General Physiology Practice Questions

Q: Tight junctions are seen in all except?

Cardiac muscle. **Explanation:** **Tight Junctions (Zonula Occludens)** are specialized intercellular connection sites that seal the space between adjacent epithelial cells, creating a selective barrier that regulates the paracellular transport of water and solutes. **Why Cardiac Muscle is the Correct Answer:** Cardiac muscle cells are connected by **Intercalated Discs**, which contain three types of junctions: **Gap junctions** (for electrical coupling/ionic flow), **Desmosomes** (Macula adherens), and **Fascia adherens** (anchoring sites for actin). Tight junctions are notably **absent** in cardiac muscle because these cells do not function as a barrier to fluid transport; instead, they require low-resistance electrical communication provided by gap junctions to function as a functional syncytium. **Analysis of Incorrect Options:** * **Renal Tubules:** Tight junctions are essential here to maintain the osmotic gradient and regulate the reabsorption of electrolytes (e.g., in the Proximal Convoluted Tubule and Collecting Ducts). * **Intestine:** The intestinal epithelium uses tight junctions to form the "mucosal barrier," preventing the uncontrolled passage of digestive enzymes and bacteria into the bloodstream. * **Choroid Plexus:** Tight junctions between the epithelial cells of the choroid plexus form the **Blood-CSF barrier**, strictly regulating the composition of cerebrospinal fluid. **High-Yield NEET-PG Pearls:** * **Gap Junctions (Nexus):** Found in the heart and smooth muscle; composed of proteins called **Connexins**. * **Blood-Brain Barrier:** Formed by tight junctions between **endothelial cells** of cerebral capillaries. * **Clinical Correlation:** Defects in tight junction proteins (like Claudins) are linked to conditions like **Hereditary Hypomagnesemia** and **Celiac Disease**.

Q: Basal metabolic rate is closely dependent on:

Lean body mass. **Explanation:** **Why Lean Body Mass (LBM) is the correct answer:** The Basal Metabolic Rate (BMR) is the energy expenditure required to maintain vital functions at rest. The primary determinant of BMR is the amount of metabolically active tissue in the body. **Lean Body Mass** (which includes skeletal muscle, organs, and bone, excluding fat) is significantly more metabolically active than adipose tissue. Muscle tissue, in particular, consumes more oxygen and energy even at rest. Therefore, LBM is the most accurate predictor of an individual's BMR. **Analysis of Incorrect Options:** * **Body Surface Area (BSA):** While BMR was historically calculated based on BSA (Rubner’s Law), BSA is a *proxy* measure. It correlates with BMR because larger surface areas generally imply larger bodies, but it does not account for body composition (muscle vs. fat). * **BMI (Body Mass Index):** BMI is a simple ratio of weight to height. It does not differentiate between fat mass and muscle mass; a bodybuilder and an obese individual may have the same BMI but will have vastly different BMRs. * **Height:** Height is a component used to estimate BMR in formulas (like Harris-Benedict), but it is not a direct physiological driver of metabolic activity. **High-Yield Clinical Pearls for NEET-PG:** * **Thyroid Status:** Thyroid hormone is the most important *hormonal* regulator of BMR. * **Gender Difference:** Males generally have a higher BMR than females primarily because they possess a higher percentage of **Lean Body Mass**. * **Age:** BMR is highest in infants (due to rapid growth) and declines with age as LBM decreases (sarcopenia). * **Specific Dynamic Action (SDA):** Proteins have the highest SDA (30%), meaning they increase metabolic rate the most during digestion.

Q: Which vitamin is required for the hydroxylation of proline?

