Capillary Exchange and Blood Flow

What is capillary exchange?

movement of substances between blood and interstitial fluid

What are the three methods of capillary exchange?

transcytosis, diffusion, bulk flow

What is transcytosis?

movement of large lipid insoluble molecules using vesicles

What is an example of a substance transported by transcytosis?

insulin

What is diffusion?

movement of solutes down their concentration gradients

What is bulk flow?

passive movement of diffusion and dissolved substances

What determines the direction of bulk flow?

difference between hydrostatic and osmotic pressure gradients

What is filtration?

movement of fluid out the capillary into the interstitial fluid

What is reabsorption?

movement of fluid into the capillary from the interstitial fluid

What is blood hydrostatic pressure (BHP)?

pressure that favors movement of fluid out of the capillary

What is blood hydrostatic pressure at the arterial end of a capillary?

35mmhg

What is blood hydrostatic pressure at the venous end?

16mmhg

What is blood colloid osmotic pressure (BCOP)?

osmotic pressure produced mainly by blood proteins that favors movement of fluid into the capillary

What is the approximate BCOP?

26mmhg

What are the approximate interstitial fluid pressures?

IFHP = 0 mmHg and IFOP = 1 mmHg

What is the net filtration pressure at the arterial end?

10mmhg, favoring filtration

What is the net filtration pressure at the venous end?

-9mmhg, favoring reabsorption

What is the overall pattern of bulk flow along a capillary?

arterial end filtration, venous end reabsorption

What is the role of lymphatic vessels in capillary exchange?

collect excess interstitial fluid that is not reabsorbed into the capillaries

What is edema?

excess accumulation of fluid in the interstitial tissues

How can hypertension cause edema?

Increased arterial blood hydrostatic pressure increases filtration from capillaries

How can heart failure cause edema?

Increased venous blood hydrostatic pressure promotes fluid movement into the tissues

How can kidney disease cause edema?

loss of blood proteins decreases bcop, reducing the osmotic force pulling fluid back into the capillaries

How can increased capillary permeability contribute to edema?

allows more fluid movement into interstitial fluid

What are the two main arrangements of circulatory vessels discussed?

series and parallel

What happens in a series arrangement?

blood flows through one vascular bed

What happens in a parallel arrangement?

different vascular beds receive blood from the arterial circulation

Why is a parallel arrangement useful?

allows blood flow to different organs to be independently regulated according to their needs

Where is blood velocity lowest?

capillaries

Why is blood velocity lowest in the capillaries?

capillaries have the largest total cross sectional area

How can the cardiovascular system increase blood supply to tissues?

increasing or redirecting cardiac output

How can cardiac output be increased?

increasing heart rate or stroke volume

How can existing cardiac output be redirected?

changing vascular resistance, including vasoconstriction

What is the relationship between pressure gradient and blood flow?

greater pressure gradient produces greater blood flow

What is the relationship between flow and radius?

flow = r 4

What are precapillary sphincters?

smooth muscle structures that regulate blood flow into capillary beds

What happens when precapillary sphincters are relaxed?

more blood flows through capillary bed, greater exchange

What happens when precapillary sphincters are contracted?

less blood flows through capillary bed