Kidney Anatomy: Complete Guide with Parts, Names & Diagram

Overview of Anatomy of the Kidney

In the human anatomy, the kidneys are vital, bean-shaped organs that keep our body healthy by filtering blood and managing fluid balance. Kidney anatomy consists of a renal capsule, cortex, hilum, fascia, perirenal fats, medulla, pyramid, column, papillae, etc. Every day, they process around 200 quarts of fluid, similar to the capacity of a large bathtub. Through this filtration, the kidneys separate waste products from the blood and then excrete them as urine—approximately two quarts daily. The remaining fluid is reabsorbed into the bloodstream. Beyond waste removal, the kidneys regulate essential minerals like sodium and potassium, maintaining a precise balance necessary for proper bodily functions. It also eliminates harmful substances, such as urea, a byproduct of protein metabolism, and creatinine resulting from muscle activity. The kidneys filter about half a cup of blood each minute to ensure the body remains balanced and toxins-free.

In this article, we will study detailed kidney anatomy with its different parts, their names and their location with labeled diagrams.

Kidney Anatomy Diagram

Parts of the Kidney

External Kidney Anatomy

Renal Capsule
Renal Cortex
Renal Hilum
Renal Fascia
Perirenal Fats

Blood Supply

Renal Artery
Segmental Arteries
Interlobar Arteries
Arcuate Arteries
Cortical Radiate (Interlobular) Arteries
Afferent Arterioles
Efferent Arterioles
Peritubular Capillaries and Vasa Recta
Renal Vein

Internal Kidney Anatomy

Renal Medulla
Renal Pyramid.
Renal Column
Renal Papillae
Renal Lobe
Renal Pelvis

Urinary Pathways

Minor Calyces
Major Calyces
Ureter

Nephron Anatomy

Glomerulus
Bowman’s Capsule
Proximal Convoluted Tubule (PCT)
Loop of Henle
- Descending Limb
- Ascending Limb
Distal Convoluted Tubule (DCT)
Collecting Duct

Nervous Supply

Renal Plexus

Kidney Anatomy – External

Renal Capsule

The renal capsule is a tough, fibrous layer surrounding the kidney and covered with a layer of perirenal fat known as the fatty capsule. This structure offers protection against physical impact and injury.

The renal fascia further surrounds it, and adjacent to the transverse fascia lies a region known as pararenal fat.

The renal capsule plays a crucial role in preventing excessive expansion of the kidney. It helps to maintain renal circulation.

When the kidney swells and stretches the renal capsule, it can lead to flank pain, highlighting its sensitivity to changes in kidney size.

Renal Cortex

Renal Hilum

The renal hilus, also called the renal pedicle, is the central area of the kidney through which blood vessels, nerves, and ureters pass.

The kidney has a bean-like shape with a concave in the central region and rounded at the ends. This central part features a deep groove with raised edges on the front and back.

The groove, known as the hilus, serves as an exit point for the renal vein, an entry point for the renal artery, and an exit for the renal pelvis.

In the left kidney, the hilus is found around the first lumbar vertebra (L1) level, while in the right kidney, it is around the L1-2 level.

The lower borders of the kidneys typically reach down to about the level of the third lumbar vertebra (L3).

Renal Fascia

The renal fascia is a tough, stretchy connective tissue layer that wraps around the kidney and adrenal gland, along with the surrounding layer of fatty tissue.

It separates the kidney fatty capsule from the outer pararenal fat. You will find layers like the fatty capsule (perirenal fat), the renal capsule, and the renal cortex’s parenchyma.

At the renal hilum, the renal capsule extends into the renal sinus. Initially thought to consist of two parts—Gerota’s fascia in front and Zuckerkandl’s fascia at the back—these were believed to merge into the lateroconal fascia on the sides.

Perirenal Fats

Perirenal fat is a layer of fat around the kidneys, located between the fibrous membrane and the surrounding fascia of the kidney.

