Renal Flashcards
Components of renal fxn
- Glomerular filtration
- Tubular secretion
- Tubular reabsorption
- Excretion
Renal corpuscle
- Where ultrafiltrate originates
- Glomerulus & Bowman’s capsule
Renal pelvis
Where ultrafiltrate leaves kidney
Renal vasculature
Renal artery –> interlobar a –> arcuate a –> interlobular a –> afferent arteriole –> glomerular capillary –> efferent arteriole –> peritubular capillary
What are the 3 capillary beds?
- Glomerular: filtration
- Peritubular: reabsorption, secretion
- Vasa recta - specialized peritubular: Osmotic exchangers
Renal blood flow (RBF)
Total volume of blood delivered to kidneys per unit time = 1.25
Renal plasma flow (RPF)
- Volume of plasma delivered to kidneys per unit time
How much of plasma is filtered?
20%
- Becomes ultrafiltrate in Bowman’s
Glomerular filtration
- Forming urine
2. RBF enters glomerular capillaries & portion of blood is filtered into 1st part of the nephron
Corpuscle
A glomerulus & Bowman’s capsule
Filtration barriers consist of what 3 layers?
- Capillary endothelium
- Basement membrane
- Capsular epithelial cells
What is the most significant layer of the filtration barriers?
Basement membrane
- Barrier to plasma proteins
Sympathetic nn
- Vasoconstriction by binding to alpha1 receptors on afferent arteriole
- Response to hemorrhage
- Decrease RBF
Angll
- Vasoconstriction of both afferent & efferent arterioles, but efferent is more sensitive
- Decrease RBP
How can RPF & GFR be controlled?
By controlling resistance of the afferent arteriole
Prostaglandins (PGE2, PGI2)
- Vasodilate
- Protective effect
- Increase RBF
Dopamine
- Vasodilate via dopamine receptors (D1, D3, D5)
- Protective effect; admin in shock
- Increase RBF
Other vasodilators
- ANP
- NO
Changes in GFR can be brought about by changes in what?
Starling forces
What does GFR depend on?
The sum of starling forces
- Forces favoring vs. forces opposing
Reabsorption
Returns substances to circulation
Secretory
Remove substances from blood & add to urine
What is the most important fxn of the kidney?
Reabsorption of sodium
Descending thin limb
- Passive permeability to H2O, NaCl & urea
Ascending thick limb
- Active NaCl reabsorption
- Load dependent
- Impermeable to H2O
Principal cells (late DT & CD)
- Aldosterone & ANF sensitive sodium reabsorption
- Also reabsorbs H2O & secretes K+
- Driving force established by Na-K- ATPase in basolateral membrane
ADH
Reabsorbs H2O & NaCl
Role of ADH
- Binds V2 receptors in basolateral membrane
- Stimulates Gs (activates adenylate cyclase, increases cAMP)
- Activates protein kinase A
- Phosphorylates intracellular structures
- H2O channels shuttled to apical membrane
- Inserted into membrane –> H2O reabsorption
Hypoosmolarity
Excess H2O in body
- Kidneys excrete urine w/ low osmolarity (H2O diuresis)
Hyperosmolarity
Deficit of H2O
- Kidneys concentrate urine (Antidiuresis)
Normal urine
Slightly hypertonic
Control of BP
- Baroreceptor reflex (neurally-mediated, reacts in secs)
- Renin-angiotensin aldosterone (hormonally-mediated, reacts in mins to hrs)
What determines volume?
Amount of Na+ in ECF
What is the single most important controller of sodium?
Renin-angiotensin-aldosterone
What conditions lead to hyponatremia?
- Excess retention or intake of H2O
- Inappropriate or uncontrolled secretion of ADH
- Increased loss or decreased intake of Na+
What conditions lead to hypernatremia
- Impaired thirst
- No access to drinking H2O
- Loss of extracellular H2O
Acute water load
Osmolarity < 290
- Drink free H2O
- Increased ECF volume, decreased ECF osmolarity
- Shift of water from ECF to ICF:
Decreased ICF osmolarity
- New steady state:
Hypoosmotic volume expansion, TBW increases
Infusion of isotonic NaCl
- Increased ECF volume
- No change in osmolarity, as infusion is isosmotic
- No need for fluid shift
- ICF volume remains unchanged
- New steady state:
Isosmotic volume expansion - TBW increases
What does the renin-Ang II-Aldo system regulate?
- Arterial pressure by regulating blood volume
- Achieved by regulating Na+ reabsorption –> affects H2O reabsorption
- Amount of Na+ in ECF determines volume
Production of hyposmotic urine
W/out ADH, H2O reabsorption does not occur in late DT & CD.
- A dilute urine is produced
- H2O is impermeable to thick ascending limb & CD
Production of hyperosmotic urine
- When ADH is present, a concentrated urine is formed
- H2O is impermeable to thin ascending limb
- H2O reabsorption is maximal at CD
