Renal Physiology Flashcards
This is an ultrafiltrate of blood
Urine
Urea is a waste product from:
Proteins
Uric acid is a waste product from:
Purines
Creatinine is a waste product from:
Muscles
Bilirubin is a waste product from:
RBCs
Life is only compatible with a plasma pH range of:
6.8 - 8.0 (beyond this, denature proteins)
2 hormones produced by the kidney:
Calcitriol, renin
Water excretion ranges between:
0.5 - 1.5 L/day
Urine pH range:
5.0 - 7.0
Osmolality of urine:
500 - 800 mOsm/kg H2O
Location and weight of the kidney:
T12 - L3, 150g
Trace the renal circulation.
Renal artery –> segmental artery –> interlobar artery –> arcuate artery –> interlobular artery (cortical radiate/radial artery) –> [afferent arteriole –> glomerular capillaries –> efferent arteriole –> peritubular capillaries/vasa recta] –> interlobular vein –> arcuate vein –> interlobar vein –> segmental vein –> renal vein
Highly fenestrated, responsible for GFR, only capillaries that lead to arterioles and not venules
Glomerular capillaries
Supplies O2 and glucose to tubular cells
Peritubular capillaries
Cells found in the peritubular capillaries that secrete EPO
Interstitial cells
Hairpin-looped shaped peritubular capillaries of the juxtamedullary nephrons that participate in countercurrent exchange
Vasa recta
Urinary bladder: capacity
600 mL
Urinary bladder: urge to urinate
150 mL
Urinary bladder: reflex contraction
300 mL
Urinary bladder: bladder muscle
Detrusor muscle
Urinary bladder: internal urethral sphincter
Involuntary
Urinary bladder: external urethral sphincter
Voluntary
Condition in which the full capacity of the urinary bladder is reached without reflex contraction
Neurogenic bladder
Functional and structural unit of the kidney
Nephron
Number of nephrons per kidney
1 million
Kidneys undergo compensatory hypertrophy when there is ___ percent damage to the nephrons
75%
Cortical nephrons vs Juxtamedullary nephrons:
75% of nephrons
Cortical
Cortical nephrons vs Juxtamedullary nephrons:
Long loops of Henle
Juxtamedullary
Cortical nephrons vs Juxtamedullary nephrons:
25% of nephrons
Juxtamedullary
Cortical nephrons vs Juxtamedullary nephrons:
Short loops of Henle
Cortical
Cortical nephrons vs Juxtamedullary nephrons:
Capillary network: peritubular capillaries
Cortical
Cortical nephrons vs Juxtamedullary nephrons:
Capillary network: vasa recta
Juxtamedullary
Other name for the renal corpuscle
Malfegian corpuscle
Components of the renal tubular system
Proximal convoluted tubule
Loop of Henle
Distal tubule
Collecting duct
Renal corpuscle: First filtration-charge barrier; 50x more permeable than skeletal muscle capillaries; secrete nitric oxide and endothelin-1
Capillary endothelium
Renal corpuscle: Main charge barrier; with Type IV collagen, laminin, agrin, perlecan, fibronectin
Basement membrane
Renal corpuscle: cells of the capillary endothelium; contains foot processes, filtration slits
Podocytes
Modified smoth muscle intimately attached to the glomerular capillaries; contractile, mediates filtration, take up immune complexes and involved in glomerular diseases
Mesangial cells
Glomerular cells of the afferent arterioles; found at the walls of the afferent arterioles; secrete renin
Juxtaglomerular cells
Found in the walls of the distal convoluted tubules; monitor Na+ concentration in the distal tubule (consequently, blood pressure)
Macula Densa
Workhorse of the nephron, most prone to ischemia and acute tubular necrosis
Proximal convoluted tubule
Site of 66% Na, K, H2O reabsorption and 100% Glucose, amino acid reabsorption
Proximal convoluted tubule
Part of the loop of Henle which is permeable to H2O but impermeable to solutes
Descending limb
Part of the loop of Henle which is permeable to solutes but impermeable to H2O
Thin ascending limb
Part of the loop of Henle which contains the Na-K-2Cl pump
Thick ascending limb
Diluting segment of the renal tubular system
Thick ascending limb of the loop of Henle
What is inhibited by loop diuretics?
Na-K-2Cl pump found at the TAL
Contains the Macula Densa
Early distal tubule
Contains the principal cells and intercalated cells
Late distal tubule
Cells responsible for Na reabsorption and K secretion
Principal cells
Cells responsible for H+ secretion and K absorption
Intercalated cells
What stimulates the principal and intercalated cells?
Aldosterone
What is the action of ADH at the collecting duct?
