The Cardiovascular System

Chapter 11

• Cardiovascular system is a closed system

• Consists of

• Heart: The heart pumps blood

• Blood vessels : Blood vessels allow blood to circulate to all parts of the body

• Function:• To deliver oxygen and nutrients and to remove carbon dioxide

and other waste products

The Cardiovascular System

Heart• Heart is transport system pump for

the blood• Heart is two pumps in one• Pulmonary Circulation:• R side of heart receives blood from body, pumps blood to lungs and returns to L heart• Systemic Circulation:• L side of heart pumps blood to tissues of the body & return to R heart• Heart of healthy person pumps approx. 7200 L of blood each day at the rate of 5L/min.

Anatomy of the Heart• Location, size and shape of Heart

• Size: size of a closed fist• Shape

– Apex: Blunt rounded cone– Base: larger flat part

• Location: – Located in thoracic cavity in left

of mediastinum (midline) between the two lungs

– Superior surface of diaphragm

– Important clinically when using a stethoscope, performing an ECG, or performing CPR

Anatomy of the Heart• Heart is enclosed by a double-walled

sac called Pericardium • Composed of:

– A superficial fibrous pericardium– A deep two-layer serous

pericardium• Parietal pericardium lines the

internal surface of the fibrous pericardium

• The visceral pericardium or epicardium lines the surface of the heart

• & separated by fluid-filled pericardial cavity

• Helps in reducing friction as heart moves within the pericardial sac

• Heart Wall: composed of 3 layers of tissues:

• Epicardium – visceral layer of the serous pericardium, lines the surface of the heart

• Myocardium – Middle layer, cardiac muscle layer forming the bulk of the heart, responsible for heart contraction

• Endocardium – Lines inner surface of heart chambers

Anatomy of the Heart

Heart Chambers and Vessels• Heart consists of 4 chambers:• Two atria, two ventricle• Atria: Thin walled, forms the superior part of heart• Ventricle: Thick-walled, forms the inferior part of heart• Large veins: carry blood to the heart:

– Superior and inferior venae cavae– carry blood from body to R atrium– 4 pulmonary veins carry blood

from lungs to L. atrium• Arteries: conveying blood away from

heart:– Aorta carries blood from L.

ventricle to the body– Pulmonary trunk carries blood

from R. ventricle to lungs

Heart Chambers and Valves

• Atria– Right atrium: three major

openings to receive blood returning from the body (superior vena cava, inferior vena cava, coronary sinus)

– Left atrium: four openings that receive blood from 4 pulmonary veins from lungs

– Two atria are separated from each other by Interatrial septum

• Ventricles

– Atrioventricular valves: openings between atria and ventricles

– Right ventricle opens to pulmonary trunk

– Left ventricle opens to aorta

– Interventricular septum between the two ventricle

Heart Chambers and Valves

Heart Valves• Heart valves ensure

unidirectional blood flow through the heart

• Atrioventricular (AV) valves: lie between the atria and the ventricles

• AV valves allow blood flow from atria to ventricle

• But prevent backflow into the atria when ventricles contract

• AV valve between L atrium & L ventricle has 2 cusps – Bicuspid Valve

• AV valve between R atrium & R ventricle has 3 cusps – Tricuspid Valve

• Semilunar Valves:• Aortic semilunar valve:

lies between the left ventricle and the aorta

• Pulmonary semilunar valve: lies between the right ventricle and pulmonary trunk

• Semilunar valves prevent backflow of blood into the ventricles

Heart Valves

• Superior and inferior vena cava dump blood into the right atrium

• From right atrium, through the tricuspid valve, blood travels to the right ventricle

• From the right ventricle, blood leaves the heart as it passes through the pulmonary semilunar valve into the pulmonary trunk

• Pulmonary trunk splits into right and left pulmonary arteries that carry blood to the lungs

Blood Flow Through the Heart

• Oxygen is picked up and carbon dioxide is dropped off by blood in the lungs

• Oxygen-rich blood returns to the heart through the four pulmonary veins from lungs

• Blood enters the left atrium and travels through the bicuspid valve into the left ventricle

• From the left ventricle, blood leaves the heart via the aortic semilunar valve and aorta

• From aorta, supply blood to all body parts

Blood Flow Through the Heart

Blood Flow Through the Heart

Cardiac Circulation• Blood in the heart chambers does not

nourish the heart muscles

• Coronary arteries in heart supply blood to heart muscles

• Coronary arteries branch from the aorta to supply the heart muscle with oxygenated blood

• Cardiac veins from heart drain blood into a

large venous cavity called Coronary sinus

• Coronary sinus then empties into the right atrium

Physiology of Heart• Heart muscle cells contract,

without nerve impulses, in a regular, continuous way

• Heart is autorhythmic

• Initiate, conduct and Initiate, conduct and impulseimpulse

• Heart contains special tissue that produces & sends electrical impulses to the heart muscle to contract

