Unit 5:
1. Discuss the composition of the hematologic system, and the role each component holds.
1. Blood Plasma:
• Composition: Plasma is the liquid portion of blood, accounting for about 55% of its volume. It is primarily water
(about 90%) but also contains proteins, electrolytes, gases, nutrients, waste products, and hormones.
• Role:
• Transports nutrients, waste products, gases (like oxygen and carbon dioxide), and hormones.
• Contains plasma proteins such as albumin (maintains osmotic pressure), globulins (involved in immune
response), and fibrinogen (important for blood clotting).
• Regulates pH and electrolytes, thus helping in maintaining homeostasis.
2. Red Blood Cells (RBCs or Erythrocytes):
• Composition: RBCs are biconcave, anucleate cells packed with hemoglobin, a protein that binds and transports oxygen
and carbon dioxide.
• Role:
• The primary function of RBCs is the transport of oxygen from the lungs to tissues and carbon dioxide from
tissues back to the lungs.
• Hemoglobin within RBCs is crucial for binding oxygen in the lungs and releasing it in tissues, and for
carrying carbon dioxide back to the lungs for exhalation.
• RBCs have a lifespan of approximately 120 days, after which they are removed by the spleen and liver.
3. White Blood Cells (WBCs or Leukocytes):
• Composition: WBCs are larger cells that contain a nucleus. There are several types of WBCs, which can be broadly
classified into granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes and monocytes).
• Role:
• Neutrophils are the first line of defense against bacterial infections and are responsible for phagocytizing
bacteria and other pathogens.
• Eosinophils are involved in combating parasitic infections and modulating allergic reactions.
• Basophils release histamine and other chemicals during allergic reactions and inflammation.
• Lymphocytes (T-cells and B-cells) are key players in the adaptive immune system, responsible for targeting
specific pathogens. B-cells produce antibodies, while T-cells help destroy infected cells.
• Monocytes differentiate into macrophages, which are important for phagocytosis and cleaning up debris in
tissues.
4. Platelets (Thrombocytes):
• Composition: Platelets are small, anucleate cell fragments derived from megakaryocytes in the bone marrow.
• Role:
• Platelets are essential for blood clotting (hemostasis). They form plugs at the sites of vascular injury to stop
bleeding and release various clotting factors that assist in forming a stable blood clot.
, • Platelets are involved in wound repair and inflammation.
• Their activation and aggregation play a key role in the formation of fibrin clots.
5. Bone Marrow:
• Composition: Bone marrow is the soft tissue found inside bones, specifically the red bone marrow, where
hematopoiesis (blood cell formation) occurs.
• Role:
• Hematopoietic stem cells in the bone marrow differentiate into all types of blood cells (RBCs, WBCs,
platelets).
• Bone marrow produces about 200 billion new blood cells every day.
• Bone marrow is also the site of the final maturation of some WBCs, such as monocytes.
6. Spleen:
• Composition: The spleen is an organ located in the left upper abdomen, composed of lymphoid tissue.
• Role:
• The spleen filters blood, removing old or damaged RBCs and recycling iron.
• It acts as a reservoir for blood and platelets.
• The spleen is involved in the immune response by acting as a site for lymphocyte activation and antibody
production.
7. Lymphatic System:
• Composition: The lymphatic system includes lymph nodes, lymph vessels, and lymphoid tissues like the tonsils and
spleen.
• Role:
• Lymph nodes filter lymph fluid, removing foreign particles and pathogens.
• The lymphatic system plays an important role in immune surveillance and response, particularly for WBCs
like lymphocytes.
• Lymph vessels return excess interstitial fluid to the bloodstream.
8. Hemoglobin:
• Composition: Hemoglobin is a protein found in RBCs that binds to oxygen in the lungs and releases it in tissues.
• Role:
• Hemoglobin is responsible for transporting oxygen and carbon dioxide throughout the body.
• It also helps to buffer the blood's pH by binding to protons (H+).
