By A. Marus. Monmouth College, Monmouth Illinois.
Not only are these cells important for the uptake or postprandial states 200 mg topamax amex. During metabolic aci- dosis 100 mg topamax overnight delivery, the uptake of glutamine by the kidney of nutrients, but they maintain a barrier against invading bacteria from the gut lumen is increased, and blood glutamine levels and are, therefore, part of our passive defense system. As a consequence, the gut takes functions, the intestinal mucosal cells are supplied with the amino acids required for up less glutamine. Liver The liver is the major site of amino acid metabolism. It is the major site of amino acid catabolism and converts most of the carbon in amino acids to intermediates of the TCA cycle or the glycolytic pathway (which can be converted to glucose or oxi- dized to CO2), or to acetyl CoA and ketone bodies. The liver is also the major site for urea synthesis. It can take up both glutamine and alanine and convert the 774 SECTION SEVEN / NITROGEN METABOLISM nitrogen to urea for disposal (see Chapter 38). Other pathways in the liver provide it with an unusually high amino acid requirement. The liver synthesizes plasma pro- teins, such as serum albumin, transferrin, and the proteins of the blood coagulation cascade. It is a major site for the synthesis of nonessential amino acids, the conju- gation of xenobiotic compounds with glycine, the synthesis of heme and purine nucleotides, and the synthesis of glutathione. AMINO ACID POOL AND NEUROTRANSMITTER SYNTHESIS A major function of amino acid metabolism in neural tissue is the synthesis of neu- rotransmitters. More than 40 compounds are believed to function as neurotransmit- ters, and all of these contain nitrogen derived from precursor amino acids. They include amino acids, which are themselves neurotransmitters (e. In general, neurotransmitters are formed in the presynaptic terminals of axons and stored in vesicles until released by a transient change in electrochemical potential along the axon. Subsequent catabolism of some of the neurotransmitter results in the formation of a urinary excretion product. The rapid metabolism of neurotransmitters requires the continuous availability of a precursor pool of amino acids for de novo neurotransmitter synthesis (see Chapter 47).
Many diseases alter the amounts of plasma proteins produced and buy 200 mg topamax visa, hence quality 200mg topamax, their concentration in the blood. These The hydrostatic pressure in an changes can be determined by electrophoresis of plasma proteins over the course of arteriole is the force that “pushes” a disease. Body Fluid Maintenance between Tissues and Blood osmotic pressure, plus the tissue pressure, is the force that “pulls” water from intersti- As the arterial blood enters the capillaries, fluid moves from the intravascular space tial spaces into the venular side of the capil- into the interstitial space (that surrounding the capillaries) because of what are lary. Thus, if the hydrostatic pressure is known as Starling’s forces. The hydrostatic pressure in the arteriolar end of the cap- greater than the osmotic pressure, fluid will illaries (~37 mm Hg) exceeds the sum of the tissue pressure (~1 mm Hg) and the leave the circulation; if it is less, fluid will osmotic pressure of the plasma proteins (~25 mm Hg). At the venous end of the capillaries, the hydrostatic pressure falls to approximately 17 mm Hg while the osmotic pres- In cases of severe protein malnutri- sure and the tissue pressure remain constant, resulting in movement of fluid back tion (kwashiorkor), the concentra- from the extravascular (interstitial) spaces and into the blood. Thus, most of the tion of the plasma proteins decreases, as a result of which the osmotic force bringing water back from the tissues is the osmotic pressure mediated by the pressure of the blood decreases. The distended bellies of famine vic- As indicated in Table 45. The major protein synthesized is albumin, the extravascular tissues because of the severely decreased concentration of plasma which constitutes approximately 60% of the total plasma protein, but because of its proteins, particularly albumin. Albumin syn- relatively small size (69 kDa) is thought to contribute 70 to 80% of the total osmotic thesis decreases fairly early under condi- pressure of the plasma. Albumin, like most plasma proteins, is a glycoprotein and is tions of protein malnutrition. CHAPTER 45 / BLOOD PLASMA PROTEINS, COAGULATION AND FIBRINOLYSIS 829 Table 45. Specific Plasma Binding Proteins Synthesized in the Liver Ceruloplasmin Binds copper; appears to be more important as a copper storage pool than as a transport protein; integrates iron and copper homeostasis Corticosteroid-binding globulin Binds cortisol Haptoglobin Binds extracorpuscular heme Lipoproteins Transport cholesterol and fatty acids Retinol-binding protein Binds vitamin A Sex hormone–binding globulin Binds estradiol and testosterone Transferrin Transports iron Transthyretin Binds thyroxine (T4); also forms a complex with retinol- binding protein Many drugs also bind to albumin, which may have important pharmacologic impli- In spite of the importance of albu- cations.