Weekly Pathology Exam - May 1, 2026 (Section A: MCQs)

Question 1

Which blood type is considered the universal donor for red blood cells?

Accepted Answer

Type O — Type O red blood cells lack A and B antigens, and Type O Rh-negative (O-) red blood cells also lack the Rh antigen, making them compatible with recipients of all blood types in emergencies when specific crossmatching is not feasible, particularly for red blood cells.

Question 2

Which blood type is considered the universal recipient for red blood cells?

Accepted Answer

Type AB — Individuals with Type AB blood have both A and B antigens on their red blood cells and therefore do not produce anti-A or anti-B antibodies. This allows them to receive red blood cells from Type A, Type B, Type AB, and Type O donors without an immediate ABO incompatibility reaction.

Question 3

What is the main function of plasma in blood transfusions?

Accepted Answer

To provide clotting factors and proteins — Plasma, particularly fresh frozen plasma (FFP), is transfused to replace clotting factors in patients with coagulopathies or significant bleeding, as well as to provide other essential plasma proteins.

Question 4

Which of the following is a contraindication for blood transfusion?

Accepted Answer

Fluid overload without signs of severe anemia — Fluid overload is a relative contraindication, especially if the patient is not severely anemic or actively bleeding, as a transfusion would exacerbate the condition. The other options represent common indications for transfusion.

Question 5

The term 'crossmatch' in blood transfusion refers to:

Accepted Answer

Mixing recipient's serum with donor's red blood cells to check for agglutination — Crossmatching involves mixing the recipient's serum with donor red blood cells to detect any antibodies in the recipient's plasma that would react with antigens on the donor red blood cells, ensuring compatibility beyond ABO/Rh typing and antibody screening.

Question 6

Which of the following is a possible complication of blood transfusion?

Accepted Answer

Hypocalcemia — Citrate, an anticoagulant used in blood products, can chelate calcium, potentially leading to hypocalcemia, especially with rapid or large volume transfusions.

Question 7

Which antigen is present on the surface of red blood cells in Type B blood?

Accepted Answer

B antigen — Type B blood is characterized by the presence of B antigens on the surface of red blood cells and anti-A antibodies in the plasma.

Question 8

What is the most important factor in determining blood compatibility between a donor and recipient?

Accepted Answer

ABO and Rh blood type matching — ABO and Rh blood group matching are critical to prevent immediate and severe hemolytic transfusion reactions caused by pre-existing antibodies in the recipient.

Question 9

Which of the following is the primary concern in transfusing Rh-negative blood to an Rh-positive patient?

Accepted Answer

It is generally safe and causes no significant issue. — Transfusing Rh-negative blood to an Rh-positive patient is generally safe because the Rh-positive recipient does not have anti-Rh antibodies and will not react to the absence of the Rh antigen. The primary concern is Rh-positive blood to an Rh-negative patient, which can cause alloimmunization.

Question 10

What is the role of the Rh factor in blood transfusion?

Accepted Answer

It is a major antigen that can cause hemolytic reactions if mismatched. — The Rh factor (D antigen) is a significant antigen after ABO, and mismatching (e.g., Rh-positive blood to an Rh-negative recipient who has been previously sensitized) can lead to severe hemolytic transfusion reactions.

Question 11

Which of the following components is typically transfused for patients with low platelet counts?

Accepted Answer

Platelets — Platelet transfusions are administered to patients with thrombocytopenia (low platelet counts) or dysfunctional platelets to prevent or treat bleeding.

Question 12

Which of the following should be monitored during a blood transfusion to detect possible complications?

Accepted Answer

Patient's temperature, heart rate, blood pressure, and respiratory rate — Vital signs (temperature, heart rate, blood pressure, respiratory rate) are crucial to monitor during a transfusion as sudden changes can indicate a transfusion reaction, such as fever, tachycardia, hypotension, or dyspnea.

Question 13

What is the normal pH range of human blood?

Accepted Answer

7.35-7.45 — The human body maintains a very narrow and tightly regulated blood pH range of 7.35 to 7.45 to ensure optimal enzyme function and metabolic processes.

Question 14

A patient with chronic obstructive pulmonary disease (COPD) has ABG results showing pH 7.28, PaCO2 58 mmHg, and HCO3- 26 mEq/L. What is the primary acid-base disorder?

