Urinary System: Kidneys, Bladder, and Ureters
Urinary System
Composed of the kidneys (urine-forming organs) and their means of disposal (calyces, renal pelvis, ureter, bladder, and urethra).
Kidneys
They are located in the abdominal cavity, supported on the posterior abdominal wall in its most superior part. The abdominal wall is formed by the psoas and the quadratus lumborum muscles (one behind the other) from the last rib to the iliac crest. These two muscles form the posterior abdominal wall, and both kidneys rely on them at the top. They are retroperitoneal viscera applied to the posterior abdominal wall. Kidneys are located on either side of the spine at the height of the last thoracic vertebra and the first two lumbar vertebrae. They have a height of ten to twelve centimeters and are protected by the last two ribs. The top of the kidneys is associated with the diaphragm muscle. Separating both kidneys are the aorta and inferior vena cava.
Kidneys have a front and back which are separated by two edges: internal and external. The inner edge is concave, with its middle part having a ditch called the renal sinus. The outer edge is larger and convex. The structures entering and leaving the renal sinus are the renal hilum. The right kidney is slightly lower than the left.
For the posterior, kidneys are related: above the diaphragm. In front, the right kidney is related to the liver, with the right angle of the colon and with the mobile loops of the small intestine (jejunum-ileum). The left kidney is related to the spleen, the left angle of the colon, stomach and part of the pancreas (the tail). At the upper pole of the kidneys, is a ductless gland: the adrenal gland, which is like a cap on each kidney. The kidney is enveloped by a fibrous capsule called the capsule itself. Outside of it, we find a rich layer of adipose tissue: the adipose capsule, which is most abundant from behind and out. That fat capsule, when the individual is thin, also thins. There is another capsule called the perirenal fascia that is left open on the inside and bottom.
Structure of the Kidneys
If we take a frontal section, we distinguish two parts in the renal parenchyma: the peripheral renal cortex, which is pale, and the inner medulla, which is the more central, darker part. In that part, it is observed what would correspond to the lobes of the kidney-shaped pyramids.
Renal pyramids, there are five to twelve in each kidney and its apex. In the renal sinus protrudes the renal papilla. At the apex of the pyramids begins the process of excretion, and urine will be collected by short membranous tubes: the minor calyces that, to accommodate the papilla, are concave-edged. These tubes are fused and form collecting ducts (major calyces). In turn, several major calyces end up together and form an enlargement called the renal pelvis, like a funnel that will collect urine. Then it narrows to form the ureter, which is a very narrow tube that will be retroperitoneal. The ureter has a very long journey: it goes down on the front of the psoas and will pass the division of the iliac vessels (external and internal) common iliac vein and common iliac artery. After that, it reaches the bladder through the back.
The Bladder
The bladder is a musculo-membranous deposit that can change greatly whether it is empty or full. It is located behind the pubic symphysis. With regard to the peritoneum, the bladder is a subperitoneal organ, and therefore the last portion of the ureter is also subperitoneal. In men, behind the urinary bladder, it is related to the vas deferens, seminal vesicle, and rectum. In women, the bladder is related to the cervix and the vagina. Below, the apex of the bladder ends in a tube called the urethra.
The Urethra
The female urethra is short, measuring three or four centimeters, is directed downward and forward, and opens in the vulva between the labia minora. In men, the urethra is longer, measuring about seventeen centimeters, and is the terminal route of the genital tract.