Ischemia-reperfusion injury US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Ischemia-reperfusion injury. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Ischemia-reperfusion injury US Medical PG Question 1: An 82-year-old woman is brought to the emergency department after losing consciousness at her nursing home. She had been watching TV for several hours and while getting up to use the bathroom, she fell and was unconscious for several seconds. She felt dizzy shortly before the fall. She does not have a headache or any other pain. She has a history of hypertension, intermittent atrial fibrillation, and stable angina pectoris. Current medications include warfarin, aspirin, hydrochlorothiazide, and a nitroglycerin spray as needed. Her temperature is 36.7°C (98.1°F), pulse is 100/min and regular, and blood pressure is 102/56 mm Hg. Physical exam shows a dry tongue. A fold of skin that is pinched on the back of her hand unfolds after 2 seconds. Cardiopulmonary examination shows no abnormalities. Further evaluation of this patient is most likely to show which of the following findings?
- A. Elevated serum concentration of cardiac enzymes
- B. Elevated serum creatine kinase concentration
- C. Absent P waves on ECG
- D. Elevated blood urea nitrogen concentration (Correct Answer)
- E. Hypodense lesions on CT scan of the head
Ischemia-reperfusion injury Explanation: ***Elevated blood urea nitrogen concentration***
- The patient presents with symptoms of **dehydration**, including a dry tongue, decreased skin turgor (skin fold taking 2 seconds to unfold), and **orthostatic hypotension** (dizziness upon standing, low blood pressure).
- Dehydration leads to **prerenal acute kidney injury**, characterized by an elevated blood urea nitrogen (BUN) concentration, often with an elevated BUN:creatinine ratio.
*Elevated serum concentration of cardiac enzymes*
- While the patient has a history of angina, there are no classic symptoms of an acute coronary syndrome such as **chest pain**, radiation, or ECG changes that would suggest myocardial injury warranting elevated cardiac enzymes.
- The syncope is more consistent with a **hemodynamic cause** (dehydration/hypotension) rather than a primary cardiac event like an MI.
*Elevated serum creatine kinase concentration*
- This is a non-specific marker for muscle damage and would be elevated if the patient experienced significant muscle injury from the fall.
- However, there is no mention of **trauma** or prolonged immobilization that would lead to rhabdomyolysis or significant muscle breakdown.
*Absent P waves on ECG*
- The patient has a history of **intermittent atrial fibrillation**, but her pulse is currently 100/min and **regular**, which indicates her current rhythm is likely not atrial fibrillation.
- Absence of P waves would specifically indicate **atrial fibrillation** or another atrial arrhythmia, but her regular pulse suggests a more sinus or junctional rhythm.
*Hypodense lesions on CT scan of the head*
- A CT scan of the head would be indicated to rule out **intracranial hemorrhage** or other structural brain lesions, especially given the fall and syncope.
- However, there are no focal neurological deficits, severe headache, or other signs strongly suggestive of a new stroke or hemorrhage, and the primary cause of syncope appears to be orthostatic hypotension due to hypovolemia.
Ischemia-reperfusion injury US Medical PG Question 2: A 23-year-old woman is brought to the emergency department 30 minutes after stepping on a piece of broken glass. Physical examination shows a 3-cm, ragged laceration on the plantar aspect of the left foot. The physician uses hydrogen peroxide to clean the wound. Which of the following is the most likely mechanism of action of this disinfectant?
- A. Formation of free radicals (Correct Answer)
- B. Intercalation of DNA
- C. Crosslinking of proteins
- D. Halogenation of nucleic acids
- E. Congealing of cytoplasm
Ischemia-reperfusion injury Explanation: ***Formation of free radicals***
- **Hydrogen peroxide** acts as an **oxidizing agent**, generating highly reactive **oxygen-free radicals** (e.g., superoxide, hydroxyl radicals) that damage microbial cellular components.
