Notes on the Heart and Cardiovascular System

Heart Functions

• Generates blood pressure
• Routes blood
• Ensures one-way blood flow via valves
• Regulates blood supply via changes in contraction rate and force

The Cardiovascular System

• Closed System: Blood is contained within vessels and does not directly bathe tissues
• Circulations:
• Pulmonary Circulation: Blood flow between the heart and lungs
• Systemic Circulation: Blood flow between the heart and the rest of the body

Heart Location

• Double Pump:
• Pulmonary Pump: Pumps blood to the lungs
• Systemic Pump: Pumps blood to the body
• Roughly the size of a closed fist, located in the mediastinum

Pericardium

• Fibrous Pericardium: Outer fibrous layer
• Serous Pericardium: Inner epithelial layer
• Parietal Pericardium: Lines the fibrous pericardium
• Pericardial Cavity: Space between the layers containing fluid
• Visceral Pericardium (Epicardium): Closest layer to the heart

Heart Wall and Coronary Circulation

• Consists of three layers: epicardium, myocardium, and endocardium
• Coronary Circulation: Blood flow to heart muscle via coronary arteries

Heart Chambers

• 4 Chambers:
• 2 Atria: Upper chambers (Right atrium & Left atrium)
• 2 Ventricles: Lower chambers (Right ventricle & Left ventricle)
• Right side is dedicated to pulmonary circulation; Left side to systemic circulation
• Myocardial Thickness: Varies based on the workload of the chambers

Heart Valves

• Prevent backflow and ensure unidirectional blood flow

Heart Vessels

• Arteries: Carry blood away from the heart
• Veins: Carry blood toward the heart

Blood Flow Through The Heart

1. Right Atrium
2. Tricuspid Valve
3. Right Ventricle
4. Pulmonary Semilunar Valve
5. Pulmonary Trunk
6. Pulmonary Arteries
7. Lungs
8. Pulmonary Veins
9. Left Atrium
10. Bicuspid Valve
11. Left Ventricle
12. Aortic Semilunar Valve
13. Aorta
14. Body
15. Veins
16. Vena cavae/coronary sinus

Cardiac Skeleton

• Fibrous connective tissue providing structure and electrical insulation between atria and ventricles
• Supports heart valves

Cardiac Muscle Characteristics

• Striated Muscle: Features stripes in fiber structure
• Branched: Uninucleate fibers; typically amitotic
• Involuntary: Cannot be consciously controlled
• Intercalated Discs: Allow for electrical connectivity

Pacemaker and Conduction System

• Autorhythmicity: Heart stimulates itself to contract
• Systole: Contraction/depolarization phase
• Diastole: Relaxation/repolarization phase
• Pacemaker Node: The SA node usually initiates the heartbeat

Electrocardiogram (EKG or ECG)

• Records electrical activity during cardiac cycle
• P wave: Atrial contraction
• QRS Complex: Ventricular contraction (Atrial diastole masked)
• T-wave: Ventricular relaxation

Cardiac Cycle

• Definition: One complete heartbeat
• Pressure Changes: Open and close heart valves; blood flows from high to low pressure

1. Relaxation Period (T wave):
   • Ventricular pressure drops, AV valves open
   • Ventricles passively fill (~70%)
2. Atrial Systole (P wave):
   • Atria contract, filling ventricles with remaining ~30%
3. Ventricular Systole (QRS complex):
   • Contraction opens semilunar valves; blood is ejected
   • Right ventricle to pulmonary trunk; Left ventricle to aorta

Heart Sounds

• Auscultation: Listening to heart sounds via stethoscope
• “Lubb: Closing of the AV valves
• “Dupp: Closing of the semilunar valves
• Heart Murmur: Abnormal sounds due to defective valves

Cardiac Output

• Definition: Volume of blood pumped from each ventricle per minute
• Calc: CO = SV × HR
• Stroke Volume (SV): Volume pumped per beat (average 70 ml/beat)
• Heart Rate (HR): Beats per minute (average 72 bpm)
• Example CO calculation: 72 bpm × 70 ml/beat = 5040 ml/min (5L/min)

Heart Disorders

• Arrhythmia: Abnormal heartbeat
• Bradycardia: Heart rate <60 bpm
• Tachycardia: Heart rate >100 bpm
• Fibrillation: Rapid, uncoordinated contraction leading to ineffective blood pumping
• Congestive Heart Failure (CHF): Inability to pump blood, causing fatigue and fluid accumulation
• Heart Murmurs: Unusual sounds from valve defects
• Myocardial Infarction: Heart attack; death of myocardium due to coronary artery blockage
• Tetralogy of Fallot: A congenital heart defect that involves four structural abnormalities.