• The heart's conducting system consists of:

• Sinoatrial (SA) node• Atrioventricular

(AV)node• Bundle of His• Bundle branches• Purkinje fibers

Physiology of Heart

– Sinoatrial (SA) NodeSinoatrial (SA) Node• Mass of autorhythmic cellsMass of autorhythmic cells• Electrical impulse that causes

rhythmic contraction of heart muscles arises in the SA node

• Pacemaker of the heart • Located in R. atrium• Send impulse 70 to 80 times a Send impulse 70 to 80 times a

minuteminute

Physiology of Heart

Physiology of Heart

• AV Node:

• The electrical impulse from the SA node spreads over the right and left atria

• causes atrial contraction

• Then impulses are conducted to the atrioventicular (AV) node

• Bundle of His (AV bundle)

• Then electrical impulse is relayed down to Bundle of HIS

• Conducts impulse to right and left Conducts impulse to right and left bundle branchesbundle branches

• Bundle BranchesBundle Branches• Right and left branchesRight and left branches• Branch into purkinje fibersBranch into purkinje fibers

• Purkinje FibersPurkinje Fibers• Enter myocardium of ventricle wallsEnter myocardium of ventricle walls• Carry impulse to ventriclesCarry impulse to ventricles• Ventricular contractionVentricular contraction

Physiology of Heart

CARDIAC CONDUCTION SYSTEM SUMMARY

Sinoatrial NodeSinoatrial Node

AV NodeAV Node

AV BundleAV Bundle

Bundle BranchesBundle Branches

Purkinje FibersPurkinje Fibers

Cardiac Cycle• Cardiac cycle: Is the

sequence of events in one heartbeat

• It is the repetitive pumping process that begins with onset of cardiac muscle contraction and ends with beginning of next contraction

• Cardiac muscle contraction is responsible for pressure and blood movement. How?

• Blood moves from high pressure to low pressure

  

Cardiac Cycle• The length of cardiac cycle is about 0.8 sec• Interval from end of one contraction to the following Interval from end of one contraction to the following

contractioncontraction• Consists of Two Phases:Consists of Two Phases:

– Systole phaseSystole phase– Diastole phaseDiastole phase

CARDIAC CYCLECARDIAC CYCLE• Systole PhaseSystole Phase

– Contraction phaseContraction phase

– Atrial SystoleAtrial Systole (0.1 sec.) (0.1 sec.)• After passive filling with bloodAfter passive filling with blood

• Atrial pressure rises above ventricular pressure

• And AV valves openAnd AV valves open• Blood is ejected from atria to Blood is ejected from atria to

ventricleventricle

• semilunar valves closedsemilunar valves closed

• Ventricles fill with bloodVentricles fill with blood

CARDIAC CYCLECARDIAC CYCLE• Ventricular SystoleVentricular Systole (0.3 (0.3

sec.)sec.)• AV and semilunar valves AV and semilunar valves

closed until Ventricle closed until Ventricle pressure rises above aorta pressure rises above aorta and pulmonary trunk and pulmonary trunk pressure pressure

• opens semilunar valvesopens semilunar valves

• Blood pushed into pulmonary Blood pushed into pulmonary trunk and Aortatrunk and Aorta

• 120 mm Hg pressure120 mm Hg pressure

• Atria in diastoleAtria in diastole

CARDIAC CYCLECARDIAC CYCLE

• Diastole PhaseDiastole Phase– Relaxation phaseRelaxation phase

– Ventricular DiastoleVentricular Diastole• Follows ventricular Follows ventricular

systolesystole

• AV valves reopen AV valves reopen and filling beginsand filling begins

• 80 mm Hg pressure80 mm Hg pressure

Electrocardiogram: ECG Electrocardiogram: ECG • When impulse pass through the heart, electric currents are generated

• Electric current that can be measured at the surface of the body - ECG

• P waveP wave: Atrial : Atrial depolarizationdepolarization

• QRS complex:QRS complex: Ventricular Ventricular depolarizationdepolarization

• T wave:T wave: Ventricular Ventricular repolarizationrepolarization

• Tachycardia—rapid heart rate over 100 beats per minute

• Bradycardia—slow heart rate less than 60 beats per minutes

Heart Contractions

Heart Sounds

• First heart sound or “lubb”– Atrioventricular valves vibrations as valves close

at beginning of ventricular systole

• Second heart sound or “dupp”– Results from closure of aortic and pulmonary

semilunar valves at beginning of ventricular diastole, lasts longer

• Cardiac output (CO)– Amount of blood pumped by heart in one minute

• Stroke volume (SV)– Volume of blood pumped by each heartbeat– Usually remains relatively constant – About 70 mL of blood is pumped out of the left

ventricle with each heartbeat

• Heart rate (HR) – Typically 75 beats per minute

Cardiac Output

• CO = HR SV • CO = HR (75 beats/min) SV (70 mL/beat)• CO = 5250 mL/min• Starling’s law of the heart— the more the cardiac muscle

is stretched, the stronger the contraction• Important factor for stretching the heart muscle is

venous return• The greater the volume of blood returned to the heart by The greater the volume of blood returned to the heart by

the veins, the greater the volume of blood the heart will the veins, the greater the volume of blood the heart will pump pump

