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Circulatory System

Chapter 13

Chapter 13 OutlineFunctions and Components of the Circulatory

SystemComposition of BloodStructure of the HeartCardiac Cycle and Heart SoundsCardiac Cycle and Heart SoundsElectrical Activity of the Heart and the ECGBlood VesselsAtherosclerosis and Cardiac ArrhythmiasLymphatic System

Functions and Components of the Circulatory System

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Functions of Circulatory System

Transportation of respiratory gasesDelivery of nutrients and hormonesWaste removalTemperature regulationClottingClottingImmune function

Components of Circulatory SystemInclude cardiovascular and lymphatic systemsHeart pumps blood thru cardiovascular systemBlood vessels carry blood from heart to cells and

backIncludes arteries, arterioles, capillaries, venules,

veinsLymphatic system picks up excess fluid filtered out

in capillary beds and returns it to veinsIts lymph nodes are part of immune system

Composition of the Blood

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Composition of Blood

Consists of formed elements (cells) suspended and carried in plasma (fluid part)

When centrifuged, blood separates into heavier formed elements on bottom and plasma on top

Composition of Blood Total blood volume is about 5LPlasma is straw-colored liquid consisting of H2O and

dissolved solutesIncludes ions, metabolites, hormones, antibodies

Red blood cells (RBCs) comprise most of formed elements% of RBCs in centrifuged blood sample = hematocritHematocrit is 36-46% in women; 41-53% in men

RBC Antigens and Blood TypingAntigens present on RBC surface specify blood typeMajor antigen group is ABO systemType A blood has only A antigensType B has only B antigensType AB has both A and B antigensType AB has both A and B antigensType O has neither A or B antigens

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Transfusion ReactionsPeople with Type A blood

make antibodies to Type B RBCs, but not to Type A

Type B blood has antibodies to Type A RBCs but not to Type B

Type AB blood doesn’t have ypantibodies to A or B

Type O has antibodies to both Type A and B

If incompatible blood types are mixed, antibodies will cause mixture to agglutinate

Transfusion Reactions If blood types incompatible,

recipient’s antibodies agglutinate donor’s RBCs

Type O is “universal donor” because lacks A and B antigensRecipient’s antibodies p

won’t agglutinate donor’s Type O RBCs

Type AB is “universal recipient” because doesn’t make anti-A or anti-B antibodiesWon’t agglutinate

donor’s RBCs

Rh FactorIs another type of antigen found on RBCsRh+ has Rho(D) antigens; Rh- does notCan cause problems when Rh- mother has Rh+

babiesAt birth, mother may be exposed to Rh+ blood of

fetusIn later pregnancies mom produces Rh antibodiesIn Erythroblastosis fetalis, Rh antibodies from

mom cross placenta and combine with Rh+antigens on fetal blood cells causing hemolysis of fetal RBCs

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Structure of the Heart

Structure of HeartHeart has 4 chambers2 atria receive blood from venous system2 ventricles pump blood to arteries2 sides of heart are 2 pumps separated by muscular septum

Cardiac Cycle and Heart Sounds

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Heart Valves

Cardiac Cycle

Cardiac Cycle

Is repeating pattern of contraction and relaxation of heartSystole refers to contraction phase Diastole refers to relaxation phaseBoth atria contract simultaneously; ventricles followBoth atria contract simultaneously; ventricles follow

0.1-0.2 sec later

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Cardiac Cycle

End-diastolic volume is volume of blood in ventricles at end of diastole

Stroke volume is amount of blood ejected from ventricles during systole

End-systolic volume is amount of blood left inEnd-systolic volume is amount of blood left in ventricles at end of systole

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Electrical Activity of Heart and the ECG

SA Node Pacemaker

In normal heart, SA node functions as pacemakerDepolarizes

spontaneously tospontaneously to threshold (= pacemaker potential)

Membrane voltage begins at -60mV and gradually depolarizes to -40 threshold

Spontaneous depolarization is caused by Na+ flowing through

SA Node Pacemaker

channel that opens when hyperpolarized (HCN channel)

At threshold V-gated Ca2+

channels open, creating upstroke and contraction

Repolarization is via opening of V-gated K+

channels

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Myocardial Action Potentials

Myocardial cells have RMP of –90 mVDepolarized to threshold by action potentials

originating in SA node

Myocardial APs

Upstroke occurs as V-gated Na+ channels open

MP rapidly declines to 15mV and stays there for 200-300 msec (plateau phase)Plateau results from

balance between slow Ca2+ influx and K+ efflux

Repolarization due to opening of extra K+

channels

Refractory Periods

Heart’s Act. Pot. lasts about 250 msec

Has refractory periodsalmost as long as Act. PotPot.

Cannot be stimulated to contract again until has relaxed

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Electrocardiogram (ECG/EKG)Is a recording of electrical activity of heart conducted

thru ions in body to surface

Types of ECG Recordings

Bipolar leads record voltage between electrodes placed on wrists and legs (right leg is ground)g )

Lead I records between right arm and left arm

Lead II: right arm and left leg

Lead III: left arm and left leg

Types of ECG Recordings

Unipolar leads record voltage between a single electrode placed on body and ground built into ECG machineLimb leads go on rightLimb leads go on right

arm (AVR), left arm (AVL), and left leg (AVF)

The 6 chest leads, placed as shown, allow certain abnormalities to be detected

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ECG

Correlation of ECG with Heart Sounds

1st heart sound (lub) comes immediately after QRS wave as AV valves close

2nd heart sound (dub) comes as T wave begins and semilunar valves close

Blood Vessels

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ArteriesSmall arteries and arterioles are muscular Provide most resistance in circulatory systemArterioles cause greatest pressure dropMostly connect to capillary bedsSome connect directly to veins to form arteriovenous

anastomoses

Provide extensive surface area for exchange Blood flow through a capillary bed is determined by

state of precapillary sphincters of arteriole supplying it

Capillaries

In continuous capillaries, endothelial cells are tightly joined togetherHave narrow intercellular channels that permit exchange

of molecules smaller than proteins Present in muscle, lungs, adipose tissue

Types of Capillaries

Present in muscle, lungs, adipose tissueFenestrated capillaries have wide intercellular poresVery permeablePresent in kidneys, endocrine glands, intestines.

Discontinuous capillaries have large gaps in endotheliumAre large and leakyPresent in liver, spleen, bone marrow

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Contain majority of blood in circulatory systemVery compliant (expand readily)Contain very low pressure (about 2mm Hg)Insufficient to return blood to heart

Veins

Blood is moved toward heart by contraction of surrounding skeletal muscles (skeletal muscle pump) And pressure

Veins

And pressure drops in chest during breathing

1-way venous valves ensure blood moves only toward heart

Lymphatic System

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Lymphatic System

Has 3 basic functions:Transports interstitial fluid (lymph) back to bloodTransports absorbed fat from small intestine to

bloodHelps provide immunological defenses against

pathogens

Lymphatic System

Lymphatic capillariesare closed-end tubes that form vast networks in intercellular spacesVery porous,

absorb proteins, microorganisms, fat

Lymphatic System

Lymph is carried from lymph capillaries tocapillaries to lymph ducts to lymph nodes

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Lymph nodes filter lymph before returning it to R. & L. subclavian veins via thoracic ductor right lymphatic duct

Nodes make

Lymphatic System

Nodes make lymphocytes and contain phagocytic cells that remove pathogens

Lymphocytes also made in tonsils, spleen, thymus