Blood Functions and Constituents Quiz

Blood Functions

• Transports gases, nutrients, hormones, and metabolic waste

• Regulates interstitial fluid composition (pH, ions, water)

• Limits fluid loss at injury sites through blood clotting

• Defends against toxins and pathogens

• Regulates body temperature by absorbing and redistributing heat

• Average blood volume for a 70 kg male is 5 L, 4 L for a 58 kg female

Blood Constituents

• Blood is composed of plasma (46-63%) and formed elements (37-54%)
• Normal hematocrit (packed red blood cell volume): males 40-54%, females 37-47%

Plasma Components

• Primarily water (92%)
• Proteins (made by liver):
  • Albumins: colloid osmotic pressure, carriers
  • Globulins: clotting factors, enzymes, carriers, antibodies
  • Fibrinogen: forms fibrin in blood clotting
  • Transferrin: iron transport
• Amino acids, glucose, lipids, trace elements/vitamins, gases (O₂, CO₂), and nitrogenous waste

Formed Elements

• Primarily red blood cells (erythrocytes) (99.9%)
• White blood cells (leukocytes) (0.1%):
  • Lymphocytes (20-40%)
  • Monocytes (2-8%)
  • Granulocytes (50-70%): neutrophils, eosinophils, basophils
• Platelets (thrombocytes)

Hematopoiesis

• Blood cell production
• In embryos: yolk sac, liver, spleen, bone marrow
• Adults: pelvis, spine, ribs, cranium, proximal ends of long bones
• Bone marrow: 25% erythrocytes, 75% leukocytes
• Stem cells: pluripotent hematopoietic stem cell → committed progenitor cells → specific cell types (e.g., erythroblast, megakaryocyte)→ mature cells (e.g., erythrocyte, platelets)

Cytokines in Hematopoiesis

• Regulate hematopoiesis
• Erythropoietin (kidney): influences red blood cell development
• Thrombopoietin (liver): influences megakaryocyte development
• Colony-stimulating factors, interleukins, stem cell factor: influence development of all blood cell types

Red Blood Cells (Erythrocytes)

• Biconcave discs
• Filled with hemoglobin and enzymes
• ~5 million RBCs/µL of blood
• Transport oxygen and carbon dioxide
• ~270 million hemoglobin molecules/RBC
• Hemoglobin: iron atom, globin (alpha and beta chains), heme
• Life span: ~120 days

Erythropoiesis

• Red blood cell production
• Stimulated by low oxygen levels (hypoxia)
• Requires iron, vitamin B12, and folate
• Involves hypoxia-inducible factor (HIF1a) activating erythropoietin gene expression
• Mature RBCs lack a nucleus (no new transcription)
• Anaerobic metabolism

Red Blood Cell Removal

• Aged/damaged RBCs are removed by macrophages in spleen, liver, and bone marrow
• Hemoglobin is broken down
• Iron is conserved
• Heme is converted to bilirubin and excreted in bile
• Bilirubin is excreted in the urine and faces

Jaundice

• Condition due to high bilirubin levels
• Caused by high turnover of RBCs, liver disease, and bile duct obstruction

Anemia

• Reduced oxygen-carrying capacity of blood
• Low RBC count or low hemoglobin levels
• Symptoms: Tired, weak, pale skin, headaches, dizziness, etc.
• Types:
  • Low production: stem cell destruction (aplastic), inadequate nutrients, low erythropoietin
  • High removal: hemolytic anemia (genetic defects, parasitic infections, drugs, autoimmune reactions), hemorrhagic anemia (excessive blood loss)

Polycythemia

• Abnormally high hematocrit (>~54%)
• Causes: abnormal erythrocyte precursors, low oxygen delivery to tissues
• Result: high blood viscosity