Local and Humoral Control of Blood Flow Flashcards
When the body is undergoing hypoxia, most tissue vasodilate to increase oxygen delivery. The lungs instead vasoconstrict. Why?
They do this so shunt blood away from poorly ventilated areas and deliver it instead to areas with greater efficiency of ventilation. If this carries on for too long, this can result in pulmonary HTN because these vessels normally do not receive this much blood flow so if this increased flow persists they can adapt and become stiffer leading to pulmonary HTN.
What happens in the coronary system if the mean arterial pressure falls below or above the range of 90 - 190mmHg?
Development of new blood supply (angiogenesis) to myocardium takes place to maintain perfusion
What tissues perform autoregulation:
- Best?
- In the middle?
- Poorest?
Why does the pulmonary circulation lack autoregulatory mechanisms?
This is a low pressure and low resistance system so there is not very much regulation that can occur since it doesn’t have a large dynamic range of values for pressure and resistance.
Under normal euvolemic conditions, do we experience significant changes in MAP (and thus perfusion pressures)?
No - the baroreceptor reflex becomes stimulated by changes in MAP and responds quickly to activate the PSNS or the SympNS in order to restore MAP
Autonomic NS
Other than nitric oxide, what other intrinsic factors affect vascular smooth muscle tone?
Why does cGMP cause smooth muscle relaxation?
Protein kinase G pho
What is active hyperemia?
What is reactive hyperemia?
- Active hyperemia is increased blood flow to a tissue due to increased metabolic demand (i.e. exercise increasing blood flow to muscles)
- Reactive hyperemia is when the tissue compensates after a period of occlusion or reduced blood flow by increasing blood flow
- What are some extrinsic sources of control of blood flow?
- What are some intrinsic sources of control of blood flow?
- Describe the relationship of these forces to vasoconstriction and vasodilation.
Blood flow through the capillary beds responds to changes in […]
Demand
Example: post-prandial hyperemia = increase in blood flow to digestive system following eating
The myogenic response is epithelium [independent or dependent] and calcium [indepenent or dependent].
Independent
Dependent
What are the two ways to describe the time course of blood flow control?
Nitric oxide is an example of an intrinsic endothelial derived factor. We learned about this in Neuro, but explain again how it works and what its physiologic effect is.
Increasing shear stress on endothelial cells of capillaries caused by increasing blood flow leads to mechanical activation of receptors that increase the activity of endothelial nitric oxide synthase (eNOS). This increases the production of NO from arginine (see image). The NO is a gas and can readily diffuse from the vascular endothelium into the smooth muscle cells of the vasculature. Here it will cause relaxation by several mechanisms, most notably stimulation of Guanylyl Cyclase, which makes cGMP.
Changes in bood flow to meet demand can be rapidly met by altering the resistance of the arterioles without changing the overall blood pressure. Why is this the case?
Because capillaries are essentially tiny blood vessels arranged in parallel, you can change their individual resistance to direct blood flow appropriately without changing the total resistance. If you don’t change the total resistance then you don’t change the pressure.
In the equation above, flow (Q) is constant, and Rtotal is kept constant to P is also kept constant.
Why do clinicians give nitroglycerine when a person has pectoral angina?
What is the myogenic response?
Let’s say that perfusion pressure to the muscles decreases. In order to keep blood flow constant, the local tissue capillaries can respond by dilating to decrease resistance to keep blood flow constant. This maintains flow and oxygen delivery despite changes in pressure.
WIth regards to vascular control, there is a hierarchy of control from lowest, mid level and highest. What mechanisms regulate vascular control at each of these levels?
