Lecture 1: Renal Function Flashcards
What is the excretion product of
- Proteins
- Nucleic Acids
- Muscle Creatine
- Hemoglobin
- Proteins: Urea
- Nucleic Acids: Uric acid (Purines)
- Muscle Creatine: Creatinine
- Hemoglobin: Urobilin
How do the kidneys regulate BP?
Decreases in renal BP lead to JG cells in the afferent to release renin.
Renin increases peripheral vasoconstriction.
What triggers the release of EPO from the kidneys?
Hypoxia.
Why do diseased kidneys not release EPO?
Hypoxia in the body is not reflected in the kidneys due to the reduced metabolism from diseased tissue. This reduces/inhibits EPO secretion.
Where are the kidneys located?
- Retroperitoneal
- Just below rib cage
What are the 3 major sections of the kidney?
- Renal Cortex
- Renal Medulla
- Renal Pelvis
How does the renal cortex look like histologically?
Spaghetti and meatballs.
Random intertwining of tubules and blood vessels, along with renal corpuscles scattered around.
What does the renal medulla look like histologically?
Bundles of pencils.
Parallel arrangements of tubules and blood vessels.
What are the parts of a nephron?
- Renal corpuscle: Glomerulus + capsule
- Tubules
- Collecting duct (merging of tubule)
- End in the terminal papilla.
What are the differences between a juxtamedullary nephron vs a cortical nephron?
- JM = longer, mainly for URINE concentration.
- Cortical = shorter, only dips a little into medulla.
Cortical nephrons make up 85% of all nephrons.
What part of the nephron corresponds to the macula densa?
Thick ascending limb closest to the capsule.
What part of the loop of Henle does a cortical nephron lack?
No thin ascending limb.
What is a horseshoe kidney and the main concerns associated with it?
- Fusion of kidneys due to failure to separate.
- Results in abnormal blood flow and ureter coursing.
- Also often lower in the ribcage, so it is more vulnerable to trauma.
Cannot move higher than the IME (Inferior mesenteric)
What is the most common complaint associated with a horseshoe kidney?
UTI in children.
What is the most common complication due to a horseshoe kidney?
Ureteropelvic junction obstruction
How is a horseshoe kidney diagnosed?
- CT w/ IV pyelogram
- UA/culture
- Renal function labs
How is a horseshoe kidney treated?
Symptomatic management.
Surgery is not always ideal due to the scar tissue that will form.
How often is our plasma volume filtered daily?
60x, around 180L/d in a healthy male at 125 ml/min for GFR.
What is primarily reabsorbed in the proximal tubule?
- 60% of NaCl and H2O
- 90% of HCO3-
- Glucose, AAs
- Most of K, PO4, Ca, Mg, Urea, and uric acid
What is primarily reabsorbed in the loop of Henle?
- Descending: H2O
- Ascending: 25% of NaCl
- Some Ca, most Mg.
What is the primary function of the Loop of Henle?
Countercurrent mechanism to generate concentrated urine.
Where do loop diuretics work on specifically?
Thick Ascending Limb
Na/K/2Cl pump location
What are the primary functions of the distal tubule?
- pH regulation via H+ and HCO3-
- Calcium regulation
- K secretion
What are the important cells of the cortical collecting duct and their functions?
- Principal cells: reabsorbing NaCl and H2O, K secretion.
- Intercalated cells: mediate HCO3- and H+ secretion/reabsorption.
Site of action for K+ sparing diuretics (principal cells)
What are the functions of the medullary collecting duct?
- Urine modification
- Reabsorption of NaCl, water, and urea
- Secretion of ammonia (NH3), H+
- Secretion/reabsorption of K+
What are the primary etiologies of AKI?
- Hypotension
- Obstruction of urine flow
- Substance use
How do the kidneys compensate for injury/loss?
Kidneys cannot regenerate nephrons, so compensatory renal hypertrophy occurs.
Often occurs as hyperfiltration.
Essentially, sending more plasma through nephrons.
What does ESRD result from?
- Loss of 80% of renal mass
- Destruction of a significant amount of nephrons, that cannot compensate enough.
Why do we use ACEIs and ARBs for proteinuria even without HTN?
Proteinuria signals the kidney that something is wrong, and will result in inflammation if left untreated.
How does GFR change for someone with kidney disease?
It can decrease, stay the same, or even increase.
What is generally considered CKD?
GFR < 60 for 3mo.
What are some of the substances used to estimate GFR?
- BUN
- Creatinine
- Cystatin C (newer)
All freely filtered
What is kidney function proportional to?
Kidney size, which is also proportional to body size.
Big people = big kidneys
What general factors affect GFR?
- Body Surface Area (BSA)
- Age
- Gender
- Race
How does higher muscle mass affect GFR?
Higher mass = higher serum creatinine = lower GFR
How does having higher serum creatinine affect GFR?
Inversely proportional. Lower GFR with higher serum creatinine.
How do antibiotics affect creatinine levels?
Inhibits renal secretion, which results in higher serum creatinine and lower GFR.
How can liver disease mask kidney damage?
50% of creatinine is produced by the liver, so damage to the liver results in a lower serum creatinine and higher GFR.
What are the measurements required for a CrCl calculation?
- Serum creatinine
- Urine creatinine
- 24-hour urine collection
Measures the upper limit of GFR
What is urea?
Liver by-product from protein digestion.
Freely filtered and reabsorbed heavily in dehydrated patients.
Functions like a sponge.
What decreases BUN?
- Liver disease
- Malnutrition
- SCD
- SIADH
What is the usual etiology of increased urea?
Dehydration
When is BUN usually used as an indicator?
Severe CKD
What is Cystatin C?
Protein made by all nucleated cells in the body and is freely filtered.
It is not as affected by muscle mass and metabolism.
What generally decreases Cystatin C?
- Female
- Smaller body mass
What is the main prohibitive factor in Cystatin C calculations for GFR?
Cost.
What equation was first used for CrCl and why?
Cockcroft-Gault, which assume stable Cr.
Does not account for BSA.
What is the successor equation to the MDRD Study equation and the Cockcroft-Gault?
CKD-EPI, mainly for normal-mildly reduced GFR with no racial adjustment.
Preferred equation in the US.
