the cardiovascular system structure of the heart the cardiac cycle structure and organization of...
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The cardiovascular system
Structure of the heart
The cardiac cycle
Structure and organization of blood vessels
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What is the cardiovascular system?
The heart is a double pump
heartarteries arterioles veinsvenules capillaries
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The double pump
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Serous membrane
Continuous withblood vessels
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Chambers of the heart; valves
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Valves control flow of blood from onechamber to another
Prevent backflow
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Blood supply to the heart
Coronary artery and vein system
Right and left coronary arteries branch off ofaorta
Branch into smaller vessels
Cardiac veins deliver blood to coronary sinus,and back to the right atrium
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Coronary artery disease results when coronaryarteries cannot deliver blood adequately
Usual cause: plaques in arterial walls
Angina pectoris (pain) when body is notreceiving adequate oxygen
Myocardial infarction (heart attack) whenblood supply to heart is completelyblocked; muscle dies
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Coordination of chamber contraction, relaxation
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Conduction system of the heart
Heart contracts as a unit
Atrial and ventricular syncytia help conductelectrical signals through the heart
Sinoatrial (S-A) node is continuous with atrialsyncytium
S-A node cells can initiate impulses on theirown; activity is rhythmic
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Electrocardiogram (ECG) can trace conductionof electrical signals through the heart
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Aberrant ECG patterns indicate damage
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Regulation of heart rate
Blood pressure and its control
What is hypertension and how is it treated?
The heart rate and exercise
Characteristics of arteries and veins
Organization of the vascular system andresponses to physiological needs
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Regulation of the cardiac cycle
Sympathetic and parasympathetic nervoussystems
Parasympathetic: from medulla oblongata(vagus nerve)
Nerve branches to S-A and A-V nodes, andsecretes acetylcholine (slows rate)
Parasympathetic activity can increase (slowheart rate) or decrease (increase heartrate)
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Sympathetic nervous systemthrough celiac plexus to heartsecretes norepinephrineincreases force of contractions
Cardiac control center in medulla oblongatamaintains balance between the two
Normally both sympathetic and parasympatheticfunction at a steady background level
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Baroreceptors detect changes in blood pressure
Rising pressure stretches receptorsvagus nerveparasympathetic system
Increased temperature increases heart rate
Ions and heart rate:excess potassium decreases it
excess calcium increases it
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Blood pressure
Blood flow is generally equal to cardiac output
Blood flow affected by pressure and resistance
Blood pressure: the force that is exerted by bloodagainst blood vessel walls
Resistance depends on size of blood vessel andthickness (viscosity) of blood
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Blood pressure is highest in large arterieswill rise and fall as heart pumps
highest with ventricular systolelowest with ventricular diastolepulse pressure is the difference betweenthe two
Resistance is highest in capillaries
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More cells constriction of bloodvessel walls
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Control of blood pressure
Regulation of cardiac outputcontraction strengthheart ratevenous return
skeletal musclesbreathing rate
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Long term regulation of blood flow (hormones)
If blood pressure is too low:
ADH (antidiuretic hormone) promotes waterretention
Angiotensin II- in response to reninsignal (renin) produced by kidney- why?drop in blood pressurestimulation by sympathetic nervous
systemsodium levels too low
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What happens?vasoconstriction (by angiotensin II)what will that do to blood pressure?ADH is secretedaldosterone is secreted
EPO (erythropoietin) secreted by kidneysif blood volume is too low
ANP secreted if blood pressure is tooHIGH
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What is hypertension?
Arterial pressure is too high
Sometimes cause is unknown, or is secondaryto disease
Variety of causes/ risk factors are knownsedentary lifestylesmokingobesitydiet (excess sodium; cholesterol; calories
in general)stressarteriosclerosisgenetic factors
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Consequences?heart has to work harder; left ventricleenlargesatherosclerosis may affect coronaryarteries as well (which have to work harderanyway) heart disease
deficient blood supply to other parts ofbody
damage to blood vessels accumulates
heart failure
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Treatment of high blood pressure
Quit smoking; adjust diet; exercise
Drug therapies- strategies differ
Reduce heart ratecalcium channel blockers
reduce calcium flow into heartmuscle and therefore heart raterelax smooth muscle liningcoronary arteries
beta blockers (reduce stimulation bysympathetic nervous system)
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Diuretics reduce blood volumeACE inhibitors interfere with renin-angiotensin pathway
Vasodilators (such as nitroglycerin) open upblood vessels (reduce resistance)
If heart is actually failing, digitalis increasesefficiency of heat muscle
Anti-hypertensive drugs may be taken incombination
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Why is exercise good for the heart?
A trained heart is biggerpumps blood more efficiently (at a lowerrate)stroke volume increases (due to strongercontractions, allowing for lower rate)
other benefits: higher aerobic capacity(contributing to efficiency)
Note that this takes training!
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Characteristics of blood vessels
Arteries and arterioles carry blood away fromheart
Capillaries- site of exchange
Venules, veins- return blood to heart
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Endothelium- prevents platelet aggregationsecretes substances that control diameterof blood vessel
Tunica media- smooth muscle and connectivetissue. Innervated by sympathetic nerves(vasoconstriction)
Missing in smallest arteries
Tunica externa- connective tissue; isvascularized
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Capillaries most permeable (and more permeablein some parts than others)
Especially so in liver, spleen and red marrow(so cells can enter and leave circulation)
Blood flow can vary to different parts of the body, too
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What does this mean?
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Blood is forced through arteries and arteriolesvessel walls are too thick for blood com-ponents to pass through
In capillaries, oxygen and nutrients move outby diffusion; CO2 in (via lipid membrane,channels, etc.)
Blood pressure moves molecules out by filtration
Plasma proteins maintain osmotic pressureof blood
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Returning blood to the heart
Venules are continuous with capillaries; takein some returned fluid (rest is retained bytissues or returned to blood via lymphaticsystem)
Veins have thinner walls;less muscle; but can hold much more blood
Many veins in limbs have valves to preventbackflow
(Varicose veins arise when pressure on valvesis prolonged)
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See pp. 351-359 for allcircuits
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Summary
The heart is a double pump, delivering bloodto the lungs for oxygenation, and thento the body
Blood leaves the heart through arteries, andreturns to the heart through veins
The heart rate is regulated by a conducting system (the heart beats about 100,000times per day!)
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The cardiac cycle is regulated by the cardiaccenter in the medulla oblongata whichregulates sympathetic and parasympa-thetic input
Exercise (i.e., needs), temperature and ionbalance also affect heart rate
Cardiac rate is also controlled by long-termresponders such as ADH, angiotensin,EPO and ANP
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Blood (arterial) pressure is affected by heartaction, blood volume, peripheralresistance, and blood viscosity
Inability to regulate blood pressure can contribute to disease
Arteries and veins have structural characteristicsappropriate to bringing blood to the cellsand then back to the heart
Circulatory system allows for adjustments to exercise, digestion and other necessaryfunctions