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By V. Nemrok. Gonzaga University. 2018.
Feedforward control is another strategy for regulating systems in the body discount 10mg levitra with visa impotence kidney disease, particularly when a change with time Depolarization of nerve or muscle is desired generic levitra 20mg with visa erectile dysfunction doctors in sri lanka. In this case, a command signal is generated, membrane which specifies the target or goal. The moment-to-moment operation of the controller is “open loop”; that is, the regu- lated variable itself is not sensed. Feedforward control mechanisms often sense a disturbance and can, therefore, take corrective action that anticipates change. For example, heart rate and breathing increase even before a person has begun to exercise. Feedforward control usually acts in combination with negative-feedback systems. One example is picking up a Entry of Increase in Na Na into cell permeability pencil. The movements of the arm, hand, and fingers are di- rected by the cerebral cortex (feedforward controller); the movements are smooth, and forces are appropriate only in part because of the feedback of visual information and sen- sory information from receptors in the joints and muscles. Respiratory and cardiovascular adjustments closely match A positive-feedback cycle involved in the FIGURE 1. CHAPTER 1 Homeostasis and Cellular Signaling 5 lisecond, leads to an actual reversal of membrane poten- at the blood capillary level. Even within cells there is com- tial and an electrical signal (action potential) conducted partmentalization. The interiors of organelles are separated along the nerve or muscle fiber membrane. The process is from the cytosol by membranes, which restrict enzymes and stopped by inactivation (closure) of the Na channels. Equilibrium occurs if sufficient time for exchange has which occurs with each heartbeat. Depolarization of the been allowed and if no physical or chemical driving force cardiac muscle plasma membrane leads to a small influx of would favor net movement in one direction or the other. This leads to For example, in the lung, oxygen in alveolar spaces diffuses an explosive release of calcium from the muscle’s sarcoplas- into pulmonary capillary blood until the same oxygen ten- mic reticulum, which rapidly increases the cytosolic cal- sion is attained in both compartments. Many rium between cells and extracellular fluid is normally pres- other examples are described in this textbook. No energy expenditure is required so weakened by disease that it cannot provide adequate to maintain an equilibrium state. This leads to a Equilibrium and steady state are sometimes confused further reduction in cardiac pumping ability, even less with each other. A steady state is simply a condition that coronary blood flow, and further deterioration of cardiac does not change with time. The physician’s task is sometimes to interrupt or concentration of a substance in a compartment is constant. In a steady state, there is no net gain or net loss of a sub- stance in a compartment. Steady state and equilibrium both suggest stable conditions, but a steady state does not nec- Steady State and Equilibrium Are Separate Ideas essarily indicate an equilibrium condition, and energy ex- Physiology often involves the study of exchanges of matter penditure may be required to maintain a steady state. For or energy between different defined spaces or compart- example, in most body cells, there is a steady state for Na ments, separated by some type of limiting structure or ions; the amounts of Na entering and leaving cells per unit membrane. But intracellular and extracellular Na ion compartments: extracellular fluid and intracellular fluid. Extracellular These two compartments are separated by cell plasma mem- [Na ] is much higher than intracellular [Na ], and Na branes. The extracellular fluid consists of all the body fluids tends to move into cells down concentration and electrical outside of cells and includes the interstitial fluid, lymph, gradients. The cell continuously uses metabolic energy to blood plasma, and specialized fluids, such as cerebrospinal pump Na out of the cell to maintain the cell in a steady fluid. In living systems, conditions Ordinary extracellular fluid is subdivided into interstitial are often displaced from equilibrium by the constant ex- fluid—lymph and plasma; these fluid compartments are sep- penditure of metabolic energy. If we were to increase the rate of in- flow (open the tap), the fluid level would rise, and with time, a new steady state might be established at a higher level.
