Cardiovascular physiology Flashcards
What causes the first heart sound?
The closure of the atrioventricular valves - mitral and tricuspid.
This indicates the beginning of systole and the start of isovolumetric contraction.
What percentage of ventricular filling does atrial contraction contribute to?
25–30%.
What are normal values for end diastolic volume (EDV) and end systolic volume
(ESV)?
EDV- volume in the ventricle at the end of diastole = 130 mL.
ESV- volume remaining in the ventricle at the end of systole = 60 mL.
How is the stroke volume (SV) calculated?
SV is the amount of blood pumped out of the ventricle in one contraction. This is calculated by; SV = EDV – ESV. SV = 130 mL – 60 mL. The stroke volume is 70 mL.
How do you calculate the ejection fraction?
This is the percentage of blood that is ejected from the ventricle each cardiac cycle. This is calculated by; EF = SV/EDV. EF = 70 mL/130 mL It is normally ~60–65%.
Are the third and fourth heart sounds always pathological?
No, the third heart sound can be physiological in children, athletes and pregnant
women. However, the fourth heart sound is pathological.
During exercise, which part of the heart cycle reduces the most (systole or diastole)? What effect does this have on coronary artery filling?
Proportionally diastole decreases more.
This means that there is less time for left coronary artery filling as this occurs
most rapidly throughout diastole.
Which ventricle ejects blood first (the right or the left)
The right ventricle. This is because the pulmonary circulation is a lower pressure
system than the systemic circulation so the pulmonary valve opens before the
aortic valve.
what causes the ‘c’ wave on the JVP waveform?
ventricular contraction as the tricuspid valve bulges into the right atrium against a closed pulmonary valve.
when does the aortic valve open?
When the pressure inside the ventricle exceeds the aortic pressure, the aortic
valve opens.
what are the four componenets of ventricular diastole?
(1) Isovolumetric relaxation and
(2) Rapid inflow
(3) Diastasis
(4) Atrial
contraction;
what is the a wave of the VAP represent in the cardiac cycle?
the artial kick
what is the third heart sound?
Third HS: Oscillation of blood between the walls of the ventricles caused by the
inflow of blood from the atria. Heard at the beginning of the middle third of
diastole. Normal in youth, athletes and pregnant women. If heard in adults, it
may indicate heart failure
what does a 4th heart sound indicate?
Fourth HS: Contraction of the atria in late diastole pushing blood into a stiff or
hypertrophic ventricle. Always pathological.
what is the V wave in the JVP representative of in the cardiac cycle?
v’ wave is from ↑ in Rt atrial pressure just before AV valves open caused by
atrial filling
- List some features of cardiac muscle cells.
(a) Striated muscle
(b) Form a syncytium
(c) Connected by intercalated discs
(d) Gap junctions that allow the action potential to propagate from cell to cell
(e) T tubules
What fuel sources do the cardiac muscle cells use?
They predominately use fatty acids. At rest, 60% fatty acid, 35% carbohydrate
and 5% ketones and amino acids.
What is the resting membrane potential (RMP) of the cardiac muscle cell?
Sinoatrial (SA) node?
The cardiac muscle cells have a lower RMP than in the conducting system e.g.
SA node. The RMP in the cardiac muscle cells is −90 mV in comparison with
−60 mV in the SA node.
Describe the changes in the membrane permeability to ions during the different
phase of the cardiac action potential in cardiac muscle cells.
(a) Phase 0- Initial depolarisation due to rapid ↑ in Na+ permeability
(b) Phase 1- Initial repolarisation is due to inactivation of fast Na channels and
outward flow of K+ ions
(c) Phase 2- Inward current due to influx of Ca2+ → plateau phase
(d) Phase 3- Inactivation of slow Ca2+ channels hence there is unopposed
outward flow of K+ ions → repolarisation
(e) Phase 4- Restoration to the RMP. Cell membrane is most permeable to K+
Which part of the electrical conduction system of the heart transmits at the fastest speed?
The Purkinje fibres, 4 ms−1
.
How does the parasympathetic nervous system (PSNS) act to slow the heart rate?
It acts on the SA node. The acetylcholine (Ach) binds to muscarinic (M2)
receptors and via G-proteins opens K+ channels. This causes further movement
of K+ out of the cell and therefore hyperpolarizes it. This means it is harder for
the SA node to reach threshold potential and the heart rate is slowed.
How do you calculate the QTc and what part of the cardiac electrical cycle does
this represent?
The QT interval corresponds to electrical systole. The QT length is inversely
proportional to the HR
What ECG changes are seen in hypokalaemia and hyperkalaemia?
