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Chapter 15Cardiovascular System

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Size of Heart

• Average Size of Heart• 14 cm long• 9 cm wide•250-350 grams

•About size of your closed fist

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Location of Heart

• Posterior to sternum• Medial to lungs• Anterior to vertebral column• Base lies beneath 2nd rib• Apex at 5th intercostal space• Lies upon diaphragm•2/3 of mass lies left of midline

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Coverings of Heart

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• Pericardium– Surrounds heart

– Fibrous pericardium• Resembles bag

that sits on the diaphragm

• Provides tough protection & anchors heart to mediastinum

Coverings of Heart

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• Pericardium

– Serous pericardium• Thinner & delicate

• Parietal layer– Attached to fibrous

pericardium

• Visceral layer– Attached to

myocardium

Coverings of Heart

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• Pericardial Fluid– Between parietal and

visceral layers of serous pericardium

– Reduces friction from beating

Coverings of Heart

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Wall of the Heart

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Wall of the Heart

•3 Parts of the wall•Epicardium

•Visceral layer of serous pericardium

•Myocardium•Muscle layer

•Endocardium•Thin layer of endothelial tissue that is continuous with the remainder of the cardiovascular system

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Heart Chambers

•Right Atrium• Receives blood from • Inferior vena cava• Superior vena cava• Coronary sinus

•Right Ventricle• Receives blood from right atrium

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• Left Atrium• receives blood

from pulmonary veins

• Left Ventricle• receives blood

from left atrium

Heart Chambers

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• Separations– Atria

• Each atrium has an auricle

• Separated by interatrial septum

– Ventricles• Interventricular septum

• Sulci show the location of septum

– Contain blood vessels and store fat

Heart Chambers

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Heart Valves

•Atrioventricular Valves•Separate atria from ventricles•Tricuspid Valve•Right side•3 cusps

•Bicuspid valve•Left side•2 cusps

•Chordae Tendineae•Fibrous cord that connects cusps to papillary muscles

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• Atrioventricular Valves– Papillary Muscles

• Anchor chordae tendineae to ventricle walls

– Chordae Tendineae & Papillary Muscles• Function to keep AV

valves from being pushed into the atria during ventricular contraction

Heart Valves

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• Semilunar Valves– Pulmonary semilunar

• Between right ventricle and pulmonary trunk

• Blood leaves heart toward lungs

– Aortic semilunar• Between left ventricle

and aorta• Blood leaves heart

toward body

– Prevent backflow to keep blood flowing in one direction

Heart Valves

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Coronal Sections of Heart

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Heart Valves

Tricuspid Valve Pulmonary and Aortic Valve

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Path of Blood Through the Heart

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• Superior/Inferior Vena Cava/Coronary Sinus bring blood to right atrium

• Blood flows through tricuspid valve to right ventricle

• Right ventricle pumps blood through pulmonary semilunar valve to pulmonary trunk/pulmonary arteries

Path of Blood Through the Heart

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• Pulmonary arteries take blood to lungs• Blood returns to heart through pulmonary veins

to left atrium• Blood flows through bicuspid valve to left

ventricle• Blood leaves left ventricle through aortic

semilunar valve to ascending aorta• Aorta takes blood to body • Blood returns to heart through veins leading to

inferior vena cava & superior vena cava

Path of Blood Through the Heart

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Path of BloodThrough the Heart

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Blood Supply to Heart

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• Left & right coronary arteries originate from the ascending aorta– Carry oxygenated blood to myocardium

• Coronary Sinus carries deoxygenated blood to right atrium

• Anastomosis– 2 different arteries connecting & supplying an area with

blood flow– Found throughout body, many in heart– Provides collateral circulation for blood to reach an

organ

Blood Supply to Heart

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Blood Supply to Heart

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Blood Supply to Heart

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Angiogram of Coronary Arteries

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Heart Actions

•Systole•Phase of contraction

•Diastole•Phase of relaxation

•Cardiac Cycle•One complete heart beat•Consists of •systole & diastole of both atria•Systole & diastole of both ventricles

