General Interview Questions - Cardiovascular  and Respiratory systems

Describe the flow of blood through the body (of a human).

Where does blood come from?  What is the source of the oxgyen and carbon dioxide in the blood?
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1. The heart is a muscular pump whose periodic contraction (beat) causes blood to flow through the circulatory system .
2. Within the circulatory system, blood carries oxygen O2 and carbon dioxide CO2 (the respiratory gases), nutrients, waste products, and hormones to and from every cell in the body .
3. The respiratory gases are exchanged (uptake of oxygen, release of carbon dioxide) within the lungs .
4. Vertebrates have a closed circulatory system, consisting of a heart, arteries, capillaries and veins .
5. The amount of blood leaving the heart each minute (cardiac output) is the product of the heart rate (number of beats/minute) and the amount of blood pumped with each beat (ml/beat) .
6. The pressure in the aorta (just outside the heart) is determined by the product of the cardiac output and the total peripheral resistance .
7. Peripheral resistance is a function of arterial diameter which can be controlled by smooth muscle cells that surround these vessels; their state of contraction is controlled by the autonomic nervous system .
8. The pressure at any point in the circulatory loop is determined by the volume of blood that is contained there and the compliance at that point .
9. The pressure gradient across an organ or tissue and the resistance to flow (a function of vessel diameter) determines the flow/minute through the organ or tissue (the perfusion rate)
10. The cardiovascular system is homeostatic.  It acts to hold constant the pressure in the aorta (mean arterial pressure) by controlling the function of the heart (heart beat rate, contraction strength) and the circulatory resistance .  
11. The resistance to blood flow in an organ or tissue is determined by the local metabolic activity and blood vessel diameter;  signals from the autonomic nervous system regulate blood vessel diameter . 
12. Most animals are aerobic.  To survive they require molecular oxygen (O2), which they use as an electron acceptor (producing water) during respiration.  O2 is obtained from the atmosphere.  Its presence in the atmosphere is due to its release as a waste product during photosynthesis .
13. Aerobic organisms produce carbon dioxide as a waste product, it must be disposed of into the atmosphere .   

13. O2 is captured from the atmosphere in the lungs and carried to the tissues (where it is used by the cells).  Carbon dioxide (produced in the cells) is carried from the tissues to the lungs, where it is released, by the circulatory system .   
14. Air, which consists of ~20% O2 and little (~0.035%) carbon dioxide, is brought into the lungs by the contraction of the inspiratory muscles (define?).  This leads to a sub-atmospheric pressure in the lungs.  Air flows in through the respiratory tree driven by the resulting pressure gradient .   

15. Air leaves the lungs (containing much less O2 and significantly higher levels carbon dioxide) when the inspiratory muscles relax; elastic recoil of the lungs creates a pressure greater than atmospheric and the resulting pressure gradient drives flow .   

16. O2 diffuses from the air in the lungs into the blood, carbon dioxide diffuses from the blood into the air in the lungs, both gases move down their respective partial pressure gradients .   

17. The partial pressure of O2 in the lungs is directly determined by alveolar ventilation and inversely determined by the rate of O2 consumption.  The partial pressure of carbon dioxide in the lungs is inversely determined by alveolar ventilation .   

18. O2 is transported in the blood bound to the protein hemoglobin, which is present within red blood cells.  Carbon dioxide is transported predominately as bicarbonate ions    

19. The respiratory system is homeostatic.  It regulates the partial pressure of O2 and carbon dioxide in arterial blood .   

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