Kidney Gross Anatomy

(Sample Lesson)

A frontal section through the kidney reveals an outer, lighter-colored region called the renal cortex and an inner darker-colored region called the medulla. Surrounding the renal cortex is the renal capsule, a tough, fibrous layer of connective tissue that helps contain, support, and protect the kidney’s soft inner tissues.

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Each kidney contains approximately 6–8 renal lobes, which can be seen without using a microscope. A renal lobe contains thousands of microscopic tubules called nephrons, which are the kidney’s functional units. The medullary portion of a renal lobe is called a renal pyramid due to its shape. The base (wide end) of a pyramid lies adjacent to the renal cortex, and the apex (narrow end) extends into the kidney’s medial indentation. A pyramid appears darker and somewhat striated because it contains a high concentration of straight, parallel tubules called collecting ducts, which transport urine to a lobe’s apex.

A renal column extends between and separates adjacent renal lobes. The columns largely consist of connective tissue and provide a supportive framework for blood vessels that enter and exit the cortex.

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The renal hilum is a recessed central fissure on the medial side of the kidney. It provides space for the passage of the renal blood vessels, nerves, and ureter.

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The renal calyces are chambers of the kidney through which urine passes while traveling to the ureter. A minor calyx surrounds the apex of the renal pyramids. Urine formed in the kidney passes through a renal papilla at the apex into a minor calyx. Two or three minor calyces converge to form a major calyx, through which urine passes before continuing through the renal pelvis into the ureter. The smooth muscles in the calyces and renal pelvis walls rhythmically contract and relax (peristalsis) to propel urine into the ureter.

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Oxygenated blood enters the kidney from the descending aorta via the renal artery. In the renal hilum, the renal artery divides into segmental arteries, followed by further branching to form interlobar arteries, which pass through the renal columns toward the renal cortex. At the bases of the renal pyramids, the interlobar arteries branch into arcuate arteries, which extend along the arched intersections between the renal pyramids and cortex. Smaller vessels branch from the arcuate arteries and circulate blood throughout the renal lobes.

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The arcuate veins carry deoxygenated blood out of the renal lobes to the interlobar veins, which pass through the renal columns. The interlobar veins converge to form the segmental veins in the renal hilum. Blood is then carried out of the kidney by the renal vein to the inferior vena cava.

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Page Attributions

OpenStax College, Anatomy and Physiology

Access for free at – https://openstax.org/books/anatomy-and-physiology/pages/1-introduction

Reference: “Gross Anatomy of the Kidney“

Wikipedia, the free encyclopedia.

Reference 1: “Kidney“

Reference 2: “Nephron“