This is the process of production of the formed elements of the blood, involves mitosis and differentiation of stem cells and progenitor cells  into the many specialized types of blood cells.  

This process mainly occurs in red bone marrow, in bones of axial skeleton and in proximal heads of humerus and femur. 

The red bone marrow contains  the stem cells and progenitor cells in a supporting stroma, consisting of  fibroblasts, macrophages, fat cells, and marrow sinusoids (thin walled blood vessels with large endothelial gaps).

Both are precursors of blood cells.  

Stem cells – can differentiate into all of the mature cell types, also can make new stem cells   

Progenitor cells – derived from stem cells, but now committed to a given cell type, so that each cell type has one parent progenitor cell type.  These cannot differentiate into all cell types and cannot make new stem cells.

This is the formation of RBCs in red bone marrow. 

Adequate iron, B12, and folic acid are necessary for RBC production. 

There are several linked mitotic divisions, early hemoglobin synthesis, cells become smaller and smaller, nucleus shrinks and

condenses until finally lost.  

Reticulocytes are almost mature RBC with no nucleus and residual RNA.  After 3 days RNA is lost and these become mature RBCs.   Mature RBC have no organelles and no nucleus, but do have metabolic ability to maintain hemoglobin, cell membrane, and anaerobic energy production

Takes 8 days total for production of mature RBC, and itslifespan of RBC is about 120 days due to wear and tear

This is the formation of WBCs which are called leukocytes in bone 

marrow. 

Leukocytes include granulocytes, monocytes, and lymphocytes

Granulocytes

(these include polymorphonuclear neutrophils /PMNs)

Lifespan is hours to few days, circulating granulocytes are mature, functional cells, can travel to tissues and carry out defensive function, PMNs are“first responders” and are predominant in acute inflammation.

Lifespan 2 to 3 months, immature in circulation, must mature in tissues to become functional macrophages.

Macrophages are most predominant in chronic inflammation

lymphocytes are T and B cells, antibody-making plasma cells that are derived from B cells, and natural killer (NK) cells.

These are all made in bone marrow. 

T cells mature in thymus, and B cells mature in bone marrow

How are platelets formed from megakaryocyte progenitor cells?

Membranes of megakaryocyte progenitor cells become discontinuous, cells extend portions of themselves through openings in marrow sinusoids

Fragments of these cells are shed into blood – à these fragments become platelets.

Platelets are fragments of cytoplasm and do not have a nucleus

Mesh of protein filaments (fibrin formed by clotting/coagulation cascade) with formed elements to form red mass

Forms in tissue spaces adjacent to damaged blood vessel, occurs only adjacent to  veins, capillaries, small arterioles  (blood flow in large arteries interferes with clot formation)

A weak plug made of platelets is formed first.  Exposure of collagen by injured tissue leads to binding of vonWillebrand factor (vWF), which normally circulates in the blood, to collagen and  also to receptors on platelets (vWF binds to platelet and collagen at the same time, linking them).  This leads to platelet activation.

Platelet activation leads to 2 events:  

a. platelet degranulation – release of granules containing ADP à promotes platelet  aggregation (sticking together) and release of more ADP (more sticking together)    

b. release of arachidonic acid from platelet membrane à converted to TXA2 inside platelet by COX 1 enzyme à TXA2 released to outside from platelet à activation of more platelets  à more ADP and TXA2 released  by platelets à more platelet aggregation (sticking together).  Also TXA2 constricts injured blood vessels.

Platelet GPIIb/IIIa receptors bind fibrinogen (each end of fibrinogen binds to a platelet), so that platelets become linked together.  But the fibrinogen must be converted to stable fibrin to stabilize the clot. 

The coagulation cascade will convert the fibrinogen to fibrin.  In order to assure that the coagulation cascade physically occurs near the fibrinogen so that fibrin is formed, platelets express a protein factor (platelet factor 3 (PF3) – NOT a circulating clotting factor) on their surfaces.  

