NEET-PG 2018 Practice Questions

Q: Trilene is degraded by:

Cytochrome P450 oxidation. ***Cytochrome P450 oxidation*** - **Trichloroethylene (Trilene)** was historically used as an inhalational anesthetic and industrial solvent - In humans, it undergoes **hepatic metabolism primarily through cytochrome P450 enzymes**, particularly **CYP2E1** - The oxidation pathway produces metabolites including **chloral hydrate, trichloroethanol, and trichloroacetic acid** - This is a classic example of **Phase I detoxification** involving oxidative biotransformation - The metabolites are then conjugated (Phase II) or excreted renally *Glutathione conjugation* - While some chlorinated compounds undergo glutathione conjugation as a Phase II reaction - For trichloroethylene, **oxidation by CYP450 is the primary metabolic pathway**, not direct glutathione conjugation - GSH conjugation may occur with some metabolites but is not the main degradation route *Direct renal excretion* - Trilene is **lipophilic** and requires hepatic metabolism before elimination - Direct renal excretion without biotransformation is **minimal** - Metabolites (after oxidation) are excreted via kidneys *Acetylation* - **Acetylation** is a Phase II conjugation reaction typically for compounds with **amino or sulfonamide groups** - Trichloroethylene lacks the appropriate functional groups for acetylation - This pathway is **not involved** in Trilene metabolism

Q: Which of the following is an example of an X-linked disorder?

Color blindness. ***Color blindness*** - **Color blindness**, particularly red-green color blindness, is a classic example of an **X-linked recessive disorder**. - It results from mutations in genes encoding **photopigments** located on the X chromosome, affecting more males than females. - Represents one of the most commonly cited examples of X-linked inheritance in medical education. *Thalassemia* - **Thalassemia** is an **autosomal recessive disorder** affecting the synthesis of hemoglobin chains (α or β chains). - Not an X-linked condition; mutations are in genes on chromosome 16 (α-thalassemia) or chromosome 11 (β-thalassemia). - Commonly seen in populations from the Mediterranean, Middle East, and Asia. *Azoospermia* - **Azoospermia** (absence of sperm in ejaculate) is a clinical finding, not a specific genetic disorder. - Can result from various genetic causes including **Y-chromosome microdeletions** and **autosomal mutations** (e.g., CFTR gene in congenital bilateral absence of vas deferens). - Not classified as an X-linked disorder. *Sickle cell anemia* - **Sickle cell anemia** is an **autosomal recessive disorder** caused by a mutation in the β-globin gene on chromosome 11. - Results from substitution of valine for glutamic acid at position 6 of the β-globin chain (HbS). - Not an X-linked condition; both males and females are equally affected when inheriting two copies of the mutant allele.

Q: Where will be the placement location for Auditory Brainstem Implant?

Recess of 4th ventricle. ***Recess of 4th ventricle*** - An **Auditory Brainstem Implant (ABI)** is placed on the **cochlear nucleus** in the brainstem, which is anatomically located near the **lateral recess of the fourth ventricle**. - The implant stimulates these nuclei directly, bypassing the damaged auditory nerve in patients who cannot benefit from cochlear implants. *Scala tympani* - The **scala tympani** is the location for electrode placement in a **cochlear implant**, not an auditory brainstem implant. - Cochlear implants stimulate the intact auditory nerve within the cochlea. *IAC* - The **internal auditory canal (IAC)** houses the auditory and facial nerves, but it is not the target site for an ABI. - The ABI is designed for patients whose auditory nerve (which passes through the IAC) is non-functional. *Back of ear* - The "back of the ear" is the general area where the **external processor of a cochlear implant** or a **bone-anchored hearing aid** is typically worn, not the surgical placement site for an ABI. - The ABI's internal component is surgically placed within the cranium.

Q: A boy presented with multiple non suppurative osteomyelitis with sickle cell anaemia. What will be the causative organism?

