Hematopoietic System

HEMATOPOIETIC SYSTEM

HEMATOPOEITIC SYSTEM SAMPLE CASE 1

3-year-old male presents with epistaxis, pain, and vomiting. Physical examination reveals generalized lymphadenopathy. Lab test results confirm a diagnosis of ▪ Description of Blood Cells acute lymphoblastic leukemia. ▪ Blood Cell Degradation 1. Acute lymphoblastic leukemia is characterized by ______. ▪ Embryology/Anatomy/Physiology/Biochemistry A. Bence-Jones proteins in the urine Included Together B. Decreased numbers of all types of blood cells C. Tumor masses in multiple contiguous lymph nodes ▪ Pathology D. The presence of Reed-Sternberg cells in the bone marrow

SAMPLE CASE #2

▪ Answer: B - Decreased numbers of all types of blood cells 57-year-old male presents with bone pain and lethargy. Imaging reveals the presence of punched-out, lytic lesions. He is diagnosed with multiple myeloma. ▪ Bence Jones proteins are found in multiple myeloma. ▪ Reed-Sternberg cells are seen in Hodgkin’s lymphoma 1. Which of the following is indicative of this condition? 1. Bence Jones proteins 2. Reed-Sternberg cells 3. Agammaglobulinemia 4. Hairy B cells

▪ Answer: A - Bence Jones proteins ▪ Blood is a specialized connective tissue ▪ Light chain of antibodies that are found in the urine due to the excessive proliferation and ▪ Composed of extracellular matrix (plasma) and suspended RBCs, WBCs, and deposition within the glomeruli of the kidneys. platelets. ▪ Reed-Sternberg cells are seen in Hodgkin’s lymphoma ▪ Hairy B cells are malignant B cells seen in leukemia. ▪ Blood is formed in bone marrow, liver, spleen, and lymphoid tissue in utero ▪ Agammaglobulinemia is characterized by the absence or very low levels of gamma ▪ Exclusively formed in the bone marrow after birth globulin. ▪ Long bone in children and pelvis, cranium, vertebrae, and sacrum in adults

CELL TYPES

▪ Erythrocytes ▪ Leukocytes ▪ Granulocytes ▪ Agranulocytes

▪ Platelets

Image: Wikimedia Commons – Author: A. Rad

ERYTHROCYTES

▪ Biconcave-shaped allows for a larger size relative to volume to optimize gas exchange ▪ RBC precursor cells are located in bone marrow ▪ Contain hemogloblin which is covalently bound to heme ▪ Average life span is 120 days

Image: Wikimedia Commons – Author: Mikael Häggström and A. Rad

▪ Smaller than RBCs Neutrophils ▪ Acute inflammation, phagocytic ▪ Migrate through the endothelial cells of the blood vessels (diapedesis) ▪ Round-shaped within the bloodstream and pleomorphic within the connective tissue Eosinophils ▪ Immediate hypersensitivity/allergic and anti-parasitic responses ▪ Include granulocytes and agranulocytes Basophils ▪ Granules contain histamine Mast cells ▪ Allergy and anaphylaxis

AGRANULOCYTES PLATELETS

Lymphocytes ▪ Non-nucleated cell fragments that arise from megakaryocytes within the bone Tcells marrow. ▪ Helper T cells (CD4+) ▪ Suppressor T cells ▪ Life span is less than 14 days ▪ Killer T cells (CD8+) Bcells ▪ Secrete immunoglobulins Natural Killer (NK) cells ▪ Specialized T helper cell-independent lymphocyte

Monocytes ▪ Differentiate into macrophages in the tissue ▪ Phagocytic and antigen-presenting

HEMATOPOIESIS & HEMOGLOBIN HEMOSTASIS ▪ Oxygen-binding protein in red blood cells ▪ Hemoglobin ▪ One hemoglobin (Hb) molecule can carry up to 4 oxygen molecules each bound ▪ Heme synthesis to one of its four heme molecules. ▪ Hemostasis ▪ Oxygen binding causes hemoglobin to transform from a tense configuration into its relaxed form to facilitate oxygen binding. ▪ Hemoglobin is one of the major buffers of pH in the blood .

