Quick Facts
The descending limb is the proximal part of the loop of Henle (Dorland, 2011).
Structure and/or Key Features
The nephron loop, more widely known as the loop of Henle, describes the recognizable loop that characterizes the nephron. Its length may measure up to 30 mm in length in juxtamedullary nephrons (Martini, Nath and Bartholomew, 2017).
The nephron loop is comprised of the proximal straight tubule (or thick descending limb), a thin descending limb, a thin ascending limb, and a distal straight tubule (or thick ascending limb).
The descending limb of the nephron loop has two distinct histological segments, the proximal straight tubule, or thick descending limb, and the thin descending limb. The epithelium of the thick descending limb is low simple cuboidal, while the epithelium of the thin segment is simple squamous. Despite being histologically distinct, the thick and thin segment of the descending limb are not as physiologically distinct as they are anatomically, thus, the two segments are often incorrectly referred to as one structure.
The descending thick limb measures approximately 30 µm in diameter while the descending thin limb measures approximately 15 µm (Kerr, 2007).
The nephron loop is supplied by a series of straight arterioles that branch from the cortical efferent arterioles; these capillaries are also known as the vasa recta.
Anatomical Relations
The proximal straight tubule or thick descending limb is located distal to the proximal convoluted tubule and proximal to the thin descending limb. The thick descending limb is proximal to the thin ascending limb of the nephron loop.
The descending limb of the nephron loop of juxtamedullary nephrons extend deep through the inner and outer medulla towards the renal papilla.
Function
The descending limb of the nephron loop is responsible for the reabsorption of water from tubular fluid via aquaporin channels (Martini et al, 2017). This reabsorption increases the osmolarity of the tubular fluid as it passes through the descending portion of the loop.
List of Clinical Correlates
—Bartter syndrome
References
Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.
Kerr, J. B. (2007) Atlas of Functional HistologyElsevier Science Health Science Division.
Martini, F. H., Nath, J. L. & Bartholomew, E. F. (2017) Fundamentals of Anatomy & PhysiologyPearson Education.
