Anatomy
2 questionsWhat is the outer layer of the blastocyst called?
Corpora arenacea is seen in?
NEET-PG 2012 - Anatomy NEET-PG Practice Questions and MCQs
Question 341: What is the outer layer of the blastocyst called?
- A. Embryo proper
- B. Trophoblast (Correct Answer)
- C. Primitive streak
- D. Yolk sac
Explanation: ***Trophoblast*** - The **trophoblast** is the outer layer of cells of the blastocyst, which goes on to form the **placenta** and other extraembryonic tissues [1]. - It plays a crucial role in the **implantation** of the blastocyst into the uterine wall and in producing hormones [1]. *Primitive streak* - The **primitive streak** is a structure that forms during **gastrulation**, much later than the initial blastocyst stage. - It establishes the **anterior-posterior axis** and initiates the formation of the three germ layers. *Yolk sac* - The **yolk sac** is an extraembryonic membrane that forms within the blastocyst cavity, but it is not the outermost layer of the entire structure. - It is involved in early **nutrient transfer** and **blood cell formation** before the placenta is fully functional. *Embryo proper* - The **embryo proper**, derived from the **inner cell mass (ICM)**, is the part of the blastocyst that will develop into the actual embryo [2]. - It is located *inside* the trophoblast layer, not forming the outer boundary of the blastocyst [2].
Question 342: Corpora arenacea is seen in?
- A. Pineal (Correct Answer)
- B. Seminal vesicle
- C. Breast
- D. Prostate
Explanation: ***Pineal*** - **Corpora arenacea**, also known as **brain sand**, are calcium deposits found in the pineal gland. - Their presence is a normal, age-related finding and increases with age, though their exact physiological role is not fully understood. *Prostate* - The prostate gland contains **corpora amylacea**, which are concentric calcifications found within the glandular acini. - While similar in appearance to corpora arenacea, they are distinct structures specific to the prostate. *Seminal vesicle* - The seminal vesicles produce a fluid component of semen, and while they may occasionally show calcifications, these are typically due to stones or chronic inflammation, not the characteristic "brain sand" seen in the pineal gland. - They do not contain corpora arenacea as a normal physiological feature. *Breast* - Calcifications in the breast are common and can be either benign (e.g., **fibrocystic changes**, vascular calcifications) or malignant (e.g., **ductal carcinoma in situ**). - These calcifications are generally not referred to as corpora arenacea and have different clinical implications and microscopic appearances.
Biochemistry
3 questionsHow do enzymes function in biochemical reactions?
Enzyme causing covalent bond cleavage without hydrolysis ?
Apoenzyme is ?
NEET-PG 2012 - Biochemistry NEET-PG Practice Questions and MCQs
Question 341: How do enzymes function in biochemical reactions?
- A. Increase in activation energy
- B. Decrease in activation energy (Correct Answer)
- C. Shift equilibrium constant
- D. Provide energy to the reaction
Explanation: ***Decrease in activation energy*** - Enzymes act as **biological catalysts** by providing an alternative reaction pathway with a lower **transition state energy**. - This reduction in the **activation energy** allows a higher proportion of reactant molecules to overcome the energy barrier and react, thereby increasing the reaction rate. *Increase in activation energy* - This statement is incorrect as increasing activation energy would slow down the reaction rate, which is contrary to the function of enzymes. - Enzymes are designed to accelerate reactions, not inhibit them, by making them energetically more favorable to proceed. *Shift equilibrium constant* - Enzymes catalyze both the forward and reverse reactions equally, meaning they accelerate the rate at which equilibrium is reached but **do not alter the equilibrium constant (Keq)** of a reaction. - The equilibrium constant is determined by the difference in free energy between reactants and products, which enzymes do not change. *Provide energy to the reaction* - This statement is incorrect because enzymes do **not provide energy** to reactions; they only lower the activation energy barrier. - Enzymes facilitate reactions by stabilizing the transition state, not by adding energy to the system, which would violate thermodynamic principles.
Question 342: Enzyme causing covalent bond cleavage without hydrolysis ?
