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