Lecture 1 - Glomerulus Flashcards
What is meant by someone being Euvolemic?
In fluid balance
What is ultrafiltrate?
The plasma like fluid that enters into the glomerulus where large proteins are no longer present
What is the average amount of urine produced in a day?
1.5L
As a general principle how are most substances moved in the kidney?
Most substanced recovered/ reabsorbed
Only a few wast products not recovered
What is the total body water in the average male?
70kg male = 42 L of TBW
How is the 42L of water distributed through the average male?
2/3 intracellular fluid
1/3 Extracellular fluid (14L)
How is the 14L of ECF in the average man distributed?
10.5L interstitial water
3.5L plasma
What are the general levels of electrolytes inside cells?
High K+, low Na+
What are the general levels of electrolytes like outside of cells (extracellularly)?
High Na+
Low K+
Main anions are Cl- HCO3-
What main transporter maintains electrolyte differences in cells?
What type of transport does this use?
Na+/K+ ATPase
What is osmolality?
The amount of a solute (like NaCl) per kg of a solvent (like water)
What is osmolarity?
The number of osmoles of a solute per litre of solvent
Meaning the number of charged particles per litre of solvent
What are the holes called in the glomerulus which allow ultra filtrate to form in the bowman’s capsule?
Fenestrations
What is Renal Blood Flow (RBF)?
Amount of blood that flows through the glomeruli per minute
Roughly what percentage of the Renal BLood FLow actually gets filtered?
20%
What is renal plasma flow (RPF)?
The liquid plasma part of thee blood flowing through the glomeruli per min
Approximately what is the average Renal Plasma Flow (RPF)?
600ml/min
What is Haematocrit?
The proportion of blood made up of RBCs (blood that’s made of RBCs)
What is the equation to calculate RPF?
RPF = RBF x (1 - Haematocrit)
What is Glomerular Filtration Rate (GFR)?
The rate at which fluid is filigree from glomeruli into the kidney
What is the approximate GFR?
125ml/min
What is meant by the Filtration fraction?
The proportion of blood flowing through the kidney that’s been filtered
What is the equation from Filtration fraction (FF)?
FF = GFR / RPF
What part of the kidney is the glomerulus found in?
Renal cortex
What is normally not found in the glomerulus filtrate?
Blood cells
Platelets
Nearly No proteins
What is it called when blood is in the urine?
Haematuria
Describe the appearance of the renal corpuscle and the PCT and DCT in histology:
The Bowmanns capsule is a clear white horse shoe which surrounds all the capilaries of the glomerulus
DCT have open and clear lumen whereas the PCT dont since they have brush borders
Refer to slide 11
What acts as a barrier in the glomerular capillary membrane to large proteins?
Foot processes of podocytes are -ve charged and so is albumin
Acting as a physical and chemical barrier
What is proteinuria?
When protein is present in the urine
How can many diseases lead to proteinuria?
Negative charge lost on filtration barrier (foot processes)
What is GFR?
Amount of filtrate produced from the blood flow per unit time
What is filtration?
When fluid/substance passes from the glomerulus into the Bowmanns capsule
What are the 3 processes that occur once the ultrafiltrate has been filtered into the nephron?
Reabsorption
Secretion
Excretion
Why may an inviduals GFR decrease?
(Worse kidney function)
Less nephrons
GFR within individual nephrons reduced for various reasons
What can happen to individual nephrons if kidney function declines slowly?
Why can this mean GFR doesn’t decline unless significant damage occurs?
Hypertrophy
Meaning invidiual nephrons start filtering more
What is the normal range for GFR?
60 - 120ml/min
What is clearance?
The volume of plasma that is cleared of a substance in a unit of time
Its essentially the kidneys ability to remove a substance form plasma and excrete it
What is the equation for clearance(x)?
C(x) = (([urine of x] X urine flow rate)) / plasma conc of x
When can clearance and GFR be used interchangeably?
When the substance x follows the filtrate without being altered by the kidney
So x isn’t reabsorbedd, secreted or metabolised by the kidney
If 100ml of water passes through the kidney per min, only 50% of it is filtered. Of the 50% of water filtered 48ml of it is reabsorbed.
What is the GFR?
What is the urine flow rate?
GFR = 50ml/min
Urine flow rate = 2ml/min
What week does nephron development finish by in babies?
35-36th week of development
How does being premature and/or low body weight affect number of nephrons?
Lower number of nephrons
GFR at birth is low, when does it increase to become normal?
Normal by 18months
At what age does GFR start to decline?
30 +
How are number of functioning nephrons affected as you get older?
What affect does this have?
Lose functioning nephrons
Leads to some compensatory hypertrophy
How is GFR and kidney size affected in pregnancy?
How does the number of nephrons change?
GFR increases by around 50%
Kidney size increases due to more fluid volume
The num of nephrons stay the same
When does the GFR and kidney size return to normal post partum?
6 months after pregnancy
What are the 4 features of a good substance that can be used to measure GFR?
Made at a constant rate
Freely filtered across glomerulus (so kidney does affect it)
Not be reabsorbed in the nephron
Not be secreted into the nephron
Inulin is freely filtered, not reabsorbed and not secreted so why dont we use it as a marker to calculate GFR?
Its not produced by the body so needs a continous IV to maintain a steady state
Needs a catheter and timed urine collections
So what is used to measure GFR?
51 Creatinine-EDTA
Why is inulin used in children and not 51 Cr-EDTA?
This creatinine is a radioactive labelled marker so would be a risk for mutations and cancers
What is Creatinine?
Product of muscle breakdown made in the body (endogenous substance)
Is creatinine a good measure of GFR and why?
Its pretty good but is sometimes inaccurate
Its not always produced at a constant rate since someone might start eating more meat and have more protein broken down
Some of it is secreted into the nephron so sometimes it overestimates GFR
Is the estimate of the true GFR from serum creatinine usuallly an overestimate or underestimate?
Usually the actual GFR is lower than what’s predicted since some creatinine gets secreted into the nephron
What can affect creatinine levels in a person?
Protein intake
Muscle mass
Renal filtration
Renal secretion
Renal excretion
What can cause increased serum creatinine?
Large muscle bulk
Young
Male
Creatinine supplements
High meat intake
Drugs like trimethoprim
What can cause reduced serum creatinine?
Reduced muscle mass
Old
Female
Vegetarian
Difference between eGFR and GFR:
eGFR is estimated GFR its a best guess not the actual GFR
What is the problem with estimating GFR?
eGFR innacurrate in mild kidney disease
Reduction in GFR causes inc blood flow
Reduced nephron number leads to nephron hypertrophy so GFR doesn’t change
Reduced creatinine filtration due to reduced GFR, leads to inc serum creatinine and inc secretion into tubule
