what is the nephron
the basic unit of the kidney, the cells of the kidney
what is the glomerular filtration rate (GFR)
the amount of renal blood flow filtered per unit of time (ml/min)
- directly related to renal perfusion
what do the GFR values indicate
N = 90ml/min or higher is normal N = 60-89ml/min might be normal to some people, especially those above 60 year olds N = below 60ml/min is abnormal and GFR should be repeated and would have CKD N = 15ml/min is kidney failure
what are the functions of the kidney (2)
- excretory: nephrons filter the blood of waste, and conserve fluids and electrolytes that the body needs = create/excrete pee
- secretory:
- Trigger: hypoxia; and low blood volume = release of renin and erythropoietin
- Control of blood pressure = RAAS b/c of low sodium and decreased renal perfusion
- Red blood cell production
- Vitamin D synthesis and calcium balance = w/o the kidney, vitamin D remains inactive
- Glucose homeostasis, if BG reaches threshold, the kidney starts to spill out glucose into pee
= has to secrete important substances
within the nephron, what does the glomerulus do?
tuft of capillaries from which blood is filtered at the Bowman’s capsule, allows substances like water, Na, Bicarb, and urea out of the blood BUT NOT albumin
describe the pathway of creating urine from the nephrons
- blood is filtered at the Bowman’s capsule, allows substances like water, Na, Bicarb, and urea out of the blood
- then to the proximal tubule where large amounts of water, Na, and potassium are reabsorbed into the bloodstream
- The remaining substances reach the Loop of Henle = large amount of Na is again reabsorbed.
- Aldosterone increases water and Na reabsorption too - then the remaining substances/fluids reach the distal tubule, where water and Na are further reabsorbed into the bloodstream
= urine is formed - whatever remains reaches the collecting duct, where ADH increases reabsorption of water in the collecting duct if the body needs more water
= URINE.
renal function tests (6)
- BUN (Blood urea Nitrogen)
- Creatinine
- 24-hour urine collection for creatinine clearance
- urinalysis
- intravenous pyelogram
- PSA (prostatic-specific antigen)
what is BUN
normal: 7-18 mg/dl
- end/waste product of protein metabolism = urea and excreted by the kidney
- the second best indicator of kidney functions b/c it also picks up liver failure so can be confused
what is creatinine (test)
normal: 0.6-1.2 mg/dl
- formed when creatinine phosphate is used in skeletal muscle contractions = excreted entirely by the kidney
- the best indicator of kidney functions, only picks up kidney
what is the 24-hour urine collection for creatinine clearance (test)
Measures the GRF and is dependent upon renal artery perfusion and glomerular filtration
what is urinalysis
- Cloudy, foul-smelling, + WBC= UTI
- Dark yellow = dehydration or B complex + vitamin C causes dark yellow pee
- urine smells like acetone or glucose = DM
- positive for protein = injured glomerular membrane, but if its minimal it could be related to exercise but should return to normal in 24-48 hours
- ketones = fatty acid metabolism
- crystals = kidney stones
what is intravenous pyelogram (test)
IV- administered radiopaque dye that allows visualization of kidneys, renal pelvis, ureters, bladder
what is PSA (test)
Used to screen prostatic cancer
what is acute renal failure or AKI and the 3 causes
This is the sudden loss of renal function; this is reversible and common among critically ill patients, can be abrupt and can be reversed within 24 hours
causes:
- prerenal
- intrarenal
- postrenal
what are prerenal conditions of AKI
- These are conditions that disrupt blood flow to the kidney.
These include:
- Extremely low blood pressure or blood volume
- Heart dysfunction
what are intrarenal conditions of AKI
- These are conditions that directly damage the structure of the kidney
These include:
1. Reduced blood supply within the kidneys
2. hemolytic uremic syndrome: assoc. w/ infection of certain strains of e. coli b/c e. coli releases toxins that damages the small BV’s of the kidney
= leading cause of kidney failure among children
3. renal inflammation (nephritis), most commonly from nephrotoxic medications like Abx (vancomycin!!)
4. toxic injury like alcohol, cocaine, contrast media (dye), or kidney stones
what are postrenal conditions of AKI
These are conditions that interfere with urine excretion like:
- Ureter obstruction
- bladder obstruction from stones or tumors
what are the 4 phases of AKI
- Initial Phase
- The person is asymptomatic; renal damage is present but functioning nephrons are compensating - Oliguric Phase
- Impaired glomerular filtration leads to solute and water reabsorption
= decreases urine output (400 ml or less per day) & waste products accumulate, normal = at least 33 cc/hour - Diuretic Phase
- Renal function gradually returns as healing and cellular regeneration occur. Diuresis happens because of the tubular damage that impairs the kidneys’ ability to concentrate the urine = could develop electrolyte imbalance or dehydration and go back to oliguric phase (as much as 5L) - Recovery Phase
- Glomerular function gradually returns to normal, can persist up to 3-12 months, full renal fxn is regained
clinical manifestations of AKI (2)
- Oliguric Phase:
- decreased urine output
- electrolyte disturbances (usually increased levels)
- Fluid volume excess
- Azotemia - abnormally high levels of nitrogen containing compounds, like BUN & Creatinine
- metabolic acidosis - b/c of elec retention - Diuretic Phase:
- Increased urine output
- dehydration
- hypotension
- Electrolyte disturbances (usually decreased levels)
what is chronic renal failure (CRF)
- There is gradual loss of renal function that is irreversible
- Scar tissue replaces injured nephrons.
what are the diagnostics for identifying clinical manifestations of AKI
- history like renal tumor, abx.
- physical examination like fluid retention
- BUN and Creatinine level
- renal ultrasound - look for stones
- renal biopsy
- blood chemistry aka basic metabolic panel (looking at electrolytes)
conditions that can lead to slow and progressive destruction of nephrons (CRF)
- DM - leading cause of CRF
- HTN - chronic/uncontrolled
- Urine obstruction - stones, BPH = urine backs up and damages kidney (hydronephrosis, pyelonephritis, glomerulonephritis)
- Renal diseases
- Renal artery stenosis - narrowing of renal arteries, less perfusion to kidney
- On-going exposure to toxins and nephrotoxic medications (vancomycin, aminoglycosides)
- Sickle cell disease - (1) increased hemolysis of RBCs = clog or damage nephrons, or (2) obstruct the small BV’s near the kidney
- SLE - disease damages kidney
- Smoking - atherosclerosis
- Aging - not a huge effect if the person is healthy
5 stages of CFR
- Stage I
- Kidney is damaged but GFR is normal or high (greater than 90) - Stage II
- GFR is 60-89 - Stage III
- GFR is 30-59 - Stage IV
- GFR is 15-29 - Stage V
- GFR less than 15; person reaches kidney failure; dialysis is needed here
clinical manifestations of GFR
- HTN
- anemia = fatigue and weakness
- Polyuria vs. oliguria vs. anuria (no urination, may still pee but less than 50ml/day)
- Easy bruising, bleeding tendencies
- electrolyte imbalance: elevated K and Mag, increased phos so decreased Ca = muscle cramps (Ca specifically)
- pruritus: itching, accumulation of waste products onto skin
- Pericarditis, pericardial effusion (fluid in pericardium), pleuritis, pleural effusion (fluid in the pleural space)
= secondary to uremia, increase in BUN - CHF
- weight gain
- edema
- azotemia
- N/V, anorexia, malaise b/c of the accumulation of toxins
- Sleep disturbances
- decreased mental alertness
- headache
- Decreased libido
- impotence
