WEEK 3 - Renal Injury Flashcards
What is the primary function of the renal system?
To regulate blood volume and composition of body fluids and to excrete wastes
What are the three additional functions of the kidneys?
- Synthesis of the active form of vitamin D
- Blood pressure regulation via the RAAS
- Erythropoietin synthesis for blood cell production via the bone marrow
Where are the kidneys located anatomically?
They lie in the retroperitoneal space, posterior to the abdominal wall, outside of the abdominal sac
Which kidney is located lower than the other?
The right is lower than the left (due to the presence of the liver)
How do the kidneys regulate pH?
Via the excretion of protons or the retention of bicarbonate
How do the kidneys regulate BGLs?
Via gluconeogenesis - conversion of amino acids to glucose
How much cardiac output do the kidneys receive? Via which artery?
20-25% via the renal artery
Major vessels, nerves and the ureters enter and exit the kidneys via which structure?
The hilum
What does the renal cortex contain?
85% of nephrons (outer region of the kidney)
What does the renal medulla contain?
15% of nephrons and the renal pyramids (inner region of the kidney)
How is the renal pelvis formed?
Minor calyces join to form the major calyces, major calyces join to form the renal pelvis
What is the structural and functional unit of the kidney?
The nephron
Which area of the nephron is responsible for filtration?
The glomerulus and Bowman’s capsule
Which areas of the nephron are responsible for reabsorption?
- Proximal convoluted tubule
- Distal convoluted tubule
Which area of the nephron is responsible for concentration?
The loop of Henle (via the peritubular capillaries)
Which area of the nephron is responsible for secretion?
The distal convoluted tubule
By what means substances reabsorbed via the nephron?
Water and urea = passive transport (descending LoH)
Ions and salts = active transport (ascending LoH)
There are three ions that are resorbed or excreted depending on hormonal influences. Which ions are these?
Na+
Ca2+
Mg2+
Define GFR (not just what the letters stand for)
Glomerular Filtration Rate
The quantity of glomerular filtrate produced each minute by ALL NEPHRONS in BOTH KIDNEYS
Normal GFR?
125mL/min OR
180L/hour
What proportion of filtrate is resorbed by the kidneys?
99%
When are you no longer considered to have a healthy GFR and why?
After the age of 30 due to age-dependent loss of nephrons
What three factors is GFR reliant on?
- Net filtration pressure
- Filtration membrane permeability
- Total surface area available
Renal injury is characterised by?
A sustained decline in GFR
Acute renal injury is characterised by?
A decline in GFR over a period of minutes-days, leading to elevated BUN and decreased urinary output
How long can acute renal failure last for and what does it become after this period?
Can last for up to 12 months
After 12 months, if ARF has not resolved, this becomes chronic kidney disease or end stage kidney disease (ESKD)
What are some causes of acute renal failure?
- Hypotension (decreased CO to kidneys)
- Tubular injury
- Interstitial injury (caused by E Coli)
- Glomerular injury (caused by strep infection)
- Obstruction eg. PCa, renal calculi, neoplasms
What are the three forms of renal failure?
- Pre-renal
- Intrinsic or Intra-renal
- Post-renal
What is the primary cause of pre-renal failure?
Impaired blood flow
May be due to
- Hypotension
- Renal hypo-perfusion
- Renal vasoconstriction
- Hypovolaemia
Clinical manifestations of pre-renal failure depend on?
Pt age, health status, increased HR, variable BP (low or normotensive), decreased urinary output
What test is used in the diagnosis for pre-renal failure? Is this test accurate in all groups?
Creatinine test
Not accurate in older populations due to age dependent changes in skeletal muscle mass - creatinine is a byproduct of skeletal muscle activity
Creatinine clearance depends on which three factors?
- Age
- Gender
- Weight
Primary cause of intra-renal failure
Damaged nephron components - glomerulus, interstitium and tubules
May be due to:
- Glomerulonephritis
- Acute tubular necrosis
- Inflammation
- Renal trauma
- Transfusion reaction
Clinical manifestations of intra-renal failure?
- Oligouria and fluid overload
- Uremia, nausea and vomiting
- Decreased EPO production = anaemia, decreased blood cell count
- Decreased production of vit. D = hypocalcaemia, hyperparathroidism
How is intra-renal failure diagnosed?
- Imaging to exclude pre-/post-renal failure
- Urine microscopy for RBCs and casts
Post-renal failure is associated with?
Urinary tract obstruction
Caused by neoplasms, PCa, renal calculi
Clinical manifestations of post-renal failure?
Fluid retention (or anuria (no peeing)), pain, electrolyte changes
Diagnostic criteria of post-renal failure?
- An abrupt reduction in renal function (in less 48 hours)
- An increase in creatinine (>50%) or anuria for at least 12 hours
First line pharmacological therapy for acute renal failure?
Thiazide diuretics eg. Hydrochlorothiazide
What characterises chronic renal failure?
The progressive destruction of renal parenchyma wit irreversible sclerosis, loss of nephrons and decline in glomerular function.
Primary clinical manifestation of chronic renal failure?
Extracellular fluid expansion and total body volume overload as a result of a failure in the kidneys’ abilities to excrete Na+ and H2O
What are the biochemical markers tested in the diagnosis of chronic renal failure?
- Urea
- Creatinine
- Sodium
- Potassium, phosphate and calcium
What are the three imaging studies used in the diagnosis of chronic renal failure?
- Plain film X-ray
- CT/MRI
- Voiding Cystoutererogram (VCUG)
Why is creatinine a better marker for chronic renal failure than urea?
As creatinine is not influenced by non-renal factors such as a high protein diet and steroids
Management for chronic renal failure is aimed at?
Delaying or halting renal failure (no cure)
When does end stage kidney failure occur?
When GFR is less than 15%
What must happen in end stage kidney failure for symptoms to be exhibited?
The loss of at least 80% of nephrons
Characteristics of STAGE 1 of ESKD?
- Asymptomatic
- Normal BUN and creatinine
Characteristics of STAGES 2-4 of ESKD?
- Increased BUN and creatinine
- Polyuria
- Nocturia
Characteristics of STAGE 5 of ESKD?
- Marked BUN and creatinine
- Anaemia
- Hypocalcaemia
- Oliguria
- Uremic syndrome
What is the mechanism of action of hydrochlorothiazide?
Decreases reabsorption of Na+/Cl- in the proximal segment of the distal convoluted tubule - stimulates Na+/K+ and H2o excretion
What are the adverse effects of hydrochlorothiazide?
- Hypokalaemia/natraemia
- Hyperuricaemia
- Hypotension
- Dizziness, weakness, muscle cramps (due to low K)
- Increased plasma glucose
What is the mechanism of action of frusemide?
Inhibits the absorption of Na+ and Cl- in the ascending limb of the Loop of Henle, short acting, causes a rapid decrease in blood volume
What are the adverse effects of frusemide?
- Dose-dependent disturbances in electrolytes Na+ and K+
- Dehydration
- Syncope
- Postural hypotension
What is the mechanism of action of mannitol?
Increases osmolality of blood = osmotic diuresis
What are the adverse effects of mannitol?
- Electrolyte loss
- Thirst, dehydration
- Headache, blurred vision, fluid shifts (pulmonary congestion)
What is the mechanism of action of Spironolactone?
Inhibits Na+ reabsorption in the distal convoluted tubule by blocking Na+ channels and aldosterone = increased Na+ and decreased K+ excretion
What are the adverse effects of Spironolactone?
- Gynaecomastia in men
- Post-menopasual bleeding in women
- Hyperkalaemia