Question 1

A 2-year-old boy has a bleeding disorder that is clinically indistinguishable from classical hemophilia (hemophilia A).However, tests for factor VIII activity reveal a normal protein with normal biological properties.Which of the following observations would suggest that the boy has hemophilia B?

Accepted Answer

Complementation tests can be used, on the basis of the fact that a 50% reduction in the concentration of a single clotting factor is not sufficient to prevent clotting.Mixed blood from two patients with hemophilia B has virtually no factor IX activity and therefore does not clot.

Question 2

The blood clotting system is blocked both in patients with classical hemophilia and as a result of high doses of coumarin-type anticoagulants.However, coumarin and related drugs can be deadly, whereas hemophiliac patients can live with their clotting disorder.The reason for this difference is:

Accepted Answer

In hemophiliac patients, the extrinsic and final common pathways are intact.

Question 3

Some clotting factors contain g-carboxyglutamate.The function of this unusual amino acid residue in the clotting factors is to bind calcium and to:

Accepted Answer

g-Carboxyglutamate is present in the clotting factors that attach to the surface of activated platelets.

Question 4

Heparin inhibits blood clotting by:

Accepted Answer

In the body, heparan sulfate proteoglycans on the surface of endothelial cells can inhibit thrombus formation in intact blood vessels by this mechanism.

Question 5

A patient presents with "blood" in the urine, but you are not sure whether the abnormal substance in the urine is hemoglobin or myoglobin.A blood test for which of the following proteins should help you to arrive at the correct conclusion?

Accepted Answer

Haptoglobin binds hemoglobin that is released during hemolysis, and the complex is removed by reticuloendothelial cells.This depletes circulating haptoglobin.

Question 6

A 32-year-old man sees the doctor because of chronic bronchitis.He used to smoke one pack of cigarettes per day for about 10 years but gave up smoking 5 years ago because of a persistent cough.Breath sounds suggest the presence of lung emphysema.The plasma protein that is most likely to be reduced in this patient is:

Accepted Answer

₁-Antiprotease is needed to prevent tissue damage by elastase and other proteases that are released from white blood cells during subclinical inflammation.

Question 7

A 40-year-old woman complains to her doctor about severe generalized itching for the past 5 months.She had no other symptoms, and she said that her alcohol consumption was low.She appeared to be slightly jaundiced, and a blood sample was analyzed with the following results: 
This patient is most likely suffering from:

Accepted Answer

The combination of high alkaline phosphatase and high g-glutamyltransferase levels is typical for cholestasis.Itching is most likely caused by bile acids.

Question 8

Patients with von Willebrand disease have abnormal bleeding tendency of varying severity.The process that is most directly abnormal in these patients is:

Accepted Answer

Von Willebrand factor binds to receptors on the platelet surface and glues the platelets to the exposed extracellular matrix.

Question 9

A patient consumes an excessive amount of bicarbonates to treat his heartburn.Which of the following values for total plasma CO₂ and plasma pH are expected as a result? The normal total CO₂ is 22 to 30 mmol, and the normal pH is 7.4.

Accepted Answer

The bicarbonate makes the blood slightly alkaline, and the respiratory center compensates by reduced breathing.Reduced breathing raises the plasma CO₂.

Question 10

A 52-year-old man was brought by his wife to the emergency room, suffering with chest pain.When questioned, his wife said that the pain had started about 4 hours earlier.You think that the most appropriate test to do at the time is cardiac troponin I but find that the test kit for this is empty.At this time, which of the following enzyme analyses would give you the same information?

Accepted Answer

This isoenzyme is specific for the myocardium, and it rises early after the onset of chest pain.

Question 11

A patient presents in the emergency room with abdominal pain.You suspect he may have acute pancreatitis.Which of the following enzyme analyses would help in confirming your diagnosis (or falsifying your hypothesis)?

Accepted Answer

α-Amylase is a digestive enzyme from the pancreas that leaks into the blood during destructive pancreatic diseases.

Question 12

One of the important regulatory roles of thrombin is the binding to receptors that can be activated by protease.These G protein-coupled receptors are important for:

Accepted Answer

The receptors actually suffer proteolytic cleavage.This irreversible process makes physiological sense in this case, inasmuch as platelet aggregation is irreversible.

Question 13

Antithrombin III is a circulating protease inhibitor that becomes active in the presence of:

Accepted Answer

This is the mechanism for the anticoagulant effect of heparin.

Question 14

The immunoglobulin (Ig) that is most directly involved in the symptoms of the common cold is:

Accepted Answer

IgE binds to the surface of mast cells, and causes degranulation when it encounters a matching antigen.This occurs in allergies and during infections, when antigens of viral or bacterial origin are encountered.

Question 15

Both heparin and warfarin can be used to treat patients who are at risk of thrombosis.Can these agents also be used to prevent blood clotting in the test tube?

Accepted Answer

Heparin acts on constituents of the plasma (antithrombin III and thrombin), whereas warfarin inhibits clotting factor synthesis in the liver.

Question 16

The following plasma and urine electrophoresis results were obtained from a 70-year-old man who complained to his doctor of back pain that he had had for several months and of feeling generally unwell.  This patient most likely has:

Accepted Answer

Bence Jones proteins are loose immunoglobulin light chains that are formed by some patients with multiple myeloma, in addition to the complete immunoglobulin that forms the band at the right end of the patient's plasma electrophoresis.Bence Jones proteins are small enough to be filtered into the urine very fast, forming the right band in the patient's urine.Because of renal excretion, they are not abundant in the plasma.Because the glomerular basement membrane becomes compromised in this condition, some albumin also appears in the urine.

Question 17

A mother finds her 4-year-old daughter with a bag of rat poison.The child has already eaten almost the whole amount in the bag.It turns out that the active ingredient of the rat poison is warfarin.On seeing this child in the emergency room 1 hour later, what should you do?

Accepted Answer

Warfarin is a competitive vitamin K antagonist.After regular consumption for a few days, or after a very high single dose, it can cause a fatal clotting disorder.This disorder develops slowly over several days, when the normal old clotting factors are gradually replaced by the defective ones that are made in the presence of the poison.

Question 18

Patients with vitamin K deficiency have prolonged bleeding because several clotting factors are abnormal, including:

Accepted Answer

Most of the proteases (but not the activator proteins) in the final steps of the cascade depend on vitamin K: factors VII, IX, and X and prothrombin.These clotting factors use γ-carboxyglutamate and calcium to attach to the surface of activated platelets.

Question 19

Elevations in the plasma level of which of the following enzymes indicate a bone disease, if the patient shows no signs of liver dysfunction?

Accepted Answer

A different isoenzyme of alkaline phosphatase is elevated in cholestasis and other liver-related conditions.Determination of g-glutamyl transferase would be one possibility to distinguish between cholestasis and bone disease in patients with elevated alkaline phosphatase levels.

Quiz 15: Plasma Proteins

A 2-year-old boy has a bleeding disorder that is clinically indistinguishable from classical hemophilia (hemophilia A) .However, tests for factor VIII activity reveal a normal protein with normal biological properties.Which of the following observations would suggest that the boy has hemophilia B?