Muscle oxygen supply

The nitrates, such as isosorbide (Isordil) and nitroglycerin, have a direct relaxing effect on die smooth muscle layer of blood vessels. The result of diis effect is an increase in the lumen of die artery or arteriole and an increase in the amount of blood flowing through diese vessels. An increased blood flow results in an increase in die oxygen supply to surrounding tissues. 

Smooth muscles do more than contract and the regulation of the mitotic activity of vascular smooth muscle is important in the maintenance of the oxygen supply to tissues and the genesis of hypertension of non-renal origin. Secretion activities of smooth muscle are just beginning to be appreciated. 

The major drawback of these models, however, is their lack of a clear reference between model components and constituent parts of the biological system (e.g. structures like ion channels, transporter proteins, receptors, etc.). These models, therefore, do not permit the simulation of patho-physiological detail, such as the series of events that follows a reduction in oxygen supply to the cardiac muscle and, ultimately, causes serious disturbances in heart rhythm. 

During phase I, each seizure causes a sharp increase in autonomic activity with increases in epinephrine, norepinephrine, and steroid plasma concentrations, resulting in hypertension, tachycardia, hyperglycemia, hyperthermia, sweating, and salivation. Cerebral blood flow is also increased to preserve the oxygen supply to the brain during this period of high metabolic demand. Increases in sympathetic and parasympathetic stimulation with muscle hypoxia can lead to ventricular arrhythmias, severe acidosis, and rhabdomyolysis. These, in turn, could lead to hypotension, shock, hyperkalemia, and acute tubular necrosis. 

Oxygen supply to the muscles depends on the following factors ... 

Some of the athletic events in which oxygen supply to muscle is limiting and can affect ATP generation are given in Table 13.6. 

Table 13.6 Indications of the oxygen supply to muscle, its limitations for performance and the pathways for ATP generation in different athletic events...

Oxygen supply to muscle in patients suffering from atherosclerosis... 

Well-known medical conditions in which oxygen supply to muscles is reduced are an attack of asthma, emphysema or heart failure. However, probably the most common condition is atherosclerosis. If the femoral arteries are affected by atherosclerosis, ATP generation from fuel oxidation may not be sufficient to satisfy the energy requirements of even mild physical activity (e.g. walking) and rapidly... 

At a constant pace (i.e. constant power output) and dierefore constant rate of ATP utilisation, the rate of glycogen breakdown decreases with time. This is due to the increase in blood supply to die muscle (vasodilation) which increases oxygen supply so that ATP generation from complete oxidation of glycogen, rather than conversion of glycogen to lactic acid, becomes increasingly more important. 

Amiodarone relaxes vascular smooth muscle one of its most prominent effects is on the coronary circulation, reducing coronary vascular resistance and improving regional myocardial blood flow. In addition, its effects on the peripheral vascular bed lead to a decrease in left ventricular stroke work and myocardial oxygen consumption. Therefore, amiodarone improves the relationship between myocardial oxygen demand and oxygen supply. IV administration may be associated with profound hypotension requiring volume expansion therapy. 

Peripheral artery disease (PAD) patients usually feel leg pain when walking, which is caused by insufficient blood flow to keep up with energy demand. The P MRS data collected in a PAD patient group showed prolonged PCr recovery rate (or time constants) in the calf muscle after exhaustive exercise, suggesting the transition from anaerobic to aerobic energy metabolism is delayed due to impaired oxygen supply or mitochondria fimction caused by atherosclerosis. ... 

Heart disease is any condition that diminishes the hearts ability to pump blood. A common heart disease is arteriosclerosis, a buildup of plaque on the inside walls of arteries. As discussed in Section 13.8, plaque deposits are mostly an accumulation of low-density lipoproteins, which are high in cholesterol and saturated fats. Plaque-filled arteries are less elastic and have a decreased volume. Both these effects make pumping blood more difficult, and the heart becomes overworked and weakens. Accumulated damage to heart muscle from arteriosclerosis or other stresses can result in abnormal heart rhythms, known as arrhythmia. Chest pains, known as angina, result from an insufficient oxygen supply to heart muscles. Ultimately, the weakened heart does not adequately circulate blood to the body. People with heart disease have decreased stamina and frequently need to catch their breath. 

Active fish have a better developed capillary system in the red muscle to supply oxygen to the mitochondria, and a higher haematocrit (Blaxter et al., 1971). The red muscle tissue also contains more cytochromes (respiratory proteins), and exhibits more cytochrome oxidase activity, which is responsible for transferring electrons in die respiratory chain, more efficient respiration control (oxidative phosphorylation and P/O coefficient) and a greater Atkinson charge, which characterizes energy reserve accumulated in adenyl nucleotides ... 

When muscles work too hard, lactic acid builds up in the muscles and this is the process that makes them sore (muscle fatigue). Once muscles form lactic acid, they can t do anything else with it. Once the oxygen supply becomes adequate again, some of the lactic acid is converted back to pyruvate and broken down to carbon dioxide and water. The rest is carried away from the muscles by the blood and eventually converted by the liver back to glucose. Once the lactic acid is removed, the muscles no longer hurt. This is why rest is the best way to recover from hard work or exercise. 

Ergot alkaloids contain lysergic acid (see ergotamine formula in A). They act on uterine and vascular muscle. Ergometrine particularly stimulates the uterus. It readily induces a tonic contraction of the myometrium (tetanus uteri). This jeopardizes placental blood flow and fetal oxygen supply. Ergometrine is not used therapeutically. The semisynthetic derivative methylergometrine is used only after delivery for uterine contractions that are too weak. 

Murray [145] analyzed this problem based on the cylindrical geometry illustrated in Figure 8.4. Here, the muscle fiber is assumed to be a homogeneous cylinder, with oxygen supplied via the capillary network to the outer boundary of the fiber. 

Q1 Coronary arteries are the first to branch off the aorta. The heart has a large blood flow (200 ml min-1) but also has great metabolic needs and so has a relatively poor oxygen supply, with little in reserve when oxygen demands increase. At each heart beat (systole), the coronary arteries are compressed by cardiac contraction and blood flow diminishes to a low level. This effect is very marked in the left ventricle, and over 80% of coronary flow to the left ventricle occurs in the periods between beats (diastole). When heart rate increases (tachycardia), the duration of diastole decreases much more than the duration of systole, and the period available for perfusion of cardiac muscle diminishes. 

Anginal pain occurs when the oxygen supply to the myocardium is inadequate, and is most commonly experienced during exercise. Some patients experience angina at rest this appears to be associated with spasm of the coronary arterial muscle. 

Similarly, measurements of blood flows to sections of muscle, which are primarily composed of a single fiber type, exhibit large differences consistent with the expected demands of oxygen supply based on mitochondrial content (32,33). Thus, mammalian skeletal muscle is typically comprised of three biochemically and functionally distinct fiber types slow-twitch red, fast-twitch red and fast-twitch white. These fiber types are also commonly referred to as Type I, Type Ila, and Type 11b, respectively (7 ). 

Role of myoglobin In the oxygen supply to red skeletal muscle. J. Biol. Chem. 250 9038-43. 

R. and Packer, L. (1982) Muscle mitochondrial bloenergetlcs, oxygen supply, and work capacity during dietary iron deficiency and repletion. Am. J. Physiol. 242 E418-E427. 

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