The Urinary System

How your body disposes of liquid waste.

Antidiuretic hormone
Up to 500 milliliters (17oz)
Maintaining a stable pH
Kidney stones
Decrease in size and function

Overview of the Urinary System

The urinary system is a vital component of human physiology, responsible for filtering waste products and excess substances from the bloodstream, maintaining fluid and electrolyte balance, and regulating blood pressure. Comprised of the kidneys, renal pelvis, ureters, bladder, and urethra, the renal system works in concert to ensure the proper functioning of our bodies.


The kidneys, in particular, play a crucial role in filtering blood and producing urine, which is then transported through the renal pelvis and ureters to the bladder for storage. Every day, your kidneys filter about 120 to 150 quarts of blood to remove wastes and balance fluids. This process produces about 1 to 2 quarts of urine per day. Finally, the urethra serves as the exit point for urine to be expelled from the body.

Anatomy of the Kidneys

Building upon the importance of the kidneys in the urinary system, these bean-shaped organs are composed of millions of functional units called nephrons. Nephrons are responsible for filtering blood and producing urine through a complex network of blood vessels.


Each nephron contains a glomerulus, a cluster of capillaries that filters blood, and a tubule, which reabsorbs and secretes substances to form urine. Blood vessels, such as the renal artery and renal vein, supply the kidneys with blood and remove filtered blood, respectively. Understanding the intricate structure of the kidneys is essential to grasping the process of urine formation. Although your kidneys pump more than 50 gallons of blood per day and ar a crucial part of the urinary system, you only need one to survive.

Urine Formation

The process of urine formation is a three-step procedure involving filtration, reabsorption, and secretion. Filtration occurs in the glomerulus, where blood pressure forces water, ions, and small molecules out of the blood and into the nephron’s tubule.


Reabsorption is the next step, where essential substances like glucose, amino acids, and water are reabsorbed back into the bloodstream through the tubule’s walls. Urine is made up of 95% water. The rest is 2.5% urea and 2.5% salts, minerals, and other enzymes produced during normal body processes.

Finally, secretion involves the active transport of waste products and excess ions from the blood into the tubule, ultimately forming urine. This intricate process ensures that our bodies maintain proper fluid balance and eliminate waste efficiently.

Regulation of Urine Concentration

The regulation of urine concentration and volume is crucial for maintaining homeostasis within the body. Hormones such as Antidiuretic hormone (ADH), Aldosterone, and the renin-angiotensin-aldosterone system (RAAS) play key roles in this process.


ADH, released by the pituitary gland, increases water reabsorption in the kidneys, leading to more concentrated urine. Aldosterone, produced by the adrenal glands, regulates sodium and potassium levels, influencing urine concentration. The RAAS system helps regulate blood pressure and fluid balance by adjusting the constriction of blood vessels and the release of aldosterone. Proper regulation of urine concentration and volume is essential for maintaining overall health and preventing dehydration or fluid overload.

Anatomy of the Urinary Tract

The urinary tract consists of the ureters, bladder, and urethra, which work together to transport, store, and expel urine from the body. The ureters are muscular tubes that propel urine from the renal pelvis of the kidneys to the bladder. The bladder, a hollow muscular organ, stores urine until it is full, typically holding up to 500 milliliters (17oz). The urethra, a tube extending from the bladder to the outside of the body, allows for the expulsion of urine during the process of micturition.


Micturition, or urination, is the process by which the bladder empties and urine is expelled from the body. This process is regulated by the coordination of the nervous system and the muscles of the bladder and urethra. Micturition begins when the bladder fills with urine, causing stretch receptors in the bladder wall to send signals to the brain. In response, the brain signals the detrusor muscle of the bladder to contract and the internal and external urethral sphincters to relax, allowing urine to flow through the urethra and out of the body.


The urinary system plays a critical role in maintaining fluid and electrolyte balance within the body. By regulating the amount of water and ions reabsorbed or secreted during urine formation, the kidneys help ensure that the body maintains the proper balance of fluids and electrolytes. This balance is essential for maintaining blood pressure, nerve function, and muscle function, among other physiological processes.


In addition to fluid and electrolyte balance, the urinary system is also responsible for maintaining acid-base balance in the body. The kidneys help regulate blood pH by excreting hydrogen ions and reabsorbing bicarbonate ions during urine formation. This process ensures that the body maintains a stable pH, which is crucial for proper enzyme function, cellular metabolism, and overall health. Acid-base balance is essential for maintaining the optimal functioning of our physiological processes.

Urinary Disorders


The urinary system, like any other system in the body, can be affected by various disorders. Common urinary disorders include kidney stones, which are hard deposits of minerals and salts that form in the kidneys and can cause severe pain when passing through the urinary tract.

Urinary tract infections (UTIs) are another common issue, often caused by bacteria entering the urethra and traveling up to the bladder, leading to inflammation and discomfort. Early detection and treatment of these disorders are crucial for maintaining overall health and preventing complications.

Urinary System and Aging

As we age, the urinary system undergoes various changes that can affect its function. The kidneys may decrease in size and function, leading to a reduced ability to filter waste products and maintain fluid balance.


The bladder’s capacity may also decrease, and the muscles controlling micturition may weaken, resulting in more frequent urination or difficulty emptying the bladder completely. These age-related changes can increase the risk of urinary disorders and complications, making it essential to monitor and maintain urinary health throughout our lives.

You will forget 90% of this article in 7 days.

Download Kinnu to have fun learning, broaden your horizons, and remember what you read. Forever.

You might also like

Introduction to Human Physiology;

What human physiology is - and why it matters.

The Endocrine System;

The system that governs all hormonal activity.

The Cardiovascular System;

Your body's way of getting oxygen to where it's needed.

The Musculoskeletal System;

The interlinked system of muscles and skeletons that holds us all together.

The Respiratory System;

The system built around the exchange of gases.

The Nervous System;

The system governing sensation and neural communications.

Leave a Reply

Your email address will not be published. Required fields are marked *