INI-CET 2024 — Physiology

Q: Sarcomere is the area between which two Z lines?

Two adjacent Z lines. ***Two adjacent Z lines*** - A **sarcomere** is defined as the fundamental contractile unit of muscle, extending from one **Z line** to the next. - The **Z lines** anchor the **actin (thin) filaments**, and their proximity helps delineate the functional sarcomere unit. *Two consecutive I bands* - The **I band** contains only **thin (actin) filaments** and is bisected by a Z line. It is not a boundary that defines a sarcomere. - A sarcomere encompasses parts of two I bands, plus an A band in the middle. *A band and I band* - The **A band** contains **thick (myosin) filaments** and overlapping thin filaments, while the **I band** contains only thin filaments. - These bands are components within a sarcomere, not boundaries that define its extent. *Two H zones* - The **H zone** is a region within the A band that contains only **thick (myosin) filaments** and is visible in relaxed muscle. - It is located in the center of the A band and does not serve as a boundary for the entire sarcomere. [Practice more Physiology PYQs on OnCourse]

Q: The interpretation of the following ABG value is: pH = 7.5, pCO2 = 50 mm Hg, HCO3 = 30 mEq/L

Metabolic alkalosis. ***Metabolic alkalosis (partially compensated)*** - The **pH of 7.5** indicates **alkalosis**, and the elevated **bicarbonate (HCO3) of 30 mEq/L** is the primary driver of this high pH. - The elevated **pCO2 of 50 mm Hg** represents **partial respiratory compensation**, where the body retains CO2 to lower the pH toward normal. - Since the pH remains elevated (not normalized to 7.35-7.45), this is **partially compensated** rather than fully compensated. *Respiratory acidosis* - This would be characterized by a **low pH** and an **elevated pCO2**, which is not seen here as the pH is high. - Although pCO2 is elevated, the **high pH** and **high bicarbonate** rule out primary respiratory acidosis. *Metabolic acidosis* - This would present with a **low pH** and a **low bicarbonate** concentration. - The given values show a **high pH** and **high bicarbonate**, which is the opposite of metabolic acidosis. *Normal acid-base balance* - A normal acid-base balance would have a **pH between 7.35-7.45**, a **pCO2 between 35-45 mm Hg**, and an **HCO3 between 22-26 mEq/L**. - All three values are outside of their normal ranges, indicating an acid-base disturbance. [Practice more Physiology PYQs on OnCourse]

Q: Which of the following statements about cardiac muscle is incorrect?

Cardiac muscle has a short refractory period.. ***Cardiac muscle has a short refractory period.*** - This statement is **incorrect** because cardiac muscle has a **long refractory period** (~250 ms), which prevents summation and tetanus by ensuring that the muscle relaxes completely before another action potential can be initiated. - The long refractory period is crucial for maintaining the heart's **pumping efficiency** and preventing arrhythmias. *Cardiac muscle obeys the all or none law.* - This statement is **correct**. Individual **cardiac muscle cells** obey the **all-or-none law**; when a stimulus reaches threshold, the cell contracts fully. - The heart as a whole organ can grade its contraction force through recruitment of more fibers and the Frank-Starling mechanism, but at the cellular level, the all-or-none principle applies. *Cardiac muscle exhibits the Frank-Starling mechanism* - This statement is **correct**. The **Frank-Starling mechanism** describes the heart's ability to increase its force of contraction and stroke volume in response to an increase in **venous return** or end-diastolic volume. - This intrinsic regulatory mechanism allows the heart to match its output to the venous return, optimizing cardiac efficiency. *Cardiac muscle has automaticity and rhythmicity* - This statement is **correct**. **Automaticity** refers to the ability of specialized cardiac cells (e.g., in the sinoatrial node) to spontaneously generate action potentials without external nervous stimulation. - **Rhythmicity** is the regular, cyclical discharge of these action potentials, which drives the rhythmic beating of the heart. [Practice more Physiology PYQs on OnCourse]

Q: Erythropoietin is secreted by which of the following organs?

