PT15 LEC: Structure, Function, and Valves of the Heart

functional properties of cardiac muscles

(1) It must contract with a regular rhythm.
(2) it must function in sleep & wakefulness, without fail or need of conscious attention
(3) it must be highly resistant to fatigue
(4) the cardiac muscle cells of a given heart chamber must contract in unison so that the chamber can effectively expel blood
(5) each contraction must last long enough to expel blood from the chamber

structural differences of cardiac vs. skeletal

- intercalated discs
- gap junctions
- mechanical junctions

intercalated discs

separates indiv cardiac muscle cells

interdigitating folds

folded plasma membrane at the end of the cell; folds of adjoining cells interlock with each other & increase the surface area of intercellular contac

mechanical junctions: fascia adherens

- most extensive
- broad band in which actin is anchored to the plasma membrane & each cell is linked to the next via transmembrane proteins

mechanical junction: desmosomes

- interrupts fascia adherens
- patches of mechanical linkage that anchors adjacent cells & prevents the contracting myocardium from pulling apart

gap junctions

- enable cardiac muscle cell to electrically stimulate neighboring cells
- AP spreads cell to cell letting heart contract as a single unit

location of the heart

- thorax (between lungs)
- enclosed within mediastinum
- superior surface of diaphragm, anterior to VC, & posterior to sternum

mediastinum

medial cavity of the thorax

apex of the heart pointed towards

left hip

base of the heart pointed towards

right shoulder

Pericardium

a thin, slippery, double walled serous membrane enclosing the heart isolating it from other thoracic organs and allows room to expand, resisting excessive expansion

Parietal pericardium

outside layer

Fibrous pericardium layer

superficial, loose, tough, dense connective tissue layer

Visceral pericardium

next to heart forming the epicardium outer layer of the heart

Pericardial cavity

a potential space between the parietal & visceral pericardium

Pericardial fluid

serous fluid filling the space between the layers of pericardium

Pericarditis

inflammation of the pericardium

epicardium

- outside layer
- contains blood vessels

myocardium

- thickest, middle layer made up of mostly cardiac muscle
- contractile portion of the heart

Fibrous skeleton of the heart

a framework of dense network of collagenous & elastic connective tissue fibers

functions of fibrous skeleton

- structural support
- anchors cardiomyocytes
- electrical insulation btwn atria & ventricles

endocardium

- inner layer
- lines heart chambers

Interatrial septum

separates the atria

Interventricular septum

separates the ventricles

Atrioventricular groove (coronary sulcus)

encircles the heart near the base, surrounding the junction of the atria & ventricles like a crown, separating each other

Anterior interventricular sulcus

cradles the anterior interventricular artery, marks the anterior position of the septum separating the right & left ventricles

Posterior interventricular sulcus

continuation of the anterior interventricular sulcus

atria

- receiving chambers
- small, thin walled chambers

Auricles

small, wrinkled, protruding ear-like flaps or appendages in the atrial wall which increases atrial volume

Pectinate muscles

internal, ridged-like muscle bundles in the posterior wall of the R-atrium & the auricles

Crista terminalis

C-shaped ridge separates two (2) atrial regions

Fossa ovalis

shallow depression in the interatrial septum which marks the opening of foramen ovale (exists during fetal life)

Foramen ovale

a shunt/opening located in the interatrial septum during fetal life; connects right & left atrium

placenta

means of picking up oxygenated blood during fetal life since lungs are nonfunctional

Right Atrium

receives deoxygenated blood from the different parts of the body (upper & lower part) via three (3) veins

Superior vena cava

returns blood from body regions superior to the diaphragm

Inferior vena cava

returns blood from body areas below the diaphragm

Coronary sinus

collects blood draining from heart/myocardium

Left Atrium

Four (4) pulmonary veins enter the left atrium & transport blood from the lungs to the heart

Ventricles

- discharging chambers
- actual pumps of the heart

Trabeculae carnae

- internal muscular ridges on the posterior wall of both ventricles
- serve to keep the ventricular walls from clinging to each other like suction cups when the heart contracts, allowing the ventricular chambers to expand more easily when blood starts to refill the ventricles

Right ventricle

pumps blood into the pulmonary trunk to lungs for gas exchange; anterior surface

Left ventricle

ejects blood into the aorta (largest artery in the circulation); posteroinferior surface

pathway of blood flow thru heart (summary)

