IC2 Blood, Erythropoiesis, Anaemia, Hemostasis, Clotting Disorders

Question 1

What are the blood functions

Answer 1

1. Transportation:
   o Respiratory gases: O2 and CO2.
   o Nutrients, waste.
   o Hormones: Transport from glands to target organs.
2. Regulation:
   o Blood pressure
   o Body temperature: Redistribution of heat.
   o pH and ion composition of interstitial fluids.
3. Protection:
   o Blood clotting: Platelets and coagulation.
   o Immune system

Question 2

What are the blood components?
What are the components of plasma?

Answer 2

1. Plasma
2. RBC
3. WBC

Components of plasma

• Water (92%)
• Proteins(7%)
  o Albumin - carrier of lipid soluble substances (drugs, hormones eg steroids); maintaining osmotic pressure
  o Globulins – immune function and clotting
  o Fibrinogen – clotting (converted to fibrin)
• Solutes(<1%)
  o Ions, Nutrients, Gases, Waste

Question 3

What is hematocrit?
What is the avg hematocrit for men and women?

Answer 3

Hematocrit: The relative volume of red blood cells out of the total blood volume
The average hematocrit for men is 46, and for women it is 42.

Question 4

Why does men have more RBC than women?

Answer 4

Androgen (but not estrogen) enhances erythropoiesis. Therefore, men have higher RBC concentrations than women.
Men have more RBC due to hormones that stimulate more RBC to be produced where estrogen does not but androgen does

Question 5

What is heaemoglobin?
How many polypeptide chains and heme does a globin has?
What is a heme?
How many Fe is present in a globin?
How many oxygen is present in a globin?

Answer 5

Hemoglobin (Hb) consist of 2 components:

1. Globin:
   a. 4 folded polypeptide chains, 2a and 2b chains (Hb chains).
   b. Amino acid sequence determines affinity to O2.
   c. Each chain binds 1 heme group.
   d. 1 globin has 4 heme groups
2. Heme:
   a. Not a protein but a pigment.
   b. Each heme group contains 1 iron (Fe), which can bind 1 O2 molecule.
   c. This binding is very weak and reversible.
   Each Hb molecule can transport 4 molecules of O2.

Question 6

What are the 3 names for haemoglobin,
what are they bound to and
what is the colour?

Answer 6

Oxyhemoglobin: Hb bound to O2. Bright red.
Deoxyhemoglobin: Hb after O2 diffuses into tissues. Dark red.
Carbaminohemoglobin: Hb bound to CO2.

Question 7

Where does erythropoiesis take place in the fetus?

Answer 7

1. Fetus: yolk sac –> then liver, spleen, lymph node.

Question 8

Where does erythropoiesis take place in people <5y/o?

Answer 8

2. < 5 years: all bone marrow.

Question 9

Where does erythropoiesis take place in people 5-20y/o?

Answer 9

3. 5 - 20 years: bone marrow in ribs, sternum, vertebrae, proximal ends of long bones.

Question 10

Where does erythropoiesis take place in people >20y/o?

Answer 10

4. > 20 years: bone marrow in ribs, sternum, vertebrae.

Question 11

What causes an increase in erythropoiesis in normal states?
What are the reasons for increase in production of erythropoietin in the kidneys?

Answer 11

Erythropoiesis is Controlled by Erythropoietin.

• If 02 delivery to the kidneys (and other tissues) is decreased,
• cells in the kidneys release more erythropoietin which increases the rate of erythropoiesis.
• Once the oxygen delivery to the kidneys is sufficient,
• the kidneys decrease their output of erythropoietin.

Erythropoietin release by the kidneys is triggered by:

1. Hypoxia due to decreased RBC number or function
2. Decreased oxygen availability
3. Increased tissue demand for oxygen
4. Anemia
5. Reduced blood flow to kidney
6. Blood donation

Erythropoietin release and RBC production are regulated by tissue oxygenation.

Question 12

What is erythropoietin?
What does it do?

Answer 12

Erythropoietin

• growth factor.
• stimulates hematopoietic stem cells to form proerythroblasts.
• enhances proliferation rate of proerythroblasts and erythroblasts.
• enhances Hb synthesis.
• can increase RBC production 10x
• about 90% is secreted by the kidneys, and about 10% by the liver.

Question 13

When is epogen (recombinant erythopoietin) used?

