The urinary bladder serves as a temporary reservoir for urine. It’s in the pelvic cavity, below the parietal peritoneum and posterior to the symphysis pubis. The size and shape of the urinary bladder change depending on how much urine it contains and how much pressure it receives from surrounding organs.

The inner lining of the urinary bladder is a transitional epithelial mucous membrane that is continuous with that of the ureters. The mucosa has numerous folds called rugae when the bladder is empty. As the bladder fills, the rugae and transitional epithelium allow it to expand.

Reference:
Urinary bladder. (n.d.). Welcome to SEER Training | SEER Training. https://training.seer.cancer.gov/anatomy/urinary/components/bladder.html

The urethra transports urine from the urinary bladder to the outside via the external urethral meatus. It also serves as a conduit for sperm in males. The urethra epithelium is derived from the urogenital sinus, which is formed when the endodermal cloaca divides into the rectum dorsally and the urogenital sinus ventrally, separated by the urorectal septum.1

In females, the urethra epithelium is derived from the urogenital sinus endoderm, whereas the surrounding connective tissue and smooth muscle are derived from splanchnic mesenchyme.

Reference:
Reuter, V. E., & Al-Ahmadie, H. A. (2020). Urethra. Science Direct. https://www.sciencedirect.com/topics/medicine-and-dentistry/urethra

The kidneys are the urinary system’s primary organs. The kidneys are the organs responsible for filtering the blood, removing wastes, and excreting wastes in the urine. They are the organs that perform urinary system functions.

Each kidney is held in place by connective tissue called renal fascia and is protected by a thick layer of adipose tissue called perirenal fat.

Reference:
Kidneys. (n.d.). Welcome to SEER Training | SEER Training. https://training.seer.cancer.gov/anatomy/urinary/components/kidney.html