WEEK V (Heart) Flashcards
What does the circulatory system consist of?
- Heart
- Blood vessels
- blood
What is the importance of the circulatory system?
The circulatory system contributes to homeostasis by serving as the body’s transport system
What is the importance of the Heart?
- All body tissues constantly depend on the life-supporting blood flow from the heart
- The heart drives blood through the blood vessels for delivery to the tissues in sufficient amounts
What is Systemic Blood Flow?
Cardiac output from the left side of the heart
What is Pulmonary Blood Flow?
Cardiac output from the right side of the heart
Describe the direction of blood flow
1) From the LUNGS to the LEFT ATRIUM via the PULMONARY VEIN
2) From the LEFT ATRIUM to the LEFT VENTRICLE through the MITRAL VALVE
3) From the LEFT VENTRICLE to the AORTA through the AORTIC VALVE
4) From the AORTA to the SYSTEMIC ARTERIES and the SYSTEMIC TISSUES
5) From the TISSUES to the SYSTEMIC VEINS and VENA CAVA
6) From the VENA CAVA to the RIGHT ATRIUM
7) From the RIGHT ATRIUM to the RIGHT VENTRICLE through the TRICUSPID VALVE
8) From the RIGHT VENTRICLE to the PULMONARY ARTERY through the PULMONIC VALVE
9) From the PULMONARY ARTERY to the LUNGS for oxygenation
What is the Heart?
The pump that imparts pressure to the blood to establish the pressure gradient needed for blood to flow to the tissues
What are the blood vessels?
Passageways through which blood is directed and distributed from the heart to all parts of the body and subsequently returned to the heart
What is blood?
The transport medium within which materials being transported long distances in the body (e.g O2, CO2, Nutrients, Wastes, Electrolytes, Hormones) are dissolved or suspended
What is pressure?
The force exerted on the vessel walls by the blood pumped into them by the heart
What is Resistance?
The opposition to blood flow largely caused by friction between the flowing blood and the vessel wall
Do both sides of the heart simultaneously pump equal amount of blood?
YES
What is the difference between Pulmonary circulation and Systemic circulation?
PULMONARY CIRCULATION is a low-pressure, low-resistance system whereas SYSTEMIC CIRCULATION is a high-pressure, high-resistance system
Why is the heart muscle on the left side thicker than the right side?
Since the left side works harder because it pumps an equal volume of blood at a higher pressure into a higher-resistance and longer system
What are the functions of atrioventricular valves?
- Let blood flow from the atria into the ventricles during VENTRICULAR FILLING
[when atrial pressure exceeds ventricular pressure] - Prevent back flow of blood from the ventricles into the atria during VENTRICULAR EMPTYING
[when ventricular pressure exceeds atrial pressure]
What would happen if the rising ventricular pressure did not force the AV valves to close as the ventricles contracted to empty?
Much of the blood would inefficiently be forced back into the atria and veins instead of being pumped into the arteries
What are the Right and Left Atrioventricular valves called?
- Right AV = Tricuspid Valve (3 cusps)
- Left AV = Bicuspid Valve/Mitral Valve (2 cusps)
What is the function of the Chordae Tendineae?
- Fasten the edges of the AV valve leaflets
- Tough, thin cords of tendinous-type tissue
- Prevent the valve from EVERTING
What do Chordae Tendineae attach to?
Papillary muscles
What happens when the ventricles contract?
Papillary muscles also contract -> Pulls downward on the CHORDAE TENDINEAE -> Pulling exerts tension on the closed AV valve cusps to hold them in position -> Action helps keep the valve tightly sealed in the face of a STRONG BACKWARD PRESSURE GRADIENT
Describe the structure of the layers of the heart
- Heart walls composed primarily of spirally arranged cardiac muscle fibers
- Outermost layer of heart is VISCERAL LAYER of SEROUS PERICARDIUM which surrounds the HEART & ROOTS of the CORONARY VESSELS
What are the layers of the heart? (outer to inner)
- FIBROUS PERICARDIUM
- PARIETAL LAYER OF SEROUS PERICARDIUM
- PERICARDIAL CAVITY
- EPICARDIUM
- MYOCARDIUM
- ENDOCARDIUM
What is the function of the Serous Pericardium?
