Renal Flashcards
Which part of the kidney is more prone to ischemic and toxic injury?
Medulla as it only received 3-10% of the overall blood flow to the kidneys.
Factors that determine the filtration of molecules at the glomerular capillaries:
- Size (< 4 nm) selectivity - lamina densa
- Charge selectivity - favour positively charged molecules - sialoglycoproteins and peptidoglycans at the capillary endothelium, lamina RI, lamina RE, podocytes all negatively charged
What are the 7 functions of the kidneys?
- Regulation of water and electrolyte balance
- Regulation of systemic blood pressure and extracellular fluid volume
a. Determine blood volume: salt and water balance
b. Production of vasoactive hormones: RAAS - Excretion of metabolic waste and foreign substances (uremic retention solutes)
- Regulation of red blood cell production: erythropoietin (synthesised by interstitial cells)
a- Stimulus: reduction in partial pressure of oxygen - Regulation of acid-base balance
- Regulation of Vit D production and calcium + phosphate balance
- Production of calcitriol (active Vit D) - Gluconeogenesis
What is the GFR of a dog?
3-5mL/kg/min
What is the GFR of a cat?
2.5-3.5mL/kg/min
What is the macula densa?
Specialised tubular epithelial cells that line the thick ascending loop of Henle at its junction with the distal tubules and sits in close contact with the afferent arterioles
What is the autoregulation range of the kidneys?
MAP 80-180mmHg
What is autoregulation
Intrinsic ability of kidneys to maintain RBF and GFR for varying BPs between 80-180mmHg
Name the 3 main ways Angiotensin II stimulates Na reabsorption:
- aldosterone secretion
- vasoconstriction of efferent arterioles
- direct stimulation of pumps in PT, LOH, DT and collecting tubules (Na-K ATPase, Na-bicarb cotransporter, Na/H+ antiporter luminal)
Where is aldosterone’s site of action?
principal cells of cortical collecting tubules
What does aldosterone do?
Na reabsorption (Na-K-ATPase basolateral, ENaC at luminal)
K+ secretion (ROMK in luminal)
Where does ADH act to increase water reabsorption?
V2 receptor in the late distal tubule and collecting ducts
How does ADH reabsorb water?
Synthesis + insertion of aquaporin 2 to luminal membrane
Where does ANP act?
- collecting ducts to inhibit Na and water reabsorption
- inhibits renin secretion
Which 2 mechanisms create the hyperosmotic medullary interstitium?
- loop of Henle’s countercurrent mechanism
- urea recycling
Which 2 mechanisms maintain the hyperosmotic medullary interstitium?
- distal tubule and collecting duct
- vasa recta
Function of the pelvic nerve (S2-3):
Sensory: detect stretch, micturition reflexes for bladder emptying
Motor: parasymathetic -> contraction of detrusor muscle
Function of the pudendal nerve (S2-S4):
External bladder sphincter (skeletal muscle)
Inhibiting it -> mictrurition
Which enzyme is the rate limiting factor in the metabolism of ethylene glycol?
Alcohol dehydrogenase
2 most important factors to promote urethral healing:
Good mucosal continuity
Prevention of urine extravasation
Why are high chloride containing fluids harmful to the kidneys?
High conc. of Cl delivered to the macula densa which would induce afferent arteriole vasoconstriction and lower GFR, RBF
What is the main causative agenet for pyeloneprhitis?
Enterobacteriaceae
What is a reasonable first choise for pyeloneprhitis while awaiting C/S?
Fluoroquinolones or cefpodoxime
What antibiotic characteristics are best for crossing the prostatic blood barrier?
- lipid soluble
- weakly alkaline
- high pKa
What defines recurrent urinary tract infection?
3 or more episodes of clinical bacterial cystitis in prev 12 months OR
2 or more episodes in preceding 6 months
Main method of solute removal for intermittent hemodialysis, continuous venovenous haemodialysis (CVVHD)
diffusion
Main method of solute removal for slow continuous ultrafiltration (SCUF) and continuous venovenous haemofiltation (CVVH):
convection
Difference between SCUF and CVVH:
in CVVH once the ultrafiltrate is removed, it is replaced with a sterile balanced electrolyte solution
Which condition is SCUF good for?
CHF - as ultrafiltate is not replaced by anything
What method of solute removal does continuous venovenous hemodiafiltration rely on:
Combines diffusion and convection
What is convection?
when solutes are dragged with plasma water across the dialysis membrane due to osmotic pressure gradient or hydrostatic pressure (solvent drag)
How does diffusion work?
Countercurrent movement of the blood and dialysate across the dialyser semipermeable membrane allows for efficient bidirectional movement of solutes from high -> low concentration
what is ultrafiltration?
Process of plasma water removal from the intravascular compartment (and ultimately from the interstitial and intracellular spaces)
In IHD and CRRT application of a negative transmembrane pressure to the dialyser will allow plasma water to shift across the membrane into the dialysate and out of the patient
what is dialysis?
Dialysis is the movement of solutes between 2 aqueous solutions separated by a semipermeable membrane
Toxin factors to consider for extracorporeal removal:
- Vd (<2L/kg)
- MW
- Degree of protein binding
- Water solubility
List 10 complications that have been reported with PD in small animals
- Catheter flow problems – obstruction with omentum, catheter kinking, fibrin clots
- Catheter exit site leaks – into subcutaneous tissue
- Catheter exit site and tunnel infection
- Electrolyte disorders
- Hypoalbuminemia (most commonly reported)
- Peritonitis
- Dyspnoea caused by ↑abdominal pressure or pleural effusion
- Changes in hydration status (overhydration)
- Dialysis disequilibrium
- Hyperglycemia
Peritoneal fibrosis
Why is urine osmolality better than USG?
Provides more information on renal concentrating ability than USG
Difference between urine osmollality and USG
USG = density per unit volume of solution (no. of particles and MW)
Osmolality = no. of particles per unit volume of solution