Salmonella. ***Salmonella*** - **Salmonella species** are a well-known cause of **osteomyelitis** in patients with **sickle cell anemia**, due to factors like gut mucosal damage and functional asplenia. [1] - The unique pathophysiology of sickle cell disease, including areas of bone infarction and compromised reticulendothelial system function, predisposes these patients to **Salmonella infections**. [1] *Staphylococcus aureus* - While **Staphylococcus aureus** is the most common cause of osteomyelitis in the general population, it is less likely to be the causative organism in patients with **sickle cell anemia** compared to Salmonella. - Its presence usually indicates other predisposing factors like trauma or prosthetic devices. *H. influenzae* - **Haemophilus influenzae** was a common cause of osteomyelitis in children before widespread vaccination but is now rare, especially with routine immunizations. - It is not specifically associated with a higher risk in patients with **sickle cell disease** for osteomyelitis compared to other pathogens. *Enterobacter species* - **Enterobacter species** can cause osteomyelitis, particularly in immunocompromised individuals or following surgery, but they are not uniquely associated with **sickle cell anemia** as a primary cause compared to Salmonella. - Their involvement in non-suppurative osteomyelitis in this specific patient population is less common.

Q: Identify the organism related to the blood smear image.

Plasmodium falciparum. ***Plasmodium falciparum*** - The image clearly displays multiple **ring-form trophozoites** within red blood cells, some of which are *appliqué* or *accolade* forms (rings on the periphery of the red blood cell) and **multiple rings per red blood cell**, which are characteristic of *P. falciparum*. - Presence of **multiple parasites per red blood cell** and various developmental stages including occasional **banana-shaped gametocytes**, though not prominent in this specific field, are key indicators of *P. falciparum* infection, differentiating it from other malarial species. - *P. falciparum* is the most dangerous malarial species and can cause **cerebral malaria** and other severe complications. *Salmonella Typhi* - This bacterium causes **typhoid fever** and is typically identified through **blood culture** or serological tests (Widal test), not by direct visualization within red blood cells on a peripheral blood smear. - *Salmonella Typhi* is an **intracellular bacterium** that primarily infects phagocytic cells (macrophages), not erythrocytes, and does not present as ring forms or other parasitic stages in blood smears. *Toxoplasma gondii* - This parasite causes **toxoplasmosis** and is typically found as **tachyzoites** or **bradyzoites** (within cysts) in tissue samples or less commonly in macrophages in disseminated disease, but not as ring forms within red blood cells on a peripheral blood smear. - Diagnosis usually involves **serological testing** for IgM/IgG antibodies or PCR, as opposed to direct visualization of unique forms in blood smears. *Treponema pallidum* - This is the spirochete responsible for **syphilis** and is too small and thin (0.1-0.2 μm diameter) to be seen with standard light microscopy on routine blood smears. - It is best identified using **dark-field microscopy** or serological tests (VDRL, RPR, TPPA, FTA-ABS) and does not infect red blood cells in the manner shown.

Q: Which of the following organisms is MOST associated with histamine production in scombroid fish poisoning?

Morganella morganii. ***Morganella morganii*** - ***Morganella morganii*** is the **MOST commonly implicated organism** in **scombroid fish poisoning** - It produces the enzyme **histidine decarboxylase**, which converts **histidine** (abundant in scombroid fish like tuna, mackerel, bonito) to **histamine** - When fish are stored at improper temperatures (>15°C), *M. morganii* proliferates and produces large amounts of **histamine** - Other histamine-producing bacteria include *Klebsiella*, *Proteus*, *Enterobacter*, and *Photobacterium* species - Symptoms mimic an **allergic reaction**: flushing, headache, palpitations, urticaria, diarrhea *Staphylococcus* - ***Staphylococcus aureus*** causes **staphylococcal food poisoning** through preformed **enterotoxins** (not histamine) - Associated with protein-rich foods left at room temperature - Causes rapid-onset nausea, vomiting, and abdominal cramps - **Not a significant cause** of scombroid fish poisoning *Salmonella* - ***Salmonella*** species cause **gastroenteritis** through direct infection and invasion of intestinal mucosa - Symptoms include **diarrhea**, **fever**, and **abdominal cramps** with longer incubation period (6-72 hours) - **Not associated** with histamine production or scombroid poisoning *P. aeruginosa* - ***Pseudomonas aeruginosa*** is an **opportunistic pathogen** causing hospital-acquired infections - Associated with wound infections, pneumonia, and UTIs in immunocompromised patients - **Not a cause** of foodborne histamine poisoning

Q: Which gene is primarily associated with Cowden syndrome?