- Protects the heart
- Provides signals for embryonic heart formation and maturation
- Secretes factors for CARDIOMYOCYTE PROLIFERATION & SURVIVAL
- Helps with the Heart’s INJURY RESPONSE & REGENERATION
Describe the Cardiac muscle
- Sarcomeres are connected end-to-end to form MYOFIBRILS
- Many of these Myofibrils can be found in the SARCOPLASM of the CARDIAC CELL
- Contains SARCOLEMMA with deep invaginations called T-TUBULES that are responsible for bringing the action potential to the SARCOPLASMIC RETICULUM
What is the heart enclosed by?
The double-walled, membranous part of the PERICARDIAL SAC
Describe the two layers of the Pericardial Sac
OUTER FIBROUS COVERING = attaches to the connective tissue partition that separates the lungs. This attachment anchors the heart so it remains properly positioned within the chest.
SECRETORY LINING = secretes a thin PERICARDIAL FLUID which provides lubrication to prevent friction between the pericardial layers as they glide over each other with every beat of the heart
What is Pericarditis?
An inflammation of the pericardial sac that results in painful friction between the two pericardial layers & occurs due to viral or bacterial infection
Cardiac myocytes can contract as a result of some sort of stimulus. Where can this stimulus come from?
- A neuron
- Nearby cardiac muscle cell
- Due to the cells own myogenic activity
Summarise the action potential in a Cardiac muscle
1) Once a stimulus reaches THRESHOLD VALUE, it will cause the rapid opening of SODIUM VOLTAGE GATED CHANNELS on the cell membrane. This will cause the movement of sodium ions into the cell which will lead to DEPOLARISATION. At -40 mV, L-type calcium channels open up
2) Once membrane voltage reaches +30mV the SODIUM CHANNELS close quickly & POTASSIUM VOLTAGE GATED CHANNELS open slowly. Movement of the +ve charged ions out of the cell causes inside to become LESS POSITIVE
3) One the cell reaches a voltage difference of 0mV, the rate of INFLUX of CALCIUM is equal to EFFLUX of POTASSIUM. This extends DEPOLARISATION PERIOD and is known as PLATEAU PHASE
4) As CALCIUM VOLTAGE GATED CHANNELS begin to close the EFFLUX OF POTASSIUM exceeds the INFLUX of CALCIUM. This causes more POTASSIUM VOLTAGE-GATED ION CHANNELS to open causing a rapid decrease in the membrane until back to normal
5) Resting potential of a cardiac myocyte is around -90mV. At the RESTING POTENTIAL, the cell has a higher concentration of SODIUM, CALCIUM and CHLORIDE IONS on the outside compared to the inside & has a higher concentration of POTASSIUM IONS than on the inside
What is the pathway of conduction in the heart?
1) SA Node
2) AV Node
3) Bundle of His
4) Right & Left Bundle Branches
5) Purkinje Fibers
Describe Atrial Systole
MAJOR EVENT - Atria contract & Final phase of ventricular filling
ELECTRODIAGRAM - P wave/PR interval
VALVES - None
HEART SOUNDS - Fourth heart sound
Describe Isovolumetric Ventricular Contraction
MAJOR EVENT - Ventricles contract, Ventricular pressure increases & Ventricular pressure is constant (all valves are closed)
ELECTRODIAGRAM - QRS Complex
VALVES - Mitral valve closes
HEART SOUNDS - First heart sound
Describe Ventricular Ejection
MAJOR EVENT - Ventricles contract, Ventricular pressure increases and reaches maximum, Ventricles eject blood into arteries, Ventricular volume decreases, Aortic pressure increases and reaches maximum
ELECTRODIAGRAM - ST segment
VALVES - Aortic valve opens
HEART SOUNDS - None
Describe Reduced Ventricular Ejection
MAJOR EVENT - Ventricles eject blood into arteries (slower rate), Ventricular volume reaches minimum, Aortic pressure starts to fall as blood runs off into arteries
ELECTRODIAGRAM - T Wave
VALVES - None
HEART SOUNDS - None
Describe Isovolumetric Ventricular Relaxation
MAJOR EVENT - Ventricles relaxed, Ventricular pressure decreases, Ventricular volume is constant
ELECTRODIAGRAM - None
VALVES - Aortic valve closes
HEART SOUNDS - Second heart sound
Describe Rapid Ventricular Filling
MAJOR EVENT - Ventricles relaxed, Ventricles fill passively with blood from atria, Ventricular volume increases, Ventricular pressure is low and constant
ELECTRODIAGRAM - None
VALVES - Mitral valve opens
HEART SOUNDS - Third heart sound
Describe Reduced Ventricular Filling/Diastasis
MAJOR EVENT - Ventricles relaxed & Final phase of ventricular filling
ELECTRODIAGRAM - None
VALVES - None
HEART SOUNDS - None
Summarise the cardiac cycle
1) Passive filling during ventricular and atrial systole
2) Atrial contraction
[both VENTRICULAR FILLING - AV valves open & Semilunar valves closed]
3) Isovolumetric ventricular contraction
[all valves closed]
4) Ventricular Ejection
[VENTRICULAR EMPTYING - Semilunar valves open & AV valves closed]
5) Isovolumetric ventricular relaxation
[all valves closed]
What are the stages of the Cardiac cycle?
