Weekly Pathology Exam - July 31, 2026 (Section A: MCQs)

Question 1

What neurotransmitter is primarily associated with the euphoric feeling experienced during a 'runner's high'?

Accepted Answer

Endorphins — Endorphins are endogenous opioid peptides that act as natural pain relievers and produce feelings of euphoria, classically linked to the 'runner's high'.

Question 2

Which neurotransmitter system is most implicated in the pathophysiology of anxiety disorders?

Accepted Answer

Gamma-aminobutyric acid (GABA) — GABA is the main inhibitory neurotransmitter in the CNS; reduced GABAergic activity and impaired GABA signaling are strongly linked to anxiety disorders, making it a target for anxiolytic medications.

Question 3

The effect of tetrodotoxin (puffer fish poison) on axons demonstrates:

Accepted Answer

That sodium channels are essential for action potential generation — Tetrodotoxin specifically blocks voltage-gated sodium channels, thereby preventing the depolarization phase of the action potential and nerve impulse conduction.

Question 4

Which neurotransmitter is most commonly associated with the regulation of mood, and its dysregulation is implicated in mood disorders like depression?

Accepted Answer

Serotonin — Serotonin is a monoamine neurotransmitter widely known for its role in mood regulation, and its dysregulation is a key component of the monoamine hypothesis of depression.

Question 5

Which neurotransmitter deficiency is strongly associated with Parkinson's disease?

Accepted Answer

Dopamine — Parkinson's disease is characterized by the progressive degeneration of dopaminergic neurons in the substantia nigra, leading to a profound deficiency of dopamine in the basal ganglia.

Question 6

A 28-year-old woman presents with fatigue and pallor. Complete blood count shows low haemoglobin level and peripheral blood film shows microcytic hypochromic red blood cells. What is the most likely diagnosis?

Accepted Answer

Iron deficiency anemia — Microcytic hypochromic red blood cells (small, pale red blood cells) are the classic morphological findings in iron deficiency anemia, which is also associated with fatigue and pallor.

Question 7

The primary site of haematopoiesis in adults is:

Accepted Answer

Bone marrow — In healthy adults, the red bone marrow is the primary site where all types of blood cells (erythrocytes, leukocytes, and platelets) are produced.

Question 8

Which blood cell type is primarily responsible for defence against parasitic infections?

Accepted Answer

Eosinophils — Eosinophils are granulocytes that play a crucial role in immune responses to parasitic infections, as well as in allergic reactions.

Question 9

Which clotting factor is deficient in Haemophilia A?

Accepted Answer

Factor VIII — Haemophilia A is an X-linked recessive bleeding disorder caused by a deficiency or defect in coagulation Factor VIII.

Question 10

A patient presents with recurrent infections, petechiae, and anaemia. A bone marrow biopsy shows reduced cellularity. What is the most likely diagnosis?

Accepted Answer

Aplastic anemia — The combination of pancytopenia (anemia, recurrent infections due to neutropenia, petechiae due to thrombocytopenia) with a hypocellular bone marrow is characteristic of aplastic anemia.

Question 11

Which chromosomal translocation is pathognomonic of chronic myeloid leukaemia?

Accepted Answer

t(9;22) — The t(9;22) translocation, known as the Philadelphia chromosome, creates the BCR-ABL fusion gene, which is the defining genetic abnormality in chronic myeloid leukaemia (CML).

Question 12

A 35-year-old man has no clinical evidence for bleeding and he feels fine. As part of a pre-operative workup for a hernia repair, laboratory studies show Hgb 14.8 g/dL, Hct 45%, MCV 96 fL, WBC count 8500/microliter, and platelet count 275,000/microliter. His prothrombin time is normal, but the partial thromboplastin time is prolonged. A deficiency of which of the following coagulation factors is most likely be associated with these findings?

Accepted Answer

Factor XII — An isolated prolonged PTT with a normal PT and no clinical bleeding history typically indicates a deficiency in a factor involved solely in the intrinsic pathway, such as Factor XII, prekallikrein, or high molecular weight kininogen. Factor XII deficiency is the most common of these and does not usually cause bleeding symptoms.

Question 13

A 20-year-old man is actively bleeding from multiple sites during surgery. He has a CBC that shows a WBC count of 4500/microliter, Hgb 7.6 g/dL, Hct 23.9%, MCV 98 fL, and platelet count 75,000/microliter. His prothrombin time is 30 seconds and partial thromboplastin time 63 seconds. What is the best blood product to use for him in this situation?

Accepted Answer

Packed Red Blood Cells (PRBCs) and Fresh Frozen Plasma (FFP) — The patient has anemia (low Hgb), thrombocytopenia (low platelets), and prolonged PT/PTT (coagulopathy). This indicates a need for both red blood cells to improve oxygen-carrying capacity (addressed by PRBCs) and coagulation factors to correct the bleeding diathesis (addressed by FFP, which contains all coagulation factors).

