By M. Temmy. Southern Oregon University.

Rh is also known transfusions may be used for any condition in which as the D antigen order pristiq 100mg visa. People with this antigen are said to be Rh there is loss of a large volume of blood pristiq 100mg online, for example: positive discount 100 mg pristiq with visa; those who lack this protein are said to be Rh neg- ◗ In the treatment of massive hemorrhage from serious ative buy pristiq 50 mg overnight delivery. If Rh-positive blood is given to an Rh-negative per- mechanical injuries son cheap pristiq 100mg overnight delivery, he or she may produce antibodies to the “foreign” Rh ◗ For blood loss during internal bleeding, as from bleed- antigens. The blood of this “Rh-sensitized” person will then ing ulcers destroy any Rh-positive cells received in a later transfusion. A mother who is Rh negative may develop ◗ For blood replacement in the treatment of hemolytic antibodies to the Rh protein of an Rh-positive fetus (the disease of the newborn fetus having inherited this factor from the father). Red cells from the fetus that enter the mother’s circulation Caution and careful evaluation of the need for a blood during pregnancy and childbirth evoke the response. In a transfusion is the rule, however, because of the risk for subsequent pregnancy with an Rh-positive fetus, some of transfusion reactions and the transmission of viral dis- the anti-Rh antibodies may pass from the mother’s blood eases, particularly hepatitis. This condition is called hemolytic disease of the Use of Blood Components newborn (HDN). HDN is now prevented by administration of im- Most often, when some blood ingredient is needed, it is not whole blood but a blood component that is given. These preformed antibodies clear the mother’s circulation A common method for separating the blood plasma of Rh antigens and prevent stimulation of an immune re- from the formed elements is by use of a centrifuge (SEN- sponse. In many cases, a baby born with HDN could be trih-fuje), a machine that spins in a circle at high speed to saved by a transfusion that replaces much of the baby’s separate components of a mixture according to density. When a container of blood is spun rapidly, all the formed Checkpoint 13-13 What are the blood antigens most often in- elements of the blood are pulled into a clump at the bot- volved in incompatibility reactions? They are thus separated from the plasma, which is less dense. The formed elements may be further separated and used for specific purposes, for ex- ample, packed red cells alone or platelets alone. The gen- Blood can be packaged and kept in blood banks for emer- eral term for this procedure is hemapheresis gencies. To keep the blood from clotting, a solution such (hem-ah-fer-E-sis) (from the Greek word apheresis mean- as citrate-phosphate-dextrose-adenine (CPDA-1) is ing “removal”) If the plasma is removed and the formed added. Blood banks usually have all Use of Plasma Blood plasma alone may be given in an types of blood and blood products available. It is impor- emergency to replace blood volume and prevent circula- tant that there be an extra supply of type O, Rh-negative tory failure (shock). Plasma is especially useful when blood because in an emergency this type can be used for blood typing and the use of whole blood are not possible, any patient. It is normal procedure to test the recipient such as in natural disasters or in emergency rescues. Plasma separated from the cellular ele- gery if needed. This practice eliminates the possibility of ments is usually further separated by chemical means into incompatibility and of disease transfer as well. Such autol- various components, such as plasma protein fraction, ogous (aw-TOL-o-gus) (self-originating) blood is stored serum albumin, immune serum, and clotting factors. The packaged plasma that is currently available is ac- tually plasma protein fraction. Further separation yields Whole Blood Transfusions serum albumin that is available in solutions of 5% or 25% The transfer of whole human blood from a healthy person concentration. In addition to its use in treatment of cir- to a patient is often a life-saving process. Whole blood culatory shock, these solutions are given when plasma THE BLOOD 273 proteins are deficient. They increase the osmotic pressure death usually results. If the loss is gradual, however, over of the blood and thus draw fluids back into circulation. Possi- creased because these blood components can be treated ble causes of chronic blood loss include bleeding ulcers, with heat to prevent transmission of viral diseases. If the cause of the blood loss can be corrected, the minister fluids known as plasma expanders. These are body is usually able to restore the blood to normal. This cell-free isotonic solutions used to maintain blood fluid process can take as long as 6 months, and until the blood volume to prevent circulatory shock.

