CVS Physiology Flashcards
Define the word “cardiovascular”
Cardio = heart pump Vascular = vessels
Role of the cardiovascular system
Bulk flow system transporting: o O2 and CO2 o Nutrients o Metabolites o Hormones o Heat
Which circulations do the left and right side of the heart pump out to?
Right side = pulmonary circulation
Left side = systemic circulation
Are the heart pumps in parallel or series? Significance of this
Series.
All the blood that flows from right side of heart must then flow through left side of heart.
Output of R and L sides must be equal, if not over time all the blood would end up in one or the other circulations
Are vascular beds in parallel or series? Significance of this
MOST are in parallel.
Ensures blood goes to all the areas of the body at the same time, ensuring all tissues get oxygenated blood. Allows for regional redirection of blood (some regions require more blood)
What is the total cardiac output (ml/min)
5000ml/min
Which vascular beds are in series? And why?
Between the gut and liver. Nutrients are picked up in the gut and moved to the liver
What is mean arterial pressure?
The high pressure blood coming out of the left side of the heart
What is central venous pressure?
The low pressure blood coming back into the right side of the heart
How is the resistance controlled?
By the radius of the vessels (arterioles) going to the vascular beds
Explain the features and functions of elastic arteries
Features: wide lumen, elastic wall
Function: absorb increase pressure during the ejection phase. The absorbed energy used to push back on blood during relaxation phase to maintain pressure and keep blood moving forward
Which arteries are elastic?
Aorta
Pulmonary trunk
Features and function of arteries
Features:
- Wide lumen
- Muscular walls (NOT elastic)
- Very low resistance
Function: get blood out as easily as possible
Features and functions of arterioles
Features:
- narrow lumen
- thick muscular wall
Function:
- control resistance therefore allowing regional redirection of blood
Features of venules and veins
Features:
- wide lumen
- distensible wall (capable of being swollen or dilated)
- low resistance
Function:
- capacitance vessels - able to store a lot of blood
Volume of blood in veins and venules
2/3 of blood volume in veins and venules moving very slowly back to heart
Features and function of capillaries
Features:
- narrow lumen
- thin wall
Function:
- exchange vessels
What seperates the two pumps in the heart?
Interventricular septum
What is the wall of the heart called? Which side is thicker & why?
Myocardium
Left side thicker as has to have higher pressure to push blood through systemic circulation
Which artery pumps to systemic circulation
Left side of the heart through the aorta
By which vein does deoxygenated blood return to the heart & which compartment?
Right sided atrium
Superior vena cava = blood from the top of the body
Inferior vena cava = blood from bottom of the body
Where does the deoxygenated blood from the right atrium go?
Enters right ventricle and pumped through pulmonary circulation via pulmonary trunk.
L and R pulmonary trunk taking blood to each lung
How does the oxygenated blood from lungs return to heart?
By 2 pulmonary veins into the left atrium
Which valves prevent back flow into the ventricles?
Aortic valve between L ventricle and aorta
Pulmonary valve between R ventricle and pulmonary artery
Structure of the aortic and pulmonary valve
Semi-lunar (allows blood to go out the heart but not back)
Which valves separate the L atrium from L ventricle and R atrium from R ventricle?
L atrium and L ventricle = mitral valve
- 2 cusps
R atrium and R ventricle = tricuspid valve
- 3 cusps
What prevents valves inverting when ventricles contract?
Cordae tendineae
+ papillary muscles which contract at same time as heart (heart shortens when it contracts so papillary muscles keep tendons at appropriate length)
What is the cardiac functional syncytium?
Syncytium is formed by fusion of individual cells. In cardiac muscle the cells are individual (don’t fuse) but act as if the the cardiac muscle is one big muscle.
Both electrically and physically connected
How are cardiac muscle cells connected? What does this allow?
