Interlobar Arteries

The interlobar arteries are major intrarenal arteries that travel between adjacent renal pyramids within the renal columns. They form an important intermediate level in the renal arterial tree, carrying blood from the segmental arterial system toward the arcuate arteries at the corticomedullary junction.

Their name reflects their course between the renal lobes. Each renal lobe consists of a medullary pyramid together with its associated cortical tissue. Interlobar arteries ascend on either side of the pyramids and, near their bases, divide into arcuate arteries that curve along the corticomedullary boundary.

Renal Arterial Supply

The kidneys receive a large blood supply through the right and left renal arteries, which arise from the abdominal aorta.

Within the kidney, the arterial system follows a progressively branching arrangement that distributes blood from the renal hilum to the cortex, medulla, and individual nephrons.

Arterial Branching Sequence

A simplified sequence of the renal arterial circulation is:

1. Renal artery
2. Segmental arteries
3. Interlobar arteries
4. Arcuate arteries
5. Cortical radiate arteries
6. Afferent arterioles
7. Glomerular capillaries

The interlobar arteries therefore connect the segmental arterial system with the arcuate arterial network.

Origin

Interlobar arteries arise from branches of the segmental arteries within the renal sinus.

The precise branching pattern can vary, but the vessels ultimately enter the renal parenchyma and travel between neighboring renal pyramids.

Segmental Arteries

The renal artery divides into segmental branches that supply defined vascular territories of the kidney.

These segmental arteries give rise to vessels that continue into the renal columns as interlobar arteries.

Renal Sinus

The renal sinus is the internal cavity of the kidney containing the renal pelvis, calyces, vessels, nerves, lymphatics, and variable amounts of fat.

Branches of the renal artery pass through this region before entering the renal parenchyma as progressively smaller vessels.

Course

Interlobar arteries extend from the renal sinus toward the cortex through the tissue located between adjacent renal pyramids.

Their general orientation is radial, passing outward toward the bases of the pyramids rather than parallel to the renal surface.

Renal Columns

The interlobar arteries travel within the renal columns, also called columns of Bertin.

Renal columns are extensions of cortical tissue that project inward between neighboring medullary pyramids.

Relationship to Renal Pyramids

Interlobar arteries pass along the lateral boundaries of the renal pyramids.

This relationship distinguishes them from arcuate arteries, which curve along the bases of the pyramids, and cortical radiate arteries, which extend outward through the cortex.

Renal Pyramids

The renal pyramids are conical masses of medullary tissue containing straight tubular structures and vessels.

The broad base of each pyramid faces the cortex, while its apex forms a renal papilla projecting toward a minor calyx.

Renal Lobes

A renal lobe consists of one renal pyramid and the cortical tissue associated with it.

Because interlobar arteries travel between adjacent pyramids and their associated lobes, their anatomical name describes their location within the kidney.

Termination

As interlobar arteries approach the bases of the renal pyramids, they divide into arcuate arteries.

This transition occurs near the corticomedullary junction.

Arcuate Arteries

Arcuate arteries curve along the bases of the renal pyramids and run approximately parallel to the renal surface.

They mark an important transition from the deeper radial arterial pathway to vessels supplying the renal cortex.

Corticomedullary Junction

The corticomedullary junction is the region where the renal cortex meets the underlying medulla.

Interlobar arteries reach this level and transition into arcuate arteries, which follow the contour of the bases of the medullary pyramids.

Cortical Radiate Arteries

Arcuate arteries give rise to numerous cortical radiate arteries, traditionally called interlobular arteries.

These smaller vessels extend outward through the renal cortex toward the renal capsule.

Afferent Arterioles

Cortical arterial branches give rise to afferent arterioles supplying the renal corpuscles.

Each afferent arteriole enters a glomerulus and forms the vascular inflow to the glomerular capillary network.

Glomerular Capillaries

The glomerular capillaries are specialized fenestrated capillaries within the renal corpuscle.

They form the vascular component of the renal filtration barrier through which plasma is filtered to produce the initial tubular fluid.

Efferent Arterioles

Blood leaves the glomerulus through an efferent arteriole.

This creates the characteristic arrangement in which the glomerular capillary bed lies between an afferent and an efferent arteriole.

