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What is the normal platelet count?
150,000-400,000 platelets/mL
Where is erythropoietin made? What stimulates the release of erythropoietin? What does erythropoietin do?
The kidneys make 90% of the erythropoietin and the liver 10%. Erythropoietin is released in response to hypoxia. Erythropoietin stimulates bone marrow to produce and release RBCs.
Explain why people at high altitudes develop increased Hgb levels.
At high altitude, inspired PO2 and PaO2 are low. Hypoxia stimulates erythropoietin production. Erythropoietin acts on bone marrow to stimulate increased RBC production. Polycythemia with increased Hbg results.
What is the normal life span of an RBC?
120 days
Where does the breakdown of Hgb occur? What are the breakdown products of Hgb?
Breakdown of Hgb occurs in the liver. Iron and porphyrin are the breakdown products.
Normal hemoglobin (HgbA) has what globin chains?
2 beta globin chains, and 2 alpha globin chains
The porphyrin arising from Hgb metabolism is converted to what substance?
What is the most important determinant of blood viscosity?
Hematocrit. A decrease in Hct decreases viscosity and can improve blood flow. However, there is a concomitant decrease in O2-carrying capacity with decreased Hct and eventually impaired O2 delivery.
Blood is how many times more viscous than water?
3x more viscous
When Hct increases to between 60 and 70%, blood viscosity increases how many fold? Do changes in either P50 or SaO2 alter blood viscosity?
An increase in Hct to between 60-70% results in a 10-fold increase in viscosity. Neither P50 nor SaO2 alter blood viscosity.
What component of the clotting mechanism becomes abnormal after aspirin therapy?
Platelet function
The most common platelet defect is due to what?
Inhibition of platelet cyclooxygenase activity by aspirin or other NSAIDs
How long are platelets inactivated by aspirin? By ketorolac and other NSAIDs?
Aspirin irreversibly inactivates COX for the life of the platelet (7-12 days or 1-2 weeks). NSAIDs reversibly inactivate COX, generally for a period of 24-96 hrs (1-3 days).
What clotting factors are synthesized by the liver?
All clotting factors except IV (calcium), VIII:vWF (Von Willebrand’s factor), and III (thromboplastin, tissue factor)
The production of what clotting factors are dependent on vitamin K?
Identify the 2 components of factors VIII. Do they act together or independently?
VIII:C and VIII:vWF. Factor VIII:C are VIII:vWF are products of different genes and have different functions.
What is the significance of factor VIII:vWF?
VIII:vWF is made in endothelial cells and is necessary for platelet adhesion to subendothelial structures (collagen) when endothelial damage occurs. VIII:vWF also regulates the production and release of factor VIII:C.
What clotting factor is not a plasma protein?
Factor IV (calcium)
What is the function of protein C in hemostasis? What are the mechanisms of protein C action?
Protein C is a vitamin K-dependent anticoagulant. Thrombin (IIa) activates protein C. Activated protein C then promotes fibrinolysis (clot resolution) by causing release of tPA from endothelial cells and by destroying plasminogen activator inhibitor. Activated protein C also cleaves factors Va and VIIa, promoting anticoagulation.
A patient has undergone several days of aspirin therapy for joint pain secondary to SLE. She is schedule for a partial gastrectomy due to gastric bleeding. What abnormality in clotting would be found?
Aspirin interferes with platelet function for 7-12 days (the life-span of the platelet). Bleeding time will be prolonged.
What substance breaks down fibrin, and where does this substance come from?
Plasmin digests fibrin. Plasmin is formed when the plasminogen system is activated by tPA.
What 2 changes are seen in the uncompensated, normovolemic patient with anemia?
Decreased Hct and decreased Hgb.
What 4 physiological compensatory mechanisms of anemia tend to restore tissue oxygenation in the anemic patient?
Flow, and hence O2 delivery, to the tissues in increased in the anemic patient because: (1) a decrease in blood viscosity, (2) dilation of peripheral vasculature (decreased SVR), and (3) an increased SV and increased CO. In addition, (4) tissues extract more O2.
What are 5 compensatory mechanisms to increase O2 delivery in chronic anemia?
(1) Increased CO, (2) increased 2,3-DPG levels, (3) increased P50 (rightward shift of oxyhemoglobin dissociation curve), (4) increased dissolved O2 in plasma volume, and (5) decreased blood viscosity (causing increased flow through tissues).
What is the treatment for the anemic patient?
pRBCs (provided the anemia is not due to hemorrhage)
Symptoms of anemia are unlikely to develop in an otherwise healthy patient until hemoglobin decreases below what level?
7 g/dL
Aplastic anemia is due to what? What is the most common cause of aplastic anemia?
Aplastic anemia is due to lack of a functioning of bone marrow. The most common cause of this disorder is the destruction of bone marrow stem cells by chemotherapeutic drugs.
Megaloblastic anemia, also known as pernicious anemia, develops when there is a deficiency of either of what 2 substances?
Vitamin B12 or folic acid. RBCs fail to mature. Large, immature erythrocytes cause megaloblastic anemia.