By gap junctions (protein channels connecting cytoplasms of 2 cells together)
- Allows electrical current and small signalling molecules to pass through
- If one cell depolarises the neighbouring cell will to = both contract
By desmosomes = physical connections preventing cells from pulling apart when they contract
How does the cardiac action potential differ from the skeletal muscle action potential
Cardiac muscle = 200-250milliseconds
Skeletal muscle = 1-2milliseconds
What are the 2 consequences of the longer action potential in cardiac muscle
- During plateau phase calcium comes into cell contributing to excitation, contraction and coupling. Also triggers cross bridge formation
- more calcium = more cross bridges
- calcium gated channels allow amount of calcium to be regulated
- regulates contraction strength
- Long refractory period
- cardiac muscle cant stay contracted
- needs to contract, relax, contract to allow heart to fill with blood
Compare action potential difference between between non-pacemaker tissue and packemaker tissue
Non-pacemaker sits at -90mV and doesn’t do anything until instructed by neighbours (gap junctions)
- rapid depolarisation, long plateau, repolarisation
Pacemaker potential spontaneously depolarises towards threshold
- action potential evoked (depolarises), then spontaneously depolarises again
List the elements of the heart involved in conduction
Sinoatrial node Annulus fibrosus Atrioventricular node (AV node) Bundle of His Purkinje fibres
Role of the sinoatrial node
Fastest pacemaker (by definition the pacemaker as reach threshold soonest)
Spreads from cell-cell creating wave of depolarisation (0.5m/sec)
Found in the right atrium
Role of annulus fibrosus
Separates the atria and ventricles
Only non-conducting part of the heart - in healthy heart depolarisation evoked in ventricles can’t get through and forced to go through AV node
Role of atrioventricular node
Conducts VERY slowly (0.05m/sec) - the delay box of heart
Allows atria time to depolarise and contract to expel blood into ventricles before ventricles contract and expel blood
Role of the Bundle of His
Bundle of His travels down interventricular septum splitting into purkinje fibres
Ensure depolarisation spreads through whole ventricle at same time to evoke sharp contraction = big pressure to eject blood
Role of Purkinje fibres
Conduct rapidly (5m/sec) Depolarisation spread to all parts of heart at same time to ensure coordination of contraction
Correlate the P wave, QRS complex, and T wave with electrical events in heart
P wave: wave of depolarisation across the atria
QRS complex: wave of depolarisation across ventricles
T wave: repolarisation of ventricles
What information does the ECG give us (3)?
Information on spread of depolarisation
Disorders of conduction
Whether the heart rhythm is correct
How many seconds does each large square on ECG correlate to?
0.2 seconds
What is Heart block?
Depolarisation doesn’t spread from atria through AV node therefore ventricles aren’t depolarised
What is 1st degree heart block?
Abnormal delay between atrial depolarisation and ventricular depolarisation
Most likely in AV node
P, QRS and T visible delay between P and QRS
What is 2nd degree heart block
Some of depolarisation don’t get through at all
E.g. P wave which isn’t followed by any QRS, T
Gradually longer interval between P and QRS complex
What is 3rd degree block
No transmission between atria and ventricle
P waves occurring as they should but not followed by QRS
Another pacemaker in ventricles has taken over and makes ventricles depolarise from different place
Upside down T from repolarisation
What is atrial flutter (supra ventricular tachycardia)
Normal P, QRS, T but compressed so P wave occurs on back of previous T wave
Each depolarisation occurs much faster than it should
What is atrial fibrillation
No coordination of P wave
Individual cells depolarising at different times across the atria
Uncoordinated depolarisation and contraction
Occasionally depolarisation gets through AV node to ventricles evoking QRS, T wave
What is ventricle fibrillation
Very dangerous
Ventricular muscle quivers not producing any coordination
Defibrillator required - resets the pacemaker system by stopping the heart
What does the PR interval on an ECG indicate?
Time from start of P wave to start of the QRS complex
Time from start of atrial depolarisation to start of ventricle
depolarisation (major time here is time taken for transmission through AV node)
0.12-0.2 seconds
What does QRS complex on ECG indicate?
Time for whole ventricle to depolarise (first cells of ventricles until last)
Determined by Purkinje fibres in bundle of His
0.08seconds
What does the QT interval on ECG indicate?
Time from start of QRS complex until end of T wave
Measures time when ventricles are depolarised
Varies with heart rate (0.42 at 60bpm)
How to measure heart rate from ECG?
Count the R waves in 30 large squares (6 seconds) and multiply by 10
What is normal bpm, bradycardia and tachycardia?
Normal = 60-100bpm Bradycardia = <60bpm tachycardia = >100bpm
What is the ST segment?
the gap between the QRS complex and the T-wave
What is STEMI vs. NSTEMI? Which is worse?
STEMI = ST elevated myocardial infarction NSTEMI = non-ST elevated myocardial infarction
STEMI is worse than NSTEMI
What causes the 4 heart sounds?
1st - closure of the AV (mitral and tricuspid valves)
2nd - closure of the semi-lunar (aortic and pulmonary valves)
3rd - rapid filling phase
4th - active filling phase
What does the period between the 1st and 2nd heart sounds represent?
Systole
What fraction of the cardiac cycle do systole and diastole take up
Systole 1/3
Diastole 2/3