Hypokalemia causes prolongation of the PR interval, U waves, T wave
inversion/flattening and ST segment depression
• Due to prolonged ventricular repolarisation
• Later you may see prolonged segments
(b) Hyperkalemia may get peaked T waves, prolonged PR and QRS intervals
How does digoxin work? What are some ECG changes seen in digoxin toxicity?
Its primary mechanism is to inhibit the Na/K ATPase in the myocardium. In
toxicity ECG changes include T wave inversion or biphasic T waves.
how does the sympathetic nervous system act on the SA node to ↑ HR
and ↑ rate of conduction through AV node as well as ↑ force of contraction.
NA → B1 receptors → ↑ in cAMP → increased sarcolemma permeability to
Na+ and Ca2+ channels
Threshold is reached quicker
What three factors determine the stroke volume?
(a) Degree of filling of the ventricle, or “preload”
(b) Contractility of the myocardium
(c) Resistance against which the ventricle has to work, or “afterload”
Why does increasing the venous return, increase the cardiac output.
This is because of the Frank-Starling mechanism (Fig. 3.10). Increased venous return
increases the end diastolic volume (EDV) → This in turn increases the pre-contraction
length of the myocytes. This results in more optimal alignment of the actin and
myosin filaments and therefore a stronger contraction and greater stroke volume.
Name some negative inotropic agents.
A negative inotrope is any agent that decreases the contractility of the heart. The
most important physiological factor is the PSNS. Other pathological conditions
such as hypoxia, hypercapnia, acidosis have negative inotrophic effects on the
heart. Pharmaceutical agents such B-blockers, Ca2+ blockers, barbiturates and
many anaesthetics.
At rest, what percentage of oxygen is extracted from the coronary circulation?
~70%. This means that the increase oxygen needed during exercise is met with
increasing blood flow, controlled by local factors, namely hypoxia.
Name the four categories of shock.
(a) Hypovolemic
(b) Distributive
(c) Cardiogenic
(d) Obstructive
what is the frank starling principle belived to be be a result of?
Thought to result from more optimal alignment of actin and myosin filaments, and ↑ sensitivity to Ca2+
what are some positive ionotropic agents?
• Sympathetic discharge and circulating catecholamines → ↑ contractility
• B-receptors → G-proteins → adenylate cyclase → cAMP → ↑ in Ca2+
influx → enhanced cross bridges → ↑ contractile force → ↑ SV
• Also, an ↑ in HR → ↑ in free intracellular Ca2+ → positive inotropic effect
• Caffeine, theophylline inhibit breakdown of cAMP → positive inotropic
effect
• Glucagon ↑ formation of cAMP → positive inotropic effect
• Digitalis inhibits NaK ATPase → ↑ Ca2+ concentration → positive inotropic
effect
In health, afterload is determined predominantly by?
In health, afterload is determined predominantly by: vascular tone
how many BPM does the SA node fire at?
100bpm
how much oxygen supply does the heart take?
• In a normal beating heart at rest this is 7–10 mL/100 g/min and in vigorous exercise this is 40 mL/100 g/min
What are the determinants of blood pressure?
CO and TPR
Where are the main baroreceptors located and what nerve innervates the carotid
sinus?
Carotid sinus near the carotid bifurcation. (‘Hering nerve’ which is a branch of glossopharyngeal CNIX) Aortic arch (vagus CNX).
Where is the vasomotor center located?
The medulla.
Where is renin produced?
In the epitheliod, granular and juxtaglomerular cells of the kidney. It is an enzyme
that converts angiotensinogen to angiotensin I.
What are the actions of angiotensin II?
(a) ↑ Na absorption in the proximal tubule
(b) ↑ secretion of aldosterone (zona glomerulosa of adrenal cortex)
• Aldosterone → ↑ Na reabsorption from 2nd part of the distal tubule and
collecting duct
(c) ↓ medullary BF → ↑ Na reabsorption
(d) ↑ sensitivity of JG feedback
(e) Potent vasoconstrictor and facilitates NA release, and ↓ vagal tone
(f) Acts on circumventricular organs in the brain → ↑ BP, ↑ thirst, ↑ ADH and
ACTH
What is the role of atrial natriuretic peptide (ANP)?
This is a peptide hormone released by the cardiac muscle cells in response to
increased extracellular fluid (ECF). It works by causing natriuresis.
What is the oxygen consumption of skeletal muscle at rest?
