APPP 14 and 15: Anatomy and Physiology of the Cardiovascular System (CVS) Flashcards
What are the great blood vessels associated with the heart?
vessels conveying blood away from the heart
- pulmonary trunk, which splits into right and left pulmonary arteries
- ascending aorta
vessels returning blood to the heart
- superior and inferior venae cavae
- right and left pulmonary veins
Do arteries or veins have bigger lumens?
veins
Do arteries and veins have valves?
veins only
- helps return flow of blood to heart
- prevents blood from reversing flow
- use the ‘milking’ action of skeletal muscles to help move blood back to heart
What are capillaries made up of?
a single layer of endothelial cells – this allows for exchanges between blood and tissue
What is the pericardium and what is its function?
- double-walled sac that surrounds the heart
- space between layers of the pericardium are filled with pericardial fluid
- prevents overfilling of the heart with blood
- allows heart to work in a relatively friction-free environment
What are the 2 ventricles separated from the atria by?
atrioventricular (AV) valves
What holds AV valves in place?
chordae tendineae anchor AV vales to papillary muscles
- when ventricles contract, so do papillary muscles, pulling downward on chordae tendineae – this puts tension on valves
- AV valves prevent backflow of blood from ventricles to atria when ventricles contract
What is the tricuspid valve?
separates right atrium from right ventricle
What is the bicuspid valve?
separates left atrium from left ventricle
What valves are open during cardiac relaxation?
AV valves are open so venous blood entering the atria continues to flow directly into the ventricles
- almost 80% of ventricle filling occurs by this means before atrial contraction
- when atria do contract more, blood is squeezed into the ventricles to complete ventricular filling
- 20% more filling of the ventricles is possible when atria contract
What are semilunar valves?
- made up of three crescent-shaped cusps or flaps shaped like half-moons
- prevent backflow of blood from pulmonary trunk and aorta to ventricles
What is the aortic semilunar valve?
between left ventricle and aorta
What is the pulmonary semilunar valve?
between right ventricle and pulmonary trunk
Describe heart sounds.
associated with closing of heart valves
- first sound (lub) occurs as AV valves (mitral and tricuspid) close, and signifies beginning of systole (contraction)
- second sound (dub) occurs when semilunar valves (aortic and pulmonary) close at the beginning of ventricular diastole (relaxation)
What are coronary blood vessels (arteries/veins)?
forms the heart’s nourishing circulatory system
- blood in the heart chambers does not nourish the myocardium
- coronary circulation is the functional blood supply to the heart muscle itself
- coronary arteries are the first blood vessels to branch from aorta
- coronary arteries supply blood
- coronary veins collect blood from heart
- resting coronary blood flow is roughly about 225 ml/min, which results in 4-5% of total cardiac output
Compare blood circulation on the left and right sides of the heart.
both sides pump equal amounts of blood, BUT left side does it against higher resistance and therefore does more work
What is the pulmonary circuit of blood circulation?
blood pathway between right side of heart, to lungs, and back to left side of heart
- delivers blood from right ventricle to lungs, and from lungs to left atrium
- low pressure, low resistance system
What is the systemic circuit of blood circulation?
pathway between left and right sides of the heart
- delivers blood from left ventricle to rest of the body, and collects blood from the rest of the body (brain, digestive tract, kidneys, muscles, etc.) and delivers to right atrium
- high pressure, high resistance system
Electrical Activity
What are pacemaker cells?
do not contract, but instead initiate and conduct electrical activity (generate their own action potential)
- make up the SA node, AV node, bundle of His, and Purkinje fibres
Electrical Activity
Compare the pacemaker rates of the SA node, AV node, bundle of His, and Purkinje fibres.
- SA node (60-100 beats/min) and AV node (40-70 beats/min) have fast pacemaker rates
- bundle of His and Purkinje fibres have slow pacemaker rates (20-40 beats/min)
Electrical Activity
Describe how action potentials occur.
- made up of both depolarizing (more positive/less negative) and repolarizing (bringing current back to resting potential) currents
- pacemaker cells in SA node sets the tone or rate of the heart – depolarize spontaneously and generate APs that are propagated throughout the cardiac cell
Electrical Activity
What are the different currents (I) of the AP in the SA node? (4)
- pacemaker current (If)
- transient calcium current (ICa(T))
- depolarizing current (ICa(L))
- repolarizing current (IK)
Electrical Activity
What is the pacemaker current (If)?
carried by slow Na+ influx responsible for starting the depolarization phase
Electrical Activity
What is the transient calcium current (ICa(T))?
open for a short period of time
Electrical Activity
What is the depolarizing current (ICa(L))?
carried by slow Ca2+ influx through long-standing Ca2+ channel that remains open for a longer period of time
Electrical Activity
What is the repolarizing current (IK)?
carried by K+ efflux
Electrical Activity
What are the special aspects of APs in the ventricular contractile tissue? (4)
- longer duration of action
- rapid depolarization due to opening of Na+ channels
- plateau phase due to opening of Ca2+ channels
- repolarization due to K+ efflux
Muscle Contraction
What does myocardium do in response to AP generation (depolarization or opening of Na+ channels) within cardiac pacemaker cells?