- A. Lyase (Correct Answer)
- B. Ligase
- C. Hydrolase
- D. Transferase
Explanation: ***Lyase*** - **Lyases** are enzymes that catalyze the cleavage of **covalent bonds** (C-C, C-O, C-N, and others) by means other than hydrolysis or oxidation, often creating a new double bond or a ring structure. - They remove groups from substrates to form double bonds, or conversely, add groups to double bonds. - **Examples:** Aldolase (cleaves C-C bonds in glycolysis), carbonic anhydrase (reversible cleavage of C-O bond), fumarase (C-C bond cleavage in TCA cycle). *Ligase* - **Ligases** are enzymes that join two large molecules by forming a new chemical bond, usually accompanied by the **hydrolysis of ATP**. - They are involved in synthesis reactions, not the cleavage of bonds. *Hydrolase* - **Hydrolases** specifically catalyze the hydrolysis of a chemical bond, involving the **addition of water** across the bond. - They break down large molecules into smaller ones using water - this is the key difference from lyases. *Transferase* - **Transferases** catalyze the transfer of a **functional group** from one molecule (the donor) to another (the acceptor). - They do not cause covalent bond cleavage without hydrolysis but rather move existing groups between molecules.
Question 343: Apoenzyme is ?
- A. Protein moiety (Correct Answer)
- B. Organic cofactor
- C. Inactive enzyme component
- D. Non-protein component required for enzyme activity
Explanation: ***Protein moiety*** - An **apoenzyme** is the **protein component of an enzyme** that is catalytically inactive by itself. - It requires a **non-protein cofactor** (either an inorganic ion or an organic molecule) to become active. *Organic cofactor* - An **organic cofactor** is also known as a **coenzyme**, which binds to the apoenzyme to form a functional holoenzyme. - While essential for enzyme activity, the apoenzyme itself is the protein part, not the organic cofactor. *Inactive enzyme component* - While an apoenzyme is **inactive on its own**, this description is too broad and doesn't specify its chemical nature. - It is specifically the **protein component** that is inactive until bound to its cofactor. *Non-protein component required for enzyme activity* - This describes a **cofactor** (either inorganic or organic), not the apoenzyme itself. - The apoenzyme is the **protein portion**, which *requires* the non-protein component for activity.
Internal Medicine
1 questionsWhich of the following complications is commonly associated with mitral valve prolapse?
NEET-PG 2012 - Internal Medicine NEET-PG Practice Questions and MCQs
Question 341: Which of the following complications is commonly associated with mitral valve prolapse?
- A. Ventricular arrhythmia
- B. Stroke
- C. Infective endocarditis (Correct Answer)
- D. Mitral stenosis
Explanation: Mitral valve prolapse (MVP) involves myxomatous degeneration of the mitral valve leaflets, which can create a rough surface predisposing to bacterial adhesion and subsequent infective endocarditis [1]. While the overall risk is low, patients with MVP and accompanying mitral regurgitation or thickened leaflets are at higher risk [1]. Patients with valvular heart disease are generally susceptible to bacterial endocarditis, often associated with procedures or dental hygiene [2]. Stroke - Although MVP can sometimes be associated with embolic events (e.g., from thrombi forming on the prolapsing valve), stroke is not considered a commonly associated complication. - The risk of stroke is generally higher in MVP patients with concomitant atrial fibrillation or other cardiovascular risk factors. Mitral stenosis - Mitral valve prolapse is characterized by the displacement of mitral valve leaflets into the left atrium during systole, which can lead to mitral regurgitation [3], not stenosis. - Mitral stenosis involves narrowing of the mitral valve orifice, usually due to rheumatic fever, which is a different pathophysiology [4]. Ventricular arrhythmia - While palpitations (often benign supraventricular ectopy) are common in MVP, clinically significant ventricular arrhythmias are less common. - Severe ventricular arrhythmias are more typically seen with significant underlying myocardial disease or severe mitral regurgitation causing left ventricular dysfunction.
Physiology
4 questionsWhat is the fixed length of a myosin filament?
Which of the following hormones does not mediate its action through cAMP?
Gastric secretions are essential for absorption of -
Which of the following is most important in sodium and water retention ?
NEET-PG 2012 - Physiology NEET-PG Practice Questions and MCQs
Question 341: What is the fixed length of a myosin filament?
- A. 0.16 nm
- B. 1.6 micrometers (Correct Answer)
- C. 16 nm
- D. 1.6 mm
Explanation: ***1.6 micrometers*** - Myosin filaments, also known as **thick filaments**, are integral components of muscle contraction and have a characteristic fixed length. This length is precisely **1.6 micrometers** in mammalian skeletal muscle. - This consistent length is crucial for the **sliding filament model** of muscle contraction, ensuring proper overlap with actin filaments and efficient force generation. *0.16 nm* - This value is significantly too small; **nanometers (nm)** are typically used for atomic or molecular distances, not for entire protein filaments like myosin. - A myosin filament is composed of hundreds of myosin molecules, making its overall length much larger than a fraction of a nanometer. *16 nm* - While nanometers are used for molecular structures, 16 nm is still too small for a myosin filament. The entire filament is roughly **100 times larger** than this value. - This dimension might be more appropriate for the diameter of a single myosin molecule's head region, but not the entire filament's length. *1.6 mm* - This value is significantly too large; **millimeters (mm)** are visible to the naked eye and represent macroscopic objects. - Muscle filaments are microscopic structures, and a length of 1.6 mm would imply they are many times longer than an entire muscle cell.
