Lecture 04 Heart Physiology 3

Question 1

Why are the coronary arteries important? Where do they come from?

Answer 1

important to perfuse the heart so that it can function

from the first branch of the aorta

Question 2

What is the structure of blood supply to the heart? Why is this important?

Answer 2

larger vessels run over the surface with arteries going from out to in
when the heart muscle contracts the arteries are compressed, cutting off its own blood supply
in diastole the muscles relax and coronary flow can occur again

Question 3

How is coronary blood flow calculated?

Answer 3

perfusion pressure / resistance
coronary blood flow is proportional to perfusion pressure
coronary blood flow is inversely proportional to resistance

Question 4

Why is the arterial resistance important?

Answer 4

small changes in resistance make large charges to flow

Question 5

What factors determine the resistance?

Answer 5

length of the tubule
viscosity of the blood
diameter of the artery

Question 6

What is the myocardial oxygen consumption (ml/min/100g) of a resting heart, muscle, brain, kidney and skin?

Answer 6

heart 8
muscle 1
brain 3
kidney 5
skin 0.2

Question 7

What is the myocardial oxygen consumption (ml/min/100g) of a heart and muscle during heavy exercise?

Answer 7

heart 70

muscle 50

Question 8

What is the equation linking force and radius?

Answer 8

force is proportional to r^4

Question 9

How much perfusion does the heart receive via the coronary arteries?

Answer 9

around 5% of all cardiac output making it one of the worst perfused tissues in terms of the metabolic activity

Question 10

How does the heart compensate for its poor perfusion?

Answer 10

the heart extracts a lot more oxygen that other organs/tissues
more efficient in its oxygen uptake from the blood
blood returning to the heart from the coronary veins is much more deoxygenated that blood returning from other parts of the body

Question 11

How is cardiac oxygen delivery (mM) calculated?

Answer 11

arterial oxygen concentration x coronary blood flow

Question 12

What determines oxygen delivery from the coronary arteries?

Answer 12

coronary blood flow - how much oxygen is bound to haemoglobin

Question 13

What is the normal aortic blood pressure?

Answer 13

contraction/systole 120mmHg

relaxation/diastole 80mmHg

Question 14

Remaining aortic pressure during diastole is linked to what valve?

Answer 14

aortic

Question 15

What is the normal ventricular blood pressure?

Answer 15

contraction/systole 120mmHg

relaxation/diastole ~0mmHg

Question 16

What physical factors influence diastolic coronary flow?

Answer 16

aortic pressure

ventricular pressure

Question 17

How does increasing heart rate affect diastolic coronary flow?

Answer 17

tachycardia decreases the window of perfusion, reducing diastole and therefore less time for coronary perfusion

Question 18

How does increasing LVEDP (i.e. heart failure or hypertension) affect diastolic coronary flow?

Answer 18

decreases the perfusion pressure through reduced gradient

Question 19

How does decreasing the diastolic aortic pressure affect diastolic coronary flow?

Answer 19

decreases the perfusion pressure through reduced gradient

Question 20

What is autoregulation of coronary blood flow?

Answer 20

the ability of an organ to maintain a constant blood flow despite changes in perfusion pressure

Question 21

What organs can autoregulate their coronary blood flow?

Answer 21

heart
brain
kidneys

Question 22

What happens during hypoxia (low pO2)?

Answer 22

local control by metabolites, suggested Adenosine

causes coronary vasodilation

Question 23

What molecules/compound build up as a result of low oxygen/hypoxia?

Answer 23

potassium ion
carbon dioxide
hydrogen ions
lactic acid

Question 24

What condition can cause reduced oxygen delivery?

Answer 24

anaemia

Question 25

What types of vascular control are less important?

Answer 25

neural/autocrine | humoral/endocrine

Question 26

What type of control are larger vessels linked to?

Answer 26

alpha-adrenoceptor vasoconstriction

Question 27

What type of control are smaller vessels linked to?

Answer 27

beat-2 vasodilation

Question 28

What has the largest impact on the resistance

Answer 28

the smaller vessels

Question 29

What is a key symptom of coronary artery disease? What does this cause?

Answer 29

stenosis - narrowing of the arteries | increased resistance and potential blocking of coronary arteries

Question 30

What type of organ is the heart? Why?

Answer 30

endocrine organ | it secretes hormones

Question 31

What type of hormone does the heart secrete? Name three and where they are released

Answer 31

Cardiac Natriuretic Peptides ANP (atrial natriuretic peptide) - atria BNP (brain natriuretic peptide) - brain and ventricles CNP - vasculature

Question 32

How are hormones released/secreted in the heart? When does this occur?

Answer 32

ANP and BNP found in secretory vesicles and released when muscle undergoes stretching occurs when there is raised atrial or ventricular pressure leading to volume overload

Question 33

What effect do the cardiac natriuretic hormones have on the body?

Answer 33

increase renal excretion of sodium - natriuresis increase renal excretion of water - diuresis relaxation of vascular smooth muscle (except efferent arteriole of renal glomeruli) increased vascular permeability

Question 34

What do cardiac natriuretic hormones inhibit the release/actions of?

Answer 34

aldosterone angiotensin II endothelin anti-diuretic hormone (ADH)

Question 35

What are Neutral Endopeptidases (NEP/neprilysin)?

Answer 35

metabolise cardiac natriuretic hormones

Question 36

Why are NEPs targeted for therapeutics? What do these therapies treat?

Answer 36

inhibiting NEPs prolongs the actions of cardiac natriuretic hormones on the body new, modern drug therapy for heart failure

Question 37

Give an example of a NEP inhibitor

Answer 37

sacubitril

Question 38

Give an example of an angiotensin II inhibitor

Answer 38

valsartan

Question 39

What is the name of Sacubitril and Valsartan drugs when given in combination

Answer 39

entresto