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Unit: Circulatory System
Regulation of Blood Flow Activity
IMAGINE that it is a beautiful clear and sunny day outside – a perfect day to go to the beach.
Steve has been tanning in the sun all day. When he finally decides to go home, he stands up
quickly and faints.
Fortunately, there is a doctor nearby. Once Steve has been revived, the doctor pulls out her
handy-dandy sphygmomanometer and gets a reading of 80/50.
Q1. What does a sphygmomanometer measure? In what units?
Q2. What does the value of 90 indicate? What does the value of 60 indicate?
90 =
pressure which is the pressure in Steve’s
50 =
pressure which is the pressure in Steve’s
Q3. Does this reading indicate low blood pressure or high blood pressure? What is
another name for it?
The doctor proclaims that Steve is suffering from a bad case of dehydration.
Q4. What has happened to the volume of blood in Steve’s body? Why?
Q5. Would Steve’s blood be thinner or thicker?
Q6. In the absence of water, what do cells tend to do?
Q7. What measures how much vessel walls are stretching as an indicator of pressure?
Before Steve even tries to drink more water, his body is trying to regulate his blood pressure.
Q8. Is Steve’s body trying to increase his blood pressure or decrease his blood pressure?
Q9. Which of the two autonomic nervous systems has to ‘kick in’?
Q9a. What happens (what’s the process) when this system is activated?
Q10. Does it cause Steve’s heart rate to increase or decrease?
Q11. Is the heart pumping more or less blood every minute?
Q11a. What is this called?
Q12. Do Steve’s blood vessels constrict or dilate?
It turns out that Steve is not able to regulate his blood pressure without help, as his blood
volume is too low. As a result, some of his capillaries start to close to try and increase the blood
pressure in major vessels. But his vessels still do not stretch as much as they should; and so his
_____________________ continues to increase.
Q13. What causes some of Steve’s capillaries to close?
Q14. What does Steve have to start doing to increase his blood pressure?
Q15. Now that Steve is taking action, what starts happening to his tissues?
Q16. Because of this, what is happening to the exchange of fluid at the capillary level?
The above is one of Steve’s many capillary beds. His precapillary sphincters have now opened
and are allowing blood to flow through.
Q17. Label the diagram above.
Q18. Now that Steve’s blood pressure is getting back to normal, in the diagram below,
indicate for each stage (filtration, no net movement, and reabsorption) what the
pressure inside the capillary, outside the capillary (in the tissues), and also what the net
pressures of fluid exchange are.
Steve is still in the sun. It is 40 degrees!
Q19. In addition to having to drink more water, Steve’s body has to do what?
Q19a. In the flow chart below, show the body’s process of cooling down.
Blood vessels
____________
Body
temperature
Brain
____________________
Very hot
outside
While the doctor is taking care of Steve (I bet you forgot about the doctor!), she decides give
Steve a full checkup.
She measures that Steve’s heart rate is 82 bpm (beats per minute) and calculates using his
weight that his cardiac output is 5.3 L/min.
Q20. If Cardiac Output = Stroke Volume x Heart rate, what is Steve’s stroke volume?
Please include units.
Next step: Make a flow chart or concept map that shows what happens when Steve’s
body is trying to increase his blood pressure and cool his body down.
Include: Cardiac output, stroke volume, heart rate, breathing rate, blood pressure,
vasoconstriction/vasodilation, O2 delivery, CO2 delivery, blood volume,
sweating/shivering, and any other components that are related.