671
edits
Sandbox: Difference between revisions
no edit summary
Jelledejong (talk | contribs) No edit summary |
Jelledejong (talk | contribs) No edit summary |
||
| Line 144: | Line 144: | ||
# Secondly, if feasible, modification of antihypertensive drugs should be considered. | # Secondly, if feasible, modification of antihypertensive drugs should be considered. | ||
Surgical or pharmacological destruction of (the oesophageal branches of) the vagus nerve has shown not to be successful. Based on predominantly positive therapeutic response in over a dozen cases, the treatment of choice of oesophageal syncope is insertion of a cardiac demand pacemaker (Basker & Cooper, 2000). Management of persisting neuralgia is symptomatic. | Surgical or pharmacological destruction of (the oesophageal branches of) the vagus nerve has shown not to be successful. Based on predominantly positive therapeutic response in over a dozen cases, the treatment of choice of oesophageal syncope is insertion of a cardiac demand pacemaker (Basker & Cooper, 2000). Management of persisting neuralgia is symptomatic. | ||
The arterial system consists of three major groups of arteries. | |||
These are: | |||
*Elastic arteries | |||
*Muscular arteries | |||
*Arterioles | |||
== Elastic arteries == | |||
Elastic arteries are the '''aorta''' and the '''major branches of it''' close to the heart. The vessel walls contain the most elastin of all vessels and elastin is found in all the vessels layers. Elastic arteries also contain smooth muscle cells, but these are mostly inactive in vasoconstriction. By elastically dilating when [[Blood pressure|blood pressure]] increases (right after a heartbeat) and contracting when [[Blood pressure|pressure]] drops they maintain [[Blood flow|blood flow]] in between heartbeats. The elasticity also gives a more constant [[Blood pressure|BP]] throughout the rest of the vascular system. The diameter of elastic arteries ranges from ''2.5 to 1 cm''. | |||
== Muscular arteries == | |||
Muscular arteries have a diameter of 1 to 0.3 cm and derive from elastic arteries. Muscular arteries regulate the [[Blood flow|blood flow]] to specific organs. They are active during vasoconstriction and contain relatively the most smooth muscle cells in the tunica media. They contain less elastin than elastic arteries and are thus less distensible. | |||
== Arterioles == | |||
The smallest arteries are called arterioles. The tunica media of the arterioles mostly contain smooth muscle cells. Their diameter ranges from 0.3 cm to 10 µm, and the smallest arterioles lead into '''capillary beds'''. [[Blood flow]] into capillary beds is regulated by these arterioles. The arterioles change in diameter due to '''neural, hormonal and local chemical influences'''. These changes in diameter lead to the changes in [[Blood flow|blood flow]] in the capillary beds. When arterioles constrict, the capillary beds that lay behind the constricting arterioles is bypassed. When they dilate, [[Blood flow|blood flow]] in the capillary beds increases dramatically. | |||
== Capillaries == | |||
[[File:Capillary_Bed_aangepast.jpg|frame|Capillary bed]] | |||
Capillaries are no arteries. They are the smallest of all blood vessels and their function is to exchange materials with every cell in the body. The average capillary diameter is 8 to 10 µm, so that red blood cells can just pass through them. | |||
A capillary bed consists of a network of interweaving capillaries. These capillary beds connect arterioles, and venules, the smallest vessels of the [[Venous system|venous system]]. In most of the capillary beds, two types of vessels are found: | |||
*a vascular shunt | |||
*and true capillaries | |||
A '''vascular shunt''' connects connects an arteriole with a [[Venous system|venule]] directly. These vessels do not exchange materials with the surrounding fluid. True capillaries exchange materials. The arteriole that directly connects with the capillaries is called a terminal arteriole and this arteriole feeds directly into the metarteriole. This metarteriole feeds into the thoroughfare channel and then the [[Venous system|postcapillary venule]]. These vessels together make the vascular shunt. | |||
'''True capillaries''' normally branch off the metarteriole and empty in the [[Venous system|postcapillary venule]]. The root of the true capillaries is surrounded by smooth muscle cells. This is called a precapillary sphincter. It acts as a valve that regulates [[Blood flow|blood flow]] through the capillary bed. If the sphincters are contracted, the blood will pass through the vascular shunt, and no exchange of materials will take place. If the valves are relaxed, blood will flow through the capillaries and exchange with the surrounding cells occurs. | |||