Renal Physiology Flashcards
What percentage of renal blood flow goes to the medulla?
10%
What is the glomerular filtration rate (GFR)?
125 ml/min
What is the hydrostatic pressure in Bowman’s capsule?
~10 mmHg
What effect does increased glomerular capillary pressure have on filtration?
It increases GFR.
What molecule is poorly filtered due to size and charge?
Albumin (69,000 Da, negatively charged).
What is the primary function of podocytes?
Create filtration slits that restrict large molecules.
What happens if the efferent arteriole resistance increases?
Glomerular pressure rises, enhancing filtration.
What factors determine the ultrafiltration coefficient (KF)?
Membrane permeability and surface area.
What is the function of autoregulation in the kidneys?
Maintain constant GFR and renal blood flow.
What role does the myogenic mechanism play in autoregulation?
Responds to stretch by inducing vasoconstriction.
What is the role of the juxtaglomerular apparatus (JGA)?
Senses changes in NaCl and flow for feedback regulation.
How does adenosine mediate tubuloglomerular feedback?
Constricts afferent arterioles to reduce GFR.
What is the effect of nitric oxide on renal blood flow?
Promotes vasodilation.
What happens to GFR during sympathetic stimulation?
It decreases due to vasoconstriction.
What is the effect of angiotensin II on renal blood vessels?
Preferentially constricts efferent arterioles.
What happens when afferent arterioles constrict?
GFR decreases.
Why is inulin the gold standard for GFR measurement?
Freely filtered, not reabsorbed, secreted, or metabolized.
What is a drawback of using creatinine to measure GFR?
Slightly secreted by tubules, leading to overestimation.
What does renal clearance represent?
Volume of plasma cleared of a substance per unit time.
What condition increases plasma creatinine concentration?
Reduced GFR.
How is renal blood flow (RBF) calculated?
RBF = RPF / (1 - Hematocrit).
What property makes PAH (Para-Aminohippuric Acid) suitable for measuring RPF (Renal Plasma Flow)?
It is almost completely cleared from plasma.
What is the renal plasma flow (RPF) value?
~600 ml/min.
Why is PAH only accurate at low concentrations?
High concentrations saturate secretion mechanisms.
What percentage of filtrate is reabsorbed by the end of the proximal tubule?
~70%.
What is the primary transport mechanism for Na+ in the proximal tubule?
Na+/K+ ATPase pump.
What role do tight junctions play in the nephron?
Facilitate paracellular transport of solutes like Cl-.
What drives reabsorption of water in the proximal tubule?
Osmotic gradients created by Na+ and HCO3- reabsorption.
Which part of the nephron generates concentrated filtrate?
Loop of Henle.
What is the function of principal cells in the collecting duct?
Regulate Na+ reabsorption and K+ secretion.
What is the role of intercalated cells in the collecting duct?
Acid-base balance via H+ and HCO3- transport.
What is the osmolarity of fluid entering the distal tubule?
Hypotonic (~100 mOsm/L).
What is the osmolality at the tip of the loop of Henle?
Up to ~1200 mOsm/kg.
Which segment of the loop actively transports NaCl?
Thick ascending limb.
How does the vasa recta maintain the medullary gradient?
Countercurrent exchange prevents gradient dissipation.
Why is the thin descending limb permeable to water?
Presence of aquaporins.
What generates the positive charge in the thick ascending limb?
K+ recycling into the lumen via channels.
How does urea contribute to medullary osmolality?
Reabsorbed in collecting ducts, recycled in the loop.
What is the effect of furosemide on the loop of Henle?
Inhibits Na+/K+/2Cl- cotransporter, reducing NaCl reabsorption.
Why does the medulla have low oxygen tension?
Countercurrent exchange lowers PO2 at the vasa recta tip.
What triggers ADH release?
Increased osmolality or decreased blood volume.
What is the role of aldosterone in potassium regulation?
Enhances K+ secretion in the distal tubule.
What hormone inhibits Na+ reabsorption in the distal nephron?
Atrial natriuretic peptide (ANP).
What makes the distal tubule impermeable to water without ADH?
Lack of aquaporins in the absence of ADH.
What drives calcium reabsorption in the distal tubule?
PTH and vitamin D activation.
What happens to osmolality in the collecting duct in the presence of ADH?
Increases as water is reabsorbed.
Which type of nephron is most involved in concentrating urine?
Juxtamedullary nephrons.
What percentage of filtered Na+ is reabsorbed in the distal nephron?
~10%.
What stimulates ANP release?
Atrial stretch due to increased blood volume.
What enzyme catalyzes angiotensin I formation?
Renin.
How does aldosterone increase Na+ reabsorption?
Upregulates Na+/K+ ATPase pumps and Na+ channels.
What effect does ANP have on GFR?
Increases it by dilating afferent arterioles.
What suppresses renin release?
Increased angiotensin II and Na+ levels.
How does sympathetic activation affect renin?
Increased angiotensin II and Na+ levels.
How does sympathetic activation affect renin?
Stimulates release via β1 receptors.
What role does ADH play in urea recycling?
Facilitates its movement into the medulla to maintain osmotic gradient.
What suppresses ADH release?
Alcohol consumption.
How is filtered bicarbonate reabsorbed in the nephron?
Combines with H+ to form CO2 and H2O.
What enzyme is critical for bicarbonate reabsorption?
Carbonic anhydrase.
Where is ammonium generated in the nephron?
Proximal tubule via glutamine metabolism.
What is the role of the Na+/H+ antiporter?
Secretes H+ into the tubular lumen.
What happens to NH4+ in the thick ascending limb?
Reabsorbed and dissociates into NH3 and H+.
What buffers H+ in the collecting duct?
Ammonia (NH3) and phosphate.
What is the renal compensation for respiratory acidosis?
Increased H+ excretion and bicarbonate reabsorption.
How does aldosterone affect acid-base balance?
Promotes H+ secretion in the distal nephron.
What type of muscle controls the internal urethral sphincter?
Smooth muscle.
What initiates the micturition reflex?
Stretch receptors in the bladder wall.
What is the detrusor muscle?
Smooth muscle responsible for bladder contraction.
What is the role of higher brain centers in micturition?
Voluntary control of the external sphincter.
Where is erythropoietin (EPO) produced?
In renal cortex fibroblast-like cells.
What triggers EPO production?
Hypoxia via HIF1-alpha stabilization.
What is the role of the kidneys in vitamin D metabolism?
Activate 25(OH)D to 1,25(OH)2D.
Which ion is most closely regulated by the kidneys to control blood volume?
Sodium.
What is the renal threshold for glucose?
~11 mmol/L.
Why is potassium regulation critical?
Prevents hyperkalemia, which can cause cardiac arrhythmias.
What happens to urine osmolality in the absence of ADH?
Becomes dilute (~50 mOsm/L).
