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Chapter 20
Organization of the Cardiovascular System
▪Pulmonary Circuit▪Systemic Circuit-.
▪Arteries▪Veins▪CapillariesAnatomy of the Heart
▪The heart is surrounded by serous membrane and divided into 4 chambers, two receiving
chambers and two pumping chambers
▫Pericardium- lining of the pericardial cavity, subdivided into two parts
-Visceral pericardium-Parietal pericardium-The small space between the two layers of the pericardium contains about 1550 mL of pericardial fluid, reduces friction between the opposing surfaces during
heart beats.
▫Auricle▫Coronary Sulcus▫Anterior and Posterior interventricular sulci▫Heart Wall- made up of three layers:
-epicardium-myocardium-endocardium▫Right Atrium- receives blood from the superior vena cava and the inferior vena cava.
-coronary sinus-fossa ovalis-pectinate muscles-
▫Right Ventricle- receives blood from the right atrium
-tricuspid valve-chordae tendonae-papillary muscles-trabeculae carneae-moderator band-pulmonary valve▫Left Atrium- receives blood from the pulmonary veins
▫Left Ventricle- receives blood from the right atrium
-Bicuspid Valve (mitral valve)-Much thicker myocardium, needs to produce enough pressure to push blood
through entire systemic circuit.
-Chordae tendonae, papillary muscles, and trabeculae carneae are also present
-aortic valve▪Connective tissue of the heart include large numbers of collagen and elastic fibers. Intricately
woven and interconnected
1. provide physical support for the cardiac muscle fibers, blood vessels, and nerves of
the myocardium.
2. help distribute the forces of contraction.
3. add strength and prevent overexpansion of heart
4. provide elasticity that helps return the heart to its original size and shape after a
contraction.
▪The Blood Supply to the Heart
▫Coronary arteries- originate at the base of the ascending aorta.
▫As the aorta recoils, blood is forced into systemic circulation as well as into the coronary
arteries.
-Right coronary artery supplies…
-Left coronary artery supplies…
▫Cardiac Veins- collect deoxygenated blood, returns it to right atrium
Cardiac Physiology
▪A single heartbeat consists of the atria contracting followed by the ventricles contracting.
▪Two types of cells are involved in a heartbeat: conducting cells and contractile cells.
▪A heartbeat lasts for about 370 msec.
▪The conducting system is responsible for the contraction of cardiac tissue in the absence of
neural or hormonal stimulation, automaticity. This system contains:
▫Sinoatrial (SA) node- located in the wall of the right atrium
▫Atrioventricular (AV) node- located at the junction between the atria and ventricles.
▫Conducting cells- interconnects the two nodes and distributes the stimulus throughout
the myocardium, it includes:
-AV bundle-Bundle branches-Purkinje fibers-conducting cells are smaller than the contractile cells
-conducting cells of the SA and AV nodes cannot maintain a stable resting
potential.
▫Electrocardiogram (ECG, EKG)- recording of the electrical events of the heart. Has
many important features:
-P wave-QRS complex-
-T wave-Analyzing the size and temporal relationships in an ECG can show indications of
problems with the heart.
-P-R interval-Q-T interval▪Contractile cells- form the bulk of the atrial and ventricular walls.
▫contract similar to skeletal muscles, few exceptions
A) nature of the action potential
-resting potential of a ventricular contractile cell is around -90 mV.
Threshold is around -75 mV.
-Threshold is met near an intercalated disc
-AP proceeds in 3 basic steps:
1. rapid depolarization
2. the plateau
3. repolarization
-Has both absolute and relative refractory periods
B) source of Ca2+ ions
-as an AP arrives, calcium concentration increases in two steps:
1. calcium ions enter from extracellular space
2. this extracellular calcium triggers more Ca2+ release from the
sarcoplasmic reticulum.
C) duration of the resulting contractions.
-since Ca2+ ions continue to enter during the plateau, summation is not
possible, and tetany cannot take place.
▪Cardiac Cycle- the period between the start of one heartbeat and the beginning of the next. Can
be divided into two phases; systole and diastole.
▫Systole-.
▫Diastole▫With a 75 bpm heart rate, a sequence of systole and diastole lasts for 800 msec.
▫Blood moves from areas of high pressure to low pressure
*work through diagrams 20-16 and 20-17 along with the text on pages 706-710*
▪Heart Sounds- the loudest heart sounds are caused by the closing of the
valves (S1 and S2)
▫S1, the loudest, is the closing of the AV valves (lub)
▫S2, a bit softer, is the closing of the semilunar valves (dup)
▫fainter heart sounds (S3 and S4) are caused by blood flowing into the ventricles and
atrial contraction, respectively.
Cardiodynamics
▪Cardiodynamics is the movements and forces generated during cardiac contractions.
▫End-Diastolic Volume (EDV)▫End-Systolic Volume (ESV)▫Stroke Volume (SV)▫Ejection Fraction▫Cardiac Output-
▪Cardiac output can be adjusted by changes in either heart rate or stroke volume
▪Factors affecting the heart rate include: autonomic innervation, hormones, and venous return.
▫Autonomic Innervation- sympathetic and parasympathetic divisions innervate the heart.
-Postganglionic sympathetic neurons are located in the cervical and upper
thoracic ganglia.
-Preganglionic parasympathetic neurons are carried in the vagus nerve
-Both innervate the SA and AV nodes and atrial muscle cells
-Sympathetic fibers far outnumber parasympathetic fibers in the ventricle muscle
walls.
-Cardiac centers of the medulla oblongata contain the autonomic headquarters
for cardiac control.
-Cardioacceleratory center-Cardioinhibitory center-Cardiac Reflexes- cardiac centers monitor baroreceptors and chemoreceptors,
these centers respond to changes in blood pressure and arterial concentrations
of oxygen and carbon dioxide.
-Autonomic Tone- both autonomic divisions are normally active at a steady state
background level.
-parasympathetic effects dominate during rest, keeps resting heart rate
around 70-80 bpm.
-allows for ANS to make very delicate adjustments in cardiovascular
function to meet the demands of other systems.
-Sympathetic and parasympathetic divisions alter the heart rate by changing the
permeabilities of cells in the conducting system.
-Atrial Reflex- adjustments in heart rate in response to an increase in venous
return.
▫Epinephrine, norepinephrine, and thyroid hormone increase the heart rate by affecting
the SA node.
-effects of epinephrine on SA node is similar to that of norepinephrine, also
effects contractile cells.
▫Venous return has an indirect effect on heart rate by way of the atrial reflex.
▪Factors affecting the stroke volume are the differences between the EDV and ESV
▫EDV- amount of blood a ventricle contains at the end of diastole, just before contraction
begins. Affected by three factors; filling time, venous return, and preload:
-filling time-venous return-preload▫ESV- amount of blood that remains in the ventricle at the end of ventricular systole.
Three factors influence ESV; preload, contractility of the ventricle, and afterload.
-contractility-positive inotropic action-negative inotropic action-positive and negative inotropic factors include ANS activity, hormones,
and changes in extracellular ion concentrations.
-Afterload-the greater the afterload, the longer is the period of isovolumetric
contraction, the shorter the duration of ventricular contraction, and the
larger the ESV (as the afterload increases, the stroke volume decreases)
-afterload is increased by any factor that restricts blood flow through the
arterial system.