- Mid-ventricular Diastole
- Late ventricular Diastole
- End of Ventricular Diastole
- Onset of Ventricular Systole
- Isovolumetric Ventricular contraction
- Ventricular Ejection
- End of ventricular systole
- Onset of Ventricular Diastole
- Isovolumetric Ventricular Relaxation
- Ventricular Filling
What happens in Mid-ventricular Diastole
- TP segment on ECG (interval after ventricular depolarisation and before another atrial depolarisation)
- Atrial pressure exceeds ventricular pressure due to continuous inflow of venous blood
- AV valve is open allowing passive filling of ventricle during relaxation
What happens in Late Ventricular Diastole?
- SA node reaches threshold and fires leading to contraction
- Impulse spreads across atria which appears as P wave on ECG
- Atrial pressure still exceeds ventricular pressure -> AV valve remains open
What happens at the end of Ventricular Diastole?
- End at the onset of ventricular contraction
- Atrial contraction & Ventricular filling are completed
- END-DIASTOLIC VOLUME (EDV) is the volume of blood in the ventricle at the end of diastole which is the max amount of blood that the ventricle contains during the cycle (135ml)
What happens on the Onset of Ventricular Systole?
- After atrial excitation, impulse travels through AV node to excite the ventricle
- QRS complex in ECG
- As ventricular contraction begins, ventricular pressure immediately exceeds atrial pressure -> forces AV valve to close
What happens during Isovolumetric Ventricular Contraction?
- AV valve closes & Aortic valve is still closed
- No blood enters or leaves the ventricle
- Ventricular chamber stays at constant volume -> muscle fibers stay at constant length -> ventricular pressure continues to rise
What happens during Ventricular Ejection?
- Ventricular pressure exceeds aortic pressure -> Aortic valve is forced open and ejection of blood begins
- Aortic pressure curve rises as blood is forced into the aorta from the ventricle faster than blood is draining off into smaller vessels at the other end
What is the Stroke volume?
The amount of blood pumped out of each ventricle with each contraction
What does Ventricular systole include?
- Isovolumetric ventricular contraction
- Ventricular Ejection
What happens at the end of Ventricular systole?
- The ventricle does not completely empty during ejection
- The amount of blood left in the ventricle at the end of systole when ejection is complete is called END SYSTOLIC VOLUME (ESV)
What happens during the onset of ventricular diastole?
- T wave in ECG
- Ventricle depolarises and starts to relax & ventricular pressure falls below aortic pressure and aortic valve closes
- Closure of aortic valve produces DICROTIC NOTCH
- No more blood leaves the ventricle because aortic valve has closed
What happens during Isovolumetric Ventricular Relaxation?
- Aortic valve closes but AV valve is not yet open since ventricular pressure exceeds atrial pressure
- No blood enters or leaves as the ventricle continues to relax and pressure steadily falls (ISOVOLUMETRIC VENTRICULAR RELAXATION)
What does the autonomic nervous system do?
It regulates the rate of the heart but does not actually initiate it
What does the cardiac muscle having myogenic activity mean?
Cardiac muscle can initiate contraction without the input of the nervous system
What is the Sinoatrial node (SA node)?
A collection of specialised cardiac muscle cells located in the upper part of the right atrium which generate action potentials on their own and set the pace at which the heart contracts (60-100 beats/min)
What happens once impulse is generated in the SA node?
It spreads through both atria and causes them to contract at the same time
What is the Atrioventricular Node?
