Cardiac Presssure and AP

Question 1

What is the name of the circle of arteries on the underside of the base of the brain AND what is its physiological function?

Answer 1

• The Circle of Willis
• provides redundancies in arterial blood supply to the brain
• provides consistent perfusion to all regions; protection from ischaemia in cases where one major artery supplying the brain is temporarily blocked or narrows

Question 2

Name two plasma secretions of the kidney that are central to RAAS

Answer 2

• ACE
• Renin

Question 3

Name three aspects of the large skeletal muscle circulation that make it stand out.

Answer 3

• can use 80% of cardiac output during exercise
• arterial supply vasodilates in response to sympathetic stimulation
• muscle pump contributes directly to venous return

Question 4

Name to stand out features of neural circulation

Answer 4

• Circle of Willis
• Auto regulation

Question 5

Name three aspects of the skin that make it suited for thermo-regulation

Answer 5

• can regulate blood perfusion up to 100-fold
• arterio-venous anastomosis allow thermal exchange without the resistance of capillary beds
• sweat glands turn fluid ultrafiltrate from plasma into a rapid heat loss system

Question 6

Skin and its response to trauma

What is the triple response of Lewis, that is seen in lighter-skinned toned people?

Answer 6

• Red reaction
• Flare
• Wheal

Question 7

What four sequential events make up the cardiac cycle?

Answer 7

• Ventricular filling
• Isovolumic ventricular contraction
• Ejection
• Isovolumic ventricular relaxation

Question 8

List the heart valves, listing the regions they seperate

Answer 8

• Tricuspid Valve: Right Atrium from Right Ventricle
• Pulmonic Valve: semilunar, Right ventricle from Pulmonary Arteries
• Mitral (bicuspid) Valve: Left Atrium from Left Ventricle
• Aortic Valve: semilunar, Left Ventricle from the Aorta

Question 9

What are the valve sounds and when do they appear during the cardiac cycle?

Answer 9

• S1: First heart sound (lub)

• when Mitral & Tricuspid close, during systole

• S2: Second heart sound (dub)

• when Aortic & pulmonic valves close, during diastole
• diastole is longer than systole

Question 10

How do the ECG waves align with the ventricular action potentials?

Answer 10

• QRS complex lines up with the depolarization of ventricles
• T wave lines u with repolarisation of ventricle

Question 11

How does an ECG align with the nodal action potential?

Answer 11

• the P wave lines up with the depolarisation of the SA node

Question 12

What are the 5 phases involved in the ventricular action potential?

Answer 12

• Depolarization: Na+ gates open in response to a wave of excitation
• Transient outward current: a tiny amount of K+ leaves cell -> small amount of repolarization
• Plateau phase: inflow of Ca²⁺, balances the outflow of K+
• Rapid repolarization: membrane potential falls as K+ leaves cell
• Return to resting potential

Question 13

What are the 3 important types of potassium channels involved in cardiac activity?

• what are their primary function?

Answer 13

• Delayed rectifier: repolarizes action potential
• Inward rectifier: maintains voltage near the resting potential, and contributes to late repolarisation of AP
• Ach-activated K+ channel: slows down the heart rate in response to vagal stimulation.

Question 14

What is tetany, and why does it not occur in cardiac muscle?

Answer 14

• Tetany is a state of maximal contraction in a skeletal muscle cell
• muscles cells are highly stimulated frequently so much so that it is too rapid for recovery and relaxation,
• so the contractions effectively become continuous and stronger than possible with a single twitch
• this is caused by calcium build up in the cytosol
• doesn’t happen in cardiomyocytes because an extended contraction without relaxation would effectively stop the beating of that cell and prevent relaxation

Question 15

What is the pacemaker potential and how does it come about?

Answer 15

• the upward drift in voltage that occurs between action potentials
• this happens in myocytes of SA node, AV node and conduction system
• it occurs instead of a resting potential: inward rectifier K+ channels do not exist to maintain the resting potential at a specific level
• the slope of the pacemaker potential determines the automatic rate of firing of the cell

Question 16

Label the appropriate parts of this graph from 1 to 4 including what is happening in these intervals.

