Editing Urinary tract (section)

== '''Kidney''' ==

* Paired bean-shaped organs     that regulate fluid balance and filter wastes from the body

=== '''Embryology''' ===

** Three separate excretory      organs appear in development, which succeed each other in time and space,      such that only the last is retained
*** Pronephros
**** Present only as clusters        of cells at the cranial part of the urogenital ridge
**** Only the duct persists,        which becomes known as the mesonephric (Wolffian) duct, which opens        caudally into the cloaca
*** Mesonephros
**** A ridge becomes visible,        the mesonephric ridge or mesonephros
**** Mesonephric tubules, the        first tubules, develop individually here and open into the mesonephric        duct
**** Some of these ducts        develop into genital structures such as epididymis
*** Metanephros (the true       precursor of the kidney)
**** Forms caudal to the        mesonephros as a mass of new tubules
**** This mass induces a bud,        the ureter, to grow from the caudal end of the mesonephric duct
**** Ureteric bud then        separates from the mesonephric duct, leaving it to form part of the        bladder and ductus deferens
**** Metanephros continues to        develop in the pelvis and is supplied by internal iliac artery. It        gradually migrates cranially, acquiring new blood supply from aorta.
**** At first, the hilum is        anterior, but the kidney rotates 90 degrees medially

=== '''Structure''' ===

** Lies in the paravertebral      gutter between T12 and L3
** Right kidney is lower due to      the liver
** Hilum
*** Contains renal vessels,       renal pelvis and a variable amount of fat (usual order of vein, artery,       ureter from front to back)
*** In the right kidney it lies       just below the trans-pyloric plane, and in the left it lies just above
** Renal pelvis
*** Funnel-shaped commencement       of the ureter
*** Usually the most posterior       of the three main structures
*** Receive two or three major       calyces
*** Lined by transitional       epithelium (like the ureter)
** Coverings
*** Covered by a strong capsule       - gives glistening appearance
*** Perinephric fat lies       outside the renal capsule - plays a part in retaining the kidney in       position
*** Renal fascia surrounds the       perinephric fat and separates the kidney from the adrenal gland - firmly       attached at the hilum to the renal vessels and ureter (also stabilises       the kidney)
** Internal structure
*** Cortex - beneath the       capsule, extends towards the pelvis as the renal columns
*** Medulla - lies between the       columns as the renal pyramids (darker and triangular striated areas)
*** The apices of several       pyramids open together into a renal papilla, each of which projects into       a minor calyx
*** The minor calcyes unite to       form two or three major calyces, which opens into the renal pelvis

=== '''Relations''' ===

** Posteriorly
*** Diaphragm
*** Quadratus lumborum muscles,       with overlap medially onto psoas and laterally onto transversus       abdominis
*** Costodiaphragmatic recess       of the pleura
*** Subcostal vein, artery and       nerve
*** Iliohypogastric and       ilioinguinal nerves - as they emerge from lateral border of psoas
** Anteriorly
*** Peritoneum of the posterior       abdominal wall
*** Right - D2, hepatic       flexure, ascending branch of right colic artery, hepatorenal pouch of       the greater sac
*** Left - tail of pancreas,       splenic flexure, upper left colic artery, peritoneum of the lesser sac
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=== '''Arterial     supply''' ===

** Renal arteries (from aorta,      L2)
** Five segmental branches to      each kidney
*** Anterior division - apical,       upper, middle and lower segments
*** Posterior division -       posterior segment
***
** Aberrant renal arteries -      segmental vessels from aorta to lower pole

=== '''Venous     drainage''' ===

** Renal veins lie in front of      the renal arteries, and behind the pancreas, and join the IVC at right      angles, at level of L2
** Each emerges from the hilum      as five or six tributaries which soon unite
** Left:
*** 7.5cm long
*** Crosses in front of aorta
*** Receives left suprarenal       vein and gonadal vein
*** Connected with left       ascending lumbar, and hence connected to azygos system
** Right
*** 2.5cm long
*** Drains only its own kidney,       except for sometimes the right testicular vein

=== '''Lymphatics''' ===

** Para-aortic nodes
** Surface of upper pole may      drain through the diaphragm into nodes in the posterior mediastinum

=== '''Innervation''' ===

** Sympathetic preganglionic      (T12-L1) - through the coeliac, renal and superior hypogastric plexuses
** Afferent fibres (pain)      accompany the sympathetic nerves and radiate to the back
** Some PNS supply from the      vagus of uncertain function

=== '''Variant     anatomy''' ===

** Persistence of fetal      arteries (30%) - especially a vessel to the lower pole from aorta
** Horseshoe kidney - fusion of      the lower poles (1 in 800). Ascent of kidney limited by IMA.
** Renal agenesis (1 in 500)

=== '''Functions of     the kidney:''' ===

** Eliminate water-soluble      waste products of metabolism
** Eliminate water-soluble      drugs
** Fluid and electrolyte      homeostasis
** Acid-base balance
** Blood pressure control      (renin-angiotensin system)
** Endocrine function -      erythropoietin and vitamin D production