Human Body Fluids

Body Fluids

• Human body mass is mostly water, ranging from 75% in infants to 45% in old age

• Changes in body water percentage are related to changing proportions of organs, muscle, fat, and bone during development

• Body water is distributed into two major compartments:

  • Extracellular fluid (ECF): Approximately 20% of total body water
  • Intracellular fluid (ICF): Approximately 40% of total body water

Extracellular Fluid (ECF)

• Represents 20% of total body water

• It is composed of:

  • Interstitial fluid: 15% of total body water, found between cells and in lymphatic system
  • Plasma: 4% of total body water
  • Transcellular fluids: 1% of total body water; includes fluids in gastrointestinal, biliary, and urinary tracts, intraocular and cerebrospinal fluids, and serosal spaces

Fluid Compartments in the Human Body

• Intracellular fluid (ICF) is within cells
• Interstitial fluid (IF) is part of the extracellular fluid (ECF) between cells
• Blood plasma is the second part of the ECF
• Materials move between cells and plasma via the IF in capillaries

Composition of Plasma and Interstitial Fluid

• Similar composition
• Sodium (Na⁺) is predominant cation, Chloride (Cl⁻) and Bicarbonate (HCO3⁻) are the predominant anions
• Plasma has a larger concentration of proteins compared to interstitial fluid
  • The capillary endothelium is permeable to water and small solutes (crystalloids) like inorganic ions, glucose, and urea
  • It has limited permeability to larger solutes (colloidal particles) like proteins and lipids
• Interstitial fluid is an ultra-filtrate of plasma
• Electrical neutrality is maintained in each compartment such that the total number of cationic charges equals the total number of anionic charges

Intracellular Fluid (ICF)

• Represents 40% of total body water
• Contains relatively low concentrations of Na⁺, Cl⁻, and HCO3⁻ compared to ECF
• Potassium (K⁺) and Magnesium (Mg²⁺) are the predominant cations
• Organic phosphates (ATP, ADP, AMP) and proteins are the predominant anions
• Composition differences between ICF and ECF are mainly attributes to the Sodium-Potassium ATPase pump in cell membranes
• The pump actively transports three sodium ions out of and two potassium ions into cells
• This accounts for high sodium and low potassium concentrations in ECF and the opposite in ICF.

Fluid Movement Between Compartments

• Hydrostatic pressure: The force exerted by a fluid against a wall. This force causes movement of fluid between compartments
• Hydrostatic pressure of blood (capillary blood pressure) in capillaries is higher than the colloid osmotic pressure at the arteriolar end
• Colloid osmotic pressure: “Constant" pressure primarily produced by circulating albumin
• Plasma and nutrients squeezed out of the capillaries into surrounding tissues
• Fluid and cellular wastes enter capillaries at the venule end where hydrostatic pressure is less than osmotic pressure
• Filtration pressure squeezes fluid out of the plasma in blood into the IF surrounding tissue cells
• Surplus fluid in the interstitial space is drained by the lymphatic system and re-enters the vascular system at the subclavian veins

Starling Forces

• Primary factors determine fluid movement through capillary membranes
• Fluid exchange across the capillary wall is achieved by a balance between four forces and capillary permeability
• The forces include:
  • Capillary hydrostatic pressure: moves fluid outward through capillary membrane; about 35 mm Hg at arteriolar end and 15 mm Hg at venous end (except in glomerular capillaries, where it is about 50-60 mm Hg)
  • Interstitial fluid hydrostatic pressure: moves fluid outward through capillary membrane when interstitial fluid pressure is negative (about -4 to -5 mm Hg); affected by lymphatic drainage and tissue tension; blocked lymphatic drainage increases interstitial fluid pressure
  • Plasma colloid osmotic (oncotic) pressure: causes osmosis of fluid inward through the membrane; normal human plasma averages approximately 25 mm Hg with the dissolved protein accounting for the majority of it
  • Interstitial fluid colloid osmotic pressure: causes osmosis of fluid outward through the membrane; about 6 mm Hg; protein concentration is influenced by fluid filtration into the interstitium, altering oncotic pressure
  • Capillary permeability: capillaries are highly permeable to small molecules and water but only slightly permeable to plasma protein, which can be altered by certain poisons, oxygen lack, and bacterial toxins

