Total Body Water (TBW)

• Total Body Water (TBW) represents about 60% of the total body weight.
• TBW is variable.

TBW in Individuals:

• Infant: 73%
• Male adult: 60%
• Female adult: 40-50%
• Old age: 45%

Functions of Body Water

• Main functions: Solvent and Transport
• Other functions:
  • Give shape and form to the cells
  • Regulate body temperature
  • Act as a Joint lubricant
  • Cushion body organs, such as CSF for CNS (central nervous system)

Fluid Compartments

• Extracellular fluid includes plasma and interstitial fluid.
• Intracellular fluid constitutes another major compartment.
• Transcellular fluid includes CSF, intraocular fluid, pleural fluid, peritoneal fluid, synovial fluid, and digestive secretions.

Body Water Distribution and Percentages

• Intracellular fluids account for 64%.
• Interstitial fluid makes up 25%.
• Plasma constitutes 8%.
• Minor components make up 3%.
• TBW (Total Body Water) = 0.6 x 70 Kg (Body Weight in adult male) = 42 L.
• Extracellular Fluid (ECF) is 1/3 of TBW = 14 L.
• Intracellular Fluid (ICF) is 2/3 of TBW = 28 L.
• Interstitial Fluid is 3/4 of ECF = 10.5 L.
• Plasma is 1/4 of ECF = 3 L.
• Transcellular Fluid is 0.5 L.

Composition of Body Fluids regarding cations (mmol/l)

• Sodium (Na): Plasma 142, Interstitial 139, Intracellular 14
• Potassium (K): Plasma 4.2, Interstitial 4.0, Intracellular 140
• Calcium (Ca): Plasma 1.3, Interstitial 1.2, Intracellular 1 x 10^-4
• Magnesium (Mg): Plasma 0.8, Interstitial 0.7, Intracellular 20

Composition of Body Fluids regarding anions (mmol/l)

• Chloride (Cl): Plasma 108, Interstitial 108, Intracellular 4.0
• Bicarbonate (HCO3): Plasma 24.0, Interstitial 28.3, Intracellular 10
• Protein: Plasma 1.2, Interstitial 0.2, Intracellular 4.0
• Hydrogen Phosphate (HPO4): Plasma 2.0, Interstitial 2.0, Intracellular 11

Water Balance

• Water balance: Input = output
• Dehydration is an abnormal reduction of the major fluid volumes.
• Overhydration is an abnormal increase of total body water.

Homeostasis

• Definition: Keeping the internal environment constant.
• It is a dynamic steady state where input or gain equals output or loss.
• A nearly constant internal environment is needed for proper function of the living cells, and disturbed homeostasis leads to illness or death.

Factors Regulated Homeostatically:

• Concentration of nutrient substances
• Concentration of O2 and CO2
• Concentration of waste products
• Concentration of water and electrolytes
• Body Temperature, pH, and blood pressure

Setpoints for Biological Variables:

• Body temperature: 37°C
• Heart rate: 70 beat/minute
• Respiratory rate: 16 breath/minute
• Blood pressure: 120/80 mmHg
• Arterial blood pH: 7.4
• Plasma Na+: 142 (mEq/L)
• Plasma osmolarity: 290 mosm/L
• Homeostatic control systems operate by negative feedback.
• Action taken opposes the change in the variable leading to maintaining a steady state.

Water Balance Mechanisms;

• ADH and thirst systems maintain osmolality within narrow limits.
• Water deprivation leads to high plasma osmolality, stimulating hypothalamic osmoreceptors and increasing ADH release.
• Water intake leads to low plasma osmolality and decreasing ADH release.

Blood

• Blood is a sticky, opaque fluid with a metallic taste.
• Color varies from scarlet (oxygen-rich) to dark red (oxygen-poor).
• The pH of blood is 7.35–7.45.
• Temperature is 38°C, slightly higher than normal body temperature.
• Blood accounts for approximately 8% of body weight.
• Average volume of blood is 5–6 L for males and 4–5 L for females.
• Without blood human life is impossible.

Blood Functions

• Substance distribution
• Regulation of blood levels of particular substances (Homeostasis)
• Body protection

Functions of Blood

• Blood transports oxygen from the lungs, nutrients from the digestive tract, metabolic wastes from cells to the lungs and kidneys, and hormones from endocrine glands to target organs.
• Blood maintains body temperature, normal pH in body tissues using buffer systems, and adequate fluid volume in the circulatory system.
• Blood prevents blood loss by activating plasma proteins and platelets and initiating clot formation.
• Blood prevents infection by synthesizing and utilizing antibodies and activating WBCs to defend the body against foreign invaders.

Blood Composition

• Fluid Portion: Plasma, consisting of water, proteins, salts, nutrients, vitamins, and hormones.
• Cellular Portion: Blood cells, including red blood cells, white blood cells, and platelets.
• Plasma constitutes 55-60% of blood and is composed of 91-92% water, albumin, globulin, crucial hormones and clotting factors.
• Red blood cells account for 40-45% of blood, transporting oxygen and returning carbon dioxide.
• White blood cells protect against diseases and infections.
• Platelets are small, plate-shaped cells that cluster together to help form blood clots.

