Transcription
In everyday medicine, we very often talk about the heart, large blood vessels, blood pressure, stroke volume or cardiac output. However, an important principle in pathophysiology is that the final destination of circulation is not the aorta but the capillary.
It is precisely the peripheral circulation and microirculation that determine whether oxygen reaches the cells, whether metabolic waste products are removed and whether tissues can maintain their function under stress. Peripheral circulation is also the part of the circulatory system where flow slows down. Pressure decreases compared to central arteries and in the capillaries exchange between blood and tissues occurs.
The blood vessels typically included in peripheral circulation are small arteries. Here we talk mainly about muscular type arteries. Then arteries and venules. Microirculation in turn includes classically capillaries but then we have also pre-capillary sphincters post capillary sphincters and atriovenous anastmoses.
Now let's talk about the sphincters here. Between capillaries and arteries and capillaries and venules there are no true ring-shaped muscle structures. So no true sphincters. However, pre-capillary and postcapillary sphincters refer to the last segments of smooth muscle present in the arteries. You can see that also here in the picture here are some of the pre-capillary sphincters pointed out. So that means if it's smooth muscle, these smooth muscle cells can still be influenced by the nervous system, hormones, and other factors allowing them to contract and dilate. is functioning similarly to sphincter.
And another special blood vessel type we have here is the atria anesmosis. These vessels are wider than capillaries and usually they are closed but they can open when needed to let's say bypass the capillary network. This can happen in case of obstruction. There are also useful as pathways for larger lucasytes since capillaries are extremely narrow often similar in size to aritroytes as you know while lucasytes some of them are larger and much larger and require wider passages and also a large number of atriovenous anesmosis are found in the skin. Although they are located deeper than capillaries they play an important role in thermo regulation.
Peripheral vessels are what determine peripheral resistance. It should be remembered that vascular tone is influenced by the nervous system, various hummeral factors, not only hormones that means, and also local metabolic signals. When talking about vascular resistance, peripheral resistance is usually much more important than the resistance of central or elastic vessels.
Many cardiovascular diseases share common features. Increased peripheral resistance, reduced elasticity of microirculation, and loss of the ability to rapidly adapt to changes in pressure and flow. Patients with conditions such as atherosclerosis, hypertension or heart failure are therefore less tolerant to changes in perfusion regime during cardopulmonary bypass even if absolute values appear acceptable.
And in this lecture we will discuss circulation, blood pressure, the heart and related pathologies.