Urinary Session 3 Flashcards
What do the efferent arterioles in cortical nephrons drain into?
Peritubular capillaries
How does the diameter of the efferent and afferent arterioles compare in cortical nephrons?
Afferent>efferent
What does the efferent arteriole of juxtamedullary nephrons drain into?
Vasa recta
How does the sympathetic supply of cortical and juxtamedullary nephrons compare?
Cortical have rich supply, juxtamedullary have poor supply
How does the renin concentration in cortical and juxtamedullary nephrons compare?
High in cortical, almost none in juxtamedullary
Where are cortical nephrons located?
Outer cortex
Where are juxtamedullary nephrons found?
Inner part of cortex
How does the size of the glomerulus compare in cortical and juxtamedullary nephrons?
Smaller in cortical
What proportion of blood flow is filtered at any one time?
20%
Does the proportion of blood filtered depend on the nephron?
No
What is the ratio of cortical to juxtamedullary nephrons in the kidney?
90% cortical
10% medullary
What does the permeable capillary endothelium allow between cells?
Water
Salts
Glucose
What repels protein movement in the basement membrane?
-ve charge acellular gelatinous collagen/glycoprotein basement membrane
What determines the size of particles that can move through the filtration barrier?
Interdigitation of pseudopodia of podocytes
What is the largest molecule that can pass through the filtration barrier?
Inulin
Why do some smaller proteins not pass through the filtration barrier?
They have a negative charge
What causes proteinuria?
Loss of -ve charge on the basement membrane so proteins are more readily filtered
What are the three forces in plasma filtration?
Hydrostatic pressure in the capillary
Hydrostatic pressure in the Bowman’s capsule
Oncotic pressure difference between capillary and tubular lumen
What allows GFR to remain constant during small fluctuations in BP?
Autoregulation of hydrostatic pressure in the capillary
What is the myogenic response to small increases in BP?
Increased BP –> stretch afferent arteriole smooth muscle –> smooth muscle contacts to decrease blood flow
What is the myogenic response to small decreases in blood pressure?
No smooth muscle stretch –> afferent arteriole dilation
What is the response via tubular-glomerular feedback to a small increase in BP?
Increased BP –> increased GFR –> increased tubular flow rate –> increased sodium and chloride concentrations detected by macula densa cells –> adenosine release
What is the tubular-glomerular feedback response to a small decrease in BP?
Decreased sodium and chloride concentrations detected by macula densa cells –> prostaglandin release
When do the myogenic and tubular-glomerular feedback responses maintain GFR?
When BP is within physiological limits
How do macula densa cells sense luminal sodium and chloride concentration?
Using concentration dependent uptake through NaK2Clco transporters in the apical membrane
What do macula densa cells stimulate the release of to control afferent arteriole vasomotor tone?
Adenosine or prostaglandins
What are the two types of nephrons found in the kidneys?
Cortical
Juxtamedullary
Why is movement of solutes and water in the nephron classed as reabsorption?
Substances have a already been absorbed into the blood once (especially in the intestines)
Why does bulk transport/isosmotic occur in the PCT?
Polarised tubule cells drive sodium uptake and other ions follow to maintain electro-neutrality
How can reabsorption occur?
Transcellular
Paracellular
Which type of reabsorption is predominantly used?
Transcellular
Which sodium transporters in the apical membrane of PCT cells are targeted by diuretics?
Na-H antiporter
Na-glucose symporter
Which sodium transporter in the apical membrane of Loop of Henle epithelial cells is targeted by diuretics?
Na-K-2Cl symporter
Which sodium transporter in the apical membrane of early distal tubule epithelial cells is targeted by diuretics?
NaCl symporter
Which sodium transporter in the apical membrane of late DCT and collecting duct epithelial cells is targeted by diuretics?
ENaC
What is the end result of reabsorption?
Reabsorption of: 100% filtered nutrients 80-90% filtered HCO3- 67% filtered Na+ 65% filtered water 65% filtered Cl- 65% filtered K+
What provides a second route of entry for solutes that need to be secreted into the tubular fluid?
Secretion
What in the 80% of unfiltered plasma needs secretion into the tubule?
H+
K+
Organic anions
Describe the process of secretion into the tubular lumen.
3Na-2K-ATPase creates concentration and electrochemical gradient
Entry of molecules by passive carrier-mediated diffusion down gradients
Na-H antiporter creates H+ gradient
H+-OC+ exchanger pumps in H+ to restore balance and in the process pumps OC+ into lumen
Why do cations compete to be transported?
Due to Tm limitation
How do cations enter and exit luminal cells?
Enter on basolateral side by one of several uniporters
Leave via H+ antiporter in apical membrane
Give some examples of endogenous cations.
ACh Dopamine Adrenaline Histamine Serotonin
Give some examples of drugs which are cations.
Sulfonamides
Morphine
Atropine
Isoproterenol
Give some examples of endogenous anions.
Urate
Bile salts
Fatty acids
Give some examples of drugs that are anions.
Penicillin
Salicylate
NSAIDs
What must be considered when choosing a drug and calculating dosages?
That administered drugs will be secreted by the kidneys
What is the normal range of GFR for males?
115-125 ml per minute
What is the normal GFR range for females?
90-100 per minute
What is the benchmark measure of kidney health?
GFR
What characteristics does a substance used to measure GFR require?
Not altered in any way in the nephron
Freely filtered
Not secreted
Can a standalone GFR be used to assess kidney health?
No, needs a series of measurements to see where a pt’s normal GFR is
What ultimately governs GFR?
Renal blood flow
What is the normal renal blood flow through the glomeruli?
~1.1 l per minute
What percentage of renal blood flow is haematocrit?
Usually 45%
What is normal renal plasma flow?
605 ml per min (0.55x1.1)
What is renal clearance?
Volume of plasma that is completely cleaned of a substance by the kidneys per unit time
How is renal clearance calculated?
(Concentration of substance in urine X urine volume)/concentration of it in plasma
What is renal clearance used to detect?
Glomerular damage
Follow progress of diagnosed renal disease
Determine GFR
What is the gold standard for measuring renal clearance?
Inulin
What substance is used clinically to measure renal clearance and why?
Creatinine as it doesn’t have to be given IV like inulin
Why does using creatinine give a slight overestimate of renal clearance?
A small amount is secreted
What does eGFR account for?
Age affecting kidney function
Mass affecting creatinine levels
What is the Tm of glucose in males and females?
Males = 375 mg per minute Females = 300 mg per minute
What happens if plasma glucose concentration is 400 mg per ml in a male?
Filtered load is 4x125 = 500 mg per minute
As renal threshold is 375 mg per minute 125 mg per minute moves into the urine
What is normal plasma glucose concentration?
~1 mg per ml
Is normal plasma glucose concentration freely filtered in the Bowman’s capsule?
Yes