Accepted Answer

Respiratory acidosis — The pH of 7.28 indicates acidosis. The elevated PaCO2 (normal 35-45 mmHg) indicates respiratory involvement. The HCO3- of 26 mEq/L (normal 22-26 mEq/L) is in the normal range, indicating that the primary problem is respiratory and there is some, but not full, metabolic compensation. This points to an acute or partially compensated respiratory acidosis.

Question 15

Which buffer system is the PRIMARY extracellular buffer system in the body?

Accepted Answer

Bicarbonate-carbonic acid buffer system — The bicarbonate-carbonic acid buffer system is the most important extracellular buffer, linking directly to the respiratory system (CO2 excretion) and renal system (HCO3- reabsorption/excretion).

Question 16

A diabetic patient presents with rapid, deep breathing (Kussmaul respirations). Which acid-base disorder is this compensatory mechanism addressing?

Accepted Answer

Metabolic acidosis — Kussmaul respirations are a compensatory mechanism (hyperventilation) to blow off CO2 and reduce carbonic acid, thereby increasing pH, in response to metabolic acidosis, commonly seen in diabetic ketoacidosis.

Question 17

What is the normal range for arterial PaCO2?

Accepted Answer

35-45 mmHg — The normal arterial partial pressure of carbon dioxide (PaCO2) is 35-45 mmHg, reflecting the efficiency of alveolar ventilation in removing CO2.

Question 18

A patient with severe vomiting develops metabolic alkalosis. Which mechanism explains this?

Accepted Answer

Loss of gastric acid (HCl) — Severe vomiting leads to the loss of hydrogen chloride (HCl) from the stomach. This loss of acid causes an increase in serum bicarbonate levels, resulting in metabolic alkalosis.

Question 19

What is the normal range for serum bicarbonate (HCO3-)?

Accepted Answer

22-26 mEq/L — The normal serum bicarbonate concentration is 22-26 mEq/L, playing a crucial role in the bicarbonate buffer system.

Question 20

Which enzyme in renal tubular cells catalyzes the reaction between CO2 and water to form carbonic acid?

Accepted Answer

Carbonic anhydrase — Carbonic anhydrase rapidly catalyzes the reversible reaction of carbon dioxide and water to form carbonic acid (H2CO3), which then dissociates into H+ and HCO3-. This is vital for acid-base balance in the kidneys.

Question 21

A patient has ABG results: pH 7.50, PaCO2 30 mmHg, HCO3- 23 mEq/L. What is the diagnosis?

Accepted Answer

Respiratory alkalosis — The pH of 7.50 indicates alkalosis. The low PaCO2 (normal 35-45 mmHg) indicates respiratory involvement, as blowing off CO2 reduces acidity. The HCO3- of 23 mEq/L (normal 22-26 mEq/L) is within the normal range, indicating that the primary problem is respiratory and there is no significant metabolic compensation, pointing to acute respiratory alkalosis.

Question 22

What is the formula for calculating anion gap?

Accepted Answer

Na+ - (Cl- + HCO3-) — The anion gap is calculated as [Na+] - ([Cl-] + [HCO3-]). It represents the concentration of unmeasured anions in the plasma, such as phosphates, sulfates, and organic acids.

Question 23

Which condition is characterized by an increased anion gap metabolic acidosis?

Accepted Answer

Diabetic ketoacidosis — Diabetic ketoacidosis (DKA) is a classic cause of increased anion gap metabolic acidosis due to the accumulation of ketone bodies (beta-hydroxybutyrate, acetoacetate), which are unmeasured anions.

Question 24

A patient at high altitude develops dizziness and tingling in the extremities. Which acid-base disorder is most likely?

Accepted Answer

Respiratory alkalosis — At high altitudes, the decreased partial pressure of oxygen (hypoxia) stimulates hyperventilation. This leads to excessive expulsion of CO2, causing a decrease in PaCO2 and an increase in pH, resulting in respiratory alkalosis. Dizziness and tingling (paresthesias) are common symptoms.

Question 25

A patient with von Hippel-Lindau (VHL) syndrome develops multiple tumors. Which molecular mechanism BEST explains the increased angiogenesis in these tumors?

Accepted Answer

Stabilization of HIF-1alpha leading to increased VEGF production — The VHL gene product normally functions as a ubiquitin ligase component, targeting hypoxia-inducible factor 1-alpha (HIF-1alpha) for degradation. In VHL syndrome, a mutated VHL gene leads to stabilized HIF-1alpha, even under normoxic conditions, which then upregulates pro-angiogenic factors like VEGF, promoting tumor angiogenesis.

Question 26

A tumor reaches 1.8 mm in diameter but fails to grow further for several years. Which statement BEST explains this phenomenon?

