4. Glomerular filtration and its control.pptx Flashcards
6 functions of the renal system?
- Regulation of ECF volume and bp
- Regulation of osmolarity
- Maintenance of ion balance
- Regulation of pH
- Excretion of waste
- Production of hormones
Kidney structure
Outer cortex (contains superficial glomeruli 90% and the remaining glomeruli are Juxtamedullary) Inner medulla (divided into renal medulla pyramids with interlobular arteries/veins inbetween). Pyramid contain duct of Bellini that drain into the renal pelvis --> ureter
5 stages that occur in the nephron from glomerulus to collecting duct
- Filtration by glomerulus
- Obligatory absorption (most of water and ions) and secretion (toxins etc) by proximal tubule
- Generation of osmotic gradient by loop of Henle
- Regulated absorption and secretion by distal tubule
- Regulation of water uptake by collecting ducts
Structures present within the glomerulus?
- Endothelial lining of the capillaries
- Basement membrane of the capillaries as it has a negative charge
- Foot processes of epithelial cells (podocytes) form filtration slit diaphragm inbetween
Limitations :
- Allows free passage of solutes up to about 60kDa
- Opposes movement of cells and large protein
- Negatively charged molecules are filtered less easily
What are podocytes?
Podocytes are cells in the Bowman’s capsule in the kidneys that wrap around capillaries of the glomerulus.
As values of glomerular filtration, what does RBF and RPF stand for?
RPF equation?
R.B.F - Renal blood flow. Total amount of blood that traverses renal artery or vein per unit time = 1100ml/min
R.P.F. - Renal plasma flow. Total amount of plasma that traverses renal artery or vein per unit time.
RPF= (100-haematocrit) x RBF
What are the factors favouring and opposing movement into the tubule?
Favouring movement INTO tubule:
- hydrostatic pressure of the blood (+55 mmHg)
- oncotic pressure of the tubule (0 mmHg)
Opposing movement into tubule:
- hydrostatic pressure of tubule (-15 mmHg)
- oncotic pressure of blood (-30 mmHg) due to proteins remaining in blood as they aren’t filtered into capsule
Balance: +10 mmHg
What is GFR?
Glomerular filtration rate (i.e. rate of filtrate production)
Normally 125-130ml/min
What are the auto regulation mechanisms of glomerular filtration?
Intrinsic and local control:
- Myogenic mechanism: Mediated by stretch receptors in the arterioles.
- Tubuloglomerular feedback (nephrogenic)
What are the 4 outcomes of myogenic auto regulation of glomerular filtration?
Afferent arteriole:
- Constriction = Reduces filtration pressure so GFR falls
- Dilation = Increases the pressure driving ultrafiltration so GFR increases
Efferent arteriole:
- Constriction = Pressure build up within the capillary, GFR increases
- Dilation = Allows blood to easily escape the capillary and pressure falls so GFR decreases
Afferent respond to increased bp by constricting, results in a relatively consistent GFR and RBF
What is the mechanism of Tubuloglomerular feedback?
A function of the juxtamedullary nephron
Flow in the DCT is indirectly monitored and high flow information fed back to the arterioles
Which ion concentrations increase when the filtrate flow is high in glomerulus?
Na+ and Ca+
What cells monitor Na and Ca levels?
The macula densa cells adjacent to the DCT monitor Na+ and Ca+ levels and signal to the afferent arteriole which causes it to constrict via adenosine release if levels are too high.
This lowers flow rate to normal limits
What are the extrinsic hormonal factors that affect RBF and GFR?
DECREASED afferent blood flow - vasoconstriction
- Sympathetic nerves release norepinephrine
- Circulating epinephrine
- Angiotensin II
INCREASED afferent blood flow- vasodilatation
- Renal prostaglandins
- Atrial natriuretic peptide
Functional unit of kidneys?
Nephron