- This **oxidative damage** disrupts proteins, lipids, and nucleic acids, leading to bacterial and viral cell death.
*Intercalation of DNA*
- This mechanism is characteristic of certain **chemotherapeutic agents** (e.g., doxorubicin, ethidium bromide) and some **antimicrobials**, which insert themselves between DNA base pairs, disrupting replication and transcription.
- Hydrogen peroxide does not typically target DNA in this manner for its disinfectant action.
*Crosslinking of proteins*
- This mechanism is characteristic of **aldehydes** like **formaldehyde** and **glutaraldehyde**, which form covalent bonds between amino groups of proteins, denaturing them and disrupting cellular function.
- While hydrogen peroxide can modify proteins, its primary disinfectant action is not through widespread protein crosslinking.
*Halogenation of nucleic acids*
- This mechanism is primarily associated with **halogens** such as **chlorine** and **iodine**, which react with nucleic acids to form halogenated compounds, thereby inactivating them.
- Hydrogen peroxide, while an oxidizer, does not lead to halogenation as its primary mode of action.
*Congealing of cytoplasm*
- This mechanism, which refers to the coagulation or solidification of cellular contents, is typical of **alcohols** (e.g., ethanol, isopropanol) and some **heavy metal salts** that denature proteins and lipids, leading to cell lysis.
- Hydrogen peroxide's action is more specific to oxidative damage rather than general cytoplasmic congealing.
Ischemia-reperfusion injury US Medical PG Question 3: What is the primary mechanism for maintaining constant cerebral blood flow despite changes in systemic blood pressure?
- A. Endothelial factors
- B. Baroreceptor reflex
- C. Myogenic autoregulation (Correct Answer)
- D. Metabolic control
Ischemia-reperfusion injury Explanation: ***Myogenic autoregulation***
- **Myogenic autoregulation** is the intrinsic ability of vascular smooth muscle to contract when stretched by increased blood pressure, thereby maintaining a constant cerebral blood flow.
- This mechanism operates within a specific range of mean arterial pressures (typically **60-150 mmHg**) to prevent both hypoperfusion and hyperperfusion of the brain.
*Endothelial factors*
- Endothelial cells release various vasoactive substances like **nitric oxide** and **endothelin**, which influence vascular tone.
- While important for local blood flow regulation, these factors play a secondary role to myogenic autoregulation in maintaining constant cerebral blood flow against systemic pressure changes.
*Baroreceptor reflex*
- The **baroreceptor reflex** primarily controls systemic blood pressure by regulating heart rate and peripheral vascular resistance.
- It does not directly regulate cerebral blood flow stability in response to systemic pressure changes; its main role is to stabilize the overall systemic arterial pressure.
*Metabolic control*
- **Metabolic control** regulates cerebral blood flow in response to the brain's metabolic demands, primarily by sensing local concentrations of **CO2**, **pH**, and **oxygen**.
- While essential for matching blood supply to neuronal activity, it is not the primary mechanism for maintaining cerebral blood flow despite changes in systemic blood pressure.
Ischemia-reperfusion injury US Medical PG Question 4: During exercise, what is the primary mechanism for increased oxygen delivery to active muscles?
- A. Decreased blood viscosity
- B. Increased cardiac output (Correct Answer)
- C. Increased hemoglobin affinity
- D. Enhanced oxygen diffusion
Ischemia-reperfusion injury Explanation: ***Increased cardiac output***
- During exercise, **cardiac output** increases significantly due to both an elevated **heart rate** and increased **stroke volume**, directly pushing more oxygenated blood to the active muscles.
- This augmentation in blood flow is the primary factor ensuring a sufficient supply of oxygen and nutrients to meet the heightened metabolic demands of exercising muscles.
*Decreased blood viscosity*
- While factors like **hemodilution** can decrease blood viscosity during prolonged exercise, this effect is relatively minor and not the primary mechanism for acute increases in oxygen delivery compared to the dramatic increase in cardiac output.