Answer 13

Epogen: Recombinant erythropoietin. Applications:

• surgery
• chemotherapy
• dialysis patients
• doping

Question 14

Describe the process of erythropoiesis.
What does reticulocyte count tell you?

Answer 14

Erythropoiesis

1. Hematopoietic stem cells in the bone marrow give rise to proerythroblasts.
2. Proerythroblasts develop into erythroblasts in 3 phases:
   a. Phase 1: Ribosome synthesis in early erythroblasts.
   b. Phase 2: Hb accumulation in late erythroblasts and normoblasts.
   c. Phase 3: Ejection of the nucleus from normoblasts and formation of reticulocytes.
3. Reticulocytes continue Hb synthesis, leave the bone marrow and complete differentiation to mature erythro- cytes in the blood.
4. Reticulocyte count is indicative of erythropoiesis (high levels means erythropoiesis is occurring); Normal range 0.8 - 1%

Question 15

How are RBCs destroyed? What happen to the different components of Hb?

Answer 15

Destruction of RBC and Reutilization of Breakdown Products

• Old RBC self-destruct
• Lack of protein synthesis makes membranes fragile. Hb degrades.
• Rupture in tiny vessels of spleen (3 μm diameter).
• Macrophages take up dying RBC or components.
• Hb –> heme + globin
• Heme –> iron + bilirubin
• Heme group: is degraded to a yellow pigment called bilirubin which is excreted via liver and bile into urine and feces (waste).
• Iron: is recycled. Reused in bone marrow or stored in the liver.
• Globin: is metabolized into amino acids and is released into the circulation.

Question 16

What are the 2 basic principle causes of anaemia?

Answer 16

a reduction below the normal capacity of the blood to carry oxygen.

• due to a reduction of erythrocyte numbers
• and / or a reduction of Hb function

Question 17

What are the different types of anaemia? (total: 7)
What happens when there is a reduction in RBC?

Answer 17

Types of anemia:

1. Nutritional anemia is caused by dietary deficiencies of factors needed for erythropoiesis, e.g. iron, folic acid. Pernicious anemia: Lack of vitamin B12 or intrinsic factor.
2. Aplastic anemia is due to the failure of the bone marrow to make adequate numbers of RBCs (e.g. due to radiation damage or chemotherapy).
3. Renal anemia is due to kidney disease, causing lack of Erythropoietin.
4. Hemorrhagic anemia is due to the loss of significant amounts of blood.
5. Malaria: Plasmodium falciparum amplifies in RBC thereby rupturing them. Offspring invades new RBC.
6. Sickle cell anemia: Mutation in b-globin gene, causing Hb to aggregate in low O2 conditions to crescents which rupture RBC membranes.
7. Erythroblastosis fetalis: Rh+ RBC of fetus are destroyed by anti-Rh antibodies of a Rh- mother.

RBC concentration in blood determines its viscosity.
RBC reduction causes very liquid blood which rushes too fast through the tissues, releasing too little O2. The resulting hypoxia widens blood vessels and reinforces the effect.
→ Greatly increased workload for the heart, and potentially cardiac arrest.

Question 18

What is polycythemia/erythremia?
What is primary polycythemia/erythremia?
What is secondary polycythemia/erythremia?
What else can cause polycythemia?
What is the viscosity of the blood in a person with polycythemia?

Answer 18

Polycythemia / Erythremia

• An excess in circulating erythrocytes → elevated hematocrit.
• Primary polycythemia is caused by a tumor or tumor-like condition in the bone marrow.
• Secondary polycythemia is an erythropoietin-induced, adaptive mechanism to improve the oxygen carrying capacity of the blood, e.g. in people living at high altitudes.

Other conditions, such as dehydration can elevate the hematocrit.

Polycytemia causes very viscous blood and potentially a plugging of capillaries
→ insufficient O2 delivery to tissues.

Question 19

Definition and what does it tell you when have high vs low:
1. hematocrit
2. reticulocyte count
3. RBC count

Answer 19

1. Hematocrit - relative volume of RBC (formed elements) out of total volume of blood
   - high: polycythemia
   - low: anaemia
2. Reticulocyte count - circulating % of reticulocytes
   - high: reticulocytosis
   - low: defect erythropoiesis
3. RBC count - no. of RBC /mL of whole blood
   - high: erythrocytosis/polycythemia
   - low: anaemia

Question 20

What are the parameters and the inference of CBC?

