Download The Cardiovascular System

The Cardiovascular System: The Heart
PART 1
Cardiology: study of the heart
 Located in the mediastinum of the chest
 Size ~ closed fist
 Mass: 250 g in females, 300 g in males
Chambers of the Heart
4 chambers: 2 atria + 2 ventricles
o Right Atrium - receives blood from body (both vena cavas +
coronary sinus)
o Right Ventricle – pumps blood to lungs via pulmonary arteries
o Left Atrium – receives blood from lungs via pulmonary veins
o Left Ventricle – pumps blood to body via Aorta
Interatrial septum – separates right & left atria
Interventricular septum – separates right & left ventricles
Pericardium: sac that contains the heart
 2 layers: parietal (outer) & visceral (inner)
 Cavity in between layers contains fluid to decrease
friction
Layers of the Heart Wall
o Epicardium – lines outside of heart
o Myocardium – middle layer of muscle
o Endocardium – lines inside of atria & ventricles
Heart Valves
- Separate chambers and/or vessels
- controls direction of blood flow
1. Atrioventricular (AV) valves – separate atria from ventricles:
o Right AV valve = tricuspid valve
o Left AV valves = bicuspid (mitral) valve
Chordae tendineae – tendon-like cords that connect AV valves to
papillary muscle
2. Semilunar valves –separate ventricles from vessels
o Pulmonary semilunar valve – R. ventricle and pulmonary
trunk
o Aortic semilunar valve – L. ventricle and ascending aorta
 Valves open and close in response to pressure:
- Atria fill with blood = ↑ pressure on AV valves
- atria contract, AV valves open
- blood flows into ventricles
-ventricles fill with blood = ↑ pressure on semilunar valves
- ventricles contract, semilunar valves open -blood flows into vessels
Coronary Circulation: Blood Supply for the Heart
 Coronary Arteries
o surround heart like a crown
o branch off the ascending aorta
o supplies heart cells with O2 and nutrients
 Coronary Sinus – returns blood to the R. atrium
Fetal Circulation
 Blood does not need to go to lungs in fetus
 O2 supplied by mom
 2 shunts:
1. foramen ovale shunts blood from r. atrium to l. atrium
closes to form fossa ovalis
2. ductus arteriosus shunts blood from pulm. trunk to
aortic arch
closes to form ligamentum arteriosum
 both shunts should close by birth or w/in 1st year
 surgery required if shunts do not close
PART 2
Cardiac Conduction System
 Cardiac muscle is autorhythmic – generates its own action
potentials for muscle contraction
 Allows atria to contract together and then ventricles to contract
together
1. Excitation begins in the Sinoatrial (SA) node (commonly called the
pacemaker) within R. atrium
2. Action potential spreads to L. atrium allowing atria to contract at
same time
3. A.P. spreads to Atrioventricular (AV) node located between R. &
L. atria
 A.P. slows at AV node for two reasons:
 AV node has smaller fibers
 Longer time allows atria to fully empty and ventricles to fill
4. A.P. spreads to Atrioventricular (AV) bundle then to the R. & L.
bundle branches within the interventricular septum
5. The Purkinje fibers then propagate the A.P. to the ventricles,
causing them to contract 0.2 seconds after the atria contract
Electrocardiogram (EKG or ECG)
 Records electrical signals associated with heart beat
 Multiple electrodes are attached to the outside of the body
 Can diagnose abnormal conduction, enlarged heart, or other damage
to heart
Parts of the EKG:
 P wave – measures atrial contraction; SA node activity
 P-Q interval – impulse delay at AV node
 QRS complex – ventricular contraction; Purkinje fiber activity
 T wave – restoring potential of ventricles to prepare for another
contraction
Stress test
- EKG during strenuous exercise
- Compares resting heart to stressed heart
Arrhythmia
– abnormal beating of the heart
– due to malfunction of conduction system
– tachycardia: beats too fast
– bradycardia: beats too slow
Cardiac Cycle
 All events associated with one heart beat
 Systole = contraction
 Diastole = relaxation
 Atrial systole = ventricular diastole
1. atria contract/ventricles relax
2. av valves are open/ sl valves are closed
3. ventricles filling with blood
 Atrial diastole = ventricular systole
1. atria relax/ventricles contract
2. av valves are closed/sl valves are open
3. atria filling with blood
PART 3
Heart sounds
-caused by turbulence of blood when heart valves close
 LUBB – AV valves close after ventricular systole begins
 DUPP – Semilunar valves close beginning of ventricular diastole
Heart murmur
- Abnormal heart sound
- Gurgling noise before, between, or after lubb-dupp
Most murmurs indicate valve disorder:
 Mitral stenosis – narrowing of the mitral valve
 Mitral valve prolapse – inherited
- valve is pushed back into atria
- occurs in 10-15% of population (65% of these are female)
Heart Disorders
1. Poor coronary circulation
- cause of most heart disorders
o Ischemia – lack of blood flow d/t constriction or obstruction of a
vessel
o hypoxia, ↓ O2 to ♥ muscle
 caused by ischemia
 weakens and kills heart cells
2. Angina – chest pain, often due to ischemia
3. Myocardial infarction
– aka: heart attack – death of heart tissue
- leaves non-contractile scar tissue
- heart unable to pump
4. Sudden Cardiac Death – conduction system stops; heart stops
beating
5. Congenital defects – structural defects present at birth
Nervous System Control
 Autonomic nervous system – involuntary; heart rate controlled by
two branches of ANS:
1. Sympathetic NS – increases heart rate and force of
contractions d/t release of norepinephrine
2. Parasympathetic NS– decreases heart rate due to
the release of acetylcholine
***Both work together to maintain homeostasis