NRS 237 Principles of PhysiologyDr. Moattar Raza Rizvi

Unit 3 Cardiovascular SystemHeart pumps over 1 million gallons per year

To understand the:• Structure and function of the heart

• Physiology underlying the cardiac cycle

• Generation of electrical impulses

• Use and interpretation of the electrocardiogram

Learning Outcome

• Heart – typically weighs 250–350 grams (healthy heart)

• Largest organ of the mediastinum area from the sternum to the vertebral column and between the lungs

• Apex lies to the left of the midline

• Base is the broad posterior surface

Location and Orientation within the Thorax

• Generating blood pressure• Routing blood

– Heart separates pulmonary and systemic circulations

• Ensuring one-way blood flow– Heart valves ensure one-way flow

• Regulating blood supply– Changes in contraction rate and force match blood

delivery to changing metabolic needs

Functions of the Heart

The Double Pump

Lungs

Body cells

THE RIGHT SIDE

OF THE SYSTEM

DEALS WITH

DEOXYGENATED

BLOOD.

THE LEFT SIDE OF THE SYSTEM

DEALS WITH OXYGENATED

BLOOD.

The Double Pump

• Protects and anchors the heart• Prevents overfilling of the heart with blood• Allows the heart to work in a relatively friction-

free environment

Membrane of Heart: Pericardium

1. Endocardium: The innermost layer of the heart (endothelial cells)

2. Myocardium: The thickest main layer, consists of cardiac muscle

Heart Walls :3الجدران Distinct Layers

3. Epicardium:• The thin, outer covering

around the heart• Made up of simple

squamous epithelium

Epicardium

Atria- (2) upper chambers– Thin walled– Receive blood from

veins– Send blood to ventricles

Ventricles- (2) lower chambers– Thick walled– Receive blood from atria– Pump blood out through

arteries

Heart Chambers

Heart Chambers

• Both ventricles (Right & left) – thick walled• Left ventricle – three

times thicker than right– Left ventricle has to

push the blood to all the body parts while RV has to push the blood to closely lying lungs only

– Flattens right ventricle into a crescent shape

Ventricles

• Chordae tendinease – “Heart strings”– Cord-like tendons – Connect papillary

muscles to tricuspid and mitral valves

– Prevent inversionof valve

• Papillary muscles– Small muscles that

anchor the cords Papillary muscle

Structures of the Heart

Valves of the Heart

• Semilunar Valves– Prevent backflow into

ventricles– At origin of pulmonary artery

& aorta.– Pulmonary (Right) & Aortic

(Left).

• Atrioventricular Valves• Allow blood to flow from atria into ventricles.• Tricuspid (Right) & Mitral (Left).

– Prevent backflow to the atria– Prolapse is prevented by the chordae tendinae– Tensioned by the papillary muscles

Function is to prevent backflow of blood

Atrioventricular and Semilunar Valves

• Oxygen-poor blood draining from the body through veins into the superior and inferior vena cava flows to the right atrium, through the tricuspid valve, and into the right ventricle.

• As the right ventricle contracts, oxygen-poor blood passes through the pulmonary valve into the pulmonary arteries and on to the lungs to receive oxygen.

Pathway of Blood Through the Heart

• Oxygen-rich blood from the lungs enters the heart through the pulmonary veins, passing into the left atrium.

• Then through the mitral valve to the left ventricle. Contraction of the left ventricle forces blood through the aortic valve into the aorta.

• Various arteries branch off from the aorta to supply blood to all parts of the body.

Pathway of Blood Through the Heart

Pathway of Blood Through the HeartRememberPulmonary Artery: Deoxygenated bloodPulmonary vein: Oxygenated Blood

• Coronary circulation is blood supply to the heart• Heart as a very active muscle needs lots of O2 • When the heart relaxes high pressure of blood in

aorta pushes blood into coronary vessels • Many anastomoses

– connections between arteries supplying blood to the same region, provide alternate routes if one artery becomes occluded

Coronary Circulation

Coronary Artery: 2 main coronary arteries, the left and right coronary arteries, and these branch further to form several major branches.Coronary Veins: Collects wastes from cardiac muscle and drains into a large sinus on posterior surface of heart called the coronary sinus and coronary sinus empties into right atrium

Coronary Circulation

• Pulmonary circulation:– Path of blood from right ventricle through the lungs and back to the

heart.• Systemic circulation:

– Oxygen-rich blood pumped to all organ systems to supply nutrients.

