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70 Cards in this Set
- Front
- Back
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What are the functions of the kidneys?
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- Excretion of metabolic waste products and foreign chemicals
- Regulation of water and electrolyte balances - Regulation of body fluid osmolality and electrolyte concentrations - Regulation of arterial pressure - Regulation of acid-base balance - Secretion, metabolism, and excretion of hormones - Gluconeogenesis |
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What is the central physiologic role of the kidneys?
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Control VOLUME and COMPOSITION of the body fluids
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What proportion of the total body water is intracellular fluid (ICF)? What percent of total body weight?
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2/3 of total body water
40% of body weight |
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What proportion of the total body water is extracellular fluid (ECF)? What percent of total body weight?
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1/3 of total body water
20% of body weight |
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What are the components of extracellular fluid (ECF)? Proportions?
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- Interstitial Fluid (3/4 of ECF, 15% total body water)
- Plasma (1/4 of ECF, 5% total body water) |
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How many liters is the ICF? Interstitial fluid component of ECF? Plasma component of ECF?
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- ICF: 28 L
- Interstitial fluid (ECF): 11 L - Plasma (ECF): 3 L (42 L total) |
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What separates the intracellular fluid (ICF) from the extracellular fluid (ECF) ? What part of the ECF? What determines distribution across this barrier?
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- Cell membrane
- Separates ICF from interstitial fluid - Distribution governed by osmotic forces (not freely permeable to solutes, but is to water) |
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What separates the two components of the ECF?
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Capillary membrane
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What are the major cations in the intracellular fluid (ICF)?
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K+
Mg2+ |
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What are the major anions in the intracellular fluid (ICF)?
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PO4(-3)
Organic anions Protein |
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What are the major cations in the extracellular fluid (ECF)?
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Na+
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What are the major anions in the extracellular fluid (ECF)?
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Cl-
HCO3- (some protein) |
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What is osmolarity? Units?
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- Concentration of osmotically active particles in total solution
- mOsm / L water |
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What is the normal osmolarity of the ECF and ICF?
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Averages 280-300 mOsm/L
(nearly identical in all major compartments of body fluids) |
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What is osmolality? Units?
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Express in terms of mOsm/kg solvent (water)
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How does osmolarity compare to osmolality?
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In relatively dilute solutions, such as those found in body, osmolality ≈ osmolarity
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What is the effect on ICF and ECF volume and osmolarity, of adding ISOTONIC NaCl?
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* Increase ECF volume
No change to ICF volume, or ECF/ICF osmolarity |
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What is the effect on ICF and ECF volume and osmolarity, of adding HYPERTONIC NaCl?
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* Increase ECF volume and decrease ICF volume (water leaves ICF because of increased osmolarity in ECF)
* Increased ECF and ICF osmolarity d/t hypertonic sol'n |
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What is the effect on ICF and ECF volume and osmolarity, of adding HYPOTONIC NaCl?
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* Increase ECF and ICF volume
* Decrease ECF and ICF osmolarit |
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What are the kidney processes that determine the composition of the urine?
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1. Filtration
2. Reabsorption 3. Secretion 4. Excretion |
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What is the relationship between filtration, reabsorption, secretion, and excretion?
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Excretion = Filtration - Reabsorption + Secretion
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What is the most likely cause for a chronic decrease in GFR?
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Decrease in total area of glomerular capillary membrane
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What is the glomerular filtrate?
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Ultra-filtrate of plasma
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What causes the formation of the Glomerular Filtrate?
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Net effect of Starling forces to move (filter) fluid out of glomerular capillaries and into Bowman's space
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What is the concentration of most salts and organic substances in glomerular filtrate compared to plasma?
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Mostly the same concentration
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What is the concentration of large proteins, substances bound to protein, and cellular elements in glomerular filtrate compared to plasma?
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Normally they are excluded from glomerular filtrate and remain in plasma
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How often does the entire plasma volume (3L) get filtered through kidneys?
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Every 30 min
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What are the physical forces causing filtration by glomerular capillaries?