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The pyridoxal phosphate then pulls electrons away from the bonds around the -carbon generic pristiq 100mg mastercard. The result is transamination order pristiq 100 mg free shipping, deamination buy cheap pristiq 100 mg on-line, decarboxylation pristiq 100mg online, -elimination buy pristiq 100 mg mastercard, racemization, and -elimination, depending on which enzyme and amino acid are involved. The coenzyme FH4 is required in certain amino acid pathways to either accept or donate a one-carbon group. Chapter 40 describes the reactions of FH4 in much more detail. Pyridoxal phosphate covalently attached to an amino acid substrate. The arrows indicate which bonds are broken for the various types of reactions in which pyridoxal phos- phate is involved. The X and Y represent leaving groups that may be present on the amino acid (such as the hydroxyl group on serine or threonine). The coenzyme BH4 is required for ring hydroxylations. The reactions involve molecular oxygen, and one atom of oxygen is incorporated into the product. BH4 is important for the synthesis of tyrosine and neurotransmitters (see Chapter 48). AMINO ACIDS DERIVED FROM INTERMEDIATES OF GLYCOLYSIS Four amino acids are synthesized from intermediates of glycolysis: serine, glycine, cysteine, and alanine. Serine, which produces glycine and cysteine, is synthesized from 3-phosphoglycerate, and alanine is formed by transamination of pyruvate, the product of glycolysis (Fig. When these amino acids are degraded, their car- bon atoms are converted to pyruvate or to intermediates of the glycolytic/gluco- neogenic pathway and, therefore, can produce glucose or be oxidized to CO2. Serine In the biosynthesis of serine from glucose, 3-phosphoglycerate is first oxidized to a 2-keto compound (3-phosphohydroxypyruvate), which is then transaminated to form phosphoserine (Fig. Phosphoserine phosphatase removes the phosphate, forming serine. The major sites of serine synthesis are the liver and kidney. Serine can be used by many tissues and is generally degraded by transamination to hydroxypyruvate followed by reduction and phosphorylation to form 2-phospho- glycerate, an intermediate of gycolysis that forms PEP and, subsequently, pyruvate. Glucose Glycine Serine also can undergo -elimination of its hydroxyl group, catalyzed by serine dehydratase, to form pyruvate. Regulatory mechanisms maintain serine levels in the body. When serine levels fall, 3-Phosphoglycerate Serine serine synthesis is increased by induction of 3-phosphoglycerate dehydrogenase and by release of the feedback inhibition of phosphoserine phosphatase (caused by higher lev- els of serine). When serine levels rise, synthesis of serine decreases because synthesis 2-Phosphoglycerate Cysteine of the dehydrogenase is repressed and the phosphatase is inhibited (see Fig. Glycine Pyruvate SO4 Glycine can be synthesized from serine and, to a minor extent, threonine. The major route from serine is by a reversible reaction that involves FH4 and pyridoxal phos- Alanine phate (Fig. Tetrahydrofolate is a coenzyme that transfers one-carbon groups Fig. Amino acids derived from interme- at different levels of oxidation. It is derived from the vitamin folate and is discussed diates of glycolysis. These amino acids can be in more detail in Chapter 40. The minor pathway for glycine production involves synthesized from glucose. Their carbons can threonine degradation (this is an aldolase-like reaction because threonine contains a be reconverted to glucose in the liver. CHAPTER 39 / SYNTHESIS AND DEGRADATION OF AMINO ACIDS 717 CH2 O P CH2OH Glycolysis Glucose HO P O C H PEP Pyruvate – – COO COO 3-Phosphoglycerate 2-Phosphoglycerate NAD+ ADP 3-phosphoglycerate dehydrogenase NADH ATP CH O P COO– 2 C C – COO CH2OH 3–Phospho- Glycerate hydroxypyruvate Glutamate NAD+ PLP α-Ketoglutarate NADH CH2 O P CH2OH + H 3 – – COO COO 3-Phospho-L-serine Hydroxypyruvate phosphoserine – PLP phosphatase Alanine Pi CH2 OH Pyruvate + H 3 COO– Serine Fig.

