Cardiovascular System: The Heart

Chapter 18

Heart Anatomy w/Review

• Size of a fist• In the mediastinum– Obliquely situated – ___?_____ to the diaphragm– ___?_____ to the vertebral column– ___?_____ to the sternum

• Lungs are ___?_____ and slightly obscure it

• Base is right and posterior, apex is point

Pericardium

• Serous membrane surrounding the heart• Protects, anchors, and prevents overfilling• Fibrous pericardium, collagen and elastic figure 8’s– Link all parts together while providing additional

support– Limits AP spread

• 2 layers– Parietal layer covers the _____?_____– Visceral layer (epicardium) covers the _____?___

• Pericardial cavity between w/ serous fluid

Heart Wall

• Epicardium (visceral pericardium)– Fatty layer

• Myocardium– Cardiac muscle

• Endocardium– Simple squamous epithelia– Continuous with blood vessels– Forms valves

www.faculty.ccri.edu

Chambers of the Heart

• 2 superior atria– Interatrial septum– Coronary sulcus

• 2 inferior ventricles – Interventricular septum– Anterior and posterior ventricular sulcus

• REMEMBER: directions for specimen/model NOT self

http://www.nku.edu/~dempseyd/HEART_1.htm

Atria of the Heart

http://www.google.com/imgres?imgurl=http://www.washingtonhra.com/resources/Heart%2Banatomy.png&imgrefurl=http://www.washingtonhra.com/2.html&usg=__6-rsXPk2HfBZ4NNeV1B4Gs7DIgI=&h=500&w=342&sz=454&hl=en&start=0&zoom=1&tbnid=hUO3hlsVbY8FXM:&tbnh=143&tbnw=98&prev=/images%3Fq%3Datrium%2Banatomy%26um%3D1%26hl%3Den%26sa%3DN%26biw%3D834%26bih%3D667%26tbs%3Disch:1&um=1&itbs=1&iact=rc&dur=414&ei=K4pxTIzAFsP38AaI2o2ACw&oei=K4pxTIzAFsP38AaI2o2ACw&esq=1&page=1&ndsp=12&ved=1t:429,r:0,s:0&tx=48&ty=73

• Receiving chambers• Auricles to increase volume• Pectinate muscles internal, anterior

walls– Fossa ovalis: remnant of fetal opening

• Right entry (O2 poor from systemic)– Superior and inferior venae cavae– Coronary sinus

• Left entry (O2 rich from pulmonary)– Right and left pulmonary veins

Ventricles of the Heart

http://www.google.com/imgres?imgurl=http://www.washingtonhra.com/resources/Heart%2Banatomy.png&imgrefurl=http://www.washingtonhra.com/2.html&usg=__6-rsXPk2HfBZ4NNeV1B4Gs7DIgI=&h=500&w=342&sz=454&hl=en&start=0&zoom=1&tbnid=hUO3hlsVbY8FXM:&tbnh=143&tbnw=98&prev=/images%3Fq%3Datrium%2Banatomy%26um%3D1%26hl%3Den%26sa%3DN%26biw%3D834%26bih%3D667%26tbs%3Disch:1&um=1&itbs=1&iact=rc&dur=414&ei=K4pxTIzAFsP38AaI2o2ACw&oei=K4pxTIzAFsP38AaI2o2ACw&esq=1&page=1&ndsp=12&ved=1t:429,r:0,s:0&tx=48&ty=73

• Discharge chambers• Trabeculae carneae, folds of

muscle• Papillary muscles• Right (anterior) exit– Pulmonary trunk• Right and left pulmonary arteries

• Left (posterior) exit– Aorta

Heart Valves

• Keep single directional blood flow• Open/close due to pressure not contraction• Atrioventricular valves (AV)– Right is tricuspid– Left is bicuspid or mitral– Anchored to papillary muscles by chordae tendineae ‘heart strings’

• Semilunar valves (SL)– Aortic– Pulmonary

Valve Function

• AV– Returning blood to atria exerts pressure = valves

open to ventricle– Ventricles contract = increase pressure = valves close– Chordae tendineae and papillary muscles prevent

inward flip• SL– Ventricles contract = increase pressure = valves open– Ventricles relax = blood flows back = close valves

Blood Flow Pathway Overview

Coronary Circulation• Arterial supply in coronary sulcus

– Right coronary splits• Marginal: lateral right myocardium• Posterior interventricular: heart apex and posterior ventricular walls (join for

right atria and ventricle)– Left coronary splits

• Circumflex: left atria and posterior wall of left ventricle• Anterior interventricular: interventricular septum and anterior ventricle walls

(join for right atria and ventricle)– Actually varies between individuals

• Venous supplies join in coronary sinus– Great cardiac in anterior interventricular sulcus– Middle cardiac in posterior interventricular sulcus– Small cardiac w/marginal artery

Cardiac Muscle Anatomy• Intercalated discs – Gap junctions: passage/exchange of ions– Desmosomes: stabilize and maintain structure

• Heart behaves as a single unit• Other characteristics (review)– Nuclei #?– Control?– Structure?