Cardiac Output

Regulation of the Heart

• To maintain homeostasis, amount of blood pumped by heart must vary:

• Eg. Cardiac output increases more during exercise than resting

• Intrinsic regulation: Results from normal functional characteristics of heart, not depend on neural or hormonal regulation

Regulation of the Heart• Extrinsic regulation: Involves neural

and hormonal control • Neural Control

– Parasympathetic stimulation

• Supplied by vagus nerve, acetylcholine is secreted,

decreases heart rate, maintainmaintain

heart beat average of 70 heart beat average of 70 beats/min.beats/min.

– Sympathetic stimulation– Supplied by cardiac nerves

– Increases heart rate and force of contraction.

– Epinephrine and norepinephrine released.

– Increased heart beat causes increased cardiac output

Regulation of the Heart

– Hormonal Control– Epinephrine and

norepinephrine from the adrenal medulla

– Increases rate and force of heart contraction

– Occurs in response to increased physical activity, emotional excitement, stress

• Transport blood to the tissues and back– Carry blood away from

the heart• Arteries• Arterioles

– Exchanges between tissues and blood

• Capillary beds– Return blood toward the

heart• Venules• Veins

Blood Vessels: The Vascular System

• Arteries and veins are composed of three tunics (layers) – tunica intima, tunica media, and tunica externa

• Lumen – central blood-containing space surrounded by tunics

• Capillaries are composed of endothelium

• Three layers (tunics)– Tunic intima

• Endothelium• Basement membrane

– Tunic media• Smooth muscle• Blood flow is regulated by smooth

muscle of Tunica Media– Vasoconstriction: smooth muscles contract,

decrease in blood flow– Vasodilation: smooth muscles relax, increase

in blood flow• Controlled by sympathetic nervous

system– Tunic externa

• Mostly fibrous connective tissue

• Thickness of each layer varies with type and diameter of blood vessel

Blood Vessels: Microscopic Anatomy

• Walls of arteries are the thicker than veins

• Lumens of veins are larger than arteries

• Because BP is low in veins and work against gravity

• Larger veins have valves to prevent backflow

• More valves in veins of lower extremities than in veins of upper extremities

• Walls of capillaries are only one cell layer thick to allow for exchanges between blood and tissue

Differences Between Blood Vessels

• Most arterial blood is pumped by the heart

• Veins use the milking action of muscles to help move blood

Movement of Blood Through Vessels

• Capillary beds consist of two types of vessels– Vascular shunt— vessel

directly connecting an arteriole to a venule

– True capillaries— exchange vessels

• Oxygen and nutrients cross to cells

• Carbon dioxide and metabolic waste products cross into blood

Capillary Beds

• The vascular system has two distinct circulations– Pulmonary circulation –

short loop that runs from the heart to the lungs and back to the heart

– Systemic circulation – routes blood through a long loop to all parts of the body and returns to the heart

• Heart pumps blood from right ventricle into pulmonary trunk

• Pulmonary trunk divides into left and right pulmonary arteries, Transport blood to each lung

• Two pulmonary veins exit each lung and enter left atrium

• Oxygenated blood enter the heart from pulmonary veins through L. atrium

• From L. atrium to L. ventricle

• From L. ventricle to aorta

• From aorta blood flows to all body parts

Aorta All arteries are derived from aorta Aorta is divided into 3 parts: Ascending aorta Aortic arch Descending aorta

– Ascending aorta: Passes superiorly to heart, has 2 branches

– right and left coronary arteries, supply blood to cardiac muscles

– Aortic arch: arching posteriorly and to the left and has 3 branches, carry blood to head and neck

• Brachiocephalic artery• Left common carotid• Left subclavian artery

Aorta Descending aorta: Longest part Consists of:

Thoracic aorta: portion in thorax

Abdominal aorta: inferior to diaphragm: branches supply blood to abdominal wall and organs

Ends as two common iliac arteries: supply blood to pelvis & lower limbs

Coronary Arteries: - Only branches of ascending

arteries, supply blood to heart

Systemic Circulation: Arteies

Major veins of the Systemic Circulation

• Return blood from body to right atrium• Major veins

– Coronary sinus : returning blood from heart walls– Superior vena cava: Returning blood from head, neck,

thorax, upper limbs– Inferior vena cava: Returning blood from abdomen,

pelvis, lower limbs

• Types of veins– Superficial, deep, sinuses (cranium & heart)