Answer 20

Complete blood count - Sample test results
What do they mean?
* Low haemoglobin – possibly anaemia
* Mean Corpuscular Volume (MCV) – average volume/ size of your RBC
* Mean Corpuscular hemoglobin (MCH) – average amount of hemoglobin in RBC (if too low, anemia)
* Mean Corpuscular hemoglobin concentration (MCHC) – average concentration of hemoglobin in RBC (amount/volume)
* Red cell distribution width (RCW) – how the RBC size varies (if too high early indicator of anemia – anisocytosis (RBC unequal in size) , iron deficient anemia

Question 21

Whatare the leukocyte disorders?

Answer 21

1. Leukopenia
   - too few leukocytes
   - often leads to opportunistic infections.
   - can be caused by radiation, chemotherapy, chemicals, viral infections, …
2. Leukocytosis
   - Normal response to bacterial or viral invasion.
   - Can indicate a cancer of WBCs.

Leukemias and lymphomas – cancers of WBC

• They are named according to the cancer-originating WBC and the cancer stage.
  Chronic Myelocytic Leukemia (CML)
  Acute Lymphocytic Leukemia (ALL)

Chronic stage can last decades. Acute stage leads quickly to death if not treated.

3. Leukemia: Cancer located in blood.
4. Lymphoma: Cancer located in lymphatic system.
   Immature WBCs are found in the bloodstream of leukemias.
   Bone marrow can become completely occupied by cancerous leukocytes.
   The WBCs produced are not functional, and displace the remaining healthy ones. That may cause immune deficiency and many infections, anemia, and hemorrhage. Treatments include irradiation, chemotherapy and bone marrow transplantations.

Question 22

What are the 3 phases of hemoastasis and the additional 2 stages after it?
What is the duration of each phase?

Answer 22

3 Phases:

1. Vasoconstriction (immediate)
2. Platelet plug (within seconds)
3. Fibrin clot (within mins)
4. Clot retraction Healing (20 min – 1 h)
5. Healing (1 – 2 weeks)

Question 23

What happens during vasoconstriction (Hemostasis)?

Answer 23

Vasoconstriction

• Initiated by sympathetic nerves.
• Mediated by vascular smooth muscle cells.
• Correlates with damage.
• Lasts for ~ 30 min (sometimes hours)
  o Provides time for platelet and coagulation phase (2nd and 3rd phase).
  o Endothelial cells of opposite sides may stick together.
• Reduces blood loss. But most times not sufficient. Endothelial cells contract, exposing basal lamina.

Question 24

What are present in platelets (in terms of organelles and proteins)?
What are the molecules that it releases (4 + 2)?

Answer 24

• lack nuclei in mammals (otherwise thrombocytes).
• contain contractile proteins (actin and myosin) –> allow them to move
• contain organelles.
• mitochondria: release of ADP. (impt for clotting cascade)
• ER and Golgi: storage of Ca2+ (factor IV), synthesis of enzymes (platelet factors).
• contain enzyme systems for synthesis of prostaglandins. (TXA2)
• contain growth factors (PDGF, VEGF).
• contain factor XIII (Fibrin-stabilizing factor).

Question 25

What happens during the platelet phase?

Answer 25

Platelet Phase
Damage to the endothelial wall exposes collagen
→ platelets stick (e.g. von Willebrand factor) and becomes activated
→ platelets secrete contents (e.g. ADP, TXA2, platelet agonist)
→ more platelets stick and aggregate + release more platelet attracting substances
→ platelet plug
= positive feedback cascade

Prevent clotting
→ Intact endothelial cells release NO & prostacyclins that inhibits unintentional platelet activation / aggregation

Question 26

What are the molecules involved in platelet adhesion?

Answer 26

Platelet Adhesion
- Mediated by Von Willebrand’s Factor (vWF).
- vWF – plasma protein produced by platelets
- vWF binds platelets to exposed collagen
- Adhesion activates platelets – morphological change (to extend the dendrites out further)
- Triggers release of granules containing platelet agonists.
- further aggregation!
- Platelet agonists from granules (Eg. ADP, Thromboxane A2 (Tbx A2) etc.)
- ADP attracts and activates more platelets.
- Tbx A2 promotes aggregation & further vasoconstriction.
o Prostaglandin, formed through arachidonic acid pathway
- Fibrinogen (factor I) links platelets through glycoprotein receptors.
o Not the only function of fibrinogen; can be broken down into fibrin
- Fibrinogen links are weak - need reinforcement! (Factor XIII)

Question 27

What is the role and actions of thrombin?

