Exam 2 part 1

• Babies have approximately 80% fluid weight, the highest percentage of body water, making them more susceptible to dehydration due to a high metabolic rate and surface area-to-volume ratio.
• Adult males have around 60% water weight and tend to have more muscle, which holds more water.
• Adult women have about 50% water weight.
• Dehydration, defined as water loss from the extracellular fluid (ECF), can cause fluid shifts from the ICF and lead to cellular dehydration.
• Edema is excess fluid in the interstitial space, resulting in swelling.
• Electrolyte imbalances disrupt fluid distribution and cell function.
• Concentration refers to the amount of solutes in a solution.
• Water moves across cell membranes from areas of low solute concentration to high solute concentration.
• Osmolality is the total number of solute particles per kilogram of water and determines the osmotic pressure that drives water movement between compartments.
• A higher osmolality signifies a higher solute concentration, drawing water towards that solution.
• Tonicity is the effective osmolality of a solution and its ability to cause water movement across a semi-permeable membrane, relative to the osmolality of intracellular fluid.
• Tonicity determines whether water moves into or out of a cell.
• A semipermeable membrane allows water to pass but not solutes.
• Water moves to dilute the area with a higher solute concentration until solute concentrations are equal on both sides.
• Sodium (Na+) concentration is highest inside the blood vessel.
• Potassium (K+) concentration is highest inside the cell.
• The ATP ace pump catches K+ and transports it back into the cell while removing Na+ in a 3-2 exchange.
• The hypothalamus detects increases in body fluid thickness.
• Hypovolemia is low blood volume, detected by the heart.
• Polydipsia is excessive thirst.

Water and Sodium Balance Overview

• Involves the composition and movement of body fluids composed of solvents (water) and solutes (electrolytes).
• Body solutions function interdependently.
• Body fluids function as lubricants, solvents for chemical reactions in metabolism, and transport oxygen, nutrients, chemical messengers, and waste.
• They play an important role in regulating body temperature and maintaining homeostasis.
• Men have approximately 60% total body water, while women have about 50%.
• Fat contains little water; women have a larger percentage of body fat than men.
• The elderly have more fat and less water, whereas newborns have less fat and more water, making them prone to dehydration due to rapid water loss.

Fluid Balance

• Fluid gains come from liquids (1400 ml), foods (700 ml), and oxidative metabolism (300 ml), totaling approximately 2400 ml per day.
• Fluid losses include urine (1-2 L), feces (100-200 ml), and from the lungs and skin (500-1000 ml), totaling approximately 2400 ml per day.
• Fluid intake and output are regulated to be equal.
• Intracellular fluid (ICF) is all fluid within the cell, approximately two-thirds of total body water (TBW), containing essential ions and electrolytes, critical for cell function and structure.
• Extracellular fluid (ECF) is fluid outside the cell, roughly one-third of TBW.
  • Intravascular fluid is blood plasma which transports nutrients, hormones, and waste.
  • Interstitial fluid is the space between cells, providing nutrients and removing waste.
• Babies have more ECF than ICF, putting them at high risk for fluid volume deficit.

Electrolyte and Fluid Movement

• Serum osmolality includes the number of osmoles per 1 L of solution, normally between 275-295, determined by sodium levels, which can be estimated by doubling the serum sodium level (135-145).
• Isotonic fluids have an equal concentration on both sides of a membrane.
• Hypotonic fluids have a lower solute concentration outside the cell, causing water to move into the cell and potentially swell.
• Hypertonic fluids have a higher solute concentration outside the cell, causing water to move out of the cell and shrink.
• Osmosis involves water moving through a semipermeable membrane from an area of ​​lower concentration to an area of higher particle concentration ​​until concentrations are equalized.

Water Concentrations

• Diffusion is when particles move from high concentration to an area of lower particle concentration and may or may not pass through a semi-permeable membrane.
• Active transport needs energy in the form of ATP to work.
• During depolarization, Na+ channels open, and Na+ moves into the cell.
• During repolarization, K+ channels open, and K+ moves out of the cell.
• The Na+/K+ pump restores resting potential.
• Hydrostatic pressure pushes fluid generated by the heart's pumping action that exerts pressure on the blood vessel, pushing fluid out into the tissues to nourish the capillaries, arterial side and promotes filtration.
• Oncotic or colloid osmotic pressure is the pulling force exerted by colloids, such as albumin, in a solution, which pulls fluid back into the capillaries, removes waste products, promotes reabsorption venous side of the capillary.

Starlings Law

• Illustrates how fluids move from capillaries to maintain balance.
• Filtration is fluid movement into capillaries.
• Reabsorption is the fluid movement into the capillaries.
• At the arterial end of the capillary, hydrostatic pressure pushes water out into the tissue, carrying nutrients.
• At the venous end, oncotic pressure pulls water back into the capillary, removing waste.

