Flashcards in Session 3 - Filtration Deck (95)
What occurs if transport maximum for glucose exceeded?
• Rest of glucose spills over into urine
• Causes polyuria
Where does reabsorption of amino acids occur?
• Proximal convoluted tubule via Na+ co-transporters
What is clearance?
• The volume of plasma from which any substance is completely removed by the kidney in a given amount of time (usually 1 minute)
What is the clearance calculation?
• Clearance rate = Urine concentration of substance x Urine flow rate / Plasma concentration of the substance
What is excretion rate?
• Amount in urine x Urine flow rate
When are the inputs and outputs of the kidney?
• One input - Renal artery
• Two outputs - Renal vein and Ureter
What can we measure from the rate at which a substance appears in the urine, provided that that substance is completely cleared
• The GFR
What is the Tm for glucose in males and females?
• Males - 375mg/min
• Female 300 mg/min females
What is glomerular filtration rate?
• The volume of plasma from which any substance (X) is completely removed by the kidney in a given amount of time
What is GFR a measure of?
• Kidneys ability to filter a substance (overall function)
What does a fall in GFR indicate?
• Kidney disease is progressing
In order to measure GFR, what properties must a substance have?
• Must be freely filtered across the glomerulus
• Must not be reabsorbed, secreted or metabolised
• Must pass directly into the urine
What is standard renal blood flow?
How can we find out renal plasma flow?
• Heamatocrit is the volume (%) of RBC in blood
• Normally 45%
• 0.55 x 1.1 (RBF) = 605ml - Plasma flow
What is the filtration fraction of 605 ml plasma?
• 605ml x 0.2 = 125ml (20% blood processed per minute)
What is GFR for males?
• 115-125 ml/min
What is GFR in females?
• 90/100 mi/min
Outline the GFR of inulin, glucose and para-aminohippurate
Inulin - 125ml/min - Not reabsorbed, not secreted
Glucose - 0 - Completely reabsorbed
Para-aminohippurate - 625 ml/min (Secreted!)
Outline use of urea
• Used as an active osmol by the kidney
What is filtration fraction?
• Proportion of a substance actually filtered
• If renal plasma flow is 605ml/min, 20% of all plasma is filtered, 125ml filtered through into bowman's space and 480ml passes through into peritubular capillaries
• Filtration fraction = Glomerular filtration rate/Renal plasma flow
• Filtration fraction about 20%
What is autoregulation?
• Auto-regulatory mechanisms keep GFR within normal limits when arterial BP within physiological limits (80-120 average BP)
What is myogenic autoregulation?
• Smooth muscles of afferent capillaries of glomerulus (those going in) contract to increase or decrease pressure
What are the limits of myogenic autoregulation?
• Normal average blood pressure between 80-120 mmHG
What is GFR?
• Glomerular filtration rate
• A measure of the kidney's ability to filter a substance
Give two mechanisms of controlling blood flow to glomerulosa
• Smooth muscle control in afferent and efferent arterioles
• Tubular Glomerular feedback
What happens to smooth muscle in afferent arterioles to glomerulosa if blood pressure drops?
What happens to smooth muscle in afferent arterioles to glomerulosa if blood pressure increases
Outline tubular glomeruola feedback
• If arterial pressure too high
• Increases glomerular capillary pressure
• Increased glomerula filtration rate
• More Na+ and Cl- in distal convoluted tubule
• Macula densa cell in the JGA respond
How do the macula densa cells in the JGA oppose high GFR
• Release adenosine (vasoconstrictor) or prostaglandin (Vasodilator)