Individuals abstinence from alcohol can generally under the influence of alcohol may have reverse these abnormalities buy levitra 20 mg visa erectile dysfunction lubricant. As a Respiratory System result cheap 10 mg levitra with amex what do erectile dysfunction pills look like, they may be injuried in falls, fires, or motor vehicle or pedestrian accidents. In combination with cigarette Gastrointestinal System smoking, a higher incidence of chronic obstructive pulmonary disease (see Chap- It is possible for alcohol to affect almost ter 12) can result from chronic alcohol every organ of the gastrointestinal tract. In addition, because chronic alco- Individuals who consume alcohol exces- hol abuse affects some of the lungs’ nat- sively have an increased incidence of can- ural defenses, individuals who abuse cer of the throat and esophagus (see alcohol have a greater tendency to devel- Chapter 16). Despite the fact that alcohol is hol has a direct toxic effect on skeletal considered a hepatotoxin (substance that muscle; destruction of muscle fibers leads is harmful to the liver), individuals who to weakness, pain, tenderness, and swel- chronically abuse alcohol differ widely in ling of affected muscles. The more common Esophagitis and Gastritis form is chronic alcoholic myopathy, which evolves over months to years. Pain may be Esophagitis is inflammation of the less severe in chronic myopathy, although esophagus. Both can occur with the muscles may atrophy (shrink or become acute and chronic abuse of alcohol. The 212 CHAPTER 7 CONDITIONS RELATED TO SUBSTANCE USE severity of these conditions depends on effects of both fatty liver and alcoholic the individual. Individuals who continue to ditions produce only a mild discomfort, abuse alcohol, however, have a high but in other instances, the irritation and chance of developing cirrhosis. Obviously, absti- nence from alcohol is a major treatment Cirrhosis is most frequently caused by objective. It Esophageal Varices involves the reaction of the liver to injury by hepatotoxins (substances that are Some individuals who abuse alcohol harmful to the liver), in this case, alcohol. Circulation within the Esophageal varices are usually a complica- liver becomes less efficient, resulting in tion of cirrhosis. Because of the fibrous Treatment is directed toward controlling changes that occur in the liver with cirrho- hemorrhage, usually by inserting a special sis, there is increased pressure in the por- tube (Sengstaken-Blakemore tube) into the tal vein, a condition known as portal esophagus. Backflow of blood results in inflated to exert pressure against the bleed- the enlargement of the spleen (splenom- ing vein. Because the esophagus needs rest egaly), accumulation of fluid in the in order to heal, other types of feeding abdominal cavity (ascites), and develop- may be instituted until the esophagus is ment of esophageal varices. Others experience Alcoholic Hepatitis weakness, nausea, loss of appetite (ano- rexia), and jaundice (yellow discoloration During alcohol metabolism, fat is de- of the skin and whites of the eyes due to posited in the liver. When individuals con- the accumulation of bile pigments in the sume excessive amounts of alcohol, the blood). Treatment of cirrhosis is largely accumulation of fat enlarges the liver, a symptomatic, but abstinence from alcohol condition called fatty liver. Individuals with continue to consume alcohol, liver cells cirrhotic changes in the liver have an may die, causing the liver to become increased risk of cancer of the liver. This inflammatory condition, in who continue to abuse alcohol despite cir- which the liver is usually enlarged and rhotic changes in the liver, or despite oth- painful, is known as alcoholic hepatitis. Use Disorders Involving Other Substances 213 Pancreatitis infant called fetal alcohol syndrome. The amount of alcohol that pregnant women A variety of conditions other than alco- must consume before the fetus is injured hol abuse may cause pancreatitis (inflam- is unknown and appears to vary with the mation of the pancreas). Fetal alcohol syndrome is pancreatitis, however, is a form of pancre- characterized by prenatal and postnatal atitis that develops in susceptible individ- growth retardation, microcephaly (abnor- uals after chronic alcohol abuse. In this mal smallness of the head), abnormalities condition, the pancreatic ducts become of the nervous system, and facial disfigura- obstructed. Other congenital anomalies may normally secretes into the small intestine include mental retardation, as well as mus- to aid in digestion become active while culoskeletal and cardiac abnormalities. As a result, the pancreas essentially USE DISORDERS INVOLVING OTHER begins to digest itself, causing progressive SUBSTANCES degeneration with scarring and calcifica- tion of pancreatic tissues. Pancreatic func- Caffeine and Nicotine tion is often severely curtailed.
