Heart Physiology Flashcards
layers of heart wall
endocardium
myocardium
epicardium
basic function unit of the heart
myoctyes
properties of myoctyes
striated, often single nucleus
joined by intercalated discs (desmosomes and gap junctions)
auto-rhythmic
left main coronary artery branches into
left anterior descending (LAD)
left circumflex
left anterior descending coronary artery supplies
blood supply to anterior, lateral, apical wall of LV
left circumflex coronary artery supplies
blood supply to posterior and lateral wall of LV
right coronary artery (RCA) branches into
Acute marginal branch
Right Posterior Descending Artery (PDA)
right coronary artery supplies
blood supply to RA, RV, SA (sinoatrial) and AV (atrioventricular) node; Descends into 2 branches
coronary collaterals
Small off-branches from main coronaries that develop during ischemia (Coronary Artery Disease)
Formed by angiogenesis
characteristics of cardiac action potentials
prolonged depolarization phase
prolonged refractory period
The membrane does not repolarize until close to the end of the contractile phase (and hence cannot undergo TETANY – sustained contraction)
Contraction, in any muscle cell, is driven by intracellular _____ (molecule)
CA++
Pacemaker cells undergo spontaneous depolarization via specialized ion channels:
Na+ leak channels,
fast and slow Ca++ channels,
K+ channels
Pathway of electrical activities through the heart
SA node
Internodal Pathways
AV Node
Bundle of His
Purkinje Fibers
3 Main Concepts of ECG
P wave – depolarization of atria
QRS complex – depolarization of ventricle
T wave – repolarization of ventricle
5 Phases of Cardiac Cycle
- Atrial systole i.e. atrial kick -
- Isovolumetric ventricular systole: AV valves close - S1 heart sound occurs
- Ventricular ejection
- Isovolumetric ventricular relaxation closure of aortic & pulmonic valves; S2 heart sound occurs
- Passive ventricular filling
receptors in the heart that regulates heart rate
β1 and β2 adrenergic receptors are located in the heart
Activation of β1 receptors increases SA, AV and ventricular firing
key SNS neurotransmitters for heart regulation
Norepinephrine and epinephrine are key SNS neurotransmitters
vascular tone can be affected by
Norepinephrine
Renin Angiotensin System
Nitric Oxide (NO) – potent vasodilator
Reactive Oxygen Species (ROS)
The Baroreceptor Reflex (4 components)
- Receptor
- Afferent pathway
- Medulla in brainstem
- The ANS is the Efferent Pathway
Bainbridge Reflex
A compensatory mechanism
With an increase in atrial pressure (detected by atrial receptors at venoatrial junctions) there is a corresponding increase in HR
An increased blood volume causes an increase in atrial pressure
Baroreceptor Reflex and brainbridge reflex relations
Act antagonistically to control HR
Baroreceptor Reflex will ↓ HR when BP ↑
When blood volume is increased the Bainbridge Reflex is dominant
When blood volume is decreased, the Baroreceptor Reflex is dominant
Atrial Receptors located at
venoatrial junctions
atrial receptors are important to regulator of blood volume & BP through what mechanism
Distension of receptors –> PNS & SNS influence–> SA node – > HR changes
Decreased secretion of antidiuretic hormone (ADH) –> increased urine output volume
Release of atrial natriuretic peptide (ANP): Diuretic effect & natriuretic effect on kidneys
Vasodilator effect on resistance & capacitance vessels
Respiratory Sinus Arrhythmia (RSA)
Direct interaction of respiratory & cardiac centres in medulla
Neural factors: SNS & PNS
Reflex factors:
Stretch receptors in lungs
Stretch receptors in right atrium (Bainbridge Reflex)
Baroreceptors in carotid sinus & aortic arch
inspiration cause ___ in heart rate
Inspiration–> SNS activity –> increase HR
decrease intrathoracic pressure –> increase venous return –> Bainbridge Reflex –> increase HR; (after time delay increase BP –> decrease HR)
Lung stretch receptors also activated –> increase HR
expiration –> __ in HR
increase PNS activity –> decrease in HR
Chemoreceptor Reflex
Effects of arterial oxygen tension (PaO2)
(primary and secondary effects)
Primary:
Stimulation facilitates medullary vagal centre –> increase HR
Secondary: mediated by respiratory system
Stimulation (hyperventilation) –> increase pulmonary inflation reflexes
–> decrease PaCO2 –> Inhibits medullary vagal centre –> increase HR
Ventricular Receptor Reflexes
Minor effect on HR
Sensory receptors near endocardial surfaces of ventricular walls
Excitation effects (similar to arterial baroreflex) –> decrease HR & peripheral resistance
Factors Affecting Blood Flow
Pressure and resistance
Neural control of total peripheral resistance
Vascular compliance
BP equation
BP = Cardiac output (HR x SV) x total peripheral resistance (TPR)
Mean arterial pressure (MAP) minimum
minimum MAP of 60 mmHG
Important factors that affect BP
Cardiac output
Increase in blood volume
Peripheral Vascular Resistance:
- Blood vessel diameter/radius (decrease radius increases vascular resistance)
- Blood viscosity
2 major functions of arteries
- Low resistance conductive pathways
- Act as pressure reservoirs
Effect of arterial elastic recoil is to
maintain capillary flow throughout the cardiac cycle
blood viscosity is determined by
Number of blood cells
Concentration of plasma proteins
Exchange Across Capillaries is Mediated by 2 Processes
diffusion (carrier mediated and non-carrier mediated)
bulk flow
Functions of Venous System
Low resistance pathway back to heart
Blood reservoir
Veins can store extra blood
Factors that Influence Venous Return
blood volume
skeletal muscle contraction
respiratory
vascular tone
gravity
cardiac suction effect
