Micturition – Class 11 | Chapter – 19 | Biology Short Notes Series PDF

Micturition: It is the process of discharging Urine from the human body. Human beings and animals have a specialized organ system for the discharge of Urine from the body. Urine is expelled from the urinary bladder through the urethra( in the penis in males, and directly in females) by the relaxing of the sphincter muscles located at the opening of the urinary bladder into the urethra under the impulse from the nervous system.  It also happens by relaxation of detrusor muscles after the voluntary relaxation of the sphincter muscles such a process is called Micturition.

Human beings and animals have an organized urinary system that consists of two kidneys ( right and left kidney located on either side of the backbone and protected by the last rib ), ureter, urinary bladder, sphincter muscles, and urethra.

Micturition is also known as the voiding phase of the bladder. It lasts for a short time, and as the bladder stretches, its firing rate increases and this increases the urge for urination and sometimes Micturition relaxation; thus it is sometimes called involuntary Micturition or involuntary urination.

Physical Properties of Micturition

Urine has a yellowish color ( due to the presence of urochrome ), and also the color varies with different diets. A healthy human being urinates around 1 to 1.5 liters per day of Urine but also varies with various conditions. Urine has a pH scale value between 5 to 8, i.e. it is slightly acidic ( pH scale value = 6) protein diet makes it acidic while vegetable diet makes it alkaline and on standing the smell of Urine becomes strong, ammonium like due to bacterial activities otherwise faint smell and its specific gravity is 1.003 to 1.035

Process of Micturition

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.

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.

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By Team Learning Mantras