Download - Cardiovascular System: The Heart
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Cardiovascular System:The Heart
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FUNCTIONS OF THE CARDIOVASCULAR SYSTEM
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• Transports O2, nutrients, CO2, cell wastes, etc. to and from body cells
• Maintaining body temperature• Homeostatic relationships with all
body systems–With the urinary system,
regulation of blood volume and pressure
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LOCATION OF THE HEART
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Thoracic cavity between two lungs• ~2/3 to left of midlineSurrounded by pericardium:• Fibrous pericardium -
– Inelastic; anchors heart in place• Inside is serous pericardium - double
layer around heart– Parietal layer fused to fibrous pericardium– Inner visceral layer adheres tightly to heart– Filled with pericardial fluid - reduces friction
during beat.
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HEART ANATOMY
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The Heart Wall• Epicardium - outer layer• Myocardium - cardiac muscle
–Two separate networks via gap junctions in intercalated discs - atrial & ventricular
–Networks- contract as a unit• Endocardium - Squamous epithelium
– lines inside of myocardium
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The Heart Wall
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The Heart Wall
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The Heart Wall
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Heart Chambers4 chambers:• 2 upper chambers = Atria
– Between is inter-atrial septum– Contains fossa ovalis - remnant of foramen ovalis
• 2 lower chambers = ventricles– Between is interventricular septum
• Wall thickness depends on work load– Atria thinnest– Right ventricle pumps to lungs & thinner than left
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External Anatomy
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External Anatomy
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Internal Anatomy
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Great Vessels of the Heart
Superior & inferior Vena Cavae• Delivers O2 depleted blood to R. atrium
from body• Coronary sinus drains heart muscle veins• R. Atrium R. VentriclePumps through Pulmonary Trunk• R & L Pulmonary Arteries• lungs
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Great Vessels of the Heart
Pulmonary Veins from lungs• O2 rich blood• L. atrium Left ventricleascending aorta bodyBetween pulmonary trunk & aortic arch is the
ligamentum arteriosum• fetal ductus arteriosum remnant
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Heart ValvesDesigned to prevent back flow in response
to pressure changes• Atrio-ventricular (AV) valves are found
between the atria and ventricles• Right AV valve = tricuspid valve (has three
flaps, or cusps)• Prevent backflow of blood into the right
atrium
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Heart Valves• Left AV valve = bicuspid, or mitral valve• Prevents backflow of blood into left
atriumSemilunar Valves are found at the base of
aorta and pulmonary trunk• Prevent backflow of blood into the
ventricles
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Heart ValvesChordae Tendinae:• Tiny white cords that anchor the AV valve
cusps to the wall of the ventricle• Help to anchor the flaps to prevent a prolapse
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Coronary CirculationBlood flow through vessels in myocardium =
coronary circulation• Left & right coronary arteries
– branch from aorta to carry blood throughout muscle
• O2 - depleted blood collected by coronary sinus (posterior)
• Empties into right atrium
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HEART PHYSIOLOGY
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Conduction System1% of cardiac muscle generate action potentials
= Pacemaker & Conduction system• Normally begins at sinoatrial (SA) node • Atria & atria contractAV node – slows the signal, then travels along:AV bundle (Bundle of His) bundle branches Purkinje fibers apex and up- then ventricles contract
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Frontal plane
SINOATRIAL (SA) NODE
ATRIOVENTRICULAR(AV) NODE
Left atrium
Left ventricle
Anterior view of frontal section
ATRIOVENTRICULAR (AV)BUNDLE (BUNDLE OF HIS)
RIGHT AND LEFTBUNDLE BRANCHES
PURKINJE FIBERS
1
2
3
4
5
Right atrium
Right ventricle
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ElectrocardiogramRecording of currents from cardiac
conduction on skin = electrocardiogram (EKG or ECG)
• P wave = atrial depolarization– Contraction begins right after peak– Repolarization is masked in QRS
• QRS complex = Ventricular depolarization– Contraction of ventricle
• T-wave = ventricular repolarization– Just after ventricles relax
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Cardiac CycleAfter T-wave ventricular diastole• Ventricular pressure drops below atrial
pressure & AV valves open ventricular filling occurs
After P-wave atrial systole• Finishes filling ventricle (about 25% of
total)
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Cardiac CycleAfter QRS ventricular systole• Pressure pushes AV valves closed• Pushes semilunar valves open and ejection
occurs• Ejection until ventricle relaxes enough for
arterial pressure to close semilunar valves
Cardiac Cycle Animations
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Cardiac Cycle: Flow Terms• Cardiac Output (CO) = liters/min pumped• Heart Rate (HR) = beats/minute (bpm)• Stroke volume (SV) = volume/beat• CO = HR x SV• Average:
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Cardiac Cycle: Control of Stroke Volume
• Degree of stretch = Frank-Starling law– Increase diastolic volume (stretch) increases
strength of contraction increased S.V.– Increased venous return increased S.V.
• Increased sympathetic activity • High back pressure in artery decreased S.V.
