Circulatory system arteries

Figure 15.1 The circulatory system. Arteries carry blood away from the heart. The smallest arterial vessels, the arterioles, are composed mainly of smooth muscle and are the major resistance vessels in the circuit. The capillaries are the site of exchange between blood and tissues. Veins carry blood back toward the heart. The small veins are the major compliance vessels in the circuit and, under resting conditions, contain 64% of the blood volume.

Figure 1.5 The blood vessel and nerve supply in the mammary glands of a cow. Circulatory system (arteries, white veins, stippled) h, heart a, abdominal aorta pa, external pudic artery pv, external pudic vein s, subcutaneous abdominal vein c, carotid artery j, jugular vein. Nerves 1, first lumbar nerve 2, second lumbar nerve 3, external spermatic nerve 4, perineal nerve. A and V show blood sampling points for arteriovenous (AV) difference determinations (Mepham, 1987).

Standardized mortality ratio (SMR) in the subgroup was 328 (5 observed/1.52 expected deaths, 95% confidence interval [Cl] 33-61, p value not reported). Kimbrough et al. (1999a) found no significant increases in mortality related to ischemic heart disease, hypertension with heart disease, other diseases of the heart, cerebrovascular disease, or circulatory system (arteries, veins, pulmonary circulation) in a study of 7,075 male and female capacitor workers. One of the subgroups (male salaried workers) in this study had a significantly decreased risk of mortality from ischemic heart as indicated by an SMR lower than 100 (44 observed/97.5 expected deaths, SMR=45, 95% Cl 107-766, p<0.01). Neither of these studies reported adequate quantitative exposure data. The inconsistent results of these studies could be due to differences in exposure levels, durations, and latencies, as well as types of Aroclors and cohort sizes. Additional information on these studies is provided in Section 3.2.8.2.I. 

Thromboxane A-2 has been implicated in a number of disorders of the circulatory system including coronary artery spasms, unstable angina pectoris, traumatic and endotoxic shock, and heart attacks. It is formed normally very near its receptors and is rapidly deactivated by metabolizing enzymes so circulating levels are quite low. Furthermore, it is opposed in its actions by the prostacyclins. When these controls are defective, pathology results and drugs can be the resort in attempts to restore the normal healthy balance. For one example, furegrelate (6) is a throm-... 

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... 

The adenohypophysis does not have a direct anatomical connection with the hypothalamus therefore, regulation of hormone secretion by way of neuronal signals is not possible. Instead, these two structures are associated by a specialized circulatory system and the secretion of hormones from the adenohypophysis is regulated by hormonal signals from the hypothalamus (see Figure 10.2). Systemic arterial blood is directed first to the hypothalamus. The exchange of materials between the blood and the interstitial fluid of the hypothalamus takes place at the primary capillary plexus. The blood then flows to the adenohypophysis through the hypothalamic-hypophyseal portal veins. Portal veins are blood vessels that connect two capillary beds. The second capillary bed in this system is the secondary capillary plexus located in the adenohypophysis. 

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

The most distensible vessels in the circulatory system are the veins. As with arteries, this feature of the veins also has important physiological implications because it allows them to serve as blood reservoirs. The veins are so distensible that they are capable of holding large volumes of blood at very low pressures. In fact, under resting conditions, 64% of the blood volume is contained within these vessels. 

Wide variations exist from individual to individual with respect to the circulatory system, the size of the respective blood vessels, and their distribution patterns. One might suppose that the main arteries arising out of the aorta, which comes directly from the heart, would always branch in about the same way and follow the same general... 

Two different circulatory systems, the bronchial and the pulmonary, supply the lungs with blood [133], The bronchial circulation is a part of the systemic circulation and is under high pressure. It receives about 1% of the cardiac output and supplies the conducting airways, pulmonary blood vessels and lymph nodes [133], It is important for the distribution of systemically administered drugs to the airways and to the absorption of inhaled drugs from the airways [18]. The pulmonary circulation comprises an extensive low-pressure vascular bed, which receives the entire cardiac output. It perfuses the alveolar capillaries to secure efficient gas exchange and supplies nutrients to the alveolar walls. Anastomoses between bronchial and pulmonary arterial circulations have been found in the walls of medium-sized bronchi and bronchioles [18, 65, 67],... 

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... 

The circulatory system moves materials (and heat) from one organ to another. It is centred on the heart which pumps blood through arteries to capillaries, where exchange occurs before the blood returns to the heart via the veins (Figure 1.16). During its passage through the tissues, there... 