Kidney. ***Kidney*** - The **kidneys** are the primary site of erythropoietin production in adults, particularly the **peritubular interstitial cells**. - Erythropoietin's main function is to stimulate **red blood cell production** in the bone marrow in response to hypoxia. *Muscle* - Muscles are involved in movement and metabolism but do not produce **erythropoietin**. - They primarily store glycogen and generate force through contraction. *Liver* - The liver produces erythropoietin during **fetal development** but contributes minimally to its production in adulthood. - Its main functions include metabolism, detoxification, and protein synthesis. *Heart* - The heart is responsible for **pumping blood** throughout the body and does not produce **erythropoietin**. - It primarily consists of cardiac muscle tissue. [Practice more Physiology PYQs on OnCourse]

Q: Which of the following neurotransmitters is primarily released from the sympathetic nervous system to increase heart rate in response to a DECREASE in blood pressure?

Norepinephrine. ***Norepinephrine*** - **Norepinephrine** is the primary neurotransmitter released by **postganglionic sympathetic neurons** directly onto the heart to increase heart rate and contractility in response to a drop in blood pressure. - It acts on **beta-1 adrenergic receptors** in the sinoatrial (SA) node, atria, and ventricles, leading to increased chronotropy (heart rate) and inotropy (contractility). *Dopamine* - While **dopamine** can have cardiovascular effects, particularly at high doses, it is not the primary neurotransmitter released by the sympathetic nervous system for direct heart rate regulation. - Dopamine is a precursor to norepinephrine and epinephrine, but its main physiological roles involve **renal blood flow regulation** and central nervous system functions. *Acetylcholine* - **Acetylcholine** is the primary neurotransmitter of the **parasympathetic nervous system**, which generally acts to **decrease heart rate** (bradycardia) through muscarinic receptors. - It is also released by **preganglionic sympathetic fibers**, but these do not directly innervate the heart to produce the desired effect of increasing heart rate. *Epinephrine* - **Epinephrine** (adrenaline) is primarily a **hormone** released from the **adrenal medulla** into the bloodstream, not directly from postganglionic sympathetic nerve terminals to the heart. - Although it has strong effects on beta-1 receptors in the heart, its release is more generalized and slower than the direct neuronal release of norepinephrine. [Practice more Physiology PYQs on OnCourse]

7 Previous Year Questions with Answers & Explanations

Questions

Sarcomere is the area between which two Z lines?

The interpretation of the following ABG value is: pH = 7.5, pCO2 = 50 mm Hg, HCO3 = 30 mEq/L

Which of the following statements about cardiac muscle is incorrect?

Erythropoietin is secreted by which of the following organs?

Which of the following neurotransmitters is primarily released from the sympathetic nervous system to increase heart rate in response to a DECREASE in blood pressure?

Spinal sensory nucleus of the trigeminal has 2nd order neurons to carry which sensation?

All of the following are true about the adrenal gland EXCEPT:

INI-CET 2024 - Physiology INI-CET Practice Questions and MCQs

Question 1: Sarcomere is the area between which two Z lines?

A. Two adjacent Z lines (Correct Answer)
B. A band and I band
C. Two H zones
D. Two consecutive I bands

Explanation: ***Two adjacent Z lines*** - A **sarcomere** is defined as the fundamental contractile unit of muscle, extending from one **Z line** to the next. - The **Z lines** anchor the **actin (thin) filaments**, and their proximity helps delineate the functional sarcomere unit. *Two consecutive I bands* - The **I band** contains only **thin (actin) filaments** and is bisected by a Z line. It is not a boundary that defines a sarcomere. - A sarcomere encompasses parts of two I bands, plus an A band in the middle. *A band and I band* - The **A band** contains **thick (myosin) filaments** and overlapping thin filaments, while the **I band** contains only thin filaments. - These bands are components within a sarcomere, not boundaries that define its extent. *Two H zones* - The **H zone** is a region within the A band that contains only **thick (myosin) filaments** and is visible in relaxed muscle. - It is located in the center of the A band and does not serve as a boundary for the entire sarcomere.