Insert aquaporins to increase water reabsorption (decrease urine volume, increase urine concentration)
Movement from glomerular capillaries to Bowman’s space
Glomerular filtration
Movement from tubules to interstitium to peritubular capillaries
Tubular reabsorption
Movement from peritubular capillaries to interstitium to tubules
Tubular secretion
Formula for excretion
Excretion = (amount filtered + secreted) - amount reabsorbed
Substances which are 100% filtered
Inulin, creatinine
Substances which undergo filtration and complete reabsorption
Glucose, amino acids
Substances which undergo filtration and partial reabsorption
Many electrolytes
Substances which undergo filtration and secretion but never reabsorbed
Paraaminohippuric acid (PAH), organic acids and bases
Substance which has the highest clearance
PAH
Substances which have zero clearance
Glucose, amino acids
Substances which can be used to estimate GFR
Inulin, creatinine
Amount filtered in the glomerular capillaries per unit time
GFR (Normal: 125mL/min or 180L/day)
Filtration fraction: GFR/RPF
What is the size of subtances which can be filtered freely?
20 angstrom or less
What is the size of substances which cannot be filtered at all?
> 42 angstrom
What is the filterability of solutes according to size?
Water, Na, Glucose, Inulin > Myoglobin > Albumin
What is the filterability of solutes according to charge?
Positive substances > neutral > negative
What is the normal net filtration?
2mL/min
Effect on GFR:
Afferent arteriole dilate
Increase
Effect on GFR:
Afferent arteriole constrict
Decrease
Effect on GFR:
Efferent arteriole dilate
Decrease
Effect on GFR:
Efferent arteriole constrict moderately
Increase
Efferent arteriole contrict severely
Decrease
What are the reasons for the decrease in GFR in a severely contricted efferent arteriole?
- Gibbs Donnan effect
(albumin which is a negative charged solute will attract positively charged Na ions, attracting H2O inside the capillaries) - Albumin, because of its size cannot pass through, will be trapped inside the capillary, and will increase the capillary oncotic pressure
Effect on GFR:
GC hydrostatic pressure increased
Increase
Effect on GFR:
GC oncotic pressure increased
Decrease
Effect on GFR:
BS hydrostatic pressure increased
Decrease
Effect on GFR:
Kf increased
Increase (Kf refers to capillary permeability)
Number one cause of increase in Bowman’s space hydrostatic pressure
Urinary tract obstruction secondary to renal stone
What are the causes of decreased Kf?
Renal diseases, DM, HTN
What is the mechanism for decreased GC hydrostatic pressure in hypotension?
Decreased arterial pressure
What is the mechanism for decreased GC hydrostatic pressure of ACEI?
Decreased efferent arteriole constriction
What is the mechanism for decreased GC hydrostatic pressure in sympathetic stimulation?
Increased afferent arteriole constriction
What are the hormones that will increase GFR?
EDRF, PGE2, PGI2, Bradykinin, glucocorticoids, ANP, BNP
Which hormone will preserve GFR?
Angiotensin II (preferentially constricts efferent arteriole)
Local autoregulation of renal blood flow occurs at a BP of:
between 75 - 160 mmHg
What do you call massive sympathetic stimulation that results in massive vasoconstriction of the kidneys?
CNS ischemic response
The CNS ischemic response is activated at what BP? optimal at what BP?
Activated at BP
This maintains the GFR at a constant 125 mL/min
Tubuloglomerular feedback/ Macula Densa feedback
What substance that is part of the TGF that vasoconstricts the afferent arteriole?
Adenosine
What substance that is part of the TGF that vasodilates the afferent arteriole?
Nitric oxide
What substances are secreted by the macula densa in response to low blood pressure (low GFR)?
Angiotensin II (vasoconstricts efferent arteriole) Nitric oxide (vasodilates afferent arteriole)
What substance is secreted by the macula densa in response to high blood pressure (high GFR)?
Adenosine (vasoconstricts afferent arteriole)
Percentage of solute reabsorbed is held constant. Buffers effect of drastic GFR changes on urine output
Glomerulotubular balance
State when substance start to appear in the urine; some nephrons exhibit saturation
Renal threshold
State when all excess substance appear in the urine; all nephrons exhibit saturation
Renal transport maximum
What is the renal threshold for glucose?
200 mg/dL
What is the transport maximum for glucose?
375 mg/dL
Rate of transport is dependent upon electrochemical gradient, membrane permeability and time; does not have a transport maximum and threshold
Gradient-time transport (all passively transported solutes; ex: Cl, Urea)
Which is more hypertonic relative to the other, fluid entering the PCT or fluid leaving the PCT?
None. There is isoosmotic reabsorption.
What is the epithelium of the PCT?
Low columnar with extensive brush border
What is the epithelium of the loop of Henle?
