Vascular system physiological function

The plasma level of fatty acids in a fed subject is between 0.3 and 0.5 mmol/L. As discussed above, the maximal safe level is about 2 mmol/L. This is not usually exceeded in any physiological condition since, above this concentration, that of the free (not complexed with albumin) fatty acids in the blood increases markedly. This can then lead to the formation of fatty acid micelles which can damage cell membranes the damage can cause aggregation of platelets and interfere with electrical conduction in heart muscle (Chapter 22). The cells particularly at risk are the endothelial cells of arteries and arterioles, since they are directly exposed to the micelles, possibly for long periods of time. Two important roles of endothelial cells are control of the diameter of arterioles of the vascular system and control of blood clotting (Chapter 22). Damage to endothelial cells could be sufficiently severe to interfere with these functions i.e. the arterioles could constrict, and the risk of thrombosis increases. Both of these could contribute to the development of a heart attack (Chapter 22) (Box 7.4). 

The majority of blood substitutes currently in use function only as plasma expanders. These maintain blood pressure by providing vascular fluid volume after haemorrhage, burns, sepsis or shock. While standard electrolyte solutions, such as physiological saline, may be administered, their elfect is transitory as they subsequently dilfuse back out of the vascular system. 

ARs play an important role in multiple physiological functions, especially in the cardiovascular and central nervous systems. a2-ARs are highly expressed in the rostral ventrolateral medulla (48), on vascular smooth muscle cells (49), and in nerve terminals (50). Within all AR subtypes, o -receptors are the only presynaptic inhibitory ARs described. 

Its formation in vascular endothelial cells, in response to chemical stimuli and to physical stimuli such as shear stress, maintains a vasodilator tone that is essential for the regulation of blood flow and pressure. NO also inhibits platelet aggregation and adhesion, inhibits leukocyte adhesion and modulates smooth muscle cell proliferation. NO is also synthesized in neurons of the central nervous system (CNS), where it acts as a neuromediator with many physiological functions, including the formation of memory, coordination between neuronal activity and blood flow, and modulation of pain. In the peripheral nervous system, NO is now known to be the mediator released by a widespread network of nerves. ... 

The outline of this chapter will follow a "system s approach" to regulation of smooth muscle relaxation and will be divided into sections dealing with ion flux regulation, key protein kinases, and regulation of cyclic nucleotides. For detail on the normal biochemi-cal/physiological function of these systems, the reader is referred to Chapters 9, 11, 12, 16, 20, and 22 in this volume. Where appropriate, differences between vascular, airway, gastrointestinal, and reproductive smooth muscle will be noted. 

The lymphatic system is a series of vessels for transporting back to the circulation, the fluid, cells and macromolecules that escape from the blood vascular system. It is therefore an essential part of the circulatory system. In normal physiology the lymphatics therefore play a key role in fluid homeostasis and immune cell trafficking. In pathological conditions aberrant lymphatic vessel function is associated with conditions such as lymphoedema and cancer (Baldwin et al 2002). 

The prevalence of CHE increases and prognosis worsens with age. Some studies demonstrate that age markedly influences all follow-up events, including total mortality, and mortality or hospitalisation related to CHE. Some studies suggest that physiological changes occur in CHE with ageing with an age-related increase in systemic vascular resistance and circulating noradrenaline (norepinephrine) concentrations and a decrease in renal function. 

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