bio005 physio Lab 3.3 Blood pressure

Capillary exchange

• Substances cross capillary walls by:

  • Diffusion

  • Transcytosis

  • Bulk flow

Diffusion

Substances such as oxygen, carbon dioxide, glucose, amino acids, and some hormones cross capillary walls via simple diffusion

Transcytosis

Large, lipid-insoluble molecules (like insulin) cross capillary walls in vesicles via endocytosis and exocytosis

Bulk Flow

• Allows large numbers of ions, molecules, or particles in a fluid move together in the same direction

  • Bulk flow occurs from an area of higher pressure to an area of lower pressure resulting in filtration and reabsorption

  • Bulk flow is more important for regulation of the blood and interstitial fluid volumes

• Bulk flow is a passive process (no ATP needed)

Hydrostatic pressure vs. colloid osmotic pressure

• Hydrostatic pressure = pressure that a liquid puts on

  the container that holds it

• Colloid osmotic pressure = like a solution, but it’s larger proteins (like the ones in our plasma) that are involved instead of smaller molecules

Bulk Flow: Filtration

• Filtration is pressure-driven movement of fluid and solutes from blood capillaries into interstitial fluid

• Pressures that promote filtration:

  • Blood hydrostatic pressure (BHP)

  • Interstitial fluid osmotic pressure (IFOP)

Bulk Flow: Reabsorption

• Reabsorption is pressure-driven movement of fluid and

  solutes from interstitial fluid into blood capillaries

• Pressures that promote reabsorption:

  • Interstitial fluid hydrostatic pressure (IFHP)

  • Blood colloid osmotic pressure (BCOP)

Bulk Flow

Bulk Flow

Starling’s Law of Capillaries

• Under normal conditions, the volume of fluid and solutes

  reabsorbed is almost as large as the volume filtered

• NFP = (BHP + IFOP) − (BCOP + IFHP)

• Lymphatic capillaries reabsorb the remaining fluid and

  solutes.

Starling’s Law of Capillaries

• Edema, a build up of interstitial fluid can be due to:

  • Increased BHP due to hypertension

  • Increased capillary permeability due to vessel trauma