Glomerular function Flashcards
What is the filtration barrier?
Blood comes into renal corpuscle, moves into glomerular capillaries, some plasma is filtered into capsular space, the rest leaves in the peritubular capillaries
Small substances are freely filtered (low molecular mass) e.g. sodium, potassium, chloride, water, urea and glucose
Large substances are not filtered (in healthy kidneys), e.g. haemoglobin and serum albumin
What is renal blood flow?
Kidneys receive 20% of cardiac output, they need the blood to be able to filter the plasma (high flow for filtration, rather than metabolism) kidneys filter entire plasma volume around 30 times a day hence requires a lot of blood
What is hydrostatic pressure?
Hydrostatic pressures are pressures due to the volume of the fluid which ‘push’ fluid away (how much blood in capillaries and how much filtrate in capsule, more blood higher pressure, more fluid more pressure) the more hydrostatic pressure you have the more fluid/blood you are ‘pushing’ away
What is colloid osmotic pressure?
Colloid osmotic pressures are osmotic pressure due to proteins which ‘pulls’ fluid towards whatever is causing the pressure (e.g. plasma capillaries trying to pull fluid towards themselves)
What is glomerular hydrostatic pressure (GHP)?
Glomerular hydrostatic pressure is caused by how much blood and pressure is in capillaries, trying to push fluid into capsule, favours filtration = positive 50mmHg
What is blood colloid osmotic pressure (BCOP)?
Blood colloid osmotic pressure, trying to pull fluid towards itself, from capsule back into blood hence opposing filtration = negative 25mmHg
What is capsular hydrostatic pressure (CsHP)?
Capsular hydrostatic pressure trying to push fluid from capsule back into blood, opposing filtration = negative 15mmHg
What is capsular colloid osmotic pressure (CsCOP)?
Capsular colloid osmotic pressure is 0 in someone with healthy kidney (should be no proteins in capsule), if someone has kidney disease that affects filtration barrier CsCOP pull increasing fluid from the blood, positive as favouring filtration
How to find net filtration pressure
To find the total amount of pressure: (GHP)+(CsCOP) - (CsHP) - (BCOP)
50 + 0 - 25 -15 = 10mmHg
How much plasma volume is in kidneys?
Blood is about 55% plasma and about 45% cells
Kidneys receive ~625ml/min of plasma
1100-1200ml flows into kidneys, some plasma is filtered and some stays in glomerular capillaries, leaves nephrons via efferent arteriole
~20% of plasma is filtered, ~80% stays in glomerular capillaries
What is the filtration fraction?
GFR/RBF
Glomerular filtration rate/renal plasma flow
125/625= 20%
What is the glomerular filtration rate?
Amount of plasma filtered per unit time is normally 180L/day and 125ml/minute, normally we only make about 1.5L of urine hence reabsorb more than 99% of plasma that we filter every day
GFR is tightly regulated as we need to filter right amount of plasma to control what is in our blood, GFR decreases as you age as nephrons begin to stop functioning
What is the renal filtered load?
Filtered load = amount of particular substance filtered per unit time
Filtered load = GFR x solute plasma concentration
E.g. Filtered load for glucose is how much glucose kidneys are filtering per minute
What is renal clearance?
How much plasma (volume) is cleared/cleaned of that particular substance every minute = renal clearance
Helps us understand how a substance is handled by kidneys and to estimate GFR
How are different substances cleared or not?
In creatinine all plasma that is filtered by kidneys is cleared of creatinine as not reabsorbed
In PAH all plasma that is filtered by kidneys is cleared of PAH as PAH is entirely secreted
In glucose, no plasma that is filtered by the kidneys is cleared of glucose as fully reabsorbed
In sodium, a small amount of plasma that has been filtered is reabsorbed without sodium and has been cleared of sodium
