Anatomy
1 questionsWhere do primitive red blood cells first originate during early embryonic development?
NEET-PG 2015 - Anatomy NEET-PG Practice Questions and MCQs
Question 221: Where do primitive red blood cells first originate during early embryonic development?
- A. Liver
- B. Yolk sac (Correct Answer)
- C. Bone marrow
- D. Spleen
Explanation: ***Yolk sac*** - The **yolk sac** is the primary site of **hematopoiesis** during the first few weeks of embryonic development. - Primitive erythroid cells (red blood cells) originate here to supply the developing embryo with oxygen. *Liver* - The **liver** takes over as the main hematopoietic organ from about the 6th week of gestation, after the yolk sac [1]. - While it produces various blood cells, it is not the *first* site of primitive red blood cell formation. *Bone marrow* - **Bone marrow** becomes the primary site of hematopoiesis during the **fetal period** (around the 20th to 24th week) and continues throughout postnatal life [2]. - It is not involved in the initial production of primitive red blood cell formation in early embryogenesis. *Spleen* - The **spleen** plays a minor role in fetal hematopoiesis, mainly producing lymphoid cells and some myeloid cells, and can take on myeloid functions if the bone marrow is compromised. - It is not the initial site of red blood cell production in the early embryo.
Biochemistry
2 questionsGlucagon activates which enzyme ?
Which of the following is required in the synthesis of acetylcholine -
NEET-PG 2015 - Biochemistry NEET-PG Practice Questions and MCQs
Question 221: Glucagon activates which enzyme ?
- A. Adenylyl cyclase (Correct Answer)
- B. Pepsin
- C. Trypsin
- D. None of the options
Explanation: ***Adenylyl cyclase*** - **Glucagon** binds to specific G protein-coupled receptors on target cells, activating the **Gαs subunit**. - The activated **Gαs subunit** then stimulates **adenylyl cyclase**, leading to the production of **cyclic AMP (cAMP)**, which mediates glucagon's metabolic effects. *Pepsin* - **Pepsin** is a protease produced in the stomach, involved in protein digestion, and its activity is regulated by **gastrin** and **acid secretion**, not glucagon. - It is synthesized as **pepsinogen** and activated by hydrochloric acid (HCl) at low pH. *Trypsin* - **Trypsin** is a digestive enzyme produced in the pancreas and secreted into the small intestine, primarily involved in protein digestion. - Its activation is dependent on **enteropeptidase**, which cleaves **trypsinogen**, and its activity is not directly regulated by glucagon. *None of the options* - This option is incorrect because **adenylyl cyclase** is indeed activated by glucagon as part of its signaling pathway.
Question 222: Which of the following is required in the synthesis of acetylcholine -
- A. Inositol
- B. Carnitine
- C. Glycine
- D. Choline (Correct Answer)
Explanation: ***Choline*** - **Choline** is a **precursor** to acetylcholine, providing the **choline moiety** for its synthesis. - The enzyme **choline acetyltransferase** combines choline with acetyl-CoA (which provides the acetyl group) to form acetylcholine. *Inositol* - **Inositol** is a sugar alcohol that plays a role in **cell signaling** and as a secondary messenger in various pathways. - It is not directly involved as a substrate in the synthesis of acetylcholine. *Carnitine* - **Carnitine** is essential for the **transport of fatty acids** into the mitochondria for beta-oxidation. - It does not participate in the enzymatic reactions that produce acetylcholine. *Glycine* - **Glycine** is an amino acid that functions as an **inhibitory neurotransmitter** in the central nervous system. - While it is a neurotransmitter, it is not a component or precursor for acetylcholine synthesis.
Physiology
7 questionsWhat is the typical pH range of intracellular fluid (ICF) compared to extracellular fluid (ECF)?
Penile erection is mediated by which system?
Increase in plasma viscosity is maximally caused by which plasma protein?
Which of the following statements about ENaC is incorrect?
Which of the following is not a component of a mature sperm cell?
What is the composition of epithelial sodium channels?
What is the nature of the relationship between insulin and glucose concentration in the human body?
NEET-PG 2015 - Physiology NEET-PG Practice Questions and MCQs
Question 221: What is the typical pH range of intracellular fluid (ICF) compared to extracellular fluid (ECF)?
