Title: Urine concentration
1Lecture 7
2Urine Concentration
- The main function of the loop of Henle is to
remove NaCl from the lumen and deposit this NaCl
in the interstitium of the medulla. - Interstitial osmolality rises from the cortex to
the tip of the medulla (corticomedullary
osmolality gradient). - The maximal interstitial medullary osmolality
occurs during antidiuresis (1200mOsmol).
p. 833 Ch. 37
3PLASMA OSMOL 290-300 mOsm.
HIGH ADH
LOW ADH
Fig. 37-1 p. 831
4WATER RESTRICTION
Increased water permeability
HIGH
1200 mOsm
HIGH WATER INTAKE
ADH Control
LOW
No water permeability
Fig. 37-2 p. 832
60 mOsm
5WATER RESTRICTION
TAL/DCT Impermeable to Water. ONLY Pumps NaCl out
fig 14-15
CONCENTRATED URINE/LOW VOLUME
6Hyperosmolality of Medulla
- Depends on net transport of NaCl across TAL (part
of single effect) - Limit of tubule-interstitium gradient at any one
point is 200 mOsm. - Countercurrent multiplier system
- multiplies the single effect of the 200 mOsm
gradient - After 39 cycles, the interstitial fluid
osmolality would be 1200 mOsm.
7Countercurrent multiplier system
-TAL pumps NaCL -equilibrium forms -fluid shifts
thru tubule -TAL pumps more NaCL
Ch. 14 in Vanders Physiology or Fig 37-3 BB
8Urea Recycling on Interstitial Medullary
Osmolality
- Urea cycle
- Absorption of urea from IMCD (intermedullary CD)
- Secretion of urea from interstitium into the tALH
- Carriage of urea up into the cortex and back down
through the nephron.
9UREA RECYCLING
IMCD is made Permeable to UREA by ADH
ONLY!
10Medullary osmotic gradient
11WATER RESTRICTION
Increased water permeability
HIGH
1200 mOsm
ADH Control
HIGH WATER INTAKE
LOW
No water permeability
Fig. 37-2 p. 832
60 mOsm
12 13POTASSIUM IS HIGH IN INTRACELLULAR FLUID
14Like Sodium and Water, Ingested Potassium is
Largely Excreted
15POTASSIUM DISTRIBUTION
- 98 of total body potassium is in the ICF.
- 2 of potassium is in ECF.
- Normal plasma range for K is (3.5-5.0mM)
- Low ECF K is necessary to maintain steep K
gradient across membranes (cellular
excitability). - Changes in ECF K can cause severe disturbances
in excitation and contraction. - Cardiac rhythmicity and muscle paralysis
- Hypo and hyperkalemia
- Diarrhea and vomiting are major causes for
hypokalemia (dehydration)
16Potassium Excretion
Reabsorption from proximal tubule
(70) Henles ascending limb (20) Collecting
duct (10) Intercalated cells Secretion
into Collecting duct (initial collecting
duct) principal cells of CD (variable) Potassium
excretion depends on K secretion from the
principal cells.
fig 14-26 Vanders Phys.
17(No Transcript)
18HORMONAL REGULATION OF POTASSIUM UPTAKE INTO CELL
Insulin Epinephrine Aldosterone
19Acidosis and Potassium uptake
Na-K pump
Co-transporter
note, opposite for alkalosis
High plasma H (low ph acidosis) Decreases K
uptake into cell by inhibiting pumps and
co-transporters, therefore you get reduced ICF K
20Regulation of potassium excretion
Same principal as sodium, the more you consume,
the more you excrete to keep in potassium
balance.
fig 14-27 Vanders phys.
21Actions of Aldosterone
4.
5.
1.
2.
3.
fig 14-13
Aldosterone actions ? Na channel activity
(luminal side reabsorption), ? Na/K ATPase
pump, ? K channel activity and
secretion/excretion
22Regulation of K excretion aldosterone
23K excretion loop thiazide diuretic stimulation
24K excretion K sparing diuretics inhibition