week -2: Renal physiology and kidney function Flashcards
Understand the function of the kidney
What are the basic parts of the urinary system?
- 2 x kidneys
- 2 x ureter (transports urine from kidney to bladder)
- urinary bladder
- urethra
List the four main domain of functions of the kidneys?
- Regulatory function
- Excretory function
- Endocrine function
- Metabolic functions
What are the REGULATORY functions of the kidney? Provide examples
- Maintains water balance;
- Maintains electrolyte and acid-base balance :Na, K+, Cl, bicarb, Ca2+, Mg
What are the EXCRETORY functions of the kidney? Provide examples
- removes metabolic wastes: urea, creatinine
- excretes bioactive substances: hormones, foreign substances, drugs
- filters toxins
What are the ENDOCRINE functions of the kidneys? Provide examples
- produce erythropoietin (RBC formation)
- release renin enzyme (regulates BP)
- produce prostaglandins: lipid molecules that act like hormones (vasodilation)
What are the METABOLIC functions of the kidneys? Provide examples
Aid in activation of vitamin D (alongside the liver)
What is the functional unit of the kidney known as? What are its major components?
Nephron
- Glomerulus (cortex)
- Tubular system (medulla): proximal tubule, diluting segment, distal tubule, collecting duct
Describe the flow of blood filtration in relation to vascular structures
- blood enters kidney from RENAL ARTERIES then through smaller arteries
- enters glomerulus via AFFERENT ARTERIOLE
- exits glomerulus via EFFERENT arteriole into smaller capillary networks (peritubular capillary)
- returns to venous system
Provide an overview of the steps in urine formation
- filtration of blood in renal corpuscle
- reabsorption of filtered material back to blood to
- secretion removes unabsorbed material into filtrate
What two components should not be filtered out in the glomerulus? Why?
- blood components: too large to pass through membrane
- proteins: proteins are negatively charges and so is the glomerular membrane = repel; so should not end up in ultra-filtrate
Define the glomerular filtration rate (GFR). What does it indicate? What are the ‘normal’ values
- GFR = estimated rate at which ultra-filtrate is formed in glomerulus
- indicates renal function
- Normal is 100 - 200 mL/min
What factors affect the GFR?
- cardiac output
- BP
- vascular volume
- SNS tone
What would happen to the GFR and urine output if BP is suboptimal?
Reduced GFR > ↓urine production.
Autoregulation kicks in
What is the feedback mechanism of the kidney GFR called?
Autoregulation
Describe the feedback mechanism for when the renal blood flow ( RBF) increases
↑RBF = ↑GFR > leads to ↑in NaCl which is detected by macula densa cells > signals the AFFERENT arteriole to ↑ vascular tone > ↓RBF > results in ↓ GFR
Describe the feedback mechanism if a slow RBF is detected
↓RBF > ↓GFR = more reabsorption of substances = less solute in filtrate > Macula densa cells detect ↓ solutes > produce and release (A) renin; (B) kidney also produces prostaglandins > (A) renin acts on angiostensin I to convert to angiotensin II > constricts efferent arteriole; (B) prostaglandins > dilate afferent arteriole
What common ailments increases stress to the kidneys?
- CKD: chronic kidney disease
- DM
- HTN
- CCF: congestive cardiac failure
Community kidney injury may be caused by taking a cocktail of medications. Provide some examples
- Diuretics
- ACE inhibitors
- Furosemide: treats oedema
- NSAIDs: non steroidal anti-inflammatory drugs
What are the reasons for assessing renal function?
- evaluate state of function
- determine extent of kidney disease and advise management plan
- determine drug doses: based on kidney clearance
- prevent further damage from nephrotoxic agents
Provide an example of what EXOGENOUS filtration marker is used to measure GFR
Insulin
List 2 ENDOGENOUS markers are used to estimate GFR?
- serum Creatinine
- Urea
for Urea:
- what is it?
- what happens to it in the kidney
- is it a sensitive marker for renal function?
- what are the reference intervals?
- End product of protein and amino acid catabolism
- filtered at glomerulus, 40-60% reabsorbed
- INsensitive - usually measured w. serum creatinine
- neonates 1-4 mmol/L; adults 3-8 mmol/L
for serum Creatinine:
- what is it?
- what happens to it in the kidney
- is it a sensitive marker for renal function?
- why is it used as a marker?
- what are the reference intervals for M & F?
- waste product of muscle metabolism in liver (breakdown of creatine)
- 90% excreted by kidney via glomerular filtration
- more sensitive than urea but should not the sole measure
- sCr is inversely proportional to GFR
- M: 60-12; F: 50-110 umol/L
What does a high number sCR indicate about the kidney function?
What would a doubling of the sCr indicate about renal function?
- poor kidney function - not being filtered out
2. represents a 50% reduction in refunction
What factors may influence sCr and what are the expected effect on sCr levels?
- age: ↓
- female:↓
- African American: ↑
- vegetarian: ↓
- muscle mass: ↑
- malnutrition: ↓
List 3 alternative methods to estimating renal function?
- Creatinine Clearance (>50 mL/min)
- eGFR (> 90 mL/min)
- Protein and albumin
Provide example of drugs that should have creatinine clearance calculations done for dosing
- metformin
- digoxin
- atenolol
Creatinine clearance can indicate grades of renal impairment. What are the rates for mild, moderate and severe states?
Mild: 25-50 mL/min
Moderate: 10-25 mL/min
Severe: <10 mL/min
What is urinary protein/albumin (ACR) used to characterise?
Severity of CKD
Also indicates increased cardiovascular risk
What factors are known to increase albuminuria?
- UTI
- High protein intake
- CCF : congestive cardiac failure
- heavy exercise
- Drugs: NSAIDs