2. Describe the physiology surrounding hemostasis.
1. Vascular Spasm (Vasoconstriction)
• Initiation: When blood vessels are injured, the immediate response is a vascular spasm, which is the constriction of
the blood vessel to reduce blood flow at the site of injury.
, • Mechanism: This vasoconstriction is initiated by the endothelial cells releasing endothelin, a vasoconstrictor, and by
the exposure of subendothelial tissues (such as collagen and smooth muscle cells), which cause vascular smooth muscle
contraction. This temporary spasm helps minimize blood loss.
• Duration: Vascular spasm is generally short-lived, lasting a few minutes to hours, and is most effective in small
vessels.
2. Platelet Plug Formation (Primary Hemostasis)
• Platelet Adhesion: When the endothelial lining of the blood vessel is damaged, underlying collagen and other
components of the subendothelial matrix are exposed. Platelets bind to these exposed structures through von
Willebrand factor (vWF), which acts as a bridge between platelets and collagen.
• Platelet Activation: Upon adhesion, platelets become activated and undergo a shape change, becoming spiny and
sticky. They also release various chemicals stored in their granules, including ADP, thromboxane A2 (TXA2),
serotonin, and calcium. These molecules further recruit additional platelets to the site of injury.
• Platelet Aggregation: Activated platelets bind to each other through fibrinogen, which binds to the glycoprotein
IIb/IIIa receptors on platelets, forming a platelet plug. This forms the primary hemostatic plug that serves as a
temporary seal for the injury site.
3. Coagulation (Secondary Hemostasis)
Coagulation involves the activation of a series of plasma proteins (coagulation factors) that work together to form a stable fibrin
clot.
• Intrinsic Pathway: The intrinsic pathway is triggered when blood comes into contact with the exposed collagen or
damaged tissue. This pathway involves Factor XII (Hageman factor) activating Factor XI, which in turn activates
Factor IX. Factor IX, along with Factor VIII, activates Factor X.
• Extrinsic Pathway: The extrinsic pathway is initiated by the exposure of tissue factor (TF) (also known as Factor
III) from the damaged vessel wall. TF binds with Factor VII, and this complex activates Factor X.
• Common Pathway: Both the intrinsic and extrinsic pathways converge at Factor X. Factor X is activated to Factor
Xa, which, in combination with Factor V, converts prothrombin into thrombin. Thrombin is the central enzyme of
coagulation.
• Thrombin’s Role: Thrombin plays a crucial role by converting fibrinogen (a soluble plasma protein) into fibrin,
which forms an insoluble mesh that stabilizes the platelet plug. Thrombin also activates Factor XIII, which cross-links
fibrin to further strengthen the clot.
4. Fibrinolysis (Clot Removal)
After the wound has healed, it is essential to remove the clot. This process is called fibrinolysis.
• Plasminogen Activation: The clot contains an inactive enzyme called plasminogen. Tissue plasminogen activator
(tPA), released by endothelial cells, activates plasminogen to plasmin.
• Fibrin Degradation: Plasmin digests fibrin, leading to the dissolution of the clot. Fibrin degradation products (FDPs)
are released during this process.
• Regulation of Fibrinolysis: The fibrinolytic system is tightly regulated by plasminogen activator inhibitors (PAI-1)
and alpha-2-antiplasmin to prevent excessive clot breakdown.
5. Regulation of Hemostasis
Hemostasis is a finely tuned process, and multiple mechanisms exist to ensure it occurs only at the site of injury, while avoiding
inappropriate clot formation elsewhere (thrombosis).
• Anticoagulants: Several anticoagulants, such as antithrombin III, protein C, and protein S, inactivate clotting
, factors to prevent clot formation. Heparin, naturally produced by endothelial cells, enhances the activity of
antithrombin III, which inhibits thrombin and other clotting factors.
• Endothelial Cells: Intact endothelial cells prevent unnecessary clotting by producing substances like prostacyclin and
nitric oxide, which inhibit platelet aggregation and vasoconstriction. Additionally, intact endothelium expresses
anticoagulant factors to prevent clot formation on non-injured areas of the vessel.
