Urinary System

Human anatomy > Urinary System

The urinary system performs one of the major functions in the body: that of successfully eliminating the by-products or waste products of metabolism. These by-products of metabolism come from substances that enter our body through our mouth, nose, skin pores, or intravenous injections. These waste substances are usually acidic; and when not eliminated, they would cause acidosis, comma and then eventual death.  That is why one of the main functions of the kidneys is to maintain acid-base balance. The body’s ability to maintain internal balance is called homeostasis.

Urinary system

Parts of the Urinary System


The major excretory organ involved in the urinary system is the kidney.  There are two kidneys: the left and the right. Each kidney contains about 3 million nephrons, which can produce urine all by themselves. Nephrons are the functional units of the kidneys.  The nephron is composed of the Bowman’s capsule and the glomerulus, which filters the blood ultra filtrate.  The ultra filtrate then goes to the proximal convoluted tubules and then to the distal convoluted tubules where reabsorption of essential substances and the acidification of urine occurs.  All of the urine formed in the nephrons are then brought to the collecting duct and then to the ureters.

The Other Functions of the Kidneys Include:

  • Excretion, filtration or re-absorption of essential nutrients. These nutrients include electrolytes; namely, sodium, chloride, magnesium, and potassium.
  • Excretion or re-absorption of water.  This will depend on the state of hydration of the body and the amount of liquid intake.  If your body needs more water, the renal tubules will reabsorb more water.  
  • Re-absorption of glucose, which is the major monosaccharide in the body. Glucose is one of the main sources of energy.
  • Excretion of hydrogen ions or bicarbonates depending on the pH state of the blood. The pH is an indicator whether the blood is acidic or alkaline.  The normal pH is 7.35 to 7.45, which is slightly alkaline.  Any slight change in the normal blood pH will result to dire consequences, including death.
  • Excretion of urea, creatinine and other nitrogenous products of metabolism.


This is a tube-like part of the system that transfers the urine formed from the kidneys to the urinary bladder. There are also two ureters.


The bladder is an elastic organ that stores the urine formed until it is ready for micturation or urination. A normal bladder can contain about 1.5 to 3 liters of urine daily.


This part is responsible in finally excreting the urine out of the body during urination with the help of the sphincter.
Some Disease Conditions Associated with the Kidneys


Presence of stones such as calcium oxalates in the kidneys. This can impede normal urination and can even become severe such that surgeons have to remove the stones.

Nephrotic syndrome

This condition is characterized by proteinuria, the presence of large amounts of protein in urine.  This is an indication of kidney dysfunction.

Acute and Chronic Glomerulonephritis

The presence of glomerular tubulointerstitial fibrosis and urinary casts characterizes this pathologic condition.  The urine gives a positive result for protein. This condition can lead to more severe diseases, if left untreated.

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