Thin segments: simple squamous with no brush border
Thick segments: simple cuboidal
The thin segments of the loop of Henle is responsible for what?
slow flow of fluid in the loop of Henle
In the loop of Henle: \_\_% of filtered H2O is reabsorbed \_\_% of filtered Na,K,Cl is reabsorbed Mg2+ and Ca2+ also reabsorbed Hydrogen is secreted via \_\_\_\_
20%, 25%, Na-H countertransport
What is the epithelium of the distal tubule?
Simple cuboidal without brush border
3 components of the juxtaglomerular apparatus
Macula densa, juxtaglomerular cells, lacis cells
Mechanisms used by intercalated cells for secretion of H+
H+-ATPase pump, Na-H+ countertransport
The distal tubule reabsorbs ___% of filtered H2O, and is impermeable to ____.
5%, urea
Site for regulation of final urine volume and concentration
Collecting duct
What happens to tubular reabsorption when peritubular capillary hydrostatic pressure increases?
Decreases
What happens to tubular secretion when peritubular capillary hydrostatic pressure increases?
Increases
What happens to tubular reabsorption when peritubular capillary oncotic pressure increases?
Increases
What happens to tubular secretion when peritubular capillary oncotic pressure increases?
Decreases
Aldosterone acts on the distal tubule to:
Increase Na and H2O reabsorption; Increase K+ and H+ secretion
Angiotensin II acts on the PCT, TAL LH, distal tubule to:
Increase Na and H2O reabsorption
Catecholamines act on the PCT, TAL LH, distal tubule and collecting duct to:
Increase Na and H2O reabsorption
Vasopressin acts on the distal tubule and collecting duct to:
Increase H2O reabsorption
ANP and BNP act on the distal tubule and collecting duct to:
Decrease Na reabsorption
Uroguanylin and guanylin act on the PCT and collecting duct to:
Decrease Na and H2O reabsorption
Dopamine acts on the PCT to:
Decrease Na and H2O reabsorption
PTH acts on the PCT and TAL LH to:
Increase Ca2+ reabsorption, stimulate 1 alpha hydroxylase, decrease PO4 reabsorption
What are the triggers for ADH secretion?
Increased plasma osmolarity, decreased blood pressure, decreased blood volume
What is the number one trigger for ADH secretion?
Increased plasma osmolarity (Normal: 300 mOsm/L)
What is the effect of alcohol on ADH secretion?
Decreases ADH secretion
Which hormone secreted by DT and CD acts similar to ANP?
Urodilatin
Rate at which substances are removed from blood in the kidneys
Renal clearance
Urine clearance is directly proportional to ______ and _____ and inversely proportional to _____.
direct: urine concentration of substance x and urine flow rate per minute
indirect: plasma concentration of substance x
If a substance has high clearance, what are the blood and urine level of this substance?
Urine: high
Blood: low
If a substance has low clearance, what are the blood and urine level of this substance?
Urine: low
Blood: high
Renal clearance:
Substance with highest clearance
PAH
Renal clearance:
Substance with zero clearance
Glucose, amino acids
Renal clearance:
Substance whose clearance is used to estimate GFR
Inulin, creatinine
Renal clearance:
Substance whose clerance is used to estimate renal blood flow and renal plasma flow
PAH
Substances that do not appear in the urine have a clearance of:
zero
Substances filtered and partially reabsorbed have a clearance ____ than the GFR
less
Substance filtered and with net secretion have a clearance ____ than the GFR
more
Clearance of inulin is ____ to that of the GFR
equal
How many percent of filtered water is reabsorbed?
87 - 98.7%
What is responsible for the regulation of glucose?
Na+-Glucose cotransport in the proximal tubule
Glucose transport from the lumen to the PCT?
SGLT-2 (secondary active transport)
Glucose transport from the PCT to the peritubular capillaries?
GLUT-1 and GLUT-2 (facilitated diffusion)
Sodium is actively tranported in all parts of the renal tubules except:
descending limb of the loop of Henle
Sodium reabsorption: \_\_\_% in the PCT \_\_\_% in the TAL LH \_\_\_% in the DCT \_\_\_% in the Descending limb \_\_\_% Excreted
67% in the PCT
25% in the TAL LH
5% in the DCT
3% in the Descending limb
Mechanism of ANP in decreased Na and H2O reabsorption
Constriction of efferent arterioles –> increase GFR
What is the normal plasma K+?
