S3 GFR and Filtration Flashcards
Describe the blood supply of the kidney from the aorta to the glomerulus
Aorta, renal artery, segmental artery, interlobar artery, arcuate artery, interlobular artery afferent arteriole, glomerulus
Describe the blood supply of the kidney from the glomerulus to the IVC
Glomerulus, efferent arteriole, peritubular capillaries/vasa recta, interlobular veins, arcuate vein, interlobar vein, segmental vein, renal vein, IVC
Describe the differences between the two types of nephrons
Cortical and juxtamedullary
Cortical is more common and found in the outer cortex.
Juxtamedullary is found in the inner cortex and dips into the medulla.
In cortical nephrons, the efferent arteriole forms peritubular capillaries, juxtamedullary EA forms vasa recta
How much blood is filtered at the glomerulus?
20%
Blood enters at AA, 20% is filtered, 80% leaves unfiltered at EA
The solutes that pass into the bowmans space are the ultrafiltrate
From inside to out, what are the layers of the glomerulus filtration barrier?
Capillary endothelium
Basement membrane
Podocyte layer
What substances can and can’t get through the filtration barrier?
Can: inulin (largest) Na+, K+, Cl-, H2O, urea, glucose
Can’t: haemoglobin, albumin
Neutral Molecule –bigger size is likely to get through
Anions – Negative charge also repels, more difficult to get through
Cations – Positive charge allows slightly bigger molecules through
In the glomerulus, what causes the hydrostatic pressure difference across the capillary?
Hydrostatic pressure in the capillary moving into bowmans capsule
Hydrostatic pressure in bowmans capsule moving into capillary
Oncotic pressure in the woman’s capsule moving into capillary.
Net movement of plasma is from hydrostatic pressure into bowmans capsule
What is autoregulation and what 4 mechanisms does it involve?
Autoregulation keeps GFR and renal blood flow (80-180 mmHg) within normal limits. Without autoregulation slight changes in BP would cause significant change in GFR.
Myogenic mechanism
Tubular glomerular feedback
Neural regulation of GFR
Glomerulotubular balance
What is the myogenic mechanism?
Arterial smooth muscle responds to increases and decreases in vascular wall tension.
How does the myogenic mechanism correct GFR?
To increase GFR: dilate afferent or constrict efferent
To decrease GFR: constrict afferent or dilate efferent
So with an increased BP, we need to decrease GFR
How does tubular glomerular feedback correct GFR?
Increased GFR means more [Na+] and [Cl-] reaches the distal tubule.
Macula densa cells in the DCT stimulate juxtaglomerular apparatus to release chemicals depending on the NaCl conc:
Increased NaCl - adenosine is released to vasodilate the EA, so decreases GFR
Decreased NaCl - prostaglandins are released to vasodilate the AA so increases GFR
How does neural regulation control GFR?
Sympathetic nerve fibres innervate AE and EA. Normally sympathetic innervation is low (no effect on GFR).
Fight or Flight or ischaemia can stimulate renal vessels causing vasoconstriction which conserves blood volume (haemorrhage) and can cause a fall in GFR.
How does glomerulotubular balance control GFR?
Whilst myogenic and TGF responses are the first way to stop GFR changes, GTB is the second line of defence which blunts Na+ excretion in response to any GFR changes.