4-1: , 1-2: , 2-3: , 3-4:

Answer 16

4-1: Filling

1-2: isovolumic contr

2-3: ejection

3-4: isovolumic relax

AV valves: Open at 4, Close at 1

Semilunar valves: Open at 2, Close at 3

Question 17

Under what circumstances would you expect a systolic or diastolic murmur?

Answer 17

Systolic: Semilunar stenosis, AV valve regurgitation

Diastolic murmur: Semilunar regurgitation, AV valve stenosis

Question 18

What is the molecular basis of cardiac muscle contraction?

Answer 18

• The Sliding filament model

Question 19

In this Wiggers plot Identify

• systole and diastole
• the four phases of the cardiac pressure cycle.
• when each pair of valves opens and closes.
• *how an ECG would match against this*

Answer 19

Question 20

What valve dysfunction does the ventricular pressure-volume graph show

Answer 20

Aortic valve stenosis

• high afterload (hence higher volume for when the mitral valves open)
• higher afterload = high pressure during ejection
• and high volumes during isovolumic relaxation

Question 21

What valve dysfunction does the ventricular pressure-volume graph show?

Answer 21

Mitral valve stenosis

• volume in the left ventricle is lower,
• as preload is lower afterload is lowered, as the ventricle generates less pressure due to reduced starling forces
• the lower afterload presents as a low isovolumic relaxation - also results in a lack of a corner as the previous systole did not pump as much blood
• as a result, there is less systemic back pressure on the aortic valve

Question 22

What valve dysfunction does the ventricular pressure-volume graph show?

Answer 22

Aortic valve regurgitation

• The preload is much higher than normal (ie the right edge of the red curve is shifted leftward).
• during diastole aortic valve allows fluid to backflow into the left ventricle, adding to the fluid from the atrium
• rounded PV curves, as there is no IVC or IVR phases
• straight lines indicate when both valves are closed, however, there is never a time when both valves are completely closed, as one valve is always leaky

Question 23

What valve dysfunction does the ventricular pressure-volume graph show?

Answer 23

Mitral valve regurgitation

• low afterload because
• during systole, blood can be ejected into the left atrium as well as into the aorta, this lowers the resistance against pumping (lower pressure)
• higher preload due to extra blood in the left atrium, this puts the left atrium under high pressure which adds to the filling of the left ventricle creating volume overload

Question 24

How is the rhythm of the heartbeat initiated and maintained?

Answer 24

the SA and AV nodes have autorthymicity

• they don’t have a constant resting potential rather they have a pacemaker potential

Question 25

What is the funny current?

Answer 25

- an inward ionic current found in nodal cells and (His- Purkinje) that drive the cells to depolarise when it is in diastole - this effect is _pacemaker potential_ - Na+ is conducted inwards and K+ ions are conducted outward - the net effect is Na+ inward - the reversal potential of the funny current is typically -10mV

Question 26

What is the dicrotic notch?

Answer 26

- seen on a WIggers plot - the moment when the aortic backpressure is greater than the left ventricular systolic pressure - this leads to a temporary backflow in blood and closure of the aortic valve

Question 27

Why does amlodipine overdose sometimes cause very high heart rates?

Answer 27

- Amlodipine is a dihydropyridine Ca2+ blocker, targets channels of blood vessels rather than cardiac channels - as a result, it does not substantially slow down the heart rate - the main effect of amlodipine is vasodilatation, and in cases of overdose, the vasodilatation leads to severely low peripheral resistance and low blood pressure - this low BP is detected by baroreceptors, which homeostatically increase the heart rate to compensate for the low blood pressure

Question 28

Quinidine is antiarrhythmic drug (use prophylactically) whose main action is to block Na+ channels. In most patients it results in an increase in the rate of sinus rhythm. Why doesn’t it slow down the heart rate?

Answer 28

The main effect of Na+ channel blockers on the heart is to slow down conduction velocity between different regions of the heart; this happens because the reduced Na+ influx slows down depolarisation in the His-Purkinje system. Sinus rate, which is controlled by cells in the SA node, is highly dependent on calcium influx for depolarisation. A Na+ channel blocker would not effect the SA node activity directly.