4.2 mEq/L
Potassium shift into the cell vs out of the cell:
Hyperinsulinemia
Into the cell
Potassium shift into the cell vs out of the cell:
Hyperaldosteronism
Into the cell
Potassium shift into the cell vs out of the cell:
Alkalosis
Into the cell
Potassium shift into the cell vs out of the cell:
Low K+ diet
Out of the cell
Potassium shift into the cell vs out of the cell:
High K+ diet
Into the cell
Potassium shift into the cell vs out of the cell:
Acidosis
Out of the cell
Potassium shift into the cell vs out of the cell:
B-adrenergic stimulation
Into the cell
Potassium shift into the cell vs out of the cell:
Cell lysis, strenuous exercise, increase ECF osmolarity
Out of the cell
Potassium shift into the cell vs out of the cell:
Potassium-sparing diuretics
Out of the cell
Potassium shift into the cell vs out of the cell:
Thiazide, loop diuretics
Into the cell
Normal plasma Calcium
2.4 mEq/L
Calcium reabsorption in the kidneys is controlled by:
Vitamin D and PTH
Acidosis causes ___; Alkalosis causes ____
Acidosis: hypercalcemia; Alkalosis: hypocalcemia
Increased or decreased Calcium excretion:
Increased PTH
Decreased
Increased or decreased Calcium excretion:
Increased exctracellular fluid volume
Increased
Increased or decreased Calcium excretion:
Decreased blood pressure
Decreased
Increased or decreased Calcium excretion:
Decreased plasma phosphate
Increased
Increased or decreased Calcium excretion:
Metabolic alkalosis
Increased
What is the transport maximum of phosphate?
0.1 mM/min
What is the normal plasma magnesium
1.8 mEq/L
Mg reabsorption: \_\_\_% TAL LH \_\_\_% PCT \_\_\_% excreted \_\_\_% stored in bones
65% TAL LH
25% PCT
10% excreted
50% stored in bones
This hormone’s effect on the collecting duct dictates final urine output and urine concentration
ADH level
If ADH levels are high, what happens to water reabsorption at the collecting duct, urine volume and urine concentration?
Water reabsorption: High (more aquaporins inserted)
Urine volume: Low (Min: 500mL/day)
Urine concentration: High (Max: 1200 mOsm/L)
If ADH levels are low, what happens to water reabsorption at the collecting duct, urine volume and urine concentration?
Water reabsorption: Low (less aquaporins inserted)
Urine volume: High (Max: 20L/day)
Urine concentration: Low (Min: 50mOsm/L)
What provides the stimulus for water reabsorption?
Countercurrent mechanism
What provides the opportunity for water reabsorption?
ADH
What creates the corticopapillary osmotic gradient?
Countercurrent multipliers: Loop of Henle
What maintains the corticopapillary osmotic gradient?
Countercurrent exchangers: Vasa recta
Whys is the loop of Henle able to act as a countercurrent multiplier?
- Countercurrent flow (hairpin-loop shape)
- Difference in permeability to H2O and electrolytes in the ascending and descending wall
- Na-K-2Cl pump in the TAL LH
- Slow flow in the LH
What is the end-result due to the countercurrent mechanism?
Corticopapillary osmotic gradient: 300 mOsm as you enter the PCT, 1200 mOsm at the tip of the LH
Why do you need a countercurrent exchanger?
Gradient would dissipate quickly if Na+ and urea+ are removed quickly
How does the vasa recta preserve the osmotic gradient?
Na and urea moves around in circles
This contributes up to 50% of renal medullary osmolarity; determines osmolarity at the tip of LH (from 600 - 1200 mOsm)
Urea recycling
Where is the thirst center found?
Anterolateral wall of 3rd ventricle and preoptic nuclei
How long does it take for absorption and distribution in the body to take place upon stimulation of the thirst center?
30 - 60 minutes
Where is the micturition center found?
Pons
Micturition can be inhibited by the:
cerebral cortex
What is the pH of Gastric HCl
0.8
What is the formula for plasma anion gap?
Plasma anion gap = [Na+] - ([HCO3-] + [Cl-])
Metabolic acidosis caused by increase in organic anions
HAGMA
Metabolic acidosis caused by increase in chloride
NAGMA
HAGMA or NAGMA?
DKA
HAGMA
HAGMA or NAGMA?
Diarrhea
NAGMA
HAGMA or NAGMA?
Acetazolamide
NAGMA
HAGMA or NAGMA?
Uremia
HAGMA
HAGMA or NAGMA?
Methanol
HAGMA
HAGMA or NAGMA?
Ureteroenteric fistula
NAGMA
HAGMA or NAGMA?
Lactic Acidosis
HAGMA
HAGMA or NAGMA?
Ethanol
HAGMA
HAGMA or NAGMA?
Salicylic acid
HAGMA
HAGMA or NAGMA?
Pancreaticoduodenal fistula
NAGMA
HAGMA or NAGMA?
Renal tubular acidosis
NAGMA
HAGMA or NAGMA?
Isoniazid
HAGMA
HAGMA or NAGMA?
Propylene glycol
HAGMA
