NEET-PG 2018 Practice Questions

Q: Which of the following has maximum smooth muscle as compared to wall thickness?

A. ***A*** - Structure A represents a **terminal bronchiole**, which has the **maximum proportion of smooth muscle relative to wall thickness** among all respiratory structures. - Terminal bronchioles lack cartilage and respiratory epithelium (no alveoli), making smooth muscle the dominant structural component of their walls, comprising a high percentage of the total wall thickness. - This abundant smooth muscle allows for precise control of **bronchoconstriction** and **bronchodilation**, which is crucial for regulating air distribution to the respiratory zones. *B* - Structure B appears to be a **respiratory bronchiole** or an **alveolar duct**, which is more distal than terminal bronchioles and has less smooth muscle relative to its wall thickness. - As airways progress distally from terminal bronchioles toward the alveoli, smooth muscle gradually decreases as the primary function shifts from conduction and airflow regulation to gas exchange. - Respiratory bronchioles have alveoli budding from their walls, which reduces the proportion of smooth muscle in the overall wall structure. *C* - Structure C points to an **alveolar sac**, which is composed primarily of **alveoli** clustered together. Alveolar walls are extremely thin to facilitate efficient gas exchange and contain very little to no smooth muscle. - The function of alveoli is gas exchange, not airflow regulation, hence they lack the contractile elements like smooth muscle that are abundant in conducting airways. *D* - Structure D points to an **individual alveolus**, which is the primary site of gas exchange. Alveolar walls are extremely thin and consist of type I pneumocytes (for gas exchange), type II pneumocytes (surfactant production), and alveolar macrophages. - **Alveoli** lack smooth muscle entirely, as their structure is optimized for diffusion and not for active constriction or dilation.

Q: The image shows the world's fastest athlete. Which of the following is used by his muscles for meeting energy demands to create world records in seconds?

Phosphocreatine. ***Phosphocreatine*** - **Phosphocreatine** is a high-energy phosphate compound stored in muscle cells, providing the most rapid source of ATP regeneration for short, intense bursts of activity lasting seconds. - During explosive activities like sprinting (0-10 seconds), the enzyme **creatine kinase** rapidly transfers a phosphate group from phosphocreatine to ADP, re-synthesizing ATP almost instantaneously. - This **phosphagen system** (ATP-PC system) is the primary energy source for world-record sprints, allowing for maximal power output before glycolysis can ramp up. *Phosphofructokinase* - **Phosphofructokinase (PFK)** is a key regulatory enzyme in glycolysis, not an energy substrate itself. - While glycolysis provides ATP for sustained high-intensity exercise (10 seconds to 2 minutes), it is significantly slower than the phosphocreatine system. - PFK catalyzes the rate-limiting step of glycolysis but does not directly provide the immediate energy for explosive movements in seconds. *Glucose 1-phosphate* - **Glucose 1-phosphate** is an intermediate in glycogenolysis (glycogen breakdown) and glycogen synthesis. - It must be converted to glucose 6-phosphate and then proceed through glycolysis to generate ATP, which takes longer than direct phosphocreatine utilization. - This pathway supports energy production but is not the immediate source for explosive power in seconds. *Creatine phosphokinase* - **Creatine phosphokinase (CPK)** or **creatine kinase (CK)** is the enzyme that catalyzes the transfer of phosphate from phosphocreatine to ADP. - While essential for the process, it is the enzyme facilitator, not the energy substrate itself. - The question asks what is "used" for energy, which refers to the substrate (phosphocreatine), not the enzyme.

Q: Which of the following is not a component of the process shown in the image?

Actin. ***Actin*** - The image depicts **microtubule-based transport** involving motor proteins (dynein and kinesin) moving cargo along microtubules. - **Actin filaments** are a completely separate cytoskeletal system and are NOT components of the microtubule-based process shown. - This is the most fundamental distinction - actin vs. microtubule cytoskeletal systems. *Dynein* - **Dynein** is clearly shown in the image, transporting **retrograde cargo** toward the minus end of the microtubule. - It is a key motor protein for minus-end directed movement along microtubules. *Kinesin* - **Kinesin** is depicted in the image, transporting **anterograde cargo** toward the plus end of the microtubule. - It is the primary motor protein for plus-end directed movement along microtubules. *Myosin* - While **myosin** typically works with actin filaments rather than microtubules, it belongs to the same functional category as dynein and kinesin (motor proteins). - Some myosin isoforms can even associate with microtubule-based processes in specific contexts. - **Actin** is the better answer as it represents a completely different cytoskeletal system, whereas myosin is still a motor protein like the others listed.

Q: Which of these is true about the highlighted transporter?

