Flow
Constant motion of a fluid
Pressure
Physical force required to create flow through any tube
Boyle's law
Pressure and force have an inverse relationship
Resistance
Force which opposes flow
Pressure gradient
Difference between area of high pressure and area of low pressure
Valves
Prevent backflow and ensure one-directional flow of blood
The heart is a ___ pump
Double
Contraction
- Decreases chamber volume
- Increases chamber pressure
Relaxation
- Increases chamber volume
- Decreases chamber pressure
Pulmonary circuit
Lungs
Systemic circuit
Tissues
Coordination of the beating heart
- Pulmonary and systemic pumps work in parallel
- They are connected to each other and highly coordinated
- Contract and relax together
- Pump roughly the same volume of blood
The heart is located in the ___ ___, protected by the ___
Thoracic cavity; pericardium
Fibrous pericardium
Outer layer, made of dense regular connective tissue
Serous pericardium
Double-layered, pericardial fluid-filled membrane
Parietal layer
Outermost layer, in contact with fibrous pericardium
Visceral layer
Surrounds and is continuous with surface of the heart
The heart is a ___-layered organ
Multi
Epicardium
- Outermost layer (superficial)
- Made of loose areolar connective tissue and adipose tissue
Myocardium
- Thickest later (middle later)
- Contains cardiomyocytes and cardiac skeleton
Endocardium
- Deepest layer
- Made of simple squamous endothelial tissue
Heart has four chambers
- Two upper chambers: atria
- Two lower chambers: ventricles
Left and right side are separated by ___
Cardiac septum
Systemic pump
- Left atrium + left ventricle
- Pumps oxygenated blood
Pulmonary pump
- Right atrium + right ventricle
- Pumps deoxygenated blood
Valves create ___ blood flow
One-directional
Blood flow through the heart and major vessels
1. Deoxygenated blood enters right atrium from body through super and inferior vena cava
2. Pumped through tricuspid valve to right ventricle
3. Blood exits heart through pulmonary arteries into pulmonary circulation
4. Oxygen-rich blood returns through pulmonary veins into the left atrium
5. Pumped through mitral valve into left ventricle
6. Blood exits heart through aorta into systemic circulation
Exceptions to blood flow during fetal development
Fetal shunts
Foramen ovale
Small hole that allows blood to bypass the right ventricle, moving directly between right atrium and left atrium
Ductus arteriosus
Connects pulmonary trunk to aorta
Cardiac anastosomes
Create different pathways for blood
Cardiomyocytes
- Have a single, centrally-located nucleus
- Short and wide
- Myofilaments are arranged into sarcomeres
- Striations are less pronounced
- Myofibrils are branched and variable in size
- Have great abundance of mitochondria
Features of cardiomyocytes
- Resist fatigue through anaerobic metabolism
- Begin to die after a few minutes without O2
- Sarcoplasmic reticulum lacks cisternae
- Membranes are fused together (intercalated discs)
- Entire tissue functions together (syncytium)
0. Resting membrane potential
(action potential in contractile cardiomyocytes)
- Typically between -80 mV and -90 mV
- Created from continuous efflux of K+ through inward rectifier potassium channels (Kir)
- Also small amount of Ca2+ and Na+ permeability
- Na/K/ATPase serves to maintain concentration gradients
1. Depolarization
(action potential in contractile cardiomyocytes)
- Similar to the process in skeletal muscle
- Voltage-gated fast sodium channels (Naf) are activated, allowing influx of positively-charged sodium ions
2. Transient repolarization
(action potential in contractile cardiomyocytes)
- Voltage-gated sodium channels rapidly inactivate at the peak of the action potential
- Sodium permeability decreases
- Cardiomyocytes go into refractory period
- Membrane potential begins to hyperpolarize due to transient outward current from potassium channels
3. Plateau phase
(action potential in contractile cardiomyocytes)
- Voltage-gated L-type calcium channels (CaL) open, bringing positively-charged Ca2+ ions into the cell
- This is opposed by the efflux of K+ ions through delayed rectifier potassium channels (Kdr)
- Two opposite electrical forces create plateau in membrane potential
4. Rapid repolarization
(action potential in contractile cardiomyocytes)
- L-type calcium channels close
- Efflux of K+ continues through voltage-gated potassium channels
- Membrane potential repolarizes to resting state
1. Pacemaker potential (aka prepotential)
(autorhythmicity is due to pacemaker cells)
- Delayed rectified channels (Kdr) allow constant efflux of K+, steadily increasing membrane potential
- Hyperpolarization-activated cyclic nucleotide gated channels (HCN) begin to open, allowing Na+ influx
- Results in "funny current": slow, incremental depolarization
- T-type calcium channels are activated, allowing influx of Ca2+, further depolarization
2. Rapid depolarization
(autorhythmicity is due to pacemaker cells)
- Inward sodium (funny current) and transient calcium influx continue depolarization until the threshold of the voltage-gated L-type calcium channel is reached
- T-type calcium and HCN channels close