3. Differentiate between the pediatric and adult hematologic system.
In the pediatric population, the hematologic system undergoes several changes as the child grows and develops. The key
differences between pediatric and adult hematologic systems are:
• Red Blood Cells (RBCs):
• Children: In infants, the fetal hemoglobin (HbF) is predominant, which has a higher affinity for oxygen. As
the child ages, HbF gradually gets replaced by adult hemoglobin (HbA), typically by 6 months of age.
• Adults: Adults predominantly have adult hemoglobin (HbA), which has a normal oxygen affinity suitable for
the adult's metabolic needs.
• Bone Marrow:
• Children: Bone marrow is the primary site of blood cell production throughout childhood, and it remains
active in all bones until around 5–7 years of age, when it becomes confined to the central skeleton (e.g.,
vertebrae, pelvis).
• Adults: In adults, hematopoiesis occurs mainly in the bone marrow of the axial skeleton (vertebrae, sternum,
ribs, and pelvis).
• Platelets:
• Children: Platelet count can be variable, and infants can have higher platelet counts than adults.
• Adults: Adults tend to have a more stable platelet count, within the normal reference range.
• Hemoglobin Levels:
• Children: Hemoglobin levels are higher in neonates (around 14-24 g/dL) but decrease after birth, reaching
adult levels (12-16 g/dL) by around 1–2 years of age.
• Adults: Adult hemoglobin levels are typically stable at 12-16 g/dL for females and 14-18 g/dL for males.
• Immune System Involvement:
• Children: Infants and children rely on maternal antibodies (IgG) passed through the placenta and breast milk
for immune protection until their immune system fully matures. Their bone marrow and lymphatic system are
developing during early years.
• Adults: Adults have a fully developed immune system, including both humoral (antibody-mediated) and cell-
mediated immunity.
• Coagulation System:
• Children: At birth, infants have lower levels of certain clotting factors, leading to an increased risk of
bleeding. This deficiency resolves with time as the liver matures and produces sufficient clotting factors.
• Adults: Adults have a fully functional coagulation system and are less prone to bleeding in the absence of
clotting disorders.
1. Discuss the composition of the hematologic system, and the role each component holds.
1. Blood Plasma:
• Composition: Plasma is the liquid portion of blood, accounting for about 55% of its volume. It is primarily water
(about 90%) but also contains proteins, electrolytes, gases, nutrients, waste products, and hormones.
• Role:
• Transports nutrients, waste products, gases (like oxygen and carbon dioxide), and hormones.
• Contains plasma proteins such as albumin (maintains osmotic pressure), globulins (involved in immune
response), and fibrinogen (important for blood clotting).
• Regulates pH and electrolytes, thus helping in maintaining homeostasis.
2. Red Blood Cells (RBCs or Erythrocytes):
• Composition: RBCs are biconcave, anucleate cells packed with hemoglobin, a protein that binds and transports oxygen
and carbon dioxide.
• Role:
• The primary function of RBCs is the transport of oxygen from the lungs to tissues and carbon dioxide from
tissues back to the lungs.
• Hemoglobin within RBCs is crucial for binding oxygen in the lungs and releasing it in tissues, and for
carrying carbon dioxide back to the lungs for exhalation.
• RBCs have a lifespan of approximately 120 days, after which they are removed by the spleen and liver.
3. White Blood Cells (WBCs or Leukocytes):
• Composition: WBCs are larger cells that contain a nucleus. There are several types of WBCs, which can be broadly
classified into granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes and monocytes).
• Role:
• Neutrophils are the first line of defense against bacterial infections and are responsible for phagocytizing
bacteria and other pathogens.
• Eosinophils are involved in combating parasitic infections and modulating allergic reactions.
• Basophils release histamine and other chemicals during allergic reactions and inflammation.
• Lymphocytes (T-cells and B-cells) are key players in the adaptive immune system, responsible for targeting
specific pathogens. B-cells produce antibodies, while T-cells help destroy infected cells.
• Monocytes differentiate into macrophages, which are important for phagocytosis and cleaning up debris in
tissues.
