Diffusie, Osmose en Convectie

• The notes below summarize the provided text, focusing on osmo- and volumeregulation

Diffusie, Osmose en Convectie (Diffusion, Osmosis, and Convection)

• Diffusie (Diffusion): The movement of dissolved particles through a permeable membrane from an area of high concentration to an area of low concentration, striving for equilibrium.
• Osmose (Osmosis): Water movement across a semipermeable membrane to an area with a higher concentration of solute particles that cannot pass through the membrane.
• This creates an osmotic gradient.
• Convectie (Convection): Water transport due to pressure, carrying dissolved particles along with it, which is filtration combined with convection.
• In the kidneys, filtration occurs in the glomerulus, and diffusion in the tubules.
• Extracellulair vs. Intracellulair:
• The extracellular compartment has high concentrations of sodium and chloride ions.
• The intracellular compartment has low concentrations of sodium and high concentrations of potassium and organic acids.
• The osmolarity in both compartments is equal at approximately 290 mOsm.
• This balance prevents net water movement between the compartments.

Osmoregulatie (Osmoregulation)

• Osmoregulation is coupled to water regulation.
• When the body has too little water, the sodium concentration increases and water shifts from intracellular to extracellular to maintain plasma osmolarity.
• Hypernatremia occurs when plasma sodium remains high despite these efforts.
• Conversely, excess water leads to hyponatremia (low sodium concentration), with more water in both intra- and extracellular compartments, but especially intracellulary due to its larger volume.
• High sodium concentration causes thirst to stimulate drinking and vasopressin (ADH) production to concentrate urine and retain water, lowering plasma osmolarity.
• Low sodium concentration inhibits thirst and ADH release.

Volumeregulatie (Volume Regulation)

• Volumeregulatie controls the effective circulating volume within the extracellular compartment to maintain homeostasis.
• Dysregulation results in issues within the extracellular compartment.
• The intracellular compartment is recognizable by potassium ions, the extracellular by sodium ions.
• If the circulating volume decreases, there is less fluid with dissolved particles and less sodium in the extracellular compartment.
• Volume can be restored by giving salt to increase the volume again.
• Low sodium lead to volume depletion, and excess sodium can cause edema.
• Baroreceptors and noradrenaline regulate effective circulating volume.
• Baroreceptors activate the sympathetic nervous system allowing noradrenaline to retain salt.
• Renin-Angiotensin-Aldosterone System (RAAS) is activated, leading to sodium retention through the action of Angiotensin II and aldosterone.
• These systems respond in cases such as blood loss due to infection, causing volume expansion through sodium retention.
• In severe cases, ADH may also be involved in water retention.
• Inemergencies, volumeregulation takes precedence over osmoregulation.
• Normally, ADH falls under osmoregulation rather than volumeregulation.

Natriuretische Peptiden (Natriuretic Peptides)

• These are produced by the heart in response to fluid retention, acting at the same location as aldosterone to reduce sodium retention.
• Their effectiveness is reduced in heart failure leading to high peptide concentrations alongside edema.

Waterregulatie (Water Regulation)

• The kidneys regulate the quantity of urine.
• We must release at least 600 osmol of waste products each day.
• In situations of water scarcity, the kidneys concentrate waste products to conserve water.
• With high water intake, the kidneys produce dilute urine.

Watervergiftiging (Water Intoxication)

• Watervergiftigning occurs with an extremely high intake of water
• Too much water in the blood disrupts the balance between water and salt.
• Water moves into cells causing them to swell.
• This swelling causes headaches due to pressure on the nerves
• Swelling of cells in the brain can cause seizures, suffocation, and death
• The lethal amount of water depends on factors like body weight, but as little as three liters per hour can be fatal.
• Drug use can also cause fluid retention.
• XTC leads to a large increase in ADH release, reducing water secretion and resulting in fluid retention. This can lead to swelling of the brain.

Osmotische Waarde (Osmotic Value)

• A 0.9% NaCl solution contains 9 grams of salt per liter.
• Osmotic value expresses osmotic pressure in a solution caused by osmotically active particles.
• Most salts split into ions in a solution. The osmotic value of 1 mol NaCl equals to 2 osmol after it splits up into Na+ and Cl-.
• Osmolality: Concentration of osmotically active particles per kilogram of solution (osmol/kg).
• Osmolarity: Concentration of osmotically active particles per liter of solution (osmol/L).
• The plasma osmolarity can be calculated as: 2x [Na +] + [glucose] + [BUN].