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Cardiac Cycle•Atrial Systole/Ventricular Diastole•blood flows passively into ventricles•remaining 30% of blood pushed into ventricles•A-V valves open/semilunar valves close• ventricles relaxed• ventricular pressure increases

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Cardiac Cycle

•Ventricular Systole/Atrial diastole

• A-V valves close• chordae tendinae prevent cusps of valves from bulging too far into atria• atria relaxed• blood flows into atria• ventricular pressure increases & opens semilunar valves• blood flows into pulmonary trunk & aorta

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Heart Sounds

Lubb• first heart sound • occurs during ventricular systole• A-V valves closing

Dupp• second heart sound• occurs during ventricular diastole• pulmonary and aortic semilunar valves closing

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• Clinical Application• Murmur – any condition that causes unusual sounds

to heard before or after the lubb-dupp

•Noises caused by turbulent blood flow

•Mitral and Aortic Stenosis– Narrowing of either valve by scar formation or

congenital defect

• Mitral and Aortic insufficiencies– Backflow of blood because the cusp doesn’t close

properly

Heart Sounds

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• Clinical Application• Mitral Valve Prolapse

– Inherited disorder in which the mitral valve is pushed back too far during contraction

– Usually asymptomatic

– About 10% of population has this disorder

Heart Sounds

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Heart Sounds

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Cardiac Conduction System

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• 4 main parts– Sinoatrial node (SA node)

• “pacemaker”

• Found in right atrial wall inferior to the opening of the vena cava

– Atrioventricular node (AV node)• Found near inferior portion of the interatrial septum

– Impulse from SA node travels across atria (stimulates atrial contraction) then stimulates AV node

Cardiac Conduction System

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• AV bundle– Conducting fibers run from the AV node to top of

interventricular septum and branches into two

– Distributes potential over medial surface of the ventricles

• Purkinje Fibers (conduction myofibers)– Pass from bundle branches into the myocardium

– Stimulates the contraction of the ventricles

Cardiac Conduction System

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Cardiac Conduction System

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Muscle Fibers in Ventricular Walls

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Electrocardiogram

• Recording of electrical changes that occur in the myocardium• Used to assess heart’s ability to conduct impulses

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P wave • Atrial depolarization• Fraction of a second after atria contract

Electrocardiogram

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QRS wave • Ventricular depolarization• Downward deflection (Q)• Large upward peak (R)• Ventricular depolarization• Fraction of a second after the completion of this wave,

ventricles may contract again

Electrocardiogram

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• T wave – ventricular repolarization

Electrocardiogram

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Electrocardiogram

A prolonged QRS complex may result from damage to the A-V bundle fibers

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Regulation of Cardiac Cycle

Autonomic nerve impulses alter the activities of the S-A and A-V nodes

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Regulation of Cardiac Cycle

• physical exercise• body temperature• concentration of various ions

• potassium• calcium

• parasympathetic impulses decrease heart action• sympathetic impulses increase heart action• cardiac center regulates autonomic impulses to the heart

Additional Factors that Influence HR

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Blood Vessels• Arteries• Carry blood away from ventricles of heart

• Arterioles• Receive blood from arteries• Carry blood to capillaries

• Capillaries• Sites of exchange of substances between blood and body cells

• Venules• Receive blood from capillaries

• Veins• Carry blood toward atria of heart

•Vasa Vasorum•Blood vessels in vascular tissue walls•Nourish vascular tissue

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Arteries and Arterioles

Artery• thick strong wall • endothelial lining• middle layer of smooth muscle and elastic tissue• outer layer of connective tissue• carries blood under relatively high pressure

Arterioles• thinner wall than artery• endothelial lining• some smooth muscle tissue• small amount of connective tissue• helps control blood flow into a capillary

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Walls of Artery and Vein

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• Composed of 3 layers (tunics)– Tunica Interna

• Inner wall (tunic)/ Endothelium

• Simple squamous epithelium

• Layer of elastic tissue (internal elastic lamina)

