Cardiovascular Physiology

1) Blood

2) Heart

3) Peripheral Circulation

The primary function of the Cardiovascular system is to

1) deliver nutrients/oxygen and

2)remove wastes/CO2

from the cells in your body

Pump

Solution of Nutrients/Wastes

Tubes

Cardiac Physiology

The primary function of the HEART is

to generate a Pressure gradient in the vascular system

Pressure gradient allows blood to move by BULK FLOW through the body & the

lungs

GradientsGradients

e.g. e.g. Pressure, concentration, temperature, energyPressure, concentration, temperature, energy

Molecules move “down” gradients Molecules move “down” gradients fromfrom “ “HiHi” ” toto “ “LoLo”, ”, spontaneouslyspontaneously

A A GRADIENTGRADIENT is a difference in any parameter over distance is a difference in any parameter over distance

Bulk FlowBulk Flow

Many molecules moving simultaneously in one Many molecules moving simultaneously in one direction, from an area of high P to low Pdirection, from an area of high P to low P

PPATMOS mm Hg ATMOS mm Hg

PPLUNGS mm Hg LUNGS mm Hg

Hi PHi P

InspirationInspiration

Lo PLo P

Lo PLo P

ExpirationExpiration

Hi PHi P

FFB B = k = kBB(P(P11 - P - P22) L/min) L/min

FFB B = Bulk Flow L/min= Bulk Flow L/min

kkB B = bulk flow constant ~ tube diameter= bulk flow constant ~ tube diameter

PP1 1 P P22

If PIf P11 > P > P22, flow goes from 1 to 2, flow goes from 1 to 2

If PIf P11 < P < P22, flow goes from 2 to 1, flow goes from 2 to 1

If PIf P11 = P = P22, no flow occurs, no flow occurs

Poiseulle’s Law of Bulk Flow: Its all about PRESSURE

Bulk Flow: Movement DOWN a Pressure Gradient

Cardiac Cycle

The cardiac cycle links

1) Electrical

2) Contractile

3) Pressure

4) Flow

through the heart!

The Heart is surround by cardiac muscle

Myocardium

Pericardium

Endocardium

Myocardial Fibers

Myocardium Anatomy

Myocardium is very similar to skeletal muscle

Except

• Intercalated discs form Gap junctions between adjacent myocardial fibers

• Myocardial fibers branch

• SR and T-tubules are weakly linked….Ca2+ is slowly released upon excitation

Pacemaker Cells: Heart is Autorhythmic!Heart is Autorhythmic!

How do pacemaker cells spontaneously produce action potentials?

Pacemaker cells have an UNSTABLE resting membrane potential!Pacemaker cells have an UNSTABLE resting membrane potential!

1

1) Prepotential: Few Na+ channels open, Na+ influx = funny current

2) Depolorization: VG Ca2+ channels open INFLUX of Ca2+

3) Repolarization: K+ channels open EFFLUX of K+

2 3

Drugs to treat Arrhythmias sometimes work on Ca2+ channels!

Myogenic signal propagates down Myogenic signal propagates down MyocardiumMyocardium

Electrical Properties of the Myocardium

Skeletal muscle AP look and behave like neural cells

Due to the SLOW CLOSING OF Ca2+, Myocardium REPOLARIZES VERY SLOWLY

Plateau

Excitation-Contraction Coupling of Cardiac Muscle

SacrolemnaECF

ICF

SR

T-tubule

1

2

3

4

6

5

Contraction

2) VG Ca2+ channels open, CA 2+ Influx

3) Ca2+ influx triggers RyR channels on SR to open

Calcium Induced Calcium Release

4) Ca2+ pours out of SR Ca2+ Spark!

5) Sparks sum to create Ca2+ signal

1) Action Potential

6) Ca2+ binds Troponin, cross- bridge formation, Contraction!