PTEN. ***PTEN*** - Cowden syndrome is an **autosomal dominant** inherited disorder caused by germline mutations in the **PTEN (phosphatase and tensin homolog) tumor suppressor gene**. - The PTEN gene plays a crucial role in cell growth, proliferation, and apoptosis, and its dysfunction leads to uncontrolled cell growth and the development of multiple **hamartomas** and increased cancer risk. *TP53* - Mutations in the **TP53 gene** are primarily associated with Li-Fraumeni syndrome, a different inherited cancer predisposition syndrome characterized by a high risk of various cancers including sarcomas, breast cancer, and adrenocortical carcinoma. - While both inherited cancer syndromes involve tumor suppressor gene mutations, the specific gene affected and the clinical presentation differ significantly. *RB1* - The **RB1 gene** is a tumor suppressor gene primarily associated with **retinoblastoma**, a rare childhood eye cancer, and an increased risk of other cancers like osteosarcoma. - It plays a critical role in cell cycle regulation, and its mutation leads to uncontrolled cell division in the retina and other tissues. *KRAS* - The **KRAS gene** is an oncogene, not a tumor suppressor gene, and its mutations are frequently found in various sporadic cancers, particularly **colorectal cancer**, pancreatic cancer, and lung cancer. - KRAS mutations lead to constitutive activation of signaling pathways that promote cell growth and survival, but they are not the primary genetic cause of inherited Cowden syndrome.

Q: What happens to gas exchange when the Va/Q ratio approaches infinity?

No exchange of O2 and CO2 occurs.. ***No exchange of O2 and CO2 occurs.*** - When the **Va/Q ratio approaches infinity**, it signifies a scenario of **ventilation without perfusion** (Q approaches zero). - This represents **alveolar dead space** - despite adequate ventilation, there is **no blood flow** to participate in gas exchange. - Therefore, **no O2 enters the blood** and **no CO2 leaves the blood**, making this the most accurate description of what happens to gas exchange. *Partial pressure of O2 becomes negligible.* - This statement is incorrect because with **no blood flow** (Q = 0), the alveolar air retains high O2 partial pressure. - O2 is being delivered via ventilation but not removed by blood, so **alveolar PO2** would approach that of **inspired air (~150 mmHg)**, not become negligible. *Partial pressure of CO2 becomes negligible.* - While this statement is technically true (alveolar PCO2 would approach zero/inspired air levels), it doesn't directly answer what happens to **gas exchange**. - With no blood flowing through the alveolus, no **CO2 from venous blood** can reach the alveolus to be excreted. - However, the question asks about **gas exchange** itself, not just partial pressures, making the first option more comprehensive. *Partial pressures of both CO2 and O2 remain normal.* - This statement is incorrect as the **Va/Q mismatch** significantly alters the partial pressures of both gases. - In infinite Va/Q scenario (dead space ventilation), **alveolar PO2 would be high** (approaching inspired air ~150 mmHg) and **alveolar PCO2 would be low** (approaching zero).

Q: What is the physiological response of the kidney during shock?

Renal blood flow decreases. ***Renal blood flow decreases*** - During shock, the **primary and most fundamental** physiological change affecting the kidney is a marked **reduction in renal blood flow (RBF)**. - Shock triggers intense **sympathetic activation** and **renin-angiotensin system (RAS) activation**, causing preferential **vasoconstriction** of renal vessels to redirect blood to vital organs (brain, heart). - RBF can drop to as low as **20-30% of normal** in severe shock, making this the hallmark renal response. - This reduction in RBF is the **upstream event** that triggers all other renal changes during shock. *Perfusion of kidney decreases* - While technically correct, "decreased perfusion" is **essentially synonymous** with decreased blood flow in this context. - The term "renal blood flow" is the **standard physiological terminology** used in medical literature to describe this phenomenon, making it the more precise answer. *Afferent arteriole resistance increases* - This is a **mechanism** by which RBF decreases, not the overall response itself. - Increased afferent arteriolar resistance is **secondary** to sympathetic activation and angiotensin II effects during shock. - It describes the "how" rather than the "what" of the kidney's response. *GFR decreases* - GFR reduction is a **consequence** of decreased RBF and increased afferent arteriolar resistance. - While clinically important (oliguria/acute kidney injury), it's a **downstream effect** rather than the primary physiological response. - The relationship: ↓RBF → ↓Glomerular hydrostatic pressure → ↓GFR

Q: Which of the following is a key distinguishing feature of delirium compared to dementia?