Vitamin C. **Explanation:** **Vitamin C (Ascorbic Acid)** is the correct answer because it acts as a vital co-factor for the enzymes **prolyl hydroxylase** and **lysyl hydroxylase**. These enzymes are responsible for the post-translational hydroxylation of proline and lysine residues during **collagen synthesis**. The underlying biochemical mechanism involves keeping the iron cofactor of these enzymes in the reduced **ferrous (Fe²⁺) state**. Hydroxylation is essential for the formation of hydrogen bonds that stabilize the triple helix structure of collagen. Without Vitamin C, collagen fibers are unstable and lack tensile strength. **Incorrect Options:** * **Vitamin A:** Primarily involved in vision (rhodopsin formation), epithelial integrity, and gene transcription. * **Vitamin D:** Essential for calcium and phosphate homeostasis and bone mineralization. * **Vitamin K:** Acts as a co-factor for the gamma-carboxylation of glutamic acid residues in clotting factors (II, VII, IX, X) and proteins C and S. **Clinical Pearls for NEET-PG:** * **Scurvy:** Deficiency of Vitamin C leads to scurvy, characterized by "corkscrew hair," petechiae, easy bruising, and **bleeding gums** due to capillary fragility (weak collagen in vessel walls). * **Wound Healing:** Vitamin C is critical for the proliferative phase of wound healing; deficiency leads to poor wound tensile strength and dehiscence. * **Localization:** Collagen synthesis occurs in the **Rough Endoplasmic Reticulum (RER)** of fibroblasts. Hydroxylation is a post-translational modification that occurs within the RER lumen.

Q: Fast fatigable motor units are recruited?

Last. This question tests the understanding of the **Henneman Size Principle**, a fundamental concept in motor unit recruitment. ### **Explanation of the Correct Answer** According to the **Henneman Size Principle**, motor units are recruited in order of increasing size (specifically, the size of the alpha motor neuron cell body). * **Small motor units (Type I, Slow-twitch, Fatigue-resistant):** These have the lowest threshold for activation. They are recruited **first** for low-intensity tasks (e.g., maintaining posture). * **Large motor units (Type IIb/IIx, Fast-twitch, Fast-fatigable):** These have the highest threshold for activation. They are recruited **last** only when high force or explosive power is required. Because fast-fatigable units have large cell bodies and high thresholds, they are the final units to be activated as the force of contraction increases. ### **Analysis of Incorrect Options** * **A. First:** This describes **Type I (Slow)** motor units. They are small, have high oxidative capacity, and are recruited first to ensure smooth, controlled movement. * **C & D. During active phase/relaxation:** Recruitment is a function of the **force required** and the **threshold of the motor neuron**, not a specific temporal phase of a single muscle twitch. ### **NEET-PG High-Yield Pearls** * **Recruitment Order:** Type I (Slow) → Type IIa (Fast, fatigue-resistant) → Type IIb (Fast, fatigable). * **Size Principle Logic:** Small neurons have higher membrane resistance ($R$), so a smaller excitatory postsynaptic potential (EPSP) is needed to reach the threshold voltage ($V = I \times R$). * **Muscle Fiber Types:** * **Type I:** "Red" fibers (high myoglobin/mitochondria), oxidative metabolism. * **Type II:** "White" fibers (high glycogen), glycolytic metabolism.

Q: Cyclic GMP acts on which of the following?

Atrial natriuretic peptide. **Explanation:** The correct answer is **Atrial Natriuretic Peptide (ANP)**. **Mechanism of Action:** ANP and Brain Natriuretic Peptide (BNP) exert their effects by binding to membrane-bound **Guanylyl Cyclase (GC-A)** receptors. This binding activates the enzyme, which converts GTP into **cyclic GMP (cGMP)**. The elevated cGMP then activates **Protein Kinase G (PKG)**, leading to smooth muscle relaxation (vasodilation) and natriuresis. Nitric Oxide (NO) also uses cGMP but via soluble guanylyl cyclase. **Analysis of Incorrect Options:** * **Thyroxine (T4):** As a lipid-soluble thyroid hormone, it acts via **nuclear receptors** to alter gene transcription. It does not use second messengers like cGMP. * **Insulin:** Insulin acts through a **Tyrosine Kinase** receptor (enzyme-linked receptor). Binding triggers autophosphorylation of the receptor and activation of Insulin Receptor Substrates (IRS). * **Growth Hormone (GH):** GH utilizes the **JAK-STAT pathway** (Janus Kinase/Signal Transducer and Activator of Transcription). It is a cytokine-type receptor that lacks intrinsic enzymatic activity but recruits cytosolic kinases. **High-Yield NEET-PG Pearls:** * **cGMP Users:** Remember the mnemonic **"V-A-N"**: **V**asodilators (Nitric Oxide), **A**NP/BNP, and **N**ight vision (Phototransduction in rods/cones via PDE6). * **cAMP Users:** Most hormones (ACTH, Glucagon, TSH, PTH, ADH-V2). * **IP3/DAG Users:** "GOAT HAG" (GnRH, Oxytocin, ADH-V1, TRH, Histamine, Angiotensin II, Gastrin). * **Sildenafil (Viagra):** Acts by inhibiting Phosphodiesterase-5 (PDE-5), the enzyme that breaks down cGMP, thereby prolonging vasodilation.

