By Z. Agenak. Butler University.
As rigid rules they could preclude the discovery of more than one type of neurotransmitter or one form of neurotransmission proven inderal 80 mg. Nevertheless, the criteria have been widely employed and often expanded to include other features which will be considered as subdivisions of the main criteria. PRESENCE Distribution and concentration It is generally felt that a substance is more likely to be a NT if it is unevenly distributed in the CNS although if it is widely used it will be widely distributed. Certainly the high concentration (5±10 mmol/g) of dopamine, compared with that of any other monoamine in the striatum or with dopamine in other brain areas, was indicative of its subsequently established role as a NT in that part of the CNS. This does not mean it cannot have an important function in other areas such as the mesolimbic system and parts of the cerebral cortex where it is present in much lower concentrations. In fact the concentra- tion of the monoamines outside the striatum is very much lower than that of the amino acids but since the amino acids may have important biochemical functions that necessitate their widespread distribution, the NT component of any given level of amino acid is difficult to establish. Nevertheless, useful information can be deduced from patterns of distribution. Glycine is concentrated more in the cord than cortex and in ventral rather than dorsal grey or white matter. This alone would be indicative of a NT role for glycine in the ventral horn, where it is now believed to be the inhibitory transmitter at motoneurons. GABA, on the other hand, is more concentrated in the brain than in the cord and in the latter it is predominantly in the dorsal grey so that although it is an inhibitory transmitter like glycine it must have a different pattern of activity. Section of dorsal roots and degeneration of afferent fibres produces a reduction in glutamate and substance P which can then be associated with sensory inputs. Temporary reduction of the blood supply to the cord causes preferential destruction of interneurons and a greater loss of asparate and glycine, compared with other amino acids and so links NEUROTRANSMITTER SYSTEMS AND FUNCTION: OVERVIEW 27 those amino acids with interneurons.
Body Water Is Distributed in The blood plasma water comprises about one fourth of the Several Fluid Compartments ECF or about 3 cheap inderal 40mg visa. The interstitial fluid and lymph are considered together be- Total body water can be divided into two compartments or cause they cannot be easily separated. The water of the in- spaces: intracellular fluid (ICF) and extracellular fluid terstitial fluid and lymph comprises three fourths of the (ECF). The interstitial fluid directly bathes most body cells, of cells in our body. The ECF is comprised of fluid outside and the lymph is the fluid within lymphatic vessels. In a young adult man, two thirds of the body wa- blood plasma, interstitial fluid, and lymph are nearly iden- tical in composition, except for the higher protein concen- tration in the plasma. Age Men Both Sexes Women Transcellular fluids include cerebrospinal fluid, aqueous hu- mor of the eye, secretions of the digestive tract and associated 0–1 month 76 organs (saliva, bile, pancreatic juice), renal tubular fluid and 1–12 months 65 bladder urine, synovial fluid, and sweat. In these cases, the 1–10 years 62 fluid is separated from the blood plasma by an epithelial cell 10–16 years 59 57 17–39 years 61 50 layer in addition to a capillary endothelium. The epithelial 40–59 years 55 52 layer modifies the electrolyte composition of the fluid, so that 60 years and older 52 46 transcellular fluids are not plasma ultrafiltrates (as is intersti- tial fluid and lymph); they have a distinct ionic composition. There is a constant turnover of transcellular fluids; they are continuously formed and absorbed or removed. Impaired for- CHAPTER 24 The Regulation of Fluid and Electrolyte Balance 405 mation, abnormal loss from the body, or blockage of fluid re- Cellular water cannot be determined directly with any moval can have serious consequences. It can, however, be calculated from the differ- ence between measurements of total body water and extra- cellular water. The Indicator Dilution Method Measures Plasma water is determined by using Evans blue dye, Fluid Compartment Size which avidly binds serum albumin or radioiodinated serum The indicator dilution method can be used to determine albumin (RISA), and by collecting and analyzing a blood the size of body fluid compartments (see Chapter 14). In effect, the plasma volume is measured known amount of a substance (the indicator), which should from the distribution volume of serum albumin. The as- be confined to the compartment of interest, is adminis- sumption is that serum albumin is completely confined to tered.