Answer 27

Thrombin

1. enhances its own generation (positive feed back loop) [1c]
2. Factor XIII activation (stabilization of fibrin mesh) [1b]
3. platelet activation [1d]
4. release of PF3 from platelets (activation of intrinsic pathway) [1d + 2]
5. activates fibrinogen into fibrin [1a]
   Thrombin is a key regulator of hemostasis  since it drives a lot of this positive feedback loop to maintain the coagulation pathway

Question 28

Describe the extrinsic, intrinsic and final common pathway of the coagluation cascade.

Answer 28

Extrinsic Pathway
Damage tissue → tissue factor (Factor III) / thromboplastin
→ VII to VIIa –Ca2+→ X to Xa

• very fast (occurs within secs)
• when damage occurs outside the blood circulation then this pathway is activated e.g. poke/cut

Intrinsic Pathway
Exposure to collagen fiber / exposure to foreign substances e.g. glass
→ platelets phospholipids (conformational change)
→ XII to XIIa
→ XI to XIa
– Ca2+→ IX to IXa
– Ca2+, VIIIa→ X to Xa

• When damage occurs inside the circulation e.g. capillaries, veins etc.

Final common pathway
X to Xa –Ca2+, Factor Va→ prothrombin to thrombin (Factor II)
→ fibrinogen to fibrin AND XIII to XIIIa
→ fibrin monomer to fibrin strands
→ cross linking of fibrin strands by factor XIIIa (fibrin-stabilizing factor)

Question 29

What are the clotting factors? (12)

Answer 29

Clotting Factors
Foolish people tried climbing long slopes after Christmas
Some people have fallen
All from liver
II, VII, IX, X need vitamin K

1. I – Fibrinogen
2. II – Prothrombin
3. III – tissue factor
4. IV – Ca2+
5. V – L (proaccelerin)
6. VII – Stable factor (proconvertin)
7. VIII – antihemophilic
8. IX – C (plasma thromboplastin)
9. X – stuart-prower factor
10. XI – plasma thromboplastin
11. XII – Hageman factor
12. XIII – fibrin stabilising factor

Question 30

What is the time frame for sealing damaged blood vessels?

Answer 30

Time Frame for Sealing Damaged Blood Vessels

1. Vasoconstriction (immediate)
2. Platelet plug (within seconds)
3. Fibrin clot (within mins)
4. Clot retraction Healing (20 min – 1 hr)
   o 20 min – 1 h: Clot retracts. Mediated by platelets.
   Few h: Clot is dissolved, or is invaded by fibroblasts
5. Healing (1 – 2 weeks)
   o 1 – 2 weeks: Fibrous tissue replaces blood clot, healing completed.

Question 31

What happens during clot retraction and healing?

Answer 31

Clot Retraction and Repair
Clot retraction (tightening):

• Stabilization of clot by squeezing serum from the fibrin clot. Further closure of leak.

Repair

• Platelet-derived growth factor (PDGF) stimulates vascular smooth muscle cells to build new vessel wall.
• Stimulated by vascular endothelial growth factor (VEGF), endothelial cells multiply and restore the inner endothelial lining.

Question 32

What are the 3 factors/molecules involved in regulating blood clotting?

Answer 32

Regulation of Blood Clotting (balance mechanism)

1. Prostacyclin, a prostaglandin produced by intact endothelial cells, inhibits platelet activation and limits spread of blood clotting.
2. Serotonin at high concentrations inhibits ADP activity (stop blood from clotting).
3. Blood clot limits spread of thrombin and other procoagulants (limit it to the location).

Question 33

What are the 3 procoagulants?
What are the anticoagulants (both endogenous and artificial)?
(possibly optional)

Answer 33

Balance between pro- and anti-coagulants
Procoagulants:

1. Tissue factor, factor III (extrinsic pathway).
2. Collagen, anything which activates factor XII (intrinsic pathway).
3. Collagen (platelet plug).

Anticoagulants:

1. artificial: Chelators (Citrate, EDTA), Vitamin K antagonists (Warfarin, Coumarin), DOAC (direct acting anticoagulants- CLC).
2. endogenous: Smoothness of endothelial surface (does not cause exposure of collagen), Antithrombin III, Heparin, Thrombomodulin, Tissue plasminogen activator.