Acute onset of confusion and disorientation. ***Acute onset of confusion and disorientation*** - Delirium is characterized by a **sudden (acute) onset** of mental status changes, including fluctuations in attention, awareness, and cognition, often presenting as **confusion and disorientation**. - Its symptoms typically develop over hours to days, contrasting sharply with the more chronic and insidious progression of dementia. *Gradual memory loss* - **Gradual memory loss** is a hallmark symptom of **dementia**, a neurocognitive disorder characterized by a progressive decline in cognitive function over months to years. - While memory impairment can occur in delirium, its onset is rapid and associated with a fluctuating course, not a steady decline. *Visual hallucinations* - While visual hallucinations can occur in **delirium**, they are not its most unique distinguishing feature from **dementia**, as they can also be prominent in certain types of dementia, such as **Lewy body dementia**. - The acute, fluctuating nature of **cognitive impairment** is a more defining characteristic of delirium. *Difficulty in recognizing familiar people* - **Prosopagnosia** or the inability to recognize familiar faces, is a symptom that can manifest in advanced stages of **dementia** due to widespread brain atrophy. - While patients with delirium might appear confused or disoriented to the point of not recognizing familiar individuals, this is usually part of a global, acute cognitive impairment and not a primary, isolated deficit.

Question 1

Trilene is degraded by:

Accepted Answer

Cytochrome P450 oxidation

Answer

Glutathione conjugation

Answer

Direct renal excretion

Answer

Acetylation

Question 2

Which of the following is an example of an X-linked disorder?

Accepted Answer

Color blindness

Answer

Thalassemia

Answer

Azoospermia

Answer

Sickle cell anemia

Question 3

Where will be the placement location for Auditory Brainstem Implant?

Accepted Answer

Recess of 4th ventricle

Answer

Scala tympani

Answer

IAC

Answer

Back of ear

Question 4

A boy presented with multiple non suppurative osteomyelitis with sickle cell anaemia. What will be the causative organism?

Accepted Answer

Salmonella

Answer

H. influenzae

Answer

Enterobacter species

Answer

Staphylococcus aureus

Question 5

Identify the organism related to the blood smear image.

Accepted Answer

Plasmodium falciparum

Answer

Salmonella Typhi

Answer

Toxoplasma gondii

Answer

Treponema pallidum

Question 6

Which of the following organisms is MOST associated with histamine production in scombroid fish poisoning?

Accepted Answer

Morganella morganii

Answer

P. aeruginosa

Answer

Staphylococcus

Answer

Salmonella

Question 7

Which gene is primarily associated with Cowden syndrome?

Accepted Answer

PTEN

Answer

RB1

Answer

KRAS

Answer

TP53

Question 8

What happens to gas exchange when the Va/Q ratio approaches infinity?

Accepted Answer

No exchange of O2 and CO2 occurs.

Answer

Partial pressure of O2 becomes negligible.

Answer

Partial pressure of CO2 becomes negligible.

Answer

Partial pressures of both CO2 and O2 remain normal.

Question 9

What is the physiological response of the kidney during shock?

Accepted Answer

Renal blood flow decreases

Answer

GFR decreases

Answer

Perfusion of kidney decreases

Answer

Afferent arteriole resistance increases

Question 10

Which of the following is a key distinguishing feature of delirium compared to dementia?

Accepted Answer

Acute onset of confusion and disorientation

Answer

Visual hallucinations

Answer

Gradual memory loss

Answer

Difficulty in recognizing familiar people

NEET-PG 2018

Biochemistry

ENT

Microbiology

Pathology

Physiology

Psychiatry