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) node Located at the junction

of the atria and the ventricles

Delay in the conduction of impulses…why?

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 … benefit?

Long ARP Time: depolarization

& 2/3 of repolarization

Relative refractory period Time: last 1/3

repolarization Strong stimulus can

give rise to contraction

The Cardiac Cycle

The Cardiac Cycle

The repeating pattern of contraction (systole) and relaxation (diastole) of the heart

Duration of cardiac cycle = 0.8 seconds

Diastole longer than systole Ventricular contraction follows

atrial contraction (0.1 to 0.2 second later)…why?

The end diastolic volume: the total volume of blood in the ventricles at the end of diastole (120 ml)

Stroke volume is the volume of blood pumped by each ventricle per beat (70 ml)

Residual volume: amount of blood left in each ventricle at the end of systole (50 ml)

The Cardiac Cycle

Ventricles contract Ventricular pressure: increasing Ventricular volume: no change AV valves: closed.. prevent

backflow of blood Semilunar valves: closed (P in

ventricles < P in vessels) Heart sounds: 1st heart sound ECG: QRS complex

The Cardiac Cycle Isovolumetric ventricular

contraction

Ventricular pressure: increasing > the pressure in the aortic and pulmonary vessels

Left ventricular pressure up to 120 mmHg

Right ventricular pressure up to 25 mmHg

Ventricular volume: decreasing Semilunar valves: open AV valves: closed.. prevent

backflow of blood

The Cardiac CycleEjection phase

Ventricles relax Ventricular pressure:

decreasing Ventricular volume: no

change AV valves: closed Semilunar valves: closed Heart sounds: 2nd heart sound ECG: T wave

The Cardiac CycleIsovolumetric relaxation

Ventricular pressure: below atrial pressure ( slightly above zero)

Ventricular volume: increasing

AV valves: open when pressure in the atria> the pressure in the ventricles

Semilunar valves: closed Passive ventricular filling via

AV valves (80%)

The Cardiac Cycle Rapid filling of the ventricles

Active filling of the ventricles (20%)

Ventricular volume: slight rise Ventricular pressure: slight rise Semilunar valves: closed AV valves: open ECG: P wave

The Cardiac CycleAtrial systole

The Cardiac Cycle

1. Isovolumetric contraction

2. Ejection phase

3. Isovolumetric relaxation

4. Rapid filling of the ventricles

5. Atrial systole

Heart Sounds

The first heart sound: Cause: closure of the AV valves

The second heart sound: Cause: closure of the semilunar

valves

Cardiac Output

Cardiac Output Cardiac output is the volume

of blood pumped by each ventricle per minute

CO = Stroke volume x Heart rate(L/min) (ml/beat) (beat/min) = 70 X 70

= 4900 ml/min= 5 L/min

Normal cardiac output (CO) = 5 L/min

Cardiac Output

Sympathetic stimulation HR (positive chronotropic

effect) CO

Parasympathetic stimulation HR CO

Cardiac centers in the medulla oblangata

Cardiac OutputRegulation of Heart Rate

End Diastolic Volume (EDV) Frank- Starling Law of the

Heart venous return EDV length

of cardiac muscle (stretch) force of contraction stroke volume cardiac output

Cardiac OutputRegulation of Stroke

Volume

Positive ionotropic effect strength of contraction

Sympathetic stimulation Adrenaline

Negative ionotropic effect strength of contraction

Parasympathetic stimulation Acetylcholine Vagal stimulation

Cardiac Output Regulation of Stroke

Volume

Blood Pressure

Blood pressure

The blood pressure is the pressure the blood exerts against the inner walls of the blood vessels

Arterial blood pressure (BP) =cardiac output (CO) x peripheral

resistance

Heart Stroke Rate volume Vasoconstriction

Normal BP = 120/80 mmHg

Sympathetic stimulation vasoconstriction Peripheral resistance BP

Parasympathetic stimulation less important b/c of limited vasodilatation in the GIT, external genitalia and salivary glands

Arterial blood pressure Peripheral resistance

Sympathetic stimulation HR (positive chronotropic

effect) CO BP

Parasympathetic stimulation HR CO BP

Arterial blood pressure Heart rate

Short term regulation Baroreceptor reflex

Long term regulation1. Renin- Angiotensin system2. Aldosterone3. Antidiuretic hormone4. ANP

Blood pressureRegulation of blood

pressure

Arterial blood pressureBaroreceptor reflex

Stretch receptors Located in:1. The aortic arch2. The carotid sinus (at the

bifurcation of the common carotid artery)

Sensory nerve activity via the vagus and glossopharyngeal nerves

Cardiac centers in the medulla oblangata

The baroreceptor reflex is activated by changes in the BP

Blood pressureRegulation of blood

pressure Long term regulation

1.Renin- Angiotensin system2.Antidiuretic hormone 3.Aldosterone

Factors affecting blood pressure

1. Age: blood pressure increases with age

2. Sex: males have higher BP than females till the age of menopause (effect of estrogen)

3. Exercise: increases BP4. Stress: increases BP due to

sympathetic stimulation5. Hormones: adrenaline,

noradrenaline and thyroid hormones increase BP