Renal and Urinary Review Flashcards
What are the functions of the kidneys?
Excretory, regulatory, Endocrine
What are the excretory functions of the kidneys?
Nitrogenous waste, phosphorus, potassium, medications
Regulatory functions of the kidneys
Fluids, electrolytes, acid -base, minerals, blood pressure
Endocrine functions of the kidney
Erythropoietin, vitamin D, RAAS
What is the most metabolically active part of the nephron?
Cortex
What % of cardiac output goes to the kidneys?
20%
Flow of blood through kidneys
Renal artery -> segmental arteries -> interlobar arteries -> arcuate arteries -> interlobular arteries -> afferent arteries -> NEPHRON (glomerulus -> efferent arteriole -> peritubular capillaries) -> venules -> interlobular veins -> arcuate veins -> interlobar veins -> renal vein
Autonomic innervation of kidneys
Entirely sympathetic
NE and dopamine releases cause vasoconstricton, Na+ reabsorption on PCT, stimulation of renin release in JGA
Afferent fibers: baroreceptors and chemoreceptor impulses
Explain endocrine function of kidneys
1) Renin is produced from JGA in kidneys.
Renin released is simulated by
-decreased renal perfusion or extracellular fluid volume sensed by granular cells in afferent arteriole
-sympathetic stimulation- systemic hypotension is detected by cardiac and arterial baroreceptors -> increased concentrations of circulating catecholamines -> stimulation of beta1 adrenergic receptors on granular cells -> renin released
-decreased Cl- delivery to macula densa
2) PCT converts 25-hydroxyvitamin D to 1,25- dihydroxyvitamin D (calcitriol)
3) Fibroblasts-like cells in the interstitium of cortex and outer medulla secrete EPO
4) Prostaglandins, kinins
Glomerular filtration
Glomerular filtration decreases drastically with kidney disease
Grams of urea/GFR (L) = BUN concentration in plasma (mg/dL)
Functions of nephrons
Reabsorption and section of ions, carbohydrates, amino acid, H2O, etc
Types of nephrons
-cortical 85%
-juxtamedullary - close to medulla, loop of Henle extends deep into pyramids
Functions of proximal tubule
1) Reabsorption of 65-70% of filtered H2O and NaCl (is osmotic), 90% of filtered HCO3-, and 100% of filtered glucose and amino acids, K+, PO4-, Ca2+, Mg2+, urea, urate
2) secretion of organic anions and cations
3) Production of NH3 (major site)
What part of the nephron do carbonic anhydrase inhibitors work on?
PCT
They block the action of CA4 on the luminal membrane -> decreases the excretion H+ -> increased loss of Na+ -> diuresis
What is Fanconi’s Syndrome?
-Defect of the proximal tubule
-Inherited or acquired
-Caused by toxins (aminoglycosides, jerky treats) or neoplastic
-Causses increased excretion of amino acids, glucose, phosphate, Na+, K+, HCO3-, uric acid
What affect does angiotensin II have on the kidneys?
- Stimulates luminal Na/H+ antiporter (NHE3) which causes increased proximal tubular reabsorption of Na+
- Stimulated aldosterone secretion which causes increased Na+ reabsorption and K+ excretion
- Causes alterations in glomerular hemodynamics to enhance Na+ and H2O reabsorption which causes decreased peritubular capillary hydrostatic pressure and increased peritubular oncotic pressure
- Increased Na+ and H2O reabsorption -> volume expansion
Renal replacement therapies
-A form of artificial blood purification
-Primarily restores homeostasis in AKI
-Removes nitrogen waste and corrects acid-base, electrolytes, and fluid imbalance
What does the loop of Henle do?
-The loop of Henle is the countercurrent multiplier
-reabsorption of 15-25% of filtered NaCl and 20% K+
-active regulation of Mg2+ excretion
Renal Replacement Therapy Modalities
- Intermittent hemodialysis: highly effective, PRN (2-3x/wk)
- Continuous RRT: less effective, continuous treatment
- Peritoneal dialysis: least effective, instill and drain dialysate from peritoneal space
Indications for Hemodialysis (AKI)
- Anuria, severe oluguria
- Failure of conventional medical therapy to initiate adequate diuresis and go control azotemia
- Life-threatening: fluid overload, electrolyte disturbances, acid-base disturbances
- Severe azotemia
Indications for Hemodialysis (CKD)
Indefinite intermittent RRT
Support for acute decompensation of CKD
Finite RRT for client transition to irreversible disease status
Bridge to and/or from staged surgery (e.g. ureteral obstruction, renal transplantation)
Indications for Hemodialysis/Other ECT
(Miscellaneous)
Severe overhydration, pulmonary edema, CHF
Acute poisoning/drug overdose
Endogenous intoxicants (i.e. liver failure)
Immune-mediated disease such as
-Myasthenia gravis
-Polymyositis
-Polyneuropathy
-IMHA
-ITP
-rapidly progressing GN
Hyperproteinemia (TPE) such as in multiple myeloma
Components of dialysate
-Purified water
-Acid concentrate
-Bicarbonate
Dialysate composition determines blood composition
Patient exposed to 120-200 liters dialysate per tx
What electrolytes can we modify in dialysate?
K+ (0 vs. 3 mEq/L)
Na+
Ca2+
Phosphorus