PF3 binds clotting factor V, which leads to binding of other clotting factors to platelet,  so that coagulation cascade takes place where needed.   

Keep in mind that the circulating clotting factors, made in liver,  are always circulating in blood in inactive form –  they are activated in coaguolation cascade

extrinsic pathway: initiated by tissue factor which is released by injured endothelial cells, fibroblasts, and other cells 

This pathway eventually causes conversion of prothrombin to thrombin, yields small amounts of fibrin   

Intrinsic pathway: initiated by exposure of Hageman factor  (factor XII) to injured tissue surfaces, thrombin (Factor IIa) and factor VIIa formed by extrinsic pathway, and more thrombin formed by intrinsic pathway, boosts intrinsic pathway at several points.  

Intrinsic pathway yields large amounts of fibrin to stabilize clot

How does the body ensure that coagulation and blood clotting does not become uncontrolled and damaging to the body?

There are 3 ways that the body  balances and controls coagulation.  

a. hemodynamics – movement of blood removes and dilutes clotting factors    

b. endothelial mediation – endothelial cells release anticlotting substances.

c. the fibrinolytic system –a mechanism for clot breakdown so that healing and repair can take place

What are the anticlotting substances that are released by endothelial cells of the blood vessels, and a circulating anticlotting substance?

a. nitric oxide (NO) – triggers release of prostacyclin, NO is also a vasodilator 

b. prostacyclin – a prostaglandin (PG), inhibits platelet aggregation at healthy endothelial cells   

c.  tissue factor pathway inhibitor (TFPI) – blocks extrinsic pathway by interference with tissue factor  

d. thrombomodulin – inhibits extrinsic pathway  

e. tPA  à plasmin formation;  A circulating inactive enzyme, made in liver, that breaks down thrombin and some other clotting factors is antithrombin III – this is activated by natural heparin on endothelial cell surfaces

This system is a mechanism for clot breakdown so that repair can take place. 

Plasminogen (precursor of plasmin) is converted to plasmin (an enzyme) by t-PA (also an enzyme).  

Plasmin is an enzyme that degrades fibrin, fibrinogen, and many other clotting factors à breaks down clots and prevents further clotting

This is activated partial thromboplastin time (APTT) –

Used to monitor activity of heparin.  

Calcium and activating agent added to patient blood sample, time to form fibrin clot is measured 

1) normal baseline time to clot is 25 to 40 sec  

2) therapeutic range for heparin is 1.5 to 2.5 X baseline

3) assesses function of intrinsic and common pathways

a. prothrombin time (PT) –useful to monitor activity of warfarin (Coumadin)  

1) normal time to clot is 9 to 12 sec    

2) assesses activity of extrinsic and  common pathways        

b. international normalized ratio (INR)  

1) INR = (PT in patient with drug  / normal baseline PT in patient without drug) ^ISI    

ISI = international sensitivity index  - this is necessary since activating agents added to patient blood sample have variable sensitivities, manufacturer states ISI for the present “batch”  so that lab techs can calculate correct value for INR   

2)  for most indications, INR should be between 2 and 3

pinpoints of hemorrhage, seen in skin, brain

larger areas of bleeding, > 2 cm –  color changes from purple, blue, green, yellow

large volume of blood trapped in a soft tissue

a. Insufficient circulating platelets, that can lead to bleeding  problems.     

b. some possible causes - 

• bone marrow suppression
• drugs (gold salts, thiazide diuretics, some antibiotics, heparin, others)
• disseminated intravascular coagulation (DIC)
• hemiangiomas
• protozoal infections
• splenomegaly

Compare idiopathic thrombocytopenic purpura (ITP) with thrombotic thrombocytopenic purpura (TTP)

A) ITP - most common reason, binding of Ab or AbAg complexes to platelets – platelets stick together in complexes so that they are effectively removed from circulation, often follows viral inection, leads to petechiae and purpura of skin and  mucous membrane