4. Platelets (Thrombocytes):
• Composition: Platelets are small, anucleate cell fragments derived from megakaryocytes in the bone marrow.
• Role:
• Platelets are essential for blood clotting (hemostasis). They form plugs at the sites of vascular injury to stop
bleeding and release various clotting factors that assist in forming a stable blood clot.
, • Platelets are involved in wound repair and inflammation.
• Their activation and aggregation play a key role in the formation of fibrin clots.
5. Bone Marrow:
• Composition: Bone marrow is the soft tissue found inside bones, specifically the red bone marrow, where
hematopoiesis (blood cell formation) occurs.
• Role:
• Hematopoietic stem cells in the bone marrow differentiate into all types of blood cells (RBCs, WBCs,
platelets).
• Bone marrow produces about 200 billion new blood cells every day.
• Bone marrow is also the site of the final maturation of some WBCs, such as monocytes.
6. Spleen:
• Composition: The spleen is an organ located in the left upper abdomen, composed of lymphoid tissue.
• Role:
• The spleen filters blood, removing old or damaged RBCs and recycling iron.
• It acts as a reservoir for blood and platelets.
• The spleen is involved in the immune response by acting as a site for lymphocyte activation and antibody
production.
7. Lymphatic System:
• Composition: The lymphatic system includes lymph nodes, lymph vessels, and lymphoid tissues like the tonsils and
spleen.
• Role:
• Lymph nodes filter lymph fluid, removing foreign particles and pathogens.
• The lymphatic system plays an important role in immune surveillance and response, particularly for WBCs
like lymphocytes.
• Lymph vessels return excess interstitial fluid to the bloodstream.
8. Hemoglobin:
• Composition: Hemoglobin is a protein found in RBCs that binds to oxygen in the lungs and releases it in tissues.
• Role:
• Hemoglobin is responsible for transporting oxygen and carbon dioxide throughout the body.
• It also helps to buffer the blood's pH by binding to protons (H+).
2. Describe the physiology surrounding hemostasis.
1. Vascular Spasm (Vasoconstriction)
• Initiation: When blood vessels are injured, the immediate response is a vascular spasm, which is the constriction of
the blood vessel to reduce blood flow at the site of injury.
, • Mechanism: This vasoconstriction is initiated by the endothelial cells releasing endothelin, a vasoconstrictor, and by
the exposure of subendothelial tissues (such as collagen and smooth muscle cells), which cause vascular smooth muscle
contraction. This temporary spasm helps minimize blood loss.
• Duration: Vascular spasm is generally short-lived, lasting a few minutes to hours, and is most effective in small
vessels.
2. Platelet Plug Formation (Primary Hemostasis)
• Platelet Adhesion: When the endothelial lining of the blood vessel is damaged, underlying collagen and other
components of the subendothelial matrix are exposed. Platelets bind to these exposed structures through von
Willebrand factor (vWF), which acts as a bridge between platelets and collagen.
• Platelet Activation: Upon adhesion, platelets become activated and undergo a shape change, becoming spiny and
sticky. They also release various chemicals stored in their granules, including ADP, thromboxane A2 (TXA2),
serotonin, and calcium. These molecules further recruit additional platelets to the site of injury.
• Platelet Aggregation: Activated platelets bind to each other through fibrinogen, which binds to the glycoprotein
IIb/IIIa receptors on platelets, forming a platelet plug. This forms the primary hemostatic plug that serves as a
temporary seal for the injury site.
3. Coagulation (Secondary Hemostasis)
Coagulation involves the activation of a series of plasma proteins (coagulation factors) that work together to form a stable fibrin
clot.
• Intrinsic Pathway: The intrinsic pathway is triggered when blood comes into contact with the exposed collagen or
damaged tissue. This pathway involves Factor XII (Hageman factor) activating Factor XI, which in turn activates
Factor IX. Factor IX, along with Factor VIII, activates Factor X.
• Extrinsic Pathway: The extrinsic pathway is initiated by the exposure of tissue factor (TF) (also known as Factor
III) from the damaged vessel wall. TF binds with Factor VII, and this complex activates Factor X.
