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Chapter: Anatomy and Physiology for Health Professionals: Urinary System

The urinary system is made up of kidneys, ureters, urinary bladder, and urethra.


The urinary system is made up of kidneys, ureters, urinary bladder, and urethra. The kidneys maintain homeostasis by removing metabolic wastes from the blood and excreting them. They are made up of an outer cortex and an inner medulla. The nephron is the functional unit of the kidney. There are about one million nephrons in each kidney. Nephrons remove wastes from blood and regulate water and electrolyte concentrations, with urine as the end product.

Urine is about 95% water and, also usually contains­ urea and uric acid. Glomerular filtration initiates urine formation in the renal corpuscle. The GFR is the ­volume of filtrate that forms every minute via the actions of the kidneys’ glomeruli. Urine formation is also influ-enced by tubular reabsorption and tubular secretion. Tubular reabsorption selectively moves substances from the tubular fluid into the blood. Tubular secretion selec-tively moves substances from the blood in the peritubu-lar capillary via the filtrate into the renal tubule.

The other primary structures of the urinary sys-tem include the ureters, urinary bladder, and urethra. The ureters connect each renal pelvis to the urinary bladder. The urinary bladder stores urine and forces it through the urethra during micturition, which is the act of expelling urine. The urethra conveys urine from the urinary bladder to outside the body.

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