The Systemic and Pulmonary Circuits
Pulmonary circulation moves blood between the heart and the lungs
Systemic circulation moves blood between the heart and the rest of the body
Heart valves
Ensure unidirectional blood flow through heart
Open and close in response to pressure changes
Two major types of valves:
- Atrioventricular valves located between atria and ventricles
- Semilunar valves located between ventricles and major arteries
Atrioventricular (AV) Valves
Two atrioventricular (AV) valves prevent backflow into atria when ventricles contract
Tricuspid valve (right AV valve): made up of three cusps and lies between right atria and ventricle
Mitral valve (left AV valve, bicuspid valve): made up of two cusps and lies between left atria and ventricle
Chordae tendineae: anchor cusps of AV valves to papillary muscles that function to:
- Hold valve flaps in closed position
- Prevent flaps from everting back into atria
The Function of the Atrioventricular (AV) Valves (opened)
AV valves open, atrial pressure greater than ventricular pressure
- ) blood returning to the heart fills atria, pressing against the AV valves. the increased pressure forces AV valves open
- ) as ventricles fill, AV valve flaps hang limply into ventricles
- ) atria contract, forcing additional blood into ventricles
The Function of the Atrioventricular (AV) Valves (closed)
AV valves closed, atrial pressure less than ventricular pressure
- ) ventricles contract, forcing blood against AV valve cusps
- ) AV valves close
- ) papillary muscles contract and chordae tendineae tighten, preventing valve flaps from everting into atria
Semilunar (SL) Valves
Two semilunar (SL) valves prevent backflow from major arteries back into ventricles
- Open and close in response to pressure changes
- Each valve consists of three cusps that roughly resemble a half moon
Pulmonary semilunar valve: located between right ventricle and pulmonary trunk
Aortic semilunar valve: located between left ventricle and aorta
The Function of the Semilunar (SL) Valves (opened)
as ventricles contract and intraventricular pressure rises, blood is pushed up against semilunar valves, forcing them to open
The Function of the Semilunar (SL) Valves (closed)
as ventricles contract and intraventricular pressure falls, blood flows back from arteries, filling the cusps of semilunar valves and forcing them to close
Heart Sounds
Two sounds (lub-dup) associated with closing of heart valves
- First sound is closing of AV valves at beginning of ventricular systole
- Second sound is closing of SL valves at beginning of ventricular diastole
- Pause between lub-dups indicates heart relaxation
Areas of the thoracic surface where the sounds of individual valves are heard most clearly…
Aortic valve sounds
heard in 2nd intercostal
space at right sternal
margin
Pulmonary valve
sounds heard in 2nd
intercostal space at left
sternal margin
Mitral valve sounds heard over heart apex (in 5th intercostal space) in line with middle of clavicle
Tricuspid valve sounds
typically heard in right
sternal margin of 5th
intercostal space
Heart murmurs
abnormal heart sounds heard when blood hits obstructions
Incompetent valve
- Blood backflows so heart repumps same blood over and over
- Causes swishing sound as blood regurgitates backward
Valvular stenosis
- Stiff flaps that constrict opening, restricting blood flow
- Heart needs to exert more force to pump blood
- Causes high-pitched sound or clicking as blood is forced through narrow valve
Defective valve can be replaced with mechanical, animal, or cadaver valve
Pathway of Blood Through Heart: Right side of the heart
Superior vena cava (SVC), inferior vena cava (IVC), and coronary sinus → Right atrium → Tricuspid valve → Right ventricle → Pulmonary semilunar valve → Pulmonary trunk → Pulmonary arteries → Lungs
Pathway of Blood Through Heart: Left side of the heart
Four pulmonary veins → Left atrium → Mitral valve → Left ventricle → Aortic semilunar valve → Aorta → Systemic circulation
The Pulmonary and Systemic Circuits: Heart is a transport system consisting of two side-by-side pumps…
Right side receives oxygen-poor blood from tissues
- Pumps blood to lungs to get rid of CO2, pick up O2, via pulmonary circuit
Left side receives oxygenated blood from lungs
- Pumps blood to body tissues via systemic circuit
Receiving chambers of heart
Right atrium: Receives blood returning from systemic circuit
Left atrium: Receives blood returning from pulmonary circuit
Pumping chambers of heart
Right ventricle: Pumps blood through pulmonary circuit
Left ventricle: Pumps blood through systemic circuit
The Heart is a Double Pump, Each Side Supplying…
its Own Circuit
Pathway of Blood Through Heart…
- Equal volumes of blood are pumped to pulmonary and systemic circuits
- Pulmonary circuit is short, low-pressure circulation
- Systemic circuit is long, high-friction circulation
Anatomy of ventricles reflects differences
- Left ventricle walls are 3× thicker than right
- Pumps with greater pressure
Anatomical Differences Between the Right and Left Ventricles
Right ventricle: thinner wall than left ventricle, crescent shape, wraps around left ventricle
Left ventricle: thicker wall than right ventricle, round shape
Coronary circulation
- Functional blood supply to heart muscle itself
- Shortest circulation in body
- Delivered when heart is relaxed
- Left ventricle receives most of coronary blood supply
Coronary arteries
- Both left and right coronary arteries arise from base of aorta and supply arterial blood to heart
- Branching of coronary arteries varies among individuals
- Arteries contain many anastomoses (junctions)
- Provide additional routes for blood delivery
- Cannot compensate for coronary artery occlusion
- Heart receives 1/20th of body’s blood supply
Angina pectoris (chest/thoracic pain)
Thoracic pain caused by fleeting deficiency in blood delivery to myocardium
Myocardium is weakened
Myocardial infarction (heart attack)
Prolonged coronary blockage
Areas of cell death are repaired with noncontractile scar tissue (fibrosis)
Damage to left ventricle most dangerous.
Microscopic Anatomy: Cardiac Muscle Fibers
Cardiac muscle cells: striated, short, branched, fat, interconnected
- One central nucleus (at most, 2 nuclei)
- Contain numerous large mitochondria (25–35% of cell volume) that afford resistance to fatigue
