Kidney - description, position, syntopy (draw scheme), birth defects

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Kidneys: Description, Position, Syntopy, and Birth Defects

General Description

The kidneys are bean-shaped retroperitoneal organs essential for homeostasis. They filter blood, excreting waste (urea, creatinine) while maintaining electrolyte balance, acid-base equilibrium, and fluid levels. Each kidney regulates blood pressure via the renin-angiotensin-aldosterone system (RAAS) and supports red blood cell production by releasing erythropoietin.

  • Location:Retroperitoneally between the T12–L3 vertebrae, with the right kidney slightly lower due to the liver.
  • Size & Shape:~10 cm long, ~5 cm wide, and ~3 cm thick. They are reddish-brown with a smooth outer surface.
    • Superior poles: T12 level.
    • Inferior poles: L3 level.
    • Hilum: At the L1–L2 level.
  • Capsule and Surrounding Structures:
    • Renal Capsule: A tough collagenous layer firmly attached to the kidney.
    • Perirenal Fat: Surrounds the kidney and acts as cushioning.
    • Renal Fascia: Encases the perirenal fat and suprarenal glands, providing stability.
    • Pararenal Fat: Lies outside the renal fascia as additional cushioning.
Kidney syntopy.png

Position and Syntopy

Kidney syntopy back.png

Right Kidney

  • Superiorly: Liver (separated by the hepatorenal recess), right adrenal gland.
  • Anteriorly: Duodenum, hepatic flexure of the colon.
  • Posteriorly: Diaphragm, 12th rib, quadratus lumborum, psoas major, and transversus abdominis muscles.
  • Medially: Inferior vena cava (IVC), renal vessels, ureter.

Left Kidney

  • Superiorly: Stomach, spleen, left adrenal gland, pancreas (tail).
  • Anteriorly: Jejunum, splenic flexure of the colon.
  • Posteriorly: Diaphragm, 11th and 12th ribs, quadratus lumborum, psoas major, transversus abdominis muscles.
  • Medially: Abdominal aorta, renal vessels, ureter.

Internal Structure

Kidney – structure.jpg
  1. Renal Cortex:
    • Lies directly beneath the renal capsule.
    • Contains glomeruli (site of filtration), proximal and distal convoluted tubules.
    • Extensions between the pyramids form renal columns, supporting blood vessels.
  2. Renal Medulla:
    • Comprises 8–12 renal pyramids.
    • Pyramids: Base faces the cortex; apex (papilla) points toward the renal sinus.
    • Zones:
      • Outer striated zone.
      • Inner pale zone.
    • Contains loops of Henle and collecting ducts for urine concentration.
  3. Renal Sinus:
    • Central cavity housing:
      • Renal pelvis.
      • Major and minor calyces.
      • Renal vessels, lymphatics, and nerves.
      • Adipose tissue for cushioning.
  4. Renal Pelvis & Calyces:
    • Renal Pelvis: Funnel-shaped origin of the ureter, which collects urine.
    • Major Calyces: Divide into 2–3 branches.
    • Minor Calyces: Surround renal papillae, collecting urine from each pyramid.

Vascular Supply and Lymphatics

  1. Arterial Supply:
    • Renal Arteries: Arise from the abdominal aorta at L1–L2.
      • Divide into 5 segmental arteries: Superior (apical), anterior superior, anterior inferior, inferior, and posterior.
      • Branching pattern:
        • Segmental → Interlobar → Arcuate → Cortical radiate arteries.
        • Some cortical radiate arteries perforate the renal capsule to supply the perirenal tissues.
  2. Venous Drainage:
    • Renal veins drain into the inferior vena cava (IVC).
    • Left Renal Vein: Longer than the right, receiving tributaries from the left gonadal vein, left suprarenal vein, and sometimes the phrenic vein.
  3. Lymphatic Drainage:
    • Follows renal veins to lumbar (caval and aortic) lymph nodes.

Ureter and Associated Structures

Ureter Engstellen.png
  • Description:
    • 25–30 cm long muscular tubes transporting urine from kidneys to the bladder.
    • Diameter: ~4–7 mm.
    • Constricted at three points:
      1. Ureteropelvic junction.
      2. Crossing of iliac vessels.
      3. Ureterovesical junction (entry into bladder).
  • Blood Supply:
    • Abdominal Ureter: Supplied by renal arteries, abdominal aorta, and gonadal arteries.
    • Pelvic Ureter: Supplied by superior vesical, middle rectal, and inferior vesical/uterine arteries.

Functional Highlights

  • Filtration: Occurs in the glomeruli. Ultrafiltrate is processed to form urine.
  • Reabsorption and Secretion: Occurs in the tubules for electrolyte and water balance.
  • Concentration of Urine: Managed by the loop of Henle and collecting ducts.

Birth Defects and Anomalies

  1. Renal Agenesis:
    • Absence of one (unilateral) or both (bilateral) kidneys. Bilateral agenesis is incompatible with life.
  2. Horseshoe Kidney:
    • Inferior poles of kidneys fuse across the midline. Often asymptomatic but may cause obstruction or infections.
  3. Ectopic Kidney:
    • Kidney fails to ascend during development, often located in the pelvis.
  4. Polycystic Kidney Disease (PKD):
    • Autosomal dominant or recessive disorder causing numerous cysts, leading to kidney enlargement and dysfunction.
  5. Duplex Kidney:
    • A single kidney with two ureters or a duplicated renal pelvis.
  6. Pelvic Kidney:
    • A kidney that remains in the pelvis due to developmental failure to ascend.
  7. Multicystic Dysplastic Kidney (MCDK):
    • Non-functional kidney with multiple cysts due to disrupted nephron development.
  8. Wilms Tumor:
    • Congenital malignancy affecting children under five, arising from primitive renal tissue
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