Question 342: Which of the following hormones does not mediate its action through cAMP?
- A. Glucagon
- B. Follicle stimulating hormone
- C. Estrogen (Correct Answer)
- D. Luteinizing hormone
Explanation: ***Estrogen*** - **Estrogen** is a **steroid hormone** that mediates its action by binding to intracellular receptors, forming a complex that directly influences gene transcription. - Steroid hormones, due to their **lipophilicity**, can cross the cell membrane and do not typically rely on cell surface receptors or second messengers like cAMP. *Glucagon* - **Glucagon** acts on a **G protein-coupled receptor (GPCR)**, specifically a Gs-coupled receptor, leading to the activation of adenylyl cyclase. - This activation increases the intracellular concentration of **cAMP**, which then activates protein kinase A to mediate its effects, primarily on glucose metabolism. *Follicle stimulating hormone* - **FSH** binds to a **GPCR** on target cells, activating the Gs protein pathway. - This activation stimulates **adenylyl cyclase** and increases intracellular **cAMP** levels, which are critical for its role in gamete development. *Luteinizing hormone* - **LH**, like FSH, binds to a cell surface **GPCR** that activates the Gs protein. - This leads to the stimulation of **adenylyl cyclase** and an increase in **cAMP**, mediating its effects on steroidogenesis and ovulation.
Question 343: Gastric secretions are essential for absorption of -
- A. Cobalamin (Correct Answer)
- B. Fat
- C. Thiamine
- D. Folic acid
Explanation: ***Cobalamin*** - **Intrinsic factor**, secreted by gastric parietal cells, is crucial for the absorption of **vitamin B12 (cobalamin)** in the terminal ileum [1]. - Without sufficient intrinsic factor, **pernicious anemia** can develop due to impaired B12 absorption [2]. *Fat* - Fat digestion primarily occurs in the **small intestine** with the help of **bile salts** and **pancreatic lipases**. - While gastric lipase begins some fat digestion, it's not essential for overall fat absorption. *Thiamine* - **Thiamine (vitamin B1)** is absorbed in the jejunum and ileum, primarily via **active transport** and passive diffusion. - Gastric secretions do not play a direct, essential role in its absorption. *Folic acid* - **Folic acid** is absorbed in the **duodenum and jejunum** as monoglutamates after being deconjugated from polyglutamate forms. - This process is not directly dependent on gastric secretions [2].
Question 344: Which of the following is most important in sodium and water retention ?
- A. Renin angiotensin system (Correct Answer)
- B. ANP
- C. BNP
- D. Vasopressin
Explanation: ***Renin angiotensin system*** - The **renin-angiotensin-aldosterone system (RAAS)** is the most important mechanism for **both sodium AND water retention**, which is what the question specifically asks about. - **Aldosterone** directly promotes **sodium reabsorption** in the principal cells of the collecting duct by increasing apical ENaC channels and basolateral Na-K-ATPase pumps. - **Angiotensin II** stimulates sodium reabsorption in the proximal tubule and also stimulates ADH release, contributing to water retention. - When sodium is retained, **water follows passively** due to the osmotic gradient, resulting in effective volume expansion. - RAAS is the primary system activated in states of volume depletion and is most important for combined sodium and water retention. *Vasopressin* - **Vasopressin (ADH)** primarily controls **water retention only** by increasing aquaporin-2 channels in the collecting duct. - While crucial for water balance, it has minimal direct effect on sodium reabsorption. - It causes retention of **free water**, which can actually dilute plasma sodium concentration. - ADH is the answer if the question asked about water retention alone, but not for combined sodium and water retention. *ANP* - **Atrial natriuretic peptide (ANP)** promotes **sodium and water excretion** (natriuresis and diuresis). - Released in response to atrial stretch from volume expansion. - Acts to *oppose* retention mechanisms, making it incorrect for this question. *BNP* - **Brain natriuretic peptide (BNP)** similarly promotes **natriuresis and diuresis**. - Released from ventricular myocytes in response to volume overload. - Like ANP, it acts to *excrete* sodium and water, not retain them.