Kidneys, Ureters and Suprarenal Glands

Position:

• Paired, bean-shaped, retroperitoneal organs lying against the posterior abdominal wall, extending approximately from T12 to L3 vertebral level.
• The right kidney sits slightly lower than the left, due to the space occupied by the liver superiorly on the right side, a consistent, frequently tested asymmetry.
• Both kidneys move slightly with respiration (descending on inspiration, due to diaphragmatic movement).

External features:

• Convex lateral border, concave medial border (containing the hilum), superior and inferior poles.
• Enclosed by a thin, tough fibrous renal capsule, directly applied to the renal surface.

Hilum:

• Located on the medial concave border, the entry/exit point for the renal vessels, ureter, and lymphatics.
• Typical anterior-to-posterior arrangement of structures at the hilum: renal Vein (most anterior), renal Artery, then the ureter/renal pelvis (most posterior): mnemonic VAP (Vein, Artery, Pelvis/ureter).

Renal sinus:

• The space within the kidney, internal to the hilum, containing the renal pelvis, major and minor calyces, renal vessels' intrarenal branches, and a variable amount of fat.

Cortex:

• Outer part of the renal parenchyma, containing the renal corpuscles (glomeruli + Bowman's capsules) and convoluted tubules; extends into the medulla as the renal columns (of Bertin), separating adjacent pyramids.

Medulla:

• Inner part, composed of the renal pyramids (typically 8-18 per kidney), containing the loops of Henle and collecting ducts, each pyramid draining via its apex (the renal papilla) into a minor calyx.

Pyramids:

• Triangular structures within the medulla, their bases facing the cortex and their apices (papillae) projecting into the minor calyces, the functional units where urine concentration/collection culminates before entering the collecting system.

Calyces:

• Minor calyces (typically 7-14), each receives urine from one (or occasionally two) renal papillae.
• Major calyces (typically 2-3), formed by the union of several minor calyces.
• Major calyces converge to form the renal pelvis.

Renal pelvis:

• The funnel-shaped, dilated proximal part of the collecting system, formed by the union of the major calyces, narrowing as it exits the renal sinus (at the pelviureteric junction) to become the ureter.

Relations:

• Anterior relations (differ between the two sides given the asymmetric abdominal organ arrangement):
• Right kidney: Liver (superiorly), right colic (hepatic) flexure, second part of the duodenum (medially), small intestine loops.
• Left kidney: Stomach, spleen (via the splenorenal ligament), pancreas (tail, crossing anteriorly), left colic (splenic) flexure, jejunum.

• Posterior relations (similar bilaterally): Diaphragm (superiorly), psoas major (medially), quadratus lumborum (laterally), transversus abdominis (most lateral/inferior), and the subcostal, iliohypogastric, and ilioinguinal nerves, which cross the posterior surface obliquely.

Renal fascia:

• Renal (Gerota's) fascia: A tough fibrous fascial envelope surrounding the kidney and suprarenal gland (and the perirenal fat), open inferiorly (allowing potential downward spread of perinephric collections/infection toward the pelvis) but fused superiorly and medially, providing structural containment.

Perirenal fat:

• Fat immediately surrounding the kidney and suprarenal gland, contained within Gerota's fascia, provides cushioning and contributes to normal renal positional stability (loss of perirenal fat, e.g., in severe weight loss, is a classic cause of acquired nephroptosis, or renal descent/mobility).

Pararenal fat:

• Fat lying external to (outside) Gerota's fascia, between it and the posterior abdominal wall musculature/transversalis fascia, a separate fat compartment from the perirenal fat, relevant to the layered anatomical description of retroperitoneal fascial planes used in cross-sectional imaging interpretation.

Blood supply:

• Renal artery: paired branches of the abdominal aorta, arising at approximately the L1-L2 level (just below the SMA origin, corresponding to the transpyloric plane); the right renal artery is longer than the left, since it must cross posterior to the IVC to reach the right kidney.
• Segmental arteries: each renal artery divides (typically into 5 segmental branches) upon entering the renal sinus, supplying distinct, relatively non-overlapping vascular segments of the kidney (anterior superior, anterior middle, anterior inferior, posterior, and inferior segments), these segmental arteries function as end-arteries with minimal collateral circulation between segments, meaning segmental arterial occlusion produces a well-demarcated area of renal infarction.
• Venous drainage: Renal veins drain directly into the IVC; the left renal vein is longer than the right, crossing anterior to the aorta (in the majority of individuals, the "nutcracker" position, between the aorta and the SMA origin) to reach the IVC, and receives the left gonadal vein and left suprarenal vein as tributaries (the right gonadal and suprarenal veins drain directly into the IVC instead, given the IVC's more immediate proximity on the right side).

Course:

• Muscular tubes, approximately 25-30 cm long, connecting the renal pelvis to the bladder, descending retroperitoneally along the psoas major muscle, crossing the pelvic brim near the bifurcation of the common iliac artery, then continuing through the pelvis to enter the bladder posteroinferiorly.

Abdominal relations:

• Lie on the anterior surface of psoas major for most of their abdominal course; crossed anteriorly by the gonadal vessels (testicular/ovarian, which arise higher and cross over the ureter as both structures descend); the right ureter is crossed by the root of the small bowel mesentery and lies close to the second/third parts of the duodenum; the left ureter is crossed by the sigmoid mesocolon.

