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The Heart. Heart Anatomy. Approximately the size of your fist Location Superior surface of diaphragm Left of the midline Anterior to the vertebral column, posterior to the sternum. Heart Anatomy. Coverings of the Heart: Anatomy.

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heart anatomy
Heart Anatomy
  • Approximately the size of your fist
  • Location
    • Superior surface of diaphragm
    • Left of the midline
    • Anterior to the vertebral column, posterior to the sternum
coverings of the heart anatomy
Coverings of the Heart: Anatomy
  • Pericardium – a double-walled sac around the heart composed of:
    • A superficial fibrous pericardium
    • A deep two-layer serous pericardium
      • The parietal layer lines the internal surface of the fibrous pericardium
      • The visceral layer or epicardium lines the surface of the heart
      • They are separated by the fluid-filled pericardial cavity
coverings of the heart physiology
Coverings of the Heart: Physiology
  • The pericardium:
    • Protects and anchors the heart
    • Prevents overfilling of the heart with blood
    • Allows for the heart to work in a relatively friction-free environment
heart wall
Heart Wall
  • Epicardium – visceral layer of the serous pericardium
  • Myocardium – cardiac muscle layer forming the bulk of the heart
  • Fibrous skeleton of the heart – crisscrossing, interlacing layer of connective tissue
  • Endocardium – endothelial layer of the inner myocardial surface
external heart major vessels of the heart anterior view
External Heart: Major Vessels of the Heart (Anterior View)
  • Vessels returning blood to the heart include:
    • Superior and inferior vena cava
    • Right and left pulmonary veins
  • Vessels conveying blood away from the heart:
    • Pulmonary trunk, which splits into right and left pulmonary arteries
    • Ascending aorta (three branches) – brachiocephalic, left common carotid, and subclavian arteries
slide10

Left common

carotid artery

Brachiocephalic

trunk

Left

subclavian artery

Superior

vena cava

Aortic arch

Right

pulmonary artery

Ligamentum

arteriosum

Left pulmonary artery

Ascending

aorta

Left pulmonary veins

Pulmonary trunk

Left atrium

Right

pulmonary veins

Auricle

Right atrium

Circumflex

artery

Right coronary

artery (in coronary

sulcus)

Left coronary

artery (in coronary

sulcus)

Anterior

cardiac vein

Left ventricle

Right ventricle

Great cardiac vein

Marginal artery

Anterior

interventricular artery

(in anterior

interventricular sulcus)

Small cardiac vein

Inferior

vena cava

(b)

Apex

external heart arteries that supply the heart
External Heart: Arteries that Supply the Heart
  • Coronary circulation is the functional blood supply to the heart muscle itself
  • Collateral routes ensure blood delivery to heart even if major vessels are occluded
external heart arteries that supply the heart12
External Heart: Arteries that Supply the Heart
  • Right coronary artery (in atrioventricular groove)
    • Supplies
      • Right atrium
      • Portions of both ventricles
      • SA and AV nodes
    • Branches
      • Marginal artery
      • Posterior interventricular artery
external heart arteries that supply the heart13
External Heart: Arteries that Supply the Heart
  • Left coronary artery
    • Supply
      • Left atrium
      • Portions of both ventricles
    • Branches
      • Circumflex
      • Anterior interventricular
external heart veins that drain the heart
External Heart: Veins that Drain the Heart
  • Veins that empty in the coronary sinus
    • Great cardiac vein
    • Posterior cardiac vein
    • Middle cardiac vein
    • Small cardiac vein
  • Vein that empty into the right atrium
    • Anterior cardiac vein
external heart major vessels of the heart posterior view
External Heart: Major Vessels of the Heart (Posterior View)
  • Vessels returning blood to the heart include:
    • Right and left pulmonary veins
    • Superior and inferior vena cava
  • Vessels conveying blood away from the heart include:
    • Aorta
    • Right and left pulmonary arteries
slide18

Aorta

Superior

vena cava

Left

pulmonary artery

Right

pulmonary artery

Left

pulmonary veins

Right

pulmonary veins

Auricle

of left atrium

Right atrium

Left atrium

Inferior

vena cava

Great cardiac vein

Right coronary

artery (in coronary

sulcus)

Posterior vein

of left ventricle

Coronary sinus

Posterior

interventricular artery

(in posterior

interventricular sulcus)

