KIDNEY & URETHERS

The Kidneys The kidneys (L. renes) lie in the paravertebral gutters, at the level of L12 to L3 vertebrae. Their long axes are almost parallel with
the axis of the body. The ureter runs inferiorly from each kidney and passes over the pelvic brim at the bifurcation of the common iliac artery. This runs along the lateral wall of the pelvis and enters the urinary bladder. The kidneys' functions are: 1. The removal of excess water, salts and products of protein metabolism; 2. The maintenance of pH; 3. Production and release of erythopoietin, which controls blood cell production; 4. Synthesis and release of renin to influence blood pressure; 5. And the production of 1,25- hydroxycholecalciferol (activated for of vitamin D) for control of calcium
metabolism. Back to top Position, Form, and Size of the Kidneys Click here for a diagram of the position of the kidney from the posterior aspect. Each kidney lies in a mass of perirenal (perinephric) fat, posterior to the peritoneum (i.e., it is retroperitoneal), on the posterior abdominal wall. These lie alongside the vertebral column,
against the psoas major. The superior parts of the kidneys are protected by the thoracic cage and are
tilted so that their superior poles are nearer to the median plane than their inferior poles. The right kidney lies at a slightly lower level than the left one. This is due to the large size of the right lobe of the liver. Each kidney has anterior and posterior surfaces, medial and lateral margins (borders), and superior and inferior poles. The lateral margin is convex. The medial margin is indented or concave where the renal sinus and renal pelvis are located. Kidneys are about: 1. 10-11 cm in length; 2. 5-6 cm in width; 3. 2.5-3 cm in thickness; 4. They weigh about 135-150 grams; 5. The left kidney is often slightly longer than the right one. Each kidney is ovoid in outline. Its indented medial margin gives it a somewhat bean-shaped appearance. At this concave part of each kidney is a vertical cleft, the renal hilum (hilus). Here, the renal artery enters and the renal vein and renal pelvis leave the kidney. The hilum leads into a space within the kidney called the renal sinus, which is about 2.5 cm deep. The renal sinus is occupied by the renal pelvis, renal calices, renal vessels and nerves, and varying amounts of fat. From anterior to posterior are the: 1. Renal vein 2. Renal artery 3. Renal pelvis Back to top Surface Anatomy and Markings of the
Kidneys In thin adults with poorly developed abdominal muscles, the inferior pole of the right kidney is usually palpable in the right lateral region. It is a firm, smooth, somewhat rounded mass that descends during inspiration. The normal left kidney is not usually palpable. The levels of the kidneys change during respiration and with changes in posture. Each kidney moves about 3 cm in a vertical direction during the movements of the diaphragm that occurs with deep breathing. The hilum of the left kidney lies in the transpyloric plane, about 5 cm from the median plane. This plane cuts through the superior part of the right kidney. From the posterior aspect of the kidney (important for surgery), the inferior pole of the right kidney is about a fingerbreadth superior to the iliac crest and that its superior pole is superior to the 12th rib. Gross Structure of the Kidneys Click here for a diagram of the gross structure of the kidneys. The Fibrous Capsule Each kidney is invested in a strong, fibrous capsule. It passes over the lips of the hilum to line the renal sinus and become continuous with the walls of the calices. The kidney and its capsule are
surrounded by pararenal fat, but it is sparse on its anterior surface. This fat is less dense and thus an outline of the kidney is usually visible in radiographs, CTs and MRIs. The Renal Pelvis This is continuous inferiorly with the ureter. It is surrounded by fat, vessels and nerves in the renal sinus. The word pelvis is derived from the
Greek word pyelos, meaning basin. Within the renal sinus, the renal pelvis usually divides into two wide, cup- shaped major calices (G. flower cups). Each major calyx (calix) is subdivided into 7 to 14 minor calices. The urine empties into a minor calyx from the collecting tubules that pierce the tip of the renal papilla obliquely. It then passes through the major calyx, renal pelvis, and the ureter to enter the urinary bladder. Back to top Renal Fascia and Renal Fat Each kidney, invested by the fibrous renal capsule, is also embedded in a substantial mass of perirenal fat that constitutes the fatty renal capsule. Very little fat lies anterior to the kidney. The fatty renal capsule is in turn covered by fibroareolar tissue called the renal fascia. This fascia encloses the kidney, its surrounding fibrous and fatty capsules, and the suprarenal (adrenal) glands. These covering help to maintain the
position of these organs. Superiorly, the renal fascia is continuous with the fascia on the inferior surface of
the diaphragm (the diaphragmatic fascia). Medially, the anterior layers of the fascia on the right and left sides blend with each other anterior to the abdominal aorta and inferior vena cava. The posterior layer of renal fascia fuses medially with the fascia over the psoas major muscle. The layers of renal fascia are loosely united inferiorly and may easily be separated. The encasement of the kidney in fat is an important factor in anchoring it in position. The extraperitoneal fat, the pararenal fat is located between the peritoneum of the posterior abdominal wall and the renal fascia. Relations of the Kidneys (Ashwell) Anterior Posterior Left
Kidney Spleen Stomach Suprarenal gland Pancreas Small intestine
(duodenum, jejunum and ileum) Left colic flexure
Splenic artery
Splenic vessels 11th and 12th ribs Diaphragm Quadratus
lumborum
Transversus
abdominis
Psoas major Subcostal vessels
Subcostal nerves
Iliohypogastric
nerve
Ilioinguinal nerve Right