– Slows semilunar valve opening• Slow heart rate increased S.V.
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Cardiac Cycle: Control of Heart Rate
Pacemaker adjusted by nerves• Cardiovascular Center in MedullaParasympathetic - ACh slows HR via Vagus nerveSympathetic - norepinephrine speeds HRSensory input for control:• Baroreceptors (aortic arch & carotid sinus)- B.P.• Chemoreceptors- O2, CO2, pH
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Cardiac Cycle: Other ControlsHormones: • Epinephrine & norepinephrine increase H.R.• Thyroid hormones stimulate H.R.• Called tachycardia (opposite: bradycardia)Ions• Increased Na+ or K+ decrease H.R. & contraction
force• Increased Ca2+ increases H.R. & contraction
force
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Exercise• Aerobic exercise (longer than 20 min)
strengthens cardiovascular system• Well trained athlete doubles maximum
C.O.• Resting C.O. about the same but resting
H.R. decreased
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BLOOD VESSELS AND CIRCULATION
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Blood VesselsArteries: carry blood away from heart
1. Elastic2. Muscular: Their smooth muscle helps
regulate blood pressure, directs flow3. Arterioles: branches of main arteries;
distribution to capillaries
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Blood VesselsCapillaries: thin-walled for diffusionVeins: carry blood back to heart
1. Venules: collect blood from capillaries2. Veins from tissues vena cavae heart
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Blood Vessel Structure: Arteries, Veins
Three Layers:• Tunica externa: connective tissue• Tunica media: smooth muscle• Tunica interna (intima): endothelial
tissue
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Blood Vessel Structure: Arteries, Veins• Arteries: thicker tunica media
– Elastic tissue and/or muscle• Arterioles
– Arterioles: control blood pressure, blood flow
• Veins– Larger lumen, thinner walls– Contain valves to prevent backflow
• Venules– Venules: very thin, no valves
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Blood Vessel Structure: Arteries, Veins
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Blood Vessel Functions• Muscular arteries, arterioles regulate flow
– Sympathetic activity to smooth muscle vasoconstriction (narrowing)
– Decreased sympathetic activity causes relaxation (dilation)
• Arterioles adjust flow into capillaries• Capillaries: sites of gas exchange• Systemic venules and veins serve as blood
reservoirs (hold ~64% total blood volume)
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Venous ReturnBlood enters veins at very low pressure• Inadequate to overcome gravity and return
blood to heart • Skeletal muscle contractions
– Contracting skeletal muscles (especially in lower limbs) squeeze veins emptying them
– Because of venous valves, flow is heart
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Venous Return• Respiratory pump has similar action
– Inhalation decreases thoracic pressure and increases abdominal pressure blood to heart
– Exhalation allows refilling of abdominal veins
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Venous Return
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Blood Flow Through VesselsBlood flow follows a pressure gradient• Greater gradient greater flow
– BP is highest in aorta: 110/70 mm Hg – BP declines as flows through more
vessels• Capillary beds ~35-16 mm Hg• 16 mm Hg at venules 0 at right
atrium
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Factors Regulating Blood Flow1. Blood volume and ventricular contraction
cardiac output2. Vascular resistance: opposition to flow
(depends on lumen diameter, vessel length, and blood viscosity) • Smaller lumen (vasoconstriction) greater
resistance• Greater vessel length (with weight gain)
greater resistance• Higher viscosity (as with high hematocrit)
greater resistance
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Cardiovascular Center• Located in medulla• Helps regulate
– Heart rate– Stroke volume– Blood pressure– Blood flow to specific tissues
• Mechanisms– By neural mechanisms– By hormonal mechanisms
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Cardiovascular Center InputTo inform brain that BP should be altered:• Input from different parts of brain
– Cerebral cortex: thoughts, decisions– Limbic system: emotions– Hypothalamus: changes in temperature or blood
volume• Input from sensory receptors and nerves
– Proprioceptors, baroreceptors, chemoreceptors
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Cardiovascular Center Input• Proprioceptors: monitor movements of
joints and muscles– Cause heart rate as exercise begins cardiac
output (CO) BP• Baroreceptors in aorta and carotid: if BP
– sympathetic stimulation CO BP– parasympathetic CO BP
• Chemoreceptors in aorta and carotid bodies– If low O2, high CO2, or high H+ (acidity)
resistance by vasoconstriction BP
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Cardiovascular Center Input
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Output Effects• ANS nerves to heart
– Sympathetic HR and force of contraction cardiac output (CO) BP
– Parasympathetic HR CO BP• Vasomotor (sympathetic nerves)
– To arterioles contract smooth muscle vascular resistance BP
– To veins contract smooth muscle move blood to heart BP
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Circulatory Routes• Pulmonary Circulation: from the right side
of the heart to the lungs and back to the left side of the heart
• Systemic Circulation: from the left side of the heart to the tissues and cells of the body and back to the right side of the heart
• Cardiac Circulation: from the left side of the heart through the coronary arteries and back to the right side of the heart
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Circulatory Routes