Cardio L6. Blood pressure

Question 1

How is blood pressure measured with a cuff?

Answer 1

-Cuff is inflated to > 120 mmHg
-Cuff pressure drops. As it passes the systolic pressure, the blood pressure is now higher than the cuff pressure and blood can force its way though the vessel.
This creates turbulent flow and the sound- this is systolic pressure
-When the pressure in the cuff drops to diastolic , there is no more pressure on the vessel so blood can flow through freely. This is the end of turbulence- second sound. Diastolic pressure.

Question 2

is blood pressure lower or higher in veins compared to arteries?

Answer 2

lower

Question 3

What are the 3 ways in which capillary exchange can happen?

Answer 3

Diffusion: solute exchange- down the conc. gradient
Transcytosis- vesicles of large, lipid-soluble molecules e.g. insulin
Bulk flow/filtration- the passive movement of fluid + substances faster than diffusion alone. The fluid flow carries solutes with it.

Question 4

What is the main purpose of BP?

Answer 4

set up hydrostatic gradient across capillary beds

Question 5

What is the blood hydrostatic pressure on arterial and venous end of the capillaries?

Answer 5

35 mmHg - arterial end
16 mmHg - venous end

Drop in pressure

Question 6

what are the key drivers of Bulk Flow/Filtration?

Answer 6

the difference in pressure on the ends of capillaries( hydrostatic pressure)
Blood Colloid Osmotic pressure ~26 mmHg( constant between arterial and venous ends of the capillary)

The positive pressure difference( between osmotic pressure and hydrostatic) on the arterial end drives fluid to move out of the capillaries

At the venous end of the capillaries, the pressure balance is -ve and favors fluid movement into the capillaries for reabsorption

There is also interstitial fluid osmotic and hydrostatic pressure outside the arteries.

Question 7

What is the net filtration pressure?

Answer 7

Question 8

How much fluid is reabsorbed back?

Answer 8

~85%

Question 9

What is the net filtration and reabsorption in Litres?

Answer 9

20 L filtration
17 L reabsorption

Question 10

Where does the extra 3 L of fluid go that is not reabsorbed?

Answer 10

Lymphatic system. Lymphatic vessels bring the fluid back to the circulation

Question 11

What is the only organ in the body that is devoid of lymph vessels?

Answer 11

brain

Question 12

What is edema?

Answer 12

Accumulation of fluid outside the blood vessels

Question 13

What can cause edema/fluid imbalance?

Answer 13

Hypertension- high pressure on the arterial side alters the gradient-> more fluid is filtrated.
Kidney disease- kidneys get leaky- excreting excess protein-> loss of protein from blood. This reduces BCOP

Heart failure - blood volume increases to increase SV. Venous blood hydrostatic pressure is increased. Veins are strethed-> pores in venous capillaries open, making the capillaries more pearmeable to larger solutes-> increases IFOP( interstitial fluid osmotic pressure)

Question 14

What is the relationship between velocity of blood flow and cross-sectional area of the blood vessels?

Answer 14

inversely proportional

Question 15

How is blood flow matched to supply and demand?

Answer 15

blood flow can be redirected to tissues that need blood more

Question 16

How does Hemodynamic regulation of flow works?

Answer 16

arterioles have a bed of smooth muscle( pre-capillary sphnictor)
Contracting these muscles can regulate blood flow