- A decrease in blood viscosity can slightly improve flow efficiency, but it doesn't fundamentally change the amount of blood pumped per minute to the muscles.
*Increased hemoglobin affinity*
- An *increased* hemoglobin affinity for oxygen would actually make it *harder* for oxygen to unload from hemoglobin to the tissues, which is counterproductive for oxygen delivery during exercise.
- In fact, during exercise, local conditions like increased temperature, decreased pH (**Bohr effect**), and increased 2,3-BPG tend to *decrease* hemoglobin's affinity for oxygen, facilitating oxygen release to active muscles.
*Enhanced oxygen diffusion*
- While exercise does improve the efficiency of oxygen extraction at the tissue level due to a steeper partial pressure gradient and increased capillary recruitment, the *rate* of oxygen diffusion across the capillary membrane isn't the primary modulator of overall oxygen delivery.
- The main determinant is the *amount* of oxygenated blood reaching the muscle, which is governed by cardiac output and local blood flow regulation.
Ischemia-reperfusion injury US Medical PG Question 5: Six days after undergoing a left hemicolectomy for colorectal carcinoma, a 59-year-old man collapses in the hospital hallway and is unconscious for 30 seconds. Afterwards, he complains of shortness of breath and chest pain with deep inhalation. He has hypertension and hyperlipidemia. He smoked one pack of cigarettes daily for 35 years but quit prior to admission to the hospital. He does not drink alcohol. He is in distress and appears ill. His temperature is 36.5°C (97.7°F), blood pressure is 80/50 mm Hg, and pulse is 135/min and weak. Oxygen saturation is 88% on room air. Physical examination shows elevated jugular venous distention. Cardiac examination shows a regular, rapid heart rate and a holosystolic murmur that increases during inspiration. His abdomen is soft and mildly tender to palpation around the surgical site. Examination of his extremities shows pitting edema of the left leg. His skin is cold and clammy. Further examination is most likely to reveal which of the following findings?
- A. Reduced regional ventricular wall motion
- B. Rapid, aberrant contractions of the atria
- C. Stenosis of the carotid arteries
- D. Dilated right ventricular cavity (Correct Answer)
- E. Anechoic space between pericardium and epicardium
Ischemia-reperfusion injury Explanation: ***Dilated right ventricular cavity***
- The patient's symptoms (shortness of breath, chest pain with deep inspiration, hypotension, tachycardia, hypoxemia, elevated JVD, holosystolic murmur increasing with inspiration, and leg edema) are highly suggestive of **acute pulmonary embolism (PE)**.
- An acute PE can lead to increased pulmonary vascular resistance and **acute right ventricular (RV) overload**, causing RV dilation and dysfunction, which is often visible on echocardiography.
*Reduced regional ventricular wall motion*
- This finding is characteristic of **myocardial ischemia or infarction**, which typically presents with anginal chest pain and ECG changes; in this case, the chest pain is pleuritic and the overall picture points away from ischemia.
- While PE can cause RV dysfunction, the primary finding is RV overload and dilation, not necessarily isolated regional wall motion abnormalities often seen in left ventricular ischemia.
*Rapid, aberrant contractions of the atria*
- This describes **atrial fibrillation** or **atrial flutter**, which can occur in critically ill patients but is not the most direct consequence or expected finding from an acute pulmonary embolism in a previously stable patient.
- While atrial arrhythmias can be precipitated by acute stress, they are not the primary direct consequence of massive PE explaining these specific cardiovascular findings.
*Stenosis of the carotid arteries*
- **Carotid artery stenosis** is a risk factor for stroke but does not explain the acute cardiopulmonary collapse, hypoxemia, chest pain, and signs of right heart strain presented in the clinical scenario.
- This finding is unrelated to the acute presentation of shortness of breath, chest pain, and hemodynamic instability following surgery.