Left ventricle

Middle cardiac vein

Apex

Right ventricle

(d)

slide19

Aorta

Superior vena cava

Left

pulmonary artery

Right

pulmonary artery

Left atrium

Pulmonary trunk

Left

pulmonary veins

Right atrium

Right

pulmonary veins

Mitral

(bicuspid) valve

Fossa

ovalis

Aortic

valve

Pectinate

muscles

Pulmonary

valve

Left ventricle

Tricuspid

valve

Papillary

muscle

Right ventricle

Chordae

tendineae

Interventricular

septum

Myocardium

Trabeculae

carneae

Visceral

pericardium

Inferior

vena cava

Endocardium

(e)

atria of the heart
Atria of the Heart
  • Atria are the receiving chambers of the heart
  • Each atrium has a protruding auricle
  • Pectinate muscles mark atrial walls
    • In the left atrium only in the wall of the auricle
  • Blood enters right atria from superior and inferior venae cavae and coronary sinus
  • Blood enters left atria from pulmonary veins
ventricles of the heart
Ventricles of the Heart
  • Ventricles are the discharging chambers of the heart
  • Papillary muscles and trabeculae carneae muscles mark ventricular walls
  • Right ventricle pumps blood into the pulmonary trunk
  • Left ventricle pumps blood into the aorta
pathway of blood through the heart and lungs
Pathway of Blood Through the Heart and Lungs
  • Right atrium  tricuspid valve  right ventricle
  • Right ventricle  pulmonary semilunar valve  pulmonary arteries  lungs
  • Lungs  pulmonary veins  left atrium
  • Left atrium  bicuspid valve  left ventricle
  • Left ventricle  aortic semilunar valve  aorta
  • Aorta  systemic circulation
heart valves
Heart Valves
  • Heart valves ensure unidirectional blood flow through the heart
  • Atrioventricular (AV) valves lie between the atria and the ventricles
  • AV valves prevent backflow into the atria when ventricles contract
  • Chordae tendineae anchor AV valves to papillary muscles
heart valves26
Heart Valves
  • Aortic semilunar valve lies between the left ventricle and the aorta
  • Pulmonary semilunar valve lies between the right ventricle and pulmonary trunk
  • Semilunar valves prevent backflow of blood into the ventricles
microscopic anatomy of heart muscle
Microscopic Anatomy of Heart Muscle
  • Cardiac muscle is striated, short, fat, branched, and interconnected
  • The connective tissue endomysium acts as both tendon and insertion
  • Intercalated discs anchor cardiac cells together and allow free passage of ions
  • Heart muscle behaves as a functional syncytium
microscopic anatomy of heart muscle32
Microscopic Anatomy of Heart Muscle
  • Heart is resistant to fatigue
    • Many mitochondria
  • Z discs, I band, A band,
  • Fewer and wider T tubules
  • Simpler sarcoplasmic reticulum
    • No triads
cardiac muscle contraction
Cardiac Muscle Contraction
  • Heart muscle:
    • Is stimulated by nerves and is self-excitable (automaticity)
    • Contracts as a unit or does not contract at all
    • Has a long absolute refractory period that prevents tetany
  • Cardiac muscle contraction is similar to skeletal muscle contraction
heart physiology intrinsic conduction system
Heart Physiology: Intrinsic Conduction System
  • Autorhythmic cells:
    • Initiate action potentials
    • Have unstable resting potentials called pacemaker potentials
    • Use calcium influx (rather than sodium) for rising phase of the action potential
the intrinsic conducting system
The intrinsic conducting system
  • Hyperpolarization leads to:
    • Loss of K
    • Opening of Na channels
  • Membrane becomes less and less negative
  • Threshold is reached
  • Ca channels opens
  • Influx of Ca causes the rising phase of the action potential
mechanisms of contraction
Mechanisms of contraction

1) Rapid depolarization

  • Threshold
  • Opening of the voltage-regulated Na channels
    • Fast channels
  • Massive influx of Na
mechanisms of contraction39
Mechanisms of contraction

2) Plateau

  • Transmembrane potential approaches +30mV
  • Na channels close and remain inactivated
  • Na is actively pumped out of the cell
  • Voltage-regulated Ca channels opens (slow channels)
  • Ca enters the cytoplasma
    • It stimulates more Ca release from the SR
mechanisms of contraction40
Mechanisms of contraction
  • This influx of Ca balances out the efflux of Na
  • Transmembrane potential is kept near 0mV
    • plateau
mechanisms of contraction41
Mechanisms of contraction