Special Circulations• Arterial Supply of Brain• Supply of blood to brain is crucial• Lack of O2 kills the brain cells that cannot

be revived• The main arteries that supply blood to brain

include– Internal carotid artery– Vertebral artery

• Internal carotid arteries divide into– Anterior and middle cerebral arteries– These arteries supply most of the

cerebrum• Vertebral arteries join once within the skull to

form the basilar artery– Basilar artery serves the brain stem and

cerebellum

• Arterial Supply of the Brain:

• Basilar artery divides to form Posterior cerebral arteries – These arteries supply the posterior

cerebrum• Anterior and posterior blood supplies

are united by small communicating arterial branches

• Result—complete circle of connecting blood vessels called cerebral arterial circle or circle of Willis around the pituitary gland

Special Circulations

Hepatic Portal System Nutrients and other substances

absorbed by stomach and intestine are transported to liver by hepatic portal system

Hepatic portal system carries blood through veins from capillaries of stomach, intestine, spleen to liver

Largest vein of the system

From liver Hepatic veins join the Inferior vena cava

• Pulse– Pressure wave of blood

• Monitored at “pressure points” in arteries where pulse is easily palpated

• Pulse averages 70–76 beats per minute at rest

Pulse

• Pressure exerted on vessel wallsPressure exerted on vessel walls

• Blood pressure measured in mm HgBlood pressure measured in mm Hg

• Measured with sphygmomanometerMeasured with sphygmomanometer

– Pressure in cuff compresses artery until no pulse heardPressure in cuff compresses artery until no pulse heard

– Systolic pressure:Systolic pressure: taken at first pulse as pressure in cuff released taken at first pulse as pressure in cuff released

(ave. 120) = pressure while heart ventricles contracting, 1(ave. 120) = pressure while heart ventricles contracting, 1stst

Korotkoff soundKorotkoff sound

– Diastolic pressure:Diastolic pressure: taken when cuff released to point where sound taken when cuff released to point where sound

no longer audible (ave. 80) = pressure when ventricles not no longer audible (ave. 80) = pressure when ventricles not

contractingcontracting

– Pulse pressurePulse pressure = systolic - diastolic (measure of stress exerted on = systolic - diastolic (measure of stress exerted on

small arteries)small arteries)

BLOOD PRESSUREBLOOD PRESSURE

• Blood Pressure varies directly with the following:Blood Pressure varies directly with the following:

Cardiac OutputCardiac Output• Stroke volume X heart rate Stroke volume X heart rate • Normal is 5.5 liters/min.Normal is 5.5 liters/min.

Peripheral ResistancePeripheral Resistance• Opposition to blood flowOpposition to blood flow

with blood viscositywith blood viscosity with length of vesselwith length of vessel with with in vessel diameter (has the greatest influence in vessel diameter (has the greatest influence

on B.P.)on B.P.)

Blood Pressure: Effects of Factors

• Blood Pressure varies directly with the Blood Pressure varies directly with the following:following:Blood VolumeBlood Volume

• Mainly regulated by kidneysMainly regulated by kidneys

in blood volume = in blood volume = in B.P. in B.P.

in blood vol. = in blood vol. = decrease in B.P. decrease in B.P.

INFLUENCES ON B.P.

REGULATION OF B.P.

• Neural Factors:Neural Factors:– Sympathetic nerve fibers causeSympathetic nerve fibers cause

• Vasoconstriction of blood vessels Vasoconstriction of blood vessels diameter, diameter, resistance resistance B.P. B.P.

• Renal Factors:Renal Factors:

• Renin (Enzyme)Renin (Enzyme)– Renin enzyme released from kidneys in response to Renin enzyme released from kidneys in response to

low B.P.low B.P.– Stimulates angiotensin II, vasoconstrictor chemicalStimulates angiotensin II, vasoconstrictor chemical– Which stimulates hormone Which stimulates hormone aldosteronealdosterone– Which enhances sodium and water reabsorption Which enhances sodium and water reabsorption blood volume and B.P.blood volume and B.P.

REGULATION OF B.P.

• Temperature– Heat has a vasodilating effect– Cold has a vasoconstricting effect

• Chemicals– Various substances can cause increase or

decrease in B.P.

• Diet

REGULATION OF B.P.

• Normal human range is variable– Normal

• 140–110 mm Hg systolic• 80–75 mm Hg diastolic

– Hypotension• Low systolic (below 110 mm HG)• Often associated with illness

– Hypertension• High systolic (above 140 mm HG)• Can be dangerous if it is chronic

Variations in Blood Pressure