Hematologic System Structure, Functions(1)

Bone marrow

• Blood cell production
• 2types of bone marrow; yellow (adipose, 지방) & red (hematopoietic, 조혈)
• Red marrow; flat, irregular bones (end of long bone, pelvic bone, vertebrae)
• Hematopoietic stem cell 조혈모세포; produce blood cells (RBC, WBC, platelets)
• Responds to increased demands via a negative feedback system

Blood

3가지 기능

1. Transportation : oxygen, nutrients, hormone, metabolic waste products
2. Regulation : fluid & electrolyte balance, acid-base balance
3. Protection : maintaining homeostasis of blood coagulation, combating invasion of pathogens

혈장 & 혈구의 성분

Plasma

1. 55% of blood
2. Composed of water, proteins, electrolytes, gases, nutrients, waste
3. Serum 혈청; plasma – clotting factors

Blood cells

1. 45% of blood
2. 3 types of cells; RBC, WBC, platelet

Erythrocyte (RBC)

1. Function : transport of gases (O2 & CO2) & assistance in maintaining acid-base balance
2. Flexibility, Biconcave shape
3. Composed of large molecule : Hb (protein-iron compound; heme + globin); binds to O2 & CO2 Normal life span; 120 days

2 components; Blood cells (cont’d)

Erythropoiesis; process of RBC production

• Stimulated by hypoxia & controlled by erythropoietin (glycoprotein growth factor; stimulate BM to ↑ RBC production)
• Affected by endocrine H (thyroxin)
• Nutrients; protein, iron, folate 엽산 (folic acid), cobalamin (vit B12), riboflavin (vit B2), pyridoxine (vit B6)
• Reticulocyte 망상적혈구; immature RBC
• Reticulocyte count; measures rate at which new RBC appear in  circulation (within 48hrs)

Hemolysis

1. Destruction of RBC
2. Occurs in bone marrow, liver, spleen -> liver (conjugate & excrete bilirubin)

Leukocyte

• Originate from stem cells within bone marrow
• Types
  • Granulocyte 과립구 (polymorphonuclear leukocytes); neutrophils 호중구, basophils 호염구, eosinophils 호산구
  • Agranulocyte (mononuclear cells) : lymphocyte 림프구, monocyte 단핵구

Leukocyte : Granulocyte

Neutrophil 호중구

1. the most common type; 50-70% of WBC
2. Phagocytosis, esp during the early phase of inflammation
3. Stimulated by hematopoietic growth factor; granulocyte colony stimulating factor (G-CSF) & granulocyte-macrophage colony-stimulating factor (GM-CSF)
4. Mature neutrophil (segmented neutrophil, seg) vs. immature neutrophil (band)
5. Indicator of infection & tissue injury

Eosinophil 호산구

1. 2-4% of WBC
2. Reduced ability of phagocytosis
3. Engulf Ag-Ab complexes from allergic response
4. Protect from parasitic infection

Basophils 호염구

1. Less than 2 % of WBC
2. Inflammatory response  allergic response; release of bradykanin, heparin, histamine, serotonin
3. Limited phagocytosis

Lymphocytes 림프구

1. 20-40% of WBC
2. Immune response
3. Subtypes; B cell & T cell

Monocytes 단핵구

1. 4-8% of WBC
2. Phagocytosis Macrophage; differentiated from monocytes

Normal Iron Metabolism

• From food, dietary supplements
• Present in all RBC as heme in Hb  & in a stored form
• 2/3 of iron; Hb & 1/3; stored as ferritin & hemosiderin (degraded form of ferritin) in bone marrow, spleen, liver, macrophages
• Transferrin
  • Synthesized in liver
  • Serves as a carrier protein for iron
• Iron is recycled after macrophages in liver & spleen phagocytizes

Normal Clotting Mechanisms

Hemostasis; blood clotting process

Vascular response

• With injury, immediate local vaso-constrictive response occurs -> enhances vessel wall stickiness -> clotting factors to be activated (triggered by endothelial injury & release of tissue factors)

Plt plug formation

• Platelet activated; exposed to interstitial collagen from injured blood vessel -> stick together -> release substances to facilitate coagulation
• Von Willebrand’s factor (vWF); forms adhesive bridge between plt & vascular sub-endothelial structures

Development of fibrin clot on plt plug

• Forms visible fibrin clot
• Plasma proteins to be activated; intrinsic or extrinsic pathways
• Intrinsic pathway; activated by collagen exposure from endothelial injury when vessel is damaged
• Extrinsic pathway; tissue factor is released extravascularly from injured tissues

Lysis of clot

• To keep blood in its fluid state
• Anticoagulation
  • anti-thrombin activity & fibrinolysis
  • Anticoagulants
    • heparin, protein C, S
  • Fibrinolysis
    • dissolution of fibrin clot
    • Initiated when plasminogen is activated to plasmin
    • With excessive fibrinolysis -> bleeding tendency

Spleen

In LUQ of abdomen

Functions

Hematopoietic

• produce RBC during fetal development

Filtration

• remove old, defective RBC
• reuse iron
• Filtering circulating bacteria (gram neg cocci)

Immunologic 면역

• supply of lymphocyte, monocyte

Storage

• storage site for RBC & platelet

Lymph System

• Lymph fluid, lymphatic capillaries, ducts, lymph nodes
• Carries fluid from interstitial spaces to blood; important in preventing development of edema
• Lymph fluid; pale, yellow interstitial fluid
• Lymphatic capillaries; do not have valve
• Lymph node
  • oval, bean shaped
  • Found in groups along lymph vessels at various sites; abdomen surrounding GI tract
  • Deep vs. superficial
  • Filtration of pathogens & foreign particles that are carried by lymph to nodes

Liver

• Function as a filter
• Produces all pro-coagulants that are essential to blood coagulation
• Stores iron
• Hepcidin
  • key regulator for iron balance
  • Produced by liver
  • Stimulated by iron overload or inflammation ↓Release of stored iron from intestine