Enzymes in health and diseas

Question 1

Energy depletion as a mechanism leading to the release of cytosolic enzymes:

Answer 1

Reduce ATP –>efflux of K+ and influx of Na+ (inhibition of Na-K ATPase –> cell swelling –> reversible damage –> over time: irreversible damage –> influx of calcium and formation of free radicals

Question 2

Effects of energy depletion

Answer 2

Stretching (due to swelling),
Degradation of phospholipids,
Decomposition of the cytoskeleton

Question 3

Generalized septicemia

Answer 3

Irreversible membrane damage causing massive increases in serum enzyme activities

Question 4

Cell necrosis causes

Answer 4

liberation of organelle enzymes

Question 5

Presence of enzymes in serum is evidence for

Answer 5

severe cell injury

Question 6

Enzymes released from intra–>extracellular space frist appear in…

Answer 6

Interstitial fluid

Question 7

Enzymes released from blood/endothelial cells first appear in

Answer 7

Intravascular space

Question 8

Pathway from interstitial fluid –>blood

Answer 8

through LYMPH** OR capillary wall (depends on permeability) ** important part of movement from intracellular–> intravascular space. Not always immediately present in blood as lymphatic flow is slow

Question 9

Mechanisms of enzyme elimination from the blood (2):

Answer 9

1. Renal excretion (not of general importance as most enzymes are larger than this method supports [ex. ~70-160 kDa])
2. Uptake by cells that degrade enzymes

Question 10

Kidney excretion is available for enzymes w/ mw lower than:

Answer 10

60 kDa

Question 11

Mechanism for degradation of enzymes among cells:

Answer 11

Receptor mediated endocytosis

Question 12

Myocardial infarction

Answer 12

Heart attack, occlusion of a coronary artery

Question 13

MI occurs as a result of… (2):

Answer 13

lack of O2 delivery to the myocardial tissue

lack of removal of metabolites

Question 14

MI is influenced by:

Answer 14

severity of ischemia (inadequate blood supply),
age,
sex

Question 15

First few seconds of MI

Answer 15

Anoxia –> depletion of energy stores –> OxPhos shutdown –> Anaerobic respiration –> leakage of intracellular electrolytes (espec. K+)

Question 16

First few minutes (reversible damage)

Answer 16

Ischemia –> impaired clearnce of metabolites (ex. inorganic P, lactate, adenosine, H+)

Question 17

Irreversible damage associated with MI:

Answer 17

Release of macromolecules
Activation of lipoprotein lipases
Loss of mitochondrial control
Spillage of mitochondrial components

Question 18

Fate of released cellular components

Answer 18

Ions/metabolites: intracellular space –> interstitial space –> circulation
Macromolecules: delayed clearance as they are released only through irreversible injury and are large and require LYMPHATIC DRAINAGE

Question 19

CK equilibrium reaction

Answer 19

Creatine + ATP Creatine phosphate + ADP

Question 20

CK

Answer 20

important in diagnosis of MI, two subunits either M or B type producing 3 different isoenzymes: BB, MB, and MM

Question 21

Stats on CK

Answer 21

High levels in neonate, fall w/in first few wks of life
Total CK is elevated in MI and injury
Males have higher values than females
Activities of CK increase w/ age + body weight

Question 22

Injuries elevating CK

Answer 22

Skeletal muscle injury and disease
IM injections
Hypothyroidism
Generalized convulsions
Cerebral injury
Infectious disease
Prolonged hypothermia

Question 23

CK: MB (CK-2)

Answer 23

has advantages over other CK isoenzymes, found in trace concentrations in skeletal muscles and higher in the myocardium

Question 24

CK nomenclature

Answer 24

due to electrophoretic mobility, most anodal receiving the lowest number

Question 25

CK: MM (CK-3)

Answer 25

found in skeletal muscle and myocardium

Question 26

CK: BB (CK-1):

Answer 26

found in the brain and gastrointestinal tract

Question 27

Method of measurement

Answer 27

Antibody based CK-MB mass assays (ug/L) | Double monoclonal antibody-based sandwich type assay

Question 28

Lactate dehydrogenase (LD)

Answer 28

responsible for catalysing the reversible reduction of pyruvate to lactate NADH + pyruvate lactate + NAD late marker of MI as it stays in the blood longer Important in glycolysis when O2 is limiting widespread tissue distribution (NONSPECIFICITY)

Question 29

Individuals who exercise heavily have...

Answer 29

high LD

Question 30

LD results for MI are obscured by...

Answer 30

Hemolysis, due to its presence in red cells

Question 31

The heart contains high amounts of

Answer 31

LD1

Question 32

Myoglobin and Troponin

Answer 32

cardiac proteins of diagnostic value in MI

Question 33

Myoglobin

Answer 33

found in skeletal muscle and heart does not exist as isoenzymes low specificity small size

Question 34

Troponin

Answer 34

3 subunits: C, I, and T Sequence unique to the cardiac muscle (high specificity) assays have monoclonal antibodies binding to the most stable region of the cTnI molecule exists in many forms in the blood

Question 35

Biochemical markers in ischemic injury

Answer 35

Initial lag phase... and then: CK: elevates after 20 hours and decreases rapidly (specifically MB), not a good early marker (NOT A GOOD TEST) Myoglobin: spike 10h after onset and rapid decrease (NOT USED) TroponinI: longer response time, elevates after 20 hours and stays elevated (GOLD STANDARD FOR MI). Stay elevated. Sensitivity higher, specificity higher. LD, LD-1: extremely useful late marker due to prolonged half life in serum. LD-1 is better specificity than LD, sensitivity similar in both. A ratio >1 is indicative of MI in LD-1>LD-2. Hemolysis gives a flipped pattern of this (NOT USED ANYMORE)

Question 36

High sensitivity troponins

Answer 36

Usually hsTnT Can measure levels in almost 100% of healthy individuals reliably 10x lower detection limit Early diagnosis Problem: number of false positives increases as we move decision threshold to the left, causes other than MI Rising/falling pattern is critical to distinguish between non-cardiac conditions and acute cardiac conditions

Question 37

Universal definition of MI

Answer 37

a rise and or fall in cTn in patients w/ evidence of myocardial ischemia with at least one cTn value above the 99th percentile of reference group

Question 38

Pancreatic enzymes of diagnostic value (2):

Answer 38

Amylase | Lipase

Question 39

Acute pancreatitis

Answer 39

inflammatory disease of the pancreas which when the attack is resolved permits restoration of normal function Causes: alcohol, biliary tract disease, post-surgery, and sever hypertriglycerdemia Symptom: acute abdominal pain, hypotension, respiratory failure, hyperglycemia, hypocalcemia, hypoalbuminemia

Question 40

Amylase

Answer 40

highest concentration in saliva and pancreas secreted into the duodenum --> hydrolysis of macromolecular carbohydrates Two types: pancreatic type and salivary type, present in about equal concentrations in normal serum and urine low mw The only serum enzyme normally found in urine isoenzyme p-amylase has high sensitivity and specificity

Question 41

Lipase

Answer 41

hydrolysing triglycerides pancreatic isoenzyme interacts with long chain triglycerides colipase is required for full activity (coenzyme) Rises to a higher extent than amylase sensitivity and specificity are higher than amylase

Question 42

Trypsin

Answer 42

20-30x more costly than amylase/lipase similar results to same not routinely used