- A. Typically around 7.0, slightly less than ECF (Correct Answer)
- B. Typically around 7.4, slightly more than ICF
- C. Approximately equal to ECF
- D. Significantly higher than ECF
Explanation: ***Typically around 7.0, slightly less than ECF*** - The **intracellular fluid (ICF)** tends to be slightly more acidic due to metabolic processes within cells that produce **acidic byproducts**. - This makes its pH typically around **7.0–7.2**, which is subtly lower than the extracellular fluid. *Typically around 7.4, slightly more than ICF* - A pH of approximately **7.4** is characteristic of **extracellular fluid (ECF)**, which includes plasma and interstitial fluid. - The ECF is maintained within a **narrow, slightly alkaline** range to support cellular function and enzyme activity throughout the body. *Approximately equal to ECF* - While both fluid compartments are maintained within a **narrow physiological range**, their pH values are not exactly equal. - This slight difference is essential for various biological processes, including maintaining **membrane potential** and **enzyme efficiency**. *Significantly higher than ECF* - The ICF pH is **not significantly higher** than ECF; in fact, it is slightly lower. - Maintaining too high a pH intracellularly would disrupt **cellular metabolism** and **protein structure**.
Question 222: Penile erection is mediated by which system?
- A. Parasympathetic system via muscarinic receptors (Correct Answer)
- B. Parasympathetic system via nicotinic receptors
- C. Sympathetic system via α-receptors
- D. Sympathetic system via β-receptors
Explanation: ***Parasympathetic system via muscarinic receptors*** - Penile erection is primarily a **parasympathetic response** mediated by the **pelvic splanchnic nerves (S2-S4)**. - The key mechanism involves **nitric oxide (NO)** release from non-adrenergic, non-cholinergic (NANC) neurons, which activates guanylate cyclase → increases cGMP → smooth muscle relaxation in the **corpora cavernosa**. - **Acetylcholine acting on muscarinic receptors** plays a **supportive role** by enhancing NO release and contributing to vasodilation. - For exam purposes, the parasympathetic system (with its cholinergic muscarinic component) is the recognized answer. *Parasympathetic system via nicotinic receptors* - **Nicotinic receptors** are located at **autonomic ganglia** and **neuromuscular junctions**, not at the effector sites in penile vasculature. - While nicotinic transmission occurs at the parasympathetic ganglia, the post-ganglionic fibers act on **muscarinic receptors** and release **NO** at the target tissue. - This option confuses the ganglionic transmission with the effector mechanism. *Sympathetic system via α-receptors* - The **sympathetic nervous system** via **α1-adrenergic receptors** causes **vasoconstriction** and maintains penile **flaccidity** (detumescence). - Sympathetic activation is responsible for **ejaculation** and the resolution phase after orgasm. - Activation of α-receptors opposes erection by causing smooth muscle contraction. *Sympathetic system via β-receptors* - **β-adrenergic receptors** are involved in functions like **cardiac stimulation** and **bronchodilation**, but play no significant role in penile erection. - The sympathetic system's role in sexual function is primarily through **α-receptors** (detumescence and ejaculation), not β-receptors.
Question 223: Increase in plasma viscosity is maximally caused by which plasma protein?
- A. Albumin
- B. All have equal effect
- C. Globulin
- D. Fibrinogen (Correct Answer)
Explanation: ***Globulin*** - Increased levels of **globulin** proteins, particularly in inflammatory or proliferative conditions, have a significant impact on plasma viscosity due to their **high molecular weight** [1]. - **Globulins** contribute to **hyperviscosity syndrome**, which can lead to clinical symptoms like fatigue and visual disturbances [1]. *Albumin* - While **albumin** is the most abundant plasma protein, its primary role is in maintaining **oncotic pressure**, not significantly affecting plasma viscosity. - An increase in albumin does not correlate with plasma viscosity increases to the extent seen with globulins. *All have equal effect* - Different plasma proteins do not have **equal effects** on viscosity; **globulins** and **fibrinogen** particularly influence it more than **albumin**. - The impact on viscosity varies significantly with protein concentration and type, making this statement inaccurate. *Fibrinogen* - **Fibrinogen** does contribute to plasma viscosity but is typically less than that caused by globulins, especially when globulin levels are markedly elevated. - Its effect is more pronounced during **coagulation**, rather than in the general increase of plasma viscosity associated with inflammatory states. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 141-142.
Question 224: Which of the following statements about ENaC is incorrect?
