Het cardiovasulaire system - Phys Chptr 13: The cardiovasular system: Cardiac function

7 important questions on Het cardiovasulaire system - Phys Chptr 13: The cardiovasular system: Cardiac function

What does the blood consist of?

The most neumerous cells are erythrocytes (red blood cells), these cells contain hemoglobin a protein that carreis oxygen. The remainder of the cells are leukocytes (white blood cells). Also present are plaelets, which are cell fragments that are important for bloodclotting. The liquid part of the blood is plasma (water, proteins, electrolytes and other solutes).

What is a portal circulation?

When the blood flows though one capillary bed to another befor returning to the heart. For instance: the hypothalamus and the anterior pituitary, cell beds in the hypothalamus are in series with those in the anterior pituitary, connected together with portal veins. Another is between the liver and intestines.

What is the conduction system?

The pacemaker cells which initiate the potentials that are trasmitted by the conduction fibers. The cells that generate the contractile force are called contractile cells.
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Why are gap junctions and desmosomes important?

Gap junctions allow the current to spread faster through the cells. Gap junctions are concentrated in structures called intercalated disks. Desmosomes are important because they keep the cells linked together and they can therdore resist stretching due to the filling of the blood.

For what two reasons does the AV node not generate potentials by itsself?

The action potentials originating in the SA node travel through the AV node on their way to the ventricles, during this refractory period the cells cannot generate their own potential.

The second reason is that the SA node has a higher beat frequency, the SA node would always beat the AV node to the chase.

The AV can though step up as a back up if the SA node would miss a beat or if the pathway was blocked..

What if the AV or SA node does not work?

The AV can step up as a back up if the SA node would miss a beat or if the pathway was blocked.

If the AV node can't drive the ventricular contraction, the heart has another backup- certain cells in the Purkinje fibers (idioventricular pacemakers), eventhough they are slower.

With an ECG, what is the p wave, QRS complex and the T wave?

The P waves is an upward deflection that is due to artrial depolarization. The QRS complex is a series of sharp upward and downward deflections due to ventricular depolarization. The t wave is an upward defletion caused by ventricular contractile cell action potential.

The p-Q or P-R interval is an estimate of conduction through the AV node.

The Q-T intercal is the time the ventricles are contracting.

The T-Q segment is an estimate of the time the ventricles are relaxing

The R-R interval is the time between heartbeats.

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