Renal Physiology Flashcards
If MAP is 160mmHg, what is the likely renal blood flow?
1200ml/min
Renal blood flow is 25% of cardiac output, and is maintained by autoregulation in the range 80-200mmHg
Where is the blood supply to the renal medulla derived from?
Capillaries close to the boundary of the cortex and medulla loop into the medulla and form the vasa recta. These surround the Loop of Henle.
They are the only blood supply to the medulla.
Where are the macula densa cells located?
The DCT
Will autoregulation still occur in the dennervated kidney?
Yes
What is renal oxygen consumption?
18ml/min
How many nephrons does each kidney contain?
1 million each
Which cells of the kidney have brush borders?
PCT cells.
Where are there more mitochondria - the DCT or PCT?
The PCT is rich in mitochondria
Do only 20% of nephrons have a LoH?
No, all nephrons possess a Loop of Henle. 20% will be juxtamedullary
What size are the pores of Bowman’s capsule?
5nm
What is the set up of the renal blood supply?
The renal arteries divide into arterioles, then capillaries, then efferent arterioles, then vasa recta
Where does 90% of the blood entering the kidneys supply?
The cortex.
It has a high blood flow-500 ml/min per 100 g of tissue. It has a low arteriovenous difference of approximately 2%.
What do PGI2 and PGE2 do?
Released in hypovolaemia and may cause vasodilation helping prevent the kidney from ischaemic damage
Do NSAIDs reduce GFR under normal circumstances?
NSAID’s do not influence GFR under normal circumstances but can cause significant loss of function if there is effective loss of circulating volume from any cause
At what point does symptomatic uraemia occur?
Symptomatic uraemia usually devlops when the GFR is about 15 ml/min
The symptoms of uraemia occur late in the loss of renal function, and are caused by retained toxic products. They are non specific and include anorexia, nausea, vomiting, lethargy, poor sleep, pruritus
What is the normal young adult renal blood flow?
1200ml/min - 25% of cardiac output
What happens to sodium in the PCT?
Sodium is pumped from tubular cells into the interstitium by the sodium-potassium-ATPase pump (actively reabsorbed)
What is reabsorbed in the PCT?
Bicarbonate, chloride, glucose, sodium and potassium
Is water reabsorption under control of aldosterone?
No, aldosterone mainly acts in the distal tubule by regulating sodioum reabsorption. Water then follows passively.
Up to 70% of filtered water is reabsorbed in the proximal convuluted tubule
Where is ammonia produced in the nephron?
Ammonia is produced in tubular cells by metabolism of glutamine. Its main role is in the buffering processes promoting the excretion of hydrogen ions.
Tubular secretion of ammonia occurs in both proximal and distal tubules
Does the kidney filter of all molecules under 5nm diameter?
No, glomerular filtration is partly determined by molecular size, charge and protein binding.
What happens to proteins in the kidney?
In health, large molecules do not pass through the glomerular membrane. Any protein molecules that do are taken up by pinocytosis at the luminal membrane
How much glucose is reabsorbed per day?
160g
99% of glucose is reabsorbed by a saturable co-transport mechanism in the proximal tubule
What happens to hydrogen ions in the kidney?
Hydrogen ions are buffered intraluminally by phosphate, not bicarbonate ions.
What is the tubular transport maximum for glucose?
380g/min
What is the renal threshold for glucose?
11 mmol/L
What causes renin release?
Renin is controlled by the macula densa and is release in response to low sodium flux.
When less filtrate reaches the macula densa, sodium concentration around the cells is reduced. This is detected by the macula densa cells and an increase in rennin secretion is triggered
Where is renin released from?
Juxtaglomerular apparatus in the wall of the afferent arteriole
How is renin release affected by hypotension, beta blockers and ADH?
Renin is released in response to the low cardiovascular pressures which occur in hypotension
Renin release is increased in response to beta-1-receptor stimulation
Release is decreased by antidiuretic hormone which acts to conserve sodium and water
What does the primary active transport of Na/K do?
3 sodium ions are pumped outwards for 2 potassium ions inward
In primary active transport, where is energy used?
In primary active transport, energy is imparted which allows the substance being transported to be moved against its electrochemical gradient
What happens to aldosterone production if sodium chloride is ingested?
Sodium chloride ingestion increases plasma osmolality and will decrease aldosterone prouction.
What effect does trauma leadning to hypovolaemia have?
Hypovolaemia causes renin release, and thus angiotensin II release. This causes aldosterone release, with the ultimate effect of increasing sodium and water reabsorption
What does aldosterone do to potassium?
Aldosterone stimulates the production of potassium channels in the luminal membrane of the cortical collecting duct. Potassium is lost through these.
=> increases urinary potassium excretion
What will aldosterone do to urinary sodium concentration?
Reduce it
What is para amino hippuric acid?
PAH is 90% cleared by the kidneys from the plasma. PAH clearance is therefore used to estimate RPF (renal plasma flow). The amount of PAH still in the blood can be corrected for.
What are the features of an ideal substance for measuring GFR?
- freely filtered
- neither secreted or reabsorbed
- not metabolised
eg inulin
