What is the Difference Between Vasa Recta and Peritubular Capillaries

The main difference between vasa recta and peritubular capillaries is that the vasa recta are the blood capillaries that surround the loop of Henle in the juxtamedullary nephrons. But, peritubular capillaries are the blood capillaries that surround the PCT and DCT of the cortical nephrons. Furthermore, vasa recta occur in the medulla of the kidney while peritubular capillaries occur in the cortex. Besides, vasa recta serve as osmotic exchangers for the concentration of urine while peritubular capillaries supply the blood for reabsorption and secretion.  

In brief, vasa recta and peritubular capillaries are the two types of blood capillaries that arise from efferent arterioles. Generally, they involve two of the four physiological functions of the nephron: reabsorption and secretion. 

Key Areas Covered 

1. What are Vasa Recta
     – Definition, Anatomy, Function
2. What are Peritubular Capillaries
     – Definition, Anatomy, Function
3. What are the Similarities Between Vasa Recta and Peritubular Capillaries
     – Outline of Common Features
4. What is the Difference Between Vasa Recta and Peritubular Capillaries
     – Comparison of Key Differences

Key Terms 

Efferent Arteriole, Loop of Henle, Nephron, Peritubular Capillaries, Vasa Recta

What are Vasa Recta 

Vasa recta are the type of blood capillaries that arise from the efferent arterioles, surrounding the loop of Henle of the juxtamedullary nephrons. Juxtamedullary nephrons only occur in the kidney of birds and mammals and are responsible for the production of concentrated urine under high physical activity or under unfavorable environmental conditions. Moreover, long and straight vasa recta run parallel to the loop of Henle, which occurs in the medulla of the kidney. 

Figure 1: Vasa Recta and Peritubular Capillaries General Anatomy

Besides, at the descending part of the vasa recta, the reabsorption of sodium chloride and urea into the blood occurs while secreting water into the loop of Henle from the blood. On the contrary, at the ascending part of the vasa recta, both sodium chloride and urea are secreted into the loop of Henle while reabsorbing water. Moreover, the blood flows very slowly through the straight blood capillaries of the vasa recta since they have a hairpin turn in the medulla. This, in turn, prevents the washing out of the concentration gradient while maintaining a countercurrent exchange. More importantly, the maintenance of a concentration gradient is responsible for the production of concentrated urine.  

What are Peritubular Capillaries 

Peritubular capillaries are the type of blood capillaries that arise from the efferent arterioles, surrounding the PCT and DCT of the cortical nephrons. Here, the loop of Henle of the cortical nephrons does not dip beyond the cortex of the kidney. Also, the majority of the nephrons of the kidney are cortical nephrons. Furthermore, cortical nephrons are responsible for the production of dilated urine under normal physiological conditions. Therefore, the main function of these capillaries is to undergo reabsorption and secretion at the distal parts of the nephron.

Figure 2: Nephron General Function

Functionally, glucose, amino acids, and ions, which must remain in the body, undergo reabsorption through active transport, secondary active transport, and transcytosis in the peritubular capillaries. However, the ions and excess water that needs to be removed from the body undergo secretion from the blood in the peritubular capillaries into the PCT and DCT, sending them towards the bladder.  

Similarities Between Vasa Recta and Peritubular Capillaries  

• Vasa recta and peritubular capillaries are the two types of blood capillaries that arise from the efferent arteriole.  
• Both of these structures provide blood to the distal parts of the nephron.  
• Besides, they involve two of the four physiological functions of the nephron; reabsorption and secretion. 

Difference Between Vasa Recta and Peritubular Capillaries 

Definition 

Vasa recta refer to one of a series of long loops of thin-walled blood vessels, which dip down alongside the loop of Henle in the vertebrate kidney. But, peritubular capillaries refer to the tiny blood vessels supplied by the efferent arteriole, which travel the alongside nephrons allowing reabsorption and secretion between blood and the inner lumen of the nephron. 

Occurrence 

Vasa recta surround the loop of Henle in the juxtamedullary nephrons, while peritubular capillaries surround the PCT and DCT of the cortical nephrons.  

Depth  

Moreover, vasa recta occur in the medulla of the kidney, while peritubular capillaries occur in the cortex.  

Abundance 

Around 15% of capillaries arising from the efferent arterioles are vasa recta, while around 85% of capillaries arising from the efferent arterioles are peritubular capillaries. 

Activity 

Vasa recta work during periods of high activity, while peritubular capillaries work during normal activity. 

Function 

Furthermore, vasa recta serve as osmotic exchangers for the concentration of urine, while peritubular capillaries supply the blood for reabsorption and secretion.  

Importance 

Also, vasa recta only occur in the kidney of birds and mammals, allowing concentrating urine mainly in drought conditions. But, peritubular capillaries are important in the production of dilated urine under normal conditions. 

Conclusion 

In brief, vasa recta are one of the two types of blood capillaries arising from the efferent arterioles of the nephron. They are less abundant and surround the loop of Henle of the juxtamedullary nephrons. Hence, they occur in the medulla of the kidney of only birds and mammals, concentrating urine. In contrast, peritubular capillaries are the other type of blood capillaries, arising from the efferent arterioles. They are abundant forms of such blood capillaries and surround the PCT and DCT of the cortical nephrons. In addition, the main function of peritubular capillaries is to produce dilated urine under normal conditions. Therefore, the main difference between vasa recta and peritubular capillaries is their depth of occurrence and function. 

References:

1. “Medical Physiology/Renal Physiology.” Medical Physiology/Renal Physiology – Wikibooks, Open Books for an Open World, Available Here.
2. “Straight Arterioles of Kidney.” Wikipedia, Wikimedia Foundation, 25 Sept. 2019, Available Here.

Image Courtesy:

1. “Figure 41 03 03” By CNX OpenStax (CC BY 4.0) via Commons Wikimedia   
2. “Kidney nephron molar transport diagram” By M•Komorniczak (CC BY 3.0) via Commons Wikimedia