It's a layer of the pericardium.

Fits loosely around the heart

attached to diaphragm

The pericardial cavity.

It's filled with percardial fluid, and allows the heart to work in a relatively friction free environment.

They provide stability, and prevent prolapse. 

Prolapse is when the valve gets pushed back into the atrium.

1%

Autorythmic Cardiac Myocytes

• smaller muscle fibers
• 1 nucleus
• smaller SR reflecting that cardiac muscle depends on extracellular Ca2+ to initiate contraciton
• Mitochondria occupy 30% of cell volume

• They allow for ionic exchange to conduct electricity between adjacent cells. They are like a electrical synapses.
• Allows waves of depolarization to spread rapidly from cell to cell so that cardiac muscle cells contract almost simultaneously

• They physically connect one cell to another. 
• Uses adjacent cells to anchor onto during contraction.
• allows force generated in one cell to be transferred to the adjacent cell.

• An AP propogates from an adjacent cell, and stimulates voltage cated Calcium Channels.
• Ca2+ from the ECF flows down its concetration gradient, into the cell. 
• The Ca2+ from the ECF binds to receptors on the Sarcoplasmic Reticulum, causing stored Ca2+ to be released further. (Calicium induced calcium release)
• Ca2+ diffuses through the cyotosol and binds to troponin, which exposes actin to myosin.
• Crossbridge cycling takes place resulting in contraction

• Ca2+ unbinds from Troponin, which blocks the crossbridge. 
• Ca2+ - ATPase in the SR membrane pumps Ca2+ out of the cyoplasm and back into the Sarcoplasmic Reticulum.
• Na+, Ca2+ - exchanger in the sarcolemma actively transports Ca2+ out of the sarcoplasm and into the ECF as Na+ diffuses into the cyotoplasm.
• Removal of Ca2+ from the cytoplasm results in relaxation

• The Concentration of Ca2+ in the cytosol. 
• The more Ca2+, the more crossbridges made between actin and myosin, the harder the force of contraction
• Length of the Fiber before contraction
• stretching a fiber before contraction, results in greater force of contraction due to recoil forces

1. rapid depolarization due to opening of voltage gated Na+
2. Slight repolarization due to closing of voltage gated Na+ channels.
3. Plateau phase due to opening of voltage gated Ca2+ channels
1. influx of Ca2+ lengthens duration of AP and refractory period
4. Repolarization phase due to opening of voltage gated K+ channels and closing of voltage gated Ca2+ channels.
5. Resting phase due to voltage gated channels being closed

Waves of Depolarization 

The electrical signal for contraction begins as the (1) ___________ fires an action potential. The action potential propogates via gap junctions to the (2) _______________.  (3) What is the purpose?

1. Sinoatrial Node
2. Atrioventricular Node
3. slows down teh speed of the AP propogation to ensure that the atria contracts before the ventricles do.

Wave of Depolarization

As the AP propogates from the AV node, it travels throuh (1) ___________ located in the septum. This propogates the AP to the (2) ___________ which are at the apex of the ventricle. The AP spreads upward from the apex.

ECG Waves

Each wave of the follows the spread of the AP from the SA node to the ventricles. Each wave represents which mechanical event?

1. P wave?
2. QRS Complex?
3. T wave? 

1. depolarization of both atria
2. depolarization of both ventricles, as well as repolarization of both atria (hidden by large ventricular depolarization)
3. Repolarization of both ventricles.

Mechanical Events of the Cardiac Cycle

The Cardiac Cycle has 5 phases which are associated with blood pressure, and blood volume changes that occur within the v enticles during ventricular diastole and systole. What are they?

1. Passive Ventricular Filling
2. Atiral Systole
3. Isovolumetric Contraction
4. Ventricular Ejection
5. Isovolumetric Relaxation

1. What is Passive Ventricular Filling?
2. How much ventricular filling does this account for?

1. When both atria and ventricles are in diastole, blood from the great veins passes through the atria, and dumps right into the ventricles 
2. 85%

What is End Diastolic Volume? (EDV)

1. What is Isovolumetric Contraction?
2. When does it occur?

1. pressure in the ventricles is enough to close the AV valves, but not enough to open the Semilunar Valves because it must rise to overcome arterial pressure. Volume in the ventricle does not change during this phase.
2. It occurs as atrial systole comes to an end.

1. What is Isovolumetric Relaxation?
2. When does it occur?

1. Ventricular pressure becomes less than pulmonary trunk/aorta, which causes back flow of blood into the ventricle. This closes the Semilunar valves. As this happens, the AV valve remains closed and the ventricle is again a closed chamber. As pressure continues to fall, AV vavles open and passive ventricular filling begins
2. It occurs when ventricular contraction comes to an end.

1. What is Cardiac Output? (CO)
2. What is the forumla for CO?

1. The Volume of blood pumped by a single ventricle in one minute. Measure of cardiac performance.
2. HR x SV = CO 

1. A hormone that binds to beta andrenergic receptors of SA nodal cells resulting in an increase in AP frequencty (increase in HR). Also opens additional Ca2+ channels and increases intracellular [Ca2+] which increaes Stroke Volume.
2. It's controlled by the cardioacceleratory center (sympathetic nervous system)

What is Preload on the ventricles?

The amount of pressurei n the ventricles at the end of ventricular filling. It stretches the ventricle out. The more it's stretched, the harder it will contract.

It aids ejection of blood out of the ventricles. 

An increase in Parasympathetic Output to the heart will _________ Stroke Volume

• It maintains a constant driving pressure for blood flow during ventricular diastole.          
• Pressure reservoirs

 NOT CHANGE

Systemic Arteries

pressure produced by the contraction of the left ventricle is stored in the elastic walls of the arteries, and is gradually released through recoil. What purpose does this serve?

maintains a driving pressure of blood flow during ventricular diastole

 pressure reservoir of the circulatory system

Systemic Arterioles

• What are their function?
•  What are they referred to as? 
• How is their diameter regulated?

• creates a high resistance for arterial flow, and directs distribution of blood flow to individual tissues by constricting and relaxing.
• site of variable resistance
• diameter regulated by CO2, autonomic nervous and endocrine system

Veins are highly compliant, and act as what? 

Precapillary sphincters

Leukocytes

Capillarys are too small in diameter

Cardiac Output

If CO is 5L/min, the blood flow thorugh all systemic capillaries is also 5L/min.

directly proportional

pressure gradient

Resistance. 

What Determines Resistance in the Vessels?

For fluid flowing through a tube, resistance influenced by 3 parameters. What are they?

The Radius - as radius increases, resistance decreases

The Length - as length increases, resistance increases

The Viscosity - as viscosity increaes, resistance increases

A balance between blood flow into the arteries and blood flow out of the arteries

   - If flow in exceeds flow out, blood collects in the arteries and arterial pressure increases and vice versa if flow out exceeds flow in.