3) Repolarization

  • Slow Ca channels start to close
  • Ca is reabsorbed by the SR or pumped out of the cell
  • Slow K channels begin to open
    • Efflux of K causes the repolarization
heart physiology sequence of excitation
Heart Physiology: Sequence of Excitation
  • Sinoatrial (SA) node generates impulses about 75 times/minute
  • Atrioventricular (AV) node delays the impulse
    • It generates impulses about 40-60 times/min
    • Smaller diameter of the fibers
    • Fewer gap junctions
  • Impulse passes from atria to ventricles via the atrioventricular bundle (bundle of His)
    • Bundle of His is the only electrical connection between atria and ventricle
heart physiology sequence of excitation44
Heart Physiology: Sequence of Excitation
  • AV bundle splits into two pathways in the interventricular septum (bundle branches)
    • Bundle branches carry the impulse toward the apex of the heart
    • Purkinje fibers carry the impulse to the heart apex and ventricular walls
      • Depolarize spontaneously at the rate of 20-40 beats/min
      • They supply the papillary muscles
        • Contract before the rest of the ventricles
heart excitation related to ecg
Heart Excitation Related to ECG

SA node generates impulse;

atrial excitation begins

Impulse delayed

at AV node

Impulse passes to

heart apex; ventricular

excitation begins

Ventricular excitation

complete

SA node

AV node

Bundle

branches

Purkinje

fibers

extrinsic innervation of the heart
Extrinsic Innervation of the Heart
  • Heart is stimulated by the sympathetic cardioacceleratory center
  • Heart is inhibited by the parasympathetic cardioinhibitory center
electrocardiography
Electrocardiography
  • Electrical activity is recorded by electrocardiogram (ECG)
  • P wave corresponds to depolarization of SA node
  • QRS complex corresponds to ventricular depolarization
  • T wave corresponds to ventricular repolarization
  • Atrial repolarization record is masked by the larger QRS complex
electrocardiography50
Electrocardiography
  • PR interval
    • Atrial depolarization and contraction
  • QT interval
    • Ventricular depolarization, contraction and repolarization
  • PR segment
    • Atrial contraction
  • ST segment
    • Ventricular contraction
heart sounds
Heart Sounds
  • Heart sounds (lub-dup) are associated with closing of heart valves
    • First sound (S1)occurs as AV valves close and signifies beginning of systole
    • Second sound (S2) occurs as SL valves close at the beginning of ventricular diastole
cardiac cycle
Cardiac Cycle
  • Cardiac cycle refers to all events associated with blood flow through the heart
    • Systole – contraction of heart muscle
    • Diastole – relaxation of heart muscle
phases of the cardiac cycle
Phases of the Cardiac Cycle
  • Ventricular filling – mid-to-late diastole
    • Heart blood pressure is low as blood enters atria and flows into ventricles
    • AV valves are open, then atrial systole occurs
phases of the cardiac cycle56
Phases of the Cardiac Cycle
  • Ventricular systole
    • Atria relax
    • Rising ventricular pressure results in closing of AV valves
    • Isovolumetric contraction phase
    • Ventricular ejection phase opens semilunar valves
phases of the cardiac cycle57
Phases of the Cardiac Cycle
  • Isovolumetric relaxation – early diastole
    • Ventricles relax
    • Backflow of blood in aorta and pulmonary trunk closes semilunar valves
  • Dicrotic notch – brief rise in aortic pressure caused by backflow of blood. This backflow causes the valve to close and creates a slight pressure rebound
cardiodynamics
Cardiodynamics
  • End-diastolic volume (EDV)
    • Maximum amount of blood held in the ventricles during diastole
  • End-systolic volume (ESV)
    • Amount of blood that remains in the ventricles after the contraction and closing of the semilunar valves
cardiodynamics60
Cardiodynamics
    • Venous return- amount of blood returning to the heart or blood flow during filling time
  • Heart rate – number of heart beats in a minute
  • Filling time- duration of ventricular diastole
  • Stroke volume (SV) – amount of blood ejected from the ventricles with each beat
    • SV = EDV – ESV
cardiodynamics61
Cardiodynamics
  • Cardiac output (CO) – the amount of blood pumped by each ventricle in one minute
cardiac output example
Cardiac Output: Example
  • CO (ml/min) = HR (75 beats/min) x SV (70 ml/beat)
  • CO = 5250 ml/min (5.25 L/min)
  • Cardiac reserve is the difference between resting and maximal CO
factors affecting stroke volume edv esv
Factors Affecting stroke volume(EDV-ESV)
  • EDV (end diastolic volume) is affected by:
    • Venous return
    • High venous return= high EDV
    • Exercise → ↑Venous return → ↑EDV→ ↑SV
    • ↓Blood volume →↓Venous return→↓EDV→↓SV
factors affecting stroke volume edv esv64
Factors Affecting stroke volume(EDV-ESV)
  • Filling time
  • Depends on the heart rate
  • ↑ HR → ↓Filling time→ ↓EDV→ ↓SV
factors affecting stroke volume edv esv65
Factors Affecting stroke volume(EDV-ESV)
    • Preload
    • Stretchiness of the ventricles during diastole
    • Directly proportional to the EDV
  • Frank-Starling principle (“more in = more out”) or increased EDV=increased SV
factors affecting stroke volume edv esv66
Factors Affecting stroke volume(EDV-ESV)
  • ESV (end systolic volume) is affected by:
    • Contractility
    • Force produced during a contraction
    • Positive inotropic (increases contractility)
      • Increased sympathetic stimuli
      • Certain hormones, some drugs
      • ↑Contractility → ↓ESV→ ↑SV
factors affecting stroke volume edv esv67
Factors Affecting stroke volume(EDV-ESV)
  • Negative inotropic (decreases contractility)
    • Increased extracellular K+
    • Calcium channel blockers
    • ↓Contractility → ↑ESV→ ↓SV
heart contractility and norepinephrine
Heart Contractilityand Norepinephrine

