5 - Renal Blood Flow Flashcards
In general what does the kidney filter?
- Forms ultrafiltrate
- Filters 180L/day
- 1.5L urine
- Only filters the ECF (10.5L and 3.5L)
What are the important ions in the ECF?
Anion: Cl-
Cation: Na+
HCO3- is also important
What is the difference between osmolality and osmolarity?
Osmolality = solute per kilogram of solvent. does not depend on temp and pressure
Osmolarity = number of osmoles of solute per litre
What is the definition of the following:
- GFR
- FF
- RPF
- GFR: Rate of filtration through the glomerulues, about 125ml/min
- FF: Fraction of fluid coming through the renal tubules that reaches the kidney. GFR/RPF. Usually 20%
- RPF: Amount of fluid following through the renal arteries
What is the main difference between the cortical and juxtamedullary nephrons and the difference between ultrafiltrate and plasma?
- The cortical nephrons can autoregulate to stop the GFR going up and down
- Ultrafiltrate is the same as plasma (e.g urea, glucose, salts) apart from large proteins and cells
What is the structure of a renal corpuscle?
- Renal afferent arteriole
- Glomerular capillaries: tuft of capillaries with fenestrated endothelium and glomerular basement membrane for filtration of blood
- Renal efferent arterioles
- Bowman’s capsule: layer of epithelial cells around glomerular capillaries, continuous with membrane of PCT
- Bowman’s space: space between visceral and parietal layer of bowman’s capsule
- Mesangium: Basement membrane matrix that the capilarries are embedded in and provides them structural support. Mesangial cells maintain this matrix
- Podocytes: Specialised epithelia that have foot processes on the basement membrane of the glomerular capillaries. Narrow area between feet are slit diaphragms
- JG Apparatus
What is the juxtaglomerular apparatus?
- Macula densa, inital portion of DCT and afferent arteriole
- Renin granular cells are part of the afferent arteriole
- Macula densa detects NaCl concentration in the urine and when this is low it causes renin to be released
What are the filtration barriers in the glomerulus?
- Basement membrane is acellular, gelatinous and has a negative charge
Why do the kidneys have such a high oxygen requirement?
Over 99% of filtered substances are reabsorbed into the blood so need lots of oxygen and glucose
What type of molecules can get through the filtration membrane the easiest?
- Small, positively charged molecules
- If negatively charged have to be small to get across
Why do fluid and small molecules move from the afferent arterioles into the glomerulus?
- Higher outward forces than inward forces
Where does tubular reabsorption occur and what molecules are reabsorbed?
- Mainly in PCT
- Molecules coupled to active reabsorption of Na. e.g glucose, aa, lactate, acetate, ketones, water-soluble vitamins
- All glucose reabsorbed
- Most water reabsorbed after sodium by osmosis (obligatory water reasorption as not controlled by PCT)
What is some tubular secretion that occurs?
- H+ to maintain pH
- K+, ammonium, creatinine, urea, hormones, drugs like penicillin
What are the mechanisms the kidney has to maintain GFR across a range of arterial pressures?
- Myogenic
- Tubulo-glomerular Feedback
How does the myogenic autoregulation system respond to changes in GFR?
- Arterial wall responds to vascular wall tension. Stetch activation cation channels allow Ca in to contract
- Usually AA over EA
How does the tubuloglomerular feeback system respond to an increase in GFR?
- In DCT
- Macula densa in JG apparatus sense increase in NaCl and therefore increase in GFR
- Contraction of afferent arteriole, fall in pressure in capillary so fall in GFR
- Increase in NaCl also inhibits release of rening from JG
How does the macula densa cause vasoconstriction of the afferent arteriole when there is an increase in GFR, and therefore an increase in NaCl?
- Na, Cl and K are transported by NKCC2 into cells of MD
- Triggers release of ATP
- In interstitium ATP converted to AMP and then adenosine
- Adenosine binds to adenosine 1 receptor on mesangial cell on AA
- Gi inhibits adenylate cyclase and Go causes increase in intracellular Ca
- Smooth muscle contracts due to increase in Ca
- Less pressure gradient so lower GFR
How does the body respond to a drop in GFR using the tubuloglomerular feedback system?
What are some medications you have to be careful with if you already have a low GFR?
- NSAIDs as they inhibit prostaglandins
- ACE inhibitor and ARBs can cause acute renal failure as Ang II vasocontricts EA when GFR falls.
Apart from myogenic and tubuloglomerular feedback, what other mechanism can rescue an altered GFR?
- Sympathetic nervous fibres innervate EA and AA
- In haemorraghe, ischaemia or flight/fight vasoconstriction can occur in AA to conserve blood and drop GFR
What is glomerulotubular balance?
- Last line of defence
- if GFR increase, the Na in the filtrate will increase, however the amount of Na reabsorbed will also increase. Na reabsorption always a constant proportion of 67%
What is hyper/hypoperfusion of the kidneys?
Hypo = arterial less than 80 mm/Hg. Can lead to hypertension and AKI
Label the following diagram.
What are the three layers of tissue surrounding the kidney?
Label the following diagram.
How can you distinguish between the ureter and nerves and vessels during surgery?
- Ureter is whiteish cord
- Adherant to peritoneum
- Peristaltic activity when pinched with forceps
How is the ureter supplied with blood?
Segmental artery from renal, gonadal, vesicle and uterine arteries
f. Renal stone that is not radio opaque
g. Sympathetic nerves T11-L2 segments
A patient with an enlarged prostate is suffering with urinary retention, how would you relieve this and why?
- Suprapubic catheter
- Distended bladder so bladder is above the pelvis and free of superficial peritoneum
- Insertion of catheter possible without damaging peritoneum
- Can’t do through penis as wouldn’t get past the prostate
