Cardiovascular Physiology

Question 1

Cardiac output at rest

Answer 1

75 bpm x 70 mL = 5 L/min

Question 2

Cardiac output during exercise

Answer 2

150 bpm x 130 mL = 19.5 L/min

Question 3

Cardiac reserve

Answer 3

Difference between cardiac output at rest and cardiac output during exercise

Question 4

Cardiac output equation

Answer 4

CO = SV x HR

Question 5

Stroke volume

Answer 5

Amount of blood pumped with each heartbeat

Question 6

Venous return

Answer 6

The volume of blood returning to the heart from the vasculature every minute

Question 7

Describe how hypertrophy can lead to heart failure in terms of cardiac output

Answer 7

Hypertrophy of the heart means the heart has increased in size and become harder to contract
During rest, cardiac output is normal but during exercise cardiac output has decreased therefore the cardiac reserve has decreased
During exercise more blood is required to be pumped around the systemic circuit but with increased size of the heart this is difficult - supply cannot meet demand

Question 8

Preload

Answer 8

The degree of stretch that the ventricle can undertake

Question 9

Afterload

Answer 9

The pressure in the major arteries (especially aorta) resisting the blood being pumped from the left ventricle

Question 10

Contractility

Answer 10

The amount the heart can contract to expel the blood from the ventricle

Question 11

3 things that regulate stroke volume

Answer 11

Preload
Afterload
Contractility

Question 12

Describe how stroke volume can be regulated

Answer 12

Preload - larger degree of stretch in the ventricle allows more blood to pool, stroke volume increases
Afterload - high pressures in the systemic arteries are more difficult to overcome, stroke volume decreases
Contractility - larger force of contractility expels more blood from the ventricle, stroke volume increases

Question 13

Inotropy

Answer 13

Change in stroke volume

Question 14

Chronotropy

Answer 14

Change in heart rate

Question 15

Describe Frank-Starlings law of the heart

Answer 15

The more the heart fills with blood during diastole the greater the force of contraction during systole
Preload is directly proportional to end diastolic volume

Question 16

End diastolic volume

Answer 16

The amount of blood remaining in the ventricle just before systole begins

Question 17

End systolic volume

Answer 17

The amount of blood remaining in the ventricle at the end of systole

Question 18

Describe what happens when the conduction system of the heart becomes out of sync

Answer 18

Slightly out of sync: Decreased contractility

Very out of sync: Arrhythmia

Question 19

3 steps of cardiac muscle contraction

Answer 19

Depolarisation
Plateau
Repolarisation

Question 20

Describe how an action potential causes ventricular contraction

Answer 20

Autorhythmic cells in the SA node initiate excitation which causes a wave of depolarisation throughout the myocardium as a result of sodium influx when voltage-gated fast sodium channels open
Influx of calcium ions when voltage-gated slow calcium channels open and efflux of potassium when some potassium channels open causes a plateau or maintained depolarisation
The calcium influx ensures that the action potential lasts almost as long as the contraction of the cell which in turn ensures the unidirectional excitation of the myocardium
Repolarisation of the myocardial cells occurs when the voltage dependent calcium channels close and additional voltage-gated potassium channels open

Question 21

Describe how the different parts of an ECG relate to action potential

Answer 21

P wave - atrial depolarisation
QRS complex - ventricular depolarisation
T wave - ventricular repolarisation

Question 22

Describe how the sympathetic nervous system sends messages to the heart

Answer 22

Input from sensory receptors or brain centres such as the limbic system or hypothalamus move down into the brainstem to the cardiovascular centre in the medulla oblongata
The nerve moves through the spinal cord into the sympathetic trunk ganglion and to the heart via the cardiac accelerator nerve
Increased rate of spontaneous depolarisation in SA node and AV node increases heart rate
Increased contractility of atria and ventricles stroke volume

Question 23

Describe how the parasympathetic nervous system sends messages to the heart

Answer 23

Input from sensory receptors or brain centres such as the limbic system or hypothalamus move down into the brainstem to the cardiovascular centre in the medulla oblongata
The nerve bypasses the spinal cord and goes straight to the heart via the vagus nerve
Decreased rate of spontaneous depolarisation in SA node and AV node decreases heart rate

Question 24

Describe how increased preload can increase cardiac output

Answer 24

Increased end diastolic volume stretches the heart
Preload is increased
Cardiac muscles contract more forcefully with stretching due to Frank-Starlings law of the heart
Stroke volume is increased
Cardiac output is increased due to CO = SV x HR

Question 25

Describe how increased contractility can increase cardiac output

Answer 25

Positive inotropic agents such as catecholamines, glucagon and thyroid hormones in the blood increase contractility Positive inotropic agents increase force of contraction at all physiological levels of stretch Stroke volume is increased Cardiac output is increased due to CO = SV x HR

Question 26

Describe how decreased afterload can increase cardiac output

Answer 26

Decreased arterial blood pressure during diastole causes decreased afterload Semilunar valves open sooner when blood pressure is lower in aorta and pulmonary artery Stroke volume is increased Cardiac output is increased due to CO = SV x HR

Question 27

Describe how the nervous system can affect cardiac output

Answer 27

Cardiovascular centre in medulla oblongata receives input from cerebral cortex, limbic system and receptors Increased sympathetic stimulation and decreased parasympathetic stimulation leads to increased heart rate Cardiac output is increased due to CO = SV x HR

