Regulation Of Cardiac Output

Question 1

Describe the process of calcium induced calcium release

Answer 1

1) a small amount of calcium enters the cardiac myocyte through calcium ion channels in the sarcolemma
- this small amount of calcium is known as trigger calcium
2) this calcium binds to ryanodine receptors on the sarcoplasmic reticulum
3) this causes stimulation of the sarcoplasmic reticulum which means calcium is realised from it

Question 2

What is the importance of calcium induced calcium release ?

Answer 2

• causes a large increase of calcium inside the cell
• this calcium is important for the coupling of actin and myosin filaments to cause a contraction
• it activates the contractile apparatus of the heart

Question 3

What are the key mechanisms that allow the return of material to the sarcoplasmic reticulum ?

Answer 3

• in diastole, calcium is taken up by the sarcoplasmic reticulum through an ATP dependent pump
• calcium is taken up across the sarcolemma by an ATP dependent pump and sodium exchange pump

Question 4

What causes trigger calcium to enter the cardiac myocyte ?

Answer 4

An action potential causes the opening of the calcium channels that bring in the trigger calcium

Question 5

How is a careful balance between the left and right side of the heart maintained ?

Answer 5

• an increase in stroke volume increases cardiac output
• this increases end diastolic volume
• the relationship between end diastolic volume and stroke volume is an intrinsic property of the heart which maintains this balance

Question 6

How is cardiac output changed or maintained through extrinsic mechanisms ?

Answer 6

changing stroke volume through extrinsic mechanisms such as the ANS will change cardiac output

Question 7

What are inotropic changes ?

Answer 7

• extrinsic factors that change the contractility of the heart
• adrenaline will increase the strength of contraction of the heart
• autonomic nerve fibres innervate cardiac muscle

Question 8

What are chronotropic changes ?

Answer 8

• extrinsic factors which cause time dependent changes in the heart

Question 9

What is the main pacemaker of the heart ?

Answer 9

The sinoatrial node

Question 10

What is the innervation of the sinoatrial node ?

Answer 10

• sympathetic and parasympathetic nerve fibres

Question 11

What is tachycardia ?

Answer 11

An increase in heart rate caused by an increase in the sympathetic activity of the sinoatrial node

Question 12

What is bradycardia ?

Answer 12

A decrease in heart rate caused by an increase in parasympathetic activity of the sinoatrial node

Question 13

What is the role of the atrioventricular nodes ?

Answer 13

• they are innervated by the ANS
• link activity in the atria and ventricles
• causes a delay in the coupling between the atria and the ventricles
• this means the atria can contract before the ventricles

Question 14

How do extrinsic factors cause a change in the inotropic state of the heart ?

Answer 14

• adrenaline binds to a receptor which activates a protein cascade
• this leads to a change in the phosphorylation of key proteins inside the cell
• this is known as a signal transduction
• the signal transduction will cause changes to the ryanodine receptors, calcium ions, calcium channels and contractile apparatus
• the signal transduction will increase the calcium available for contraction
• adrenaline will increase contraction of the heart

Question 15

What is the lucitropic effect ?

Answer 15

• phosphorylation of tropomysin will lead to an increase in muscle contraction
• whatever happens in systole must be reset in diastole
• the excess calcium in systole must be removed in diastole which will lead to an increased relaxation rate

Question 16

How do extrinsic factors cause changes to the chronotropic state of the heart ?

Answer 16

• parasympathetic regulation means it takes longer for the pacemaker potential to reach threshold and so this leads to bradycardia
• sympathetic regulation leads to tachycardia

Question 17

How is cardiac output measured ?

Answer 17

• the most common method is using Fick’s law
• it is easy to measure using spirometry
• a sample of blood is taken from the pulmonary artery and the oxygen content is determined per 100ml
• a sample of blood is taken from the pulmonary vein also
• cardiac output is calculated by oxygen consumption divided by the arteriovenous oxygen difference