Golovko Loop of Henle

Describe the role of urea in the medullary osmotic gradient.

-Contributes to half of medullary osmolarity -passively reabsorbed from tubule -ADH; water is reabsorbed from cortical collecting ducts, but urea is not (urea conc. increases) -more water reabsorbed in medullary collecting ducts and urea concentration further increases) -Urea diffuses into renal intersitium -osmolarity of renal intersitium increases

Give an overview of the mechanism of the loop of Henle.

-Na+ pump -High osmolarity in medulla near collecting duct -water flow from collecting duct -conc. urine -descending limb is permeable to water -thin ascending is impermeable to water but permeable to NaCl -thick ascending is impermeable to water but has Na+ pump and cotransporters -late collecting duct is permeable to water

Describe transport in the thin descending limb.

-Reabsorbs 20% of filtered water -uses aquaporins -minimal metabolic activity -impermeable to NaCl

Describe the mechanism of the vasa recta.

-blood flows in (water, solutes, nutrients, O2 leave blood; medullary osmolarity increases) -blood flows out (water, solutes, waste, CO2 move back to blood; medullary osmolarity increases back to initial values) -total osmolarity is unaffected but cells are supplied w/ nutrients and O2 -increased medullary blood flow reduces urine concentration ability

What are causes of maximum diuresis?

-decreased antidiuretic hormone levels (synthesis problem, suppression with chemicals, diabetes insipidus) -defective ADH receptors in collecting duct (genetic, renal disease, nephrogenic diabetes insipidus)

What is the mechanism of maximum diuresis?

-decreases corticomedullary gradient -transverse gradient intact -hypotonicity maintained -decreased passive water reabsorption from distal tubule and collecting duct -decreased urea reabsorption from the inner medullary collecting ducts -decreased corticomedullary gradient (dilute urine)

What are causes of antidiuresis (increased ADH)?

-inappropriate synthesis and release -homeostatic response (dehydration, increased extracellular osmolarity, decreased extracellular fluid volume and blood volume, decreased blood pressure)

What is the mechanism of antidiuresis?

-increased corticomedullary gradient -transverse gradient intact -hypotonicity maintained -increased water reabsorption from late distal tubule and collecting duct -increased urea reabsorption from collecting duct -increased corticomedullary gradient -concentrated urine and decreased volume

Describe the structure of the loop of henle.

-leads from the PT to the DT -hairpin bend (descending limb, ascending limb) -in renal medulla -juxtamedullary loops longer than cortical

Describe transport in the thin ascending limb.

-permeable to NaCl and low permeability to water

Describe transport in the thick ascending limb.

-reabsorbs 25% of filtered Na+, K+, Cl- -Na+/K+ pumps, high level of metabolism -NaKCl2 cotransporter -Impermeable to water -reabsorbs Ca2+, Mg2+, bicarb

What is the transverse gradient?

200 mOsm/L gradient at any level of the loop between ascending and descending limbs (pump salt out of ascending limb, pull water out of descending limb)

What is the function of the countercurrent multiplier?

Establishes medullary osmotic gradient that is required for urine concentrating

How does furosemide work on the loop of Henle?

Inibits the Na-K-2Cl cotransporter in the thick ascending limb

What substances are reabsorbed in the ascending loop of Henle?

Na+, Cl-, K+, Mg2+, Ca2+

What is the corticomedullary gradient?

difference in osmolality from the cortex to the tip of the medullary loop (diuresis-lose water, antidiuresis-retain water)

What is the definition of obligatory water loss?

minimum volume of water that must be excreted in urine per day (normal 600 mOsm/day, max 120 mOsm/day) -necessary to eliminate non-reabsorbed and waste solutes

What is the function of the vasa recta?

prevents dissipation of the medullary osmotic gradient; removes excess water and salt from kidney

What is the function of the loop of Henle?

to create a concentration gradient in the medulla

What substances are reabsorbed in the descending loop of Henle?

water