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- Glomerular hydrostatic pressure promotes filtration
- Glomerular colloid osmotic pressure opposes filtration - Bowman's capsule pressure opposes filtration |
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What is the net filtration pressure? Contributions?
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Net filtration pressure (10 mmHg) = Glomerular Hydrostatic Pressure (60 mmHg) - Bowman's Capsule Pressure (18 mmHg) - Glomerular Oncotic Pressure (32 mmHg)
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What is the normal Renal Plasma Flow (RPF)?
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700 mL/min
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What is the normal Glomerular Filtration Rate (GFR)?
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125 mL/min
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What is the normal Efferent Plasma Flow (EffPF)?
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575 mL/min
(RPF (700) - GFR (125) = EffPF) |
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How can you calculate GFR?
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GFR = Kf * (Pgc - πgc - Pbs)
Kf = ultrafiltration coefficient (product of hydraulic permeability and surface area of glomerular capillary membranes) Pgc = glomerular capillary hydrostatic pressure πgc = glomerular capillary oncotic pressure Pbs = Bowman's space hydrostatic pressure |
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Why do you not include πbs in calculating GFR?
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There should not be protein (oncotic pressure) in Bowman's space normally
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How are RBF and GFR auto-regulated? What are the implications of this?
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- As arterial pressure increases, urine output increases
- This means that RBF and GFR will remain relatively constant from 50 - 150 mmHg - Only at very low arterial pressures (causes drop) or high arterial pressures (causes increase) do you get changes in RBF or GFR |
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Which of these will increase when renal perfusion pressure goes from 100mHg to 130mmHg?
- Renal Blood Flow (RBF) - GFR - Urinary osmolarity - Urine flow rate |
Urine flow rate
(RBF and GFR are auto-regulated and only fluctuate at arterial pressure <50 mmHg or >150 mmHg) |
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What are the mechanisms of GFR and RBF Auto-Regulation?
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- Myogenic mechanism
- Tubuloglomerular feedback |
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Where is the myogenic mechanism? Function?
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- Intrinsic property of blood vessels
- Stretch of vascular smooth muscle, as experienced during increased arterial pressure, elicits contraction, which elevates vascular resistance and maintains constant blood flow (and GFR) - GFR and RBF auto-regulation mechanism |
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Where is tubuloglomerular feedback? Function?
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- Auto-regulatory mechanism unique to kidney
- In response to an elevation of perfusion pressure, increased fluid is filtered leading to increased delivery of NaCl to macula densa - This increased delivery elicits an increase in vascular resistance - GFR and RBF auto-regulation mechanism |
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What is the major determinant of resistance in renal blood flow to kidney?
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Afferent arterioles
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How does a drop in arterial pressure affect the kidney?
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- ↓ Arterial pressure →
- ↓ Glomerular hydrostatic pressure → - ↓ GFR → - ↓ NaCl sensed at Macula Densa (also d/t ↑PT NaCl reabsorption) → - ↑Renin → ↑AngII → ↑Efferent arteriolar resistance - ↓Afferent arteriolar resistance - ↑Efferent arteriole resistance and ↓Afferent arteriole resistance → ↑ Glomerular Hydrostatic Pressure |
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What factors cause ↓ NaCl sensing at Macula Densa?
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- ↑ Proximal tubule NaCl reabsorption
- ↓ GFR (d/t ↓ arterial pressure) |
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What are the outcomes of ↓ NaCl sensing at Macula Densa?
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- ↑Renin → ↑AngII → ↑Efferent arteriolar resistance
- ↓Afferent arteriolar resistance - Both lead to ↑ Glomerular hydrostatic pressure (↑GFR) |
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Which hormones decrease GFR?
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- NE
- Epi - Endothelin - AngII (or no change) |
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Which hormones increase GFR?
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- Endothelial derived NO
- Prostaglandins |
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What are the components of the glomerular filtration barrier?
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- Capillary wall (w/ 700 Å fenestrations)
- Basement membrane - Podocytes (w/ processes and slit pores - 40x140 Å) |
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How is the filtration barrier selective? Implications?