A collection of specialised cardiac myocytes that are found in the wall between the atria and ventricles of the heart
Describe the electrical conduction in heart
1) SA node generates action potential which travels through conduction channels and to AV node. Once AV node receives signal, it delays it slightly in order to ensure that atria contract effectively and all blood enters the RELAXED VENTRICLES
2) AV node depolarises and sends electrical signal via BUNDLE OF HIS found in ventricles of heart. Bundle of his splits into LEFT & RIGHT BRANCHES which runs along INTERVENTRICULAR SEPTUM
3) Right & Left bundles divide to form PURKINJE FIBRES. BUNDLE OF HIS + PURKINJE FIBRES distribute the electrical signal to both ventricles simultaneously causing them to contract at the same time
How does the parasympathetic system affect the heart?
Can slow down the heart rate via VAGUS NERVE which extends into the heart from the CNS
How does the sympathetic system affect the heart?
Can speed up heart rate
What are the properties of the Sinoatrial node?
- Pacemaker of heart
- Has unstable restin potential
- Exhibits phase 4 depolarisation/automaticity
- AV node and His-Purkinje systems are LATENT PACEMAKERS that may exhibit automaticity and override the SA node if suppressed
- Intrinsic rate of phase 4 depolarisation is fastest in SA node and slowest in His-Purkinje system
Describe what happens from Phase 0 to Phase 4
PHASE 0
- Upstroke of action potential
- Increase in Ca2+ conductance causes inward Ca2+ current that drives the membrane potential towards the Ca2+ equilibrium potential
PHASE 1&2
- not present in SA node action potential
PHASE 3
- Repolarisation
- Caused by an increase in K+ conductance. Increase results in outward K+ current that causes depolarisation of the membrane potential
PHASE 4
- Slow depolarisation
- accounts for the pacemaker activity of the SA node
- Caused by an increase in Na+ conductance which results in an inwards Na+ current called Lf
- Lf is turned on by REPOLARISATION of membrane after action potential
Upstroke of the action potential in the AV node is the result of what?
Inward Ca+ current
Describe the action potential in the Sinoatrial node
DURATION - 150 msec
UPSTROKE - Inward Ca2+ current
PLATEAU - None
PHASE 4 DEPOLARISATION - Inward Na+ current
Describe the action potential in Atrium
DURATION - 150 msec
UPSTROKE - Inward Na+ current
PLATEAU - Inward Ca2+ current (slow inward current)
PHASE 4 DEPOLARISATION - None
Describe the action potential in Ventricle
DURATION - 250 msec
UPSTROKE - Inward Na+ current
PLATEAU - Inward Ca2+ current (slow inward current)
PHASE 4 DEPOLARISATION - None
Describe the action potential in Purkinje fibers
DURATION - 300 msec
UPSTROKE - Inward Na+ current
PLATEAU - Inward Ca2+ current (slow inward current)
PHASE 4 DEPOLARISATION - Latent pacemaker
What is Conduction Velocity?
Reflects the time required for excitation to spread throughout cardiac tissue
What are the properties of Conduction Velocity?
- Depends on the size of the inward current during the upstroke. Larger the inward current -> Higher the conduction velocity
- Fastest in the PURKINJE SYSTEM
- Slowest in the AV NODE (allowing time for ventricular filling before ventricular contraction)
What is Excitability?
The ability of cardiac cells to initiate action potentials in response to inward, depolarising current
What are the properties of Excitability?
- Reflects the recovery of channels that carry the inward currents for the upstroke of the action potential
- Changes over the course of the action potential
When is the Absolute refractory period (ARP)?
Begins with the upstroke of the action potential and ends after the plateau
Describe Negative Dromotropic effect?
- Decreases conduction velocity through the AV node
- Action potentials conducted more slowly from the atria to the ventricles
- Increases PR interval
- Decreased inward Ca2+ current and increased outward K+ current
Describe Positive Chronotrophic effect
- Increases heart rate by increasing the rate of phase 4 depolarisation
- More action potentials since threshold potential is reached more quickly & frequently
- Increased Lf (the inward Na+ current that is responsible for phase 4 depolarisation in the SA node)
Describe Positive Dromotrophic effect
- Increases conduction velocity through the AV node
- Action potentials conducted more rapidly from the atria to ventricles and ventricular filling may be compromised
- Decreases PR interval
- Increased inward Ca2+ current
