Phys 21: Local Control Of Blood Flow

Front 1

what are the two theories used to decribe autoregulation based on tissue metabolism

Back 1

1. vasodilator substances 2. oxygen theory

Front 2

Describe how the vasodilatory theory contributes to autoregulation

Back 2

active cells release substances such as histamine, potassium, adenosine, CO2, and latic acid that signal the vasculature to dilate and increase blood flow

Front 3

Describe how the oxygen theory contributes to autoregulation

Back 3

negative feedback- the reduction in PO2 that occurs in active tissue relaxes teh precaipllary sphincters and leads to increased blood flow which increases oxygen delivery.

Front 4

What is reactive hypermeia

Back 4

Excess blood flow to tissue following occulsion, the build of of dilators during the oculusion triggers a rush of blood onces it is available. Eventually this blood "washes away" the dialators and the diameter and thus flow can return to normal

Front 5

Describe myogenic autoregulation

Back 5

important in smaller arterioles, a stretch of the vascular smooth muscle due to an increase in pressure causes the muscle to contract. Note that this acts to increase the pressue even more so it can augment the response of vasconstrictors. Note also that this mechanism cannot regulate flow precisley becasuse it depends only on strech and is not a sensor of tissue metabolism

Front 6

How does local metabolic dilation at the precapillary sphincter signal dilation further upstream to deliver more blood to the capillary bed (dirt road to Hwy concept)

Back 6

The local dilation results in an increase in flow. This increase in flow causes a mechanical sheer stress on the endothelial cells which triggers them to release NO. NO dilates the smooth muscles aroun the arterioles which further increases the flow to the capillary bed.

Front 7

Explain the signaling cascasde that NO triggers to cause vasodilation

Back 7

Activation of NOS leads to the formation of NO from L-arginine. NO activates guanylyl cyclase which converts GTP to cGMP. cGMP can trigger further events that lead to vasodilation.

Front 8

What does Laplace's Law describe

Back 8

wall tension=pressurex radius, an increased radius increases wall tension because the wall is thinner, for a thinner wall, the same increase in pressure will cause a greater increase in tension

Front 9

If a issue demands a 100ml/min increase in blood, CO must increase from 5L/min to 5.1 L/min if all of other tissues are to continue to receive their blood on top of this new demand. Describe the "cascade" that occurs to ensure an increase in CO as a certain tissue demands more blood.

Back 9

At the local tissue site, metabolic and oxygen demand leads to local dilation and a decrease in arteriole resistance which allows for more flow. An increase in local flow will result in an increase in venous volume and venous return which will increase right atrial pressure. Increased right atrial volume/pressure increases stroke volume by an amount exactly equilvant to the tissue demand- 100ml/min.