Cardiovascular System | Medical Science Optional Notes for UPSC PDF Download

Cardiovascular physiology Repeats

Q1: Define cardiac output. How can it be measured? Discuss the factors controlling it (1994).
Q2: What are the main factors which maintain and regulate venous return (2000)?
Q3: What is cardiac output? What are the factors affecting it (2003)?
Q4: Define cardiac output. What factors maintain it? What happens to it during exercise (2009)?
Q5: Enumerate the functions of cardiovascular system. What will happen if valves would not have been there? (2010) 
Q6: Define Blood Pressure. Enumerate the various factors affecting the blood pressure. How is the blood pressure regulated in the long term? (2011) 
Q7: What are the effects of exercise on cardiovascular system? What is the importance of exercise in maintaining the health of CVS? (2012) 
Q8: Define 'cardiac output' and 'cardiac index'. Describe the regulation of cardiac output in the body. (2015)
Q9: Describe baroreceptor reflex mechanism in the regulation of blood pressure. (2017) 
Q10: Define the " cardiac reserve". Explain how is its control governed? (2018)

Functions of cardiovascular system

The cardiovascular system consists of the heart, blood vessels, and blood.
This system has three main functions: 

• Transport of nutrients, oxygen, and hormones to cells throughout the body and removal of metabolic wastes (carbon dioxide, nitrogenous wastes). 
• Protection of the body by white blood cells, antibodies, and complement proteins that circulate* in the blood and defend the body against foreign microbes and toxins. Clotting mechanisms are also present that protect the body from blood loss after injuries. 
• Regulation of body temperature, fluid pH, and water content of cells.

Impact of Exercise on the Cardiovascular System

1. Blood Composition Changes

• Hypoxia-induced Erythropoiesis: Mild hypoxia during exercise stimulates the release of erythropoietin, triggering bone marrow to release red blood cells.
• CO2 Increase: Elevated carbon dioxide levels reduce blood pH.

2. Effects on Blood Volume

• Heat-induced Sweating: Exercise generates heat, activating the thermoregulatory system, leading to increased sweat secretion.
  • Fluid loss
  • Reduced blood volume
  • Hemoconcentration
  • Potential dehydration

3. Impact on Heart Rate

• Heart Rate Elevation:
  • Exercise and mental preparation stimulate heart rate increase.
  • Mechanisms involve cerebral cortex impulses, vagal tone reduction, and sympathetic activation.
  • Moderate exercise: Heart rate peaks at 180 beats/minute; severe exercise: 240 to 260 beats/minute.

4. Changes in Cardiac Output

• Cardiac Output Increase: Up to 20 L/minute in moderate exercise, 35 L/minute in severe exercise.
• Contributors to Output Increase:
  • Higher heart rate
  • Enhanced stroke volume due to vagal withdrawal and increased force of contraction.

5. Influence on Venous Return

• Venous Return Enhancement: Occurs through the muscle pump, respiratory pump, and splanchnic vasoconstriction.

6. Blood Flow to Skeletal Muscles

• Increased Blood Flow: Significant rise during exercise due to multiple factors, including sympathetic cholinergic activity.
• Factors Influencing Blood Flow:
  • Vasodilatation induced by sympathetic nerves
  • Hypercapnea, hypoxia, potassium ions, lactic acid, temperature rise, adrenaline, and increased sympathetic cholinergic activity.

7. Blood Pressure Dynamics

• Isotonic Exercise:
  • Systolic pressure increases; diastolic pressure remains unchanged.
• Isometric Exercise:
  • Both systolic and diastolic pressures increase due to heightened peripheral resistance.
• Post-Exercise Blood Pressure:
  • Falls below resting levels due to vasodilatation caused by accumulated metabolic end products.

Limitations on Maximal Exercise Abilities

• Cardiac Output Constraints: Maximal heart rate and stroke volume achieved.
• Oxygen Utilization: Muscles can extract up to 100%, but total blood oxygen utilization limited to 75%.
• Olympic Athlete Scenario: Even elite athletes reach maximum limitations on heart rate and stroke volume.

Energy stores for exercise

• Oxidative phosphorylation provides the most amount of energy; followed by anaerobic glycolysis and then reserved pool/store of high energy phosphates 
• However high energy phosphates have the highest rate of energy delivery (power); followed by anaerobic glycolysis then oxidative phosphorylation !

Switch from oxidative phosphorylation to glycolysis when high energy phosphate concentration falls to half of max value
(*note = oxidative phosphorylation and glycolysis provide energy in the form of high energy phosphates (ATP) and contribute to the pool of high energy phosphates)

Summary 

• Beginning of exercise (events are listed in order in which they occur) 
• mean circulatory pressure increases by contraction of muscle and abdomen that compress veins and vena cava → increase CO 
• autonomic mediated increase in mean circulatory pressure → increase CO
•  increase in ionotropic effect on myocardium → increase CO * 
• increase in HR → increase CO 
• decrease in peripheral resistance → increase CO