Renal medulla

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Renal cortex and related structures.

The renal medulla comprises the central and inner parts of the kidney's parenchyma where it contains about 8-12 cone-shaped structures known as the renal pyramids. 

The renal medulla contains the following structures:

• Nephron loops, also known as loops of Henle, which are U-shaped tubules extending into the renal pyramids and facilitate water and ion reabsorption.
• Collecting ducts, which pass through renal medulla and assist in fluid-electrolyte balance and transfer of urine to the renal pelvis.
• Vasa recta, which are capillary beds surrounding the nephron loops and maintain the osmotic gradient required for water reabsorption
• Interstitium, which comprises the extravascular intertubular spaces of the renal parenchyma.

The primary function of the renal medulla is to assist with the reabsorption of filtrate and ions which regulates fluid retention as well as balancing electrolytes. It also plays a role in regulating blood pH by reabsorbing bicarbonate from the urine into the bloodstream and excreting hydrogen ions into the urine. 

Additionally, excretion of different kinds of waste such as urea, ammonia and creatinine is achieved through different channels which are subsequently directed to the urinary bladder, via the ureters. Lastly, the renal medulla is responsible for transporting urine to the renal pelvis where it is collected and funneled into the respective ureter.