- deox blood returns to right side of heart thru superior & inferior vena cavae and coronary sinus into right atrium
- pass thru tricuspid valve into right ventricle
- pumped thru pulmonic SL valve into pulmonary trunk & 2 pulmonary arteries
- spread to pulmonary circulation; picks up O2 and eliminates CO2
- ox blood returns to left side of heart thru 4 pulmonary veins into the left atrium
- pass thru mitral valve into left ventricle
- pumped thru aortic SL valve into aorta
- spread to all body tissues via systemic circulation; delivers O2 and picks up CO2

Pulmonary circuit (gas exchange)

right side of the heart

Systemic circuit

left side of the heart

pulmonary circuit pump

moves blood between the heart and the lungs

systemic circuit pump

moves blood between the heart and rest of the body

functional differences of pulmonary & systemic circuit

- pulmonary is short, low pressure circulation
- systemic is a long pathway & encounters resistance to blood flow
- LV walls are 3x thicker w/ circular cavity and thus generate more pressure
- RV cavity is flat, crescent-shape that partially encloses the LV

coronary circulation

- functional blood supply of the heart
- distributing oxygenated & draining deoxygenated from the heart
- shortest ciruclation

coronary artery

- right & left coronary arteries encircles the heart in the AV groove; sits in coronary sulcus
- provide intermittent, pulsating blood flow to the myocardium

venous drainage

cardiac veins to coronary sinus to right atrium

cardiac veins

collects the venous blood which passes the capillary beds in the myocardium

coronary sinus

union of cardiac veins & empties blood into RA

ineffective delivery of blood occurs when ventricles contract due to:

- coronary arteries compression by myocardium, obstructing blood flow
- aortic SL valve flaps blocking entrances to CA
- backflow of blood during ventricular diastole

arterial blood supply

- variable
- efficient blood delivery when heart is relaxed & not contracting

Angina pectoris

a crushing chest pain felt when the myocardium is deprived of oxygen

infarct

formed when oxygen-deprived heart cells die

Ischemia

deficiency of blood flow to the tissues/cells (cardiac muscle/myocardium)

Myocardial Infarction (MI) aka HEART ATTACK

results from sudden death of a patch/portion/area of myocardium from prolonged, long-term obstruction of the coronary circulation leading to complete/total deprivation of oxygen in the myocardium

cardiac arrest

- refers to absence of heart rate due to loss of pump contraction & loss of pacemakers (electrical impulses)
- heart attack LEADS TO cardiac arrest

Atheroma

fatty deposit on the inner walls of the coronary arteries

Fibrillation

a rapid, uncoordinated quivering of the ventricles (looks like a bag of wiggling worms); heart contracting asynchronously

functions of heart valves

- keep compartments separate
- prevent backflow
- open in response to BP changes

atrioventricular (AV) valves

- between atria & ventricles
- prevent backflow of blood into atria

tricuspid valve

right AV valve; btwn RA and RV

mitral valve / bicuspid valve

left AV valve; btwn LA and LV

semilunar (SL) valves

- between ventricle & artery
- prevent backflow of blood intro ventricles

pulmonary/pulmonic SL valve

between RV & the pulmonary trunk (pulmonary arteries)

aortic SL valve

- between LV & aorta

chordae tendinae

- heart strings / tendinous cords
- ensures AV valves remain completely closed during ventricular contraction
- govern timing of electrical excitation of papillary muscles

operation of AV valves

- open when blood passively fills heart chambers during relaxation
- close when ventricles contract; atrial pressure < ventricular pressure

operation of SL valves

- open when ventricles contract
- close when ventricles relax; intraventricular pressure falls

mechanism of incompetent heart valves

valve does not close properly -> blood backflows -> forces the heart to pump & re-pump the same blood -> increase workload of the heart -> heart weakens -> heart failure

mechanism of valvular stenosis

stiff valve cusps due to repeated bacterial infection of the endocardium -> forces the heart to contract more vigorously than normal to create enough pressure to drive blood through the narrowed valve -> increase workload of the heart -> heart weakens -> heart failure

synthetic valve replacement

- cryopreserved human valve
- chemically treated valve from a pig's heart