Q: Which of the following is NOT an action of bradykinin?

Vasoconstriction. **Explanation:** Bradykinin is a potent endogenous nonapeptide and a key mediator of the kinin-kallikrein system. It acts primarily through B1 and B2 receptors to modulate vascular and inflammatory responses. **Why Vasoconstriction is the Correct Answer:** Bradykinin is one of the most potent endogenous **vasodilators**. It induces vasodilation by stimulating the release of nitric oxide (NO), prostacyclin ($PGI_2$), and endothelium-derived hyperpolarizing factor (EDHF) from vascular endothelial cells. Therefore, it causes a decrease in peripheral vascular resistance and blood pressure, rather than vasoconstriction. **Analysis of Incorrect Options:** * **Increased vascular permeability:** Bradykinin causes contraction of endothelial cells in post-capillary venules, leading to gap formation and leakage of plasma into the interstitium (edema). * **Chemoattractant:** Bradykinin acts as a chemical mediator that attracts leukocytes to the site of injury or inflammation, facilitating the immune response. * **Pain on injection:** Bradykinin is a potent algogenic substance. It directly stimulates nociceptors (sensory nerve endings) and sensitizes them to other stimuli, which is why its injection causes intense local pain. **High-Yield Clinical Pearls for NEET-PG:** * **ACE Inhibitors & Cough:** ACE (Angiotensin-Converting Enzyme) is responsible for the degradation of bradykinin. ACE inhibitors lead to bradykinin accumulation in the lungs, causing the classic side effect of a **dry cough** and, rarely, **angioedema**. * **Hereditary Angioedema:** This condition is caused by C1 esterase inhibitor deficiency, leading to overproduction of bradykinin, resulting in recurrent episodes of swelling. * **Triple Response of Lewis:** Bradykinin plays a role in the "flare" component of the triple response due to its vasodilatory properties.

Question 1

Tight junctions are seen in all except?

Accepted Answer

Cardiac muscle

Answer

Renal tubules

Answer

Intestine

Answer

Choroid plexus

Question 2

Basal metabolic rate is closely dependent on:

Accepted Answer

Lean body mass

Answer

Body Surface Area

Answer

BMI

Answer

Height

Question 3

What is true about Galvanic Skin Response?

Accepted Answer

It is an indicator of thermal sweating.

Answer

It is affected by sweating because sweat contains electrolytes.

Answer

It falls when sympathetic activity is high.

Answer

It falls in association with yogic practice.

Question 4

Which of the following is NOT an integral membrane protein?

Accepted Answer

Enzyme receptors

Answer

Na+/K+ ATPase pump

Answer

Insulin receptor

Answer

G-protein coupled receptors

Question 5

Which vitamin is required for the hydroxylation of proline?

Accepted Answer

Vitamin C

Answer

Vitamin A

Answer

Vitamin D

Answer

Vitamin K

Question 6

Fast fatigable motor units are recruited?

Accepted Answer

Last

Answer

First

Answer

During active phase of contraction

Answer

During relaxation

Question 7

Cyclic GMP acts on which of the following?

Accepted Answer

Atrial natriuretic peptide

Answer

Thyroxine

Answer

Insulin

Answer

Growth hormone

Question 8

Which of the following is NOT an action of bradykinin?

Accepted Answer

Vasoconstriction

Answer

Increased vascular permeability

Answer

Chemoattractant

Answer

Pain on injection

Question 9

With respect to oxygen and carbon dioxide transport in the blood, which of the following statements is correct?

Accepted Answer

The presence of oxygen lowers the carbon dioxide content in the blood.

Answer

The slopes of the oxygen and carbon dioxide dissociation curves are similar.

Answer

Equal amounts of oxygen and carbon dioxide can be carried in 100 mL of blood.

Answer

The presence of carbon dioxide increases the P50 for O2.

Question 10

According to Fick's law, which factor causes an increase in flux across a membrane?

Accepted Answer

Concentration gradient

Answer

Temperature

Answer

Increased size of molecule

Answer

Area of membrane

General Physiology — MCQs

General Physiology — MCQs

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