Muscle Metabolism

Question 1

Primary purposes of skeletal muscle

Answer 1

Contraction to perform work (must make ATP), return plasma glucose levels to homeostasis following a carbohydrate meal

Question 2

Skeletal muscle response to a carbohydrate meal

Answer 2

Insulin binds insulin receptor, GLUT-4 goes to cell surface to bind glucose, then glucose-6-phosphate can be stored as glycogen (when ATP levels are sufficient) or used in glycolysis/TCA/ETC to make ATP

Question 3

Endocrine hormonal response to carbohydrate meal

Answer 3

Fasted state: Glucose low, insulin low, glucagon high

Fed state: Glucose high, insulin high, glucagon low

Question 4

Fuel source during exercise and fasting

Answer 4

Muscle glycogen used for the first hour or so, then blood-borne fatty acids and glucose can be used

Question 5

Muscle metabolism during fasting or exercise with glycogen

Answer 5

Epinephrine binds receptor on cell to activate the phosphorylation of glycogen into glucose-6-phopshate with the coactivation of AMP and Ca2+ to continue through glycolysis/TCA/ETC and produce ATP, in anaerobic conditions, lactate is made from pyruvate

Question 6

Muscle metabolism during fasting or exercise without glycogen

Answer 6

Fatty acids utilized using a FATP and converted into fatty acyl-CoA, then in the mitochondrial outer membrane is bound by carnitine to take into inner membrane, where it is turned back into FA-CoA and then into acetyl-CoA through beta oxidation for use in the TCA/ETC to make ATP

Question 7

Normal liver and muscle function

Answer 7

Liver can make and store glycogen from glucose and then release when needed to go to the muscles as glucose, which can also make and store glycogen, or can use the glucose in glycolysis/TCA/ETC to create ATP

Question 8

Glycogen storage disease basic mechanism - hepatic type

Answer 8

Liver cannot turn glycogen into glucose anymore, resulting in low blood glucose

Question 9

Glycogen storage disease basic mechanism - myopathic type

Answer 9

Glycogen cannot be metabolized in muscle so no ATP can be made in the absence of glucose, leading to low energy output

Question 10

Enzyme deficient in von Gierke’s disease

Answer 10

Glucose-6-phosphatase

Question 11

Enzyme deficient in Cori’s disease

Answer 11

Glycogen debrancher

Question 12

Enzyme deficient in McArdle disease

Answer 12

Muscle glycogen phosphorylase

Question 13

Enzyme deficient in Hers’ disease

Answer 13

Liver glycogen phosphorylase

Question 14

Enzyme deficient in Pompe’s disease

Answer 14

Acid maltase (alpha 1,4-glucosidase)

Question 15

Hepatic forms of glycogen storage diseases

Answer 15

Von Gierke’s, Cori’s, Hers’

Question 16

Muscle forms of glycogen storage diseases

Answer 16

Pompe’s, McArdle’s

Question 17

Von Gierke’s clinical presentation

Answer 17

Massive hepatomegaly, short stature, failure to thrive, severe hypoglycemia, retinal lesions

Question 18

Von Gierke’s laboratory findings

Answer 18

Increased lactate, pyruvate, triglycerides, cholesterol, uric acid in serum, decreased enzyme activity of increased glycogen levels on liver biopsy

Question 19

Cori’s clinical presentation

Answer 19

Similar presentation as von Gierke’s but less severe (hepatomegaly, short stature, hypoglycemia, retinal lesions)

Question 20

Cori’s laboratory findings

Answer 20

Normal lactate and uric acid, cholesterol, triglycerides in serum, can only be diagnosed with enzyme assay

Question 21

Hers’ clinical presentation

Answer 21

Mild hepatomegaly, mild hypoglycemia

Question 22

Hers’ laboratory findings

Answer 22

Minimal, increased liver glycogen

Question 23

Pompe’s clinical presentation

Answer 23

Massive cardiomegaly, hypotonia, early death from cardiorespiratory failure, milder forms in adults

Question 24

Pompe’s laboratory findings

Answer 24

Increased CPK levels

Question 25

McArdle’s clinical presentation

Answer 25

Exercise-induced muscle pain and cramps, rhabdomyolysis

Question 26

McArdle’s laboratory findings

Answer 26

Increased CPK with episodes, no blood lactate with exercise, increased glycogen and decreased enzyme activity on muscle biopsy