- Rapid depolarization of membrane potential due solely to calcium ions
3. Repolarization
(authorhythmicity is due to pacemaker cells)
- L-type calcium channels close at peak of action potential
- Inward rectifying potassium channels (Kir) open
- Increased permeability to K+ returns cell to hyperpolarized membrane potential
SA node
- Where pacemaker cells are located
- Generate action potentials faster than any other heart cell
Internodal pathways
Conducts action potentials from SA node to the myocytes in the atria through gap junctions
AV node
- Contains slower pacemaker cells
- Slows action potential conduction to allow time for an atrial refractory period
Bundle of his
Conducts action potential from AV node to interventricular septum, where it splits into left and right bundle branches
Right and left bundle branches
Propagate action potential through interventicular septum to heart apex
Purkinje fibers
Spread action potentials from apex to left and right ventricles rapidly due to their high proportion of intercalated discs
Arrhythmias
Family of disorders characterized by abnormal electrical activity within the heart
Causes of arrhythmias
Breakdown in coordination of the electrical conduction system
Effects of arrhythmias
Changes in pumping activity, producing a variety of effects, from harmless to fatal
- Atrial fibrillation
- Ventricular fibrillation
ECG
- Provides an electrical picture of heart function
- Obtained through leads placed on the surface of the skin
- Summary of electrical changes taking place within all cells of an entire organ
- Not a direct measure of action potentials within individual cells
Positive end of lead
- Depolarizing current: produces upward deflection
- Repolarizing current: produces downward deflection
Negative end of lead
- Depolarizing current: produces downward deflection
- Repolarizing current: produces upward deflection
P wave
Depolarization of atria
QRS complex
Ventricular depolarization
Q wave
Depolarization of septal region of ventricle
R wave
Depolarization of anterior region of ventricle
S wave
Depolarization of inferior portions of ventricle
T wave
Ventricular repolarization
P-Q interval
Time required for atrial depolarization and action potential to reach ventricles
P-R interval
Time required for atrial depolarization to propagate through the ventricles
S-T segment
Time course of ventricular depolarization
Q-T interval
Combined time required for ventricular depolarization and repolarization
The force of cardiac contraction is ___ to the amount of calcium released into the cytoplasm during excitation-contraction coupling
Proportionate
1. Atrial systole
(cardiac cycle)
- Corresponds with contraction of the atria
- Atrial pressure: greater than ventricle
- AV valves: open
- Ventricles: blood volume increasing, eventually reaching the maximum they can hold (end diastolic volume, or EDV)
2. Early ventricular systole
(cardiac cycle)
- Corresponds with contraction of the ventricles
- Ventricular pressure: greater than atria, less than great vessels
- Blood volume: constant at EDV
- AV valves: closed
- SL valves: closed
3. Late ventricular systole
(cardiac cycle)
- Ventricular pressure: greater than atria, greater than great vessels
- Blood volume: decreasing as stroke volume (SV) is ejected, until residual end systolic volume (ESV) is left
- AV valves: closed
- SL valves: open
4. Early ventricular diastole
(cardiac cycle)
- Corresponds to relaxation in ventricles
- Ventricular pressure: greater than atria, less than great vessels
- Blood volume: constant at ESV
- AV valves: closed
- SL valves: closed
5. Atrial diastole
(cardiac cycle)
- Atrial pressure: less than ventricles
- Ventricular blood volume: decreasing
- AV valves: open
6. Late ventricular diastole
(cardiac cycle)
- Ventricular pressure: less than atria, less than great vessels
- Ventricular blood volume: increasing through passive filling
- AV valves: open
- SL valves: closed
Cardiac output
Amount of blood pumped by a ventricle in a period of time
Cardiac output (CO)
Stroke volume (SV) x heart rate (HR)
Cardiac reserve
Difference between cardiac output at rest and during exercise
The force of cardiac muscle contraction is proportional to the ___ of its fibers
Resting length
During exercise ___
Ventricles stretch to accommodate increasing amounts of passively-entering blood (preload)
Extrinsic regulation of cardiac output through neural mechanisms
Innervated by both sympathetic and parasympathetic branches of the autonomic nervous system
Sympathetic effects
Catecholamines are released onto B1-adrenergic receptors
- Activation of PKA, phosphorylation of targets and production of cAMP
Parasympathetic effects
Acetylcholine is released onto muscarininc receptors
- Decreases cAMP and speed of cardiac contraction
Phosphorylation of PKA ___ the strength of cardiac contraction
Increases
PKA activation results in
- Phosphorylation of L-type Ca2+ channels: increase conductance
- Phosphorylation of the ryanodine receptor: open
- Phosphorylation of troponin C: increases Ca2+ sensitivity
- Phosphorylation of regulatory protein PLB: increases SERCA activity