It is 250 mL/min and this can increase to 1600 mL/min in hard work.
what is the nucleus in the brain responsible for Arterial baroreceptors, cardiopulmonary, arterial chemoreceptors,
pulmonary stretch and skeletal muscle receptors?
nucleus of tractus solitarius
once the vasomotor centre in the medulla is triggered what does it do?
↓ SNS firing and ↑ PSNS firing → ↓ BP
what function is the opposite fo RAA system?
ANP
Natuiretic increases renal excretion fo sodium
What is the other name for endothelial-derived-relaxing-factor and what is its
role?
It is also known as nitric oxide. It is synthesized from the amino acid L-arginine
and it a powerful vasodilator.
What is the function of thromboxane A2?
It acts as a vasoconstrictor as well as promoting platelet aggregation.
What is the effect of ↑ CO2 on cerebral circulation?
The cerebral circulation is very sensitive to carbon dioxide. ↑ CO2 causes vasodilation and increased cerebral blood flow.
Explain the Monro-Kellie doctrine.
Monro-Kellie doctrine describes the pressure-volume relationship between ICP, volume of CSF, blood, brain tissue, and the cerebral perfusion pressure (CPP). As the
skull is fixed, the sum of volumes of brain, CSF, and intracranial blood is constant.
An increase in one should cause a decrease in one or both of the remaining two.
What is the blood flow of the cerebral circulation per minute?
750 mL/min.
What is the main function of the blood flow to the skin?
As the skin has a low metabolic demand, its main function is for temperature
regulation
n the fetal circulation, where does blood entering the heart from the IVC get
preferentially directed?
This is the blood with the highest oxygen content, hence it is preferentially
shunted through the foramen ovale to the left side of the heart, where it is directed
to the fetal brain and arms.
What causes closure of the foramen ovale at birth?
This is due to the loss of resistance in the pulmonary circulation when the first
breath is taken, as well as a rise in the left atrial pressure due to the rise in systemic pressure when the umbilical cord is cut.
what are the mediators responsible for vasodilation?
Histamine, prostaglandins (E series), prostacyclins, kinins (however contraction of SM epithelium), NO released from endethelium. CO2, H+, K and Mg also cause vasodilation.
what are some mediators causing vasoconstriction?
Angiotensin 2 ADH 5HT, released from platelets thromboxane A2 from platelets. leukotrienes. prostaglandins (F series) Endothelians calcium
what substances can permeate the BBB?
H20, dissolved gasses and some lipid soluable substances.
cerebral blood flow accounts for how much CO?
Cerebral blood flow is approx 50–55 mL/100 g/min = 15% CO
blood flow is greater to grey or white matter in the brain?
grey matter
in response to increased co2 cerebral arteries will do what?
vasodilate
discribe the fetal circulation of blood returning form the placenta?
Blood returning from placenta → umbilical vein → ductus venous → IVC → RA
→ foramen ovale → LA → LV
how does the foramen ovale shut?
Resultant change is low pressure in right atrium and high pressure in left atrium,
shuts the foramen ovale. due to w increases systemic vascular resistance + pulmonary
vascular resistance
the most important factor determining the resistance to flow is?
is the radius of the vessel.
veins are how many times more distensible than arteries ?
8 x
Describe the law of Laplace and how it relates to the left ventricle
This law states that wall tension is proportional to the pressure times radius and
inversely proportional to wall thickness. This is why a thin, dilated left ventricle
has to generate more wall tension than a hypertrophied LV.
Is there pulsatile flow in the capillaries?
No, due to the compliance of the arterial tree the pressure of pulsations is usually decreased by the time that the blood reaches the capillary so that flow is not
pulsatile at all.
In which part of the body are there specific blood reservoirs?
(1) Spleen (2) Liver (3) Large abdominal veins (4) Venous plexus beneath the skin
What is the total lymph production per day?
2–3 L. This is of high importance as proteins can not be absorbed from the tissues in any other way.
how is pulse pressure calculated?
Pulse pressure = systolic pressure − diastolic pressure
how is MAP calculated?
MABP = diastolic + 1/3 (systolic pressure – diastolic pressure)
when is pulsus paradoxus seen?
asthma and cardiac tamponade
what is the average pulmonary artery pressure?
Pulmonary BP = 25/8 = average 16 mmHg
what is the average central venous pressure?
5 -30 mmHg
3 factors promoting venous retrun
skeletam muscle pump
cardiac action of ventricular systole reducing RA pressures adn increasing venous return.
during inspiration the intrathoracic pressure decreases promotes venous return
do Larger lymphatics have smooth muscle in the walls?
yes
do Lymphatic capillaries have one-way valves?
yes