Kidney Right suprarenal gland Right lobe of liver Right colic flexure Small intestine
Duodenum As for left except no 11th rib For the anterior relations of the left kidney, it is composed of 7 "S": 1. Suprarenal; 2. Splenic; 3. Stomach (gastric part); 4. Splenic vessels; 5. Sweetbread (the pancreas); 6. Small intestine (duodenum, ileum and
jejunum); 7. Splenic flexure (or left colic flexure). Back to top Blood Supply of the Kidney Renal Arteries Click here to go to the renal arteries under "The Blood Vessels of the Abdomen
and Pelvis." This arises from the aorta below the level of the superior mesenteric artery. Each renal artery gives off one or more inferior suprarenal arteries and branches that supply the perirenal tissue, renal capsule, pelvis and the proximal part of the ureter. Accessory renal arteries are common (30% of individuals). They usually arise above or below the
main renal artery and follow the hilum. Segmental Arteries Near the hilum each artery divides into anterior and posterior divisions, which in turn divide into segmental arteries. These supply the 5 renal vascular segments (apical, superior (anterior), inferior, middle (anterior) and posterior). Each vascular segment is supplied by end arteries, i.e., there are no anastomoses. The initial branches of the segmental
arteries are lobar, usually one to each pyramid. However, before entry they subdivide into 2 or 3 interlobar arteries. At the junction of the cortex and medulla, each interlobar artery divides into arcuate arteries. These diverge at right angles. Interlobular arteries diverge from the arcuate arteries to ascend into the cortex, to give rise to the glomerular arteries. Venous Drainage of the Kidneys Click here to go to the "Blood Vessels of the Abdomen and Pelvis." The renal veins drain into the IVC. The left renal vein is longer than the right renal vein and receives the left suprarenal veins and left gonadal vein. On the right, these drain directly into the IVC. Back to top Renal Innervation Click here to go to "The Nerves and Lymphatics of the Abdomen and Pelvis." The renal plexus is formed from the rami from the: 1. The coeliac ganglion and plexus; 2. The aorticorenal ganglion; 3. The lower thoracic splanchnic nerves; 4. The 1st lumbar splanchnic nerve; 5. And the aortic plexus. The plexus usually continues into the kidney around the renal arteries. Most renal nerves are vasomotor. Sensory nerves pass back to the CNS with the thoracic splanchnic nerves. The renal plexus gives rise to the ureteric and gonadal plexuses. Lymphatic Drainage of the Kidneys This is to the lumbar nodes. Back to top The Ureters These are thick-walled, expandable muscular ducts with a narrow lumen. They carry urine from the kidneys to the urinary bladder. As urine passes along the ureters, peristaltic waves occur in their walls. Each ureter is continuous above with the funnel-shaped renal pelvis. The Abdominal Ureter The abdominal part of the ureter is about 12.5 cm long and 5 mm wide. This closely adheres to the parietal peritoneum and is retroperitoneal throughout its entire course. It descends almost vertically, anterior to the psoas major muscle. As the right ureter descends, it is closely related to the IVC, the lumbar lymph nodes and the sympathetic trunk. The ureter crosses the brim of the pelvis and the external iliac artery, just beyond the bifurcation of the common iliac artery. The Pelvic Ureter This part of the ureter course posteroinferiorly on the lateral wall of the pelvis, external to the parietal peritoneum and anterior to the internal iliac arteries. They continue to a point about 1.5 cm superior to the ischial spines. Each ureter then curves anteromedially, superior to the levator ani muscle, where it is closely adherent to the peritoneum. The ureters pass obliquely through the bladder wall. When the bladder distends, the ureters are compressed and flattened, thus preventing regurgitation of urine and the chance of ascending infections. The narrowest parts of the bladder are at the pelviureteric region, when it begins. It is also narrow along the intramural course in the bladder. Furthermore, the ureter may kink at the pelvic brim. At these sites, there is the likelihood of
impaction of ureteric stones. In the Male In the male, the only structure that passes between the ureter and the peritoneum is the ductus deferens. The ureter lies lateral to this duct and enters the posterosuperior angle of the bladder, just superior to the seminal vesicle. In the Female In the female, the ureter descends on the lateral wall of the pelvis minor. Here it forms the posterior boundary of the ovarian fossa. As it descends, the ureter passes medial to the origin of the uterine artery. It continues to the level of the ischial spine. Here it is crosses superiorly by the uterine artery. It passes close to the lateral part of the fornix of the vagina, especially on the left side. Like in the male, the ureter enters the bladder at the posterosuperior angle. Back to top Blood Supply of the Ureters Click here to go to "The Blood Supply of the Abdomen and Pelvis." The blood supply is from the following
arteries: 1. The renal; 2. The abdominal aorta; 3. The gonadal; 4. The common iliac; 5. The internal iliac; 6. And the vesical and uterine arteries. Depending on the part of the ureter,
there is a different arterial supply. There are good longitudinal anastomoses between these vessels. The venous drainage follows a similar pattern to arterial supply. Innervation of the Ureters Click here to go to "The Innervation and Lymphatic Supply to the Abdomen and
Pelvis." This is through the ureteric plexus, which is derived from the renal, aortic, superior and inferior hypogastric plexuses. Ureteric supply is these is derived from- 1. Sympathetic: T10-12, L1; 2. Parasympathetic: S2-4. Afferent pain fibres pass back to T11, T12 and L1. Ureteric pain is severe and spasmodic (renal colic) and is referred to the groin, labia majora, scrotum and anterior thigh.