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- Size-selective: more permeable to small molecules
- Charge-selective: more permeable to positively charged molecules (proteins are generally negatively charged) |
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What structures are in the slits between podocyte foot processes?
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- Nephrin (N)
- P-Cadherin (P-C) |
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How does the molecular weight compare to the filterability of a substance by glomerular capillaries?
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Smaller MW → greater filterability
- H2O, Na+, glucose, inulin = 100% filterable - Myoglobin = 75% filterable - Albumin = .5% filterable |
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What happens in the thin descending loop of Henle?
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Reabsorption of H2O secondary to cortical-medullary osmotic gradient
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What happens in the thin ascending loop of Henle?
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- Impermeable to H2O
- Passive reabsorption of Na+, dilution of tubular fluid - Permeable to urea, urea is secreted |
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What happens in the thick ascending loop of Henle?
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- Reabsorbs 25% of filtered Na+ by Na+/K+/2Cl- transport
- Lumen positive potential drives paracellular reabsorption of Na+, K+, Mg2+, Ca2+ - Impermeable to H2O, dilutes tubular fluid |
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What are the mechanisms of Na+, Cl-, and K+ transport in the thick ascending loop of Henle? What inhibits this?
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- Na+/K+/2Cl- co-transporter reabsorbs these ions from tubular lumen
- Inhibited by loop diuretics: furosemide, ethacrynic acid, bumetanide - Na+/H+ exchanger also reabsorbs Na+ while secreting H+ - Paracellular diffusion of Na+, K+ into interstitium |
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What happens in the early distal tubule?
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- Reabsorbs Na+, Cl-, Ca2+, and Mg2+
- Impermeable to H2O |
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Which part of the nephron is sensitive to thiazide diuretics? What transporter does it act on?
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Early Distal Tubule - acts by inhibiting Na+/Cl- co-transporter
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What happens in the late distal tubule and cortical collecting duct in principal cells?
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- Reabsorbs Na+, secretes K+
- Regulated by aldosterone - Water permeability regulated by ADH |
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Which part of the nephron is sensitive to K+-sparing diuretics?
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Late distal tubule and cortical collecting duct (principal cells)
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What is the Na+ channel on the apical membrane of principal cells? What drugs inhibit this channel?
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- ENaC - epithelial sodium channel
- Inhibited by Amiloride and Triamterene |
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What happens in the medullary collecting duct?
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- Reabsorbs Na+ (similar to principal cells)
- ADH-stimulated water reabsorption - Urea reabsorption in medullary collecting duct |
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Where is the action of aldosterone? Effects?
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- Acts in principal cells of late distal tubule and collecting duct
- Increases NaCl reabsorption - Increases K+ secretion - Increases H2O reabsorption |
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Where is the action of Angiotensin II? Effects?
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- Proximal tubule, thick ascending loop of Henle / distal tubule, collecting tubule
- Increases NaCl, H2O reabsorption - Increases H+ secretion |
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Where is the action of Anti-Diuretic Hormone? Effects?
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- Distal tubule / collecting tubule and duct
- Increases H2O reabsorption |
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Where is the action of Atrial Natriuretic Peptide? Effects?
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- Distal tubule / collecting tubule and duct
- Decreases NaCl reabsorption |
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Where is the action of Parathyroid Hormone? Effects?
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- Proximal tubule, thick ascending loop of Henle / distal tubule
- Decreases PO4 reabsorption - Increases Ca2+ reabsorption |
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Which hormones increase NaCl reabsorption?
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- Aldosterone
- Angiotensin II |
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Which hormones decrease NaCl reabsorption?
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Atrial Natriuretic Hormone
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Which hormones increase H2O reabsorption?
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- Aldosterone
- Angiotensin II - ADH |
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Which hormones increase K+ secretion?
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Aldosterone
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Which hormones increase H+ secretion?
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Angiotensin II
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Which hormones affect PO4 and Ca2+ reabsorption? How?
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Parathyroid Hormone:
- Decreases PO4 reabsorption - Increases Ca2+ reabsorption |
