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Body Fluids and Circulation - Regulation of cardiac activity

Grade 11CBSEBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The human heart is 'myogenic', meaning the normal activities of the heart are regulated intrinsically by specialized muscles (nodal tissue) without direct external stimulation.

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The Medulla Oblongata in the brain contains a special neural center that moderates cardiac function through the Autonomic Nervous System (ANSANS).

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Sympathetic nerves (part of ANSANS) can increase the heart rate, the strength of ventricular contraction, and thereby the cardiac output (COCO) by releasing norepinephrine.

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Parasympathetic neural signals (another component of ANSANS, primarily via the Vagus nerve) decrease the rate of heartbeat, the speed of conduction of action potentials, and consequently the cardiac output.

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Adrenal medullary hormones, such as Adrenaline (Epinephrine) and Noradrenaline (Norepinephrine), are secreted during emergency situations to increase cardiac output.

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The concentration of ions like Ca2+Ca^{2+}, Na+Na^{+}, and K+K^{+} in the blood also plays a crucial role in regulating the heart's electrical activity and contractility.

📐Formulae

Cardiac Output (CO)=Heart Rate (HR)×Stroke Volume (SV)Cardiac\ Output\ (CO) = Heart\ Rate\ (HR) \times Stroke\ Volume\ (SV)

Stroke Volume (SV)=End Diastolic Volume (EDV)−End Systolic Volume (ESV)Stroke\ Volume\ (SV) = End\ Diastolic\ Volume\ (EDV) - End\ Systolic\ Volume\ (ESV)

💡Examples

Problem 1:

During a 'fight or flight' response, how does the body rapidly increase the supply of oxygenated blood to the muscles?

Solution:

The body activates the Sympathetic Nervous System (SNSSNS) and triggers the release of Adrenaline from the adrenal medulla. This leads to an increase in HRHR and SVSV, resulting in an elevated COCO.

Explanation:

The Sympathetic nerves increase the rate of depolarization of the SASA node. Adrenaline further enhances the force of contraction of the ventricles, ensuring more blood is pumped per minute (calculated as CO=HR×SVCO = HR \times SV).

Problem 2:

Calculate the Cardiac Output (COCO) of an individual if their heart beats 7575 times per minute and the amount of blood pumped by each ventricle during a cardiac cycle is 70 mL70\ mL.

Solution:

CO=75×70=5250 mLCO = 75 \times 70 = 5250\ mL or 5.25 L5.25\ L.

Explanation:

The formula for Cardiac Output is CO=HR×SVCO = HR \times SV. Given HR=75 beats/minHR = 75\ beats/min and SV=70 mL/beatSV = 70\ mL/beat, the product gives the total volume of blood pumped by the heart per minute.

Regulation of cardiac activity - Revision Notes & Key Diagrams | CBSE Class 11 Biology