• Common Pathway: Both the intrinsic and extrinsic pathways converge at Factor X. Factor X is activated to Factor
Xa, which, in combination with Factor V, converts prothrombin into thrombin. Thrombin is the central enzyme of
coagulation.
• Thrombin’s Role: Thrombin plays a crucial role by converting fibrinogen (a soluble plasma protein) into fibrin,
which forms an insoluble mesh that stabilizes the platelet plug. Thrombin also activates Factor XIII, which cross-links
fibrin to further strengthen the clot.
4. Fibrinolysis (Clot Removal)
After the wound has healed, it is essential to remove the clot. This process is called fibrinolysis.
• Plasminogen Activation: The clot contains an inactive enzyme called plasminogen. Tissue plasminogen activator
(tPA), released by endothelial cells, activates plasminogen to plasmin.
• Fibrin Degradation: Plasmin digests fibrin, leading to the dissolution of the clot. Fibrin degradation products (FDPs)
are released during this process.
• Regulation of Fibrinolysis: The fibrinolytic system is tightly regulated by plasminogen activator inhibitors (PAI-1)
and alpha-2-antiplasmin to prevent excessive clot breakdown.
5. Regulation of Hemostasis
Hemostasis is a finely tuned process, and multiple mechanisms exist to ensure it occurs only at the site of injury, while avoiding
inappropriate clot formation elsewhere (thrombosis).
• Anticoagulants: Several anticoagulants, such as antithrombin III, protein C, and protein S, inactivate clotting
, factors to prevent clot formation. Heparin, naturally produced by endothelial cells, enhances the activity of
antithrombin III, which inhibits thrombin and other clotting factors.
• Endothelial Cells: Intact endothelial cells prevent unnecessary clotting by producing substances like prostacyclin and
nitric oxide, which inhibit platelet aggregation and vasoconstriction. Additionally, intact endothelium expresses
anticoagulant factors to prevent clot formation on non-injured areas of the vessel.
3. Differentiate between the pediatric and adult hematologic system.
In the pediatric population, the hematologic system undergoes several changes as the child grows and develops. The key
differences between pediatric and adult hematologic systems are:
• Red Blood Cells (RBCs):
• Children: In infants, the fetal hemoglobin (HbF) is predominant, which has a higher affinity for oxygen. As
the child ages, HbF gradually gets replaced by adult hemoglobin (HbA), typically by 6 months of age.
• Adults: Adults predominantly have adult hemoglobin (HbA), which has a normal oxygen affinity suitable for
the adult's metabolic needs.
• Bone Marrow:
• Children: Bone marrow is the primary site of blood cell production throughout childhood, and it remains
active in all bones until around 5–7 years of age, when it becomes confined to the central skeleton (e.g.,
vertebrae, pelvis).
• Adults: In adults, hematopoiesis occurs mainly in the bone marrow of the axial skeleton (vertebrae, sternum,
ribs, and pelvis).
• Platelets:
• Children: Platelet count can be variable, and infants can have higher platelet counts than adults.
• Adults: Adults tend to have a more stable platelet count, within the normal reference range.
• Hemoglobin Levels:
• Children: Hemoglobin levels are higher in neonates (around 14-24 g/dL) but decrease after birth, reaching
adult levels (12-16 g/dL) by around 1–2 years of age.
• Adults: Adult hemoglobin levels are typically stable at 12-16 g/dL for females and 14-18 g/dL for males.
• Immune System Involvement:
• Children: Infants and children rely on maternal antibodies (IgG) passed through the placenta and breast milk
for immune protection until their immune system fully matures. Their bone marrow and lymphatic system are
developing during early years.
• Adults: Adults have a fully developed immune system, including both humoral (antibody-mediated) and cell-
mediated immunity.
• Coagulation System:
• Children: At birth, infants have lower levels of certain clotting factors, leading to an increased risk of
bleeding. This deficiency resolves with time as the liver matures and produces sufficient clotting factors.
• Adults: Adults have a fully functional coagulation system and are less prone to bleeding in the absence of
clotting disorders.
