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Anatomy 2 Chap 18

Terms in this set (37)

Heart Anatomy
Approximately size of fist
• Location:
- In mediastinum between second rib and fifth
intercostal space
- On superior surface of diaphragm
- Two-thirds of heart to left of midsternal line
- Anterior to vertebral column, posterior to sternum
- Apex points down and to the left at 45º.
Pericardium
The heart is surrounded by a double-walled sac called
the...
• protects
• anchors to surrounding structures
• prevents overfilling
Pulmonary Circuit
Right side circuit
pumps to oxygen-poor
lungs to get rid of CO2 and to pick up O2,
Systemic Circuit
Left side circuit
pumps oxygenated blood out
to the bodily tissues and transport CO2 to the lungs
Interatrial Septum
separates atria
Interventricular Septum
separates ventricles
Atria
Small, thin-walled
• Contribute little to propulsion of blood
• Three veins empty into right atrium:
- Superior vena cava
- Inferior vena cava
- Coronary sinus
• Four pulmonary veins empty into left atrium
Ventricles
Thicker walls than atria
• Actual pumps of heart
• Right ventricle
- Pumps blood into pulmonary trunk
• Left ventricle
- Pumps blood into aorta (largest artery in body)
Pulmonary Circuit
- Right atrium à tricuspid valve à right ventricle
- Right ventricle à pulmonary semilunar valve à
pulmonary trunk à pulmonary arteries à lungs
- Lungs à pulmonary veins à left atrium
Systemic Circuit
-Left atrium à mitral valve à left ventricle
- Left ventricle à aortic semilunar valve à aorta
- Aorta à systemic circulation à Right atrium
Atrioventricular Valves (AV Valves)
- Prevent backflow into atria when ventricles contract
- Tricuspid valve (right AV valve)
- Mitral valve (left AV valve, bicuspid valve)
- Chordae tendineae anchor cusps to papillary
muscles
• Hold valve flaps in closed position
Semilunar Valves
Prevent backflow into ventricles when ventricles relax
- Open and close in response to pressure changes
- Aortic semilunar valve
- Pulmonary semilunar valve
Incompetent Valve
• Blood backflows so heart repumps same blood
over and over
Valvular Stenosis
• Stiff flaps - constrict opening à heart must exert
more force to pump blood
The sequence of excitation
- Sinoatrial node à
- Atrioventricular node à
- Atrioventricular bundle à
- Right and left bundle branches à
- Subendocardial conducting network (Purkinje
fibers)
EKG waves
- P wave - depolarization SA node à atria
- QRS complex - ventricular depolarization and atrial
repolarization
- T wave - ventricular repolarization
Arrhythmias
- irregular heart rhythms
fibrillation
rapid, irregular contractions; useless for
pumping blood à circulation ceases à brain death
Cardiac Cycle
- Blood flow through heart during one complete
heartbeat: atrial systole and diastole followed by
ventricular systole and diastole
- Systole—contraction
- Diastole—relaxation
- Series of pressure and blood volume changes
- The mechanical events always follow the electrical
events.
Ventricular Filling
— mid-to-late diastole
- AV valves are open; pressure low
- 80% of blood passively flows into ventricles
- Atrial contraction occurs, delivering remaining 20%
- Ventricles are now full of blood
Ventricular systole, atria in diastole
Atria relax; ventricles begin to contract
- Rising ventricular pressure à closing of AV valves
- In ejection phase, ventricular pressure exceeds
pressure in large arteries, forcing SL valves open and
emptying the ventricles
Isovolumetric relaxation: early diastole
The ventricles relax.
- Blood in the aorta and pulmonary trunk flows back
towards the heart, which causes the semilunar valves
to close.
cardiac output
Volume of blood pumped by each ventricle in one minute
Cardiac output
CO=HR x SV
-Heart Rate (HR) = number of beats per minute
- Stroke Volume (SV) = volume of blood pumped out by one ventricle with each beat
LUB


DUB
- First as AV valves close; beginning of systole

=Second as SL valves close; beginning of ventricular diastole
Heart Murmurs
abnormal heart sounds; usually
indicate incompetent or stenotic valves
Preload,
Contractility
Afterload
The three main factors that affect Stroke Volume
Preload
-degree of stretch of cardiac muscle cells before
they contract
Cardiac muscle exhibits a length-tension relationship
- At rest, cardiac muscle cells shorter than optimal
length
- Most important factor stretching cardiac muscle is
venous return - amount of blood returning to heart
Contractility
—contractile strength at given muscle length.
• Increased by
- Sympathetic stimulation à increased Ca2+ influx à
more cross bridges
- Positive inotropic agents (Thyroxine, glucagon,
epinephrine, digitalis, high extracellular Ca2+)
• Decreased by negative inotropic agents
Afterload
- pressure ventricles must overcome to eject
blood
• Hypertension increases afterload, resulting in increased
ESV and reduced SV
Regulation of Heart Rate
-Positive chronotropic factors increase heart rate
• Negative chronotropic factors decrease heart rate
• Positive inotropic factors increase heart contraction
strength
• Negative inotropic factors decrease heart contraction
strength
Tachycardia
abnormally fast heart rate
(>100 beats/min)
- If persistent, may lead to fibrillation
Bradycardia
heart rate slower than 60 beats/
min
- May result in grossly inadequate blood circulation in
non-athletes
Congestive Heart failure
Progressive condition; CO is so low that blood
circulation inadequate to meet tissue needs
- Reflects weakened myocardium caused by
• Coronary atherosclerosis—clogged arteries
• Persistent high blood pressure
Pulmonary congestion
Left side fails à blood backs up in lungs
Peripheral congestion
Right side fails à blood pools in body organs à
edema
Autonomic Nervous system regulation
Sympathetic nervous system activated by emotional or physical stressors

Parasympathetic nervous system opposes sympathetic effects

• Heart at rest exhibits vagal tone
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