Accepted Answer

The tumor has outgrown its blood supply and failed to induce angiogenesis. — Tumors cannot grow beyond 1-2 mm in diameter without developing their own blood supply through angiogenesis. If angiogenesis fails, the tumor becomes dormant due to lack of oxygen and nutrients.

Question 27

During tumor angiogenesis, MMP-9 performs multiple functions. Which combination of activities is CORRECT?

Accepted Answer

Degrades basement membrane and activates VEGF. — Matrix metalloproteinase-9 (MMP-9) plays a crucial role in angiogenesis by degrading components of the extracellular matrix (like the basement membrane), which allows endothelial cells to migrate and form new vessels. It can also release matrix-bound growth factors, including certain forms of VEGF, making them bioavailable.

Question 28

A researcher studies newly formed tumor vessels and compares them to normal capillaries. Which characteristic would MOST likely be observed in tumor vasculature?

Accepted Answer

Leakiness and abnormal pericyte coverage — Tumor vasculature is typically disorganized, tortuous, and highly permeable (leaky) due to defective endothelial cell junctions and incomplete or absent pericyte coverage. This leads to inefficient and erratic blood flow.

Question 29

Normal p53 plays a role in preventing angiogenesis. Which mechanism explains this anti-angiogenic effect?

Accepted Answer

Upregulating inhibitors of angiogenesis, such as thrombospondin-1 (TSP-1), and inhibiting HIF-1alpha activity — Wild-type p53 can suppress angiogenesis by several mechanisms, including upregulating expression of anti-angiogenic factors like thrombospondin-1 (TSP-1) and inhibiting the activity or expression of pro-angiogenic factors like HIF-1alpha and VEGF.

Question 30

Three angiogenesis inhibitors—angiostatin, endostatin, and vasculostatin—share what common characteristic?

Accepted Answer

They are all fragments of extracellular matrix proteins. — Angiostatin is a fragment of plasminogen, endostatin is a fragment of collagen XVIII, and vasculostatin is a fragment of collagen IV. They are all endogenous inhibitors of angiogenesis derived from larger matrix proteins.

Question 31

Newly formed endothelial cells in tumor vessels contribute to tumor growth through which mechanism BEYOND providing nutrients?

Accepted Answer

Secreting growth factors that directly stimulate tumor cell proliferation — Beyond simply supplying oxygen and nutrients, tumor endothelial cells can actively secrete various growth factors (e.g., PDGF, FGF, IGF) and cytokines that directly stimulate the proliferation, survival, and migration of nearby tumor cells, thus creating a pro-tumorigenic microenvironment.

Question 32

A metastatic tumor cell must successfully complete multiple steps to establish a distant metastasis. At which stage do MOST tumor cells fail?

Accepted Answer

Colonization and growth at the secondary site — While many cells fail at various steps, the vast majority of circulating tumor cells fail to successfully colonize and grow into a macroscopic secondary tumor at a distant site. This step is highly inefficient and represents a major bottleneck in the metastatic cascade.

Question 33

Loss of E-cadherin function promotes metastasis through which TWO mechanisms?

Accepted Answer

Decreased cell-cell adhesion and increased cell motility. — E-cadherin is a critical cell-cell adhesion molecule. Loss of its function (e.g., through mutation or downregulation) leads to reduced cell-cell adhesion, allowing tumor cells to detach from the primary tumor, and increases their motility and invasiveness, key steps in metastasis.

Question 34

A breast cancer sample shows high expression of CXCR4 and CCR7 chemokine receptors. To which organs is this tumor MOST likely to metastasize?

Accepted Answer

Bone marrow and lymph nodes — CXCR4 and CCR7 are chemokine receptors that bind to specific ligands highly expressed in particular organs. CXCR4 ligands (like CXCL12) are abundant in bone marrow and lung, while CCR7 ligands (like CCL19/CCL21) are high in lymph nodes. This often guides tumor cells to these specific metastatic sites (the 'seed and soil' hypothesis).

Question 35

During ECM invasion, tumor cells must complete four sequential steps. Which is the FIRST step?

Accepted Answer

Attachment of tumor cells to ECM components. — The first step in ECM invasion is the detachment of tumor cells from each other (often via loss of E-cadherin) and their attachment to components of the extracellular matrix, such as laminin and fibronectin, which serves as a foothold for subsequent degradation and migration.

Weekly Pathology Exam - May 1, 2026 (Section A: MCQs)

Questions, Answers & Explanations