Physiology: Cardiology

Systemic circulation = Circulation to and from the body

Pulmonary circulation = Circulation to and from the lungs

Atrioventricular valves:

• Tricuspid (Right side)
• Mitral (Left side) 

Semilunar Valves:

• Pulmonary Valve
• Aortic Valve

Arteries = Away from heart

Veins = To the heart 

Chordae Tendinae are attached to the walls of the heart into the valves, which keeps the valves in check, preventing it from dis-functioning.  

Three layeres of heart:

1. Endocardium
2. Myocardium
3. Epicardium

-There is also the pericardium, which secretes percardial fluid that provides lubrication to prevent friction between pericardial layers. 

Bronchial arteries carry oxygen to the lungs in the systemic circulation.

Coronary arteries carry oxygen to the heart in the systemic circulation.

Heart sound/Phases: 

• Lub, or S1 (AV valves shutting, and Semilunar valves opening)
• Dub, or S2 (Semilunar valves shutting, and AV valves opening)
• Systole = Between S1 and S2
• Systole can simply be defined as ventricular contraction.
• First stage of systole - Isovolumetric contraction (Contraction while all valves are closed)
• Second stage of systole - Blood being sent through the pulmonary arteries + aorta. 
• Diastole = Between S2 and S1
• Comes from the word dilation. 
• First phase when the blood flows back from the semilunar valves into the ventricles. Accounts for some of the ventricular filling (All valves are closed during this) 
• Second stage of diastole is when the AV valves open to allow atria to contract and fill the ventricles with blood. This accounts for most of the ventricular filling.
• Thus, systole and diastole can be viewed as centered around the ventricle, where systole means ventricular contraction, and diastole, is ventricular relaxation, or dilation. 

RBC's don't use oxygen and don't have mitochondria. All they do is carry oxygen. Hemoglobin sits inside RBC's. 

Generally: Arteries = High pressure + Low volume, & Veins = Low pressure, High volume

Cardiac muscle structure acts as a functional synctium (a meshwork of muscle cells interconnected by contiguous cytoplasmic bridges) in which cells function as a unit. 

     -Includes desmosomes and gap junctions

Conduction System:

SA node --> AV node --> AV bundle --> Bundle of His --> purkinje fibers.

Coronary Circulation:

Both the left and right coronary artery branch off the aorta, hence, the very backflow of blood during the closure of the aortic valve fills the coronary arteries. 

After going through cardiac veins, blood enters the coronary sinus to drain into the right atrium. 

     -Several veins drain directly into the right atrium. 

• Myocardial ischemia - Inadequate delivery of oxygenated blood to heart tissue
• Necrosis - Death of tissue
• Acute myocardial infarction (Heart attack) - When blood vessels are blocked. 

Coronary artery disease (CAD) - Where pathological changes lead to diminishment of blood flow through the vessels, can cause myocardial ischemia and lead to heart attacks. 

Peripheral artery disease (PAD) - The diminishment of blood flow through vessels in the periphery, due to mainly blockage or narrowing of the vessels. 

Narrowing or blockage of coronary vessels can lead to angina, or chest pain when you heart doesn't get enough oxygen rich blood. 

• Aneurysm - Local enlargement of the artery walls due to the weakening of the artery wall. 
• Atherosclerosis - Thickening and toughening of arterial walls
• Type of Arteriosclerosis

Conduction System:

*Pacemaker of the heart = SA Node

Contractile cells - Do mechanical work of pumping, and don't initiate own AP's (Most cardiac cells)

Autorhythmic cells - Specialized for initiating APs

SA node located in the right atrial wall. 

AV node located at base of right atrium. 

Bundle of His originate at AV node and enter interventricular septum

     -Divides and forms right and left branches. 

Purkinje fibers extend from bundle of His and spread throughout ventricular myocardium.

AP of Autorhythmic cells: 

The "funny channels" permit inward Na+ current and closure of K+ channels, which reaches threshold at around -40. 

AP of Contractile Myocardial cells: 

EKG:

Waves: P, QRS, T

Segments: PR, ST

Intervals: wave-segment combos: PR, QT

40 ms required for depolarization to spread from SA to AV node. 

An extra 50 ms are required to fully depolarize both atria. 

Depolarization is delayed in the AV node and arrives at bundle branches 120 ms after it reaches the AV node. 

     -This delay allows for atria to fully depolarize and contract before ventricular depolarization begins, as indicated by the PR segment of the ECG. 

Action potentials per minute: SA > AV > Bundle of his 

U wave can follow the T wave, indicating the last remnants of ventricular repolarization. 

The ECG is the recording of the overall spread of activity throughout the heart during depolarization and repolarization. 

Tachycardia = Rate > 100

Bradicardia = Rate < 60

Because long refractory period occurs in conjunction with prolonged plateau phase, summation and tatanus of cardiac muscle is impossible. 

Arrhythmia Examples: 

• Atrial flutter - associated with tachycardia
• Atrial fibrillation - abnormal heart rhythm which becomes longer over time
• Ventricular fibrillation - uncoordinated contraction of the ventricles of the heart
• Heart block - fault of the pacemaker system due to a construction in the electrical conduction system. 

Antiarrhythmic drugs: