Duy's Anki - Mod 4

• Involvement of Kidneys in Homeostatic functions

  • Regulating electrolytes
  • Acid-base control
  • Blood volume control
  • Regulation of blood pressure
• Primary goal of kidneys

  Water balance
• Intracellular Fluid (ICF)


  Fluid within cells and comprises about two thirds of total body fluid
• Extracellular Fluid (ECF)


  Fluid surrounding cells which includes plasma, interstitial fluid, lymph, and transcellular fluid (e.g., cerebrospinal fluid); ⅓ of total body fluid
• Transcellular fluid


  Portion of total body water contained within epithelial lined spaces
• Composition of ECF


  • Plasma → ⅕ of ECF
  • Interstitial fluid: → ⅘ of ECF
  • Lymph and transcellular fluid → Negliglble
• Major compartments for water (fluid) — three pools that remain distinct due to presence of "barriers" between the ICF and ECF


  • ICF
  • Plasma
  • Interstitial fluid
• Purpose of barriers that separate body-fluid compartments

  Limits the movement of water and solutes between the various compartments to differing degrees
• Barriers between the plasma and the interstitial fluid

  At the level of the capillaries, water and everything else in the plasma (except proteins) can freely exchange with the interstitial fluid. The composition of the plasma and interstitial fluid are essential identical, except for plasma proteins. Any change in one of these compartments is quickly reflected in other
• Barriers between the intracellular fluid and the ECF

  Plasma membrane
• Composition of ICF


  Proteins that do not exchange with the ECF
• Distribution of ions across plasma membrane

  Unequal. Concentration of K+: Greater in the ICF. Concentration Na+: Greater in the ECF. Barrier does not allow the passive movement of either ICF or ECF constituents across the plasma membrane, preventing them from equilibrating through the process of diffusion
• All exchanges of water and other constituents between the ICF and the external world are dependent upon

  the ECF. Even though cells tightly regulate their own ICF, it can be said that overall control of fluid balance is dependent upon regulating the ECF
• Two factors that are regulated to maintain fluid balance in the body

  • ECF Volume
  • ECF Osmolarity
• Purpose of ECF volume regulation

  Closely regulated to maintain blood pressure
• How ECF volume is regulated

  Maintenance of salt balance is important in the long-term regulation of ECF volume
• Purpose of ECF osmolarity regulation

  Closely regulated to prevent the swelling or shrinkage of cells
• Relationship between ECF and blood pressure

  Direct relationship between ECF volume and blood pressure via plasma volume: ↑ ECF volume → ↑ plasma volume → ↑ arterial blood pressure. Mechanisms exist to adjust blood pressure until the ECF volume is returned to normal values
• Short-term control factors of ECF

  • Baroreceptor Reflex
  • Fluid Shifts
• Long-term control factors of ECF

  • Fluid Input/Output
• Baroreceptors


  Mechanoreceptors that are located in the carotid artery and the aortic arch (areas within major arteries of the body). Purpose: Detect changes in arterial blood pressure
• How do baroreceptors regulate blood pressure

  Through the effects of the autonomic nervous system on the heart and blood vessels, the baroreceptor reflex regulates blood pressure. Cardiac output: Amount of blood pumped by the heart per minute. Total peripheral resistance: Resistance to blood flow due to the constriction of blood vessels → ↑ TPR, ↑ BP. When pressure falls too low, cardiac output and total peripheral resistance will increase to raise blood pressure. When blood pressure rises above normal, CO and TPR decreases to reduce blood pressure
• Fluid Shifts


  ↓ Plasma volume → temporarily be compensated for by a shift of the fluids out of the interstitial compartment to the plasma. ↑ Plasma volume → Fluid to shift into the interstitial compartment
• Primary function of kidneys and thirst mechanism

  Controlling fluid output and input, respectively, to long-term regulate blood pressure. Control of urine output by kidneys is critical to long-term BP regulation
• 90% of ECF's solutes


  • Sodium
  • Anions associated with it (mainly Cl)
• Relationship between salt and water transportation

  Whenever salt is transported across a membrane, water follows due to osmosis. By controlling salt levels, ECF volume is being controlled. To maintain salt balance, salt input must equal salt output
• Regulation of salt input

  Poor; dependent upon dietary salt
• Necessary daily salt intake


  Necessary on a daily basis to replace the salt lost in the feces and sweat, which is about 0.5g/day for normal activity levels (higher activity levels will increase the amount lost in sweat)
• Location of excess salt elimination

  • Feces
  • Sweat
  • Kidneys
• Osmolarity


  Measure of the concentration of a particular solute in solution. High osmolarity: More solute, therefore less water, in solution
• Osmosis


  Water moves down its concentration gradient until osmotic pressure across a membrane is equalised. Regulating osmolarity is very important in preventing changes in cell volume
• Decrease in water in the ECF

  Osmolarity increases, and the ECF is hypertonic. Hypertonic: One in which the concentration of solutes within that solution is greater than that of another solution that is separated by a membrane. Since there is normally a balance in the osmolarity of the ICF and ECF, hypertonicity of ECF causes water to move out of the cells into the ECF until osmotic pressure equalized. Loss of water from cells causes them to shrink
• Hypertonic


  One in which the concentration of solutes within that solution is greater than that of another solution that is separated by a membrane
• Increase in water in the ECF

  Osmolarity decreases, and the ECF would be hypotonic. Hypotonic: One in which the concentration of solutes within that solution is lower than that of another solution. Result in water moving into the cells until the osmotic pressures were equalised. Movement of water into the cells would cause them to expand. If very hypotonic ECF, amount of water moving into cells would cause them to burst
• Hypotonic


  One in which the concentration of solutes within that solution is lower than that of another solution
• Hypotonicity of ECF


  Insufficient concentration of ECF solutes. Associations: Overhydration, or excess free H2O. Three major causes: Renal Failure, Rapid water ingestion, Over secretion of vasopressin
• Associations of Hypotonicity of the ECF

  • Renal Failure
  • Rapid water ingestion
  • Over secretion of vasopressin
• Hypertonicity of ECF


  Excessive concentrations of ECF solutes. Associations: Dehydration, with three major causes: Insufficient water intake, Diabetes insipidus, Excessive water loss. Cellular consequences generally relate to a decrease of normal cell function as the ICF is decreased. Brain is particularly sensitive and shrinking of neurons can cause confusion, delirium, and even coma or death
• Associations of hypertonicity of the ECF

  • Insufficient water intake
  • Diabetes insipidus
  • Excessive water loss
• Isotonic solution


  Equal osmolarity to that of normal body fluids. Use in medicine: Saline solution is being injected into the blood plasma within the veins, which makes up approximately one fifth of the ECF. Purpose: Prevent fluctuations of intracellular volume