Acute responses

Question 1

What are extrinsic factors that contribute to an increase in heart rate?

Answer 1

• Increased sympathetic nervous system activity.
• Increased myocardial contractility.
• Increased concentration of catecholamines.

Question 2

What are the intrinsic factors that contribute to an increase in heart rate?

Answer 2

• Stretching of the sinoatrial node increased firing.
• Increased temperature speeds up the action potentials within the heart conduction system.

Question 3

Describe the acute responses experienced in the cardiac cycle.

Answer 3

• An increase in heart rate during exercise is achieved by a decreased diastolic phase.
• At higher heart rates there is a decreased systolic phase too.

Question 4

What are 3 acute responses that occur during exercise that impact venous return?

Answer 4

• Venocontriction.
• Muscle pump.
• Respiratory pump.

Question 5

What is venoconstriction as an acute response in venous return?

Answer 5

• Venous return is increased by decreasing the volume capacity by which veins can store blood.
• This occurs via a sympathetic reflex which contracts venous smooth muscle.

Question 6

What is a muscle pump as an acute response in venous return?

Answer 6

As muscles contract, they compress veins and push blood towards the heart.

Question 7

What is a respiratory pump as an acute response in venous return?

Answer 7

• Rhythmic pattern of breathing.
• And changes in the intrathoracic pressure.
• Provide a mechanical pump by which venous return is promoted.

Question 8

How is the acute response of an increase in blood flow to working muscles achieved?

Answer 8

• Increased cardiac output.
• Vasodilation in the working muscle.
• Diversion of blood to decrease blood flow to non-working muscles + organs.

Question 9

What are the determinants of blood flow to working muscles?

Answer 9

1. Arterial pressure.
2. Degree of blood vessel dilation.
3. Speed of removal of blood through the venous system.
4. Oxygen demand in the tissues.