Question 28

Describe how chemicals can affect cardiac output

Answer 28

Catecholamines or thyroid hormones in the blood increase heart rate Cardiac output is increased due to CO = SV x HR

Question 29

How to calculate mean arterial pressure

Answer 29

Diastole + 1/3 systole = MAP

Question 30

Hypertension blood pressure

Answer 30

140/90

Question 31

Normal blood pressure

Answer 31

120/80

Question 32

Blood volume in the systemic capillaries

Answer 32

7%

Question 33

Describe how blood pressure affects gas exchange

Answer 33

Increased blood pressure means more blood is coming into the capillaries and more gas is available for exchange Increased BP = increased exchange Stable BP = stable gas exchange in capillary beds

Question 34

Describe how blood pressure varies throughout the cardiovascular system

Answer 34

In the aorta and arteries, systolic blood pressure and diastolic blood pressure are very different In the arterioles the blood pressure drops and gets more stable. There is still some difference between diastolic and systolic because of the arterioles ability to adjust diameter Capillaries have lower blood pressure Venules, veins and vena cavae have very low blood pressure with almost no fluctuation

Question 35

Starlings law of the capillaries

Answer 35

(BHP + IFHP) - (BCOP + IFOP) = NFP Blood hydrostatic pressure + interstitial fluid hydrostatic pressure - blood colloid osmotic pressure + interstitial fluid osmotic pressure = net filtration pressure

Question 36

Describe how capillary flow works

Answer 36

Lymphatic fluid from lymphatic capillary returns to the blood plasma The blood flows from arterioles into the arterial end of the capillary where blood hydrostatic pressure and interstitial fluid osmotic pressure are pushing into the interstitial fluid. These are pressures promoting filtration. This is balanced somewhat by blood colloid osmotic pressure pushing into the capillary. The blood continues to flow through the capillary to the venous end where blood hydrostatic pressure continues to push out of the capillary but interstitial fluid hydrostatic pressure and blood colloid osmotic pressure are now pushing into the capillary. These are pressures promoting reabsorption. Leftover blood not filtrated or reabsorbed flows from the capillary into a venule to continue into veins and back to the heart.

Question 37

Describe why circuits are arranged in parallel

Answer 37

To distribute even pressure among organs

Question 38

Poiseuilles law of the heart

Answer 38

R ∝ Ln Vessel resistance is directly proportional to the length of the vessel and the viscosity of the blood R is inversely proportional to r^4

Question 39

Describe the relationship between blood flow velocity and total-cross sectional area of vessels

Answer 39

The larger the total cross-sectional area of a blood vessel the slower blood will move through it e.g. capillaries have the largest cross-sectional area of any blood vessels therefore blood moves the most slowly through them

Question 40

How to calculate blood pressure

Answer 40

BP = CO x TPR

Question 41

Factors influencing blood pressure

Answer 41

Increased heart rate Increased contractility Vasoconstriction and vasodilation Blood volume increase or decrease

Question 42

Factors influencing TPR

Answer 42

Blood vessel radius Blood viscosity Blood vessel length

Question 43

Describe how norepinephrine affects blood pressure

Answer 43

Norepinephrine is released by stimulation of the sympathetic nervous system Norepinephrine increases heart rate and contractility Increased blood pressure

Question 44

Describe how Angiotensin II affects blood pressure

Answer 44

``` Angiotensin II (and ADH) is a potent vasoconstrictor Vasoconstriction increases total peripheral resistance which increases blood pressure ```

Question 45

Describe how nitric oxide affects blood pressure

Answer 45

NO (and ANP and epinephrine in some cases) is a potent vasodilator Vasodilation decreases total peripheral resistance which decreases blood pressure

Question 46

Describe how aldosterone affects blood pressure

Answer 46

Aldosterone (and ADH) retain water from being excreted by the kidneys, increasing blood volume and increasing blood pressure

Question 47

Describe how ANP affects blood pressure

Answer 47

Atrial Natriuretic Peptide promotes water excretion through urine via the kidneys, decreasing blood volume and increasing blood pressure

Question 48

Describe where the baroreceptors are found

Answer 48

Carotid sinus and arch of aorta

Question 49

4 things that increase venous return

Answer 49

Vasoconstriction Respiratory pump Skeletal muscle pump Increased blood volume

Question 50

Describe how increased venous return could affect mean arterial blood pressure

Answer 50

Increased venous return increases stroke volume Increased stroke volume increases cardiac output Increased cardiac output increases MAP MAP = CO x TPR

Question 51

Describe how the body acts to restore homeostasis during hypovolemic shock

Answer 51

Hypovolemic shock occurs when you lose more than 20% of your blood supply Massive decrease in blood pressure means baroreceptors in carotid sinus and aortic arch fire less in response to decreased stretch Decreased rate of nerve impulses from the baroreceptors signals the cardiovascular centre in the medulla oblongata to increase sympathetic stimulation and hormones from adrenal medulla Decreased rate of nerve impulses from baroreceptors also signals the hypothalamus to synthesis ADH and the posterior pituitary to release the ADH The ADH acts on the kidneys to conserve salt and water, rate of urine production decreases which increases blood volume ADH also acts on blood vessels to constrict them to increase total vascular resistance Sympathetic stimulation acts on the heart to increase heart rate and contractility which increases cardiac output The three results: Increase in blood volume Increase in vascular resistance Increase in cardiac output All act together to increase blood pressure and restore homeostasis