B) thrombotic thrombocytopenic purpura (TTP) – Ab damages endothelium of blood vessels, platelets adhere to endothelium so that they are effectively removed from circulation, leading to thrombocytopenia, also there is widespread coagulation in small blood vessels in TTP

These are both  seen early in life, ecchymoses and hematomas are typical, bleeding may occur  excessively, or with no apparent cause

a.Von Willebrand’s disease – autosomal dominant, deficiency of vWF, platelets cannot bind to  injured surfaces, also defects in coagulation cascade    

b. hemophilia  -  sex linked, affects males  – lack of factor VIII or  factor IX

a. impaired hepatic synthesis of clotting factors – as with advanced liver disease, vitamin K deficiency

 b. disseminated intravascular coagulation (DIC) – depletion of clotting factors  

c. anticoagulant drug therapy

• immune complex deposition in blood vessels  - as with SLE, drugs, allergies 
• direct damage – bacterial toxins, snake venom   
• genetic problems causing defective blood vessels – such as hereditary hemorrhagic telangiectasia, Marfan’s syndrome
• vitamin C deficiency (scurvy) – poor formation of blood vessels 
• Cushing’s disease – breakdown of blood vessels   
• senile purpura – age related – hands, wrists, upper arms, calves are mainly affected   

Results include - bleeding from microvasculature, called vascular purpura – mainly seen in skin and GIT (petechiae and purpura) , kidneys (hematuria)

This is a deficiency of RBCs with decreased oxygen carrying capacity of blood.  iI Hb < 7 – 8g/dl, symptoms are  pallor, weakness, lethargy, exercise intolerance, cardiac arrhythmias, hepatic necrosis, fatty change in heart and liver

A protein growth factor that stimulates formation of RBCs, released by juxtaglomerular cells of kidney in response to low oxygen levels in blood

a. hematocrit = volume of cells / total blood volume – a measure of RBC volume –  normal is 45%             

b.mean corpuscular volume (MCV)  - also a measure of RBC volume   

• 1) normal MCV – normocytic   
• 2)  low MCV – microcytic anemia    
• 3)  high MCV – macrocytic anemia             

c. mean corpuscular Hb concentration (MCHC) – a measure of oxygen carrying capacity of blood   

• 1) normal MCHC – normochromic
• 2) low  MCHC – hypochromic  (not as much red colored Hb)     
• 3) high MCHC – hyperchromic(large amount of red colored Hb)    

d. reticulocyte count – reticulocytes are large, immature RBCs - provides information as to cause of deficient RBCs   

• 1) low – means bone marrow production problem    
• 2)high – means response to destruction of RBCs due to increased erythropoetin  - more immature RBCs (reticulocytes) are formed, but mature RBCs are  destroyed

a. Pancytopenia – deficiency of all formed elements of blood due to bone marrow problems -- impaired production or RBCs (causes anemia) and all other blood cells.      

Causes  may be

• 1) genetic – developmental abnormality  
• 2)      due to bone marrow suppressants – infection, chemotherapy, radiation, drugs 
• 3) idiopathic     

b. aplastic anemia – this is a type of pancytopenia 

All precursor cells are  reduced in number, replaced by fat cells in bone marrow à anemia, bleeding, infections

What are the characteristics of iron deficiency anemia and what usually causes this?

Since B12 is necessary for normal DNA synthesis, this deficiency leads to pancytopenia, and includes anemia. 

This anemia is macrocytic (high MCV), normochromic (Normal MCHC), and megaloblastic (many enlarged reticulocytes/RBC precursors since they cannot divide to form mature RBCs)     

Also, B12 deficiency results in loss of myelin à neuropathy.

The most common cause of B12 deficiency is autoimmune chronic gastritis.

This leads to intrinsic factor (IF) deficiency.  Since IF is necessary for absorption of B12 across GI mucosa, B12 is not absorbed.

This deficiency leads to pancytopenia and anemia.   Anemia due to autoimmune chronic gastritis with lack of IF is called pernicious anemia.

Since folic acid is necessary for normal DNA synthesis, this deficiency leads to pancytopenia, and includes anemia.

