Blood Vessels
The braching network of blood vessels carries blood from the heart to the tissues of the body. End-to-end, the body's blood vessels would stretch almost 100,000 km.
Arteries transport blood from the heart to capillaries, where nutrient and waste diffusion occurs. Veins cary blood back to the heart.
Endothelial cells line the inside of the cardiovascular system. Regulation of CV function is mediated primarily by smooth muscle cells and cardiomyocytes.
Arteries
Arteries are the thick-walled vessels transporting blood from the heart to tissue beds. Their stiff but elastic walls allow them to stretch under proessure and provide constant blood pressure to capillaries .The aorta is roughly 2.5 cm in diameter, while arterioles have a diameter of 0.3 mm or less.
Microvascular control ensures blood gets to the right spots. The sympathetic system can shut down blood flow to skeletal muscle and the skin in order to pool blood in the vital organs. Precapillary sphincters serve as gates to control blood flow into individual capillary beds.
see pg 478, B and B, to learn about local regulation of vessels using O2, CO2, pH, lactic acid, and others.
Veins
Veins contain most of the systemic circulation's blood volume due to their large compliance, giving them the name 'capacitance vessels'. This is not due so much to the elastic properties of their walls, but rather their ability to change shape.
Capillaries
Capilalries are the smalles of vessels, made up simply of porous endothelial cells. It is here that gases, nutrients, and wastes diffuse between the cardiovascular system and the tissues.
| Heart Output | 5000 ml/min |
| skeletal muscle | 1450 |
| GI system | 1250 |
| kidney | 1000 |
| brain | 700 |
| skin | 375 |
| coronary circulation | 225 |
Blood flows through these systems due to differences in pressure at either end.
Changes across the Vasculature
The enormous branching of the vasculature creates large differences in cross-sectioanal area and flow.
| Number | Aggregate cross-sectional area (cm2) | Mean velocity (cm/s) | |
|---|---|---|---|
Aorta |
1 |
4 |
21 |
Arteries |
8000 |
63 |
1.3 |
Arteriloles |
2 x 107 |
141 |
0.6 |
Capillaries |
1-4 x 1010 |
2827 |
0.03 |
Hemodynamics describes blood flow throughout the vessels of cardiovascular system.
Vessel autoregulation during ischemia
adenosine, increased[K]out , and decreased pH all lead to vasodiation in ischemic areas