Human Physiology Extracellular Fluids and Blood

Extracellular Fluids

• Three extracellular fluids: blood, interstitial fluid, and lymph
• Nutrients move from blood to interstitial fluid to tissues

Blood: Composition and Characteristics

• Blood is formed elements (cells) in a liquid extracellular matrix (ECM) called blood plasma
• Blood is part of the cardiovascular system (blood, blood vessels, heart)
• Hematology is the study of blood and blood-forming tissues
• Blood accounts for ~8% of body mass
• Average male blood volume: 5-6 L; Average female blood volume: 4-5 L
• Blood is more viscous (thick) than water
• Blood temperature: ~38ºC; Blood pH: 7.35-7.45
• Three main functions:
  • Transportation: oxygen, nutrients, hormones, heat, waste
  • Regulation: pH, body temperature, osmotic pressure
  • Protection: against blood loss, invasion, and disease

Blood Composition

• Two components:
  • Blood plasma (55%): pale yellow liquid ECM with dissolved substances (mostly water)
    • Proteins: albumin (54%): maintains osmotic pressure; globulins (38%): antibodies and transport proteins; fibrinogen (7%): blood clotting
    • Other solutes (1.5%): electrolytes, nutrients, enzymes, hormones, gases, metabolic wastes
  • Formed elements (45%): erythrocytes, leukocytes, platelets

Formed Elements

• Erythrocytes (red blood cells):
  • Most abundant
  • Transport oxygen (O2) and carbon dioxide (CO2)
  • Mature cells lack organelles; filled with hemoglobin
• Leukocytes (white blood cells):
  • Many types, fight infection and invasion
• Platelets (thrombocytes):
  • Cell fragments
  • Form clots

Blood Cell Formation (Hemopoiesis)

• Continuous process in red bone marrow
• Red bone marrow locations: epiphyses of long bones and most of the axial skeleton
• Starts from pluripotent stem cells
• Two lineages: myeloid and lymphoid stem cells
• Develop into precursor cells that differentiate into blood elements
• Only WBCs divide after leaving bone marrow

Regulation of Blood Cell Formation

• Hematopoietic growth factors regulate blood cell formation
• Erythropoietin (EPO): produced in kidneys; stimulates erythrocyte production
• Thrombopoietin (TPO): produced in liver; stimulates platelet production
• Cytokines: stimulate leukocyte and lymphocyte proliferation

Erythrocytes: Structure and Function

• Biconcave discs for large surface area and flexibility
• Anucleate and lack most organelles at maturity
• Filled with hemoglobin (Hb) for oxygen transport (up to 4 molecules)
• Can carry ~23% of carbon dioxide
• Contain carbonic anhydrase: converts CO2 into bicarbonate, important in blood buffering
• Nitric oxide (NO): acts as a hormone, released by endothelial cells; causes vasodilation

Erythrocyte Life Cycle

• ~120 days life span
• Worn-out/damaged RBCs are destroyed by macrophages in liver, spleen, or red bone marrow
• Components of hemoglobin broken down:
  • Globin is recycled into amino acids
  • Iron (Fe) is salvaged and reused
  • Heme products are excreted in the bile, urine, or feces

Erythropoiesis

• Tightly controlled process
• Stimulus: low tissue oxygen (hypoxia)
• Sensors: kidney cells
• Control center: kidney cells produce EPO
• Effectors: proerythroblasts in red bone marrow, mature faster; increased reticulocytes in circulation
• Result: more erythrocytes for increased oxygen delivery

Leukocytes: Structure and Function

• Granular leukocytes: neutrophils, eosinophils, basophils
• Agranular leukocytes: lymphocytes, monocytes
• All organelles present, no hemoglobin
• Key Functions during infections/damage: inflammation, chemotaxis, emigration, tissue disinfection, tissue healing

Phagocytic Leukocytes

• Neutrophils: most rapid responders, phagocytic, multi-lobed nucleus, release lysozyme, oxidizing chemicals. defensins.

• Eosinophils: fight parasites, two-lobed nucleus with linker bridge,, acidic granules, secrete histaminase

• Basophils: two-lobed or obscured nucleus, basic granules, release histamine, heparin, serotonin - inflammatory response

Agranular Leukocytes

• Lymphocytes: various sizes, originate from lymphoid stem cells, key role in immunity and viral/cancerous cell defence

• Monocytes: originate from myeloid stem cells, differentiate into macrophages (wandering phagocytosis)

Leukocyte Function: Inflammation and Immunity

• WBCs defend against infection and invasion.
• MHC proteins identify cells as "self".
• Mucous membranes trap invaders.
• Accumulation at infection sites upon successful invasion
• Emigration (WBC exit bloodstream into tissue)
• Chemotaxis (WBCs move towards infection site using chemical signals).

Platelets (Thrombocytes)

• Formed from megakaryocytes fragments
• Contain granules with clotting factors
• Life span: 5-9 days
• Crucial for hemostasis (preventing excessive bleeding)

Hemostasis

• Three steps:
  • Vascular spasm: blood vessel constriction
  • Platelet plug formation: platelets adhere, activate, aggregate
  • Blood clotting: coagulation (reinforces platelet plug with protein fibers)

Blood Clots

• Coagulation requires clotting factors (calcium ions, enzymes, and substances from platelets and damaged tissues)
• Two pathways: intrinsic and extrinsic (activated by different triggers)
• Common pathway: activation of factor X, prothrombinase, thrombin, conversion of fibrinogen to insoluble fibrin, and factor XIII activation

Regulation of Blood Clotting

• Tightly regulated to prevent thrombosis (clots) or hemorrhage
• Risks of thrombosis: stroke, pulmonary embolism
• Risk of hemorrhage: excessive bleeding
• Associated diseases: Hemophilia (insufficient clotting factors, common in males), Anemia (lower than normal erythrocytes) , Polycythemia (too many erythrocytes)

Blood Groups (ABO and Rh)

• ABO blood groups based on glycolipid antigens on erythrocytes
• Agglutinins (antibodies) bind to foreign antigens
• Agglutination (clumping of RBCs) occurs upon antibody binding
• HDN (hemolytic disease of the newborn) occurs when maternal and fetal blood mix (Rh incompatibility)

Diseases of Blood

• Anemia (low RBC count)
• Sickle cell disease (genetic mutation affecting hemoglobin folding)
• Hemophilia (disorder affecting clotting factors)

Explore the fundamentals of extracellular fluids, focusing on blood, interstitial fluid, and lymph. This quiz delves into the composition, characteristics, and vital functions of blood, including its role in transportation, regulation, and protection in the body. Test your knowledge on the specifics of blood composition and its importance in human physiology.