Ch 10.3 -- Arterioles -- VTPP 435

Ch 10.3 -- Arterioles -- VTPP 435

Arterioles

-main resistance vessels
-small radius
-highly muscular
-primary resistance vessels
-determine distribution of cardiac output

Arterioles 2 main functions

-change cardiac output distribution
-regulate arterial blood pressure

Vascular Tone

-state of partial constriction of arteriolar smooth muscle that establishes a baseline of arteriolar resistance
-tonic smooth muscle
-sympathetic fibers stimulate it

Active Hyperemia

-increased blood flow to an organ in response to enhanced tissue activity

Active Hyperemia Steps

1) increased Local metabolic activity
2) Greater O2 usage and CO2 production
3) decreased O2 & increased CO2
4) local release of vasodilating paracrines
5) local arteriolar vasodilation
6) increased blood flow to tissue
7) increased O2 delivery and increased CO2 removal

Local Chemical Factors that Produce Relaxation of Arteriolar Smooth Muscle

-decreased O2
-increased CO2
-increased acid
-increased K+
-increased osmolarity
-adenosine release

Nitric Oxide (NO)

-paracrine released from endothelial cells
-causes vasodilation

Endothelin

-paracrine released by endothelial cells
-causes vasoconstriction

Vascular Endothelial Growth Factor (VEGF)

paracrine released from endothelium stimulates new vessel growth -- angiogenesis

Reactive Hyperemia

-post occlusion increases in blood flow
-high blood flow after blockage
-vessels vasodilate

Histamine

-chemical released from mast cells or basophils
-causes vasodilation
-increases capillary permeability
-helps with allergic responses and inflammation

Reactive Hyperemia Steps

1) decreased mean arterial pressure
2) decreased blood flow to tissue
3) O2 depletion and CO2 accumulation
4) local release of vasodilating paracrines
5) local arteriolar dilation of occlusion prevents blood flow
6) occlusion removed and increased blood flow
7) increased O2 delivery and increased CO2 removal

Myogenic Autoregulation of Tissue Blood Flow

1) decreased mean arterial pressure
2) decreased blood flow to a tissue
3) decreased stretch of local arteriolar smooth muscle
4) myogenic relaxation of local arterioles (decreased tone)
5) vasodilation
6) blood flow tot issue normal despite decreasing driving pressure

Autoregulation

ability of an organ to adjust its own rate of blood flow despite changes in driving mean arterial blood pressure

Shear Stress

-due to friction, blood flowing over surface of vessel lining creates a force applied on cells in direction of flow
-when increased, cells release NO to reduce shear stress

Total Peripheral Resistance (TPR)

-resistance offered by all peripheral blood vessels
-most of it comes from arteriolar
-all resistance from systemic peripheral vessels

Epinephrine on Arteriolar Vessels

-on Beta 2 vasodilates
-on Alpha 1 vasoconstricts

ADH & Angiotensin II on Arterioles

-cause vasoconstriction
-triggered by sudden loss of blood volume

Sympathetic Stimulation on Arterioles

-causes vasoconstriction
-contributes to vascular tone