Calcium Sparks Video

Ca2+

Ca2+

Ca2+ Spark

Ca2+ Signal

RyR

VG Ca2+ Channel

Sarcomere

Myocardium contraction is GRADED!

Amount of Ca2+ entering myocardium is proportional to contraction strength

Amount of Calcium INFLUX

Fo

rce

of

Myo

card

ium

Amount of Calcium INFLUX

# o

f C

ross

brid

ge

s F

orm

ed

Contraction

Ca2+

Ca2+

Ca2+ Spark

Ca2+ Signal

Excitation-Contraction Coupling in Myocardium vs. Skeletal Muscle

Skeletal Muscle

Myocardium

Ca2+ Plateau prolongs the refractory period…..summation cannot happen!Ca2+ Plateau prolongs the refractory period…..summation cannot happen!Guarantees that Cardiac Muscle Contract-Relaxes Rhythmically!!!!!Guarantees that Cardiac Muscle Contract-Relaxes Rhythmically!!!!!

Refractory

Don’t get CONFUSED!

• Pacemaker Potentials • Cardiac Muscle Excitation

Pacemaker EXCITATION >>>>>>>>>>>>>>>>>>>>.Cardiac Muscle Excitation- Contraction

Heart’s Electrical Conducting System

SA = 100 min-1

AV node = 40 min-1

AV bundleBundle branchesPurkinje Fibers 10-30 min-1

Why do the SA pacemaker cells beat a higher frequency than AV, Bundle Branches & Purkinje?

SA NODE

AV NODE

SA Node has More Funny Current (Na+) channels

What about Bundle Branches and Purkinje (10-30 min-1)?

SA Node

Atrial Muscle

AV Node

AV Bundle

Bundle Branches

Purkinje Fibers

Ventricular Muscle

Excitation involves Calcium PLATEAU

Huge Refractory Period

No Plateau Phase

Shorter Refractory Period

Ventricular Systole: Contraction Ventricular Diastole: Relaxation

Atria have Systole and Diastole TOO!

5

43

2

1 Late diastoleAtria & Ventricles

Atrial systole

Early Ventricular SYSTOLE

START

Late Ventricular Systole

Early Ventricular DIASTOLE.

S1

S2

Cardiac Cycle

The cardiac cycle links

1) Electrical

2) Contractile

3) Pressure

4) Flow

through the heart!

High Ventricular Pressure ForcesAV Valves Shut

Low Ventricular Pressure Forces Aortic/Pulmonary Valves Shut

Valves respond to pressure!Guarantees One-Way Blood Flow

Relaxed ventricular muscle (diastole)

Low pressure in ventricle

AV valve flops openAortic Valve Shuts

Contracting ventricular muscle (systole)

High pressure in ventricle

AV valve forced shutAortic Valve Opens

Chordae Tendinae

Papillary Muscle

Isovolumetric CONTRACTION

Isovolumetric RELAXATION

Blood Flow through heart is driven by Pressure!

Blood Flow through Heart

R. AV Valve

L. AV Valve

Cardiac Cycle

The cardiac cycle links

1) Electrical

2) Contractile

3) Pressure

4) Flow

through the heart!

Wiggers Diagram

1 2 3 4 5

1) No electrical activityAtrial & Ventricular Diastole Pressure is lowVolume is increasing

2) P-wave = Atrial Depol. Atrial Systole

Atrial Pressure Rises Ventricular volume increases

3) QRS = Atrial Repol, Ventricular Depol. Ventricular Systole, Atrial DiastoleVentricular Pressure rises dramaticallyAtrial Pressure risesVentricular Volume flat, then decreases

as AV closes and Aortic and Pulmonary Valves Open

4) T-wave = Ventricular Repol. Ventricular Diastole Pressure drops dramatically in ventricle

& rises in Atria Ventricular Volume decreases then is flat as aortic and pulmonary valves CLOSE

5) No electrical activity Atrial & Ventricular Diastole Pressure & Volume slowly rise as blood fills