Lecture 12 - Control of Cardiac Output

Question 1

Define Cardiac Output

Answer 1

The volume of blood ejected by each ventricle per minute

Question 2

What is the formula for Cardiac Output?

Answer 2

CO = Heart Rate x Stroke Volume

Question 3

Where are chemoreceptors found and what do they respond to?

Answer 3

They are found in the carotid body and aortic arch - they respond to changes in arterial oxygen + carbon dioxide concentrations, and pH

Question 4

What are the terms for pathologically high or low heart rate?

Answer 4

Low - Bradycardia
High - Tachycardia

Question 5

How does the Parasympathetic nervous system affect ion channels at the SA Node?

Answer 5

Acetylcholine causes more K+ channels to open -> K+ leave, so membrane is hyperpolarised -> depolarisation takes longer so heart rate is slower

Question 6

How does the Sympathetic nervous system affect ion channels at the SA Node?

Answer 6

Noradrenaline causes Na+ and Ca2+ channels to open -> these ions move in, so reduced repolarisation -> this makes depolarisation more rapid, increasing heart rate

Question 7

Define Vagal Tone

Answer 7

Vagal tone is the background parasympathetic activity that keeps heart rate below the intrinsic rate of 100bpm, while at rest. (Endurance athletes have increased vagal tone)

Question 8

How does increased Venous Return affect heart rate?

Answer 8

Increases it both directly (stretch SAN pacemaker cells -> more rapid depolarisation) and indirectly (atrial reflex -> stretch receptors activate SNS)

Question 9

What are the three determinants of End Systolic Volume and End Diastolic Volume

Answer 9

Preload, Contractility and Afterload

Question 10

Define Preload

Answer 10

The extent to which ventricular muscles are stretched at the end of diastole

Question 11

Define Contractility

Answer 11

The force produced by ventricular muscle cells during systole at a given preload

Question 12

Define Afterload

Answer 12

The resistive force the ventricle needs to overcome to open the semi-lunar valves and eject blood

Question 13

State the Frank-Starling Law

Answer 13

The force developed in muscle fibre is dependent on the degree to which it is stretched

Question 14

What 3 factors affect Venous Return?

Answer 14

Posture (decreased when standing still), the Skeletal Muscle Pump and the Respiratory Pump

Question 15

Name 4 hormones which affect Contractility (and +ve or -ve?)

Answer 15

Adrenaline, Noradrenaline, Glucagon and Thyroid Hormones ALL INCREASE contractility

Question 16

What is the main factor affecting Afterload?

Answer 16

Vasoconstriction and Vasodilation