- AP spreads along sarcolemma
- T-tubules contain voltage-gated Ca2+ channels (L-type) that open upon depolarization
- this extracellular Ca2+ enters myocadial cell and binds to RyR (ryanodine receptor) Ca2+ release channels on sarcoplasmic reticulum (SR)
- Ca2+ is released from SR – aka Ca2+ induced Ca2+ release
- release of Ca2+ from SR causes a Ca2+ spark
- multiple Ca2+ sparks form a Ca2+ signal – there is an increase in cytosolic Ca2+ (from 50 to 500 nM)
- increase in Ca2+ activates contractile proteins and muscle contracts
- note: SR contains more than 99% of intracellular Ca2+ that is bound to calcium-binding proteins (ie. calsequestrin)
- note: in active muscle, Ca2+ binding to TnC shifts troponin-tropomyosin complex, enabling actin to interact with myosin cross bridges – hydrolysis of myosin-bound ATP enables “rowing” of actin thin filaments toward the
centre
(excitation-contraction coupling – ‘coupling’ by Ca2+)
Muscle Contraction
What is the force of contraction of the myocardial cell directly related to?
concentration of free (unbound) Ca2+
Muscle Contraction
What are the mechanisms of removal of free cytosolic Ca2+? (2)
- sodium-calcium exchanger: reversible exchanges Ca2+ ions for Na+ ions across the cell membrane, causing Ca2+ extrusion from the cell
- re-uptake of Ca2+ back into SR via SR Ca2+ pump
Muscle Contraction
How does the muscle relax?
- Ca2+ is transported back into SR
- Ca2+ is transported out of cell via Na+-Ca2+ exchanger (NCX)
- as intracellular Ca2+ levels drop, interactions between myosin/actin are stopped and muscle relaxes
- sarcomere lengthens
- note: in relaxed muscle, troponin C – TnC is not bound to Ca2+ and troponin-tropomyosin prevents actin in thin filament from interacting with myosin cross-bridges
Regulators of Heart Function
What is sympathetic stimulation?
activated by stress, anxiety, excitement, or exercise
Regulators of Heart Function
What is beta-adrenergic stimulation?
with norepinephrine
What are the regulators of heart function?
- on sympathetic and beta-adrenergic stimulation, cAMP second-messenger system is activated with adenyl cyclase, converting ATP to cAMP (and therefore increasing PKA) – this helps open L-type Ca2+ channels (via phosphorylation), causing increased Ca2+ entry into the cell and eventually into the SR
- in response to next AP, increased release of intracellular Ca2+ is possible (inotropic response)
- cAMP also activates hyperpolarization activated-cyclic nucleotide gated channel (HCN channel) in SA node, allowing for an increase in slow Na+ current (pacemaker current), therefore increasing heart rate
- PKA increases rate of Ca2+ uptake into SR, which enhances rate of cardiac relaxation
- sympathetic and parasympathetic stimulation
How does stimulation of the sympathetic nervous system affect heart function?
releases norepinephrine, which increases heart rate and contractility
How does stimulation of the parasympathetic nervous system (vagus nerve) affect heart function?
releases ACh, which reduces cAMP to decrease heart rate
*What are the receptors of the heart and what are their effects?
- beta-1/HCN: heart rate
- beta-1: increased contractility
*What are the receptors of the blood vessels and what are their effects?
- alpha-1: constriction/contraction
- beta-1: dilation/relaxation
(sum total effect of contraction and relaxation)
*What is the optimal blood pressure?
120/80
*Why reduce high blood pressure?
slows progressive organ damage
- brain (thrombosis)
- eyes (retinopathy)
- kidney (nephropathy)
- heart (hypertrophy)
*Why reduce high cholesterol?
- myocardial infarction (heart attack)
- heart failure
*What is an angioplasty?
procedure in which a balloon catheter is used to stretch open narrow or blocked coronary arteries
- restores blood flow to heart muscle without open-heart surgery
*What is an arterial stent?
short wire mesh tube that acts like a scaffold to help keep artery open
- inserted with balloon catheter
*What is a coronary artery bypass graft (CABG)?
procedure that uses your own veins (usually from legs) or arteries (usually from chest or arm) to bypass narrowed areas and restore blood flow to heart muscle
*What is atrial fibrillation?
irregular heart rhythm (arrhythmia) in which atria beat rapidly and irregularly
*What is ventricular fibrillation?
irregular heart rhythm (arrhythmia) in which ventricles contract in a very rapid and uncoordinated manner due to disorganized electrical activity, therefore the heart does not pump blood to the rest of the body
*What is cardioversion?
medical treatment that uses quick, low-energy shocks to restore a regular heart rhythm
- used to treat some arrhythmias
*What is an artificial implantable pacemaker?
implanted medical device that generates electrical pulses delivered by electrodes to one or more of chambers of the heart to treat some arrhythmias
- helps heart beat at a normal rate and rhythm
*What is catheter ablation?
type of heart ablation procedure used to treat abnormal heart rhythms (arrhythmias)
- uses radio-frequency energy or other sources to terminate or modify a faulty electrical pathway from sections of the heart
- strategically destroy abnormal tissue and restore proper heart function
What are the characteristics of left ventricular hypertrophy?