Amino acids, sugars, and minerals pass through the small intestine into the circulatory system, where they are mixed with blood. The primary reactor organs in processing blood are muscle and the kidneys. The fluid flows in nearly total recycle through arteries and veins, which are basically the pipes in the system, and capillaries, where most of the transfer to and from the reactors and separators occurs. 

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] ... 

Guanethidine reduces blood pressure by its ability to diminish vascular tone both the arterial and venous sides of the circulatory system are involved. The resulting venous pooling contributes to orthostatic hypotension, a prominent feature of guanethidine treatment. The reduction in blood pressure is more prominent when the patient is standing than recumbent. 

Figure 3.2 Schematic of distribution and elimination of pharmaceutical compound on normal administration. Compound is distributed through the (a) lungs, (b) arteries, (c) other tissues (e.g., muscles, subcutenous tissues), (d) veins, and (e) gastrointestinal tract (i.e., oral). Notice the enteroheptic cycle where recirculation occurs between the hver and the GIT with most of the drug being excreted in the bile and is released into the gall bladder, transits into the small intestine, and is absorbed into the circulatory system.

Cardiovascular Effects. Histological examination of the heart and circulatory system of rats and mice exposed to 2,3-benzofuran by gavage for up to 2 years showed a compound-related increase in mineralization of the pulmonary artery in chronically-exposed rats (NTP 1989). The NOAEL values for cardiovascular effects are identified as the highest doses for which histological examinations were performed (250 mg/kg/day for acute-duration exposure and 500 mg/kg/day for intermediate-duration exposure). Pulmonary artery mineralization, which was considered secondary to increased severity of nephropathy, was seen only in the low-dose groups of rats exposed for 103 weeks (30 mg/kg/day in male rats and 60 mg/kg/day in female rats) (NTP 1989). The lack of effect at the higher doses was attributed to reduced survival (NTP 1989). ... 

Primary routes of entry of toxicants to the human body are dermal, gastrointestinal, and respiratory. Methods for studying these different routes are numerous, but they are perhaps best developed for the study of dermal absorption because this route is subject to more direct methodology, whereas methods for studying respiratory or gastrointestinal absorption require more highly specialized instrumentation. Additional routes encountered in experimental studies include intraperitoneal, intramuscular, and subcutaneous routes. When direct entry into the circulatory system is desired, intravenous (IV) or intra-arterial injections can be used to bypass the absorption phase. Information from this more direct route of entry (e.g., IV) should, however, be used in addition to data from the extravascular route of interest to adequately assess the true extent of absorption of a toxicant. 

Example. What would be the pressure drop per unit length for blood (a dispersion of red blood cells in plasma), flowing in an artery which has an internal diameter of 1 mm, in an animal s circulatory system at 37 °C ... 

The capability of LDL receptors to remove LDL cholesterol from the circulation can rationalize these clinical observations. If little cholesterol is available in the diet, the cells of the peripheral tissues respond by up-regulating the number of LDL receptors on the cell surface. The higher concentration of receptors means that more of the cholesterol will be removed from the circulatory system. Because the inappropriate deposition of cholesterol is a major contributor to blocked arteries, if the cholesterol is removed from the circulation, less risk of blockage exists. On the other hand, if a large amount of cholesterol exists in the diet, and the cells have enough for their needs, they will synthesize fewer LDL receptors, less cholesterol will be removed from the circulatory system, and the risk of artery disease increases further. 

These traits have received most study in tunas, a group of fishes noted for continuous swimming and for major anatomical differences from other fishes. Of particular importance in the anatomical organization of tunas is the internalization of red muscle, an anatomical feature that appears critical for allowing endothermy to develop. In most fishes, the red muscle is located superficially, where it would be difficult, if not impossible, to prevent loss of metabolically generated heat to the environment. The internalization of the red muscle mass in tunas isolates this tissue from close contact with seawater. There is also an effective isolation from the medium of the circulatory system within red muscle countercurrent exchangers interspersed between red muscle and the arterial circulation supplying the tissue allow much of the heat produced in red muscle to be retained, rather than lost to the environment. 

Figure 8.6 Schematic representation of the ring shaped tube that models the circulatory system of a mammal. Blood flows clockwise. The tube is divided into segments corresponding to the arterial, venular, pulmonary arterial, and pulmonary venular trees.

Based on the above, an elementary pharmacokinetic model considering the entire circulatory system was constructed. Thus, apart from the arterial and venular trees, a second set of arterial and venular trees, corresponding to the pulmonary vasculature, must be considered as well. These trees follow the same principles of (8.10) and (8.13), i.e., tubes of radius p0 are considered with appropriate length to accommodate the correct blood volume in each tree. 

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