This anemia is macrocytic (high MCV), normochromic (Normal MCHC), megaloblastic anemia (enlarged reticulocytes/ RBC precursors since they cannot divide to form mature RBCs).   

However, folic acid deficiency, unlike B12 deficiency, does NOT result in loss of myelin and neuropathy.

 In chronic disease states, anemia is believed to occur due to a variety of mechanisms.

• sickle cell anemia
• sickle cell trait
• thalassemia

Describe sickle cell anemia and sickle cell trait. 

A)  sickle cell anemia -  patient has abnormal Hb (HbS instead of HbA) which forms long filaments, distorting shape of RBCs into sickle shape.   

• Patient has 2 copies of defective gene for abnormal Hb. 
• Occurs mainly in Blacks of Africa, also occurs in Saudi Arabia, India, eastern Mediterranean.   
• Life span of “sickled” RBCs is much shorter than for normal RBCs. 
• Sickled  RBCs may become trapped in microcirculation à obstructed blood flow and ischemia.  Clinical course is variable – most patients have chronic anemia and weakness.  
• Sickle crisis is when a patient has episode of acute sickling -à obstructed blood flow à ischemic organ  damage, pain due to bone necrosis. 

Causes of sickle crisis include

• hypoxemia
• acidosis
• cold weather
• pregnancy.

B). sickle cell trait – 1 copy of defective gene, patients are carriers of this gene. Causes few problems, but increased risk of of splenic damage if hypoxia

How does thalassemia cause anemia, and what is the difference between thalassemia major/Cooley’s anemia and thalassemia minor? 

• Thalassemia is a genetic disorder causing impaired Hb synthesis. 
• This looks like iron deficiency anemia (also causes impaired Hb synthesis) and is microcytic (low MCV), and hypochromic (low MCHC) anemia. 
• Occurs mainly in Mediterranean ethnic groups.  

In thalassemia major/Cooley’s anemia – patient has 2 defective genes, a  severe condition, patient needs frequent blood transfusions. 

In thalassemia minor, patient has one defective gene and is asymptomatic

List and explain causes of extrinsic hemolytic anemia in patients that are genetically normal.

a.       immune hemolysis – Abs bind to antigen on RBC surfaces à more rapid clearance from blood or  lysis due to complement

Examples include Rh antigen or blood type transfusion reaction

b. autoimmune hemolytic anemias – 50% associated with autoimmune disease, 50% idiopathic

c. drug related hemolytic anemia – many drugs can stick to cell surfaces and act as antigens – including penicillins, methyldopa, L-dopa, sulfonamides – Ab then bind and cause lysis due to complement

d. mechanical hemolysis – due to RBC trauma or physical injury – such as artificial heart valves

e. other causes – snake venom, microorganisms

Splenomegaly can result in excessive clearance of formed blood elements by spleen, results in anemia, thrombocytopenia, leukopenia.

Removal of spleen may be necessary.

What is the difference between absolute and relative polycythemia? 

Polycythemia is increased RBC concentration in blood.

Absolute polycythemia is increased RBC numbers with normal plasma volume.  

Relative polycythemia is due to plasma deficiency (lower volume) with normal RBC numbers. 

Both types result in increased hematocrit values.

a. secondary polycythemia due to  increased erythropoetin (EPO) secretion by kidneys – increased EPO can be induced by hypoxia – as with lung or heart conditions, high altitude, heavy smoking (CO displaces oxygen from hemoglobin binding sites), abnormal hemoglobin; also by tumors or  decreased  renal blood flow       

b. primary absolute polycythemia – increased proliferation of stem cells  à  increased RBCs this is a benign “tumor” condition, decreased EPO secretion

c.   polycythemia vera – idiopathic – in males 60-80 years old

a. decreased plasma volume – dehydration, extensive burns, diuresis, diarrhea    

b. smoker’s polycythemia – reason unknown

c. stress polycythemia –  occurs in “driven” males – predisposed to heart and brain vascular disease

• Leukopenia – deficiency of leukocytes; 

• Leukocytosis –nonneoplastic elevation of WBC counts, due to normal, increased physiological demand;

• leukemia – neoplastic elevation of WBCs in blood

• Neutropenia is a leukopenia in which there is a deficiency of neutrophils, defined as < 1,800 / mm3.
• There is significantly increased risk of infection  if < 500 /mm3.   
• Agranulocytosis is severe neutropenia with numbers of neutrophils  < 200 – 300/ mm3.    

