Cardiovascular system: Cardiac output

Question 1

What is the function of the heart?

Answer 1

To supply the right amount of O2 and nutrients to the body

Question 2

What is the resting vs intrinsic heart rate of a normal heart?

Answer 2

Resting = 60-70, intrinsic = 90

Question 3

What set the intrinsic heart rate?

Answer 3

The sinoatrial node

Question 4

What lowers the normal resting heart rate?

Answer 4

parasympathetic nerves

Question 5

What is the cardiac output (CO) formula?

Answer 5

Heart rate (HR) * Stroke volume (SV)

Question 6

What is the cardiac output at rest?

Answer 6

4-5Lmin-1

Question 7

What is venous return?

Answer 7

The volume of blood returning to the heart from the vasculature (vascular system of the body) every minute

Question 8

What is the cardiac reserve?

Answer 8

The difference between resting CO and and max CO (i.e. rest = ~5Lmin-1, exercise = ~20Lmin-1 therefore cardiac reserve = 15Lmin-1)

Question 9

How can the CO be regulated?

Answer 9

By regulating the heart rate and stroke volume

Question 10

How is the stroke volume regulated?

Answer 10

By pre-load, after-load and contractility

Question 11

What is pre-load?

Answer 11

The pressure of the blood retuning to the heart

Question 12

How does pre-load affect the SV? What determines the affect?

Answer 12

The greater the pressure of the blood on the heart the more force the heart exerts to push it out therefore increasing stroke volume

The Frank-Starling law determines the relationship between pressure on the heart and how hard it contracts

Question 13

What is after load?

Answer 13

The pressure that must be exceeded in order for blood to be moved into and out of the ventricle

Question 14

How does after load affect stroke volume?

Answer 14

The greater the after load in the pulmonary artery, the more force the right ventricle needs to exert to pump blood into the pulmonary system

The great the after load in the aorta, the more force the left ventricle needs to exert to pump blood into the systemic circuit

Question 15

What is contractility?

Answer 15

The strength of the contraction of the heart

Question 16

How is contractility affected?

Answer 16

By the inotropic agents, i.e. an increase of positive inotropic agents causes an increase in contraction strength (and heart rate FYI), an increase in negative inotropic agents decreases contraction strength (and heart rate FYI) (FYI this strength is for all physiological levels of stretch in the heart)

Question 17

What are some examples of positive inotropic agents? What do they do to increase contractility?

Answer 17

Norepinephrine and epinephrine, they increase Ca2+ release

Question 18

How do negative inotropic agents decrease contractility?

Answer 18

Reducing Ca2+ flow therefore decreasing strength of the heart beat

Question 19

What is the Frank - Starling law of the heart?

Answer 19

That the more blood that comes into the heart during diastole, the harder the contraction during systole OR the energy of contraction of the ventricle is a function of the initial length of ht muscle fibres comprising its walls

Question 20

What happens when pre-load increase but stroke volume doesn’t change?

Answer 20

It causes an increase in pulmonary congesting (i.e. pooling of liquid in the venous system)

Question 21

What is the ejection fraction?

Answer 21

The percentage of the max blood that is ejected per stroke (i.e. if volume of heart = 120ml and max ejected blood = 80ml, ejection fraction = 66%)

Question 22

How does the ejection fraction change during heart failure?

Answer 22

The ejection fraction begins to decrease

Question 23

What does a decreasing ejection fraction indicate about the heart?

Answer 23

A decreasing ejection fraction indicates that the heart is pumping out less per contraction which means that it will struggle to pump against the after load

Question 24

Hw can the heart rate be affected?

Answer 24

Nervous system, chemicals, health and environment

Question 25

How can the nervous system affect heart rate?

Answer 25

The sympathetic and parasympathetic stimulation affection the release of chemical and influence Ca2+ fluxes influencing the depolarisation of the SA and AV node

Question 26

How can chemicals affect heart rate?

Answer 26

positive inotropic chemicals increase extracellular Ca2+ concentrations causing increase in heart rates

Question 27

How can health affect heart rate?

Answer 27

Old/young, gender, fitness etc. all affect the resting heart rate based on the physiological needs on the body and the size and condition of the heart

Question 28

How can the environment affect heart rate?

Answer 28

For example, increasing body temperatures causes an increase in heart rate for cooling purposes