Cardiac Muscle Contraction

• Neural stimulation not needed = autorhythmicity– Can influence pace

• Whole organ (not just motor units) contracts– Signals carried through gap junctions

• Longer absolute refractory period – Regulates contraction rate– Prevents sustained contraction (tetanus)

• Lots of mitochondria– Greater dependence on O2

– Presence of fuel source more important than type

Autorhythmic Cells• Initiate action potentials in the heart• Due to pacemaker potential or unstable resting period

– Basic steps of an AP (review)– Changes

• Continuous depolarization to threshold (no flat line)• Ca 2+ channels open and Ca2+

rushes in• AP NOT triggered by Na+

• Found in specific locations– Sinoatrial and atrioventricular nodes– Right and left bundle branches– Ventricular walls (Pukinje fibers)

Beating to It’s Own Drum

• Sinoatrial (SA) node or ‘pacemaker’– Depolarization rate is fastest– Impulse ~75 times/min

• Atrioventricular (AV) node delays impulse

• Bundle of His electrically connects chambers

• Bundle branches to apex• Pukinje fibers to contractile fibers in

ventricles

Extrinsic Heart Control

• Cardiac centers in medulla• Cardioacceleratroy center– Sympathetic NS– Pre- from T1-T5 up– Post- through cardiac plexus to

SA and AV nodes & arteries• Cardioinhibitory center– Parasympathetic NS– Pre- from vagus to heart– Post- to SA and AV nodes

Electrocardiogram (ECG or EKG)• Records all electrical

autorhythmic cell activity• Distinguishable waves– P wave: SA node depolarizes

atria• Atria contracts• Drop from AV node delay

– QRS complex: ventricle depolarization• Ventricle contracts• Masks atrial repolarization

– T wave: ventricle repolarization

Heart Sounds

• ‘Lub’ when AV valves close– Ventricular systole (contraction)

begins– Bicuspid (mitral) before tricuspid

• ‘Dup’ when SL valves close– Ventricular diastole (relaxation)begins– Aortic before pulmonary

• Listen to 4 regions for differences

Cardiac Cycle

• Ventricular filling– Relaxed chambers creates low pressure allows passive blood flow in– Atria contract, ‘topping off’ ventricles = end diastolic volume (EDV)

• Ventricular systole (contraction)– Ventricles contract increasing pressure (isovolumetric contraction phase)– AV valves close and SL valves open

– End systolic volume (ESV) remains

• Early diastole– Ventricles relax decreasing pressure (isovolumetric relaxation phase)– SL valves close

Cardiac Output (CO)

• Amount of blood pumped by each ventricle– CO (ml/min) = HR (beats/min) x SV (ml/beat)• Stroke volume (SV) is amount of blood per ventricular

contraction

• Variable and increases with demand– Max CO – rest CO = cardiac reserve– Athletes have higher

Regulating Stroke Volume• SV = EDV – ESV

– EDV is amount of blood in ventricle during diastole– ESV is amount of blood in ventricle after systole

• Affecting factors– EDV by preload: degree of cardiac stretch pre-contraction in ventricles

• Slow HR increases volume of return• Exercise increases speed of return

– ESV by contractility: contractile force of cardiac cells• SNS innervation, Ca2+ entry, and hormones increase

– More blood leaves = decrease in ESV• Ca2+ blockers, increased extracellular K+ , and acidosis decrease

– ESV by afterload: pressure needed to eject blood• High BP more difficult to eject blood = increased ESV

Regulating Heart Rate

• ANS– SNS stimulates with stress, excitement, or exercise– PNS stimulates with ACh and opposes SNS

• Majority of autonomic stimuli; slows heart rate

• Chemical controls– Hormones: epinephrine, norepinephrine, and thyroxine

increase– Ions

• Other factors– Temperature– Age and exercise

Homeostatic Imbalances• Pericarditis: inflammation of pericardium roughens serous membrane• Cardiac tamponade: heart is compressed by fluid in pericardial cavity• Angina pectoris: deficient blood flow to myocardium• Myocardial infarction: prolonged coronary blockage; heart attack• Incompetent valves: valves fail to close allowing blood backflow• Stenosis: valves are stiff or obscure opening; heart must work harder• Ischemia: depriving tissue of oxygen• Arrhythmia: uncoordinated atrial/ventricular contractions• Fibrillation: rapid, out of phase contraction• Heart block: AV node damage; ventricles contract on own• Heart murmurs: blood swooshing; valves fail to close• Tachycardia: abnormally fast HR; stress, drugs, or temp cause• Bradycardia: abnormally slow HR; drugs, endurance training, or PNS