The thickness of perirenal fat and the amount of fat in the kidney’s sinus have been linked to chronic diseases like chronic kidney disease (CKD), arteriosclerosis, hypertension, and diabetes.

Patients with acute decompensated heart failure (ADHF) suggested that perirenal fat can worsen kidney function by pressing the blood vessels of the kidney. This pressure can activate harmful hormonal pathways and reduce blood flow to the kidneys.

It is believed that a thicker perirenal fat pad may increase internal kidney pressure, leading to blood vessel compression and kidney problems.

Kidney Anatomy – Internal

Renal Medulla

The renal medulla is the center portion of the kidney tissue, consisting of 8-12 cone-shaped structures known as renal pyramids. These pyramids have several important components:

Nephron loops (Loops of Henle): These are U-shaped tubules that extend into the renal pyramids and are responsible for reabsorbing water and ions.
Collecting ducts: Pathways through the medulla that regulate fluid and electrolyte levels while transporting urine to the renal pelvis.
Vasa recta: Capillary networks around the nephron loops maintain the osmotic gradient required for water reabsorption.
Interstitium: The gaps between tubules and blood arteries in the kidney tissue.

The function of the renal medulla is to control fluid retention and electrolyte balance by reabsorbing filtrate and ions. It also helps to regulate blood pH by reabsorbing bicarbonate into the circulation and excreting hydrogen ions in the urine.

Furthermore, the medulla aids in the elimination of waste products such as urea, ammonia, and creatinine by directing them to the urine bladder via the ureters.

Then, the medulla transfers urine to the renal pelvis, which is collected and sent to the ureter.

Renal Pyramid

Renal pyramids, or Malpighian pyramids, are cone-shaped structures in the kidneys. Most people have around seven of these pyramids, but the number can vary between seven and eighteen. They are located in the innermost part of the kidney, called the renal medulla.

Each pyramid’s base faces the kidney’s outer layer, known as the renal cortex. Surrounding the kidney is a tough, fibrous layer called the renal capsule, which is covered by a layer of fatty tissue.

The striped look of the renal pyramids comes from the parallel arrangement of the nephrons, the kidney’s functional units.

Renal Column

Renal columns are extensions of the outer layer of the kidney, called the renal cortex. It extends into the inner part of the kidney, known as the renal medulla.

They provide structural support to the kidney and contain blood vessels, urine-carrying tubules, and connective tissue.

Sometimes, a renal column can enlarge, which may look like a tumor on medical scans. This condition is known as a renal pseudotumor, which is usually harmless and not cancerous.

Renal Papillae

The renal papillae are the pointed tips of the renal pyramids in the kidney. These structures collect urine before it moves into the ureters. At the end of each pyramid, the renal papillae are where the kidney’s collecting ducts meet.

Urine from the renal papillae flows into small chambers called minor calyces. Several of these minor calyces form a larger chamber called the major calyx.

This major calyx directs the urine into the ureter, which carries it to the bladder, where it is eventually expelled from the body.

The renal papillae also contain adult kidney stem cells, which are important for the kidney’s ability to repair and regenerate itself.

Renal Lobe

A renal lobe in the kidney consists of a renal pyramid and the overlying section of the renal cortex. In humans, there are typically between 7 to 18 renal lobes.

Each lobe comprises multiple renal lobules, microscopic structures that can’t be seen without a microscope. However, the overall lobe itself is visible to the naked eye.

Renal Pelvis

The renal pelvis is a funnel-shaped area inside the kidney where urine collects before moving into the ureter. It forms at the junction of the major calyces. It is the region where urine from different parts of the kidney comes together.

The inner surface of the renal pelvis is lined with a stretchy tissue called transitional epithelium. It allows us to expand and contract as needed.

A layer of connective tissue beneath this lining is called the lamina propria. The renal pelvis is found in the renal sinus, a space within the kidney that also houses other important kidney structures.

Kidney Anatomy: Complete Guide with Parts, Names, Functions & Diagram