1. LOOP OF HENLE - 1. LOOP OF HENLE Loop of Henle Medical Editor...

LOOP OF HENLE RENAL PHYSIOLOGY: Note #3. 1 of 2

1. LOOP OF HENLE

Loop of Henle Medical Editor: Mariel Antoinette L. Perez

OUTLINE

I) NEPHRON

II) LOOP OF HENLE

III) VASA RECTA

IV) SUMMARY

V) APPENDIX

VI) REVIEW QUESTIONS

VII) REFRENCES

I) NEPHRON

Nephron is made of the following:

• Renal corpuscle

 Glomerulus  Bowman’s Capsule

 Process: Glomerular Filtration

• Proximal Convoluted Tubule

 Processes • Tubular Secretion • Tubular Reabsorption

• Loop of Henle
• Distal Convoluted Tubule

Each kidney has 1.2 million nephrons

• 2.4 million nephrons in two kidneys

II) LOOP OF HENLE

Broken into two parts

• Descending limb
• Ascending limb

(A) OSMOLALITY

(1) Osmolality Classification Hypertonic

• osmolality
• solutes (e.g., Na

+ ,Cl –

), H 2O

Hypotonic

• osmolality
• solutes (e.g., Na

+ ,Cl –

), H 2O

Isotonic

• solutes = H

2O (2) Osmolality Values

inside the glomerulus: ~300 mosm

• blood plasma

In Bowman’s capsule: ~300 mosm

• Isotonic with the blood plasma

When it leaves the PCT: 300 mosm

• Still isotonic with the blood plasma
• It didn’t change because equal amounts of solutes

and water were being reabsorbed  Due to obligatory water reabsorption • E.g., 65% H 2O, 65% Na +

• Recall (from Ninja Nerd Proximal Convoluted

Tubule lecture): obligatory water reabsorption

is the concept wherein water feels obliged to follow sodium.

• Isotonic with the blood plasma

Medullary interstitial osmolality gets saltier or more hypertonic as we go down the renal medulla

• 300 mosm  500 mosm  700 mosm  900 mosm

 1200 mosm (3) Concepts (i) Why does it get saltier?Na + /K + /2Cl – Cotransporter

• Transports sodium, chloride, and potassium from

lumen of filtrate into tubule cell of ascending limb

• There are specific channels for each ion in the cell

 Na + and Cl – will be pushed out • Increases osmolality (saltier)  Only some of the K + leaks out, some of the K +

stays out • Some K + gets pushed back in the lumen

• Creates depolarization of the inner side of

the membrane of the ascending limb  Causes Mg 2+ and Ca 2+ to undergo paracellular transport

Note the following:

• The descending limb of loop of Henle is completely

impermeable to solutes

• Exact opposite of the ascending limb which is only

permeable to solutes, but impermeable to water (ii) What happens due to the salty medullary interstitial space?Counter-Current Multiplier Mechanism

• Water will flow out to the area where the salt is

 From the descending limb to the ascending limb  Due to obligatory water reabsorption  Via Aquaporin-I • This is always open in the descending limb of Loop of Henle

• Since the medullary interstitial space is saltier as we

go down, more water will leave as we go down the descending limb

• Hence, by the time the loop of Henle takes a turn to

go up, its osmolality will be 1200 mosm  Becomes hypertonic

• When it goes up, however, the osmolality starts to go

down because the ascending limb is losing salt

• By the time it reaches the Distal Convoluted Tubule,

osmolality will be around 120-200 mosm  Becomes hypotonic to the plasma

III) VASA RECTA

Peritubular capillary in the medulla Branch of the E fferent Arteriole Known as the “Counter-Current Exchanger”

Plasma Osmolality Gradient:

• 300  500  700  900  1200

Blood flow to vasa recta is really slow

Function:

• Prevents rapid removal of sodium chloride

 Does not develop the medullary interstitial gradient or the counter -current multiplier mechanism  It’s maintaining the gradient; not generating it

• Carries Oxygen

 Cells depend on oxygen  Vasa recta also delivers oxygen and nutrients

IV) SUMMARY OF LOOP OF HENLE

Descending Limb

• H2O permeable
• Solute impermeable
• Aquaporin-I

Last edited: 11/21/2021 AfraTafreeh.com

AfraTafreeh.com

• / 1