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Cardiovascular system anatomy and physiology
Lymphatic system anatomy and physiology
Abnormal heart sounds
Normal heart sounds
Changes in pressure-volume loops
Cardiac and vascular function curves
Altering cardiac and vascular function curves
Law of Laplace
Measuring cardiac output (Fick principle)
Stroke volume, ejection fraction, and cardiac output
Physiological changes during exercise
Cardiovascular changes during hemorrhage
Cardiovascular changes during postural change
Cardiac conduction velocity
Electrical conduction in the heart
ECG normal sinus rhythm
ECG QRS transition
ECG rate and rhythm
ECG cardiac infarction and ischemia
ECG cardiac hypertrophy and enlargement
Control of blood flow circulation
Microcirculation and Starling forces
Blood pressure, blood flow, and resistance
Compliance of blood vessels
Laminar flow and Reynolds number
Pressures in the cardiovascular system
Resistance to blood flow
Action potentials in myocytes
Action potentials in pacemaker cells
Cardiac excitation-contraction coupling
Excitability and refractory periods
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The main job of the heart is to pump blood all over the body, to our organs and tissues and keep them oxygenated.
It does so by contracting around 70 times per minute.
The physiological basis of cardiac contractility is the synchronous contraction of heart muscle cells, aka cardiomyocytes.
Cardiac contractility is a measure of the strength of cardiomyocytes, to contract.
In order for cardiomyocytes to contract, they first need to depolarize.
Depolarization is when ions move across the membrane of a cell, and the membrane potential becomes less negative or even slightly positive.
Think of a really pessimistic negative cell throwing his hands up and enjoying a moment of joy.
When one cell depolarizes enough - it can cause some ions like calcium to flow into neighboring cells and trigger them to depolarize as well.
If one cell after another depolarizes, then there’s a depolarization wave which you can imagine would look like a wave moving through a crowd at a football stadium.
Each depolarization wave causes a heart muscle contraction, so the rate at which depolarization waves ripple through the heart actually sets the heart rate.
This depolarization wave starts with the sinoatrial node, which sometimes gets called the SA node and then moves through the rest of the heart to cause a contraction.
So if depolarization waves are going through about once per second, that means that your heart beats once per second, or sixty times in a minute.
Now let’s zoom in on a cardiomyocyte.
These hard working cells have branches and intercalated disks along their edges which have small holes called gap junctions that allow ions to flow from one cardiomyocyte to the next.
When ions like calcium move from that cell into a neighboring cell, this triggers depolarization, and cardiomyocytes depolarize one after another.
Contractility is the ability of the heart muscle to contract and thereby pump blood. Cardiac contractility is determined by the interaction between intracellular calcium concentration, and the myofilament cross-bridge cycling. The Frank-Starling mechanism is a key factor in determining cardiac contractility. This mechanism states that the more stretched (tensed) a heart muscle fiber is, the more calcium it will release from its stores, leading to increased contraction force.
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