Question 34

Describe fibrinolysis.

Answer 34

Fibrinolysis
Fibrinolysis = dissolution of clots
During clot formation plasminogen is trapped inside the clot.

• Plasminogen is a plasma protein and protease precursor made by the liver.
• The surrounding tissue and vascular endothelial cells slowly release tissue plasminogen activator (tPA) which cleaves the inactive plasminogen to the protease plasmin.
• Plasmin digests fibrin, thereby dissolving the clot.
• Macrophages remove the remains of the clot.

Question 35

What are the blood clotting disorders (7)?

Answer 35

Blood Clotting Disorders

1. Hemophilia (X linked genetic disease) - Men
   - Excessive bleeding after an injury.
   - Usually affect intrinsic pathway
   Hereditary Hemophilias are caused by lack of clotting factors.
   - Hemophilia A: Deficiency of factor VIII, 83% of all Hemophilia cases. Treatment by recombinant factor VIII.
   - Hemophilia B: Deficiency of factor IX (plasma thromboplastin).
   - Hemophilia C: Deficiency of factor XI (plasma thromboplastin).
2. Liver disease
   - e.g. hepatitis, hepatocellular carcinoma or liver cirrhosis may result in the inability to:
   o synthesize procoagulants. Most clotting factors are produced by the liver.
   o produce bile and to absorb fat and Vitamin K. (then decrease procoagulatns, blood cant clot properly
3. Vitamin K deficiency
   - Vitamin K is essential for the synthesis of several clotting factors.
   - About half of our Vitamin K comes from gut bacteria, half from the diet.
   - Long-term antibiotic use results in Vitamin K deficiency and bleeding disorders.
4. Thrombocytopenia
   - A condition in which the number of circulating platelets is too low (< 50 million/ml; normal range: 200 - 500 million/ml).
   - Results in spontaneous, widespread hemorrhage, visible by small purple spots on the skin.
   - Caused by damage / destruction of bone marrow (e.g., malignancy, chemotherapy). Treated with fresh whole blood transfusions or platelet transfusions.
5. Thrombosis
   - Inappropriate clotting, e.g. caused by a roughened surface of a vessel, endothelial cell injury, disturbed blood flow (stasis).
   - Thrombus – a clot that develops and persists in an unbroken blood vessel.
   Thrombi can block circulation, resulting in tissue death.
   - Coronary thrombosis: A thrombus in a blood vessel of the heart. Can cause heart attack.
   - Cerebral thrombosis: A thrombus in the brain. Can cause stroke.
6. Thromboembolism
   - Often results from deep vein thrombosis (DVT), (economy class syndrome).
   - Embolus: A thrombus freely floating in the blood stream.
   o Pulmonary emboli impair the ability of the body to obtain oxygen.
   o Cerebral emboli can cause strokes.
   o Cardiac emboli can cause heart attack.
   - Treatment with tPA or with Heparin + Vit K antagonists.
   - Risk factors: Smoking, dehydration, oral contraceptives, polycythemia, surgery, immobility.
   - Frequency: 1 in 1000. Mortality 1 - 5%
7. Strokes and Afib (more in CLC)
   - Atrial fibrillation (irregular heartbeat) causes blood to collect in heart, causing clot formation and increased risk of strokes.
   - 1 in 7 stroke patients have Afib Treatment depends on type of stroke

Question 36

What are the 3 blood clotting test present?
When are they used, like monitoring of ___therapy?

Answer 36

Blood Coagulation Tests
to diagnose bleeding or thrombotic episodes, and to monitor anticoagulant therapy

1. Partial thromboplastin time (PTT) or activated PTT (aPTT):
   Measures the efficacy of the intrinsic and the common coagulation pathways (factors I, II, V, VIII, IX, X, XI and XII).
   - Citrated plasma + Ca2+ + Phospholipid + Kaolin (activate platelets).
   - Used to monitor Heparin therapy. Normal range: 25 – 39 sec.
2. Prothrombin time (PT):
   - Measures the efficacy of the extrinsic and common pathways (factors I, II, V, VII, and X).
   - Citrated plasma + Ca2+ + Tissue factor.
   - Used to monitor Warfarin therapy. Normal range: 12 – 15 sec (since have less steps).
3. International normalized ratio (INR):
   - Ratio of patient PT to the PT of a healthy person. Normal range: 0.9 – 1.3.
   - Should be 2 – 3 for patients on Warfarin therapy.