- A. Present in kidney and GIT
- B. Epithelial channel
- C. Inhibited by amiloride
- D. Composed of 2 homologous subunits (Correct Answer)
Explanation: ***Composed of 2 homologous subunits*** - ENaC (Epithelial Sodium Channel) is a **heterotrimeric complex** composed of **three distinct subunits**: α, β, and γ. - The functional channel typically has a stoichiometry of 2α:1β:1γ, forming a heterotrimer. - These subunits share sequence homology but are **non-identical proteins**, not just two homologous subunits. - A fourth related subunit (δ) exists and can substitute for α in some tissues, but the classical ENaC is a three-subunit channel. *Epithelial channel* - ENaC is indeed an **epithelial channel** responsible for critical **sodium reabsorption** in various epithelia. - It plays a vital role in regulating **fluid and electrolyte balance** across tight epithelial layers. *Present in kidney and GIT* - ENaC is abundantly expressed in the **distal nephron of the kidney**, specifically in the collecting duct, where it mediates fine-tuning of sodium reabsorption. - It is also present in the **lower gastrointestinal tract (colon)**, contributing to sodium absorption, and in the airways and salivary glands. *Inhibited by amiloride* - **Amiloride** is a well-known **potassium-sparing diuretic** that specifically acts by blocking ENaC. - This inhibition reduces sodium reabsorption and, consequently, water reabsorption, leading to increased diuresis.
Question 225: Which of the following is not a component of a mature sperm cell?
- A. Lysosome
- B. Golgi apparatus
- C. Mitochondria
- D. Endoplasmic reticulum (Correct Answer)
Explanation: ***Endoplasmic reticulum*** - The **endoplasmic reticulum** is prominent in spermatogonia and spermatocytes but largely absent in **mature sperm** as organelles are shed during spermiogenesis to reduce cell volume. - Its primary functions of protein synthesis and lipid metabolism are not required in a terminally differentiated, motile cell like a mature sperm. *Golgi apparatus* - The **Golgi apparatus** reorganizes during spermiogenesis to form the **acrosome**, which is a crucial structure for fertilization. - While the distinct Golgi stacks are not present, its modified derivative, the acrosome, is an essential component. *Mitochondria* - **Mitochondria** are abundant in the midpiece of the sperm tail, arranged in a spiral sheath. - They are vital for generating the **ATP** required for the flagellum's motility, enabling the sperm to swim. *Lysosome* - Although typical lysosomes are not found, the **acrosome** of the sperm is considered a modified lysosome. - The acrosome contains **hydrolytic enzymes** similar to lysosomes, which are critical for penetrating the egg's outer layers during fertilization.
Question 226: What is the composition of epithelial sodium channels?
- A. 2α, 1β, 1γ
- B. 1α, 1β, 1γ (Correct Answer)
- C. 2α, 1β
- D. 2α, 1β, 2γ
Explanation: ***1α, 1β, 1γ*** - Epithelial sodium channels (**ENaCs**) are heterotrimeric complexes composed of one **alpha (α)**, one **beta (β)**, and one **gamma (γ) subunit**. - This specific subunit composition is essential for the channel's proper function in **sodium reabsorption** across epithelial tissues. *2α, 1β* - This composition is incomplete as it lacks the **gamma (γ) subunit**, which is a crucial component of the functional ENaC. - While alpha and beta subunits are present, the absence of the gamma subunit would impair the channel's ability to efficiently transport sodium. *2α, 1β, 2γ* - This composition is incorrect because a functional ENaC typically includes only **one gamma (γ) subunit**, not two. - An imbalance in subunit stoichiometry can lead to misfolding or improper assembly, affecting channel function. *2α, 1β, 1γ* - This combination correctly includes all three types of subunits (alpha, beta, gamma) but incorrectly states there are **two alpha (α) subunits**. - A functional ENaC has a single alpha subunit, making this option incorrect.
Question 227: What is the nature of the relationship between insulin and glucose concentration in the human body?
- A. Linear
- B. Hyperbola
- C. Sigmoidal (Correct Answer)
- D. Bell Shaped
Explanation: ***Sigmoidal*** - The relationship between insulin and glucose concentration is best described as **sigmoidal**, characterized by a slow initial rise in insulin secretion at low glucose levels, followed by a steep increase at physiological glucose concentrations, and then a plateau at very high glucose levels. - This shape reflects the **beta cell's sensitivity to glucose**, where a minimal threshold of glucose is required to trigger insulin release, and then a maximal release capacity is reached. *Linear* - A **linear relationship** would imply that for every unit increase in glucose, there is a constant, proportional increase in insulin secretion, which is not physiologically accurate. - While insulin secretion does increase with glucose, the rate of increase varies significantly across different glucose concentrations. *Hyperbola* - A **hyperbolic relationship** typically suggests a rapid initial response that then gradually plateaus, often seen in enzyme kinetics. - While there is a plateau in insulin secretion at high glucose levels, the initial phase is not as rapid or proportionally inverse as a hyperbolic function would suggest. *Bell Shaped* - A **bell-shaped curve** describes a relationship where there is an optimal point, and deviations in either direction lead to a decrease in the response (e.g., enzyme activity vs. pH). - This is not characteristic of insulin secretion, as insulin levels generally continue to rise or plateau at higher glucose concentrations and do not decrease beyond an optimal point.