netter67

Control of Artcriolar Tonę

CARDIOVASCULAR PHYSIOLOGY

Yasopressin (AI)H)

J. Pcrkins

MS, MfA

IBM

Shear stress    Shear

I listamine    stress

Acety (cholinę Bradykinin

Purinergics <e.g., ATP)

High shear stress Cytokines Thrombin

Ficure 4.15 Control oe Arteriolar Tonę_

Smali artenołes are Ule major determinants of Ihe resistance of Ihe vascular system. Release ot norepinephrine by sympathetic nerves contributes to the resting tonę ot thc srnooth muscle celi and, with increased sympathetic firmg, turther increases tonę. Circulating hor-mones such as atrial rratriuretic peptide (ANP), angiotensin II (A-lli and vasopressin (ADH) also act on the arterial srnooth muscle cells to alter their tonę. Substances produced by the endothelial cells in rcsjronse to a host of factors (C-g., slreat stress due to bkiod tlowing through the vessel and acetylcholine released trom parasympathelir nerves) act on the adjacent arterial srnooth musde cells to modulate their tonę. The surtace of the endothelial celi also contains angiotensin-converting enzyme (ACE), which is necessary to convert the inactive angiotensin I (A-l) molecule to its active form, A-fl.

80