Department of Physiology: Blood Physiology-Critical thinking

Thinking questions:

1. Compare the osmotic pressure of plasma with that of plasma proteins.

2. Why is albumin the first plasma protein to appear in the urine in renal disease?

3. How does administration of anti-D help mothers with Rh incompatibility?

4. Why are vaccines given after 3 months of age generally more effective than those given before?

5. How does the Human Immunodeficiency Virus paralyse the immune system?

6. What is CD?

7. In the ABO system, if a blood group antigen is absent, why is the corresponding antibody present?

8. What is the youngest and oldest age at which a person may donate blood?

9. Why is circulatory overload following blood transfusion more serious if the patient has renal disease?

10. Should donor and recipient plasma be matched prior to transfusion?

11. Why does ABO incompatibility not give rise to haemolytic disease of the newborn (HDN) the way Rh incompatibility may?

12. In case of Rh incompatibility, why does anti-D given during pregnancy not damage fetal red cells the way naturally induced antibodies may?

13. Why does a clean straight line cut with a knife or blade bleed longer than an irregular injury caused by a stone?

14. Why does a faulty venipuncture give a bigger haematoma in elderly patients than in young patients?

15. Explain briefly why prothrombin time may be prolonged: a. after administration of antibiotics b. when the bile duct is obstructed c. in malabsorption syndrome d. in liver disease

16. Will dicumarol prevent the clotting of blood in a test tube? Give reason(s) for your answer.

17. Can a female suffer from haemophilia? If yes, why does it happen so rarely as to be generally considered impossible?

18. If the thymus of an experimental animal is removed immediately after its birth, the animal exhibits the following characteristics: (a) an increased susceptibility to infections, (b) decreased numbers of lymphocytes in lymphatic tissue, and (c) a greatly decreased ability to reject grafts. Explain these observations.

19. If the thymus of an adult experimental animal is removed, the following observations can be made: (a) No immediate effect occurs, and (b) after 1 year, decreases occur in the number of lymphocytes in the blood, the ability to reject grafts, and the ability to produce antibodies. Explain these observations

20. Tetanus is caused by bacteria that enter the body through wounds in the skin. The bacteria produce a toxin that causes spastic muscle contractions. Death often results from failure of the respiratory muscles. A patient goes to the emergency room after stepping on a nail. If the patient has been vaccinated against tetanus, he or she is given a tetanus booster shot, which consists of the toxin altered so that it is harmless. A patient who has never been vaccinated against tetanus is given an antiserum shot against tetanus. Explain the rationale for this treatment strategy. Sometimes both a booster and an antiserum shot are given, but at different locations on the body. Explain why both vaccinations are given and why they are injected in different locations.

21. An infant appears healthy until about 9 months of age, when he develops severe bacterial infections, one after another. Fortunately, the infections are treated successfully with antibiotics. When infected with the measles and other viral diseases, the infant recovers without unusual difficulty. Explain the different immune responses to these infections. Why did it take so long for this disorder to become apparent?

22. In hereditary hemolytic anemia, massive destruction of red blood cells occurs. Would you expect the reticulocyte count to be above or below normal? Explain why one of the symptoms of the disease is jaundice. In 1910, physicians discovered that hereditary hemolytic anemia can be treated successfully by removing the spleen. Explain why this treatment is effective.

23. Red Packer, a physical education major, wanted to improve his performance in an upcoming marathon race. About 6 weeks before the race, 500 mL of blood was removed from his body, and the formed elements were separated from the plasma. The formed elements were frozen, and the plasma was reinfused into his body. Just before the competition, the formed elements were thawed and injected into his body. Explain why this procedure, called blood doping or blood boosting, would help Red’s performance. Suggest any possible bad effects.

24. Some people habitually use barbiturates to depress feelings of anxiety. Barbiturates cause hypoventilation, a slower than normal rate of breathing, because they suppress the respiratory centers in the brain. What happens to the red blood count of a habitual user of barbiturates? Explain.

25. According to an old saying, “good food makes good blood.” Name three substances in the diet that are essential for “good blood.” What blood disorders develop if these substances are absent from the diet?

26. Grace has a plasma membrane defect in her red blood cells that makes them more susceptible to rupturing. Her red blood cells are destroyed faster than they can be replaced. Are her RBC, hemoglobin, hematocrit, and bilirubin levels below normal, normal, or above normal? Explain.

27. Shilpa has recently been on broad-spectrum antibiotics for a recurrent urinary bladder infection. While slicing vegetables, she cut herself and had difficulty stopping the bleeding. How could the antibiotics have played a role in her bleeding?