Three major constrictions (clinically significant as the classic sites of ureteric stone impaction, given the narrowest luminal diameter at each point):

1. Pelviureteric junction (PUJ): where the renal pelvis narrows to become the ureter.
2. Pelvic brim: where the ureter crosses the bifurcation of the common iliac vessels, entering the pelvis.
3. Vesicoureteric junction (VUJ): where the ureter enters the bladder wall obliquely (an oblique course that also serves a valve-like function, preventing vesicoureteric reflux under normal circumstances).

Blood supply:

• Segmental, from multiple sources along its length: renal artery (proximal ureter), gonadal artery, direct branches of the abdominal aorta and common iliac artery, and (in the pelvis) branches of the internal iliac artery (superior/inferior vesical arteries), this multi-source segmental supply, approaching from different directions at different levels, is surgically important, since excessive lateral dissection/stripping of the ureter during pelvic surgery can devascularise a segment despite the vessels appearing to enter from a seemingly "safe" medial or lateral direction depending on the level.

Innervation:

• Autonomic (renal and hypogastric plexuses), carrying visceral afferent pain fibres that produce the classic severe, colicky, radiating pain pattern of ureteric colic: pain typically begins in the flank/loin (corresponding to the level of obstruction) and radiates anteriorly and inferiorly toward the groin/genitalia as the stone migrates distally, reflecting the segmental (T11-L2 approximately) visceral afferent supply shared with the corresponding somatic dermatomes.

Position:

• Paired endocrine glands situated at the superomedial pole of each kidney, within Gerota's fascia (sharing the perirenal fat compartment, though functionally and embryologically entirely distinct from the kidney itself, a gland, not an accessory renal structure).

Shape:

• Right suprarenal gland: Pyramidal ("cap-like").
• Left suprarenal gland: Crescentic/semilunar shape, typically somewhat larger and more elongated than the right.

Relations:

• Right gland: IVC (medially), liver (anteriorly/superiorly), right kidney (inferiorly), diaphragm (posteriorly).
• Left gland: Aorta (medially), stomach and pancreas (anteriorly, separated by the lesser sac/peritoneum), spleen (superolaterally, via the splenorenal ligament region), left kidney (inferiorly), diaphragm (posteriorly).

Arterial supply (three sources, a distinctive "triple supply" pattern reflecting the gland's high metabolic demand and endocrine function):

• Superior suprarenal artery: from the inferior phrenic artery.
• Middle suprarenal artery: direct branch of the abdominal aorta.
• Inferior suprarenal artery: from the renal artery.

Venous drainage:

• Asymmetric, unlike the arterial supply: a single suprarenal vein on each side: the right suprarenal vein drains directly into the IVC (a short, wide vein, making right-sided adrenal vein sampling/cannulation technically more challenging in clinical procedures such as selective venous sampling for hyperaldosteronism localisation); the left suprarenal vein drains into the left renal vein (often via a common trunk with the left inferior phrenic vein), reflecting the same asymmetric venous drainage pattern seen with the gonadal veins.

Innervation:

• Distinctive among abdominal viscera: the adrenal medulla receives direct preganglionic sympathetic innervation (via the splanchnic nerves, particularly the greater splanchnic nerve, synapsing directly on the chromaffin cells rather than in a peripheral ganglion first), reflecting the medulla's embryological origin as a modified sympathetic ganglion itself, and explaining its function as an endocrine "amplifier" of the sympathetic nervous system (secreting adrenaline/noradrenaline directly into the bloodstream in response to sympathetic stimulation, rather than acting via direct synaptic transmission at a target organ).
• The adrenal cortex (a separate embryological derivative, from mesoderm rather than neural crest) receives only indirect autonomic influence and is instead primarily regulated by the hypothalamic-pituitary-adrenal (HPA) axis (ACTH) and the renin-angiotensin-aldosterone system, rather than direct neural control.

Renal angle:

• The angle between the 12th rib and the lateral border of erector spinae (specifically, the costovertebral angle), overlying the kidney's posterior surface, the site of renal angle tenderness (costovertebral angle tenderness), a classic clinical sign of renal pathology (pyelonephritis, renal stone, perinephric abscess).

Ureteric stones:

• Impact classically at the three constrictions (PUJ, pelvic brim, VUJ), producing the characteristic colicky, radiating "loin to groin" pain pattern as the stone migrates and the level of obstruction/distension changes.

Renal artery stenosis:

• Narrowing of one or both renal arteries (atherosclerotic in older patients, fibromuscular dysplasia in younger patients, particularly young women) reduces renal perfusion, activating the renin-angiotensin system and producing secondary (renovascular) hypertension: a classic cause of hypertension resistant to standard medical therapy, particularly when accompanied by an abdominal bruit on examination.

Adrenal vascular anatomy:

• The asymmetric venous drainage pattern (right: directly to IVC, short vein; left, via renal vein, longer vein) is clinically significant in adrenal venous sampling (used to lateralise the source of excess hormone secretion, e.g., in primary hyperaldosteronism), where the technically more difficult right-sided cannulation (given the short, variable, and sometimes multiple right adrenal vein anatomy) is a recognised source of sampling failure/inaccuracy compared to the left side.