Urinary System 101

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Eleven different systems make up the human body and must work together to maintain health. The urinary system is one of these.

The urinary system, also known as the renal system, consists of all the organs involved in the formation and urine release. These are the kidneys, ureters, bladder, and urethra. Waste products from the metabolism of the food we eat must be removed from the body. When urine is formed in the kidneys, the tubes called ureters transport it to the urinary bladder, where it is stored and excreted via the urethra. The endocrine system regulates this system through hormones, including antidiuretic hormone, aldosterone, and parathyroid hormone. (1)

Front view of urinary tract, image courtesy of Hopkins Medicine (5)

The main functions of the urinary system include:

  • Remove waste products and medicines from the body
  • Balance the body’s fluids and regulate blood volume
  • Balance electrolytes and metabolites including sodium, potassium, calcium
  • Release hormone renin to control blood pressure
  • Release hormone erythropoietin to control red blood cell production in bone marrow
  • Regulate the acid-base balance and blood pH
  • Help synthesize calcitriol, the active form of vitamin D


The kidneys are two bean-shaped organs, each about a fist’s size towards the abdomen’s back. They are located just below the rib cage, one on each side of the spine. Each kidney consists of an outer renal cortex where blood is filtered and an inner renal medulla where urine formation occurs. The renal arteries and veins feed the kidneys an extensive blood supply.

Healthy kidneys filter about a half cup of blood every minute, removing wastes and extra water to make urine.  Average adult urine production is about 30-70 ounces per day, depending on the state of hydration, activity level, environmental factors, weight, and the individual’s health. Urine produced is also influenced by water loss from perspiration and breathing, diuretics, medications, and beverages like water, coffee, and alcohol. (1)

The renal cortex contains many nephrons, which act as filtering units. Each nephron is supplied by a ball of small blood capillaries called glomeruli that produce a mixture that is the precursor of urine. This mixture then passes through more tubules where water, salt, and nutrients are reabsorbed and then collected in the medulla.

Hydrostatic and osmotic pressure gradients facilitate the filtration process. Larger molecules such as proteins and blood cells are prevented from passing through the membrane. The amount of filtrate produced every minute is called the glomerular filtration rate and amounts to about 6000 ounces per day. Typically 99% of this filtrate is reabsorbed as it passes through the nephron and the remaining 1% becomes urine. (2)


The ureters are 10-12 inch long tubes lined with smooth muscle that carries the urine to the bladder. The ureters’ muscular tissue helps force urine downwards where they enter the bladder at an angle, so urine does not flow up the wrong way.


The bladder is a triangular-shaped hollow muscular organ whose primary function is to store urine. It releases it into the urethra under the appropriate signals, which carry the urine out of the body. The bladder has three openings: two for the ureters and one for the urethra. Small amounts of urine are emptied into the bladder from the ureters about every 10 to 15 seconds.

A healthy adult bladder can store up to two cups of urine for two to five hours. When we need to urinate, stretch receptors in the bladder are activated, which send signals to our brain and tell us that the bladder is full. (1)


The urethra is a smooth muscle tube that allows urine to pass from the bladder out of the body. The male urethra is 7-8 inches long, running from the bladder to the tip of the penis. The female urethra is 2-3 inches long, running from the bladder into an external hole located at the top of the vaginal opening. (1)

Urine Examination 

Observing and testing a person’s urine can evaluate the health of the urinary tract system.


  • Normal, healthy urine is a pale straw or transparent yellow color.
  • Darker yellow or honey-colored urine means you need more water.
  • A darker, brownish color may indicate a liver problem or severe dehydration.
  • Pinkish or red urine may mean blood in the urine. 


Substances that cause cloudiness but that are not considered unhealthy include mucus, sperm, prostatic fluid, cells from the skin, normal urine crystals, and contaminants such as body lotions and powders. Other substances that can make urine cloudy, like red blood cells, white blood cells, or bacteria, indicate a condition that requires attention.


Tests of urine detect and measure several substances that are byproducts of normal and abnormal metabolism.

  • Specific Gravity: the amount of dissolved substances compared to pure water
  • Protein: no or a small amount is normal
  • pH: slightly acidic ranging from 4.5-8.0 
  • Glucose:  negative
  • Ketones:  negative, trace from low-carb diets
  • Nitrites:  negative, positive usually indicates a bacterial infection
  • Microscopic exam:  reveals WBC, RBC, epithelial, bacteria, yeast, crystals (3)

Glomerular Filtration Rate

Glomerular Filtration Rate, or GFR, is a simple blood test. The lower the GFR, the more damage your kidneys have. 

Kidney Problems and Abnormalities 

Kidney stones are clumps of minerals and salts, mostly calcium oxalate and uric acid, that can be found anywhere in the urinary tract. High oxalate diet, excess body weight, some medical conditions, and certain supplements and medications are among the many causes of kidney stones. (4)

Urinary tract infections can affect the urethra, bladder, or even the kidneys. According to the American Urological Association, about 8.1 million people have a urinary tract infection each year— mainly women due to their shorter urethras.

Incontinence means a person leaks urine by accident.  According to the National Institute on Aging, older people are more common, especially women, often due to a weakened bladder or urethra muscle control. In men, it is usually due to an enlarged prostate causing pressure on the bladder.

The urinary system is a complex but important aspect of human anatomy. There are so many ways to care for our bodies and help them thrive through a long and healthy life. A healthy diet, proper hydration, and regular checkups from your doctor can all support this vital system. 


  1. Ameerally P., “Anatomy.” UK: Harcourt Publishers Ltd; 2000 https://healthengine.com.au/info/urinary-system-renal-system   
  2. Default – Stanford Children’s Health. Stanfordchildrens.org. https://www.stanfordchildrens.org/en/topic/default?id=anatomy-of-the-urinary-system-85-P01468  Published 2021. 
  3. Lerma E., “Urinalysis.” Medscape Reference, December 16, 2015. http://emedicine.medscape.com/article/2074001-overview#a 
  4. Tefekli, Ahmet; Cezayirli, Fatin (2013). “The History of Urinary Stones: In Parallel with Civilization.” The Scientific World Journal. 2013: 423964. doi:10.1155/2013/423964. PMC 3856162. PMID 24348156
  5. Diagram of Urinary System: https://www.hopkinsmedicine.org/health/wellness-and-prevention/anatomy-of-the-urinary-system 

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