• Extremely thin in veins

Walls of Artery and Vein

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– Tunica media

• Middle tunic

• Thickest smooth muscle

• Elastic fibers

• Thinner in veins

Walls of Artery and Vein

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– Tunica Externa• Outer tunic

• Composed of elastic and collagenous fibers

• Thicker in veins

Walls of Artery and Vein

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Walls of Artery and Vein

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Walls of Artery and Vein

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• Elastic conducting arteries– Conduct blood from the heart to the medium

sized arteries– Large diameter with relatively thin walls• Tunica media has more elastic fibers and less

smooth muscle

– Must be able to withstand high blood pressures

– Aorta, Common carotid

Types of Arteries

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• Muscular Distributing Arteries– Distribute blood to the rest of the body

– More smooth muscle in tunica media

– Regulate blood needs of structures they serve

– Anastomoses likely to occur in this type of artery

– Axillary, brachial, femoral, popliteal

Types of Arteries

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• Arterioles– Smallest arterioles only have a few smooth muscle

fibers– Capillaries lack muscle fibers

– Deliver & regulate blood to capillaries

Types of Arteries

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Metarteriole

• Connects arteriole directly to venule

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Capillaries• Smallest diameter blood vessels•Only one RBC at a time

• Extensions of inner lining of arterioles• Walls are endothelium only•Only 1 cell layer thick

• Semi-permeable• Found near almost every cell in the body• The higher the tissue’s activity, the more capillaries present

• Sinusoids – leaky capillaries

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Capillaries

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Capillary Network

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Regulation of Capillary Blood Flow

• Precapillary sphincters • may close a capillary• respond to needs of the cells• low oxygen and nutrients cause sphincter to relax

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Exchange in the Capillaries

• Water and other substances leave capillaries because of net outward pressure at the capillaries’ arteriolar ends

• Water enters capillaries’ venular ends because of a net inward pressure

• Substances move in and out along the length of the capillaries according to their respective concentration gradients

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Exchange in the Capillaries

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Venules and Veins

Venule• thinner wall than arteriole• less smooth muscle and elastic tissue than arteriole• collects blood from capillaries & drain into the veins

Vein• thinner wall than artery• three layers to wall but middle layer is poorly developed• some have flaplike valves• carries blood under relatively low pressure• serves as blood reservoir

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Venous Valves

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• Disorders– Varicose Veins• Valves are weak allowing gravity to force large

quantities of blood into distal parts of the veins

• Pressure stretches vein and causes it to lose elasticity

• Veins become stretched and flabby

• Deep veins are not susceptible

Venous Valves

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Blood Volumes in Vessels

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Arterial Blood Pressure

Blood Pressure – force the blood exerts against the inner walls of the blood vessels

Arterial Blood Pressure• rises when ventricles contract• falls when ventricles relax• systolic pressure – maximum pressure• diastolic pressure – minimum pressure

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• Blood Pressure (BP)– Pressure on arterial wall due to the left ventricle

contraction– Blood flows from high to low pressures– Average aorta pressure is 100mmHg– Average right atrium pressure is nearly 0 mmHg– Normal resting BP is 120 mmHg (systolic)

80 mmHg (diastolic)

– Measured with a sphygomanometer

Blood Flow Factors

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Blood Flow Factors

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• Resistance– Friction as blood travels– Related to• Viscosity

– Ratio of RBC and solutes to liquid– Anything that decreases viscosity (dehydration) increases

BP

• Blood Vessel Length– Longer vessel = higher resistance

• Blood Vessel Radius– Resistance inversely proportional to the 4th power, the

radius of the vessel

Blood Flow Factors

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Pulse

• alternate expanding and recoiling of the arterial wall that can be felt

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Factors That InfluenceArterial Blood Pressure

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• Cardiac Output– Amount of blood ejected by the left ventricle into

the aorta each minute

– Main factor of BP

• Blood Volume– Average is about 5 liters

– Decreased volume = decreased pressure

– Increased volume = increased pressure• High salt intake retain water increased blood volume

