Introduction to Loop of Henle

The human kidney comprises a million nephrons- the filtering units of this complex and highly vascular organ. Each Nephron is made up of highly coiled tubules, one end of which is designed in the form of a cup-shaped structure. Inside this cup, there is a network around the wall that has a tuft of capillaries called the glomerulus, with a special fenestrated basement membrane.

Each glomerulus filters out water and solutes from the blood passing through it into the surrounding space and is the cavity between the two walls of the cup. The next part of the tubule is coiled and looks in the form of a U-shaped loop carrying the filtered fluid deep down into the medulla. This part of the Nephron is called the Loop of Henle.

The loop of Henle function is to reabsorb water and sodium chloride from the filtrate. This conserves water for the organism, resulting in highly concentrated urine. In other words, the Loop of Henle is a heterogeneous segment that comprises the pars recta of the proximal tubule, the thin descending and ascending limbs along the medullary and cortical thick.

Species that live in arid environments such as deserts carry highly efficient loops of Henle. In the anatomy area, the loop of Henle is divided into three different sections- thin descending limb, thin ascending limb and thick ascending limb.

The first portion of the loop is the thin descending limb which is permeable to water. The descending loop of Henle is an important function. The liquid that reaches the bend of the loop is richer in salt and urea than the blood plasma. As the liquid returns through the thin ascending limb, sodium chloride diffuses out of the tubule into the surrounding tissue.

In the third segment of the loop, the thick ascending limb, affects further removal of salt, against the concentration gradient.

There is net potassium reabsorption in the loop Henle. The procedure to transport potassium in Henle's loop is quite complex. Here the potassium is concentrated in the fluid passing through the descending loop of Henle to such an extent that the concentration in the fluid at the papilla is ten times higher than plasma.

The Function of the Loop of Henle

The absorption of water within the descending limb leads to an increasing osmotic gradient within the tubule. The loop of Henle is supplied by two vasa recta which straight vessels closely accompany the tubule’s hairpin- are shaped course. These vessels carry blood in the opposite direction, similar to the tubular fluid- the countercurrent mechanism. These result in water absorbed on one hand, and solute on the other.

It is also called the countercurrent multiple systems, responsible for maintaining osmotic medullary gradient in the outer medullary tissue. The thick descending limb of the loop of Henle expresses a sodium-potassium-chloride cotransporter and helps reabsorb approximately a third of the filtered sodium and chloride from the fluid in the tubular lumen into the blood.

Some of the Loops of Henle Functions are-

  • Homeostatic mechanisms to regulate extracellular fluid volume

  • Regulating potassium, calcium and magnesium excretion at the lowest energy costs

  • Regulating composition of the urinary protein

Role of Ascending Loop of Henle is -

The ascending loop of Henle function is impermeable to water. In this, sodium chloride is transported from a thick portion of the ascending limb without accompanying water so an osmotic gradient of approximately 200 mosm/kg is generated. Active sodium transport is accomplished by Na+, K+ -ATPase located in the basolateral membranes of the tubular cells.

Role of the Descending Loop of Henle Function

The descending limb is highly permeable to water and the reabsorption occurs via AQPI channels. During this process, low amounts of urea  Na+ and other ions are reabsorbed.

Functions of Nephron

The primary function of Nephron is to flush out waste products which include solid waste and other excess from the blood. This blood is converted into urine, secretion and excretion.

Nephron, which is a basic structural unit of the kidney, is in the form of a microscopic structure composed of a renal corpuscle and renal tubule.

The cell present in each tube absorbs different molecules, excluding glucose and beneficial molecules. The blood surrounding the Nephron travels back to the body through renal blood vessels free from toxins.

FAQs (Frequently Asked Questions)

1) What are the Three Essential Parts of Nephron?

Nephron carries three different parts of tubules for secretion purpose. These three are-

1. Proximal Convoluted Tubule (PCT)

The blood brought by the renal artery is filtered by the glomerulus and then passed to the PCT. Maximum reabsorption takes place in the PCT of the Nephron. PCT is a vital region of the renal tubule where reabsorption of essential substances takes place. The surface area for re-absorption is facilitated by the lining of the simple cuboidal epithelium in them. Re-absorption takes place at the expense of energy.

2. Henle's Loop

Also called the loop of Henle, the Henle’s loop carries both descending limb of loop of henle and ascending limb of loop of Henle. Since the loop of henle location is at the Nephron; both the descending and ascending limbs carry a spongy feeling. The descending limb is the preamble to water but impermeable to the electrolyte. The electrolyte gets reabsorbed at the ascending loop of Henle, the filtrate diluted while moving towards the ascending.

3. Distal Convoluted Tubule (DCT)

DCT is the last part of the Nephron and is known for emptying its contents into collecting ducts that line medullary pyramids.

2) What are the Major Functions of the Loop of Henle?

Loop of Henle is found in the kidney location and has three major functions.

  • Re-absorption: It absorbs 15% of filtered water and 25% of the filtered load of Na+.

  • Production of Dilute (hypo-osmotic) filtrate entering the distal tubule

  • Development of hypertonic interstitium in the medullary regions of the kidney (via countercurrent Multiplication)

3) What Activity happens in the Ascending Loop of Henle?

The ascending loop of Henle carries a thin and thick segment. It helps in draining urine into the distal convoluted tubule. The sodium reabsorption in a thin ascending limb is quite passive and occurs paracellularly because of the difference in osmolarity between the tubule and interstitium.