NEET-PG 2015 - Physiology Practice Questions

Q: What is the average size of platelets in micrometers?

2-3 µm. ***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.

Q: Which part of the stomach is primarily responsible for receiving and storing ingested food?

Body. ***Body*** - The **body (corpus)** is the largest part of the stomach, situated between the fundus and the antrum [1]. - This region is **primarily responsible for receiving and storing ingested food** as the main reservoir [2]. - It also produces **gastric acid and enzymes** (like pepsinogen) for the initial digestion of food [1]. - The body serves as the **principal storage chamber** where food accumulates after passing through the cardia [2]. *Fundus* - The **fundus** is the dome-shaped upper part of the stomach, located superior to the cardia. - While it can temporarily hold food and gas, it is **not the primary storage site** [2]. - Its main role is to serve as a **pressure buffer** and accumulation site for gases during digestion [2]. *Antrum* - The **antrum** is the lower, narrower part of the stomach, located before the pylorus. - It plays a crucial role in **mixing and grinding food with gastric juices** and propelling chyme towards the pylorus [1], [2]. - This is the **grinding chamber**, not a storage area [2]. *Pylorus* - The **pylorus** is the opening that connects the stomach to the duodenum, controlled by the pyloric sphincter. - Its main function is to **regulate the emptying of chyme** into the small intestine, not to store food [3].

Q: How many phases are there in the action potential of cardiac muscles?

5 phases. ***5 phases*** - The cardiac myocyte action potential is classically described in **five phases** (phases 0, 1, 2, 3, and 4), which encompass depolarization, repolarization, and the resting state. - Each phase is characterized by specific ion channel activities leading to distinct electrical changes essential for proper cardiac function. *2 phases* - Action potentials in nerve cells typically follow a simpler two-phase model: **depolarization** and **repolarization**. - This model does not account for the additional plateau and resting phases characteristic of cardiac muscle cells. *3 phases* - Some simplified models might describe three phases (depolarization, repolarization, and a resting phase), but this still **omits specific nuances** of cardiac repolarization and the sustained plateau phase. - This simplification leaves out the early repolarization and the critical plateau phase (phase 2), which is vital for the prolonged contraction of the heart. *4 phases* - While some sources might refer to four phases, they typically combine certain repolarization steps or omit the distinct early repolarization phase. - This description would likely miss the **early, rapid repolarization phase (phase 1)**, understating the complex ion movements.

Q: Which hormone is primarily responsible for maintaining the luteal phase of the menstrual cycle?

Progesterone. ***Progesterone*** - **Progesterone**, secreted by the **corpus luteum** after ovulation, is crucial for maintaining the luteal phase by preparing the **endometrium** for implantation. - It causes the endometrial lining to thicken and become more vascularized, creating a suitable environment for a fertilized egg. *Estrogen* - While **estrogen** is important throughout the menstrual cycle for endometrial proliferation, its primary role is in the **follicular phase**, not the maintenance of the luteal phase. - Estrogen levels are higher during the follicular phase, promoting the growth of the dominant follicle. *Follicle-stimulating hormone (FSH)* - **FSH** is primarily responsible for stimulating the growth and development of **ovarian follicles** during the follicular phase. - Its levels decrease significantly after ovulation, and it does not play a direct role in maintaining the luteal phase. *Luteinizing hormone (LH)* - **LH** triggers **ovulation** and the formation of the **corpus luteum** from the ruptured follicle. - While essential for initiating the luteal phase, its levels decline afterward, and it's not the primary hormone for *maintaining* the corpus luteum's function.

Q: What is the Haldane Effect?

CO2 delivery by increased O2. ***CO2 delivery by increased O2*** - The **Haldane effect** describes how **oxygenation of hemoglobin** decreases its affinity for **carbon dioxide (CO2)**, leading to the release of CO2 from the blood. - This is crucial in the lungs, where high oxygen levels promote CO2 unloading for exhalation. *O2 delivery by increased CO2* - This describes the **Bohr effect**, where an increase in **carbon dioxide (CO2)** or acidity in the tissues causes hemoglobin to release **oxygen (O2)**. - The Haldane effect is the converse, relating oxygen binding to CO2 release, not the other way around. *CO2 delivery by increased CO2* - This statement is inherently circular and does not describe a physiological effect. - It confuses the mechanism with the substance being transported. *O2 delivery by increased CO* - **Carbon monoxide (CO)** has a much higher affinity for hemoglobin than oxygen, forming **carboxyhemoglobin** and impairing oxygen delivery. - This is related to **carbon monoxide poisoning**, not a physiological regulatory effect like the Haldane or Bohr effects.

Q: Which protein primarily contributes to oncotic pressure in the blood?

