The kidneys are essential organs responsible for performing various crucial functions that help maintain overall health and homeostasis in the human body. An understanding of the gross anatomy of the kidneys provides insights into how these organs perform their vital functions and highlights the significance of kidney health. In this article, we will examine the gross anatomy of the kidney, discussing its location, size, shape, external structures, and surrounding tissues.
The kidneys are a pair of bean-shaped organs situated in the retroperitoneal space, which is the area between the posterior wall of the abdominal cavity and the posterior abdominal muscles. The right kidney typically lies slightly lower than the left due to the presence of the liver, which occupies a considerable space in the upper right abdomen. The kidneys are located at approximately the level of the T12 to L3 vertebrae and are surrounded by several structures, including the adrenal glands, the diaphragm, and the ribs (Saladin, 2018).
Size and Shape
Each kidney is roughly the size of a fist, measuring about 10-12 cm in length, 5-7 cm in width, and 3 cm in thickness. The concave medial border of the kidney, known as the hilum, is the point where the renal artery, renal vein, and ureter connect to the kidney (Taal et al., 2012).
The external surface of each kidney is covered by a fibrous, protective layer called the renal capsule. This capsule surrounds the kidney and helps maintain its shape, protecting it from damage and infection. Just beneath the renal capsule, a layer of adipose tissue, known as perirenal fat, provides further cushioning and protection. An additional layer of connective tissue, the renal fascia, surrounds the perirenal fat and anchors the kidneys to the surrounding structures, such as the abdominal wall and the vertebral column (Saladin, 2018).
Hilum and Renal Sinus
The hilum is a concave indentation located on the medial border of each kidney. It serves as the entry and exit point for various structures, including the renal artery, renal vein, and ureter. The renal artery branches off from the abdominal aorta and delivers oxygenated blood to the kidney, while the renal vein carries deoxygenated blood back to the inferior vena cava. The ureter transports urine from the kidney to the bladder for storage and eventual elimination (Taal et al., 2012).
Within the kidney, the hilum expands into a cavity called the renal sinus. The renal sinus contains the renal pelvis, which is a funnel-shaped structure that collects urine from the kidney and delivers it to the ureter. The renal sinus also houses the renal calyces, which are cup-like structures that collect urine from the renal pyramids before it flows into the renal pelvis (Saladin, 2018).
Surrounding Tissues and Organs
The kidneys are surrounded by several tissues and organs that provide support, protection, and functional interactions. These surrounding structures include:
- Adrenal glands: Located superiorly to each kidney, the adrenal glands are responsible for producing various hormones, including cortisol, aldosterone, and adrenaline. These hormones play important roles in stress response, electrolyte balance, and blood pressure regulation (Tortora & Derrickson, 2018).
- Diaphragm: The diaphragm, a large, dome-shaped muscle that separates the thoracic and abdominal cavities, lies superior and posterior to the kidneys. The diaphragm helps to maintain the position of the kidneys and plays a critical role in respiration (Saladin, 2018).
- Ribs: The lower ribs provide additional protection to the kidneys by partially covering their superior aspect. The 11th and 12th ribs, known as the “floating ribs,” partially protect the kidneys from direct trauma (Tortora & Derrickson, 2018).
- Pararenal fat: The pararenal fat is a layer of adipose tissue external to the renal fascia. This fat pad helps to cushion and stabilize the kidneys within the retroperitoneal space (Saladin, 2018).
The relationship between the kidneys and their surrounding tissues and organs is crucial for maintaining proper kidney function and overall health. Disruptions to these relationships, such as inflammation or injury, can impact kidney function and result in various health complications.
- Saladin, K. S. (2018). Anatomy & Physiology: The Unity of Form and Function (8th ed.). New York, NY: McGraw-Hill Education.
- Taal, M. W., Chertow, G. M., Marsden, P. A., Skorecki, K., Yu, A. S., & Brenner, B. M. (Eds.). (2012). Brenner and Rector’s The Kidney (9th ed.). Philadelphia, PA: Elsevier Saunders.
- Tortora, G. J., & Derrickson, B. H. (2018). Principles of Anatomy and Physiology (15th ed.). Hoboken, NJ: Wiley.