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 501: 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
3 questionsWhich protein is responsible for conserving iron in the body?
Converging point of both pathways in coagulation is at:
Glucagon activates which enzyme ?
NEET-PG 2015 - Biochemistry NEET-PG Practice Questions and MCQs
Question 501: Which protein is responsible for conserving iron in the body?
- A. Ferritin (Correct Answer)
- B. Hepcidin
- C. Hemopexin
- D. Transferrin
Explanation: ***Ferritin*** - **Ferritin** is the primary intracellular protein that **conserves iron** in the body by storing it in a safe, non-toxic, and bioavailable form - It is found mainly in the liver, spleen, and bone marrow, serving as the body's **iron reserve** - When iron is abundant, ferritin stores it; when iron is needed, ferritin releases it, thus **conserving iron for future use** - Serum ferritin levels directly reflect total body iron stores *Hepcidin* - **Hepcidin** is a regulatory peptide hormone that controls iron homeostasis by inhibiting **ferroportin**, the iron export channel - It reduces iron absorption from the intestine and iron release from macrophages during inflammation or iron overload - While it regulates iron distribution, it is a hormone, not a storage protein, and does not directly conserve iron within cells *Hemopexin* - **Hemopexin** binds free **heme** in plasma, preventing oxidative damage and delivering it to the liver for catabolism - It helps recover iron from heme but does not store or conserve iron in the body *Transferrin* - **Transferrin** is a plasma protein that **transports iron** from absorption sites (intestine) and storage sites (liver, spleen) to tissues that need it - Its role is iron delivery, not conservation or storage
Question 502: Converging point of both pathways in coagulation is at:
- A. Factor VIII
- B. Stuart factor X (Correct Answer)
- C. Factor IX
- D. Factor VII
Explanation: ***Stuart factor X*** [1][2] - It is the main **converging point** of the coagulation cascade, where both the intrinsic and extrinsic pathways meet to initiate the common pathway [1]. - Activated factor X leads to the conversion of **prothrombin to thrombin**, pivotal for clot formation [2]. *Factor VII* [2] - Primarily involved in the **extrinsic pathway** of coagulation, activating factor X, but does not serve as a converging point. - Its function is limited to starting the coagulation cascade, particularly upon tissue injury. *Factor IX* [2] - A key component of the **intrinsic pathway**, it leads to the activation of factor X but is not the point where both pathways converge. - It requires **factor VIII** for its activation, further illustrating its role within a specific pathway. *Factor VIII* - Also part of the **intrinsic pathway**, it acts as a cofactor for factor IX but does not integrate both pathways into a common point. - Its deficiency is associated with **Hemophilia A**, underscoring its specific pathway involvement. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Hemodynamic Disorders, Thromboembolic Disease, and Shock, pp. 128-130. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Blood And Bone Marrow Disease, pp. 582-583.
Question 503: 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.
Physiology
6 questionsAcrosome reaction is seen in?
Which of the following is considered the most important intracellular buffer in human physiology?
Penile erection is mediated by which system?
Inhibition of heart by vagus is mediated by which receptors?
What is the average size of platelets in micrometers?
What is the respiratory quotient?
NEET-PG 2015 - Physiology NEET-PG Practice Questions and MCQs
Question 501: Acrosome reaction is seen in?
- A. Spermatogenesis
- B. Oogenesis
- C. Fertilization (Correct Answer)
- D. Menstruation
Explanation: ***Fertilization*** - The **acrosome reaction** is a crucial event that occurs when a **spermatozoon** comes into contact with the **zona pellucida** surrounding the oocyte. - This reaction involves the release of **hydrolytic enzymes** from the acrosome, which are essential for the sperm to penetrate the zona pellucida and fuse with the oocyte membrane. *Spermatogenesis* - **Spermatogenesis** is the process of sperm formation in the testes, involving meiosis and spermiogenesis. - While it produces the sperm cell with an acrosome, the **acrosome reaction itself does not occur** during this developmental stage. *Oogenesis* - **Oogenesis** is the process of egg cell formation in the ovaries. - This process is entirely **separate from sperm function** and does not involve the acrosome or the acrosome reaction. *Menstruation* - **Menstruation** is the monthly shedding of the uterine lining in females when fertilization does not occur. - This process is part of the female reproductive cycle and has **no direct involvement with sperm or the acrosome reaction**.
Question 502: Which of the following is considered the most important intracellular buffer in human physiology?
