Glomerular filtration

Question 1

What is the basic anatomy of the nephron?

Answer 1

• Contains nephrons which are hollow tubes that are the functional unit of the kidney
  
  • Nephrons are closed at the distal end and open at the proximal end
  • Each nephron is independent from the other. There are around 1.25 million nephrons per kidney and they are 3-4 mm long. Each produces tiny amounts of urine
  • Nephrons contain the glomerulus, bowman’s capsule, PCT, loop of Henle, DTC and collecting ducts
  • Fluid is modified by the cells lining the nephron as the fluid passes its length
  • Coiled up capillaries is called glomerulus
  • Bowmans capsule is where the filtrate /plasma collects
  • Blood vessels arriving =Afferent
  • Blood vessels exiting = efferent
  • Arterioles have more smooth muscles to allow contraction so can constrict or dilate of change blood flow
  • Afferent Arterioles will turn into capillary (glomerulus) this will turn into the efferent arteriole which goes into another capillary
  • Glomerulus capillary is 100x more permeable than normal capillary due to fenestrations in the capillary

Question 2

Explain glomerular structure .

Answer 2

• Blood enters the glomerulus via the afferent arteriole which is wider than the efferent arteriole of which blood exits the glomerulus this creates a high hydrostatic pressure inside the glomerulus
  
  • the glomerulus is a collection of collided up capillaries
  • The capillaries of the glomerulus have large pores where the plasma can escape from.
  • Plasma if filtered out of the glomerulus into the bowman’s capsule the plasma will carry dissolved substances and is forced out by the high hydrostatic pressure
  • The visceral layer is the inner wall of the bowman’s capsule and touches the glomerulus
  • Parietal layer is the outside of the Bowmans capsule
  • endothelium cells
    ○ Pores in endothelium all of glomerulus encourages the fluid to exit the capillary
  • Basement membrane is negatively changed to repel proteins
  • The visceral layer has podocytes-finger like protections to ensure that no proteins or cels can pass though into the filtrate (forms a filtration barrier)
  • the endothelium lining, basement membrane (which is thicker than usual) and podocytes stop large particles e.g. proteins entering the bowman’s capsule

Question 3

Starlings forces

Answer 3

• In a normal capillary- not in a glomerulus capillary
  
  • Water at the arteriole side of the capillary moves out into the interstitial fluid
  • This lowers the hydrostatic pressure in the venous end of the capillary
    1. lots of water in the capillaries at the arteriole end so there is a high water potential and a high hydrostatic pressure/osmotic pressure
    2. This causes Water to move out of capillary into the interstitial fluid down a water potential/osmotic pressure gradient due to osmosis
    3. Water will also move with the dissolved substances e.g. ions however large molecules, proteins and cells cant exit the capillary
    ○ Proteins and other molecules are chargedso effect the water potential of the blood plasma
    4. As proteins and cells can’t move out of the blood the oncotic pressure remains the same
    5. This will decrease the water potential and hydrostatic pressure/osmotic pressure of the blood
    ○ The hydrostatic pressure inside the interstitial fluid negligible as not a contained space
    6. At the venous end of the capillary the oncotic pressure of the blood draws water from the interstitial fluid into the capillary
    7. No all water will be reabsorbed this way so some must enter the lymphatic capillaries
    8. This means that there is no net movement of water from the capillaries

Question 4

How is the blood filtered in the glomerulus?

Answer 4

1. Blood enters the glomerulus from the afferent arteriole and exits via the efferent arteriole. the afferent arteriole is wider than the efferent arteriole, this creates a high hydrostatic pressure inside the glomerulus.
   ○ Hydrostatic pressure is the pressure water exerts in a contained space
   
   2. Water and dissolved substances is forced out of the glomerulus capillaries (through the endothelium lining, basement membrane and podocytes into the bowman’s capsule
      ○ Water here is called filtrate
      ○ Basement membrane is made out of collagen so is made from proteins (negatively charged so repeals proteins)
      ○ The proteins and the cells remains in the blood although the oncotic pressure in the glomerulus is higher than the bowman’s capsule the high hydrostatic pressure from the glomerulus ensures that water will move into the bowman’s capsule more than moving out
   3. Lower hydrostic pressure in the bowman’s capsule than the glomerulus
   4. Composition of filtrate is the same/very similar to blood plasma except the proteins don’t enter the bowman’s capsule so protein content in filtrate is much lower than plasma
      * Pressure in the glomerulus capillary stay constant as the Afferent and efferent Arterioles put pressure on the capillary opts both ends
      * Oncotic pressure in bowman’s capsule if 0mm/mg
      * More proteins will cause water to move in more/exit less (Na+ and Glusoe won’t have an effect of the GFR -unless the volume of blood is effected-)

Question 5

What problems can effect glomerular filtration? Important for exams

Answer 5

• Causes of proteinuria (protein in the urine)
  ○ Diabetes mellitus (diabetes)
  ▪ Excessive plasma glucose will damage the filter (basement membrane, pods tubes and endothelium layer) if filter layers are damaged then large molecules e.g. proteins can enter the Bowmans capsule
  ○ Hypertension (high blood pressure)
  ▪ The already high glomerular hydrostatic pressure will be increased due to hypertension so proteins can be forced out of the glomerulus
  ○ Glomerulonephritis (inflammation due to immunological attack)
  ▪ Damages filtration layers and means that large molecules/proteins ca diffuse into the filtrate
  
  • Oedema (swelling in face, feet and frothy urine-due to proteins being present in the urine)
    ○ If the Kidneys not working and proteins are leaking out into urine the protein concertation In the blood is lowered
    ▪ This decreases the oncotic gradient between interstitial fluid and blood at the venous end of the capillary
    ▪ Less water will move back into the capillary causing water/fluid retention in the body
    ▪ May look like swelling
    ○ Can also happen if not enough protein is in diet so capillaries will leak fluid and cause swelling
    ○ If protein got into bowman capsule the oncotic pressure would be less so less water would move back into the glomerulus so more filtrate

Question 6

What is the glomerular filtration rate and how is it controlled?

Answer 6

• Glomerular filtration rate is the volume of fluid that the kidneys will filter in a certain time period
  
  • Kidneys will filter 180 litters of blood plasma each day
    ○ Only have 3 litres of blood plasma so kidneys filter this 60 times a day
  • The GFR must be maintained
  • 21% of blood from the heart goes straight to the kidneys
  • Not all plasma exits the glomerulus (only 20% exits) so blood and proteins do not ends up blocking capillary as a sludge
  • 6 litre of blood so 3 litres of plasma this means that the 3 litres of plasma will be circulates 60 times in the kidneys (constant remove of toxins -dialysis will build up toxins-)
  • If the GRF is too high then the useful substances e.g. glucose and amino acids won’t be reabsorbed as flow of filtrate is too fast for the transport proteins
  • If the GFR is too slow then the transport proteins may put waste products back into the blood 9reabsorb waste produces e.g. urea which is mildly toxic)