pressures and movement of fluids between capillaries and interstitial fluid.

Transcytosis

-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.

reabsorption

Pressure‐driven movement from interstitial fluid into blood capillaries

IFHP pushes fluid from __________________ back into______________________.

"pushes" fluid from interstitial spaces back into capillaries.

interstitial fluid osmotic pressure (IFOP)

-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.

net filtration pressure (NFP)

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

the capillaries of the brain

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

interstitial fluid hydrostatic pressure (IFHP),

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

Blood colloid osmotic pressure (BCOP)

-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.

Bulk flow

-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.

The blood hydrostatic pressure (BHP)

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

what are the intercellular clefts like in sinusoids?

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

Simple Diffusion

-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.

capillary exchange

-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.

Starling's law of the capillaries.

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

Two pressures promote filtration:

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.

two situations may cause excess filtration:

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.

BHP "pushes" fluid out of _______________ and into ________________.

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

key point

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

filtration

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

situation that causes inadequate reabsorbtion:

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.

Substances enter and leave capillaries by three basic mechanisms:

diffusion, transcytosis, and bulk flow.

Lipid‐soluble materials may pass across capillary walls by ___________________

directly through the lipid bilayer of endothelial cell plasma membranes.

Whether fluids leave or enter capillaries depends on the balance of pressures: If the pressures that push fluid out of capillaries exceed the pressures that pull fluid into capillaries, where will the fluid move?

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

Whether fluids leave or enter capillaries depends on the balance of pressures:If the pressures that push fluid out of interstitial spaces into capillaries exceed the pressures that pull fluid out of capillaries, where will the fluid move?

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

Water‐soluble substances such as glucose and amino acids pass across capillary walls through ______________

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.

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.