*Anechoic space between pericardium and epicardium*
- This finding represents a **pericardial effusion**, which can lead to cardiac tamponade if large and rapid in onset, but the associated holosystolic murmur increasing with inspiration and left leg edema are not typical for cardiac tamponade.
- While pericardial effusion can cause hypotension and shock, the specific constellation of symptoms, including pleuritic chest pain and signs of right heart strain, makes acute PE with RV dilation a more fitting diagnosis.
Ischemia-reperfusion injury US Medical PG Question 6: Which factor most strongly influences coronary blood flow during exercise?
- A. Endothelin release
- B. Metabolic demand (Correct Answer)
- C. Myogenic response
- D. Neural regulation
- E. Baroreceptor reflex
Ischemia-reperfusion injury Explanation: **Metabolic demand**
- During exercise, increased **myocardial activity** leads to a higher demand for oxygen and nutrients, prompting a significant increase in coronary blood flow.
- Local release of **metabolites** such as adenosine, nitric oxide, and hydrogen ions causes powerful vasodilation of coronary arteries, closely matching blood supply to demand.
*Endothelin release*
- **Endothelin** is a potent vasoconstrictor and plays a role in regulating vascular tone, but its primary influence is not the immediate or strongest factor dictating increased coronary flow during exercise.
- While it can modulate flow, metabolic changes are the dominant driver for the rapid and substantial increases needed during exertion.
*Myogenic response*
- The **myogenic response** is an intrinsic property of vascular smooth muscle cells to contract when stretched (due to increased pressure) and relax when pressure decreases, helping to maintain relatively constant blood flow.
- This mechanism primarily contributes to **autoregulation** and flow stability, but it does not account for the massive increase in flow required by the heart during exercise.
*Neural regulation*
- **Neural regulation**, primarily sympathetic stimulation, increases heart rate and contractility, which indirectly increases metabolic demand.
- However, direct neural effects on coronary arteries can be complex (both vasodilation and vasoconstriction depending on receptor type), and the overriding control during exercise is typically metabolic.
Ischemia-reperfusion injury US Medical PG Question 7: A 28-year-old male presents to his primary care physician with complaints of intermittent abdominal pain and alternating bouts of constipation and diarrhea. His medical chart is not significant for any past medical problems or prior surgeries. He is not prescribed any current medications. Which of the following questions would be the most useful next question in eliciting further history from this patient?
- A. "Does the diarrhea typically precede the constipation, or vice-versa?"
- B. "Is the diarrhea foul-smelling?"
- C. "Please rate your abdominal pain on a scale of 1-10, with 10 being the worst pain of your life"
- D. "Are the symptoms worse in the morning or at night?"
- E. "Can you tell me more about the symptoms you have been experiencing?" (Correct Answer)
Ischemia-reperfusion injury Explanation: ***Can you tell me more about the symptoms you have been experiencing?***
- This **open-ended question** encourages the patient to provide a **comprehensive narrative** of their symptoms, including details about onset, frequency, duration, alleviating/aggravating factors, and associated symptoms, which is crucial for diagnosis.
- In a patient presenting with vague, intermittent symptoms like alternating constipation and diarrhea, allowing them to elaborate freely can reveal important clues that might not be captured by more targeted questions.
*Does the diarrhea typically precede the constipation, or vice-versa?*
- While knowing the sequence of symptoms can be helpful in understanding the **pattern of bowel dysfunction**, it is a very specific question that might overlook other important aspects of the patient's experience.
- It prematurely narrows the focus without first obtaining a broad understanding of the patient's overall symptomatic picture.
*Is the diarrhea foul-smelling?*
- Foul-smelling diarrhea can indicate **malabsorption** or **bacterial overgrowth**, which are important to consider in some gastrointestinal conditions.
- However, this is a **specific symptom inquiry** that should follow a more general exploration of the patient's symptoms, as it may not be relevant if other crucial details are missed.
