Questions on the Amazing Heart

[sonnysingh]

hi, i am a novice in the field of physiology, with tons of questions about the heart. I hope that my questions will find answers and that others may benefit from them.

 

1.why do 4 chambers exist in the heart?

2.what contracts first? the left, right atria or both at the same time.

3.what is the main factor responsible for opening, closing the valves? Pressure or electrical activity?

4.when the action potential passes from sa node and travels throughout the heart where is the final destination of the action potential? does it "get used up" or does it dissipate?\

5.when the ventricles contract does this action make the pulmonary, aortic valves open? and how do the valves know when to close once the blood leaves?

6.when the pulmonary artery enters the lungs and branches off, and further branches are made, doesnt this reduce the radius and increase resistance in the vessels?

if so why does rt heart have a lower pressure when there are 300 million alveoli all being supplied by small branches of pulmonary artey ?

 

thank you all for your help and sorry of these questions are too simplistic..

[ewmon]

Sounds like homework.

[SMF]

Sonnysingh, quick answers:

 

1. Why is not a good question for biological devices. An intelligent engineer could design a heart with a single chamber that would be more efficient. It is just the result of the way this mechanism was developed naturally by the evolutionary process.

 

2. The right atrium contracts first and the activity spreads to the left.

 

3. Valves are passive and thus open and close from pressure and flow.

 

4. Action potentials do not dissipate; they are an all or none phenomenon. In the heart, action potentials spread in the muscle from cell to cell and where there are no further cells to spread to the activity stops. However, The spread of activity from the S-A node, across the right ventricle, eventually triggers cells in the A-V node by the spread of action potentials.

 

5. Same answer as number 3.

 

6. This is a fluid dynamics question that some physicist should answer. From a simpler perspective, consider that when you blow air through a single small straw it takes a lot of pressure to get a good volume of flow, but if you could get 20 straws in your mouth there would be hardly any resistance at all and the pressure for good air flow would be low. The capillary bed that makes up the inter-alveolar septa is very, very large and is also very delicate.

 

See this other post for a description and simple illustration of heart electrophysiology- http://www.scienceforums.net/topic/56489-overview-of-the-heart/page__view__findpost__p__601257

 

SM

 

 

[Joshua201]

Sounds like homework.

 

yea. read the forum rules