Exam 1 Review:  Chapter 19:  Capillary Exchange

capillary exchange - The movement of respiratory gases (oxygen and carbon dioxide) and nutrient and waste molecules between the plasma and the interstitial fluid by a variety of active and passive means; O2 and nutrients tend to move to the interstitial fluid while CO2 and wastes tend to move to the plasma.

diffusion - The movement of molecules or ions from a region of higher concentration to a region of lower concentration until equilibrium is reached; it is a passive transport process.

vesicular transport - The method of transport by which soluble proteins are packaged in membrane bound droplets which bud off from one compartment and fuse with the membrane of an other; this transport sees the flow of protein out from the ER via the Golgi to the outside of the cell by a process known as exocytosis, or to lysosomes, or inwards from the cell membrane by enodocytosis to endosomes and fusion with lysosomes; in addition to simple transport of these molecules, it  presents the opportunity for modification of the proteins; it also provides opportunity for the recycling of membrane lipids.

bulk flow - The movement of a fluid from a region of higher pressure to one of lower pressure, e.g., filtration in the kidney nephron and absorption in the interstitial spaces of the tissues; it is a passive process.

Starling's law of the capillaries - The observations and mathematical relationships which explain how fluid and dissolved solutes either leave the capillaries ("filtration") for the tissue spaces or the reverse, leave the interstitial space for the plasma; these movements depend on a set of four forces:  blood hydrostatic pressure (BHP), interstitial fluid hydrostatic pressure (IFHP), blood colloid osmotic pressure (BCOP), and interstitial fluid osmotic pressure (IFOP); see the details under "net filtration pressure" below.

blood hydrostatic pressure (BHP) - The hydrostatic force which is the mechanical pressure exerted on the fluid of plasma by the pumping of the heart during systole and by the elastic recoil and smooth muscle contraction in the walls of the arteries between heart beats during diastole, which tends to push water from the capillaries into the nterstitial fluid; this pressure is a component variable of Starling's Law of the Capillaries.

interstitial fluid hydrostatic pressure (IFHP) - The hydrostatic force which is the mechanical pressure exerted on the interstitial fluid by the the elastic recoil of the tissues in any region of the body, which tends to push water from the interstitial fluid back into the capillaries; this pressure is a component variable of Starling's Law of the Capillaries.

blood colloid osmotic pressure (BCOP) - The osmotic force (water concentration gradient) which is the result of differences in water concentration between plasma and interstitial fluid, which tends to pull water from the interstitial fluid and back into the plasma in the capillaries; this pressure is a component variable of Starling's Law of the Capillaries.

interstitial fluid osmotic pressure (IFOP) - The osmotic force (water concentration gradient) which is the result of differences in water concentration between plasma and interstitial fluid, which tends to pull water from the plasma in the capillaries into the interstitial fluid; this pressure is a component variable of Starling's Law of the Capillaries.


net filtration pressure - The dynamic equilibrium force which may be measured at any point along the capillaries from the arterial to the venous end; on the arterial side because the blood hydrostatic pressure (BHP) dominates, fluid moves from the capillary lumen into the tissue space; on the venous side because the blood colloidal osmotic pressure (BCOP) dominates, fluid moves from the tissue space back into the capillary lumen;

The net filtration pressure at any point is the sum of these four forces:

NFP = (BHP + IFOP) - (BCOP + IFHP)

        = Pushing forces - Pulling forces

This pressure is a component variable of Starling's Law of the Capillaries.

The BCOP and the IFOP are the same at both ends of the capillary; however, the BHP differs at the arterial and venous ends of the capillary (about 35 mmHg at arterial end, and 16 mmHg at venous end).



oncotic pressure - The osmotic pressure created by colloids (mainly plasma proteins) which are normally retained within the vascular system; oncotic pressure nearly offsets the hydrostatic pressure which acts to drive fluid out of vessels into the extravascular space; the result is that small amounts of fluid cross the vascular barrier, which are then transported back to the blood via the lymphatics; a decrease in oncotic pressure can be a cause of non-inflammatory edema.

edema - Any excessive accumulation of serous fluid or interstitial fluid (lymph) in tissue spaces or a body cavity; significant edema will produce obvious swelling of the involved tissues; it may be llocalized, due to venous or lymphatic obstruction or to increased vascular permeability (e.g., in inflammation), or it may be systemic due to heart failure or renal disease.

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