Module 5

Circulatory System

Transport vital material throughout body

Heart

Double pump
Left and right separated by septum
Generate pressure to move blood

Blood Vessels

Conduct blood
Deliver nutrients to cells
Carry metabolic waste away

Blood

Transport media
Material dissolve, suspend, or bound to blood

Circulatory Function: Gas Exchange

Deliver O2
Remove CO2

Circulatory Function: Nutrient and Water

Delivery
Absorb by cells

Circulatory Function: Heat and Waste

Remove by blood flow

Circulatory Function: Immunity and Defense

Transport immune cells
Identify and neutralize foreign pathogens

Circulatory Function: Cell Communication

Carry chemical messages

Circulatory Organization

Closed loop system
Serial blood flow (left heart, systemic, right heart, lungs)

Pulmonary Circulation

Blood to and from lungs

Systemic Circulation

Blood throughout body

Blood Flow

Serial in whole system
Parallel in systemic circulation

Blood Flow: Parallel

Simultaneous blood delivery to tissues
Converge at right heart

Heart: Atrium

Upper chamber
Receive returning blood
Transfer to ventricles

Heart: Ventricles

Lower chamber
Pump blood out

Major Blood Vessel: Veins

Carry blood to heart

Major Blood Vessel: Artery

Carry blood away from heart

Blood Flow 1

Left ventricle to aorta (artery)
Pump O2 rich blood

Blood Flow 2

Blood deliver O2 to tissues
In arteries

Blood Flow 3

Material exchange
Remove O2 and nutrients from blood
Add CO2 and waste to blood

Blood Flow 4

O2 poor blood in veins
Return to right atria through vena cava

Blood Flow 5

Right ventricle to pulmonary artery
O2 poor blood

Blood Flow 6

Lungs remove CO2 and add O2 to blood

Blood Flow 7

Pulmonary veins to left atria to left ventricle
O2 rich blood

Heart Valves

Unidirectional flow
Pressure-operated

Heart Valves: Open

Increase pressure behind valve

Heart Valves: Close

Decrease pressure behind valves
Prevent backflow

Atrioventricular Valve (AV)

Between atria and ventricles
Open when larger atrial pressure
Close when larger ventricular pressure
Connected to ventricle papillary muscles via chordae tendinae to prevent eversion

AV: Tricuspid Valve

Right AV valve
3 leaflets

AV: Bicuspid Valve

Left AV valve
2 leaflets
Mitral valve

Semilunar Valve

Between ventricles and arteries
3 leaflets
No chordae tendinae
Valve shape prevents inversion

Semilunar: Pulmonary Valve

Between right ventricle and pulmonary artery

Semilunar: Aortic Valve

Between left ventricle and aorta

Valvular Heart Disease

Valve dysfunction
Cannot maintain unidirectional blood flow

Valvular Regurgitation

Improper valve closure
Blood flows backwards
Decrease blood leaving heart
Irregular heart beat
Stress on walls
Cardiac failure

Valvular Stenosis

Narrow valve
Inhibit blood flow out
Increase pumping force

Cardiac Muscle Features

Striated
Branched fibres
Ca2+ activated troponin and tropomyosin for cross-bridges
T-tubules and SR
Length-tension relationship
Gap junctions spread excitation
ANS innervation modify contractions

Cardiac Muscle Fibres

Branching network
Spiral arrangement
Contractions squeeze and generate pressure

Cardiac Muscles: Intercalated Discs

Muscle fibre connections
Contain desmosomes and gap junctions

Intercalated Discs: Desmosomes

Hold cells together

Intercalated Discs: Gap Junctions

Cell communication
Spread action potentials
Wave-like contractions push blood out

Pericardial Sac

Double-walled membrane
Lubrication prevent friction
Protect heart

Pericardium: Fibrous Layer

Anchor heart to surrounding walls
Keep in place during movement
Prevent blood overfill

Pericardium: Serous Layer

2 layers
Parietal and visceral
Lubricate with pericardial fluid
Prevent friction

Electro-Mechanical Heart

Electrical and muscular activity
Generate and conduct action potentials
Large muscle contractions

Heart Cell: Contractile

Mechanical work

Heart Cell: Electrical

Generate and propagate action potentials to contractile cells
Independent generation
Not dependent on CNS or PNS

Neural Effects: Exercise

Sympathetic
Increase heart rate
Blood and O2 delivery
CO2 and waste removal

Neural Effects: Fear

Sympathetic
Increase heart rate
Fight of flight

Neural Effects: Illness and Injury

Sympathetic
Increase heart rate and blood flow

Autorhythmic Cells

Muscle cells
Contain ion channels depolarizing membrane potential
Generate action potentials

If Channels

Allow current flow
Na+ and K+ enter cell
Membrane potential depolarize

If Channel: Activation

Hyperpolarization-activated cyclic nucleotide-gated channel (HCN) family
T-type Ca2+ channel (action potential upstroke)

Autorhythmic Cells: Sinoatrial Node (SA)

In right atrial wall
Near superior vena cava opening

Autorhythmic Cells: Atrioventricular Node (AV)

