Micturition - The Process Of Urination

Excretion is a life process which is as important as nutrition. In animals, including humans, as a part of metabolism, many waste products are produced. Animals excrete them in different forms, such as urine, sweat, faeces, and tears. Among these, the usual form of excreta, urine, is produced and discarded from our body as fluid. Let us explore the different stages of micturition and its physiology.

Micturition Meaning

“Micturition is the process of discharging urine from the urinary bladder.” 

What is Micturition?

Micturition is a process where urine is expelled from the body. Animals and humans have a specialised system of organs known as the excretory system to eliminate the waste products from the body. In other words, the process of expelling urine from the body is called micturition.

The human excretory system consists of a pair of kidneys and ureters, a urinary bladder, and a urethra. The kidneys play a major role in the process of urine formation and its excretion. The urine formed is stored in the urinary bladder.

As the bladder becomes full, the stretch receptors increase their firing rate. This increase the urge to urinate and causes micturition reflex. It sometimes even causes involuntary urination. Micturition is also termed as the voiding phase to expel the stored urine.

Also Read: Excretory Products and their Elimination

Human Urine

On average, a normal adult excretes 1 to 1.5 L of urine per day. Normal human urine is a light yellow fluid majorly consisting of 95 per cent water and 5 per cent solid wastes. It is slightly acidic with a pH close to 6.

Many endocrinal disorders can be diagnosed through urine analysis. For example, if a patient has diabetes, the presence of glucose and ketone bodies in the urine can help detect the disease. Thus it is a major clinical diagnostic element.

Also Refer: Urine Formation And Osmoregulation

Micturition Process

Micturition process consists of two phases:

• Storage phase
• Voiding phase

Storage Phase

The urinary bladder is a balloon-shaped, hollow, muscular, organ that acts as the storage organ for urine. The urinary bladder in a healthy urinary system can store up to 16 ounces of urine for 2 to 5 hours easily. The circular sphincter muscles prevent leakage of urine. They tightly close around the opening of the bladder into the urethra, that allows the passage of urine outside the body.

Voiding Phase

When the bladder is filled with urine, the nerves in it are triggered and there is an urge to urinate. The brain signals urinary bladder to contract. The receptors of the urinary bladder send a signal to the central nervous system, in response to which the nervous system sends a signal that incites the contraction of the urinary bladder.  Through the urinary opening at the urethra, the urine is eliminated, and the process is called micturition. The neural mechanism involved is called the micturition reflex.

Also Read: Urine Infection Symptoms

Problems Associated With Micturition

There are several factors which affect the process of micturition. Some of these can be due to physical trauma or disease; others are psychological in nature. Following are a few disorders that affect micturition:

• Detrusor Instability – This is a condition where the detrusor muscle contracts without any apparent reason. This muscle is responsible for contracting the bladder and help with the micturition process. As a result, detrusor instability results in urinary incontinence.
• Urinary Retention – This condition is characterized by the inability to empty the bladder completely. The onset may be gradual or sudden. The causes can range from a blockage in the urethra, nerve problems and weak bladder muscles.
• Spinal Cord Trauma – Injuries to the spinal cord, specifically the tenth thoracic vertebra (T10) can cause the bladder to be overactive or cause urinary incontinence.

Management of Micturition Disorders

• The nerve pathway to the urinary tract should be intact.
• The bladder capacity should be normal.
• Normal muscle tone should be observed in the sphincters, detrusors, and pelvic floor muscles.
• There should be no obstruction to the urine flow in any region of the urinary tract.
• The environmental and psychological factors that inhibit micturition should be absent.
• The coordinated activity of sympathetic, parasympathetic, and somatic nerves help in normal micturition.

Key Points on Micturition

• Urine is collected in the nephrons and flows into the ureters.
• The smooth muscle contractions of ureters facilitate micturition.
• The urine is stored in a hollow, muscular, elastic organ known as the urinary bladder.
• The urine flows out of the body through the urethra.

Also Read: Test for the presence of Sugar in Urine