Chemical Regulation

• A 2% water loss or increased osmolality triggers thirst.
• Osmoreceptors in the hypothalamus are activated by dry mouth, hyperosmolality, or plasma volume depletion, causing thirst.
• Heart detects a decrease in blood fluid volume.
• Plasma volume is restored after drinking, diluting ECF osmolality.
• Antidiuretic hormone (ADH), also known as vasopressin, regulates water output to maintain pressure and fluid homeostasis.
• ADH is stimulated by water deficit, increasing plasma osmolarity or decreasing blood pressure.
• Osmoreceptors stimulate the release of ADH, increasing water permeability in the distal tubules and collecting duct, decreasing urine output, and increasing water reabsorption into plasma.
• Increased circulating plasma volume elevates blood pressure.
• ADH causes vasoconstriction and is triggered by a 1-2% increase in plasma osmolality.
• Serum osmolality is the concentration of solutes in the blood.
• Sodium (Na+) indicates ECF balance.
• Chloride (Cl-) pairs with Na to maintain osmotic pressure.
• Potassium (K+) reflects intracellular and extracellular potassium balance.
• BUN (blood urea nitrogen) reflects particles waste that are too large to shift in and out of the vessel waste.
• Creatinine reflects kidney function and hydration status.
• Hemoglobin and hematocrit test the blood concentration and hydration status.
• Urine output reflects kidney function and fluid balance.
• Urine specific gravity measures urine concentration.
• Hemoconcentration results from fluid volume deficit where the blood becomes more concentrated.
• Hemodilution results from fluid volume excess, causing blood dilution, due to increased plasma volume.

Continued Chemical Regulation Details

• Disorders affecting ADH include Syndrome of Inappropriate Antidiuretic Hormone (SIADH) and Diabetes Insipidus (DI).
• SIADH causes excessive water retention, hyponatremia, high blood pressure, fluid overload, dilution of the blood, and low urine output.
• Diabetes insipidus reduced ADH and causes excessive water excretion, dehydration, polydipsia, and polyuria.
• Aldosterone regulates sodium levels
• The Renin-Angiotensin-Aldosterone System (RAAS) activates to increase sodium levels when there is decreased blood pressure or blood volume or sodium deficiency.
  • Sodium and potassium have inverse relationships.
• Sodium levels are regulated by the renal tubule.
• Decreased Na levels cause renin release, converting angiotensin to angiotensin I, which converts to angiotensin II in the lungs
• Aldosterone is a primary regulator of sodium and is stimulated when there is a decrease in Na or elevation in K in the blood vessels of the lungs, thus increases blood pressure
• Potassium and sodium have an inverse relationship.
• Angiotensin II constricts blood vessels to increase blood pressure, decreases glomerular filtration.
• Increased sodium retention raises plasma osmotic pressure, triggering the hypothalamus to secrete ADH, which increases water reabsorption.

Atrial Regulation

• The atrial natriuretic peptide hormone (ANP) is activated with prolonged aldosterone elevation of chronic fluid retention or adrenal tumors.
• ANP increases volume.
• Vasodilatation increases sodium excretion and reduces blood pressure.

Fluid Imbalances

• Atrial muscle stretching inhibits ADH, renin, and aldosterone secretion where Na and water are excreted, decreasing the blood volume and pressure.
• Isotonic volume deficit (dehydration) causes reduced ECF without changes in osmolality, equal Na and water loss, and normal serum osmolality with primarily ECF loss and is not disturbing the ICF.
• Results in hypovolemia-decreases blood fluid volume.
• Hemorrhage, low intake, vomiting, diarrhea, gastric suctioning, fever, environmental heat, excessive sweating, large burns, diuretics, third space fluid shifts, which have increased thirst, urine concentrations with high specific gravity, dry skin with tenting, dry tongue, elevated heart rate.
• Isotonic volume excess (overhydration) can be caused by renal failure, congestive heart failure (CHF), and excessive IV fluids of equal gain of Na and water, normal serum osmolality, increased ECF, BV and BP.

Hypernatremia vs Hyponatremia

• Hypertonic fluid volume deficit: Cellular dehydration, increased Na. Exceeds Na in proportion to water. High serum osmolality. There is increased dehydration, sodium and osmolality. If the patient is hypernatremic and hyperosmolar replace fluids with hypotonic IV fluids

• Hyponatremia is low sodium in proportion to water and low serum osmolality can cause increased hypertonic IV fluids. Cells swell b/c water in vessels move to cell.

• Edema is classified as localized(Sprain or organ system (brain, lungs, heart, peritoneal cavity)), generalized ((organ failure), more water distribution in intestinal spaces)

  • Dependent is gravity (legs sacral areas)
  • Third space is shifting (excess fluid trapped in water spaces)
  • Treat all with normal saline

IV and Electrolytic Treatments

• Isotonic/crystalloids are water that matches size and evenly distributed slute.
• Hypotonic is a cell that swells, low solute, more water that moves into cell.
• Hypertonic is a cell that shrinks, high solute and water moves to cell.
• Albumin, blood produces plasma
• Sodium is 135 to 145. and is a major cation in the ECF. The regulation is directly aldosterone. It is indirectly ADH and ANP.

Explore fluid balance regulation in the body. Understand the roles of plasma osmolarity, ADH, and capillary dynamics. Learn about hypovolemia and hypoproteinemia and their effects on fluid movement.