Lab 3.3

Blood pressure

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

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

Filtration

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)

Reabsorption

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)

Arterial end

(35+1)-(26+0)+10mmHg

Net filtration

Venous end

(16+1)-(26+0)=-9 mmHg

Net reabsorption

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

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

1. Increased BHP due to hypertension

2. Increased capillary permeability due to vessel trauma

3. Decreased BCOP due to liver disease or burns

Myocytes

mechanically and

electrically coupled by desmosomes

and gap junctions at visible

intercalated discs (via histology)

Cardiac myocytes are linked

by gap junctions

and held

together by desmosomes at

intercalated discs