Peritubular Capillaries

Efferent arterioles associated with many cortical nephrons divide into peritubular capillaries.

These capillary networks surround renal tubules and support reabsorption and secretion between tubular fluid and the circulation.

Vasa Recta

Efferent arterioles associated particularly with juxtamedullary nephrons contribute to the vasa recta.

These straight vessels descend into the renal medulla and participate in countercurrent exchange that helps preserve the medullary osmotic gradient.

Blood Supply to the Cortex

Interlobar arteries do not directly form the principal small-vessel network of the renal cortex.

Instead, blood passes from interlobar arteries into arcuate arteries and then into cortical radiate arteries before reaching the glomerular circulation.

Blood Supply to the Medulla

The medullary circulation is supplied largely through vessels associated with juxtamedullary nephrons and through small arterial branches arising from the deeper intrarenal circulation.

The interlobar arteries form part of the major arterial pathway that delivers blood to these downstream vascular systems.

Interlobar Arteries and Renal Architecture

Structure	Relationship to Interlobar Arteries
Renal columns	Contain the interlobar arteries
Renal pyramids	Interlobar arteries pass between adjacent pyramids
Renal sinus	Contains proximal arterial branches before they enter the parenchyma
Corticomedullary junction	Region where interlobar arteries give rise to arcuate arteries
Arcuate arteries	Major terminal continuations of interlobar arteries

Interlobar and Arcuate Arteries

Feature	Interlobar Arteries	Arcuate Arteries
Location	Renal columns	Corticomedullary junction
Relationship to pyramids	Pass between pyramids	Arch along pyramid bases
General orientation	Radial toward cortex	Curved, approximately parallel to renal surface
Origin	Segmental arterial system	Interlobar arteries
Major downstream vessels	Arcuate arteries	Cortical radiate arteries

Interlobar and Cortical Radiate Arteries

The similarly named interlobar and interlobular arteries can be confused.

Interlobar arteries are relatively large vessels between renal pyramids, whereas the smaller vessels traditionally called interlobular arteries are cortical radiate arteries located within the renal cortex.

Interlobar Arteries Versus Interlobular Arteries

Feature	Interlobar Arteries	Interlobular/Cortical Radiate Arteries
Size	Larger	Smaller
Location	Between renal pyramids	Within renal cortex
Origin	Segmental arterial branches	Arcuate arteries
Major branches	Arcuate arteries	Afferent arterioles

Relationship to Interlobar Veins

Interlobar veins accompany the arterial vessels through the renal columns.

They receive blood from arcuate veins and carry it toward the renal vein.

Renal Venous Drainage

The venous system generally follows the major organization of the arterial tree, although there are important differences in detailed branching and communication.

A simplified pathway is cortical radiate veins to arcuate veins, then interlobar veins and finally the renal vein.

Interlobar Veins

Interlobar veins travel between the renal pyramids alongside corresponding arterial pathways.

They converge within the renal sinus and contribute to formation of the renal vein.

Renal Arterial Segmentation

The kidney is divided into vascular segments based largely on the distribution of segmental arterial branches.

These territories are clinically important because major segmental arteries have limited effective anastomoses with neighboring segmental territories.

End-Artery Organization

The renal arterial system is commonly described as having an end-artery pattern.

Limited collateral circulation means that obstruction of a substantial arterial branch can produce ischemia and infarction of its downstream territory.

Interlobar Arterial Occlusion

Occlusion of an interlobar artery can compromise perfusion to arcuate and cortical branches arising downstream from the affected vessel.

The resulting ischemic territory depends on the location and extent of the arterial obstruction.

Renal Infarction

Renal infarction results when arterial blood flow to a region of kidney becomes sufficiently interrupted to cause ischemic tissue necrosis.

Occlusion of larger proximal branches affects broader renal territories than obstruction of small cortical vessels.

Renal Artery Disease

Pathological changes in the renal arterial circulation can affect perfusion at multiple levels, from the main renal artery to microscopic arterioles.

The branching arrangement of the renal vascular tree determines which portions of the parenchyma are affected by a particular vascular lesion.

Histological Identification

Interlobar vessels may be encountered in sections passing through renal columns between medullary pyramids.