In interatrial septum
Right atria and right ventricle interface

Autorhythmic Cells: Bundle of His

Specialized AV node cells
2 branches in septum

Autorhythmic Cells: Purkinje Fibres

Branches of bundle of His
In inner endocardial ventricle surface

Pacemaker Cells

In SA node
Fast depolarization
Control heart beat rate
Override pacemaker activity of other cells

Contraction Criteria: Complete Atrial Contraction

Complete atrial contraction before ventricular contraction
Relaxation lowers ventricle pressure and open AV valves
Blood fill ventricles from atria during relaxation and contraction

Contraction Criteria: Coordinate Muscle Excitation

Coordinated muscle fibre excitation
Uncoordinated causes ventricular fibrillation

Contraction Criteria: Coordinate Atria and Ventricles

Atria contract together
Ventricles contract together
Move blood at same time

Bundle Branch Block

Block 1 bundle of His branch
Different contraction times cause ventricular stress
Uneven blood pumping
Pacemaker re-coordinate contraction

Atrial Excitation

SA node fires action potential
Travel through atria

Atrial Excitation Gap Junctions

Between atrial cells

Atrial Excitation Pathways

Move excitation faster

Interatrial Excitation Pathway

Spread wave from right atrium to left atrium

Internodal Excitation Pathway

Connect SA and AV nodes

AV Node Delay

Electrical signal conduction slows from SA to AV node
Atrial and ventricular muscle cells separated by connective tissue
AV node and bundle of His is only path for electrical signals
Atria contract before ventricles

Ventricular Excitation

Gap junctions only
Top contract before bottom
Bundle of His and Purkinje fibres contract together

Ventricular Conduction 1

After AV nodal delay
Excitation spread down bundle of His and Purkinje fibres

Ventricular Conduction 2

Gap junctions spread excitation to non-innervated cells

Cardiac Action Potential

RMP of -80 mV
No pacemaker current

Cardiac Action Potential 1

Excitation and threshold
Voltage-gated Na+ channels open
Membrane potential depolarizes to +50 mV

Cardiac Action Potential 2

Depolarization
Activate transient outward K+ channels, delayed rectifying K+ channel, and L-type Ca2+ channels
K+ out of cell counter Na+ in
Stabilize membrane potential
Plateau potential

Cardiac Action Potential 3

Repolarization
Transient outward K+ and L-type Ca2+ channels inactivate
K+ out from delayed rectifying channels
Hyperpolarize cell
Reach RMP

Ca2+ in Cardiac Myocytes

Depend on Ca2+ entry for contraction

Excitation-Contraction 1

Action potential plateau
L-type Ca2+ channels open in T-tubules

Excitation-Contraction 2

Ca2+ enter through L-type Ca2+ channels

Excitation-Contraction 3

Ca2+ interact with contractile apparatus

Excitation-Contraction 4

Ca2+ interact with ryanodine receptors on SR membrane
Ca2+-induced-Ca2+-release (CICR)

Excitation-Contraction 5

Ca2+ influx initiate contraction
Ca2+ pump from cytosol into SR ends contraction

Action Potential Length

Long plateau/depolarization
Inactive Na+ channels
Prevent twitch summation
No restimulation during refractory period

ECG

Electrical activity pattern from coordinated contractions

Einthoven Triangle ECG

3 leads
1: Right arm to left arm
2: Right arm to left leg
3: Left arm to left leg
Measure electrical activity changes between leads

Modern ECG

12 leads
3: Limb
6: Around heart
3: Math
Measure changes in electrical potential and summation

ECG Recording

Trace around isoelectric line
Depolarization up
Repolarization down

ECG: P Wave

SA node fires
Initiate heart beat
Small electrical activity
Trigger atrial excitation and depolarization

ECG: QRS Complex

Flat ECG
No net charge movement during AV node delay
Excitation wave travel down bundle of His and Purkinje fibres after AV node delay
Depolarize ventricles

ECG: T Wave

Flat ECG
No net current after ventricular depolarization
Ventricular repolarization
No net current until SA node fires

ECG: PR Segment

AV node delay

ECG: ST Segment

Ventricles contract and empty

ECG: TP Interval

Ventricles relax and fill

ECG: QT Segment

Ventricle depolarization and repolarization

ECG: Atrial Repolarization

During ventricle depolarization
Lost in QRS summation

Tachycardia

Fast heart rate
Wide/narrow QRS complex
Reduce ventricule filling
Decrease cardiac output

Extrasystole

Heartbeat initiation by Purkinje fibres (not SA node)
Chest palpitations
Decrease oxygenation to heart muscles
Ventricles contract before atria
Reduce ventricular filling
Decrease cardiac output

Ventricular Fibrillation

Heart quiver
Abnormal electrical activity in ventricles
Cardiac arrest
Cause by coronary artery disease, intracranial bleed
Irregular, unformed QRS complex
No clear P waves

Complete Heart Block

Third degree AV block
SA node impulse does not reach ventricles
AV node pacemaker cells activate ventricles independently
Low heart rate and blood pressure
P wave with regular intervals
QRS complex not following P wave

Cardiac Cycle

Alternating contraction (systole) and relaxation (diastole)
Left and right sides contract simultaneously