Copyright Pass NPLEX 2018 3 OXYGEN HEME SYNTHESIS CARRYING 2,3-BPG 2,3-BPG ▪ Occurs primarily in the bone marrow and liver ▪ Right shift = O2 dissociates ▪ Key regulatory enzyme is delta-aminolevulinate synthase from hemoglobin easily ▪ Cofactor = vitamin B6 (pyridoxal phosphate) ▪ 2,3-bisphosphoglycerate (BPG) is a byproduct of glycolysis in ▪ Uroporphyrinogen III decarboxylase does not require a co-factor unlike most RBCs and stabilizes the tense other decarboxylase enzymes. form of hemoglobin (decreases ▪ Synthesis is inhibited by lead because ALA dehydratase contains zinc. its affinity for O2) ▪ Lead binds the sulfhydryl groups in ferrochelatase ▪ Binding of CO2 to hemoglobin ▪ Negative feedback control of ALA synthase by the final heme product and high causes it to release oxygen iron levels. (Bohr effect)

Image: Wikimedia Commons – Author: Ratznium

HEMOSTASIS

▪ Vascular spasm restricts blood loss to allow the platelet plug to form. ▪ Platelets adhere to collagen via von Willebrand factor (vWF) which is secreted by endothelial cells and platelets. ▪ Coagulation ▪ Extrinsic or intrinsic pathway

▪ Heparin ▪ Stored in mast cells and basophils and released at sites of injury ▪ Prevents new clots from forming by binding to antithrombin thus activating it and inhibiting thrombin and clotting factor Xa.

Image: Wikimedia Commons – Author: Wmheric

BLOOD CELL DEGRADATION

▪ The spleen and other reticuloendothelial organs split hemoglobin into heme and globin. ▪ The heme ring is opened up by heme oxygenase into biliverdin and CO. ▪ Albumin carries bilirubin to the liver because it isn’t water soluble. ▪ Bilirubin is conjugated to two glucuronides by two isoforms of UDP-glucuronosyl transferase. ▪ Bilirubin diglucuronide is actively transported into the bile for excretion. ▪ Within the intestine gut flora can deconjugate the bilirubin and convert it to urobilinogen. ▪ Urobilinogens can be reabsorbed and oxidized back to bilirubin by hepatocytes.

Image: Wikimedia Commons – Author: Jng46 Image: Wikimedia Commons – Author: Johndheathcote

Copyright Pass NPLEX 2018 4 ▪ Iron from hemoglobin is stored bound to hepatic protein ferritin. ▪ If ferritin is saturated, iron is deposited within the cell hemosiderin. ▪ Hepcidin is the key regulator of iron absorption. ▪ Ferroportin is a transport protein for iron on erythrocytes. ▪ Hepcidin synthesis decreases when Fe levels are low by binding to ferroportin. ▪ Transferrin is a protein that transports iron in the blood. PATHOLOGY Vitamin C increases iron absorption within the intestines.

Heme iron-containing molecules: ▪ Hemoglobin, myoglobin, cytochrome P450 enzymes, peroxidases, catalase

Non-heme iron-containing molecules: ▪ Xanthine oxidase, ribonucleotide reductase, 5’-deiodinase

DISEASES INVOLVING PATHOLOGY PRODUCTION OF BLOOD

▪ Diseases involving production of blood cells ▪CELLSAnemias ▪ Iron deficiency anemia ▪ Hemolytic anemias ▪ Macrocytic anemia ▪ Clotting abnormalities ▪ Aplastic anemia ▪ Blood & lymph neoplasms ▪ Polycythemia vera ▪ Lymph node diseases ▪ Secondary polycythemia ▪ Infectious diseases of the blood