• Rate of blood flow through systemic circulation = flow rate through pulmonary circulation.

Pulmonary and Systemic Circulations

The Pulmonary and Systemic Circuits (الدائرة)

Systemic circuit–Longer than pulmonary circuit–Offers greater resistance to blood flow

1. Pulmonary circuit carries CO2-rich blood from the heart to the gas-exchange surfaces of the lungs and returns O2-rich blood back to the heart

2. Systemic circuit transports O2-rich blood from the heart to the rest of the body’s cells, returning CO2-rich blood back to the heart

• To pump effectively, large portions of cardiac muscle must receive an action potential nearly simultaneously.

• Cardiac muscle tissue has intrinsic ability to– Generate and conduct impulses (نبضات)– Signal these cells to contract rhythmically

• Inherent and rhythmical beat is due to autorhythmic fibers of the cardiac muscle.

• These fibers have 2 important function- Act as pace maker (Nodal cells)- Form the conduction system

Conducting System ( النظام (إجراء

• Specialized muscle cells (autorhythmic cells) conduct APs to time and synchronize the action of the chambers

• SA node -PACEMAKER, spontaneously depolarizes most rapidly and initiate heart beat, positioned on back wall of right atrium , transmits action potential to AV node via intermodal pathway

• AV node - (where the four chambers meet).– Allows atria to communicate with ventricle

• AV bundle (bundle of His) transmits down top of interventricular septum where it divides into two

• Bundle branches, one of which supplies each ventricle where they branch into

• Purkinje fibers reflect up external walls of ventricles and stimulate contraction of cardiac muscle cells as a unit.

• Purkinje fibers extend into papillary muscles as well

Conducting System of the Heart

– Initiated by the Sino-Atrial node (SA node) which is myogenic at 70-80 action potentials/minute

• First conducting tissue to be depolarized– Depolarization is spread through the atria via gap

junctions and internodal pathways to the Atrio-Ventricular node (AV node)

– A slight delay at the AV node occurs– Action potentials travel down the Atrioventricular

bundle (Bundle of His) which splits into left and right atrioventricular bundles (bundle branches) and then into the conduction myofibers (Purkinje cells)

– Stimulation تنبيهof Purkinje fibers cause both ventricles to contract simultaneously معا.

Electrical Conduction Pathway

Electrical Conduction Pathway

1. SA Node2. Internodal pathways3. AV Node4. AV Bundle 5. Bundle Branches6. Purkinjee fibers

Sino-Atrial node (SA node) First conducting tissue to be depolarized

Cardiac Cycle• Sequence of events as blood enters the atria, leaves the ventricles

and then starts over• Synchronizing this is the Intrinsic Electrical Conduction System• In each cycle, atria and ventricles alternately contract (systole) and

relax (diastole)– During atrial systole, ventricles are relaxed– During ventricle systole, atria are relaxed

• Forces blood from higher pressure to lower pressure• During relaxation period, both atria and ventricles are relaxed

– The faster the heart beats, the shorter the relaxation period– Systole and diastole lengths shorten slightly

• All events associated with one heartbeat– At 75 beats/min, one cycle requires 0.8 sec.

• Phases of the cardiac cycle1. Late diastole

• Both atria and ventricles in diastole• Blood is filling both atria and ventricles due to low

pressure conditions2. Atrial Systole

• Completes ventricular filling3. Isovolumetric Ventricular Contraction

• Increased pressure in the ventricles causes the AV valves to close… why?

– Creates the first heart sound (lub)• Atria go back to diastole• No blood flow as semilunar valves are closed as well

Mechanical events of the cardiac cycle: Heart Chambers and the Beat Sequence

• Phases of the cardiac cycle4. Ventricular Ejection

• Intraventricular pressure overcomes aortic pressure– Semilunar valves open– Blood is ejected

5. Isovolumetric Ventricular Relaxation• Intraventricular pressure drops below aortic pressure

– Semilunar valves close = second heart sound (dup)

• Pressure still hasn’t dropped enough to open AV valves so volume remains same (isovolumetric)

Back to Atrial & Ventricular Diastole

Mechanical events of the cardiac cycle: Heart Chambers and the Beat Sequence

Cardiac Cycle: Mechanical events

Figure 14-25: Mechanical events of the cardiac cycle

Cardiac Cycle: Blood Volumes & Pressure

Cardiac Cycle• Refers to the repeating pattern of contraction and

relaxation of the heart.– Systole:

• Phase of contraction.– Diastole:

• Phase of relaxation.– End-diastolic volume (EDV):

• Total volume of blood in the ventricles at the end of diastole.

