Body Water Distribution and Movement

• Total body water (TBW) accounts for 60% of body weight in adults.
• Intracellular fluid is inside cells, while extracellular fluid is outside cells.
• Extracellular fluid includes interstitial fluid and intravascular fluid, also known as plasma or serum and is inside blood vessels, arteries, veins, and capillaries.
• Transcellular fluids, which make up the smallest amount of fluid, include urine, synovial fluid, cerebral spinal fluid, gastrointestinal fluids, pleural fluids, and peritoneal fluids.
• Aging leads to less total body weight, decreased renal function, and diminished thirst.

Water Movement Between Fluid Compartments

• Hydrostatic pressure pushes water out of capillaries and capillary hydrostatic pressure is blood pressure while interstitial oncotic pressure pulls water.
• Osmotic/oncotic pressure pulls water into capillaries for reabsorption.
• Oncotic pressure is created by proteins, mainly albumin, in the blood, pulling water into blood vessels.
• Interstitial hydrostatic pressure is the force pushing back on the fluid trying to leave the capillaries.

Sodium & Chloride

• Sodium acts as a "water magnet" to help control water balance.
• Sodium is the primary extracellular fluid (ECF) cation, found outside cells in blood and tissues
• Sodium regulates osmotic forces and water movement, helping to control the amount of water in the bloodstream and around cells.
• Chloride follows sodium and is the main negative ion in the fluid outside cells [like your blood], helping to balance fluid + electrical charges in the body.

Renin-Angiotensin-Aldosterone System (RAAS)

• Aldosterone is the key hormone in the RAAS system.
• Aldosterone helps the kidneys reabsorb sodium and water back into the blood, increasing fluid in the bloodstream and pushes potassium out of the blood and into the kidneys to be excreted in urine.
• Reabsorbing sodium and water raises blood pressure and fluid volume, while excreting potassium maintains electrolyte balance.

Natriuretic Peptides (NP)

• These are hormones that work opposite to aldosterone.
• NP stimulates the kidneys to excrete sodium and water, reducing blood volume and pressure.

Antidiuretic Hormone (ADH)

• ADH helps control water balance and increases water reabsorption from the kidneys into the bloodstream for plasma.
• Osmoreceptors detect salt concentration, triggering ADH release to save water if blood is too salty.
• Volume receptors detect fluid volume, triggering ADH release to conserve water if blood volume is low.
• Baroreceptors detect blood pressure changes, releasing ADH to increase blood volume if blood pressure drops too low.
• When the body needs more water, ADH induces thirst.

Alterations in Water Balance

• Isotonic alterations involve changes in total body water where both water and electrolytes change proportionately, resulting in no change in concentration
• Isotonic fluid loss (hypovolemia) is a fluid volume deficit where both water and electrolytes are lost equally, leading to symptoms like dizziness, tachycardia, low blood pressure, decreased urine output, and weight loss.
• Isotonic fluid excess (hypervolemia) involves retaining both water and electrolytes equally, increasing fluid volume and leading to symptoms like weight gain, tachycardia, elevated blood pressure, and hemodilution.
• Edema is the accumulation of excess fluid in the interstitial space, leading to swelling in tissues.

Types of Edema

• Dependent edema occurs in the lower parts of the body when standing or sitting.
• Periorbital edema is swelling around the eyes due to fluid retention or kidney disease.
• Pulmonary edema is fluid in the lungs, causing difficulty breathing and low oxygen levels.

Fluids

• Oral rehydration solutions are used to prevent or treat dehydration, containing a precise balance of salts [electrolytes] and sugar [glucose] to enhance water absorption in intestines.
• Intravenous fluids are injected directly into the bloodstream.
• Colloid fluids contain larger particles (protein/starches) suspended in fluid to maintain osmotic pressure, for example, albumin.
• Crystalloid fluids contain small particles that easily pass through the cell membrane and are used for hydration and electrolyte replacement: Isotonic, Hypotonic, and Hypertonic.

Isotonic Fluids

• Isotonic fluids have the same osmotic pressure as blood plasma and do not cause fluid shifts, replacing fluid volume and maintaining blood pressure.
• 0.9% Sodium Chloride [normal saline, NS, NSS] is commonly used for rehydration and maintaining blood pressure.
• Lactated Ringers [LR] contains electrolytes like sodium, potassium, calcium, and lactate and is often used in surgery or trauma care.

Hypotonic Fluids

• Hypotonic fluids have lower osmotic pressure than blood plasma, leading to water entering cells and potentially causing swelling and used when cells need to absorb water.
• .45% Sodium Chloride (½ NS, Half- Strength Normal Saline) can treat dehydration when the cells need water but with less sodium.
• 0.33% Sodium Chloride (0.33% NaCl,⅓ NS) offers a lower concentration, is used for gradual rehydration.
• 0.225% Sodium Chloride (0.225% NaCl, ¼ NS) can provide milder rehydration and electrolyte management.

Hypertonic Fluids

• Hypertonic fluids have higher osmotic pressure than blood plasma, drawing water out of cells and potentially causing shrinkage.
• Used to treat low sodium levels (hyponatremia) and/or to reduce intracranial pressure.
• 3% Sodium Chloride (3% NaCl) is a strong hypertonic solution for severe hyponatremia and brain swelling.
• Dextrose 10% in Water (D10W) provides both glucose and water for energy and is often used when blood sugar needs to be elevated.
• Dextrose 50% in Water (D50W) is used for treating hypoglycemia to severe low blood sugar.

Immunity: First Line of Defense

• Consists of physical, mechanical, and biochemical barriers to prevent pathogens from entering the body.
• Physical barriers include the skin and mucous membranes.
• Mechanical barriers include cilia, saliva, and tears.
• Biochemical barriers include normal microbiota, sebaceous glands, & acidic pH.

Immunity: Second Line of Defense

• Inflammation is part of the body's nonspecific immune response to injury or infection and is rapid.
• Inflammation is rapid and nonspecific.

Immunity: Third Line of Defense

• Antibodies (Immunoglobulins) are proteins produced by B-Lymphocytes in response to specific antigens.
• Adaptive (acquired) immunity is a body's defense mechanism that is specific to particular pathogens, and develops over time.

Acute Inflammation

• Body's immediate response to injury or infection and involves both local and systemic manifestations

Local Manifestations of Acute Inflammation

• Heat, swelling [edema], redness [erythema], pain, and loss of function

Systemic Manifestations of Acute Inflammation

• Fever, leukocytosis [increase # of WBC] and cascades

Cascades

• Coagulation forms blood clots to prevent excessive bleeding after vascular injury.
• Complement enhances the immune response, especially in fighting infections.
• Kinin: involved in vasodilation, inflammation, and pain

Adaptive Immunity

• Adaptive immunity is part of the immune response that specifically targets

Overview of total body water (TBW) distribution in adults and the various fluid compartments including intracellular, extracellular, and transcellular fluids. Discussion of hydrostatic and oncotic pressures that govern water movement between these compartments. The impact of aging on TBW and renal function is also addressed.