Renal functions and body fluids

Question 1

What is the major functions of the kidneys?

Answer 1

• Filtration
  ○ Removes any soluble waste products from the blood and puts them into urine
  ○ H+, Na+, K+, urea etc….
  ○ Excess proteins from diet can’t be sorted. The amine group of the animo acids is a waste product and so is converted to ammonia by the liver. Ammonia is toxic so can’t be in the body for long and is converted into less toxic compound urea by liver. The kidneys will filter urea out and remove it via the urine.
  § NH3 also created from DNA and RNA is converted into uric acid
  ○ Creatin is produced during long exercise periods and constantly secreted during muscle break down
  § Kidneys will filter tis out the blood
  § Blood creatine tests ca show a high creatine level if the kidneys do not work
  
  • production
    ○ Kidneys creates renin which helps regulate blood pressure
    ○ Kidneys creates erythropoietin to create red blood cells - as the kidneys revive a lot of blood (kidneys can sense anaemia and will produce erythropoietin ) erythropoietin goes to bone marrow and increases creation of red blood cels
    ○ Creates Prostaglandin- dilates blood vessels so more blood can go to the kidneys (modify blood flow to the kidneys)
    Patients with denial disease may have a lack of vit d as
    Sunlight on skin converts cholesterol into vit D(inactive) kidney convert inactive vit d into activated vit D.
    § Kidneys convert inactive vitamins d int active vitamin d which can be used to create transport proteins for Ca2+ absorption
    §
  • Regulation
    ○ Maintains the volume of extracellular fluids and their osmolality to ensure no water will enter or exit the cell
    ○ Maintains the concertation of ions in the fluid/blood
    ○ Controls pH of the blood
    ○ Regulates blood pressure and red blood cell levels
    ○ Must regulate volume, concertation and distribution of fluids in the body
    ○ Help from adrenal glands and brain

Question 2

Why must we regulate body fluids?

Answer 2

• Due to volume of water
  ○ Humans have 40-45l of water in the body
  § Women have less water in their body as they have more fat in their body then men do
  ○ If we get dehydrated the cells will shrivel and if overhydrated the cells will burst
  ○ If we have too much water the kidneys will create high volume of dilute urine
  ○ If we have too little water the kidneys create lower volumes of concentrated urine
  
  • Due to osmolality (ion concentration)
    ○ Ions will determine the water potential of a fluid e.g. a high concertation of ions outside the cell will result in a lower water potential. Water will move down a water potential gradient by osmosis out of the cell and cause the cell to shrink.
    § can occur the other way around too
    ○ Normal osmolality is 285mOsm/Kg H20 textbook in all fluid compartments
    § 285 per litter of water/ plasma in the body
    *

Question 3

What is the fluid compartments of the body?

Answer 3

• Intracellular fluid (water in the cells) 40% of all fluid
• Extracellular fluid (water outside of cells) 60% of all fluid
  ○ Plasma (water in the blood) 20%
  ○ Interstitial fluid 80%
• Barrier between plasma and interstitial fluid is the endothelium lining
  ○ Water can only move in capillaries’ due to this lining in the vessels
• Barrier between the interstitial fluid and the intracellular fluid is the cell membrane
  *

Question 4

What is the composition of the fluid compartments?

Answer 4

• Plasma, interstitial and intracellular fluid have the same osmolality (285mOsm/Kg H20) but contains a different concentration of each ion
• Plasma and interstitial is similar because the endothelium lining is permeable to ions
• The Na+ and K+ concertation is controlled by Na+/K+ATPase
• Plasma contains significantly more protein than the other 2
  *

Question 5

What is the movement of fluid between compartments?

Answer 5

• Starling forces
  ○ H2O and ions move across the endothelium lining to and from the interstitial fluid and plasma by bulk flow and leads to changes in the hydrostatic pressure gradient
• Osmotic pressure
  ○ Movement of H2O and ions to and from the intracellular fluid to interstitial by osmosis to change the ion concretion/water potential
• Hydrostatic pressure= any pressure that is exerted by a fluid inside a contained space
  ○ Hydrostatic pressure = blood pressure at level at capillaries
  ○ Hydrostatic pressure= osmosis at the level of the cells
• Water will move from a high water potential to a low water potential
  ○ e.g. if the blood plasma has more ions than the interstitial fluid water will move from the interstitial to the plasma
• Osmotic pressure= pressure caused by water at different concentrations due to the dilution of water by dissolved molecules (solute), notably salts and nutrients