28. Mrs. Brown is in renal failure. Her recent blood tests indicated a hematocrit of 22. Why is her hematocrit low? What can she be given to raise her hematocrit?

29. Thomas has hepatitis, which is disrupting his liver functions. What kinds of symptoms would he be experiencing based on the role(s) of the liver related to blood?

30. A test for prothrombin time is used to identify deficiencies in the extrinsic clotting pathway; prothrombin time is prolonged if any of the factors are deficient. A test for activated partial thromboplastin time is used in a similar fashion to detect deficiencies in the intrinsic clotting pathway. Which factor would be deficient if a person had a prolonged prothrombin time but a normal partial thromboplastin time?

31. In the disease mononucleosis (“mono”), the spleen enlarges because of increased numbers of phagocytes and other cells. Common signs and symptoms of this disease include pale complexion, a tired feeling, and a lack of energy sometimes to the point of not being able to get out of bed. What might cause these signs and symptoms?

32. Almost half of our vitamin K is synthesized by bacteria that inhabit the large intestine. Based on this information, how could taking a broad-spectrum antibiotic for a long time cause frequent nosebleeds?

33. After Randy was diagnosed with stomach cancer, nearly all of his stomach had to be removed. Postoperative treatment included regular injections of vitamin B12. Why was this vitamin prescribed, and why were injections specified?

34. A patient has a low red blood cell count, and microscopic examination of his blood reveals an abnormally high proportion of circulating reticulocytes. Upon subsequent examination, the patient is diagnosed with a bleeding ulcer. This is surgically corrected, and in due course his blood measurements return to normal. What was the reason for the low red blood cell count and high proportion of reticulocytes?

35. A chemical called EDTA, like citrate, binds to (or “chelates”) Ca²⁺. Suppose a person had EDTA infused into their blood. What effect would this have on the intrinsic and extrinsic clotting pathways? How would these effects differ from the effects of aspirin on blood clotting?

36. A person has a hematocrit of 62. Can you conclude from this finding that the person has polycythemia? Explain.

37. There are diﬀerent forms of hemoglobin. Hemoglobin A is normal adult hemoglobin, which has two a chains and two b chains. The abnormal form hemoglobin S, which has a single “typographical error” in the genetic code for the b chains, causes RBCs to warp into fragile, sickle-shaped cells. Fetal RBCs contain hemoglobin F, the production of which stops soon after birth. Hemoglobin F contains two g chains instead of two b chains, along with the two a chains. This substitution increases hemoglobin’s affinity for O₂. Now researchers are trying to goad the genes that direct hemoglobin F synthesis back into action as a means of treating sickle cell anemia. Explain how turning on these fetal genes could be a useful remedy. (Indeed, the first eﬀective drug therapy for treating sickle cell anemia, hydroxyurea, acts on the bone marrow to boost production of fetal hemoglobin.)

38. What types of blood in the ABO and Rh blood systems could safely be transfused into a person with Type A1 blood?

39. Heather L., who has Rh-negative blood, has just given birth to her first child, who has Rh-positive blood. Both mother and baby are fine, but the doctor administers an Rh immunoglobulin preparation (short-lived antibodies against the Rh factor antigen) so that any future Rh-positive babies Heather has will not suﬀer from erythroblastosis fetalis (hemolytic disease of the newborn). During gestation (pregnancy), fetal and maternal blood does not mix. Instead, materials are exchanged between these two circulatory systems across the placenta, a special organ that develops during gestation from both maternal and fetal structures. Red blood cells are unable to cross the placenta, but antibodies can cross. During the birthing process, a small amount of the infant’s blood may enter the maternal circulation.

A. Why did Heather’s first-born child not have erythroblastosis fetalis—that is, why didn’t maternal antibodies against the Rh factor attack the fetal Rh-positive RBCs during gestation?

B. Why would any subsequent Rh-positive babies Heather might carry be likely to develop erythroblastosis fetalis if she were not treated with Rh immunoglobulin?

C. How would administering Rh immunoglobulin, immediately following Heather’s first pregnancy with an Rh-positive child, prevent erythroblastosis fetalis in a later pregnancy with another Rh-positive child? Similarly, why must Rh immunoglobulin be given to Heather after the birth of each Rh positive child she bears?

D. Suppose Heather were not treated with Rh immunoglobulin after the birth of her first Rh-positive child, and a second Rh-positive child developed erythroblastosis fetalis. Would administering Rh immunoglobulin to Heather immediately after the second birth prevent this condition in a third Rh-positive child? Why or why not?

40. Three decades have passed since the first cases of AIDS were reported in the United States and millions of research dollars have been spent studying this disease. Much has been learned, and drugs have been developed that delay or manage the condition, but no AIDS vaccine has been approved despite many unsuccessful attempts. Why does the frequent mutation of HIV (the AIDS virus) make it difficult to develop a vaccine against this virus?