Extracellular fluid

Norepinephrine

b1-Adrenergic

receptor

Ca2+

Adenylate cyclase

Ca2+

channel

  • Sympathetic stimulation releases norepinephrine and initiates a cyclic AMP second-messenger system

Cytoplasm

GTP

1

GDP

GTP

ATP

cAMP

Active

protein

kinase A

Inactive

protein

kinase A

Ca2+

3

Ca2+

uptake

pump

2

Enhanced

actin-myosin

interaction

binds

Troponin

to

Ca2+

SR Ca2+

channel

Cardiac muscle

force and

velocity

Sarcoplasmic

reticulum (SR)

factors affecting stroke volume edv esv69
Factors Affecting stroke volume(EDV-ESV)
  • Afterload
  • The pressure that must be overcome for the ventricles to eject blood (back pressure exerted by blood in the large arteries leaving the heart)
  • Increased by factors that restricts arterial blood flow
  • ↑Afterload→↑ESV →↓SV
regulation of heart rate autonomic nervous system
Regulation of Heart Rate: Autonomic Nervous System
  • Sympathetic nervous system (SNS) stimulation is activated by stress, anxiety, excitement, or exercise
  • Parasympathetic nervous system (PNS) stimulation is mediated by acetylcholine and opposes the SNS
  • PNS dominates the autonomic stimulation, slowing heart rate and causing vagal tone
atrial bainbridge reflex
Atrial (Bainbridge) Reflex
  • Atrial reflex (Bainbridge Reflex) – a sympathetic reflex initiated by increased blood in the atria
    • ↑Venous return→ Stimulates baroreceptors in the atria→ ↑Sympathetic stimulation→ ↑Stimulation of SA node→ ↑HR
chemical regulation of heart rate
Chemical Regulation of Heart Rate
  • The hormones epinephrine and thyroxine increase heart rate
  • Intra- and extracellular ion concentrations must be maintained for normal heart function
    • Hypocalcemia depresses the heart and hipercalcemia stimulates the heart
    • Hyperkalemia cause heart block and hypokalemia causes arrhythmias
other factors influencing heart rate
Other factors influencing heart rate
  • Age
  • Exercise
  • Body temperature
  • Tachycardia
  • Bradycardia
figure 20 23 factors affecting stroke volume
Figure 20-23 Factors Affecting Stroke Volume

Factors Affecting Stroke Volume (SV)

Filling time (FT)

Venous return (VR)

Increased by

sympathetic

stimulation

Decreased by

parasympathetic

stimulation

Increased by E, NE,

glucagon,

thyroid hormones

FT = EDV

VR = EDV

FT = EDV

VR = EDV

Contractility (Cont)

of muscle cells

Decreased by

vasodilation

Increased by

vasoconstriction

Cont = ESV

Preload

Cont = ESV

Afterload (AL)

End-diastolic

volume (EDV)

End-systolic

volume (ESV)

AL = ESV

AL = ESV

STROKE VOLUME (SV)

ESV = SV

EDV = SV

ESV = SV

EDV = SV

congestive heart failure chf
Congestive Heart Failure (CHF)
  • Congestive heart failure (CHF) is caused by:
    • Coronary atherosclerosis
    • Persistent high blood pressure
    • Multiple myocardial infarcts
    • Dilated cardiomyopathy (DCM)
developmental aspects of the heart79
Developmental Aspects of the Heart
  • Fetal heart structures that bypass pulmonary circulation
    • Foramen ovale connects the two atria
    • Ductus arteriosus connects pulmonary trunk and the aorta
age related changes affecting the heart
Age-Related Changes Affecting the Heart
  • Sclerosis and thickening of valve flaps
  • Decline in cardiac reserve
  • Fibrosis of cardiac muscle
  • Atherosclerosis