Blood

• Blood is essential for life
• Oxygen is delivered through blood cells
• Blood is a complex tissue pulsating through arteries, interacting via capillaries, and returning through veins
• Blood carries oxygen and carbon dioxide, protects against diseases, and eliminates waste products

Components of Blood

• Consists of cells suspended in plasma
• Serum is what is left when blood is allowed to clot
• There are three types of blood cells:
  • Red blood cells (erythrocytes): most abundant; necessary for oxygen delivery
  • White blood cells (leukocytes): colorless; involved in defense mechanisms
  • Platelets (thrombocytes): involved in blood clotting, preventing blood loss

Plasma

• Liquid part of blood
• Straw-colored
• Consists of 91-92% water
• Can be obtained by collecting blood with an anticoagulant and centrifuging it

Serum

• Liquid part of blood after clotting
• Contains plasma constituents except fibrinogen
• Serum = plasma - fibrinogen

Properties of Blood

• Color: Red
  • Arterial blood: Scarlet red
  • Venous blood: Purple red
• Volume:
  • Adults: ~5L
  • Newborns: 450ml
  • Accounts for 6-8% of body weight
• Reaction and pH: Slightly alkaline, with a pH of 7.4
• Density: ~1.050
• Viscosity: 3.5-5.5 times more viscous than water

Functions of Blood

• Transport: Carries substances like oxygen, carbon dioxide, antibodies, ions, hormones, nutrients, and heat
• Immunity: Leukocytes and plasma proteins defend the body against pathogens
• Hemostasis: Controls bleeding through hemostatic mechanisms
• Homeostasis: Maintains a stable internal environment

Red Blood Cells (Erythrocytes)

• Most numerous cells in blood; "Erythros" means red. Red color is due to the pigment hemoglobin.
• Characteristics:
  • Lack a nucleus and DNA.
  • Biconcave disc shape
  • Maintain its shape by a complex membrane skeleton made of actin and spectrin.
  • Specific gravity of 1.092 to 1.101.
  • Suspension stability (remain uniformly in the blood).
  • Single Erythrocyte cell lives only for 120 days and in that duration. It is removed from circulation by Macrophages found in bone marrow, liver and spleen.

Function of RBCs

• Transport of respiratory gases (O2 and CO2) and buffering action
  • Hemoglobin combines with oxygen to form oxyhemoglobin, transporting about 97% of oxygen
  • Hemoglobin combines with CO2 to form Carb-hemoglobin, transporting about 30% of CO2
  • Hemoglobin in RBCs is an excellent acid-base buffer, regulating hydrogen ion concentration

Red Cell Values

• Important to determine hemoglobin concentration, red cell count, and hematocrit in patients
• Values can be used to deduce other important blood values
• Includes:
  • Mean Cell Hemoglobin Concentration (MCHC)
  • Mean Cell Hemoglobin (MCH)
  • Mean Cell Volume (MCV)
  • Blood Oxygen Carrying

Equations

• MCHC = Hb (g/l) / hematocrit
• MCH = Hb (g/l) / Red cell count (cells/l)
• MCV = Hematocrit (PCV) / Number of red cells
• Each gram of hemoglobin can combine & transport 1.34ml of oxygen
• The oxygen carrying capacity of 1dL of normal blood containing 15g of hemoglobin is 15x1.34 =20.1ml of oxygen
• Red blood cell count: ~ 5.5 mil/µl (µl=mm3) equivalent to 2.5 trillion blood cells in whole body
• RBC lives an average of 100-120 day.