- A. Albumin protein
- B. Ammonia buffer
- C. Bicarbonate buffer
- D. Phosphate buffer (Correct Answer)
Explanation: ***Phosphate buffer*** - The **phosphate buffer system (H₂PO₄⁻/HPO₄²⁻)** is the most important intracellular buffer due to relatively high concentrations of inorganic phosphates within cells - The pKa₂ of approximately **6.8 is close to intracellular pH** (~7.0-7.2), providing optimal buffering capacity - Plays a crucial role in buffering acids and bases generated by metabolic processes within cells and is also important in renal tubular buffering *Albumin protein* - **Proteins**, including albumin, are important **extracellular buffers** in plasma due to their abundant ionizable amino acid residues - While proteins do contribute to intracellular buffering (especially hemoglobin in RBCs), the **phosphate system is more significant** for general intracellular pH regulation *Ammonia buffer* - The **ammonia buffer system (NH₃/NH₄⁺)** is primarily a **renal buffer system** that plays a crucial role in acid excretion via urine - It is not considered the primary intracellular buffer for metabolic acid-base balance within cells *Bicarbonate buffer* - The **bicarbonate buffer system (HCO₃⁻/H₂CO₃)** is the **most important extracellular buffer system**, critical for maintaining blood pH - Although present intracellularly, its buffering capacity is less prominent than phosphate within cells due to lower intracellular bicarbonate concentration and its pKa of 6.1 being further from intracellular pH
Question 503: 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 504: Inhibition of heart by vagus is mediated by which receptors?
- A. M1
- B. M2 (Correct Answer)
- C. NN
- D. NM
Explanation: ***M2*** - The **vagus nerve** primarily mediates its inhibitory effects on the heart through **muscarinic M2 receptors**. - Activation of M2 receptors by **acetylcholine** (released from the vagus nerve) decreases heart rate and contractility. *M1* - **M1 receptors** are primarily found in neuronal tissue and glands, playing a role in **gastric acid secretion** and cognitive functions. - They are not the primary muscarinic subclass responsible for vagal inhibition of the heart. *NN* - **NN receptors** are **nicotinic receptors** found on postganglionic neurons in autonomic ganglia. - They are involved in **ganglionic transmission** and are not directly responsible for efferent vagal effects on the heart. *NM* - **NM receptors** are **nicotinic receptors** found at the **neuromuscular junction** of skeletal muscles. - Their activation leads to **skeletal muscle contraction**, and they have no role in regulating heart function.
Question 505: What is the average size of platelets in micrometers?
- A. 4-5 µm
- B. 3-4 µm
- C. 2-3 µm (Correct Answer)
- D. 1-2 µm
Explanation: ***2-3 µm*** - Platelets, also known as **thrombocytes**, are small, anucleated cell fragments crucial for **hemostasis**, and their average diameter generally falls within the range of 2-3 micrometers. - This **small size** allows them to easily navigate through capillaries and aggregate rapidly at sites of vascular injury. *3-4 µm* - While platelets can vary slightly in size, an average of 3-4 µm is generally considered a bit on the larger side and not the typical average diameter. - Larger platelets might be seen in certain conditions like **idiopathic thrombocytopenic purpura (ITP)**, but this is not the average normal size. *4-5 µm* - This range is significantly larger than the typical size of normal circulating platelets. - Platelets this large would be considered **macroplatelets** and could indicate specific pathological conditions or inherited platelet disorders. *1-2 µm* - This size range is generally considered smaller than the average normal platelet size. - Very small platelets might be seen in some specific conditions, but it's not the usual average for healthy individuals.
Question 506: What is the respiratory quotient?
- A. CO2 released to O2 consumed (Correct Answer)
- B. CO2 consumed to O2 released
- C. O2 released to CO2 consumed
- D. O2 consumed to CO2 released
Explanation: **CO2 released to O2 consumed** - The **respiratory quotient (RQ)** is a ratio used in metabolism to describe the proportion of **carbon dioxide (CO2) produced** by the body relative to the **oxygen (O2) consumed**. - It is calculated as the **volume of CO2 released** divided by the **volume of O2 consumed** over a specific period. - RQ = VCO2/VO2, where VCO2 is CO2 production and VO2 is O2 consumption. *CO2 consumed to O2 released* - This option is incorrect as it reverses the correct order and refers to **CO2 consumption and O2 release**, which are not the standard components of the RQ calculation. - The body primarily **releases CO2** and **consumes O2** during cellular respiration. *O2 released to CO2 consumed* - This option is also incorrect because it inverts both the gases and the direction of their metabolic flow (release vs. consumption). - Metabolic processes involve **O2 consumption** and **CO2 release**, not the other way around. *O2 consumed to CO2 released* - This option incorrectly reverses the numerator and denominator in the RQ formula. - The standard definition places **CO2 production** in the numerator and **O2 consumption** in the denominator.