Factors That InfluenceArterial Blood Pressure

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• Peripheral Resistance

– All of the vascular resistance offered by the cardiovascular system

– Major function of arterioles is to control resistance

• Capillary Exchange

– Blood flow is at its slowest to aid in exchange of gases and nutrients

– Depends on concentration differences

Factors That InfluenceArterial Blood Pressure

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Control of Blood Pressure

Controlling cardiac output and peripheral resistance regulates blood pressure

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Venous Blood Flow

• Not a direct result of heart action

• Dependent on • Skeletal muscle contraction• Breathing• Venoconstriction

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• Velocity of blood flow• Skeletal muscles and valves in veins– Venous milking• Muscle contracts and “squishes” blood upward• Valves keep blood from flowing backward with

gravity

• Breathing– Decreases pressure in thoracic cavity and

increases pressure in abdominal cavity

Venous Blood Flow Factors

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Central Venous Pressure

• pressure in the right atrium

• factors that influence it alter flow of blood into the right atrium

• affects pressure within the peripheral veins

• weakly beating heart increases central venous pressure

• increase in central venous pressure causes blood to back up into peripheral vein

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Pulmonary Circuit• consists of vessels that carry blood from right ventricle of the heart to the lungs and back to the left atrium of the heart

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Blood Flow Through Alveoli

• cells of alveolar wall are tightly joined together• the high osmotic pressure of the interstitial fluid draws water out of them

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Systemic Circuit

• Composed of vessels that lead from the heart to all body parts (except the lungs) and back to the heart

• Includes the aorta and its branches

• Includes the system of veins that return blood to the right atrium

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• Coronary– Circulation through blood vessels supplying

the heart

• Hepatic Portal– Runs from GI tract to the liver

Additional Circuits

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• Time required for blood to travel from the right atrium through pulmonary circulation and systemic circulation and back to the right atrium

• Average is about 1 minute

Circulation Time

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• Alternating expansion and recoil of an arterial wall

• Stronger closer to the heart

• Measured by counting for 15 seconds and multiplying by 4

• Most commonly used artery is the radial artery

Pulse

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• Other commonly used arteries– Temporal– Facial– Common carotid lateral to the larynx– Brachial artery medial sides of biceps brachii– Femoral– Popliteal behind the knee– Posterial Tibial posterior to medial malleolus– Dorsalis Pedis superior to the longitudinal arch of

the foot

Pulse

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Life-Span Changes• cholesterol deposition in blood vessels

• heart enlargement

• death of cardiac muscle cells

• increase in fibrous connective tissue of the heart

• increase in adipose tissue of the heart

• increase in blood pressure

• decrease in resting heart rate

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Clinical Application

Arrhythmias

Ventricular fibrillation• rapid, uncoordinated depolarization of ventricles

Tachycardia• rapid heartbeat

Atrial flutter• rapid rate of atrial depolarization

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• Angina Pectoris– Chest pain

– Reduced oxygen supply weakens cardiac cells but doesn’t kill them

– Symptoms• Tightness of choking sensation

• Squeezing pressure type of sensation for short durations

– Causes• Stress, exertion, hypertension

Clinical Application

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• Myocardial Infarction (MI)– Heart attack– Infarction means death of tissue due to lack

of blood supply– Myocardial tissue behind blocked arteries

dies– Dead tissue may disturb conducting system

of the heart which could lead to sudden death (ventricular fibrillation)

Clinical Application

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• Shock– Failure of cardiovascular system to deliver

adequate amounts of oxygen and nutrients to meet the metabolic needs of body cells because of inadequate cardiac output

Clinical Application

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• Shock Signs and Symptoms– Systolic PB lower than 90 mmHg as a result

of vasodilation and decreased cardiac output– Clammy, cool, pale skin due to

vasoconstriction of blood vessels in the skin– Sweating due to increased levels of

epinephrine– Rapid heart rate

Clinical Application

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• Signs and Symptoms– Lactic acid build-up– Weak pulse– Altered mental state– Thirst due to extra-cellular fluid loss

Clinical Application