The Cardiovascular System

Dr. Mona Soliman, MBBS, MSc, PhD

Department of PhysiologyCollege of Medicine

KSU

November 2012

Structure of the Heart

The Atria Thin walled Receives blood

from: the systemic

circulation (right atrium)

the pulmonary circulation (left atrium)

Open into the ventricles via the: Atrioventricular

valves (AV valves)

Structure of the Heart

The Ventricles Thick muscular

walled (why?) Pump blood into:

Pulmonary trunk (right ventricle)

Aorta (left ventricle)

A fibrous tissue ring separate the atria from the ventricles (importance: electrical activity, AV valve)

Structure of the Heart

The Valves of the HeartThe Atrioventricular Valves

1. The Tricuspid Valve… between the right atrium and the right ventricle, 3 cusps

2. The Mitral Valve (bicuspid valve) … between the left atrium and the left ventricle, 2 cusps

Prevent back flow of blood from the ventricles to the atria

Held by chordae tendineae to papillary muscle

Contraction of papillary muscle…

The Valves of the HeartThe Atrioventricular

Valves

The Valves of the Heart The Semilunar Valves

Located at the origin of the pulmonary artery and aorta

Open during ventricular contraction…why?

Close during ventricular relaxation…why?

1. The Aortic Valve2. The Pulmonary

Valve

Cardiac muscle cell

Cardiac Muscle cell

Striated Contain actin and myocin

filaments arranged in sarcomeres…contract by sliding mechanism

Branch and interconnect

Cardiac Muscle cell

Gap junctions Trans-membrane channel proteins,

connecting the cytoplasm of the cells

Allow spreading of the action potential from one fiber to another

Allow cardiac muscle to function as a syncytium “all or none law”: stimulation of a single muscle fiber results in contraction of all the muscle fibers

Intercalated discs

Cardiac Muscle cell

Cardiac Muscle cell

Electrical Activity of the

Heart

Electrical Activity of the Heart

Automaticity: capable of originating action potential

Resting membrane potential in myocardial cells -90 mVStimulation of myocardial cell

Myocardial action potential

Myocardial action potential

Myocardial action potential

Phases of cardiac AP

Ionic changes

Rapid depolarization (+20 mV)

Na+ in

Partial repolarization (5-10mV)

K+ out

Action potential plateau (0 mV)

Ca2+ in (slow)

Repolarization (back to RMP)

K+ out

Myocardial action potential

Conduction of Impulses The sinoatrial node

(SA node): Located in the right

atrium Pacemaker of the heart Is capable of

originating action potentials

Highest frequency The atrioventricular

(AV) nodeLocated at the junction of the atria and the ventricles

Delay in the conduction of impulses so the atrium can contract before the ventricle

Conduction of Impulses The

atrioventricular (AV) bundle (Bundle of His)

The right and left bundle branches

Purkinje fibers Spread within

the muscle of the ventricular walls

Highest speed of conduction

Contractility Contractility is the ability of

cardiac muscle to convert chemical energy into mechanical work

Depolarization of myocardial cell

Opening of Ca2+ channels

Ca2+ increase in the cytoplasm

Ca2+ binds to troponin

Contraction

Contractility

Repolarization of myocardial cell

Ca2+ OUT

Ca2+ decrease in the cytoplasm

Relaxation

Contractility

Contractility Absolute refractory

period Cardiac muscle

cannot be excited while it is contracting

Long ARP Time: depolarization

& 2/3 of repolarization

Relative refractory period Time: last 1/3

repolarization Strong stimulus can

give rise to contraction