*Please rate your abdominal pain on a scale of 1-10, with 10 being the worst pain of your life*
- Quantifying pain intensity is useful for assessing the **severity of discomfort** and monitoring changes over time.
- However, for a patient with intermittent rather than acute, severe pain, understanding the **character, location, and triggers** of the pain is often more diagnostically valuable than just a numerical rating initially.
*Are the symptoms worse in the morning or at night?*
- Diurnal variation can be relevant in certain conditions, such as inflammatory bowel diseases where nocturnal symptoms might be more concerning, or functional disorders whose symptoms might be stress-related.
- This is another **specific question** that should come after gathering a more complete initial picture of the patient's symptoms to ensure no key information is overlooked.
Ischemia-reperfusion injury US Medical PG Question 8: An 84-year-old man is brought to the physician by the staff of a group home where he resides because of worsening confusion and decreased urinary output. His nurse reports that the patient has not been drinking much for the last 3 days. Examination shows a decreased skin turgor and dry oral mucosa. His pulse is 105/min and blood pressure is 100/65 mm Hg. His serum creatinine is 3.1 mg/dL and a urea nitrogen is 42 mg/dL. Urine studies show multiple brownish granular casts. Which of the following processes is most likely involved in the pathogenesis of this patient's condition?
- A. Immune complex deposition in mesangium
- B. Leukocytic infiltration of renal interstitium
- C. Necrosis of renal papillae
- D. Necrosis of tubular epithelial cells (Correct Answer)
- E. Disruption of glomerular podocytes
Ischemia-reperfusion injury Explanation: ***Necrosis of tubular epithelial cells***
- The patient presents with classic signs of **acute kidney injury (AKI)**, including confusion, decreased urinary output, decreased skin turgor, dry oral mucosa, tachycardia, hypotension, elevated creatinine (3.1 mg/dL), and urea nitrogen (42 mg/dL).
- The presence of **brownish granular casts** in the urine is highly suggestive of **acute tubular necrosis (ATN)**, secondary to ischemia caused by severe dehydration and hypoperfusion.
*Immune complex deposition in mesangium*
- This typically points to a **glomerular pathology**, such as IgA nephropathy or post-infectious glomerulonephritis.
- These conditions would usually present with **hematuria** and **proteinuria**, not necessarily brownish granular casts or the acute dehydration found here.
*Leukocytic infiltration of renal interstitium*
- This finding is characteristic of **acute interstitial nephritis**, which is often caused by drug hypersensitivity or infection.
- The clinical presentation with dehydration and granular casts is not typical for acute interstitial nephritis.
*Necrosis of renal papillae*
- **Renal papillary necrosis** is often associated with analgesic abuse, sickle cell disease, diabetes, or obstruction.
- While it can cause AKI, it typically presents with **flank pain** and **hematuria**, and the urine sediment would show ghost cells or fragments of necrotic papillae, not specifically brownish granular casts.
*Disruption of glomerular podocytes*
- **Podocyte disruption** is seen in primary glomerular diseases like minimal change disease or focal segmental glomerulosclerosis.
- These conditions primarily cause **nephrotic syndrome** (heavy proteinuria, edema), which is not the main presentation here.
Ischemia-reperfusion injury US Medical PG Question 9: An 87-year-old woman is admitted to the intensive care unit after a neighbor found her lying on the floor at her home. Her respirations are 13/min and shallow. Despite appropriate therapy, the patient dies. Gross examination of the brain at autopsy shows neovascularization and liquefactive necrosis without cavitation in the distribution of the left middle cerebral artery. Histological examination of a brain tissue sample from the left temporal lobe shows proliferation of neural cells that stain positive for glial fibrillary acidic protein. Based on these findings, approximately how much time has most likely passed since the initial injury in this patient?
- A. 2 days
- B. 2 hours
- C. 10 days (Correct Answer)
- D. 25 days
- E. 12 hours
Ischemia-reperfusion injury Explanation: ***10 days***
- **Neovascularization** and the absence of cavitation with **liquefactive necrosis** are indicative of a subacute phase of ischemic injury, typically seen around 1-3 weeks.
