Untitled Quiz

Fluid Balance

• Cellular function necessitates a precisely regulated fluid medium.
• Homeostatic balance encompasses three key aspects: water balance, electrolyte balance, and acid-base balance.
• These balances are maintained through the coordinated action of several bodily systems: urinary, respiratory, digestive, integumentary, endocrine, nervous, cardiovascular, and lymphatic systems.

Body Water

• Newborn babies' body weight is approximately 75% water.
• Young men typically have 55-60% body water, while women have slightly less.
• Obese and elderly individuals may have as little as 45% body water.
• A 70 kg (150 lb) young man has approximately 40 liters of total body water (TBW).

Fluid Compartments

• The body's fluid is primarily divided into intracellular fluid (ICF) and extracellular fluid (ECF).
• ICF constitutes approximately 65% of the total body water.
• The ECF comprises 35% of the total body water.
  • ECF can be further divided into tissue (interstitial) fluid (25%), blood plasma and lymphatic fluid (8%), and transcellular fluid (2%).

Water Movement Between Fluid Compartments

• Fluid is constantly exchanged between various compartments.
• Water movement occurs primarily via osmosis.
• Osmotic pressure differences stemming from solute concentrations govern fluid shifts between compartments.
• Electrolytes, the most common solutes, play a pivotal role in water distribution.
  • Sodium salts are abundant in the extracellular fluid.
  • Potassium salts are abundant in the intracellular fluid.

Water Gain

• Fluid balance requires that daily gains and losses are equal.
• Water gain originates from two primary sources: preformed water and metabolic water.
  • Preformed water (2,300 mL/day) encompasses water ingested through food and beverages.
  • Metabolic water (200 mL/day) is a byproduct of aerobic metabolism and dehydration synthesis. -This is also known as metabolic water formation.

Water Output

• Water output totals 2,500 mL per day.
  • Outputs include urine (1,500 mL), sweat (100 mL), cutaneous transpiration (400 mL), expired air (300 mL), and feces (200 ML).
  • Food contributes 700 mL. Drinking is 1600 mL

Regulation of Fluid Intake

• Thirst, mostly driven by dehydration, is the primary regulator of fluid intake.
• Dehydration reduces blood volume and blood pressure, and increases blood osmolarity.
• Osmoreceptors within the hypothalamus respond to changes in blood osmolarity and angiotensin II production.
• Hypothalamus stimulation leads to the production and release of antidiuretic hormone (ADH).
• Cerebral cortex interprets these feedback loops and produces the sensation of thirst.

Regulation of Water Output

• Controlling urine volume is the main mechanism for managing water output.
• Kidneys can't replace water or electrolytes but adjust their rate of elimination.
• Adjusting sodium reabsorption impacts water reabsorption and excretion.
• a) Changes in urinary volume are adjusted through varying sodium reabsorption.
  • Water follows sodium's reabsorption or excretion.
• b) ADH acts by concentrating urine.
  • ADH secretion is triggered by hypothalamic osmoreceptors during dehydration.
  • Aquaporins, synthesized in response to ADH, facilitate water movement into renal collecting ducts' renal medulla, consequently concentrating urine.
  • ADH release is suppressed when blood volume and pressure are high and blood osmolarity is low.

Disorders of Water Balance

• Volume depletion (Hypovolemia): Equal loss of water and sodium, with normal osmolarity, caused by hemorrhage, severe burns, prolonged vomiting, or diarrhea; can lead to circulatory shock, and neurological dysfunction.

• Dehydration (negative water balance): More water loss than sodium leads to elevated osmolarity. Causes include inadequate water intake, diabetes, profuse sweating, or diuretic misuse; can result in circulatory shock, neurological dysfunction and infant mortality.

• Fluid excess: Kidneys typically compensate for excessive fluid intake by increasing urine output.

  • Volume Excess: Both sodium and water are retained; ECF remains isotonic, leading to increased blood volume. Causes include aldosterone hypersecretion or renal failure.
  • Hypotonic Hydration (Water Intoxication): More water than sodium is retained or ingested; ECF becomes hypotonic. Symptoms include cellular swelling, edema in brain and lungs, which can be life threatening

Electrolyte Balance

• Electrolytes are crucial for metabolic processes, determining electrical potentials across cell membranes, and affecting water distribution and content within the body.
• Major cations/positively charged ions include sodium (Na+), potassium (K+), calcium (Ca2+), and hydrogen (H+).
• Major anions/negatively charged ions include chloride (Cl-), bicarbonate (HCO3-), and phosphate (PO43-).
• Intracellular and extracellular fluid compartments have differing electrolyte concentrations, but maintain the same overall osmolarity.

Sodium - Functions

• Sodium is essential for maintaining resting membrane potential in nerves and muscles,
• Sodium (Na+) accounts significantly for ECF osmolarity and total body water volume.
• Sodium gradients are critical for cotransporting various substances, like glucose, K+, and Ca2+ across cell membranes.
• Sodium-potassium pumps are responsible for generating body heat.

Sodium - Homeostasis

• Adults typically need approximately 0.5 grams of sodium per day.
• a) Aldosterone: A "salt-retaining hormone" that regulates sodium reabsorption in specific nephron parts that results in a lower number of sodium ions in the body's urine.
• b) ADH: Modifies water excretion; high blood sodium levels trigger ADH release, promoting water reabsorption and counteracting the elevation.
• c) ANP & BNP: Inhibit sodium and water reabsorption & renin/ADH secretion, thus promoting sodium and water excretion for blood pressure reduction.

