Renal (4) Flashcards
How does Kidney affect RBC
Produces Erythropoietin for RBC production in hypoxia
Types of Nephrons
- Juxtamedullary Nephron
- Cortical Nephron (90%)
Renal Circulation Arteries
Renal A, Segmental A, Interlobar A, Arcuate A, Intralobular A, Afferent a, Glomerular cap, Efferent A, Peritubular cap, Vasa recta
Renal Circulation Veins
Venules, Intralobular v, Arcuate v, Interlobar v, Renal V
Renal Blood Flow
1200 - 1300 ml/min
(20 - 25% of CO)
Renal Plasma Flow
600 - 700 ml/min
Natriuresis
When body excretes excess Na+ in Urine
What determines Renal vascular resistance
Afferent & Efferent Arterioles
Why do we need to regulate BP to kidney
To protect Glomerular Capillaries from Overfiltration
2 Autoregulatory Mechanisms to regulate RBF and GFR
- Myogenic Mechanism (Bayliss)
- Tubulo-glomerular Mechanism
Myogenic Autoregulatory mechanism (Bayliss)
Tendency of smooth muscle to contract when stretched (AFFERENT ARTERIOLE ONLY)
(90 - 180 mmHg)
Tubulo-glomerular Autoregulatory Mechanism
Feedback loop where change in GFR leads to alteration in conc. of NaCl in tubular fluid, sensed by macula densa sending signals to affect the Afferent arteriolar resistance
Adenosine A1 receptor
- Gi
- Less cAMP
- Vasoconstriction in Afferent arteriole
(inh. of granular cells)
Adenosine A2 receptor
- Gs
- More cAMP
- Cardiac/Skeletal m
- Vasodilator
Granular cells
Synthesize, store, and release Renin into bloodstream
Renin Production vs GFR
- High GFR: Inh. Renin production
- Low GFR: Renin angiotensin cascade leads to Efferent art. vasoconstriction
What happens when ECFV drops
Sympathetic nerves release NE and dopamine and E by adrenal Medulla
- NE/E act on a1-AR (Gq) = VC in Afferent art.
- NE/E act on B1-AR on granular cells (Gs)
- Renin-Ang cascade activated, ANGII, VC in Efferent art.
Angiotensin II
Constricts Afferent and Efferent arterioles
(Efferent more sensitive)
ANP
- VD in Afferent art.
- VC in Efferent art.
- Increased GFR and same RBF (since VC and VD act together)
Glomerular Filtration Rate (GFR)
120 ml/min
(180 L/day)
Filtration Fraction (FF)
20%
Ratio of plasma filtered to total plasma flowing through glomerulus
FF = GFR / RPF = 120/600
Glomerular capillary Pressure vs normal capillaries
Twice as much Pressure in Glomerular
Filtration Barrier
1) Fenestrated Endothelium
2) Basement Membrane
3) Podocytes
(repel negative charges)
General Filtration Rule
The larger and more negative a molecule is, the less likely it will pass the filtration barrier
Renal Clearance
Volume of plasma / time
From which all given substances pass through the filtrate and are excreted in the urine (ml/min)
How to determine Amount excreted in Urine?
Filtered - Reabsorbed + Secreted
Albumin fate
Not filtered
Fate of different substances in Kidney
- Not filtered (albumin)
- Filtered & Completely reabsorbed (glucose)
- Filtrated and Completely secreted (PAH)
- Filtrated and not Reabsorbed, Secreted, or metabolized by Kidney. (creatine)
What can give us an Idea of GFR
Blood creatine levels since it is filtrated and not reabsorbed or secreted, all goes into urine.