Question 14

A 31-year-old woman has oozing of blood from mucous membranes over the past 3 days. Laboratory studies show a platelet count of 10,000/microliter. She receives 6 units of platelets. An hour following this transfusion, her platelet count is 2,000/microliter. What is the most probable explanation for the change in pre- to post-transfusion platelet count?

Accepted Answer

Platelet refractoriness — Platelet refractoriness is the failure to achieve the expected rise in platelet count after transfusion. This can be caused by immune factors (e.g., alloantibodies to HLA or platelet-specific antigens) or non-immune factors (e.g., fever, sepsis, DIC, splenomegaly). Given the immediate and dramatic drop in count, a rapid destruction mechanism, often immune-mediated (part of platelet refractoriness), is highly probable.

Question 15

A 12-year-old boy has had multiple episodes of bleeding since infancy. It is characterized by hemarthroses and decreased joint mobility. His prothrombin time (PT) is normal, but the partial thromboplastin time (PTT) is elevated. When his plasma is mixed with normal plasma, the PTT is not elevated. His platelet count is normal. Which of the following is the most likely cause for his illness?

Accepted Answer

Hemophilia A — Hemarthroses (joint bleeding), normal PT, elevated PTT, normal platelet count, and correction of PTT upon mixing with normal plasma are classic findings of a congenital intrinsic pathway factor deficiency, most commonly Hemophilia A (Factor VIII deficiency) or Hemophilia B (Factor IX deficiency). Hemophilia A is the most common severe form.

Question 16

A 44-year-old man has had congestive heart failure for 2 years. His serum ferritin is markedly elevated. His CBC shows WBC count 6300/microliter, Hgb 7.8 g/dL, Hct 22.6%, MCV 69 fL, and platelet count 177,000/microliter. A hemoglobin electrophoresis reveals 2% Hgb A, 8% Hgb A2, and 90% Hgb F. Which of the following hematologic conditions is he most likely to have?

Accepted Answer

Beta thalassemia major — The patient's microcytic anemia (MCV 69 fL), elevated ferritin (indicating iron overload, common in transfused thalassemia patients), very high Hb F, and significantly reduced Hb A are diagnostic features of Beta Thalassemia Major (Cooley's anemia). Congestive heart failure can be a complication of iron overload.

Question 17

Which lipoprotein is responsible for transporting dietary triglycerides from the intestines to tissues?

Accepted Answer

Chylomicrons — Chylomicrons are large lipoproteins synthesized in the intestinal epithelial cells. Their primary function is to transport dietary fats (triglycerides and cholesterol) from the intestines to various tissues throughout the body.

Question 18

What is the primary function of HDL cholesterol?

Accepted Answer

Reverse cholesterol transport from peripheral tissues to the liver — HDL (High-Density Lipoprotein) is known for its role in reverse cholesterol transport, where it collects excess cholesterol from peripheral cells and tissues and transports it back to the liver for excretion or reprocessing.

Question 19

Which enzyme is responsible for breaking down triglycerides in adipose tissue during lipolysis?

Accepted Answer

Hormone-sensitive lipase — Hormone-sensitive lipase (HSL) is a key enzyme in adipose tissue that catalyzes the hydrolysis of stored triglycerides into free fatty acids and glycerol, a process known as lipolysis, especially in response to hormonal signals like glucagon and epinephrine.

Question 20

What happens to VLDL as it loses triglycerides?

Accepted Answer

It is converted into IDL and then LDL — VLDL (Very Low-Density Lipoprotein) is secreted by the liver. As it circulates, lipoprotein lipase hydrolyzes its triglycerides, leading to its transformation first into Intermediate-Density Lipoprotein (IDL) and then into Low-Density Lipoprotein (LDL).

Question 21

What is the genetic defect in familial hypercholesterolemia?

Accepted Answer

Defect in the LDL receptor gene — Familial hypercholesterolemia (FH) is primarily caused by mutations in the LDL receptor gene, leading to reduced or absent functional LDL receptors on cell surfaces. This impairs the clearance of LDL from the blood, resulting in very high LDL cholesterol levels.

Question 22

What is the chromosomal location of the RB gene?

Accepted Answer

13q14 — The retinoblastoma (RB) gene, a crucial tumor suppressor gene, is located on the long arm of chromosome 13 at band 14 (13q14).

Question 23

According to Knudson's two-hit hypothesis, how many mutations are required to develop retinoblastoma?

Accepted Answer

Two mutations — Knudson's two-hit hypothesis states that two 'hits' (mutations or deletions) in the RB gene are required for the development of retinoblastoma. In hereditary forms, the first hit is germline, and the second is somatic. In sporadic forms, both hits are somatic.