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The liver also synthesizes bile acids for fat digestion in the intestine buy pristiq 100 mg with amex. The liver recy- cles cholesterol and triglyceride through its uptake of intermediate density lipopro- tein (IDL) buy pristiq 100mg on line, chylomicron and VLDL remnants purchase pristiq 50mg visa, and low-density lipoprotein (LDL) particles purchase 100mg pristiq overnight delivery. Because of its protective nature and its strategic location between the gut and the systemic circulation order 100mg pristiq with visa, the liver has “first crack” at all compounds that enter the blood through the enterohepatic circulation. Thus, xenobiotic compounds can be detoxified as they enter the liver before they have a chance to reach other tissues. Muscle cells contain unique pathways that allow them to store energy as creatine phosphate and to closely regulate their use of fatty acids as an energy source (see Chapter 47). The adenosine monophosphate (AMP)-activated protein kinase is an important regulator of muscle energy metabolism. Muscle is comprised of different types of contractile fibers that derive their energy from different sources. For exam- ple, the slow-twitch type I fibers use oxidative energy pathways, whereas the type II fast-twitch fibers use the glycolytic pathway for their energy requirements. The nervous system consists of various cell types that are functionally intercon- nected so as to allow efficient signal transmission throughout the system (see Chapter 48). The cells of the central nervous system are protected from potentially toxic com- pounds by the blood-brain barrier, which restricts entry of compounds into the nerv- ous system (ammonia, however, is a notable exception). The brain cells communicate with each other and with other organs, through the synthesis of neurotransmitters and neuropeptides. Many of the neurotransmitters are derived from amino acids, most of which are synthesized within the nerve cell. Because the pathways of amino acid and neurotransmitter biosynthesis require cofactors (such as pyridoxal phosphate, thi- amine pyrophosphate, and vitamin B12), deficiencies of these cofactors can lead to neuropathies (dysfunction of specific neurons within the nervous system). Because of the restrictions imposed by the blood-brain barrier, the brain also must synthesize its own lipids. An adequate supply of lipids is vital to the central nervous system because they are constituents of the myelin sheath that surrounds the neurons and allows them to conduct impulses normally. The neurodegenerative disorders, such as multiple sclerosis, are a consequence of varying degrees of demyelination of the neurons. Connective tissue, which consists primarily of fibroblasts, produces extracellular matrix materials that surround cells and tissues, determining their appropriate posi- tion within the organ (see Chapter 49). These materials include structural proteins (collagen and elastin), adhesive proteins (fibronectin), and glycosaminoglycans (heparan sulfate, chondroitin sulfate). The unique structures of the proteins and car- bohydrates found within the extracellular matrix allow tissues and organs to carry out their many functions. A loss of these supportive and barrier functions of con- nective tissue sometimes leads to significant clinical consequences, such as those that result from the microvascular alterations that lead to blindness or renal failure, or peripheral neuropathies in patients with diabetes mellitus. The major hormones that influence nutrient metabolism and their actions on muscle, liver, and adipose tissue are listed in Table 43. It promotes the storage of nutrients as glycogen in liver and muscle, and as triacylglycerols in adipose tissue. It also stimulates the synthesis of proteins in tissues such as muscle. At the same time, insulin acts to inhibit fuel mobilization. The term counterregula- tory means that its actions are generally opposed to those of insulin (contrainsu- lar). The major action of glucagon is to mobilize fuel reserves by stimulating glycogenolysis and gluconeogenesis. These actions ensure that glucose will be available to glucose-dependent tissues between meals. Epinephrine, norepinephrine, cortisol, somatostatin, and growth hormone also have contrainsular activity. Thyroid hormone also must be classified as an insulin counterregulatory hormone because it increases the rate of fuel consump- tion and also increases the sensitivity of the target cells to other insulin counter- regulatory hormones. Insulin and the counterregulatory hormones exert two types of metabolic regu- lation (see Chapter 26). The first type of control occurs within minutes to hours of the hormone–receptor interaction and usually results from changes in the cat- alytic activity or kinetics of key preexisting enzymes, caused by phosphorylation or dephosphorylation of these enzymes.

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