Their location helps distinguish them from arcuate vessels at the corticomedullary boundary and cortical radiate vessels within the cortex.

Gross Anatomical Identification

In gross sections of the kidney, the course of the interlobar arteries corresponds to the cortical tissue extending between adjacent pyramids.

Tracing these vessels outward demonstrates their transition into arcuate arteries near the bases of the pyramids.

Imaging

Modern vascular imaging can demonstrate progressively smaller branches of the renal arterial tree depending on the technique and spatial resolution.

Recognition of the normal branching pattern is useful when evaluating renal vascular anatomy, planning interventions, or interpreting vascular abnormalities.

Renal Angiography

Renal angiographic studies demonstrate the branching pattern from the renal arteries into segmental and intrarenal vessels.

Interlobar arteries can be recognized by their radial distribution between renal pyramidal territories before the vessels curve into the arcuate level.

Importance in Renal Surgery

Knowledge of intrarenal vascular anatomy is important during nephron-sparing surgery and other procedures involving renal parenchyma.

The relationship of segmental, interlobar, arcuate, and cortical vessels helps surgeons understand the vascular consequences of dividing or preserving particular arterial branches.

Partial Nephrectomy

During partial nephrectomy, preservation of adequate blood flow to the remaining renal tissue is an important consideration.

Understanding the branching pattern of intrarenal arteries assists in identifying the vessels associated with the portion of kidney being treated.

Renal Transplantation

Renal transplantation primarily requires detailed knowledge of the main renal arteries and their segmental branching, including accessory arteries when present.

Once arterial inflow is established, the intrarenal interlobar and downstream vessels distribute blood throughout the transplanted kidney.

Functional Pathway to the Nephron

1. Blood enters the kidney through the renal artery.
2. The renal artery divides into segmental branches.
3. Segmental branches give rise to interlobar arteries.
4. Interlobar arteries travel through the renal columns.
5. They reach the bases of the renal pyramids.
6. They divide into arcuate arteries.
7. Arcuate arteries give rise to cortical radiate arteries.
8. Cortical arterial branches give rise to afferent arterioles.
9. Afferent arterioles deliver blood to glomerular capillaries.
10. Blood leaves each glomerulus through an efferent arteriole.
11. Efferent vessels form peritubular capillaries or contribute to the vasa recta.

Spatial Organization of Intrarenal Arteries

Artery	Characteristic Location
Segmental artery	Renal sinus and segmental territory
Interlobar artery	Renal column between pyramids
Arcuate artery	Base of pyramid at corticomedullary junction
Cortical radiate artery	Extends through renal cortex
Afferent arteriole	Enters individual renal corpuscle

Key Anatomical Features

• Interlobar arteries are major intrarenal arterial branches.
• They arise from the segmental arterial system.
• They pass through renal columns between adjacent renal pyramids.
• Their course is generally directed outward toward the renal cortex.
• They reach the corticomedullary junction at the bases of the pyramids.
• Interlobar arteries give rise to arcuate arteries.
• Arcuate arteries curve along the bases of renal pyramids.
• Cortical radiate arteries arise from arcuate arteries and enter the cortex.
• Afferent arterioles ultimately arise from the cortical arterial network and supply glomeruli.
• Interlobar arteries should not be confused with interlobular, or cortical radiate, arteries.
• Interlobar veins accompany the corresponding arterial pathways through the renal columns.
• The renal arterial circulation has limited effective collateral supply between major vascular territories.

Clinical Importance

The interlobar arteries form a major vascular bridge between the segmental arteries and the arcuate circulation. Their characteristic passage through the renal columns between adjacent pyramids makes them important landmarks for understanding the three-dimensional organization of renal blood supply.

Because each interlobar artery supplies downstream arcuate and cortical arterial branches, interruption of its blood flow can compromise a substantial region of renal parenchyma. This reflects the relatively limited collateral circulation within major renal arterial territories.

Understanding the interlobar arteries provides the anatomical foundation for studying renal arterial branching, renal columns, renal pyramids, segmental arteries, arcuate arteries, cortical radiate arteries, glomerular circulation, renal vascular segmentation, renal infarction, and surgical anatomy of the kidney.