Urinary System Overview

Study Notes

The urinary system's primary function is to cleanse the blood of metabolic wastes and remove them in urine.
It consists of six main organs: two kidneys, two ureters, the urinary bladder, and the urethra.
Kidneys are located in the upper part of the posterior abdominal wall, on either side of the vertebral column.
The right kidney is positioned at the level of T12 to L3, while the left kidney is located at the level of T11 to L2. The left kidney is situated higher than the right.
The hilum renale is a fissure on the kidneys' medial surface where structures enter and exit the organ, approximately at the level of the L1 vertebra.
Kidneys are composed of functional units called nephrons. Each kidney contains over 1 million nephrons.
Urine formation involves three stages: filtration, reabsorption, and excretion.
Filtration is the passage of plasma fluid from the glomerulus to the glomerular capsule at a rate of 120 mL/min.
Reabsorption is the active and passive transport of beneficial substances (water, glucose, electrolytes) back into the bloodstream.
Excretion is the transfer of metabolic waste products from the capillaries to the tubules forming urine.

The bladder serves as a reservoir for urine.
It is located behind the symphysis pubis.
In females, it is anterior to the uterus and in males, it is anterior to the rectum.
The normal capacity of the bladder is roughly 220 mL but can hold up to 500 ml.
An empty bladder sits within the pelvis minor, but when full, it can extend up to the level of the umbilicus.

The urethra is a tube that expels urine from the bladder.
In males, it is 20-25 cm long.
In females, it is approximately 3-5 cm long.
The urethra includes the internal and external sphincter muscles, which control urine release.

Renal artery delivers blood to the kidneys. It branches into increasingly smaller segments of arteries.
The renal vein carries blood from kidneys toward the inferior vena cava. This vein receives blood from renal capillaries within the urinary system
The blood vessels within the nephron play essential roles in filtration and reabsorption processes.

The kidney segments are composed of medulla (inner part) and cortex (outer part).
Blood filtration occurs in nephrons located in the cortex.
The medulla contains renal pyramids and minor and major calyxes.
Collecting ducts in the medulla lead to renal pelvis and ureter.