It does not exist as an independent unit (e.g., analogous to the ribosome), but assembles de novo at the origin for each replication cycle.

TLS Online TPP Program

#Id: 5565

#Unit 7. System Physiology – Animal

A countercurrent system is a system in which the inflow runs parallel to, counter to, and in close proximity to the outflow for some distance. This occurs for both the loops of Henle and the vasa recta in the renal medulla

TLS Online TPP Program

#Id: 5566

#Unit 7. System Physiology – Animal

Assume first a condition in which osmolality is 300 mOsm/kg of H2O throughout the descending and ascending limbs & medullary interstitium

TLS Online TPP Program

#Id: 5567

#Unit 7. System Physiology – Animal

Assume first a condition in which osmolality is 300 mOsm/kg of H2O throughout the descending and ascending limbs & medullary interstitium

TLS Online TPP Program

#Id: 5568

#Unit 7. System Physiology – Animal

Assume in addition that the pumps in the thick ascending limb can pump 100 mOsm/kg of Na+ & Cl– from the tubular fluid to the interstitium, increasing interstitial osmolality to 400 mOsm/kg of H2O 

TLS Online TPP Program

#Id: 5569

#Unit 7. System Physiology – Animal

Meanwhile, hypotonic fluid  flows into the distal tubule, andisotonic and subsequently hypertonic fluid flows into the

ascending thick limb

TLS Online TPP Program

#Id: 5570

#Unit 7. System Physiology – Animal

The process keeps repeating & the final result is a gradient of osmolality from the top to the bottom of the loop