One molecule goes in, other molecule goes out. ***One molecule goes in, other molecule goes out*** - The highlighted transporter is the **Na+/K+ ATPase**, which actively pumps 3 **Na+ ions out** of the cell and 2 **K+ ions into** the cell, maintaining an electrochemical gradient. - This counter-transport (one molecule type going in and another going out) is characteristic of an **antiporter** pump. *Both molecules go in* - This option would describe a **symporter** mechanism where two different molecules move in the **same direction** across the membrane. - The Na+/K+ ATPase explicitly shows Na+ moving out and K+ moving in, which contradicts simultaneous inward movement. *Both molecules go out* - This would mean two molecules are expelled from the cell. The Na+/K+ ATPase, however, has K+ entering the cell. - While Na+ is pumped out by this transporter, K+ is actively transported inward. *One molecule goes in and two exit* - The Na+/K+ ATPase transports three Na+ ions out of the cell and two K+ ions into the cell, which is a 3:2 ratio and not one in and two out. - This option incorrectly describes the stoichiometry and directionality of ions for the Na+/K+ ATPase.

Q: The following marked recordings in GIT are produced by:

Interstitial cells of Cajal. ***Interstitial cells of Cajal*** - The image displays characteristic **slow waves** (also known as basal electrical rhythm) and superimposed **spike potentials** in the gastrointestinal tract, which are generated by the interstitial cells of Cajal (ICCs). - ICCs act as **pacemaker cells** in the GI tract, initiating the bioelectrical activity that dictates the rhythm of smooth muscle contractions. *Smooth muscle* - While GI smooth muscle cells contract in response to these electrical activities, they **do not generate the slow waves or spike potentials** themselves. - Smooth muscle cells are responsible for **muscle tension**, as shown in the lower tracing, which is directly triggered by the spike potentials. *Myenteric plexus* - The myenteric plexus primarily consists of **neurons** that regulate GI motility and secretions, influencing the activity of smooth muscle cells and ICCs. - It does not directly produce the characteristic slow waves or spike potentials observed as the intrinsic electrical rhythm. *Parasympathetic stimulation* - Parasympathetic stimulation, primarily via the **vagus nerve**, generally **increases the frequency and amplitude** of slow waves and spike potentials. - However, it modulates the activity rather than initiating the intrinsic electrical rhythm itself.

Q: Compare the two ECG recordings taken before and after activation of low pressure atrial stretch receptors. Which reflex explains the findings?

Bainbridge reflex. ***Bainbridge reflex*** - The Bainbridge reflex, also known as the **atrial reflex**, is an increase in heart rate due to an increase in **central venous pressure**, which activates stretch receptors in the atria. - Activation of these low-pressure receptors signals the medulla to **increase sympathetic stimulation** to the heart, resulting in tachycardia, which is reflected in a faster heart rate on the ECG. *Frank Starling Law* - The Frank-Starling law of the heart describes the relationship between **end-diastolic volume** and the force of contraction. - It states that an increase in venous return stretches the ventricular myocardium, leading to a more forceful ventricular contraction, not primarily affecting heart rate. *Bezold Jarisch Reflex* - This reflex is characterized by a triad of **bradycardia, hypotension, and coronary vasodilation**. - It is triggered by ventricular mechanoreceptors, usually in response to **decreased ventricular filling** or myocardial ischemia. *Vasovagal reflex* - The vasovagal reflex is a common cause of **syncope**, characterized by **bradycardia** and **vasodilation**, leading to a drop in blood pressure. - It is often triggered by emotional stress, pain, or prolonged standing, and results in a **slowing of the heart rate**, not an increase.

Question 1

Which of the following has maximum smooth muscle as compared to wall thickness?

Accepted Answer

A

Answer

B

Answer

C

Answer

D

Question 2

What is correct about the vitamin shown below?

Accepted Answer

γ-carboxylation of glutamic acid residues to clotting factor 2,7, 9 and 10

Answer

γ-carboxylation of glycine residues to clotting factor 2,7, 9 and 10

Answer

γ-carboxylation of glutathione residues to clotting factor 2,7, 9 and 10

Answer

γ-carboxylation of aspartic acid residues to clotting factor 2,7, 9 and 10

Question 3

The image shows the world's fastest athlete. Which of the following is used by his muscles for meeting energy demands to create world records in seconds?

Accepted Answer

Phosphocreatine

Answer

Phosphofructokinase

Answer

Glucose 1-phosphate

Answer

Creatine phosphokinase

Question 4

Which of the following is not a component of the process shown in the image?

Accepted Answer

Actin

Answer

Dynein

Answer

Kinesin

Answer

Myosin

Question 5

Which of these is true about the highlighted transporter?

Accepted Answer

One molecule goes in, other molecule goes out

Answer

Both molecules go in

Answer

Both molecules go out

Answer

One molecule goes in and two exit

Question 6

The following marked recordings in GIT are produced by:

Accepted Answer

Interstitial cells of Cajal

Answer

Smooth muscle

Answer

Myenteric plexus

Answer

Parasympathetic stimulation

Question 7

Compare the two ECG recordings taken before and after activation of low pressure atrial stretch receptors. Which reflex explains the findings?

Accepted Answer

Bainbridge reflex

Answer

Frank Starling Law

Answer

Bezold Jarisch Reflex

Answer

Vasovagal reflex

NEET-PG 2018

Anatomy

Biochemistry

Physiology