Metabolism and Hormone Action

Tissues Store Biochemical Energy in Three Major Forms Each Tissue Makes Characteristic Demands and Contributions to the Energy Pool 

Brain Tissue Makes No Contributions to the Fuel Needs of the Organism 

Heart Muscle Utilizes Fatty Acids in Preference to Glucose to Fulfill Its Energy Needs Skeletal Muscle Can Function Aerobically or Anaerobically 

Adipose Tissue Maintains Vast Fuel Reserves in the Form of Triacylglycerols The Liver Is the Central Clearing House for All Energy-Related Metabolism  

Pancreatic Hormones Play a Major Role in Maintaining Blood Glucose Levels Hormones Are Major Vehicles for Intercellular Communication 

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Chapter 24, Integration of Metabolism and Hormone Action, explains the organization strategies used to integrate metabolic processes in a multicellular organism. Like the first chapter in part 4, the content of chapter 24 relates to all of the chapters on metabolism (chapters 11-24). This chapter emphasizes the fact that hormones and closely related growth factors play a dominant role in regulating metabolic activities in different tissues. 

Metabolism is tightly regulated by a number of mechanisms feedback inhibition, compartmentalization, covalent modification of enzymes (e.g., phosphorylation), and hormone action, among others. 

Many hormones affect fuel metabolism, including those that regulate appetite as well as those that influence absorption, transport, and oxidation of foodstuffs. The major hormones that influence nutrient metabolism and their actions on muscle, liver, and adipose tissue are listed in Table 43.1. 

Oppenheimer JH, Samuels HH. The nuclear receptor-triiodothyronine complex relationship to thyroid hormone distribution, metabolism and biological action. In Oppenheimer JA, Samuels HH, eds. Molecular Basis of Thyroid Hormone Action. New York Academic Press, 1983, pp. 1-34. 

Cyclic AMP Metabolism 530 Mode of Action of Cyclic AMP Calcium and Hormone Action 532 Conclusion 533... 

Figure 3.1 shows the nucleotides formed from the purine adenine - the adenine nucleotides, adenosine monophosphate (AMP), adenosine diphosphate (ADP) and adenosine triphosphate (ATP) - as well as the nucleotide triphosphates formed from the purine guanine and the pyrimidine uracil (see also section 10.3.2 for a discussion of the role of cyclic AMP in metabolic regulation and hormone action). 

Adrenaline (epinephrine) is a catecholamine, which is released as a neurotransmitter from neurons in the central nervous system and as a hormone from chromaffin cells of the adrenal gland. Adrenaline is required for increased metabolic and cardiovascular demand during stress. Its cellular actions are mediated via plasma membrane bound G-protein-coupled receptors. 

Bone metabolism comprises the processes of bone formation and bone resorption, the key actions by which skeletal mass, structure and quality are accrued and maintained throughout life. In the mature skeleton, anabolic and catabolic actions are mostly balanced due to the tight regulation of the activity of bone forming ( osteoblast) and bone resorbing ( osteoclast) cells through circulating osteotropic hormones and locally active cytokines. 

Metabolic pathways are regulated by rapid mechanisms affecting the activity of existing enzymes, eg, allosteric and covalent modification (often in response to hormone action) and slow mechanisms affecting the synthesis of enzymes. 

Be Pyridoxine, pyridoxal, pyridoxamine Coenzyme in transamination and decarboxylation of amino acids and glycogen phosphorylase role in steroid hormone action Disorders of amino acid metabolism, convulsions... 

Pyridoxal phosphate is a coenzyme for many enzymes involved in amino acid metabolism, especially in transamination and decarboxylation. It is also the cofactor of glycogen phosphorylase, where the phosphate group is catalytically important. In addition, vitamin Bg is important in steroid hormone action where it removes the hormone-receptor complex from DNA binding, terminating the action of the hormones. In vitamin Bg deficiency, this results in increased sensitivity to the actions of low concentrations of estrogens, androgens, cortisol, and vitamin D. 

Although clinical deficiency disease is rare, there is evidence that a significant proportion of the population have marginal vitamin Bg status. Moderate deficiency results in abnormalities of tryptophan and methionine metabolism. Increased sensitivity to steroid hormone action may be important in the development of hormone-dependent cancer of the breast, uterus, and prostate, and vitamin Bg status may affect the prognosis. 

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