NEET-PG 2018 - Physiology Practice Questions

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 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 2

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 3

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 — Physiology