So higher creatine means lower GFR
Proximal Tubule structure
- Brush border
- Highly invaginated BL membrane with mitochondria for active T
Cells in Collecting Duct
- Principal cells
- Intercalated cells
Principal Cells (collecting duct)
- Moderately invaginated BL membrane with few mitochondria
- Important for reabsorption of NaCl and K+
Intercalated Cells (collecting duct)
- High mitochondria density
- Important for Acid-Base balance
- Some secrete H+ (a) and some HCO3- (B)
Formation of Urine 3 Processes
1) Ultrafiltration
2) Reabsorption
3) Secretion
What drives Ultrafiltration
Starling forces
(Hydrostatic & Oncotic pressures of Capillaries and Interstitial fluid)
Hydrostatic vs Oncotic Pressures
- Hydrostatic drives fluid/substance OUT
- Oncotic pressure KEEPS fluid
Hydrostatic Pressure in Capillaries
- Afferent: + 53 mmHg
- Efferent: + 51 mmHg
Oncotic Pressure in Capillaries
- Afferent: - 26 mmHg
- Efferent: - 33 mmHg
Hydrostatic Pressure in Bowman’s
- Afferent: - 12 mmHg
- Efferent: - 12 mmHg
Oncotic Pressure in Bowman’s
- Afferent: 0 mmHg
- Efferent: 0 mmHg
NET ultrafiltration Pressure
- Afferent: 15 mmHg
- Efferent: 6 mmHg
Proximal Tubule functions
- 60-70% of Na reabsorption
- Any protein/albumin filtered reabsorbed
- Any osmotically active substances reabsorbed are followed by water to prevent a gradient
First half of Proximal Tubule
- Na is primarily reabsorbed with HCO3 (a.a, gluc, Pi)
- Only 20% of Na reabsorbed
Second half of Proximal Tubule
- High Cl- conc due to first half taking other substances
- other 40% of Na absorbed here
Ways to reduce Na and Water reabsorption in Proximal Tubule
- Acetazolamide: Inhibits carbonic anhydrase (no Na/HCO3)
- Hg-containing compounds: Aquaporin inh.
- Non-reabsorbing osmolarities: excessive gluc, ketone, cause water drawn back to tubules
Loop of Henle
- 20-25% NaCl absorption
- Only passive transport in thin ascending/descending limbs
- TAL has active transport
Thin Descending limb (LOH)
- Passive transport of Water via Aquaporin 1, poorly to NaCl
- Water reabsorption without solutes leaves tube hyperosmotic
- At the end of the TDL osm. goes from 300mosm to 1200 mosm.
Thin Ascending Limb (LOH)
- Passive Transport
- Impermeable to water (no aq1)
- Permeable to NaCl and Urea leaving tube hyposmotic
Thick Ascending Limb TAL (LOH)
- Active transport and reabsorption of osmolytes NKCC
- No water reabsorption (no aq1)
What inhibits the NKCC transporter in TAL
Furosemide
Distal Convoluted tubule
- 5-7% of NaCl reabsorption
- Na/Cl Cotransporter
- No water reabsorption
What inhibits Na/Cl transporter in Distal convoluted tubule
Thiazide
Collecting ducts
- eNaCs drive Na into cells
- Negative luminal potential created
- Drives Cl absorption paracellularly
- Luminal K+ channels to balance charge
What affects eNaCs
- Aldosterone: Increases expression/activity to raise BP
- ANP: Inhibits eNaC causing Natriuresis (lower BP)
- Amiloride: inhibits eNaC, no effect on K+
Water reabsorption overview
- Water absorbed from PT to end of TDL
- Water IMPERMEABLE from thin descending limb to distal convoluted tubule
- Water reabsorption from collecting duct to medullary collecting duct in presence of ADH
Vasopressin (ADH) action
1) Binds basolateral Gs coupled V2-R
2) cAMP to PKA
3) Vesicle release of AQ2 on luminal side
4) More water reabsorption
Where is Urea reabsorbed?
Inner medullary collecting ducts
Overall K+ transport
- PT: Paracellular K+ reabsorption
- TAL: K+ reabsorption via NKCC
- CD: K+ Secretion and Na reabsorption Na/K atpase and ROMK
Overall Ca2+ transport
- PT: Paracellular reab. with Na+
- TAL: Paracellular reab. with Na+
- DCT: Active transcellular reabsorp. (PTH stim.)
What helps recover/reabsorb filtered proteins
Megalin & Cubulin
(endocytosis)
Countercurrent Multiplication
Active Process to generate an osmotic gradient to enable water reabsorption from filtrate & to concentrate urine
Countercurrent Exchange
- Happens between Vasa recta and interstitium
- Passive process
- Maintains a gradient, doesnt create it
Urea recycling
- When water absorption is increased by ADH/Vasopressin
- More water & Urea reabsorbed
- Water in Outer medullary duct
- Urea in Inner medullary duct only to form gradient for countercurrent multiplication
Effective Arterial Blood Volume (EABV)
Portion of the ECF contained in the arteries and perfusing the tissues that is sensed by the Kidneys and is regulated by changes in Na+ excretion
4 Mechanisms that affect Na+ excretion due to EABV
- Sympathetic inn.