Plasma

• Clear liquid consisting of 90% water and 10% organic/inorganic biochemicals.
• Plasma proteins include albumin, fibrinogen, prothrombin and globulin

Plasma Proteins

• Albumin: Synthesized in the liver and is the protein in highest concentration making the greatest contribution to the colloid osmotic pressure of plasma.
• Fibrinogen: Converted to fibrin during clotting.
• Prothrombin: Has a role in blood clotting.
• Globulins: Gamma globulins or immuno globulins act as circulating antibodies.

Erythrocytes (RBCs)

• Biconcave discs, anucleate, with no organelles.
• Filled with hemoglobin (Hb), and functions in gas transport and can reversibly bind with oxygen.
• Production occurs in the bone marrow in response to erythropoietin.
• Red blood cells live about 120 days
• The average red blood cell count is 5 million in a cubic millimeter for males (4.5 to 6.5 ) and females (4.5 to 5.5).
• Hemoglobin reversibly binds with oxygen.
• Each hemoglobin molecule can transport four molecules of oxygen.
• Erythropoiesis is hormonally controlled and depends on adequate supplies of iron, amino acids, folic acid and B vitamins, along with a healthy liver, kidney, and bone marrow.
• Erythropoietin (EPO) released by the kidneys is triggered by hypoxia, decreased oxygen availability, and increased tissue demand for oxygen.
• Anemia: Reduced RBC count or decreased hemoglobin content
• Polycythemia: Excess RBCs increase blood viscosity

Mechanism of Erythropoietin

• Hypoxia stimulates the kidneys (and liver to a smaller extent) to release erythropoietin, which stimulates red bone marrow.
• Erythropoiesis increases RBC count, increasing the oxygen-carrying ability of blood.

Leukocytes (WBCs)

• Leukocytes are complete cells and less numerous than RBCs.
• Leukocytes make up 1% of the total blood volume.
• Leukocytes can leave capillaries via diapedesis and move through tissue spaces.
• A normal WBC count is 4,000 - 11,000 per cubic millimeter.
• Are a normal response to bacterial or viral invasion

WBCs:

Granulocytes

• neutrophils, eosinophils, and basophils - contain granules and are all phagocytic cells.

Agranulocytes

• lymphocytes & monocytes - lack granules but similar structurally

Neutrophils

• 60-70% of WBCs.
• Highly mobile & can engulf debris or foreign organisms by phagocytosis.

Eosinophils

• Account for 1-4% of WBCs.
• They are phagocytic & are involved in destruction of parasitic worms

Basophils

• Account for 0.5% of WBCs
• Contain histamine

Lymphocytes

• Account for 25-30% of WBCs,
• Two types: T cells and B cells

Monocytes

• Account for 2-5% of WBCs and are the largest leukocytes.
• They leave the circulation and enter tissue, and differentiate into macrophages

Platelets

• Are fragments of large cells called megakaryocytes, found in bone marrow.
• They lack nuclei but, like leukocytes, are capable of amoeboid movement.
• A normal platelet count is from 130,000 to 400,000, per cubic millimeter.
• Platelets have a life span: about 5-9 days before being destroyed by the spleen and liver.
• Platelets play an important role in blood clotting.

Hemostasis

• A series of reactions for stopping bleeding.
• During hemostasis, three phases occur in rapid sequence:
  • Vascular spasms
  • Platelet plug formation
  • Coagulation (blood clotting)

Haemostasis overview:

• BV Injury causes contact/Tissue Factor.
• Blood Vessel Constriction is caused by neural activity -Platelet Aggregation cause platelets
• Coagulation Cascade

Hemostasis:

• the process where a series of reactions to stop bleeding occurs

Vasoconstriction:

• The contraction of vessels result from:
  • local myogenic spasm,
  • local autacoid factors from the traumatized tissues and blood platelets (thromboxane A2).
  • nervous reflexes (pain nerve impulses).

Platelet Plug Formation:

• Upon damage to blood vessel endothelium, platelets:
  • Stick to exposed collagen fibers and form a platelet plug
  • Release serotonin and ADP, which attract more platelets;
  • Limited to the immediate area of injury

Coagulation:

• Coagulation follows intrinsic and extrinsic pathways
• The final three steps of reactions are:
  • Prothrombin activator is formed
  • Prothrombin converts into thrombin
  • Thrombin catalyzes the joining of fibrinogen into a fibrin mesh.

Pathological Terms

Hemophilia:

• A hereditary disorder in which there is a lack of the clotting factor VIII and is treated with medications and blood transfusions.

Thrombocytopenia:

• Bleeding disorder with a lack of platelets.
• Occurs in the condition called purpura which is the presence of multiple tiny hemorrhages under the skin.