2/28

Volume of Body Fluids

• Body fluids are divided into compartments: intracellular and extracellular.

  • Intracellular Fluid (ICF):

    • Contains mainly potassium (K+) and magnesium (Mg2+).

    • Balanced by proteins and organic phosphates.

    • pH around 7.1.

  • Extracellular Fluid (ECF):

    • Primarily composed of sodium chloride (NaCl) and bicarbonate (HCO3-).

    • Regulates fluid balance and pH in the blood with a pH around 7.4.

    • Contains calcium (Ca2+).

Electrolytes

• Electrolytes: Charged particles (ions) dissolved in body fluids.

  • Cations: Positively charged ions (e.g., Na+, K+, Mg2+).

  • Anions: Negatively charged ions (e.g., Cl-, HCO3-).

  • Importance of maintaining balance between cations and anions in both compartments.

Fluid Transport and Osmolarity

• Water moves freely across cell membranes creating an osmotic balance, preventing cell swelling or shrinking.

• Osmolarity is similar in both compartments (~290 mOsm).

  • Plasma Proteins: Notably albumin, which remains in the blood and pulls water back into capillaries to prevent excess fluid loss in tissues.

Importance of Extracellular Fluid Volume

• Directly affects blood pressure:

  • Low extracellular fluid leads to low blood pressure.

  • High extracellular fluid increases blood pressure.

• ECF osmolarity is critical for regulating ECF volume influenced by sodium concentration.

Kidneys and Fluid Balance

• Kidneys adjust sodium excretion to stabilize ECF volume.

• Dehydration or blood loss leads to low extracellular volume.

• The maintenance of electrical neutrality in fluid compartments means equal numbers of cations and anions.

Plasma Membrane

• Acts as barrier between intracellular and extracellular fluids, controls ion movement.

  • Composed of phospholipid bilayer with embedded proteins.

• Water (H2O) is polar, contributing to cohesion and serving as a universal solvent.

Aquaporins and Water Movement

• Aquaporins are special channels facilitating water transport across cell membranes.

  • More aquaporins lead to higher water flow depending on the cell's needs.

• Daily water outputs include urine, sweat, and respiratory losses.

Regulation of Water Loss

• Antidiuretic Hormone (ADH) regulates water absorption in kidneys, crucial for maintaining blood volume and pressure.

  • High ADH levels decrease urine output; low ADH increases urine output.

Blood Composition

• Total blood volume in adults is around 5 liters.

• Plasma is the liquid component, comprising 90% water and various solutes.

  • Includes metabolites, hormones, antibodies, proteins like albumin, globulins, and fibrinogen.

Plasma Proteins

• Albumin: 60-80% of plasma proteins; maintains colloid osmotic pressure, drawing water into capillaries.

• Globulins: Transport lipids and function in immune response as antibodies.

• Fibrinogen: Essential for blood clotting; converts to fibrin during clot formation.

Blood Cell Formation

• Blood cells, including red blood cells (RBCs) and white blood cells (WBCs), are produced through hematopoiesis in bone marrow.

  • Erythropoiesis: Formation of red blood cells, stimulated by erythropoietin (EPO) from the kidneys in response to low oxygen levels.

  • Increased red blood cell production can lead to polycythemia and associated hypertension.

White Blood Cells

• Leukopoiesis: Formation of white blood cells, stimulated by cytokines, crucial for immune response.

  • Neutrophils: First responders to infection.

  • Eosinophils: Associated with allergic reactions and parasitic infections.

  • Basophils: Release heparin and histamine for inflammation response.

  • Lymphocytes: Produce antibodies and regulate immune response; Monocytes become macrophages that engulf pathogens.

Platelets (Thrombocytes)

• Smallest blood cells, crucial for blood clotting; lack a nucleus.

• Release serotonin for vasoconstriction to reduce blood loss.

Blood Vessel Layers

• Tunica Adventitia: Outermost layer; provides support made of connective tissue.

• Tunica Media: Thick middle layer containing smooth muscle; regulates blood flow and pressure.

• Tunica Intima: Thinnest inner layer; smooth surface facilitates blood flow and prevents clotting.

Types of Arteries

• Conductive (large) arteries (e.g., aorta): More elastic tissue for strength and recoil.

• Nutrient (medium-sized) arteries: Control blood flow to specific regions.

• Arterioles: Control blood flow to capillaries, adjusting for local needs.

Capillaries and Microcirculation

• Capillaries allow exchange of gases and nutrients; respond to pH, CO2, and oxygen levels.

  • High CO2 levels lead to dilation for increased blood flow; low CO2 leads to constriction.