- ANP
- Peritubular capillary starling forces
- Renin-ANG-Aldosterone system
K+ overall movement
- Proximal tubule reabsorption (2/3)
- TAL by NKCC (20%)
- DCT principal secrete under high K+
- DCT a-intercallated cells reabsorb K using K/H atpase
Aldosterone effect on K+
Increase K+ secretion in DT and CD
- Increased eNaC expression
- Increased Na/K atpase quantity
- Increase of luminal ROMK
How do diuretics mostly affect K+
Increase K+ to drive secretion
How to ensure Aldosterone specificity in Kidney
11B-OHSDH to convert gluco and mineralocorticoids to inactive form to allow Aldosterone to only bind MC-R
What happens when Hyperosmotic activity is detected
Thirst is triggered by Osmoreceptor cells in Hypothalamus and Baroreceptors
How do we prevent Overhydration after thirst?
Peripheral osmoreceptors in GI and stomach and mouth stop thirst
Osmoreceptor responce in high Plasma effective osmolarity
- Signal to Supraoptic & Paraventricular nuclei
- Vasopressin secretion
Amount of Non-volatile acid produced per day
- 30 mmol/day Dietary
- 40 mmol/day Metabolism
= 70 mmol/day total which can not be exhaled
How does the Kidney combat non-volatile acids
- Produces 70mmol of HCO3- to buffer
- 30 mmol buffered to H2CO3 then CO2 and exhaled
- 40 mmol is trapped by NH3 to NH4+ and excreted in Urine
pH
7.35 - 7.45
paCO2
38 - 40 mmHg
Standard HCO3-
23 - 25 mmol/L
(= to actual in normal acid-base balance)
Base Buffer (BB)
and its use
44 - 49 mEq/L
- Indicates buffering capacity: How many proton molecules can be buffered in the blood
Base Excess (BE)
and its use
+/- 2.5 mEq/L
- Shows difference/deviation from the normal value
Volatile acids
Acids that can be converted into gaseous form and thus be eliminated by the Lungs
(mainly CO2)
Nonvolatile (fixed) acids
Acid produced from sources other than CO2 and not excreted by the Lungs
How are nonvolatile acids formed?
- Amino acids with Sulfur (sulfuric acid)
- Phospholipids (phosphoric acid)
Buffers
A solution which resists change in pH when a small amount of acid/base is added
(weak a/b with its conjugate a/b)
Open system
System where buffers can quickly be altered
(CO2 buffer - HCO3/H2CO3)
Role of Proteins as Buffers
They can be Protonated/Deprotonated
- Usually bound to Ca2+ but in acidic conditions H+ can bind instead
What is most important buffer in body
CO2/HCO3
Why does CSF only use 1 type of buffer
No proteins in CSF so only HCO3 buffer can be used
Respiratory Acidosis
- High pCO2
- No change in BB / BE
- Unchanged Standard HCO3-
- Increased Actual HCO3-
Respiratory Alkalosis
- Low pCO2
- No change in BB / BE
- Unchanged Standard HCO3-
- Lower HCO3-
Metabolic Acidosis
- No change in pCO2
- Lower BB / BE
- Lower Standard HCO3-
- Lower Actual HCO3-
Metabolic Alkalosis
- No change in pCO2
- Higher BB / BE
- Higher Standard HCO3-
- Higher Actual HCO3-
Mixed Type Acidosis
- High pCO2
- Low BB / BE
- Lower Standard HCO3-
- complex Actual HCO3-
Anion gap
- The difference between measured Cations and measured Anions in the plasma
- Used to diagnose metabolic acidosis
= 8 - 16 mEq/L (normal)
Na - (Cl + HCO3)
High anion gap
- Lower HCO3
- Means there is unmeasured anions / new acid appearance
Calcium Levels in High/Low pH
- Low: More free Ca
- High: Less free Ca (Albumin loses H+ and binds more Ca)
Potassium Levels in High/Low pH
- Low: High (ROMK inh. so less excreted)
- High: Low
How to calculate NAE
Titratable acidity (H bound to urinary buffers like phosphate) + NH4 excretion - HCO3 excreted
Renal Buffers capacities
- Phosphate buffer: 18 mmol
- Criatinine buffer: 5.5 mmol
= Total 23.5 mmol out of 70 mmol
How does Kidney make NEW HCO3-
- From Glutamine via Glutaminase
- yields NH4+ and HCO3-
- NH4+ broken to NH3 + H+
- NH3 diffuses into tubule
- H+ taken out by Na/H exchanger