Question 2: The interpretation of the following ABG value is: pH = 7.5, pCO2 = 50 mm Hg, HCO3 = 30 mEq/L

A. Respiratory acidosis
B. Metabolic acidosis
C. Metabolic alkalosis (Correct Answer)
D. Normal acid-base balance

Explanation: ***Metabolic alkalosis (partially compensated)*** - The **pH of 7.5** indicates **alkalosis**, and the elevated **bicarbonate (HCO3) of 30 mEq/L** is the primary driver of this high pH. - The elevated **pCO2 of 50 mm Hg** represents **partial respiratory compensation**, where the body retains CO2 to lower the pH toward normal. - Since the pH remains elevated (not normalized to 7.35-7.45), this is **partially compensated** rather than fully compensated. *Respiratory acidosis* - This would be characterized by a **low pH** and an **elevated pCO2**, which is not seen here as the pH is high. - Although pCO2 is elevated, the **high pH** and **high bicarbonate** rule out primary respiratory acidosis. *Metabolic acidosis* - This would present with a **low pH** and a **low bicarbonate** concentration. - The given values show a **high pH** and **high bicarbonate**, which is the opposite of metabolic acidosis. *Normal acid-base balance* - A normal acid-base balance would have a **pH between 7.35-7.45**, a **pCO2 between 35-45 mm Hg**, and an **HCO3 between 22-26 mEq/L**. - All three values are outside of their normal ranges, indicating an acid-base disturbance.

Question 3: Which of the following statements about cardiac muscle is incorrect?

A. Cardiac muscle has a short refractory period. (Correct Answer)
B. Cardiac muscle obeys the all or none law.
C. Cardiac muscle exhibits the Frank-Starling mechanism
D. Cardiac muscle has automaticity and rhythmicity

Explanation: ***Cardiac muscle has a short refractory period.*** - This statement is **incorrect** because cardiac muscle has a **long refractory period** (~250 ms), which prevents summation and tetanus by ensuring that the muscle relaxes completely before another action potential can be initiated. - The long refractory period is crucial for maintaining the heart's **pumping efficiency** and preventing arrhythmias. *Cardiac muscle obeys the all or none law.* - This statement is **correct**. Individual **cardiac muscle cells** obey the **all-or-none law**; when a stimulus reaches threshold, the cell contracts fully. - The heart as a whole organ can grade its contraction force through recruitment of more fibers and the Frank-Starling mechanism, but at the cellular level, the all-or-none principle applies. *Cardiac muscle exhibits the Frank-Starling mechanism* - This statement is **correct**. The **Frank-Starling mechanism** describes the heart's ability to increase its force of contraction and stroke volume in response to an increase in **venous return** or end-diastolic volume. - This intrinsic regulatory mechanism allows the heart to match its output to the venous return, optimizing cardiac efficiency. *Cardiac muscle has automaticity and rhythmicity* - This statement is **correct**. **Automaticity** refers to the ability of specialized cardiac cells (e.g., in the sinoatrial node) to spontaneously generate action potentials without external nervous stimulation. - **Rhythmicity** is the regular, cyclical discharge of these action potentials, which drives the rhythmic beating of the heart.

Question 4: Erythropoietin is secreted by which of the following organs?

A. Muscle
B. Kidney (Correct Answer)
C. Liver
D. Heart

Explanation: ***Kidney*** - The **kidneys** are the primary site of erythropoietin production in adults, particularly the **peritubular interstitial cells**. - Erythropoietin's main function is to stimulate **red blood cell production** in the bone marrow in response to hypoxia. *Muscle* - Muscles are involved in movement and metabolism but do not produce **erythropoietin**. - They primarily store glycogen and generate force through contraction. *Liver* - The liver produces erythropoietin during **fetal development** but contributes minimally to its production in adulthood. - Its main functions include metabolism, detoxification, and protein synthesis. *Heart* - The heart is responsible for **pumping blood** throughout the body and does not produce **erythropoietin**. - It primarily consists of cardiac muscle tissue.

