Vascular Reactivity

First post for PHYL3002! This one's later than the others, because the first lecture was just an introduction lecture, and the second lecture basically went through a semester's worth of stats in 45 minutes (far too much information for me to try and explain adequately in a single blog post). This post will hopefully be short, as it touches on a lot of things that were covered in PHYL2001.

Describe the main features of the vascular system and how they influence blood flow and BP.

See earlier post: The Vascular System. One thing that I don't think is covered in that post is the concept of axial streaming. Basically, the faster the flow, the more blood vessels line up bang smack in the centre of the vessel (as opposed to taking up the entire width of the vessel, as in slower flow).

Understand how the features are affected by age and disease.

As we get older, many of our blood vessels stiffen. This causes systolic blood pressure to increase, diastolic blood pressure to decrease and pulse pressure to increase. Disease isn't actually mentioned in the slides, but I can think of several examples: diabetes can cause stiffening of the blood vessels (if I remember correctly), and atherosclerotic plaques effectively narrow the diameter of the blood vessel.

Explain flow-mediated vasodilation and the role of NO as a signalling molecule in the cardiovascular system.

Flow-mediated vasodilation (FMD) is, simply put, vasodilation in response to increased flow. Blood flow through a vessel exerts a shear stress on the vessel wall, and the reason why it's a shear stress is because blood flow is actually slightly slower right against the vessel wall (due to friction) than slightly further away. This stress is sensed by mechanosensitive Ca2+ channels, which activate eNOS (endothelial nitric oxide synthase). eNOS catalyses the production of NO (nitric oxide) from L-arginine, which goes to smooth muscle cells and increases the formation of cGMP, thereby inducing vasodilation. FMD can be measured by using ultrasound images of blood vessels.

Age and smoking habits can decrease FMD. Age decreases FMD because production of NO is reduced due to down-regulation of eNOS, reduced availability of L-arginine (which gets converted to NO) and increased levels of ADMA (an inhibitor of eNOS). Age also increases the breakdown of NO via increased production of superoxide anions.

Explain the roles of endothelial cells, myogenic regulation and tissue metabolism in regulating blood flow.

Endothelial cells: see above- you need an intact endothelium for FMD as that's where NO is produced.
Myogenic regulation: Special Circulations and Temperature Regulation
Tissue metabolism: Microcirculation and Blood Flow

Describe how the distribution of blood flow changes during exercise.

See Special Circulations and Temperature Regulation, it'll tell you more than you need to know.