pressures and movement of fluids between capillaries and interstitial fluid. – Flashcards

-the movement of substances between blood and interstitial fluid. -The mission of the entire cardiovascular system is to keep blood flowing through capillaries to allow capillary exchange.

diffusion, transcytosis, and bulk flow.

-the most important method. -important for solute exchange between blood and interstitial fluid -Many substances, (such as oxygen, carbon dioxide, glucose, amino acids, and hormones,) enter and leave capillaries by simple diffusion. -Because O2 and nutrients normally are present in higher concentrations in blood, they diffuse down their concentration gradients into interstitial fluid and then into body cells. -other wastes released by body cells are present in higher concentrations in interstitial fluid, so they diffuse into blood.

intercellular clefts or fenestrations. Lipid‐soluble materials, such as , , and steroid hormones, may pass across capillary walls directly through the lipid bilayer of endothelial cell plasma membranes. Most plasma proteins and red blood cells cannot pass through capillary walls of continuous and fenestrated capillaries because they are too large to fit through the intercellular clefts and fenestrations.

directly through the lipid bilayer of endothelial cell plasma membranes.

they are too large to fit through the intercellular clefts and fenestrations.

-so large that they allow even proteins and blood cells to pass through their walls.

-The endothelial cells of most brain capillaries are sealed together by tight junctions. -the blood-brain barrier.

-A small quantity of material crosses capillary walls by transcytosis. -substances in blood plasma become enclosed within tiny pinocytic vesicles that first enter endothelial cells by endocytosis, then move across the cell and exit on the other side by exocytosis. -transport of mainly large, lipid‐insoluble molecules that cannot cross capillary walls in any other way.

-is a passive process. -more important for regulation of the relative volumes of blood and interstitial fluid. -large numbers of ions, molecules, or particles in a fluid move together in the same direction. -The substances move at rates far greater than diffusion. -occurs from an area of higher pressure to an area of lower pressure, and it continues as long as a pressure difference exists. Diffusion is more important for solute exchange between blood and interstitial fluid, but bulk flow is more important for regulation of the relative volumes of blood and interstitial fluid. Pressure‐driven movement of fluid and solutes from blood capillaries into interstitial fluid is called filtration. Pressure‐driven movement from interstitial fluid into blood capillaries is called reabsorption.

Pressure‐driven movement of fluid and solutes from blood capillaries into interstitial fluid

Pressure‐driven movement from interstitial fluid into blood capillaries

1. blood hydrostatic pressure (BHP), the pressure generated by the pumping action of the heart. 2. interstitial fluid osmotic pressure. The main pressure promoting reabsorption of fluid is blood colloid osmotic pressure.

-The balance of these pressures. -determines whether the volumes of blood and interstitial fluid remain steady or change.

-the near equilibrium regarding the volume of fluid and solutes reabsorbed normally is almost as large as the volume filtered.

-is about 35 millimeters of mercury (mmHg) at the arterial end of a capillary, and about 16 mmHg at the capillary's venous end.

BHP "pushes" fluid out of capillaries into interstitial fluid.

-The opposing pressure of the interstitial fluid. -close to zero. - IFHP equals 0 mmHg all along the capillaries.

"pushes" fluid from interstitial spaces back into capillaries.

Blood hydrostatic pressure pushes fluid out of capillaries (filtration), and blood colloid osmotic pressure pulls fluid into capillaries (reabsorption).

-a force caused by the colloidal suspension of these large proteins in plasma that averages 26 mmHg in most capillaries. -"pulls" fluid from interstitial spaces into capillaries.

-Opposes BCOP. -"pulls" fluid out of capillaries into interstitial fluid. -Normally, IFOP is very small—0.1-5 mmHg—because only tiny amounts of protein are present in interstitial fluid. -The small amount of protein that leaks from blood plasma into interstitial fluid does not accumulate there because it passes into lymph in lymphatic capillaries and is eventually returned to the blood.

fluid will move from capillaries into interstitial spaces (filtration).

fluid will move from interstitial spaces into capillaries (reabsorption).

1. increased capillary blood pressure -causes more fluid to be filtered from capillaries. 2. increased permeability of capillaries: raises interstitial fluid osmotic pressure by allowing some plasma proteins to escape. this leakiness may be caused by the destructive effects of chemical, bacterial, thermal, or mechanical agents on capillary walls.

decreased concentration of plasma proteins: lowers the blood colloid osmotic pressure. inadequate synthesis or dietary intake or loss of plasma proteins is associated with liver disease, burns, malnutrition.