Lecture 04 Heart Physiology 3 Flashcards
1. Understand the heart as an endocrine organ 2. Understand myocardial contractility and how cardiac output is a function of stroke volume and heart rate 3. Describe how treatment is personalised to the patient
Why are the coronary arteries important? Where do they come from?
important to perfuse the heart so that it can function
from the first branch of the aorta
What is the structure of blood supply to the heart? Why is this important?
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
How is coronary blood flow calculated?
perfusion pressure / resistance
coronary blood flow is proportional to perfusion pressure
coronary blood flow is inversely proportional to resistance
Why is the arterial resistance important?
small changes in resistance make large charges to flow
What factors determine the resistance?
length of the tubule
viscosity of the blood
diameter of the artery
What is the myocardial oxygen consumption (ml/min/100g) of a resting heart, muscle, brain, kidney and skin?
heart 8 muscle 1 brain 3 kidney 5 skin 0.2
What is the myocardial oxygen consumption (ml/min/100g) of a heart and muscle during heavy exercise?
heart 70
muscle 50
What is the equation linking force and radius?
force is proportional to r^4
How much perfusion does the heart receive via the coronary arteries?
around 5% of all cardiac output making it one of the worst perfused tissues in terms of the metabolic activity
How does the heart compensate for its poor perfusion?
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
How is cardiac oxygen delivery (mM) calculated?
arterial oxygen concentration x coronary blood flow
What determines oxygen delivery from the coronary arteries?
coronary blood flow - how much oxygen is bound to haemoglobin
What is the normal aortic blood pressure?
contraction/systole 120mmHg
relaxation/diastole 80mmHg
Remaining aortic pressure during diastole is linked to what valve?
aortic
What is the normal ventricular blood pressure?
contraction/systole 120mmHg
relaxation/diastole ~0mmHg
What physical factors influence diastolic coronary flow?
aortic pressure
ventricular pressure
How does increasing heart rate affect diastolic coronary flow?
tachycardia decreases the window of perfusion, reducing diastole and therefore less time for coronary perfusion
How does increasing LVEDP (i.e. heart failure or hypertension) affect diastolic coronary flow?
decreases the perfusion pressure through reduced gradient
How does decreasing the diastolic aortic pressure affect diastolic coronary flow?
decreases the perfusion pressure through reduced gradient
What is autoregulation of coronary blood flow?
the ability of an organ to maintain a constant blood flow despite changes in perfusion pressure
What organs can autoregulate their coronary blood flow?
heart
brain
kidneys
What happens during hypoxia (low pO2)?
local control by metabolites, suggested Adenosine
causes coronary vasodilation
What molecules/compound build up as a result of low oxygen/hypoxia?
potassium ion
carbon dioxide
hydrogen ions
lactic acid
What condition can cause reduced oxygen delivery?
anaemia
What types of vascular control are less important?
neural/autocrine
humoral/endocrine
What type of control are larger vessels linked to?
alpha-adrenoceptor vasoconstriction
What type of control are smaller vessels linked to?
beat-2 vasodilation
What has the largest impact on the resistance
the smaller vessels
What is a key symptom of coronary artery disease? What does this cause?
stenosis - narrowing of the arteries
increased resistance and potential blocking of coronary arteries
What type of organ is the heart? Why?
endocrine organ
it secretes hormones
What type of hormone does the heart secrete? Name three and where they are released
Cardiac Natriuretic Peptides
ANP (atrial natriuretic peptide) - atria
BNP (brain natriuretic peptide) - brain and ventricles
CNP - vasculature
How are hormones released/secreted in the heart? When does this occur?
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
What effect do the cardiac natriuretic hormones have on the body?
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
What do cardiac natriuretic hormones inhibit the release/actions of?
aldosterone
angiotensin II
endothelin
anti-diuretic hormone (ADH)
What are Neutral Endopeptidases (NEP/neprilysin)?
metabolise cardiac natriuretic hormones
Why are NEPs targeted for therapeutics? What do these therapies treat?
inhibiting NEPs prolongs the actions of cardiac natriuretic hormones on the body
new, modern drug therapy for heart failure
Give an example of a NEP inhibitor
sacubitril
Give an example of an angiotensin II inhibitor
valsartan
What is the name of Sacubitril and Valsartan drugs when given in combination
entresto