Question 5: Which of the following neurotransmitters is primarily released from the sympathetic nervous system to increase heart rate in response to a DECREASE in blood pressure?

A. Norepinephrine (Correct Answer)
B. Dopamine
C. Acetylcholine
D. Epinephrine

Explanation: ***Norepinephrine*** - **Norepinephrine** is the primary neurotransmitter released by **postganglionic sympathetic neurons** directly onto the heart to increase heart rate and contractility in response to a drop in blood pressure. - It acts on **beta-1 adrenergic receptors** in the sinoatrial (SA) node, atria, and ventricles, leading to increased chronotropy (heart rate) and inotropy (contractility). *Dopamine* - While **dopamine** can have cardiovascular effects, particularly at high doses, it is not the primary neurotransmitter released by the sympathetic nervous system for direct heart rate regulation. - Dopamine is a precursor to norepinephrine and epinephrine, but its main physiological roles involve **renal blood flow regulation** and central nervous system functions. *Acetylcholine* - **Acetylcholine** is the primary neurotransmitter of the **parasympathetic nervous system**, which generally acts to **decrease heart rate** (bradycardia) through muscarinic receptors. - It is also released by **preganglionic sympathetic fibers**, but these do not directly innervate the heart to produce the desired effect of increasing heart rate. *Epinephrine* - **Epinephrine** (adrenaline) is primarily a **hormone** released from the **adrenal medulla** into the bloodstream, not directly from postganglionic sympathetic nerve terminals to the heart. - Although it has strong effects on beta-1 receptors in the heart, its release is more generalized and slower than the direct neuronal release of norepinephrine.

Question 6: Spinal sensory nucleus of the trigeminal has 2nd order neurons to carry which sensation?

A. Pain (Correct Answer)
B. Proprioception
C. Touch
D. Vibration

Explanation: ***Pain*** - The **spinal trigeminal nucleus** receives nociceptive (pain) and thermal sensations from the face - Its **second-order neurons** relay these signals to higher centers for pain perception - This is the primary function of the spinal (descending) trigeminal nucleus *Proprioception* - **Proprioception** from the face and masticatory muscles is primarily processed by the **mesencephalic trigeminal nucleus** - This nucleus contains the **first-order neurons** for proprioception, which is unique among sensory nuclei *Touch* - **Discriminative touch** and pressure sensations from the face are primarily processed by the **principal (chief) sensory trigeminal nucleus** - This nucleus is distinct from the spinal trigeminal nucleus *Vibration* - **Vibration** sense is a type of mechanoreception, falling under the broader category of discriminative touch - Like other fine touch sensations, it is primarily processed by the **principal sensory trigeminal nucleus**

Question 7: All of the following are true about the adrenal gland EXCEPT:

A. Zona fasciculata secretes cortisol
B. Medulla produces mineralocorticoids (Correct Answer)
C. Zona glomerulosa produces aldosterone
D. Zona reticularis secretes androgens

Explanation: ***Medulla produces mineralocorticoids*** - The **adrenal medulla** primarily produces **catecholamines** (epinephrine and norepinephrine), not mineralocorticoids. - **Mineralocorticoids** (like aldosterone) are secreted by the **zona glomerulosa** in the adrenal cortex. *Zona fasciculata secretes cortisol* - The **zona fasciculata** is the middle and largest layer of the adrenal cortex. - Its primary function is the secretion of **glucocorticoids**, mainly **cortisol**, which is crucial for stress response and metabolism. *Zona glomerulosa produces aldosterone* - The **zona glomerulosa** is the outermost layer of the adrenal cortex. - It is responsible for producing **mineralocorticoids**, with **aldosterone** being the most significant. *Zona reticularis secretes androgens* - The **zona reticularis** is the innermost layer of the adrenal cortex, adjacent to the medulla. - It primarily secretes **adrenal androgens** (like DHEA and androstenedione), which are precursors to sex hormones.