ANEMIAS IRON DEFICIENCY ANEMIA

▪ Any condition that causing the total number of RBCs, the amount of Hb, or the ▪ Due to chronic blood loss, increased need for blood and oxygen (pregnancy), volume of packed RBCs to decrease. deficiency intake or poor absorption. ▪ Caused hypoxia in tissues ▪ Microcytic, hypochromic anemia ▪ General symptoms include dyspnea on exertion, fatigue, dizziness, tinnitus, ▪ Fatigue, lethargy, pale mucous membranes, low Hb, low RBC, low hematocrit, headache small RBCs, low MCV, MCH and MCHC, low serum ferritin and iron. ▪ Long-term anemia can cause pallor, tachycardia, systolic ejection murmur, ▪ Long-term deficiency can result in chronic fatigue, low energy, and depression. orthostatic hypotension. ▪ Severe deficiency can result in gastritis, glossitis, Plummer-Vinson syndrome

▪ Vitamin B12 or folic acid deficiency or malabsorption which affects DNA synthesis. Pernicious anemia ▪ Folic acid deficiency can be caused by alcoholism, pregnancy, intestinal ▪ An autoimmune disease that reduces the absorption of food-bound B12 by destroying malabsorption, and folic acid antagonists intrinsic factor (IF) ▪ Megaloblastic anemia – enlarged abnormal prescursor cells in the bone marrow. ▪ Anti-parietal Ab and anti-intrinsic factor Ab ▪ Chief cells are damaged resulting in achlorhydria and lack of pepsinogen secretion ▪ Fatigue, lethargy, low RBC, low Hb, low hematocrit, large cells (increased MCV, MCH, and normal MCHC), ferritin and iron levels normal, low serum B12, low serum folate, ▪ Autoimmune atrophic gastritis often results. increased serum/urine methylmalonic acid (B12 deficiency), high serum ▪ Complications include recurrent GI infection and the same issues as B12 deficiency homocysteine levels (folate deficiency), polysegmented neutrophils, pancytopenia ▪ Complications include dementia, depression, glossitis, stomatitis, paranoia, neuropathies, ataxia, hyperreflexia, death

APLASTIC ANEMIA POLYCYTHEMIA VERA

▪ Severe anemia that results from a loss of the precursor cells of RBCs ▪ Myeloproliferative disorder that result in the neoplastic clonal proliferation of myeloid stem cells within the marrow. ▪ Results from toxic exposure (drugs, radiation, chemicals) or viral infection. ▪ Results in an increased number of circulating RBCs, increased hemoglobin, and a ▪ Bone marrow is hypocellular and all cell lines are decreased (peripheral moderate increase in circulating granulocytes and platelets. pancytopenia). ▪ Splenomegaly and decrease erythropoietin results. ▪ Weakness, fatigue, vertigo, irritability, tinnitus, facial flushing,extremity pain/erythema, blue/black spots on the skin can occur.

SECONDARY POLYCYTHEMIA HEMOLYTIC ANEMIAS

▪ Secondary to another condition that causes an increased need for RBCs ▪ Sickle cell anemia ▪ High altitude exposure, right-to-left shunts, shock, abnormal Hb ▪ Thalassemias ▪ Can also be caused by inappropriate production of erythropoietin by tumors ▪ Hereditary spherocytosis (renal cell carcinoma and hepatocellular carcinoma) ▪ Glucose-6-phosphate dehydrogenase deficiency ▪ Pheochromocytoma and Cushing’s syndrome can also cause this condition. ▪ High erythropoietin (EPO) results

▪ Destruction of RBCs ▪ Abnormal hemoglobin (HbS) is produced due to a genetic disease. ▪ Can cause anemia ▪ People who are heterozygous for the gene are generally asymptomatic. ▪ Jaundice, hemosiderosis, and usual anemia symptoms ▪ Those who are homozygous for the defective gene results in deformed RBCs. ▪ Can obstruct capillaries and are removed and destroyed by the spleen ▪ Causes include: ▪ Mechanical trauma to cells ▪ Severe hemolytic anemia, chronic leg ulcers, infarcts of the lungs and spleen, ▪ Heart valves, clots vaso-occlusive painful crisis (limbs, back, chest, abdomen), and aplastic crises ▪ Complement-induced damage ▪ Extravascular hemolysis (within the spleen)