- thickening in walls of ventricles
- hypertensive heart
What are the characteristics of right ventricular hypertrophy?
- enlarged right ventricle
- narrowing of pulmonary artery
How do AV valves open and close?
- blood returning to heart fills atria, putting pressure against AV valves which are forced open
- as ventricles fill, AV valve flaps hang limply into ventricles
- atria contract, forcing additional blood into ventricles
- ventricles contract, forcing blood against AV valve cusps
- AV valves close
- chordae tendineae tighten, preventing valve flaps from everting into atria
How do semilunar valves open and close?
- as ventricles contract and intraventricular pressure rises, blood is pushed up against semilunar valves, forcing them open
- as ventricles relax and intraventricular pressure falls, blood flows back from arteries, filling the cusps of semilunar valves and forcing them to close
*What is mitral valve prolapse?
one or both of the mitral valve leaflets have extra tissue or stretch more than usual
- mitral valve bows or flops back into left atrium during systole
*What are the 3 layers of arteries and veins?
- connective tissue
- smooth muscle
- endothelium
*How does pressure change in the blood vessels during blood flow?
decreases
- aorta (highest mean systemic blood pressure)
- arteries
- arterioles
- capillaries
- venules
- veins
- venae cavae
*Describe the structure of a normal artery.
- endothelial cells – with tight junctions between
- intima – contains collagen and proteoglycans
- internal elastic laminae – in intima
- media
- adventitia
What is the direction of electrical impulse in the heart?
- SA node
- AV node
- AV bundle / left and right bundle branches
- Purkinje fibres
*What is the Bachmann bundle?
conducts electricity from right atrium to left atrium
*How is electrical activity conducted through the heart?
- SA node activity and atrial activation begin
- stimulus spreads across the atrial surfaces and reaches AV node
- there is a 100 ms delay at AV node, then atrial contraction begins
- impulse travels along interventricular septum within the AV bundle and bundle branches to Purkinje fibres, and also to the papillary muscles of the right ventricle (via the moderator band)
- impulse is distributed by Purkinje fibres and relayed throughout the ventricular myocardium – atrial contraction is completed, and ventricular contraction begins
*Describe the ionic basis for cardiac APs.
- Na+ (depolarizing): extracellular > intracellular
- K+ (repolarizing): extracellular < intracellular
- Ca2+ (depolarizing): extracellular > intracellular
*What establishes electrical impermeability?
AV fibrous tissue
*What are the parts/readings on electrocardiograms (ECGs) and what do they represent?
- P wave: atrial depolarization
- QRS complex: ventricular depolarization
- T wave: ventricular repolarization
- PR interval: conduction time from atrium to ventricle
- QT interval: duration of ventricular AP
What pumps are involved in the heart contraction? (2)
- Na+-Ca2+ exchanger
- Na+-K+ ATPase
*What are the two main parts of the cardiac cycle?
- diastole: ventricular relaxation and filling
- systole: ventricular contraction and ejection
*Describe the phases of the cardiac cycle.
- late diastole: both sets of chambers are relaxed and ventricles fill passively
- atrial systole: atrial contraction forces a small amount of additional blood into ventricles
- isovolumic ventricular contraction: first phase of ventricular contraction pushes AV valves closed, but does not create enough pressure to open semilunar valves
- ventricular ejection: as ventricular pressure rises and exceed pressure in arteries, semilunar valves open and blood is ejected
- isovolumic ventricular relaxation: as ventricles relax, pressure in ventricles fall, and blood flows back into cusps of semilunar valves and snap them closed
*What is stroke volume?
volume of blood pumped by each ventricle in one contraction
- end diastolic volume (EDV) - end systolic volume (ESV)
*What is end-diastolic volume (EDV)?
volume of blood in left or right ventricle at the end of diastole (filling), just before systole (contraction) starts
*What is end-systolic volume (ESV)?
volume of blood in ventricle at the end of contraction (systole) and beginning of filling (diastole)
*What is ejection fraction?
percentage of the total amount of blood in the heart that is pumped out with each heartbeat
- stroke volume (SV) / end-diastolic volume (EDV)
*How is blood pressure calculated?
cardiac output (CO) x total peripheral resistance (TPR)
*What is cardiac output (CO)?
amount of blood pumped by each side of the heart in one minute
- CO = heart rate (HR) x stroke volume (SV)
*What are some ways of lowering blood pressure?
- reduce heart rate – beta blockers
- reduce end-diastolic volume (EDV) – diuretics
- reduce peripheral vascular resistance – vasodilators
*What are baroreceptors?
type of mechanoreceptors that allow relaying of information derived from blood pressure within the autonomic nervous system
*How does baroreceptor firing affect blood pressure?
- arterial pressure decreases
- baroreceptor firing decreases
- increase in sympathetic activity due to firing increases CO and SVR
- decrease in vagal activity due to firing increases CO
- increase in CO and SVR results in negative feedback to decrease arterial pressure
*What are the receptors of the kidney and what are their effects?
- beta-1: renin release
Congestive Heart Failure
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