Muscle Ch 10 D&P Flashcards
What is creatine kinase and what does it do? Where does it come from?
Makes ATP available for muscle contraction (it phosphorylates, its a kinase).
Creatnine phosphate + CK = ADP > ATP (it takes a phosphate from CP). At rest CK moves the process in reverse. The muscle has reservoir of CP to make ATP for high energy muscle contraction.
Its pretty muscle specific, skeletal and cardiac and a little in the brain.(ITS PROBABLY IMPORTANT TO REMEMBER A LITTLE COMES FROM THE BRAIN).
What are the four muscle enzymes?
CK
AST
ALT
LDH
What does AST do and where does it come from? Compare to CK.
Helps make oxaloacetate and glutamate for the Krebs cycle. Present in many cells and so is not tissue specific but muscle and liver are the major sources.
Has longer half life than CK.
Hemolysis may elevate it.
What is ALT, where does it come from and when do you see elevations?
It makes pyruvate and glutamate for the Krebs cycle. Its mostly a liver enzyme by reported elevated in some muscle dz like muscular dystrophy.
May be muscle specific in large animals cause hepatic ALT activity is very low.
What is LDH and where does it come from? Compare to the other muscle enzymes.
Cytosolic enzyme that makes L Lactate to pyruvate.
Comes from muscle, liver and RBCs.
Less useful than CK and AST cause its not tissue specific and elevated by even mild hemolysis.
What is the most sensitive serum enzyme indicator of striated muscle damage and the enzyme of choice for skeletal muscle damage?
CK - its very sensitive, even minor injuries, injections, txport, etc. strenuous exercise may cause increases
How fast does CK return to normal once muscle injury stops?
Within 48-72 hours, it maxes out at 12 hours post injury.
If persistently high that means continued muscle injury. The magnitude of increase generally correlates with extent of muscle injury.
But in cats even minor increases are considered significant and anorexic cats may have increased CK activity.
Compare the half life of CK and AST?
Serum AST activity increases slower than CK and LDH after muscle injury and may persist several days after injury abates.
Where else may CK be measured besides serum and where does it come from?
Remember it also has activity in the brain and can be measured in the CSF and this does not affect serum CK activity. (increased serum CK in CNS dz likely originates from injury to muscle from convulsions, recumbency etc.
INcreased serum LDH has been associated with what condition in what two species?
Lymphoma (L for LDH and L for lymphoma) in dogs and cattle.
What are troponins?
Globular proteins bound to tropomyosin that help modulate interaction between actin and myosin in striated muscle. Released in the blood during degen or necrosis of cardiac muscle cells.
There are three different ones I, T and C and either I or T are measured as markers of acute cardiac injury. CTnI is more common but you can also measure CTnT. Short half life so they decrease quickly unless injury ongoing.
What are natriuretic peptides?
They include A type (ANP) and brain / B type (BNP).
They are released as prohormones from cardiac muscle in response to mechanical stress or cardiac muscle stretching.
Active ANP and BNP contribute to cardiovascular homeostasis by inhibiting the renin-angiotensin-aldosterone system, promoting vasodilation and decreasing blood pressure. They are markers for congestive heart failure in humans.
What is myoglobin and what is it a marker for? Compare to AST an CK. What about in the urine? How do you diff it from Hgb?
Its a heme protein and txports and stores oxygen inmuscle cells.
Normally absent in serum.
Sensitive and specific marker of muscle necrosis. Enters blood rapidly (faster than CK and AST) but also falls rapidly once injury abates.
It does not bind plasma proteins (unlike Hgb) and passes readily thru the glomerulus. Plasma may not become discolored - usually its normal and that helps diff it from hemoglobinemia and hemolysis as a cause for discolored urine, also the Hct would be normal and there should be some other evidence of muscle injury.
Which electrolyte is related to muscle injury?
- K+ in intracellular fluid and degen or necrosis of a large muscle mass may release enough protein to cause hyperkalemia.
- HYPP in horses is d/t Na channel defect and K+ is high right after clinical signs but not between episoides.
- Hypokalemic polymyopathy may occur in cats with chronic renal failure or fed acidifying diets.
Where does lactate come from and what is blood lactate a reflection of ?
Byproduct of anaerobic glycolysis (prod by skeletal muscle, RBCs, brain, skin, renal medulla.
Balance between lactate production, metabolism by the liver in gluconeogenesis and elimination in urine.
INCREASE rapidly after exercise in some mitochondrial and lipid storage mypathies and in Labs with hereditary myopathy.
