CVS RESP Physiology Revision MCQ

Regarding properties of cardiac muscle cells

• it demonstrates stretch response

• it is connected by gap junctions

• it has the ability to change in response to workload

• its' contractile force can be modulated by hormones

• it has the ability to contract without external stimulation.

Regarding cardiac skeleton

• It provides structural support for the heart valves.

• It is made of contractile cells as to maintain the shape of the heart.

• It ensures a directed impulse of SA node, Purkinje fibres and Bundle of His.

• It allows electrical impulses to move freely between the atria and ventricles

• it prevents the heart from over-expanding during intense physical activity

Regarding action potential in cardiac muscle cells

• Phase 0 is caused by the rapid influx of calcium (Ca2+) ions.

• Phase 1 involve calcium influx; the slight efflux of potassium and a brief period of no significant ion movement.

• Phase 2 results in a sustained depolarization.

• The plateau phase is caused by sodium (Na+) ion influx

• Phase 3, potassium ions exit the cell, contributing to repolarization.

Regarding cardiac contractility

• sympathetic nervous system increases contractility

• The Frank-Starling law applies to the length of sarcomere

• Increased afterload results in a decrease force of contraction

• The Frank-Starling law applies to both (right and left) ventricles

• decreased preload results in a decreased stroke volume.

Regarding cardiac conducting system

• The SA node generates impulses at a faster rate than the AV Node.

• Purkinje fibers are responsible for conducting impulses to the atria.

• the AV node serves as a relay station, allowing the atria to contract before the ventricles.

• The bundle of His is responsible for directly stimulating the atria to contract.

• The electrical impulses in the cardiac conduction system move in a random manner.

A heart beat

• lasts 0.8 second when heart rate is 80/min.

• reflects one cardiac cycle.

• becomes more prolonged during emotional excitement.

• becomes stronger after a cup of a tea.

• decreases during inspiration.

Right ventricular stroke volume

• is less than that of the left ventricle.

• is equal to that of left ventricle.

• is about 5 liters.

• increases when myocardial beta-adrenergic receptors are stimulated.

• is decreased by Ca2+ channel blockers.

a 72-year-old lady with history of heart failure presented to ED with a 2-week history of bilateral lower limb edema. Which of the following BEST describes the underlying mechanism of edema formation in this patient?

• Increased hydrostatic pressure in capillaries due to imparied venous return.

• Decreased oncotic pressure in capillaries due to hypoalbuminaemia.

• Increased lymphatic drainage leading to reduced fluid reabsorption.

• Increased capillary permeability caused by inflammation or tissue injury.

• Increased renal retention of fluid and salt due to RAAS activation.

A 55-year-old man who is a smoker, complained of dyspnoea. He reported experiencing more difficulty in exhalation than inhalation. The underlying mechanism related to this includes

• the loss of lung elastic recoil leading to air trapping during expiration.

• increased airway resistance from bronchoconstriction and mucus hypersecretion.

• the destruction of airway causing dynamic airway compression.

• decreased residual volume due to reduced lung compliance.

• decreased expiratory muscle strength due to respiratory muscle fatigue.

Haldene effect in carbon monoxide poisoning causes

• impaired CO2 unloading in the lungs.

• enhanced CO2 transport by deoxygenated Hb.

• increased availability of Hb for CO2 binding.

• accumulation of CO2 in the blood.

• improved buffering of CO2 due to high carboxy-Hb levels.

Answer explanation

1. 1. CO prevent O2 from binding, hence reduced oxy-Hb to promote CO2 release.

2. 2. Haldene effect is blocked causes inability for CO2 unloading. It lead to CO2 accumulation giving hypercapnia and acidosis to patient.

3. 3. CO reduces amount of deoxygenated Hb, therefore reduce CO2 transport.

4. 4. Hb bound to CO cannot bind CO2, hence reduce CO2 carrying capacity.

5. 5. Carboxyhaemoglobin has no role in buffering CO2. It actually reduces CO2 buffering by displacing both O2 and CO2.