Typical symptoms of infection due to neutropenia – malaise, fever, weakness, fatigue, infections of oral and pharyngeal mucosa

Causes of neutropenia include 

• 1) reduced production of neutrophils - cancer chemotherapy, radiation therapy, other drugs, tumors, infections, deficiency of B12 or folic acid
• 2) increased clearance of neutrophils – autoimmune destruction, drug-induced immune effects, hypersplenism/splenomegaly

acute inflammation      

chronic autoimmune diseases, chronic infections

acute viral infections, chronic infections

Leukemias are primary malignant “tumors” of leukocyte precursors in bone marrow       

The neoplastic leukocyte precursors are rapidly dividing, but do not produce a tumor mass – normal bone marrow is displaced and suppressed, and in most cases there is also an excessive number of “pre-leukocyte” cells in different stages of differentiation in the blood.  

These include:

• agranulocytosis with susceptibility to infection
• anemia with fatigue and weakness
• thrombocytopenia with bleeding
• bone destruction with pain
• metastases with compromise of function to spleen (splenomegaly) liver (hepatomegaly), meninges, lymph nodes (lymphadenopathy)

a. acute – acute onset, more severe symptoms, immature, undifferentiated cell forms   

b. chronic – gradual onset, less severe symptoms, differentiated cell forms

What is the difference between myeloblastic/granulocytic leukemia and lymphocytic/lymphoblastic leukemia?

a. In myeloblastic/granulocytic leukemia  - neoplastic cells develop from precursors of granulocytes (such as neutrophils, PMNs)  

b. In lymphocytic/lymphoblastic leukemia, neoplastic cells develop from precursors of lymphocytes (such as T and B cells)

a. acute lymphocytic leukemia (ALL)  -  mainly in children and adolescents, prognosis – good in children due to chemotherapy and BM transplants, poorer in adults                 

b. acute myeloblastic leukemia (AML) -  mainly in adults >55 years old, there are  specific chromosomal abnormalities seen on biopsy,  prognosis – good, high remission rate with therapy     

c. chronic lymphocytic leukemia (CLL) – usually excessive, non-functional B cells,  mainly in adults > 50 years old, prognosis – fair,

chemotherapy to prolong  survival    

d. chronic myeloblastic leukemia (CML) -  mainly in adults 25 to 60 years old, patients often have hepatomegaly, splenomegaly, blast crisis late in disease, 90% of patients have “Philadelphia chromosome”, prognosis – poor, treatments do not prolong survival

These are solid malignant tumors arising in lymphocytes or lymphocyte precursors in lymphoid tissue.  

Tumor cells divide rapidly – normal lymphoid tissue and bone marrow is displaced and suppressed, adjacent organs are compressed or invaded.

There is loss of normal immune function with infections, also

• anemia
• fatigue
• wasting
• fever
• splenomegaly
• lymphadenopathy

• 4 subtypes
• orderly spread
• occurrs mainly in young adults
• especially males and blacks

Starts as a single enlarged, painless, cervical lymph node; later – spread to other lymph nodes; presence of Reed-Sternberg cells upon lymph node biopsy

prognosis – usually good - depends on stage of disease, age   

• 10 subtypes
• disorderly spread
• different subtypes affect different populations
• if extensive metastasis may mimic leukemia
• prognosis – variable – according to low, intermediate, and high grade

Bone marrow Transplantation – to restore marrow function

• 750 ml from hip of donor
• IV injection to recipient
• donor cells become established in recipient bone marrow