Muscle tissue handling

If the fish is not prepared for extraction at the time of collection, thaw it, and remove the head, skin, and fins. Remove the fat and viscera for separate handling. Cut off portions of the muscle tissue. Weigh out 20-gram samples of muscle and of fat-and-viscera for extraction. Re-freeze these samples. 

Data relating to normal and faulty cuts of meat are summarized in Table 12.14. Both defects mentioned may occur in different muscles of the same animal. The PSE effect is not significant in beef muscle tissue since energy is available from fat oxidation so glycogen breakdown can occur slowly. These meat defects may be avoided in hog muscles by careful handling of stress-sensitive animals and by rapid cooling of carcasses. 

Table V contains data for two model substances, p-aminohippurate (PAH) and phenol red. Consideration of the highest values in this table tells you where the major portions of the substances appear. For example, urine and bile show the largest concentrations of PAH and phenol red. Both compounds appear in significant concentrations in the kidney while the values in muscle, brain and cerebrospinal fluid (CSF) are invariably lower than the values seen in plasma. The values in parentheses (Table V) are percent of the administered dose in a given tissue or fluid compartment. They add to the previous information by revealing the overall importance of a particular compartment in the disposition of a substance. For example, while the hepatic concentrations of PAH and phenol red at 4 hrs. are only about 2-fold those of plasma, the large size of the shark liver relative to its body weight, typically about 10%, leads to the appearance of 30-40% of these substances in the liver. The relative handling of these compounds by the urinary and biliary system is obvious from considering the percentage figures. Thus in 24 hours phenol red is about equally distributed in the bile and urine (38 vs 31%) the urinary route is the dominant route of excretion of PAH, i.e., 56 vs 2%.

The microdialysis probe is the heart of the method, as a chromatographic column is the heart of the HPLC instrument. Rigid CMA probes, Models 10, 11, and 12, are used for stereotaxic implantations into the brain, where the probe can be fixed (cemented) to the skull. A flexible probe design (CMA 20) allows the placement of such a catheter into the moving tissues (muscle) or peripheral organs for studies in freely moving animals. The technical difficulties of microdialysis experiments impose requirements for precise liquid delivery, minimized dead volumes, and the capability of handling small sample volumes. 

Pyruvate kinase is the enzyme that catalyzes this reaction. Like phospho-fructokinase, it is an allosteric enzyme consisting of four suhunits of two different types (M and L), as we saw with phosphofructokinase. Pyruvate kinase is inhibited hy ATP. The conversion of phosphoenolpyruvate to pyruvate slows down when the cell has a high concentration of ATP—that is to say, when the cell does not have a great need for energy in the form of ATP. Because of the different isozymes of pyruvate kinase found in liver versus muscle, the control of glycolysis is handled differently in these two tissues, which we will look at in detail in Chapter 18. 

In Topic 41, we considered in general terms the way in which hormones act as chemical messengers, transmitting information from one tissue to another. In this topic, we are going to look at three of the most important hormones and the way in which they control how we handle major foodstuffs in three major tissues muscle, liver and adipose tissue (which, between them, make up a high percentage of total body mass). The three hormones are insulin, glucagon and adrenaline, two of them produced by the pancreas and the third, as its name implies, by the adrenal medulla. Their effects, explained below, are summarised in Table 43.1. 

A wound is defined as a breakdown in the protective function of the skin with or without loss of underlying coimective tissue like muscle, bone or nerves (locono et al., 1998). The injury of the skin or underlying tissue may be due to surgery or caused by cuts, chemicals, temperature (heat or coldness) or pressure stress beyond what the protective function of the skin can handle. The skin s ability to endure different stressors can be lowered due to disease, for example, the skin s ability to stand pressure typically is affected by disease-related local ischemia (Robson et al., 2001). 

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