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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