Difference Between Afferent and Efferent Arterioles

Main Difference – Afferent vs Efferent Arterioles

Afferent and efferent arterioles are responsible for the supply of blood to the glomerulus of the kidney. The main difference between afferent and efferent arterioles is that afferent arterioles carry blood to the glomerulus whereas efferent arterioles take the blood away from the glomerulus. An afferent arteriole is a branch of the renal vein, which carries blood containing nitrogenous wastes. An efferent arteriole is a branch of the renal artery, which carries filtered blood back to the circulation. The blood pressure of the afferent arteriole is high, facilitating the ultra-filtration of blood plasma at the glomerulus. Bowman’s capsule contains the filtered blood plasma at the glomerulus. Since most of the water content and small molecules are filtered out, the blood pressure of the efferent arteriole is less than that of the afferent arteriole.

Key Areas Covered

1. What are Afferent Arterioles
      – Definition, Anatomy, Physiology
2. What are Efferent Arterioles
      – Definition, Anatomy, Physiology
3. What are the Similarities Between Afferent and Efferent Arterioles
      – Outline of Common Features
4. What is the Difference Between Afferent and Efferent Arterioles
      – Comparison of Key Differences

Key Terms: Afferent Arteriole, Bowman’s Capsule, Efferent Arteriole, Glomerulus, Kidney, Renal Artery, Renal Vein, Ultra-Filtration

What are Afferent Arterioles

Afferent arterioles are branches of the renal vein, approaching the proximal portion of the nephron. The blood pressure of the afferent arteriole determines the filtration rate of the blood plasma at the glomerulus. The diameter of the afferent arteriole changes with the changing blood pressure of the body, maintaining a constant glomerulus filtration. Afferent and efferent arterioles are shown in figure 1.

Figure 1: Afferent and Efferent Arterioles

When the blood pressure is reduced, afferent arterioles release renin to activate the renin-angiotensin-aldosterone system, increasing the reabsorption of sodium ions from the glomerular filtrate. This may ultimately increase the blood pressure.

What are Efferent Arterioles

Efferent arterioles are the branches of the renal artery, approaching the distal portion of the nephron. Therefore, they take the blood away from the glomerulus. Since the blood in the efferent arterioles is already filtered, the blood is drained back to the circulation through the renal artery. Since the diameter of the efferent arterioles is less than that of the afferent arterioles, a pressure difference occurs between the two ends of the glomerulus. This causes the filtration of blood plasma into the space of the Bowman’s capsule. Since the blood plasma filtration occurs under high pressure, it is called ultra-filtration or the high pressure-filtration.

Similarities Between Afferent and Efferent Arterioles

• Both afferent and efferent arterioles are involved in the supply blood to the glomerulus of the kidney.
• Both afferent and efferent arterioles contain blood cells.

Difference Between Afferent and Efferent Arterioles

Definition

Afferent Arteriole: Afferent arterioles are branches of the renal vein, approaching the proximal portion of the nephron.

Efferent Arteriole: Efferent arterioles are branches of the renal artery, approaching the distal portion of the nephron.

In the Glomerulus

Afferent Arteriole: Afferent arteriole carries blood to the glomerulus.

Efferent Arteriole: Efferent arteriole takes blood away from the glomerulus.

Branch of

Afferent Arteriole: Afferent arteriole is a branch of the renal vein.

Efferent Arteriole: Efferent arteriole is a branch of the renal artery.

Nitrogenous Wastes

Afferent Arteriole: The blood carried by the afferent arteriole contains nitrogenous wastes.

Efferent Arteriole: The blood in the efferent arteriole lacks nitrogenous wastes.

Diameter

Afferent Arteriole: The diameter of the afferent arterioles is high.

Efferent Arteriole: The diameter of the efferent arterioles is low.

Blood Pressure

Afferent Arteriole: Afferent arteriole contains blood with high pressure.

Efferent Arteriole: The pressure of the blood in the efferent arteriole is less than that of the afferent arterioles.

Constituents

Afferent Arteriole: The blood of the afferent arteriole contains water, blood cells, platelets, glucose, amino acids, ions, and nitrogenous wastes.

Efferent Arteriole: The blood of the efferent arteriole contains less water, glucose, amino acids, ions, and nitrogenous wastes.

Maintenance

Afferent Arteriole: Afferent arterioles maintain the blood pressure.

Efferent Arteriole: Efferent arterioles maintain the glomerular filtration rate.

Conclusion

Afferent and efferent arterioles are the two types of blood vessels that supply blood the glomerulus of the kidney. The main function of the glomerulus is to filter blood plasma. Afferent arterioles carry blood to the glomerulus while efferent arterioles take blood away from the glomerulus. Therefore, afferent arterioles contain blood with nitrogenous wastes whereas efferent arterioles contain filtered blood. The main difference between afferent and efferent arterioles is the structure, function, and composition of each type of blood vessels in the glomerulus of the kidney.

Reference:

1.“ Afferent Arteriole.” LifeMap Discovery®, Available here.
2.“Efferent Arteriole.” InnerBody, Available here.

Image Courtesy:

1. “Glomerular Physiology” By Tieum – original version here (CC BY-SA 4.0) via Commons Wikimedia