Osmotische Druk (Osmotic Pressure)

• Osmotic pressure occurs during diffusion of water between two solutions with different concentrations of dissolved substances.
• Divided into colloid osmotic preasure and crystalloid osmotic pressure
• The osmotic pressure of a 0.9% NaCl solution can be calculated using the following formula:
• π = ix CXRXT
  • π = osmotic pressure in kPa;
  • i = number of ions in the molecule;
  • C = concentration in mol/L;
  • R = gas constant (8.31);
  • T = temperature in Kelvin (37°C = 310°K);

Natriumtransport (Sodium Transport)

• Sodium is the key electrolyte for maintaining extracellular fluid balance, and where sodium goes, water follows.
• Sodium is reabsorbed in large quantities each day throughout the entire nephron.
• Most sodium (67%) is reabsorbed in the proximal tubule, followed by the loop of Henle (25%), distal tubule, and collecting duct.
• Approximately 99.6% of filtered sodium is reabsorbed.
• The distal nephron reabsorbs only a small portion of sodium, but can establish transepithelial concentration gradient.

Paracellulair vs. Transcellulair Transport (Paracellular vs. Transcellular Transport)

• Sodium is absorbed through two different mechanisms:
• Paracellulair: Passive transport via electrochemical gradient
• Transcellulair: Two steps. Sodium transport over the apical membrane, and moving sodium out of the cell (active transport), over the basolateral membrane into the interstitial space using Na/K pump.

Vloeistofcompartimenten (Fluid Compartments)

• Total Body Water (TBW):
  • Men: Body weight x 0.6
  • Women: Body weight x 0.5
• Extracellular fluid (ECF): Body weight x 0.2
• Intracellular fluid (ICV): Body weight x 0.4
• Interstitial fluid is 3/4 of the ECF, with the remaining 1/4 being blood plasma.

Bloedserum Waarden (Blood Serum Values)

• Normal ECF values include:
  • Potassium: 4-6 mmol/L
  • Calcium: 2.1-2.55 mmol/L
  • Sodium: 135-145 mmol/L
  • Chloride: 95-105 mmol/L
  • Bicarbonate: 25 mmol/L
  • Phosphorus: 2 mmol/L
  • pH: 7.4

Serum [K+]

• Low potassium (hyperpolarization) reduces cell excitability.
• High potassium reduces cell polarity causing continuous activation.

Serum [Ca²+]

• Low calcium leads to bradycardia and conduction delays.

Serum [Na]

• Hyponatremia is often due to excess water, not sodium deficiency.
• Check for undervulling (volume depletion) or overvulling (normovolemic).
• A low urine sodium indicates reduced circulating volume.

Oplossingen en Hun Effect (Solutions and Their Impact)

• Adding isotonic saline, pure water, or salt to the extracellular fluid (ECF) affects ECF volume, the intracellular fluid (ICF), and their osmolarities.

Toediening Isotone Zoutoplossing (Isotonic Saline Administration)

• The addition of an isotonic saline solution (0.9% NaCl in water) does not alter the ECV osmolarity and does not shift water in either direction of the ICV.
• This method enlarges the ECV non-invasively

Toediening Oplossingsvrij Water (Solution-free Water Administration)

• Adding solution-free water (or isotonic glucose) lowers the ECV osmolarity.
• The water distributes into the ECF, and water from there makes its way into the ICV due to the existing gradient

Reactie in Het Lichaam (Reaction in the Body)

• Adding salt leads to high sodium concentration and osmolarity, causes thirst and AVP production;
• There is an increase in the extracellular fluid volume.
• The kidneys signal increased volume and excrete more sodium. The body monitors effective circulating volume.

Excretieverlaging (Excretion Reduction)

• Lowering Sodium Secretion:
  • Via the Renine-Angiotensine-Aldosteronsysteem (RAAS
  • Neuraal
  • Hormonaal

Hemodynamische Veranderingen (Hemodynamic Changes)

• Rapid decrease in blood pressure: Kidneys reabsorb Na.
• Rapid increase in blood pressure: Enhances natriuresis.

Transporten (Transporters)

• The Na +-K+-ATPase pump, depends on oxygen
• Addition of NaCl-infuus, or hypotonic fluid impacts fluid balance.

Zouttransport (Salt Transport)

• The Western Diet is more salt than advised.
• The ability of the kidney to dilute an concentrate urine depends on an osmotische gradiënt (osmotic gradient).

Hypo En Hypernatriëmie (Hypo and Hypernatremia)

• Check AVP concentration, water-, protein- and osmol-intake.
• Check age and Nierfunctie (kidney function)