of meninges or spinal cord tissue, seen as a sac on the lower back.

Fracture with Bone Fragments

Question:
An X-ray shows multiple bone fragments after a hip injury. What type of fracture is this?

Answer:
This is a comminuted fracture, where the bone breaks into several pieces, often requiring surgical treatment.

Ankle Sprain Severity

Question:
Which ankle injury is characterized by swelling, bruising, and difficulty bearing weight?

Answer:
A Grade II sprain, indicating partial ligament tears with moderate functional impairment.

Glucocorticoids and Bone Health

Question:
Why do glucocorticoid-treated patients develop bone diseases such as rickets?

Answer:
Glucocorticoids impair vitamin D–mediated calcium absorption, leading to hypocalcemia and defective bone mineralization.

Cervical Degenerative Disc Disease

Question:
Which symptom is not associated with cervical degenerative disc disease?

Answer:
Low back pain is unrelated; cervical disease affects the neck and upper limbs.

Compartment Syndrome After Tibial Fracture

Question:
What serious complication can arise due to increased pressure in muscle compartments after a fracture?

Answer:
Compartment syndrome, which requires urgent decompression to prevent tissue necrosis.

Melanoma Identification

Question:
What diagnosis fits a dark, irregular, flat lesion over 6 mm in diameter?

Answer:
Melanoma, a potentially fatal form of skin cancer.

Burn Classification After Sun Exposure

Question:
What burn type causes redness and pain without blisters?

Answer:
A superficial (first-degree) burn.

Burn Surface Area Estimation

Question:
If burns cover the anterior face, neck, both arms, lower legs, and upper torso, what is the approximate total body surface area burned?

Answer:
Approximately 58.5%, according to the Rule of Nines.

Vitiligo and Skin Depigmentation

Question:
What causes smooth white patches of depigmented skin?

Answer:
Vitiligo, an autoimmune disorder causing destruction of melanocytes.

Fungal Infection of the Scalp

Question:
A child has a scaly, itchy scalp lesion fluorescing yellow-green under Wood’s light. What is the diagnosis?

Answer:
Tinea capitis, a fungal infection of the scalp.

Hemorrhagic Stroke Mechanism

Question:
What happens during a hemorrhagic stroke?

Answer:
A cerebral blood vessel ruptures, causing brain bleeding and ischemia.

Peripheral Neuropathy in Diabetes

Question:
What causes diabetic peripheral neuropathy?

Answer:
Microvascular damage to nerve blood vessels (vasa nervorum) due to chronic high blood glucose levels.

Iron-Deficiency Anemia

Question:
What characterizes iron-deficiency anemia?

Answer:
Microcytic, hypochromic red blood cells due to inadequate iron for hemoglobin synthesis.

Table 5
Common Anemia Types and Characteristics

Pernicious Anemia

Question:
Which vitamin deficiency causes pernicious anemia, and why?

Answer:
Vitamin B₁₂ deficiency due to autoimmune destruction of gastric parietal cells leading to lack of intrinsic factor.

Leukemia and Bone Marrow Function

Question:
How does leukemia affect blood cell production?

Answer:
Uncontrolled proliferation of immature white cells suppresses normal hematopoiesis, causing anemia and immunodeficiency.

Disseminated Intravascular Coagulation (DIC)

Question:
What is disseminated intravascular coagulation?

Answer:
A pathological state with widespread clotting that exhausts clotting factors, paradoxically leading to bleeding.

Hypertension Pathophysiology

Question:
What physiological change underpins primary hypertension?

Answer:
Increased systemic vascular resistance due to chronic vasoconstriction.

Atherosclerosis Development

Question:
What are the key stages in atherosclerosis formation?

Answer:
Endothelial injury → LDL cholesterol infiltration → foam cell formation → fibrous plaque development → plaque rupture and thrombosis.

Table 6
Stages of Atherosclerosis

Myocardial Infarction (MI)

Question:
What causes chest pain during myocardial infarction?

Answer:
Ischemia leads to anaerobic metabolism and lactic acid buildup, irritating nerve endings and causing pain.

Heart Failure

Question:
Why do patients with left-sided heart failure experience pulmonary symptoms?

Answer:
Blood backs up into the lungs, increasing hydrostatic pressure and causing pulmonary edema.

Right-Sided Heart Failure

Question:
What signs indicate right-sided heart failure?

Answer:
Peripheral edema, ascites, and jugular vein distension caused by systemic venous congestion.

Shock States

Question:
How does shock induce cellular injury?

Answer:
Reduced tissue perfusion causes hypoxia, leading to anaerobic metabolism and cellular energy failure.

Table 7
Types of Shock

Deep Vein Thrombosis (DVT)

Question:
What are the three predisposing factors for DVT?

Answer:
Venous stasis, endothelial injury, and hypercoagulability, collectively known as Virchow’s triad.

Pulmonary Embolism (PE)

Question:
What physiological effects result from a large pulmonary embolism?

Answer:
Impaired gas exchange and elevated pulmonary artery pressure, which may cause right heart failure.

Endocarditis

Question:
How does infective endocarditis develop?

Answer:
Bacteria colonize damaged heart valves forming vegetations, impairing valve function and causing embolic events.

Rheumatic Heart Disease

Question:
What causes valve damage in rheumatic fever?

Answer:
Autoimmune cross-reactivity between streptococcal antigens and cardiac tissue leads to inflammation and scarring.

Peripheral Arterial Disease (PAD)

Question:
Why does PAD cause intermittent claudication?

Answer:
Exercise-induced ischemia results in muscle pain due to insufficient oxygen delivery.

Varicose Veins

Question:
What causes varicose veins?

Answer:
Valve incompetence in veins leads to blood pooling and vein dilation.

Aneurysm Formation

Question:
What predisposes arteries to aneurysm formation?

Answer:
Degeneration of the tunica media weakens the vessel wall, promoting arterial dilation.

Hypertensive Crisis

Question:
Why is a hypertensive crisis dangerous?

Answer:
Sudden blood pressure spikes damage the endothelium, risking encephalopathy or renal failure.

Raynaud’s Phenomenon

Question:
What triggers Raynaud’s phenomenon?

Answer:
Cold or stress-induced vasospasm of small arteries reduces blood flow, causing skin color changes and numbness.

References

Guyton, A. C., & Hall, J. E. (2020). Textbook of Medical Physiology (14th ed.). Elsevier.

Ganong, W. F. (2019). Review of Medical Physiology (26th ed.). McGraw-Hill Education.

Kumar, V., Abbas, A. K., & Aster, J. C. (2021). Robbins Basic Pathology (10th ed.). Elsevier.

D236 Pathophysiology Final Exam Study Guide.