KidneysThe two organs that filter the blood and make urine. The right kidney sits lower than the left, pushed down by the liver.
Renal arteriesBranch directly from the aorta and bring blood to the kidneys. The right one passes behind the inferior vena cava.
Renal veinsReturn cleaned blood from the kidneys to the inferior vena cava. The left one crosses in front of the aorta.
Aorta (abdominal)The body's main artery, running down beside the vena cava. The renal arteries branch from it.
UretersTwo tubes that carry urine from the kidneys to the bladder.
Urinary bladderCollects urine from both ureters. It stretches a great deal: from nearly empty to 500 to 600 mL in an adult.
UrethraCarries urine from the bladder out of the body. It is the only urinary organ that differs much between males and females.
Organs and tubes: 4 1
Adrenal glandsOne sits on top of each kidney. Their cortex makes aldosterone, which acts on the kidney.
Blood vessels: 4 1
Inferior vena cavaThe large vein returning blood from the lower body to the heart. The renal veins drain into it.
Inside the bladder: 6 5
Detrusor muscleCrisscrossing bands of smooth muscle that make up the bladder wall. They contract to empty it.
TrigoneThe triangle at the base of the bladder. It lies between the two ureteral openings and the start of the urethra.
Ureteral openingsWhere the ureters open into the bladder. They form two corners of the trigone.
Internal urethral sphincterSmooth muscle round the start of the urethra. It is controlled involuntarily by the autonomic nervous system.
External urethral sphincterSkeletal muscle below the internal sphincter, under voluntary control.
How this list was compiled: Read 2026-09-26. OpenStax Anatomy and Physiology 2e, section 25.2 Gross Anatomy of Urine Transport, https://openstax.org/books/anatomy-and-physiology-2e/pages/25-2-gross-anatomy-of-urine-transport : the urethra carrying urine from the bladder out of the body, the only urologic organ with a significant difference between males and females; the trigone between the two ureteral openings and the start of the urethra; the involuntary internal urinary sphincter of smooth muscle and the voluntary external sphincter of skeletal muscle below it; the bladder collecting urine from both ureters, its detrusor muscle of crisscrossing smooth muscle bands, adult volumes from nearly zero to 500 to 600 mL, and an urge to void sensed at about 150 mL. Section 25.3 Gross Anatomy of the Kidney, https://openstax.org/books/anatomy-and-physiology-2e/pages/25-3-gross-anatomy-of-the-kidney : the right kidney lower than the left because of the liver; the adrenal gland on each kidney, its cortex making aldosterone; renal arteries from the aorta and renal veins to the inferior vena cava. Wikipedia, Renal artery, https://en.wikipedia.org/wiki/Renal_artery : the right renal artery passes behind the inferior vena cava; Wikipedia, Renal vein, https://en.wikipedia.org/wiki/Renal_vein : the left renal vein passes through the angle with the abdominal aorta behind it and the superior mesenteric artery in front. Licence: own work
The drawing: Drawn for this site on 2026-10-05 by script. Our own drawing, nothing traced. The kidneys, adrenal glands, great vessels, renal vessels and ureters were laid out by eye after a public domain plate in Henry Gray, Anatomy of the Human Body (20th US edition, 1918), fig. 531, the abdominal aorta and its branches (https://commons.wikimedia.org/wiki/File:Gray531.png), and the opened bladder after fig. 1140, the interior of the bladder (https://commons.wikimedia.org/wiki/File:Gray1140.png). A plan, not to scale: the trunk is shortened so the bladder sits close under the kidneys, the kidneys are set wider apart than in the body, and the great vessels are cut short above the bladder. The ureters are drawn reaching the bladder high on its sides; in the body they reach it low at the back and run slantwise through the wall. The funnel where each ureter begins (the renal pelvis) hardly shows. Licence: own work
How it works
A urinary system diagram labeled with 14 parts, seen from the front: the kidneys and their blood supply, the ureters, and the bladder drawn cut open down to the urethra. Start with the 7 main parts.
Read the full guide
From kidney to bladder
The kidneys make urine from the blood that the renal arteries bring from the aorta; the renal veins take it back to the inferior vena cava. The ureters carry urine down to the bladder.
Inside the bladder
The detrusor muscle forms the wall. On the floor, the two ureteral openings and the start of the urethra mark the corners of the trigone. Two sphincters guard the urethra: the internal one is involuntary, the external one voluntary.
The drawing faces you: the body's right kidney is on your left, and it sits lower because the liver is above it.
Questions and answers
What are the main organs of the urinary system?
The two kidneys, which make urine; the two ureters, which carry it down; the urinary bladder, which stores it; and the urethra, which carries it out of the body.
How much urine can the bladder hold?
In an adult, from nearly nothing up to about 500 to 600 mL. The urge to go is usually felt at around 150 mL.
What is the trigone of the bladder?
The triangle on the floor of the bladder, with the two ureteral openings and the start of the urethra at its corners.