Circulatory system functions

Well-rounded physical fitness includes four basic elements that can be improved with regular exercise cardiovascular endurance, muscular strength, muscular endurance, and flexibility. To be tmly fit, each element should be developed, but the most vital is cardiovascular endurance. Physiologically, cardiovascular endurance is the sustained ability of the heart, blood vessels, and blood to carry oxygen to the cells, coupled with the ability of the cells to use oxygen, and the ability of the blood to carry away waste products. Since every cell in the body requires oxygen to function, there is no more basic element of fitness than this—to see that the heart, lungs, and circulatory system function properly. 

The principal function of the circulatory system is to supply oxygen and vital metabolic substrates to cells throughout the body, as well as removal of metabolic waste products. Circulatory shock is a life-threatening condition whereby this principal function is compromised. When circulatory shock is caused by a severe loss of blood volume or body water it is called hypovolemic shock, the focus of this chapter. Regardless of etiology, the most distinctive manifestations of hypovolemic shock are arterial hypotension and metabolic acidosis. Metabolic acidosis is a consequence of an accumulation of lactic acid resulting from tissue hypoxia and anaerobic... 

Shock A condition wherein the principal function of the circulatory system to supply oxygen and vital metabolic substrates to cells throughout the body as well as removal of metabolic waste products is compromised. The four major shock types are hypovolemic, obstructive, cardiogenic, and distributive. 

The human heart begins pumping approximately 3 weeks after conception and must continue this activity without interruption all day, every day, for an entire lifetime. In a typical individual, this means the heart pumps over 100,000 times per day and propels about 2000 gallons of blood through almost 65,000 miles of blood vessels. This function of the heart will be discussed here as well as in the following chapter on cardiac output. The function of the blood vessels will be considered in the chapter on the circulatory system. 

The circulatory system carries out many important functions that contribute to homeostasis. It obtains oxygen from the lungs nutrients from the gastrointestinal tract and hormones from the endocrine glands and it delivers these substances to the tissues that need them. Furthermore, it removes metabolic waste products, such as carbon dioxide, lactic acid, and urea, from the tissues. Finally, it contributes to the actions of the immune system by transporting antibodies and leukocytes to areas of infection. Overall, the circulatory system plays a vital role in maintenance of optimal conditions for cell and tissue function. 

The circulatory system is composed of several anatomically and functionally distinct blood vessels including (1) arteries, (2) arterioles, (3) capillaries, and (4) veins. 

Therefore, depending upon the degree of constriction of the vascular smooth muscle, these vessels may alter their diameter, and consequently their blood flow, across a very wide range. For this reason, the arterioles are the major resistance vessels in the circulatory system. In fact, the primary function of arterioles is to regulate the distribution of the cardiac output and to determine which tissues receive more blood and which receive less, depending upon the tissue s and the body s needs. 

The integrated function of the vasculature and heart, as a closed circulatory system, supplies nutrients and oxygen to critical organs and removes metabolic wastes and carbon dioxide. This integrated system results from the careful control of cardiac output, arterial blood pressure (systolic and diastolic pressures integrated to derive mean arterial pressure), and systemic vascular resistance, thereby maintaining blood perfusion through... 

Aviado DM, Belej MA Toxicity of aerosol propellants in the respiratory and circulatory systems. V. Ventricular function in the dog. Toxicology 3 79-86, 1975... 

Nitrogen oxides (NO ) are formed during the combustion at high temperature of fossil fuels and of biomasses and are blamed for the production of acid rain, the formation of ozone in the troposphere and of secondary particulate matter and for causing a reduction in breathing functionality and damage to the cardio-circulatory system in humans. 

The relatively acidic thiol on serum albumin forms a fairly stable S-nitroso adduct with nitric oxide, which may serve to preserve and carry NO throughout the circulatory system [162,163]. Bacterial toxins released in toxic-shock syndrome induce excessive NO-synthase activity in macrophages. The resulting arterial expansion may induce the cardiovascular collapse associated with toxic shock syndrome [164]. Nitrous acid reacts with DNA to form dG-N2-dG interstrand crosslinks at the sequence 5 CG [165]. NO can also deaminate cytidine [166] and deoxyguanosine [167] and so may function as a mutagen. The rate law for NO reacting with O2 has been measured electrochemically as [168] ... 

The circulatory system of fish is also unique structurally and functionally. Structurally, the membranous nature of the vasculature makes for a friable high-capacitance system under low pressure. Low blood flows result in somewhat longer distributional phases for many drugs. Processes such as heart rate and stroke volume that influence drug distribution are themselves influenced by external factors such as temperature and stress. In addition, total plasma protein content differs in fish as compared to mammals. Total plasma protein in the trout and flounder is approximately one-half that of mammals such as dogs and cats. For many compounds protein binding is considerably lower in fish than their mammalian counterparts (19, 20). 

The hver is interconnected with other organs (pancreas, spleen, intestine) along the portal venous circulatory system. Thus, it is clear that an ad hoc view of the liver function of removing toxins is insufficient in light of the other duties it performs. 

Nitric oxide and NO synthases. Nitric oxide (NO) is a reactive free radical whose formula is often written as NO to recognize this characteristic. However, NO is not only a toxic and sometimes dangerous metabolite but also an important hormone with functions in the circulatory system, the immune system, and the brain.510 512 The hormonal effects of NO are discussed in Chapter 30, but it is appropriate here to mention a few reactions. Nitric oxide reacts rapidly with 02 to form nitrite (Eq. 18-61). 

If the eicosanoids are to serve a useful hormonal function, there must be a rapid means for their removal when their action is no longer required. Consistent with this principle, it has been found that eicosanoids have very short half-lives in vivo injected prostaglandins do not survive a single pass through the circulatory system. 

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