- The proliferation of **glial fibrillary acidic protein (GFAP)** positive neural cells (astrocytes) signifies **astrogliosis**, a repair response common after approximately one week, peaking around 2-3 weeks post-injury.
*2 days*
- At 2 days, the primary histological findings would be **neutrophilic infiltration** and initial stages of neuronal necrosis.
- **Neovascularization** and significant astrogliosis are generally not prominent until later in the recovery phase.
*2 hours*
- Within 2 hours, there would be minimal to no gross changes, and microscopic examination might show only **red neurons** (eosinophilic neurons with pyknotic nuclei) reflecting early irreversible neuronal damage.
- There would be no signs of inflammation, tissue breakdown, or repair processes like neovascularization or astrogliosis.
*25 days*
- By 25 days (approximately 3-4 weeks), **cavitation** with a **cystic astrocytic glial scar** would likely be prominent at the site of liquefactive necrosis, which is explicitly stated as absent in the question.
- While astrogliosis would still be present, the lack of cavitation points to an earlier stage of repair.
*12 hours*
- At 12 hours, gross changes are typically still absent or subtle, and microscopic findings would primarily involve **edema** and early signs of neuronal injury (e.g., changes in Nissl bodies, mild eosinophilia).
- Inflammatory cell infiltration and reparative processes like neovascularization or astrogliosis would not yet be significant.
Ischemia-reperfusion injury US Medical PG Question 10: A 72-year-old female is brought to the emergency department by ambulance because she was unable to walk. She says that she cut her leg while falling about a week ago. Since then, the wound has started draining fluid and become progressively more painful. She is found to have necrotizing fasciitis and is taken emergently to the operating room. Histological examination of cells along the fascial planes reveal cells undergoing necrosis. Which of the following represents the earliest sign that a cell has progressed to irreversible damage in this patient?
- A. Fragmentation of the nucleus
- B. Membrane blebbing from organelles
- C. Chromatin dissolution and disappearance
- D. Ribosomal detachment from the endoplasmic reticulum
- E. Condensation of DNA into a basophilic mass (Correct Answer)
Ischemia-reperfusion injury Explanation: ***Condensation of DNA into a basophilic mass***
- **Karyopyknosis**, or the **condensation of nuclear chromatin into a dense, shrunken mass**, is an early microscopic sign of irreversible cell injury leading to necrosis. It indicates the cell has committed to a death pathway.
- This nuclear change is characterized by the nucleus appearing as a **small, dense, and deeply basophilic structure** due to chromatin clumping.
*Fragmentation of the nucleus*
- **Karyorrhexis**, the fragmentation of the pyknotic nucleus, occurs *after* karyopyknosis, indicating a later stage of irreversible injury.
- This process involves the breakdown of the condensed nuclear fragments, leading to their subsequent disappearance.
*Membrane blebbing from organelles*
- **Membrane blebbing** can occur in both reversible and irreversible injury, but its presence on *organelles* specifically doesn't necessarily represent the *earliest* sign of irreversible damage compared to nuclear changes.
- While significant blebbing points towards severe damage, **nuclear changes** are often considered more definitive early markers of irreversible commitment.
*Chromatin dissolution and disappearance*
- **Karyolysis**, the dissolution and fading of the nucleus due to enzymatic degradation, represents a *later* stage of irreversible injury, occurring after karyopyknosis and karyorrhexis.
- In this stage, the nucleus eventually completely disappears, leaving only an anucleated ghost cell.
*Ribosomal detachment from the endoplasmic reticulum*
- **Ribosomal detachment** from the endoplasmic reticulum is an early sign of **reversible cell injury**, leading to decreased protein synthesis.
- It indicates initial cellular stress but not necessarily a commitment to irreversible damage or necrosis.
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