– Stroke volume (SV):• Amount of blood ejected from ventricles during systole.

– End-systolic volume (ESV):• Amount of blood left in the ventricles at the end of systole.

Heart Sounds and Cardiac Cycle• “Lub-dup” –

Closing of the AV and semilunar valves.

• Lub (first sound):– Produced by closing

of the AV valves• Dub (second sound):

– Produced by closing of the semilunar valves when pressure in the ventricles falls below pressure in the arteries.

– Composite record of action potentials produced by all the heart muscle fibers

– Compare tracings from different leads with one another and with normal records

– 3 recognizable waves• P, QRS, and T

Electrocardiogram (ECG/EKG)

ECG• P wave:– Atrial

depolarization.

• QRS complex: – Ventricular

depolarization.– Atrial

repolarization.

• T wave:– Ventricular

repolarization.

Electrocardiogram (ECG/EKG)

Electrocardiogram (ECG/EKG)

• First heart sound:– Produced immediately

after QRS wave.– Rise of intraventricular

pressure causes AV valves to close.

• Second heart sound:– Produced after T wave

begins.– Fall in intraventricular

pressure causes semilunar valves to close.

Correlation of ECG with Heart Sounds

• Arterial blood pressure is of 2 types:

• Systolic blood pressure- defined as the pressure which the blood exerts on the wall of the blood vessels at the end of systolic contraction of ventricles. It is normally 120 mmHg

• Diastolic blood pressure – defined as the pressure which the blood exerts on the wall of arteries when the ventricles are maximally relaxed. It is normally 80mmHg.

Arterial Blood Pressure

• Is via auscultation (to examine by listening)• No sound is heard during laminar flow (normal,

quiet, smooth blood flow)• Korotkoff sounds can be heard when

sphygmomanometer cuff pressure is greater than diastolic but lower than systolic pressure

Measurement of Blood Pressure (BP)

• Blood pressure cuff is inflated above systolic pressure, occluding artery

• As cuff pressure is lowered, blood flows only when systolic pressure is above cuff pressure, producing Korotkoff sounds

• Sounds are heard until cuff pressure equals diastolic pressure, causing sounds to disappear

Measurement of Blood Pressure (BP)

Cardiac Output (CO)• Cardiac output is amount of blood pumped out of the ventricle

– CO = HR (beats/minute) X SV (liters/beat)– Normal adult: 4-8 liters/minute

• Stroke volume (SV) = blood pumped/beat by each ventricle– The average resting stroke volume is about 70 mL, and Cardiac

output can be affected by changes in either stroke volume or heart rate.

• Heart rate (HR) = the number of beats/minute– the heart rate is 60 to 80 beats per minute (bpm)– CO = SV x HR– (72 beats/m 70 ml/beat = 5040 ml)– Total blood volume = about 5.5L

• The percentage of the end-diastolic volume that is ejected with each stroke is called the ejection fraction (EF)

• Ejection fraction = Stroke Volume/ EDV• (EF) = 50-70%• Useful clinical diagnostic tool

Ejection Fraction

• Mean arterial pressure (MAP) represents average arterial pressure during cardiac cycle– Has to be approximated because period of diastole is

longer than period of systole– MAP = diastolic pressure + 1/3 pulse pressure– Pulse pressure = (systolic pressure) – (diastolic pressure)

– MAP=CO x PR (Peripheral Resistance)– PR is total resistance against which blood must be

pumped

Mean arterial pressure (MAP)

