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 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. It is brought about by reflex contraction of a special muscle called the detrusor muscle after voluntary relaxation of the sphincter muscle.
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.
Micturition is also known as voiding phase of bladder control and lasts for a short time. 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.
Also Read: Excretory Products and their Elimination
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 consists of two phases:
- Storage phase
- Voiding 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 close tightly around the opening of the bladder into the tube (urethra) that allows the passage of urine outside the body.
When the bladder is filled with urine, the nerves in it are triggered, which in turn stimulates the need 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
Frequently Asked Questions
1. What is Micturition?
Micturition is the process of urine excretion from the urinary bladder.
2. Write a brief note on the micturition process.
The micturition process contains two phases – the storage phase and the voiding phase.
3. What is the storage phase?
The storage phase is characterized by the storage of urine by the urinary bladder. The movement is controlled by the circular sphincter muscles.
4. What is the voiding phase?
The voiding phase is said to occur when the brain sends signals to begin urinating until the bladder becomes empty.
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