USMLE Step 1 Physiology Review 56 15 Blood pH, Local blood pressure reg, starling forces

USMLE Step 1 Physiology Review 56 15 Blood pH, Local blood pressure reg, starling forces

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Play USMLE Audio MP3 56 15 Blood pH, Local blood pressure reg, starling forces Below

Begin 56 15 Blood pH, Local blood pressure reg, starling forces Transcription

Okay now for some questions on blood pH. What is the Henderson Hasselbalch equation? (Please pause the tape)

  • pH equals pK plus the log of the base concentration over the acid concentration.

How is the equation normally used with blood? (Please pause the tape)

  • pH equals pK plus the log of the bicarbonate concentration over the CO2

What is the normal pH for arterial blood?

  • 7.4

And for venous blood?

  • 7.37

Student doctor please pause the tape and summarize the information discussed on blood pH.

  • Henderson Hasselbalch equation is pH equals pK plus the log of the base concentration over the acid concentration. The equation is normally used with blood as follows; pH equals pK plus the log of the bicarbonate concentration over the CO2. The normal pH for arterial blood is 7.4 and for venous blood is 7.37.

Okay, now for some questions on local blood pressure regulation? What four organs regulate their own blood flow resistance to some level?

  • The lungs, the kidneys, the brain and the heart.

Which one is unique in that hypoxia triggers vasoconstriction to increase resistance?

  • The lungs

Elsewhere in the body hypoxia usually triggers what?

  • Vasodilation

Which organ acts internally to maintain arterial pressure within a very narrow constant range?

  • The kidneys

Which organs will change blood flow up or down to meet metabolic needs?

  • The brain and heart.

Student doctor please pause the tape and summarize the information discussed on local blood pressure regulation.

  • The lungs, the kidneys, the brain and the heart regulate their own blood flow resistance to some level. The lungs are unique in that hypoxia triggers vasoconstriction to increase resistance. Elsewhere in the body, hypoxia usually triggers vasodilation. The kidneys act internally to maintain arterial pressure within a very narrow constant range. The brain and heart will change blood flow up or down to meet metabolic needs.

Now for some questions about the Starling forces. For capillaries, net filtration pressure equal Pnet which equals what?  (Please pause the tape)

  • The total hydraulic pressure minus the total osmotic pressure, that difference multiplied by the filtration constant called kf.

How is the total hydraulic pressure determined? (Please pause the tape)

  • The hydraulic pressure in the capillaries minus the hydraulic pressure in the interstitial fluid outside the capillaries

How is the total osmotic pressure determined?

  • The plasma osmotic pressure minus the interstitial osmotic pressure.

If we use the absolute values, that is ignored minus signs what are we really talking about here with these two pressures? (Please pause the tape)

  • The hydraulic pressure is simply the difference between the capillary and the interstitial hydraulic pressures, and the osmotic pressure in the capillaries is simply the difference between the plasma osmotic pressure and the interstitial osmotic pressure

Why do we subtract the pressure in the interstitial fluid from the capillary pressure?

  • Because it is smaller

And why do we subtract the interstitial osmotic pressure from the capillary osmotic pressure?

  • Because it is smaller. In both cases we get a positive number.

And then we are going to subtract the total osmotic pressure from the total capillary pressure to receive the difference of the actual net pressure in the capillary. Now the total osmotic pressure in the capillaries is greater than the total hydraulic pressure in the capillaries, what would happen to our net filtration pressure?

  • It would be negative

In which way, will water flow across the endothelium of the capillaries?

  • It would flow into the capillaries

Student doctor please pause the tape and summarize the information on Starling forces.

  • For capillaries, net filtration pressure equal Pnet which equals the total hydraulic pressure minus the total osmotic pressure, that difference multiplied by the filtration constant called kf. The total hydraulic pressure is determined by the hydraulic pressure in the capillaries minus the hydraulic pressure in the interstitial fluid outside the capillaries. The total osmotic pressure is the plasma osmotic pressure minus the interstitial osmotic pressure. If we use the absolute values, that is ignored minus signs what are we really talking about here with these two pressures is the hydraulic pressure is simply the difference between the capillary and the interstitial hydraulic pressures, and the osmotic pressure in the capillaries is simply the difference between the plasma osmotic pressure and the interstitial osmotic pressure. We subtract the pressure in the interstitial fluid from the capillary pressure because it is smaller. We subtract the interstitial osmotic pressure from the capillary osmotic pressure because it is smaller. In both cases we get a positive number. And then we are going to subtract the total osmotic pressure from the total capillary pressure to receive the difference of the actual net pressure in the capillary. Now the total osmotic pressure in the capillaries is greater than the total hydraulic pressure in the capillaries, our net filtration pressure would be negative. Water flow across the endothelium of the capillaries and into the capillaries

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