41. What eﬀect would failure of the thymus to develop embryonically have on the immune system afer birth?

42. Medical researchers are currently working on ways to “teach” the immune system to view foreign tissue as “self.” What useful clinical application will the technique have?

43. When someone looks at you, are the cells of your body that person is viewing dead or alive?

44. A patient is suffering from edema in the right-lower limb. Explain why elevating and massaging the limb help remove the excess fluid.

45. If the thymus of an experimental animal is removed immediately after its birth, the animal exhibits the following characteristics: (a) an increased susceptibility to infections, (b) decreased numbers of lymphocytes in lymphatic tissue, and (c) a greatly decreased ability to reject grafts. Explain these observations.

46. If the thymus of an adult experimental animal is removed, the following observations can be made: (a) No immediate effect occurs, and (b) after 1 year, decreases occur in the number of lymphocytes in the blood, the ability to reject grafts, and the ability to produce antibodies. Explain these observations.

4. Adjuvants are substances that slow but do not stop the release of an antigen from an injection site into the blood. Suppose injection A is given without an adjuvant and injection B of the same amount of antigen is given with an adjuvant that causes antigen to be released over a period of 2–3 weeks. Does injection A or injection B result in the greater amount of antibody production? Explain.

47. Tetanus is caused by bacteria that enter the body through wounds in the skin. The bacteria produce a toxin that causes spastic muscle contractions. Death often results from failure of the respiratory muscles. A patient goes to the emergency room after stepping on a nail. If the patient has been vaccinated against tetanus, he or she is given a tetanus booster shot, which consists of the toxin altered so that it is harmless. A patient who has never been vaccinated against tetanus is given an antiserum shot against tetanus. Explain the rationale for this treatment strategy. Sometimes both a booster and an antiserum shot are given, but at different locations on the body. Explain why both vaccinations are given and why they are injected in different locations.

48. An infant appears healthy until about 9 months of age, when he develops severe bacterial infections, one after another. Fortunately, the infections are treated successfully with antibiotics. When infected with the measles and other viral diseases, the infant recovers without unusual difficulty. Explain the different immune responses to these infections. Why did it take so long for this disorder to become apparent? (Hint: Consider IgG.)

49. A patient has many allergic reactions. As part of the treatment scheme, doctors try to identify the allergen that stimulates the immune system’s response. A series of solutions, each is containing an allergen that commonly causes a reaction, is composed. Each solution is injected into the skin at different locations on the patient’s back. The following results are obtained: (a) At one location, the injection site becomes red and swollen within a few minutes; (b) at another injection site, swelling and redness appear 2 days later; and (c) no redness or swelling develops at the other sites. Explain what happened for each observation by describing what part of the immune system was involved and what caused the redness and swelling.

50. Ivy Hurtt developed a poison ivy rash after a camping trip. Her doctor prescribed a cortisone ointment to relieve the inflammation. A few weeks later, Ivy scraped her elbow, which became inflamed. Because she had some of the cortisone ointment left over, she applied it to the scrape. Was the ointment an effective treatment for the poison ivy? Was the ointment an appropriate treatment for the scrape?

51. Billie Boards was riding her skateboard down a newly paved road from the top of a hill. Part of the way down, she fell and skinned her knees on the asphalt. From the following list, choose the immune response(s) that occurred in the next several hours.

(1) increased capillary permeability

(2) chemotaxis of neutrophils

(3) coagulation

(4) release of mediators of inflammation

(5) increased mitosis of B lymphocytes

a. 1,2,3,4,5

b. 1,2,3,4

c. 1,2,3

d. 1,2

52. Upon first exposure to an antigen, a sequence of events results in antigen processing and an increase in the number of helper T cells. Given the following list of events, select the sequence that results in an increased number of helper T cells.

(1) Unprocessed extracellular antigen is ingested by a macrophage.

(2) The MHC II complex is presented at the cell surface.

(3) Costimulation occurs.

(4) Interleukin-1 is released from macrophages, and interleukin-2 is released from T lymphocytes.

(5) A specific helper T cell recognizes and binds to the MHC II complex.

(6) Mitosis of helper T cells takes place.

(7) The ingested antigen is broken down to fragments.

(8) The processed antigen and MHC II molecules are joined and transported to the cell surface.

a. 1,7,8,2,5,3,4,6

b. 1,7,8,5,2,3,4,6

c. 7,8,1,2,5,3,4,6

d. 1,2,3,4,5,6,7,8

e. 1,8,7,2,3,5,6,4