TEST 1: Fluid & Acid-Base Balance Flashcards
Sodium homeostasis mechanisms
- Renin-Angiotensin Aldosterone System (RASS):
- Antidiuretic Hormone (ADH)
- Atrial Natriuretic Hormone (ANP)
Renin-Angiotensin Aldosterone System as a mechanism for sodium homeostasis
- Renin release: low BP/ blood volume triggers release of renin from the juxtoglomerular cells of the kidney
- Angiotensin II formation: renin converts angiotensin (from liver) into angiotensin I, which is then converted to angiotensin II by the angiotensin-converting enzyme (ACE) in the lungs
- Aldosterone secretion: angiotensin II stimulates adrenal cortex to release aldosterone
- Sodium reabsorption: aldosterone acts on distal tubule and collecting ducts of the kidneys to increase sodium reabsorption and water retention (thus elevating blood pressure and volume)
Anti diuretic hormone as a mechanism for sodium homeostasis
- Released in response to high osmolarity: high plasma osmolarity triggers the release of ADH from the posterior pituitary gland
- Water reabsorption: ADH increases the permeability of collecting ducts in the kidneys to water, which promotes water reabsorption and dilution of the sodium concentration of the blood.
ANP as a mechanism for sodium homeostasis
- Release in response to high blood volume: stretch receptors in the atria of the heart sense increased blood volume and release ANP
- Inhibition of RAAS: ANP inhibits renin, aldosterone, and ADH— promoting the excretion of sodium and water (lowering the BP and pressure)
Potassium homeostasis mechanisms
- Aldosterone
- Insulin
- Acid-Base Balance
- Kidney function
Aldosterone as a mechanism for potassium homeostasis
-Aldosterone promotes excretion of K by the distal tubule and collecting ducts in exchange for sodium reabsorption
-Critical for regulating serum K levels
Insulin as a mechanism for potassium homeostasis
-Insulin facilitates the uptake of K into cells (particularly muscle cells) by activating the sodium-potassium ATP-ase pump
-This lowers extracellular K levels
Acid-Base balance as a mechanism for potassium homeostasis
-Acidosis: hydrogen ions enter cells in exchange for K ions—> hyperkalemia
-Alkalosis: hydrogen ions move out of the cell and K ions enter —> hypokalemia
Kidney function as a mechanism for potassium homeostasis
- Filtration and reabsorption: the kidneys filter K in the glomerulus. Most of the filtered K is reabsorbed in the proximal tubule and loop of Henle. The distule tubule and collecting ducts regulate final excretion of K based on body needs.
- K secretion: K is secreted in exchange for sodium under the influence of aldosterone.
Regulation of NA and K
- Body uses negative feedback mechanisms where deviation from normal levels trigger a response to restore balance.
- Hormones like aldosterone, ADH, and ANP play critical roles in regulation of NA and K
- Adequate dietary intake of NA and K is critical for maintaining balance and the kidneys adjust excretion rates to match intake levels.
Sodium and Potassium homeostasis
-Sodium: primarily regulated by RAAS, ADH, and ANP
-Proper NA balance maintains fluid volume, BP, osmotic balance.
Potassium: mainly controlled by aldosterone, insulin, acid-base balance, and kidneys.
-Proper K balance maintains normal cell function, nerve transmission, and muscle contraction.
3 main fluid compartments
-Intravascular (plasma)
-Interstitial
-Intracellular
Intravascular fluid compartment
(Plasma)
-Includes fluid WITHIN the blood vessels
-Contains a high concentration of proteins (esp albumin) which contribute to oncotic pressure as well as a significant amount of electrolytes
-5% of total body weight
Interstitial Compartment
-The fluid that surrounds the cells IN the tissues, OUTSIDE the blood vessels
-Acts as bridge between the Intravascular compartment and the cells, facilitating nutrient and waste exchange
-Accounts for 15% total body weight
Intracellular compartment
-Fluid WITHIN the cells
-Contains high concentrations of K, phosphate, and proteins
-Accounts from 40% total body weight
Mechanisms of fluid shifts
- Osmosis
- Hydrostatic Pressure
- Oncotic Pressure (colloid osmotic pressure)
Osmosis
-Movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration
-Driven by osmolarity, heavily influenced by electrolytes like NA and K.
Hydrostatic pressure
-Pressure exerted by the fluid within the blood vessels
-Pushes fluid out of the capillaries into the interstitial space.
Oncotic pressure (Colloid osmotic pressure)
-Exerted by plasma proteins (albumin) within the blood vessels
-Pulls fluid into the capillaries from the interstitial space
Patterns of fluid shifts between Intravascular and interstitial compartments
- Capillary hydrostatic pressure: drives fluid out of capillaries into the interstitial space (balanced by—>
- Interstitial hydrostatic pressure: opposes movement of fluid out of the capillaries
- Capillary oncotic pressure: pulls fluid back into the capillaries from the interstitial space
- Interstitial oncotic pressure: pulls fluid out of the capillaries into the interstitial space
Starlings Law of Capillary Forces
-The net movement of fluid is determined by the balance of pressures
-Fluid that moves out of capillaries is usually reabsorbed but any excess is drained by lymphatic system
Pattern of fluid shift between interstitial and intracellular compartments
-Osmotic gradient: drives water movement in and out of the cells.
-If interstitial fluid becomes hypertonic (high solute concentration) water will move out of cells into interstitial space
-If interstitial fluid becomes hypotonic (low solute concentration) water will move into the cells.
Pathological fluid shifts
- Edema
- Dehydration
- Third spacing
Edema
-Accumulation of fluid in the interstitial space
Causes:
-Increased capillary hydrostatic pressure (CHF, venous obstruction)
-Decreased capillary oncotic pressure (low albumin d/t liver disease)
-Increased capillary permeability (inflammation, trauma)
-Lymphatic obstruction
(Lymphedema)