Question 24

In familial retinoblastoma, what is the origin of the first hit?

Accepted Answer

Germline mutation — In familial (hereditary) retinoblastoma, individuals inherit one defective copy (the 'first hit') of the RB gene from a parent in their germline cells. The second hit occurs somatically in a retinal cell, leading to tumor development.

Question 25

What is the critical cell cycle checkpoint controlled by the RB gene?

Accepted Answer

G1-S phase — The RB protein is a key regulator of the G1-S cell cycle checkpoint, preventing cells from entering the S (synthesis) phase unless conditions are appropriate for DNA replication.

Question 26

In its active tumor suppressor form, what is the phosphorylation state of RB protein?

Accepted Answer

Hypophosphorylated — Hypophosphorylated (or underphosphorylated) RB protein is the active tumor suppressor form. In this state, it binds to E2F transcription factors, blocking transcription of genes required for S-phase entry.

Question 27

What transcription factor does hypophosphorylated RB bind to?

Accepted Answer

E2F — Hypophosphorylated RB protein exerts its tumor suppressive function by binding to the E2F family of transcription factors, thereby inhibiting the transcription of genes necessary for cell cycle progression from G1 to S phase.

Question 28

Which syndrome is associated with germline mutation in one TP53 allele?

Accepted Answer

Li-Fraumeni syndrome — Li-Fraumeni syndrome (LFS) is an inherited cancer predisposition syndrome characterized by a germline mutation in one allele of the TP53 tumor suppressor gene, leading to a high lifetime risk of various cancers.

Question 29

A 45-year-old male smoker presents with chronic productive cough for 4 months every year for the past 3 years. What is the histologic hallmark in the large airways?

Accepted Answer

Mucous gland hypertrophy and hyperplasia — The clinical definition of chronic bronchitis is a productive cough for at least 3 months in 2 consecutive years. The histologic hallmark in large airways is hypertrophy and hyperplasia of submucosal mucous glands.

Question 30

A child presents with inspiratory stridor and harsh barking cough. The most common causative agent is:

Accepted Answer

Parainfluenza virus — The symptoms of inspiratory stridor and a harsh barking (croupy) cough are classic for Croup (laryngotracheobronchitis), which is most commonly caused by parainfluenza viruses.

Question 31

A 30-year-old presents with spontaneous pneumothorax. The most likely underlying emphysema type is:

Accepted Answer

Paraseptal emphysema — Spontaneous pneumothorax, especially in young adults without significant smoking history, is often associated with the rupture of subpleural blebs, which are characteristic of paraseptal (distal acinar) emphysema.

Question 32

Which cytokine is released within 30 minutes of acute lung injury and drives neutrophil chemotaxis?

Accepted Answer

Interleukin-8 (IL-8) — IL-8 is a potent chemokine that rapidly recruits neutrophils to sites of inflammation and injury, including the lungs during acute lung injury and ARDS. TNF-alpha and IL-1 also play early roles.

Question 33

The FEV1/FVC ratio is characteristically decreased in which condition?

Accepted Answer

Asthma — A decreased FEV1/FVC ratio is the hallmark of obstructive lung diseases, where airflow is limited. Asthma is a classic example of an obstructive lung disease due to bronchoconstriction and airway inflammation.

Question 34

A patient with α1-antitrypsin deficiency develops emphysema. Which type and distribution is expected?

Accepted Answer

Panacinar, lower lobe predominant — Alpha-1 antitrypsin (AAT) deficiency leads to reduced protection against elastase, resulting in premature and severe emphysema. This typically manifests as panacinar emphysema with a lower lobe predominance, contrasting with smoking-related centriacinar emphysema that often affects upper lobes.

Question 35

Which morphologic finding is the HALLMARK of ARDS on microscopy?

Accepted Answer

Intra-alveolar hyaline membranes — The histological hallmark of Acute Respiratory Distress Syndrome (ARDS) is diffuse alveolar damage (DAD), characterized by alveolar edema, inflammation, and the formation of hyaline membranes lining the alveolar walls.

Question 36

Streptococcal tonsillitis is important to recognize early because it can lead to all EXCEPT:

Accepted Answer

Acute bronchiolitis — Streptococcal tonsillitis (strep throat) can lead to complications such as acute rheumatic fever, post-streptococcal glomerulonephritis, and local suppurative complications like peritonsillar abscess. Acute bronchiolitis is typically a viral infection of the lower respiratory tract, most commonly caused by RSV, and is not a direct complication of streptococcal tonsillitis.

Weekly Pathology Exam - July 31, 2026 (Section A: MCQs)

Questions, Answers & Explanations