GLUCOSE-6 PHOSPHATE THALASSEMIAS DEHYDROGENAGE

▪ Genetic disorders characterized by deficient production of either of the two DEFICIENCY globin chains of hemoglobin. ▪ X-linked disorder which causes hemolytic anemia during oxidative stress and is caused by a number of drugs ▪ Hypochromic, microcytic anemia ▪ G6PD is the rate-limiting enzyme for the HMP shunt ▪ Beta-thalassemias is the most common form in the Mediterranean and US ▪ It maintains NADPH levels and reduced glutathione ▪ Major and minor forms ▪ Defects in the beta chain of hemoglobin ▪ Major: anemia, splenomegaly, distortion of the facial and long bones, hemosiderosis ▪ Minor: generally asymptomatic

▪ Alpha-thalassemias is most common in Southeast Asia ▪ Results from a defect of one or more of 4 alpha hemoglobin genes ▪ The higher the number of deletion the more clinical abnormalities

HEREDITARY SPHEROCYTOSIS ERYTHROBLASTOSIS FETALIS

▪ Occurs when the mother and fetus have different blood types ▪ Genetic defect that causes spherical red blood cells that get stuck in the spleen and destroyed ▪ Mother is Rh- but baby is Rh+ where the mother generates antibody against the Rh antigens ▪ ABO incompatibility ▪ Autosomal dominant ▪ Hemolysis results in elevated bilirubin levels and jaundice. ▪ Risk of kernicterus, hepatosplenomegaly

▪ No complications occur in the initial pregnancy. ▪ In subsequent pregnancies, maternal antibodies cross the placenta and lyse fetal RBCs which causes anemia, hypoalbuminemia, and possibly high-output heart failure, or fetal death. ▪ Maternal sensitization and antibody production due to Rh incompatibility can be prevented by giving the woman Rh immune globulin.

▪ Disseminated intravascular coagulation (DIC) COAGULATION▪ Common hemorrhagic syndrome that occurs after uncontrolled activation of clotting factors and fibrinolytic enzymes throughout small blood vessels. ▪ Hemophilia ▪ Triggered by massive tissue damage, sepsis, pregnancy, cancer ▪ Thrombocytopenia ▪ Caused by the release of tissue thromboplastin or activation of the intrinsic pathway of coagulation ▪ Von Willebrand’s disease ▪ Results in prolonged PT, APTT, bleeding and thrombin time ▪ Vitamin K deficiency ▪ Acute DIC results in fibrin deposition everywhere and platelets and clotting factors are consumed ▪ Fibrin degradation products (D-dimers) inhibit fibrin polymerization and block platelet function. ▪ Outcome is lethal tissue necrosis and bleeding. ▪ Chronic DIC occurs primarily as a result of certain cancers, retained dead fetuses, hemangiomas, and aneurysms.

HEMOPHILIA THROMBOCYTOPENIA

▪ Blood coagulation disorders due to absence, deficiency, impaired activity of clotting factors which results in prolonged bleeding. ▪ Reduction in the number of platelets which results from decreased production, ▪ X-linked recessive sequestration, or increased destruction of platelets. ▪ Hemophilia A - Factor VIII deficiency ▪ Decreased production of platelets occurs with bone marrow damage, congenital ▪ Normal bleeding time, platelet count, prothrombin time but prolonged activated partial thromboplastin time abnormalities, or nutrition deficiencies (B12 and folate). ▪ Bleeding occurs in the muscles, subcutaneous tissues, and joints. ▪ Hemophilia B - Factor IX deficiency ▪ Petechial cutaneous bleeding and prolonged bleeding time. ▪ Similar to Hemophilia A ▪ Hemophilia C (Autosomal Recessive) - Factor XI deficiency ▪ Sequestration occurs in splenomegaly → causes platelets to accumulate in the spleen ▪ Mild (5-40% of factor levels) ▪ Increased destruction of platelets occurs in disseminated intravascular coagulation ▪ Asymptomatic or experience prolonged bleeding only after serious injury (DIC) or purpura. ▪ Moderate (1-5% normal factor levels) ▪ Prolonged bleeding after injuries and occasional spontaneous bleeding. ▪ Severe (<1% normal factor levels) ▪ Prolonged bleeding even after minor injury, frequent spontaneous bleeding