Albumin. ***Albumin*** - **Albumin** is the most abundant plasma protein and its small size and high concentration make it the primary determinant of **oncotic pressure** in the blood. - Its presence in the capillaries draws water from the **interstitial space** back into the blood vessels, maintaining **fluid balance** and blood volume. *Fibrinogen* - **Fibrinogen** is a crucial protein involved in **blood clotting**, where it is converted into **fibrin** to form a clot. - While a plasma protein, its contribution to **oncotic pressure** is minor compared to albumin, as it's less abundant and larger in size. *Globulins* - **Globulins** are a diverse group of proteins involved in immune function (**immunoglobulins**), transport (e.g., **alpha** and **beta globulins**), and clotting. - While they contribute to total plasma protein concentration, their collective impact on **oncotic pressure** is secondary to that of albumin due to lower concentrations and varied molecular weights. *Transferrin* - **Transferrin** is a specific **beta-globulin** that plays a vital role in **iron transport** in the blood. - Its primary function is not related to **oncotic pressure**, and its concentration is significantly lower than albumin.

Q: Tetany in muscle occurs in spite of normal serum Ca2+ level. Which ion is responsible?

Ionized Ca2+. ***Ionized Ca2+*** - While total serum calcium might be normal, **tetany** is specifically caused by a decrease in the concentration of **ionized (free) calcium** in the extracellular fluid. - Ionized calcium is the physiologically active form of calcium responsible for neuromuscular excitability. *Mg2+* - **Hypomagnesemia** can exacerbate hypocalcemia and contribute to tetany, but it is not the primary ion directly responsible for tetany when **total serum calcium is normal**. - A deficiency in Mg2+ can impair the release of **parathyroid hormone** and reduce target organ responsiveness to PTH. *K+* - Abnormalities in **potassium levels** (hypokalemia or hyperkalemia) primarily affect cardiac and muscular excitability, leading to arrhythmias or muscle weakness/paralysis. - While electrolyte imbalances are interconnected, changes in potassium are not the direct cause of tetany due to calcium's role. *Na+* - **Sodium ions** are crucial for nerve impulse transmission and muscle contraction by establishing the resting membrane potential and initiating action potentials. - However, direct changes in sodium concentration do not typically cause tetany; rather, they can lead to neurological symptoms like seizures (hyponatremia) or altered mental status (hypernatremia).

Q: What is the composition of epithelial sodium channels?

1α, 1β, 1γ. ***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.

Q: Which of the following is not a component of a mature sperm cell?

Endoplasmic reticulum. ***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.

Q: What is Proaccelerin?

Factor V. ***Factor V*** - **Factor V**, also known as **proaccelerin** or **labile factor**, is a **plasma protein** that plays a crucial role in the coagulation cascade. - It is activated by thrombin to **Factor Va**, which then combines with Factor Xa, calcium, and phospholipid to form the **prothrombinase complex**, significantly enhancing thrombin generation. *Factor II* - **Factor II** is **prothrombin**, a precursor to **thrombin**, which is central to coagulation. - It is not referred to as preaccelerin. *Factor VII* - **Factor VII** is primarily involved in the **extrinsic pathway** of coagulation, becoming activated to Factor VIIa upon contact with tissue factor. - It works to activate Factor IX and Factor X, but it is not preaccelerin. *Factor X* - **Factor X**, also known as **Stuart-Prower factor**, is a key enzyme in the **common pathway** of coagulation, converting prothrombin to thrombin. - It is distinct from Factor V, which acts as a cofactor.

Question 1

What is the average size of platelets in micrometers?

Accepted Answer

2-3 µm

Answer

4-5 µm

Answer

3-4 µm

Answer

1-2 µm

Question 2

Which part of the stomach is primarily responsible for receiving and storing ingested food?

Accepted Answer

Body

Answer

Antrum

Answer

Pylorus

Answer

Fundus

Question 3

How many phases are there in the action potential of cardiac muscles?

Accepted Answer

5 phases

Answer

2 phases

Answer

3 phases

Answer

4 phases

Question 4

Which hormone is primarily responsible for maintaining the luteal phase of the menstrual cycle?

Accepted Answer

Progesterone

Answer

Estrogen

Answer

Follicle-stimulating hormone (FSH)

Answer

Luteinizing hormone (LH)

Question 5

What is the Haldane Effect?

Accepted Answer

CO2 delivery by increased O2

Answer

O2 delivery by increased CO2

Answer

CO2 delivery by increased CO2

Answer

O2 delivery by increased CO

Question 6

Which protein primarily contributes to oncotic pressure in the blood?

Accepted Answer

Albumin

Answer

Globulins

Answer

Fibrinogen

Answer

Transferrin

Question 7

Tetany in muscle occurs in spite of normal serum Ca2+ level. Which ion is responsible?

Accepted Answer

Ionized Ca2+

Answer

Mg2+

Answer

K+

Answer

Na+

Question 8

What is the composition of epithelial sodium channels?

Accepted Answer

1α, 1β, 1γ

Answer

2α, 1β, 1γ

Answer

2α, 1β

Answer

2α, 1β, 2γ

Question 9

Which of the following is not a component of a mature sperm cell?

Accepted Answer

Endoplasmic reticulum

Answer

Lysosome

Answer

Golgi apparatus

Answer

Mitochondria

Question 10

What is Proaccelerin?

Accepted Answer

Factor V

Answer

Factor VII

Answer

Factor II

Answer

Factor X

NEET-PG 2015 — Physiology