Movements of Glycogen

Starvation ( ] glucagon i insulin) Glycogen exhaustion Diabetes ( glucagon [ insulin) Glycogen degradation Excitement ( ] epinephrine) Glycogen degradation 

In muscle, all the glucose 6-phosphate arising from glycogen degradation (via glucose 1-phosphate) either goes down glycolysis or enters the HMP pathway. 

Glycogen is basically a short-term supply. In the absence of food intake, glycogen stores are depleted in about 24 hours. Over longer periods of fasting or starvation, glucose equivalents cannot be provided by glycogen stores and must come from protein sources. 

6-phosphate for local use through glycolysis, particularly if the muscle exerts itself so much that it restricts its blood supply and becomes anaerobic. Epinephrine has the same effect on liver glycogen ( degradation) however, liver ships the glucose out for consumphon by other tissues, including muscle. 

Fat provides a long-term storage form for energy (ATP). Fat provides zero glucose equivalents. 

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Phosphorylation Glycogen Metabolic Movements of Glycogen Fat Metabolic Movements of Fat Protein Metabolic Movements of Protein Tissue Cooperation Liver Muscle Ketone Bodies... 

Glycogen Formation of Glycogenin Binding of Condensation Movement of Not known, Hydration of... 

Figure 21.1 Metabolite and fuel movements in the fed state (high insulin/glucagon). Arrows indicate net movement of metabolites. There is a net synthesis of glycogen and fat in the liver. Glucose is converted to pyruvate and lactate during muscular activity. Both the Cori and alanine cycles are shown.

Activity Like the chemically and physiologically related (R)- noradrenaline (/f)-A., as an adrenal hormone, increases the degradation of glycogen in the liver and of fat in adipose tissue as well as the oxidative metabolism in muscle. As neutrotransmitter of the adrenergic nerve system (R)-A. increases heart rate as a sympathicomimetic, constricts blood vessels of the skin, mucous membranes, and abdominal viscera, and dilates vessels of the skeletal musculature and liver. The relaxation of smooth musculature in the intestine or bronchi effected by (R)-A. leads to a reduction of peristalsis (intestinal movements) or to dilatation of the bronchi. (S)-A. is about 12 times less active than (R)-adrenaline. 

Moreover, as a result of the operation of various ion pumps present in the membranes of the cell, ions may be very unevenly distributed within the various compartments and any factor that modifies the movement of ions through membranes may have an appreciable influence on metabolic processes. For example, Na and ions are required by the membrane ATPase which is believed to be involved in active transport processes, and movements of Ca are becoming increasingly implicated in the control of reactions, for example the breakdown of glycogen. 

From the earliest measurements of tissue calcium, it was clear that total calcium is largely a measure of stored calcium. Through the years, scientists have used a variety of indirect measures of [Ca2+]j. These include shortening of or tension in muscles secretion from secretory cells the activity of Ca2+-dependent enzymes, most notably glycogen phosphorylase and flux of K+, or K+ currents, as a reflection of Ca2+-activated K+ channels. In addition, investigators often use the radioactive calcium ion [45Ca2+] as an indirect indicator of Ca2+ concentrations and Ca2+ movements. 

Hochachka and Somero, 1977). Even glycogen and glucose are used intensively in red muscle of tuna under aerobic conditions (so-called aerobic glycolysis). In contrast, the sluggish scorpion fish and whiting can perform only relatively slow movements using the white muscle. 

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