What kind of RBCs result in iron deficiency anemia?
Hypochromic, microcytic RBCs are typically found in iron deficiency anemia. When the quantity of iron in the plasma falls to very low levels, hypochromic (RBC with diminished Hgb) and microcytic (small, spherical RBCs) anemia results.
What causes hemolytic anemia?
Even though the number of RBCs formed is normal, the RBC life span is so short, that serious anemia results. Causes of hemolysis are diverse and include abnormalities of RBC membranes (hereditary spherocytosis), enzyme defects (glucose-6-phosphate dehydrogenase deficiency), and abnormal Hgb (sickle cell disease).
What hematological defect will you see in the patient who has a deficiency in glucose-6-phosphate dehydrogenase?
Chronic hemolytic anemia
What 2 drugs should be avoided in the patient who has a deficiency in glucose-6-phosphate dehydrogenase? Why?
Nitroprusside and prilocaine. These individuals are vulnerable to cyanide toxicity.
A patient with glucose-6-phosphate dehydrogenase deficiency presents for a surgical procedure. In addition to nitroprusside and prilocaine, what other drugs should be avoided?
Aspirin, penicillin, streptomycin, sulfonamides, quinidine, doxorubicin, and methalyne blue.
What drugs may trigger a hemolytic crisis 2-5 days after administration to the patient with a deficiency in glucose-6-phosphate dehydrogenase?
Nonopioid analgesics, antibiotics, sulfonamides, and antimalarials may trigger a hemolytic crisis five days after administration.
What segment of the population has a deficiency of glucose-6-phosphate dehydrogenase?
1% of the black population
What diseases result from defective rate of production of either alpha-globin strands or bet-globin strands?
The consequence of impaired synthesis of alpha-globin or beta-globin strands results from alpha-thalassemia or beta-thalassemia, respectively.
What is the hereditary defect in thalassemia?
There is a defect in the production of one or more of the subunits of hemoglobin. There is alpha thalassemia (defect in alpha chain) and beta thalassemia (defect in beta chain).
What sign is seen in the patient with thalassemia? Why does this occur?
Anemia is the principle sign seen in thalassemia. Various degrees of hemolysis and ineffective blood cell formation (decreased hematopoiesis) cause the anemia.
In patients of what geographical roots are thalassemias most common?
Southest Asian, African, Mediterranean, and Indian
What disease results from a mutation on each of the beta-globin strands of HgbA?
When the mutant beta-globin strand has valine instead of glutamate at the 6th position, HgbS results. The patient has sickle cell anemia. Mutations on the beta-globin strands results in sickle cell anemia.
What is HgbS? How does it differ from normal adult HgbA?
In sickle cell anemia, RBCs contain an abnormal type of hemoglobin called hemoglobin S. HgbS differs from HgbA by the substitution of valine for glutamic acid at the 6th position of the beta chain of the hemoglobin molecule.
Are patients with sickle cell train heterozygous or homozygous for HgbS? Does sickling occur frequently or infrequently in these patients?
Heterozygous. Unlike homozygous patients (HgbSS), sickling rarely occurs In patients with sickle cell train. Sickling occurs in patients with sickle cell train only under extreme hypoxemia or in low-flow states.
Are patients with sickle cell anemia heterozygous or homozygous for HgbS? What hematocrits are seen in these patients?
Homozygous (HgbSS). Hematocrits are typically 18-30%
What percent of black Americans have sickle cell anemia (are homozygous for HgbS) and what percent have sickle cell trait (are heterozygous for HgbS)?
0.2-0.5% homozygous (HgbSS – chromosomes from both maternal & paternal sides of the gene for HgbS). 8-10% heterozygous (only 1 chromosome has the gene for HgbS)
What percent of the total hemoglobin pool is HgbS in the patient with sickle cell anemia?
HgbS is > 70% of total hemoglobin
The patient with sickle cell trait has how much HgbA (normal) and how much HgbS?
HgbA = 55-60% and HgbS = 35-40%
By what physiological mechanism does HgbS alter RBC shape?
When the partial pressure of O2 is low and HgbS release O2, HgbS molecules attach to each other and form aggregates. This aggregation (polymerization) of HgbS molecules, which occurs in HgbS because of the substitution of valine for glutamic acid, results in deformation of the RBC into a sickle shape.
In what 3 ways does HgbS differ from HgbA?
HgbS: (1) has lower affinity for O2 (P50 for HgbS = 31 mmHg), (2) is less soluble in aqueous solution, and (3) polymerizes (aggregates) and precipitates in RBCs upon deoxygenation, causing RBCs to sickle.
Sickling in the patient with sickle cell disease begins when the PO2 falls below how many mmHg?
PO2 < 50 mmHg
What causes the crisis in sickle cell patients?
When HgbS is exposed to low concentrations of O2, precipitates of long crystals form, which damage cell membranes of RBCs, resulting in serious anemia. “Crisis” implies low O2 tension causing sickling which results in decreased blood flow through tissues causing a further decrease in O2 tension. This progresses rapidly causing a serious decrease in RBC mass within a few hours, leading to death.
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