VON WILLEBRAND’S DISEASE VITAMIN K DEFICIENCY

▪ Platelets require vWF to adhere to the endothelial basement membranes in order ▪ Vitamin K is required for the synthesis of factor II (prothrombin), VII, IX, and X to begin clot formation. ▪ It negatively affects blood clotting. ▪ vWF is also important in stabilizing factor VIII ▪ Can be caused by malabsorption problems including biliary tract disease, ▪ vWF is either absent or abnormal in this disease which causes increased pancreatic diseases, and small intestine diseases. bleeding time (PTT). ▪ Autosomal dominant ▪ Acquired Von Willebrand disease can occur in some autoimmune diseases, aortic stenosis, Wilm’s tumor, and hypothyroidism. ▪ Results in impaired platelet adhesion and prolonged bleeding time. ▪ Results in mild prolonged bleeding to severe, hemophilia A-like spontaneously bleeding into joints.

▪ Leukemias ▪ Acute or chronic heterogenous neoplastic disorders of WBC (lymphoid or myeloid) ▪ Lymphoma ▪ Acute → poorly differentiated blast cells in circulation ▪ Hodgkin ▪ Chronic → more differentiated cells ▪ Non-Hodgkin ▪ Lymphocytic forms are most often B-cells ▪ Multiple myeloma ▪ Myelogeous forms show non-lymphocytic precursor cells (granulocytes)

Acute myelogenous leukemia (AML) ▪ At least 3 chromosomal translocations ▪ Anemia, fatigue, SOB, easy bleeding and bruising, frequent infections, thrombocytopenia HODGKIN’S LYMPHOMA Acute lymphocytic leukemia (ALL) (MC in children) ▪ Many chromosomal translocations ▪ Associated with Fanconi anemia, X-linked agammaglobulinemia, severe combined ▪ Mature B cell lymphoma (CD20 present on most cells) immunodeficiency ▪ Reed-Sternberg cells (bi- or multi-nucleated giant cells that are unable to make Abs) ▪ Anemia, fatigue, frequent infections, fever, dyspnea, lymphadenopathy, easy bruising, petechiae, arthralgias, thrombocytopenia ▪ Painless lymphadenopathy is most common, moderate enlargement of the spleen and Chronic myelogenous leukemia (CML) liver, pruritis, night sweats, fever, leukocytosis, weight loss. ▪ Associated with the Philadelphia chromosomal translocation between chromosomes 9 and 22 ▪ Pel-Ebstrain fever – cyclic high-grade fever ▪ Asymptomatic leukocytosis initially (high WBC), normal RBC and platelets ▪ Causes malaise, low-grade fever, frequent infections, gout, anemia, splenomegaly, easy bruising Chronic lymphocytic leukemia (CLL) (MC leukemia esp. in older men) ▪ Affects B cells (high WBCs), normal RBC and platelets ▪ Has a very slow progression ▪ Associated with ionizing radiation exposure ▪ Isolated lymphocytosis → anemia or thrombocytopenia, splenomegaly, lymphadenopathy

NON-HODGKIN’S LYMPHOMA MULTIPLE MYELOMA

▪ Malignant neoplasm of plasma cells ▪ B cell lymphoma and T cell lymphoma which are sometimes associated with EBV and HTLV-1 infection ▪ Affects 50-60 year old men and women ▪ Bone pain and fractures Burkitt’s lymphoma ▪ punched-out, lytic lesions in the bone caused by activation of osteoclasts ▪ Rare subtype caused by EBV infection which involves the maxilla or mandible ▪ Hypercalcemia (resorbed bone) → confusion and lethargy ▪ Lymphadenopathy, tonsilar enlargement, fatigue, anemia, fever, weight loss, night ▪ Increased bacterial infections sweats ▪ Rouleaux formation of RBC ▪ GI lymphomas cause diarrhea, abdominal pain, malabsorption, obstruction, perforation, and/or abdominal mass. ▪ Increased ESR ▪ Renal failure due to excess proliferation and deposition in the glomeruli of light chains of ▪ Most commonly affects the elderly Ab (Bence Jones proteins) ▪ M-spike (M protein is the most common IgG) ▪ Hyperglobulinemia