Variations

• Polycythemia: Increase in RBC count
• Can be physiological or pathological
• Physiological polycythemia: temporary and marginal increase
  • Occurs due to:
    • Age; at birth, the RBC count is 8 to 10 million/cu mm of blood
    • Sex: Similar in males and females
    • High altitude: Inhabitants of mountains (above 10,000 feet from mean sea level) have an increased RBC count of more than 7 million/cu mm
    • Muscular exercise and Emotional conditions
    • Increased environmental temperature
    • After meals: There is a slight increase in the RBC count after taking meals.

Erythrocyte Disorders

• Anemia: Inability of blood to carry enough O2
  • Due to inadequate RBC's (low hematocrit) or inadequate hemoglobin
  • Types: Hemorrhagic, Hemolytic, Aplastic, Nutrition Deficiency
  • Abnormal Hemoglobin; Anemia like symptoms:
    • Includes:
      • Thalassemias
      • Sickle cell

Leukocytes (White Blood Cells)

• Mobile units of the body's protective system

• Formed in bone marrow and lymph tissue

• Transports to different parts of the body in the blood

• Compared to RBCs:

  • Larger in size
  • Lesser in number
  • Irregular in shape
  • Nucleated
  • Granules present in some types
  • Shorter lifespan

• Based on presence/absence of granules, are classified as:

  • Granulocytes
  • Agranulocytes

• Leukocytes are of five types:

  • Neutrophils
  • Eosinophils
  • Basophils
  • Monocytes
  • Lymphocytes

Platelets

• Platelets: The formed elements of blood
• Are small colorless, non-nucleated and moderately refractive bodies
• Platelets have the following:
• Diameter of 2.5 µ (2 to 4 µ)
• Volume of 7.5 cu µ (7 to 8 cu µ)
• Inactivated platelets are without processes or filopodia
• Activated platelets develop processes or filopodia Second most abundant formed elements average is average 250,000/µL range: 150,000 – 350,000/µL

Functions and Variation of Platelets

• Age: Platelets count is less in infants (150000 to 200000/cu mm) and increase to a normal level at 3 months after birth
• Sex: There is no variation in platelet count between males and females except in females who are menstruation
• Other factor: increase can be observed in an individual at High attitude or after meals
• Also is key to blood clotting and hemostasis

Function of platlets

• Play role in blood clotting
• Help in hemostasis
• Role in defense mechanism
• Help in repair of the wall of vessels
• Aid in clot retraction

Process of platelet separation

• Stem cells differentiate into CFU-M.
• CFU-M creates megakaryocyte.
• Pseudopodium separates and forms platelet.
• It transports to to other parts of the body; stimulated by factors from monocytes T lymphocytes.
• • Thrombopoietin is the glycoprotein like erythropoietin. It is secreted by liver and kidneys.

How long platlets survive

• Lifespan is about 10 days, ranging from, and gets destroyed by tissue macrophage system in spleen
• An individual with splenomegaly (enlargement of spleen; causes decreased platelet count) and splenectomy (removal of spleen; causes increased platelet count)

Hemeostasis

• Include:
  • Vascular spasm
  • Platelet plug
  • Clotting cascade
  • Help stop excessive bleeding

How vascular spasm occures

• This process occurs instantly
• Serotonin and thromboxane are released from platlets
• Vasoconstriction occures at site of injury and reduces blood loss

How platlet plug occurs

• Process:
  • Platlates become more sticky.
  • Starts mostly 1 to 5 seconds after injury
  • These get mixed at injury and form fibers -Plug is produced if there is exposure if collagen fibers.

Cascade process of blood clotiting

• Cascade: rapid process to prevent extensive injury

• Trigger: includes rough spot in lining of blood vessel slow blood flow and also at the bedside

• A series of reaction that cause the clumpng of platlets at sit after one to two second

• -Clotting factors e.g thromboplastin, prothrombin activator release

  • These triggers Enzymatic reactions

• Conversion of to fibrin at by Thrombin

  • Key components are Fibrinogen as a soluble protein
  • Key components are fribin as an the insoluble protein

When the clot is not need platelets are secreted again

• Clot occurs continuously.
• plasmins & fibrolysin: substances or clot buster

Platelet Issues

• Spontaneous clotting
• Thrombocytopenia