Filtration and control Flashcards
Define clearance
Volume of plasma cleared of a substance in a minute
Forces affecting filtration
Hydrostatic pressure in blood vessels
Hydrostatic pressure in bowmans space
Oncotic pressure of blood
How to calculate clearance
Urine conc X urine flow
Plasma conc
Define GFR
Volume of blood filtered per minute
Normal value for GFR
125ml/min
Clearance of a substance completely reabsorbed
0
Clearance of a substance completely filtered but not reabsorbed or secreted
125
Clearance of a substance completely secreted
625
Explain the myogenic response
BP detected in afferent arteriole
Narrows at high pressure
Relaxes at low pressure
Maintains GFR
Explain tubular glomerular feedback
Na conc detected in macula densa
If high release adenosine, causing vasoconstriction of afferent arteriole
If low release prostaglandins causing vasodilation of afferent arteriole
Why is the filtrate leaving the PCT isotonic
Volume leaving is equal to ions removed
Explain glomerular tubular balance
Filtered load (amount removed) changes for different GFRs so the filtration fraction is the same
What activates the RAAS system
Sympathetic nerves
Low Na in the macula densa
Low BP in the afferent arteriole
Effects of aldosterone
Up regulate Na/K ATPases and ENaC in the DCT and CD
Trigger for the release of ADH
Low pressure in the right atrium