Copyright Pass NPLEX 2018 9 INFECTIOUS DISEASES OF THE BABESIOSIS BLOOD ▪ Babesiosis ▪ Infection caused by Babesia microti found in Ixodid ticks ▪ Malaria ▪ Most are asymptomatic or cause mild fever/flu-like symptoms ▪ Schistosomiasis ▪ Immunocompromised people suffer severe periodic fevers, chills, hemolytic anemia, malaria-like syndrome ▪ Complications include hemolytic anemia, ARDS, multiorgan failure, death

MALARIA

▪ Infection by Plasmodium falciparum, P. malariae, P. ovale, or P, vivas ▪ Jaundice, hepatomegaly, splenomegaly, anemia, malarial paroxysm which coincides with the release of merozoites from ruptures RBCs. ▪ Female Anopheles mosquitoes transmit the above. ▪ Paroxysms starts with malaise, abrupt chills and fever, rapid pulse, polyuria, nausea, ▪ Sporozoites infect hepatocytes and divide to form merozoites within the liver. headache, profuse sweating ▪ These erupt and invade RBCs where they become trophozoites and schizonts before full ▪ Occurs every 48 hour with P. vivax, P. falciform, and P. ovale and every 72 hours with P. malariae. maturing to merozoites. ▪ Giemsa stain is used to identify the species ▪ Merozoites erupt from RBCs and erythrocytes are destroyed and hemoglobin is ▪ Chronic infection with fatigue and lassitude and death can occur (exclusively from consumed. P. falciparum infection) ▪ Merozoites mature into male and female gametocytes which are consumed by a mosquito. ▪ P. ovale and P. vivax also produce hyponozoites which remain dormant in hepatocyes.

SCHISTOSOMIASIS

▪ Infection by Schistosoma spp. of the GI or genitourinary tracts. ▪ Blood flukes (worms)

▪ Urinary bladder, bowel, and liver dysfunction. ▪ Burrows through the skin and enters the blood steam ▪ Causes itching then later fever, hives, headache, cough, weight loss ▪ Complications include pulmonary and portal hypertension. ▪ Eggs induce granuloma formation and fibrosis which is associated with a high incidence of cancer.

Image: Wikimedia Commons – Author: Centers for Disease Control and Prevention

▪ Blood cells: what they originate from, what they turn into, where they are located, 1. Under which condition would hemoglobin release oxygen more readily? what they do A. Increase in pH ▪ Process of heme synthesis B. Decrease in temperature C. Metabolic alkalosis ▪ Clotting cascade, various pathways and factors D. Increase in 2,3-bisphosphoglycerate concentration ▪ Anemias

▪ Blood neoplasms 2. What is the rate limiting enzyme in heme synthesis? A. Uroporphyrinogen III decarboxylase B. Delta-aminolevulinate synthase C. Porphobilinogen synthase D. Ferrochelatase

ANSWERS IN THE NEXT SECTION…

▪ 1. D - Increase in 2,3-bisphosphoglycerate concentration ▪ Section 6: Immunological System ▪ Increase in pH/metabolic alkalosis, decrease in temperature, (and a decrease in 2,3- bisphosphoglycerate) cause the opposite

▪ 2. B - Delta-aminolevulinate synthase

▪ Delta-aminolevulinate synthase is the rate limiting enzyme of heme synthesis. It is the first enzyme of many.

▪ All the enzymes options are involved in heme synthesis.

▪ Porphobilinogen synthase converts ALA to porphobilinogen.

▪ Uroporphyrinogen III decarboxylase converts uroporphyrinogen III to coproporphyrinogen III

▪ Ferrochelatase is the final enzymatic step which converts protoporphyrin IX to heme via the addition of iron.