• Baroreceptor reflexes is activated by changes in blood pressure

• Which is detected by baroreceptors (stretch receptors) located in aortic arch & carotid sinuses– Increase in BP causes walls of

these regions to stretch, increasing frequency of Action Potentials

– Baroreceptors send APs to vasomotor & cardiac control centers in medulla

• Is most sensitive to decrease & sudden changes in BP

Baroreceptor and Chemoreceptor Reflexes

Autonomic regulation of the Heart• Extrinsic regulation: Involves neural and hormonal control• Sympathetic stimulation (Supplied by cardiac nerves) –

releases NE: Has 2 separate effects• In SA and AV node speeds rate of spontaneous

depolarization (increase in HR and force of contractions) through stimulation of beta receptors on nodal and contractile cells

• In contractile fibers enhances Ca2+ entry increasing contractility

– Parasympathetic stimulation (Supplied by vagus nerves release acetylcholine

– Decreases heart rate by slowing rate of spontaneous depolarization stimulation of muscarinic receptors of nodal and contractile cells

Autonomic regulation of the Heart

Autonomic regulation of the Heart

• Blood is carried in a closed system of vessels that begins and ends at the heart

• 5 Classes of Blood Vessels1. Arteries:

– carry blood away from heart2. Arterioles:

– Are smallest branches of arteries3. Capillaries:

– are smallest blood vessels– location of exchange between blood and interstitial

fluid4. Venules:

– collect blood from capillaries5. Veins:

– return blood to heart

BLOOD VESSELS

Generalized Structure of Blood Vessels

Structure: 3 layers or tunics• Tunica interna (intima)

– Inner lining in direct contact with blood– Endothelial layer that lines the lumen of all vessels– Active role in vessel-related activities

• Tunica media– Muscular and connective tissue layer– Greatest variation among vessel types, maintains BP– Smooth muscle regulates diameter of lumen

• Tunica externa– Elastic and collagen fibers– Vasa vasorum– Helps anchor vessel to surrounding tissue

A Comparison of a Typical Artery and a Typical Vein

• Blood flows through the blood vessels from the heart and back to the heart in the following order:– Elastic Arteries e.g. Aorta, pulmonary artery– Muscular Arteries– Arterioles– Capillaries – the only vessels that allow exchange– Venules– Medium Veins– Large Veins e.g. vena cava, pulmonary vein

Blood Flow Through the Blood Vessels

Blood Flow Through the Blood Vessels

ARTERIES

• Blood flow through the capillary is regulated by pre-capillary sphincter.

• Very thin walled; large total cross-sectional area– Walls consisting of a thin tunica interna, one cell

thick– Allow only a single RBC to pass at a time – Pericytes on the outer surface stabilize their walls

• There are three structural types of capillaries: continuous, fenestrated, and sinusoids

Capillaries

Figure 21-5

Capillary bed or capillary plexus connect 1 arteriole and 1 venule

Capillary Networks

Types of Capillaries

– Thin walled compared to arteries; highly distensible; large radii

– Primary resistance vessels; determine distribution of cardiac output

– Veins are formed when venules converge– Composed of three tunics, with a thin tunica media

and a thick tunica externa consisting of collagen fibers and elastic networks

– Capacitance vessels (blood reservoirs) that contain 65% of the blood supply

Venous System: Veins

1. Venules:• very small veins• collect blood from capillaries

2. Medium-sized veins:• Thin tunica media and few smooth muscle cells• Tunica externa with longitudinal bundles of elastic

fibers

3. Large veins:• Have all 3 tunica layers• Thick tunica externa• Thin tunica media• Tunica intima

Three vein categories

S. No. ARTERIES VEINS

1 Most arteries are located deep in the body

Veins are situated superficially

2. They appear pink (وردي) in color They appear dark red in color

3. They contain oxygenated blood except pulmonary artery

They contain deoxygenated blood except pulmonary vein

4. They carry blood away (بعيدا) from heart into various organs and tissue

They bring blood from various organs and tissues into or towards (نحو) heart

5. Their wall is thick, strong, and less distensible ( للنفخ (قابل

Their wall is thin, weak and more distensible

6. They are non collapsible They are collapsible ( للطي (قابلة

7. Lumen of arteries is small Lumen ( عضو of veins is large (تجويف

8. The flow (تدفق) of blood is fast, jerky and with great pressure

The flow of blood is slow, steady and with less pressure

9. Valve absent Valve present and prevents back flow of blood

10. They become empty after death They contain blood even after death