Difference Between Renal Cortex and Renal Medulla

Main Difference – Renal Cortex vs Renal Medulla

Renal cortex, renal medulla, and renal pelvis are the two zones of the kidney. Kidney is a bean-shaped organ, which lies against the back of the abdominal cavity, outside the peritoneal cavity. It is the major organ that maintains the homeostasis of the body while removing nitrogenous wastes from the body. Nephron is the functional unit of the kidney, which filters blood. Around one million of nephrons are arranged into the renal pyramids. The main difference between renal cortex and renal medulla is that renal cortex is the outer region of the kidney which contains blood vessels connected to the nephrons whereas renal medulla is the inner region of the kidney which contains 8-12 renal pyramids. Renal pyramids empty into the calyx of the kidney.

Key Areas Covered

1. What is Renal Cortex
      – Definition, Structure, Function
2. What is Renal Medulla
      – Definition, Structure, Function
3. What are the Similarities Between Renal Cortex and Renal Medulla
      – Outline of Common Features
4. What is the Difference Between Renal Cortex and Renal Medulla
      – Comparison of Key Differences

Key Terms: Bowman’s Capsule, Collecting Tubules, Glomeruli, Kidney, Loop of Henle, Nephron, Proximal and Distal convoluted Tubules, Renal Cortex, Renal Medulla, Renal Pyramids

What is Renal Cortex

Renal Cortex refers to the part of the kidney that contains the glomeruli and the proximal and distal convoluted tubules. It is covered by the renal fascia and the renal capsule. Since renal cortex contains structures of the nephrons, it is considered as a granular tissue. This smooth, continuous layer of the kidney filters blood. This filtration is called ultra-filtration or high pressure-filtration. Renal artery carries high-pressure blood. Glomeruli are the tiny, ball-shaped arteries, which are encircled by a Bowman’s capsule. The fluid in the glomeruli blood leaks into the Bowman’s capsule but, red blood cells, white blood cells, platelets, and fibrinogens stay inside the blood capillaries. Blood plasma, glucose, salt, and urea are leaked into the nephrons. Glomeruli leak 160 liters of blood in every 24 hours. Most of the fluid is reabsorbed into the blood in the renal medulla.

Figure 1: Kidney

Proximal and distal convoluted tubules are also found in the renal cortex. The re-filtration of glucose occurs in the proximal convoluted tubules while the distal convoluted tubules re-filter salts. Renal cortex also provides space for arterioles and venules as well as glomerular capillaries. Renal cortex produces hormones called erythropoietin, which facilitates the synthesis of new red blood cells.

What is Renal Medulla

Renal medulla refers to the inner-most part of the kidney. It is composed of 8-12 renal pyramids. Renal pyramids are triangular structures, which consist of densely-packed network of nephron structures. The loops of Henle and the collecting tubules are located in the renal pyramids of the renal medulla. The U-shaped portion of a nephron is called the loop of Henle. It re-filters water, sodium ions, and chloride ions from the filtrate. Renal medulla also contains collecting tubules of the nephrons. Collecting tubules concentrate the final filtrate or urine and transport it to the renal calyces. The distribution of a nephron in the renal cortex and medulla is shown in figure 2.

Figure 2: Distribution of a Nephron in Renal Medulla and Cortex

Since both loop of Henle and collecting tubules reabsorb water from urine, the length of these structures determines the amount of water that is going to be absorbed from the urine. If the two types of tubules are lengthy, a high amount of water is going to be absorbed from the urine.

Similarities Between Renal Cortex and Renal Medulla

• Both renal cortex and renal medulla are two zones of the kidney.
• Both renal cortex and renal medulla contain nephrons.
• Both renal cortex and renal medulla are involved in the removal of nitrogenous wastes from the body.

Difference Between Renal Cortex and Renal Medulla

Definition

Renal Cortex: Renal Cortex refers to the part of the kidney that contains the glomeruli and the proximal and distal convoluted tubules.

Renal Medulla: Renal medulla refers to the inner-most part of the kidney which is mainly composed of collecting tubules.

Position

Renal Cortex: Renal cortex is the outer layer of the kidney, situated between the renal capsule and renal medullas.

Renal Medulla: Renal medulla is the inner-most layer of the kidney.

Color

Renal Cortex: Renal cortex is pale brown or reddish color.

Renal Medulla: Renal medulla is dark, reddish-brown in color.

Components

Renal Cortex: Renal cortex consists of blood vessels that are connected to the nephrons.

Renal Medulla: Renal medulla consists of most of the structures of nephrons.

Nephron Structures

Renal Cortex: Renal cortex contains glomeruli and convoluted tubules of nephrons.

Renal Medulla: Renal medulla contains loops of Henle and collecting tubules.

Function

Renal Cortex: Renal cortex filters blood.

Renal Medulla: Renal medullas regulates water and salts in the blood.

Conclusion

Renal cortex and renal medulla are two zones of the kidney. Since both renal cortex and renal medulla consist of different structures of the nephrons, both zones are considered to be involved in the filtration of blood. Renal cortex consists of glomeruli, Bowman’s capsules, and proximal and distal convoluted tubules. Therefore, renal cortex is involved in the filtration of blood. Renal medulla consists of loops of Henle and collecting tubules, which mainly reabsorb water. Thus, the main difference between renal cortex and renal medulla is their structure and function.

Reference:

1. “The Kidneys.” The Kidneys | Boundless Anatomy and Physiology, Available here.

Image Courtesy:

1. “2610 The Kidney” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia
2. “Structure of the mammalian kidney” By Davidson, A.J., Mouse kidney development (January 15, 2009), StemBook, ed. The Stem Cell Research Community, StemBook, doi/10.3824/stembook.1.34.1. (CC BY 3.0) via Commons Wikimedia

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