General Physiology Practice Questions

Q: What is the primary function of cyclic AMP (cAMP)?

Activation of protein kinase. **Explanation:** **1. Why Option B is Correct:** Cyclic AMP (cAMP) is a classic **second messenger** used in signal transduction. When a ligand (like Epinephrine or Glucagon) binds to a G-protein coupled receptor (GPCR), it activates the enzyme **Adenylyl Cyclase**, which converts ATP into cAMP. The primary and most direct function of cAMP is to bind to the regulatory subunits of **Protein Kinase A (PKA)**. This binding causes the release of active catalytic subunits, which then phosphorylate specific target proteins (enzymes or transcription factors), leading to the cellular physiological response. **2. Why Other Options are Incorrect:** * **Option A (Ion exchange):** While cAMP can indirectly influence ion channels (like HCN channels in the heart), it is not a primary ion exchanger. Ion exchange is typically handled by transmembrane proteins like the Na+/K+ ATPase or Na+/Ca2+ exchanger. * **Option C (Activation of Ryanodine receptors):** Ryanodine receptors (RyR) are primarily activated by **Calcium** (Calcium-induced calcium release) or by cyclic ADP-ribose, not cAMP. * **Option D (Release of acetylcholine):** The release of neurotransmitters like Acetylcholine at the neuromuscular junction is primarily triggered by **Calcium influx** through voltage-gated calcium channels, not by cAMP. **High-Yield Clinical Pearls for NEET-PG:** * **Phosphodiesterase (PDE):** This enzyme breaks down cAMP. Drugs like **Theophylline** and **Sildenafil** work by inhibiting PDE, thereby increasing cAMP/cGMP levels. * **Vibrio Cholerae:** Cholera toxin causes permanent activation of Gs alpha subunits, leading to overproduction of cAMP in intestinal cells, resulting in massive secretory diarrhea. * **Memory Tip:** Remember the "Hungry" hormones (Glucagon, Epinephrine) often use the cAMP pathway to mobilize energy.

Q: Centrioles are absent in which of the following organs?

Liver. **Explanation:** The correct answer is **Liver (Option A)**. **Understanding the Concept:** Centrioles are paired, barrel-shaped organelles located in the cytoplasm of animal cells near the nuclear envelope. They play a critical role in organizing the microtubule network and forming the mitotic spindle during cell division. In the human body, **mature hepatocytes (liver cells)** are unique because they are often considered to be in a "quiescent" or $G_0$ phase of the cell cycle. While they can regenerate, mature hepatocytes frequently lack functional centrioles or have them in a modified state, as they primarily rely on non-centrosomal microtubule organizing centers (MTOCs) for their cellular architecture. **Analysis of Options:** * **Liver (Correct):** Mature hepatocytes are the classic example cited in medical physiology where centrioles are absent or non-functional, reflecting their specialized regenerative and metabolic state. * **Spleen, Intestine, and Kidney (Incorrect):** These organs consist of cells that undergo regular or periodic mitosis. The intestinal epithelium, in particular, has a very high turnover rate. These cells require active centrioles to form mitotic spindles for successful cell division. **High-Yield NEET-PG Pearls:** * **Centriole Structure:** They consist of a "9+0" arrangement of microtubule triplets. * **Cilia/Flagella Connection:** Centrioles give rise to **basal bodies**, which are essential for the formation of cilia and flagella (which have a "9+2" arrangement). * **Other cells lacking centrioles:** Mature neurons (which do not divide) and mature red blood cells (which lack all organelles) are also notable examples. * **Function:** The primary role of the centriole is to serve as the core of the **Centrosome**, the main MTOC of the cell.

Question 1

Type I muscle fibers are rich in myosin heavy chain. What is their characteristic property?

Accepted Answer

Slow contracting, resistant to fatigue

Answer

Fast contracting, susceptible to fatigue

Answer

Slow contracting, susceptible to fatigue

Answer

Fast contracting, resistant to fatigue

Question 2

What is the primary function of cyclic AMP (cAMP)?

Accepted Answer

Activation of protein kinase

Answer

Ion exchange

Answer

Activation of Ryanodine receptors

Answer

Release of acetylcholine

Question 3

The number of muscle fibers innervated by a single motor axon is smallest in which of the following?

Accepted Answer

Orbicularis oculi

Answer

Gastrocnemius

Answer

Single unit smooth muscle

Answer

Soleus

Question 4

A disease that produces decreased inhibitory input to the internal segment of the globus pallidus should have what effect on the motor area of the cerebral cortex?

Accepted Answer

Decreased excitatory output from the thalamus to the cerebral cortex

Answer

Increased excitatory feedback directly to the cerebral cortex

Answer

No effect

Answer

Increased excitatory output from the putamen to the cerebral cortex

Question 5

Centrioles are absent in which of the following organs?

Accepted Answer

Liver

Answer

Spleen

Answer

Intestine

Answer

Kidney

General Physiology — MCQs

General Physiology — MCQs

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