Cardiac Output and Regulation of Cardiac Function

Question 1

At rest how much blood does each ventricle pump out?

Answer 1

5L of blood/min

Question 2

Define cardiac output

Answer 2

The rate at which ventricle pumps blood is called the cardiac output

Question 3

Define heart rate

Answer 3

Number of contraction per minute

Question 4

How do you calculate cardiac output (CO)?

Answer 4

Heart rate x stroke volume

HR x SV=CO

Question 5

Define extrinsic control

Answer 5

Regulation of the heart by neural input, circulating hormones or any other factor from OUTSIDE the heart

Question 6

Define intrinsic control

Answer 6

Regulation by factors originating in the heart

Question 7

What does the central nervous system (CNS) do?

Answer 7

Controls muscles and other organs by way of signals sent through the efferent branch of the peripheral nervous system

Question 8

How many branches does the peripheral nervous system (PNS) have? Name them

Answer 8

2 branches

The branches: Autonomic and somatic

Question 9

How many branches does the autonomic system have? Name them

Answer 9

2 branches
The branches:
Sympathetic and parasympathetic

Question 10

What is the parasympathetic nervous system described as?

Answer 10

Resting state

“Rest and Digest”

Question 11

What is the sympathetic nervous system described as?

Answer 11

Fight or flight

Question 12

The autonomic nervous system consists of ________ neurones. Which 3 different types of cells do these neurones control?

Answer 12

Efferent neurones

The three types of cells of cells they control are:

1. Smooth muscle
2. Cardiac muscle
3. Some gland cells

Question 13

Give 5 features of the sympathetic nervous system

Answer 13

1. Starts at the middle of the spinal cord
2. Usually consists go a chain of 2 neurones from CNS to target cells
3. It changes blood flow from intestines to skeletal muscles
4. increases heart output
5. Activates sweat glands

Question 14

Give 5 features of the parasympathetic nervous system

Answer 14

1. Starts in either the brain stem or bottom of the spinal cord
2. Usually consists go a chain of 2 neurones from CNS to target cells
3. Increases blood flow to intestines as you are ‘resting and digesting”
4. Decreases heart rate
5. Activates salivary glands

Question 15

Which neurotransmitters is associated with the sympathetic nervous system?

Answer 15

Noradrenaline

Question 16

Which neurotransmitters is associated with the parasympathetic nervous system?

Answer 16

Acetylcholine

Question 17

What is the range for a normal heart rate?

Answer 17

30-180bpm

Question 18

Explain the sympathetic control of heart rate

Answer 18

When sympathetic activity increases:
Pacemaker cells of the SAN produce more action potentials. So heart rate increases and cardiac output also increases
Speed of conduction also increases. So ventricular contraction occurs more rapidly after atrial contraction. This decreases the duration of systole

Question 19

Explain the parasympathetic control of heart rate

Answer 19

When parasympathetic activity increases:
Pacemaker cells of the SAN produce less action potentials. So heart rate decreases and cardiac output also decreases
Speed of conduction decreases. So ventricular contraction occurs less rapidly after atrial contraction. This increases the duration of systole

Question 20

Describe 2 ways hormones can affect heart rate

Answer 20

1. Adrenaline in the blood stream can increase action potentials from the SAN increasing heart rate (speed of action potentials also increases)
2. Thyroid hormones, like glucagon and insulin, increase the force of myocardial contractions increasing heart rate

Question 21

What three factors affect stroke volume?

Answer 21

Ventricular contractility
End diastolic volume
Afterload

Question 22

What is ventricular contractility

Answer 22

The force of the ventricular contraction

Question 23

Explain how ventricular contractility affects stroke volume

Answer 23

Sympathetic neurons project to the ventricular myocardium influencing the myocardial contractility
Increase in sympathetic activity leads to an increase in ventricular contractility which ultimately increases cardiac output

Question 24

How does ventricular contractility increase?

Answer 24

Increase in Ca^2+ concentration and permeability which increases contractility

Question 25

Which hormone can also increase myocardial contractility?

Answer 25

Adrenaline

Question 26

Is end diastolic volume controlled by intrinsic or extrinsic factors?

Answer 26

Intrinsic control

Question 27

State Starling’s Law of the heart

Answer 27

When the rate at which blood flows into the heart from the veins (that is venous return) changes, the heart automatically adjusts its output to match the inflow

Question 28

Explain how end diastolic volume affects stroke volume

Answer 28

End diastolic volume increases then force of ventricular contraction increases and as a result both stroke volume and cardiac output increases.

Question 29

How does an increase in end diastolic volume affect muscle fibres of ventricular myocardium?

Answer 29

Muscle fibres of ventricular myocardium lengthen.

This stretch increases the force of contraction

Question 30

How does an increase in end diastolic volume lengthen the muscle fibres of ventricular myocardium and result in a greater ventricular contractility?

Answer 30

1. Affinity of troponin in muscle fibres for calcium increases. This increases number of cross bridges activated by contraction
2. Cardiac muscle increases to the optimum length. So EDV brings muscle fibres closer to their optimum length for contractility which results in a contraction of greater force.

Question 31

How does sympathetic activity affect Starling’s curve?

Answer 31

Increase in sympathetic activity shifts Starling’s curve upwards. This increases stroke volume at any EDV due to increased ventricular contractility

Question 32

How does Starling’s law regulate heart size?

Answer 32

By adjusting stroke volume so that cardiac output matched venous return

Question 33

What 2 factors affect end diastolic volume?

Answer 33

End diastolic pressure

Preload

Question 34

What is end diastolic pressure determined by?

Answer 34

Determined by the pressure of blood inside the heart before contraction tension on the myocardium

Question 35

What is preload determined by?

Answer 35

Is determines by the filling time and atrial pressure

Question 36

What does increasing the arterial pressure do to the stroke volume?

Answer 36

When the heart ejects blood it has to work against arterial pressure
increasing the arterial pressure causes the stroke volume to decrease

Question 37

What is after load?

Answer 37

Arterial pressure places a load on the myocardium after contraction starts. This is called after load

Question 38

What is the afterload determined by in the left ventricle?

Answer 38

Pressure in the aorta