Sodium Imbalances

• Hypernatremia: High levels (>145 mEq/L) of blood sodium (Na+) typically caused by loss of water faster than sodium (e.g., diarrhea) or insufficient water intake; is associated by water retention, hypertension, and edema.
• Hyponatremia: Low levels (<130 mEq/L) of blood sodium (Na+), often caused by large fluid losses or replacing lost fluids inadequately with pure water, quickly corrected by the body via water excretion.

Potassium - Functions

• Potassium is the most prevalent intracellular cation (positive ion).
• Potassium (K+) significantly impacts intracellular fluid osmolarity and cell volume.
• It's crucial for generating resting and action potentials in muscle and nerve cells.
• Potassium is essential for the sodium-potassium pump's function.
• It's involved in protein synthesis and other metabolic processes.

Potassium - Homeostasis

• Potassium homeostasis is closely related to sodium homeostasis.
• The proximal convoluted tubule reabsorbs 90% of filtered potassium.
• The distal convoluted tubule and collecting duct secrete potassium in response to blood levels, with aldosterone influencing this secretion.

Potassium Imbalances

• Hyperkalemia: Excessive amounts of potassium (K+), often resulting from rapid K+ release (crush injury).
  • Symptoms encompass nerve and muscle cell excitability alterations, possibly leading to cardiac arrest due to excessive K+ in extracellular fluid.
• Hypokalemia: Insufficient potassium (K+), arising from excessive fluid loss (e.g., sweating, chronic vomiting, diarrhea).
  • Symptoms include weaker and less excitable nerve and muscle cells leading to muscle weakness, decreased reflex responses and cardiac arrhythmias.

Chloride - Functions

• Chloride (Cl-) is the major extracellular anion (negative ion).
• It's critical for maintaining proper stomach hydrochloric acid (HCl) production.
• It is vital in the chloride shift, a process that aids in the transport of carbon dioxide (CO2) in red blood cells.
• Chloride helps regulate the body's pH.

Chloride - Homeostasis

• Chloride follows sodium. When Na+ is reabsorbed, Cl- passively follows.

Chloride Imbalances

• Hyperchloremia: High Cl- levels, stemming from excessive dietary intake or IV saline administration.
• Hypochloremia: Low Cl- levels, a side effect of hyponatremia, sometimes linked to hyperkalemia or acidosis.
  • Both conditions primarily disrupt acid-base balance.

Calcium - Functions

• Calcium (Ca2+) strengthens bones and teeth.
• It's fundamental to muscle contraction and neurotransmitter release.
• It plays a role in blood clotting formation.

Calcium - Homeostasis

• Calcium homeostasis is primarily regulated by parathyroid hormone (PTH), calcitriol (Vitamin D), and calcitonin through their impact on bone deposition and resorption, intestinal absorption, and urinary excretion.
• Intracellular calcium levels are low to prevent calcium phosphate crystal formation. Cells need to efficiently regulate and sequester calcium.

Calcium Imbalances

• Hypercalcemia: Elevated calcium levels, tied to conditions like alkalosis, hyperparathyroidism, and hypothyroidism.
  • Symptoms encompass muscular weakness, reduced nerve/muscle responsiveness, and cardiac arrhythmias.
• Hypocalcemia: Decreased calcium levels, stemming from factors like low Vit D, diarrhea, pregnancy, acidosis, lactation, hypoparathyroidism, and hyperthyroidism.
  • Symptoms encompass heightened nerve and muscle excitability, ultimately causing potentially life-threatening muscle spasms.

Acid-Base Balance

• Maintaining a precise pH is critical for enzyme function. Enzymes are sensitive to pH. Even small shifts can affect metabolic processes and protein structure.

• The normal pH range for blood and tissue fluids is 7.35 to 7.45.

• Metabolism generates acids continuously (e.g., lactic acid, fatty acids, carbonic acid).

Acid-Base Buffers

• Buffers are mechanisms that resist drastic pH changes.
  • Physiological Buffers: the respiratory and urinary systems control the amount and type of acids/bases excreted/preserved in the body via their respective processes.
  • Chemical Buffers: binds H+ when concentrations rise or releases H+ when concentrations fall to restore the normal pH quickly (<1 second). The 3 major chemical buffers are Bicarbonate, Phosphate, and Protein.

Renal Control of pH

• Kidney neutralize more acid or base than respiratory systems or chemical buffers.
• Renal tubules secrete H+ into the tubules fluids and it is bound to bicarbonate, ammonia and phosphate buffers. These buffers are then excreted via urine.

Respiratory Control of pH

• Adding CO2 to fluids increases H+, lowering pH while CO2 expulsion raises pH. The lungs expel CO2.

Disorders of Acid-Base Balance

• Acidosis: pH < 7.35. H+ influx in cells pushes out K+, increasing extracellular amounts. This disturbs membrane potential and results in nerve and muscle cell reduced responsiveness and potential for loss of consciousness, coma, and death.
• Alkalosis: pH > 7.45. H+ efflux from cells drives K+ in, resulting in increased membrane excitability and overstimulation of nerves and muscles which can cause death.

Compensation for Acid-Base Imbalances

• Compensated: The kidneys or lungs adjust to counteract pH imbalances originating from respiratory or metabolic causes.
• Uncompensated: The body's pH regulation mechanisms are ineffective, requiring medical intervention.
• Respiratory compensation involves adjusting ventilation to control CO2 levels.
• Renal compensation involves adjusting H+ secretion by the kidneys.
• Short-term imbalances are compensated for better by the lungs, whereas the kidneys are far more efficient and crucial for longer-lasting imbalances.