Steps and Neural Control of the Micturition Reflex
Excretion is the process of removal of chemical wastes( mainly nitrogenous wastes) from the body. It plays a vital role in maintaining the Homeostatic( steady-state) condition of the body and organs concerned with the formation, storage and elimination of Urine constitute are " excretory system " (the urinary system is more appropriate than the excretory system for the removal of nitrogenous wastes product).
Bladder voiding is another name for this action. Humans have two kidneys, two ureters, a urinary bladder, and a urethra as part of their excretory system.
The Urine is filtered by the kidneys and carried to the bladder via the ureters, where it is stored until it is expelled. The neurological system, as well as the muscles of the bladder and urethra, control the Micturition process. Before excreting pee, the urinary bladder can retain 350-400ml of Urine.
Micturition Meaning:
It's the process of discharging Urine from the urinary bladder along the urinary tract from the body.
What is Micturition?
Micturition 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.
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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
Chemical Composition of Urine
The normal human Urine consists of about 95% of water and 5% solid wastes dissolved in it. The percentage of solid waste may slightly vary according to the food taken and the time after taking food. Still, usually, these are approximately ( in grams per liter in Urine) as follows:
Besides the normal constituents, the Urine may pass out specific hormones and also certain medicines like antibiotics and excess vitamins.
Micturition Process
The Micturition process is divided into two steps or phases:
Resting or Filling Stage
The Urine contained in the urinary bladder ( it acts as the primary storage organ ) is a balloon-shaped, hollow, muscular organ. A healthy urinary bladder can hold up to 16 ounces of Urine for 2 to 5 hours easily, and there opening is tightly closed by sphincter muscles which also prevents the leakage of Urine from the urinary bladder, and sphincter muscles facilitate the center of Urine from the urinary bladder into ureter that allows the Urine to pass outside the body.
During this phase of the bladder, Urine travels from the kidneys to the bladder via the ureters. The ureters are narrow muscular tubes that stretch downhill from each kidney and obliquely enter the bladder.
The ureters' oblique placement in the bladder wall serves as an important function. The ureter's passage into the Urine bladder is protected by no sphincters or muscles. As a result of the oblique shape of the hole, Urine cannot re-enter the ureters. The detrusor muscle, the urinary bladder's main muscle, relaxes at the same moment, allowing the bladder to expand and accommodate more Urine.
Voiding Stage
Both the urinary bladder and the urethra are involved during this stage. Whenever the Urine is filled in the urinary bladder, it triggers the muscles and nerves, which in turn stimulates the need for urination, and the brain signals the urinary bladder to contract. The responses sent to the central nervous system by nerves in the urinary bladder encouraged by the filling of Urine in the urinary bladder and the answer sent back by the central nervous system to nerves in the urinary bladder signals the incitement of the contraction of the urinary bladder. Through the opening of the urinary bladder into the ureter and the Urine is eliminated and the process is called Micturition, and the neural mechanism involved is called the Micturition reflex.
The internal and external urethral sphincters are two muscles that govern the urethra. The internal sphincter is made up of smooth muscles, whereas the external sphincter is made up of skeletal muscles. During the filling stage, both of these sphincters are contracted.
Potential Problems of Micturition
Disturbances of the bladder's storage function and disturbances of the bladder's emptying function are the two types of Micturition disorders. Frequency, urgency, and incontinence are the most common signs of storage function problems. There are many diseases related to the Micturition process, and some of them are due to physical trauma or another physiological illness, and urination problems include initiating urination and bladder impairing bladder encrypting and urination inconvenience. A few of the diseased mentioned :
Detrusor Instability
It is a problem caused by which detrusor muscles contract without any reason. The muscles are responsible for the contraction of the urinary bladder and help in the processes of Micturition thus resulting is that it causes urination inconvenience.
In neurologically normal patients, detrusor instability is a common cause of urgency and urge incontinence. While the patient is striving to suppress Micturition, an involuntary phasic detrusor contraction of any pressure linked with urge or leakage is characterized.
Urinary Retention
It is a problem in which the inability to urinate completely occurs and the onset may occur suddenly or gradually, and the cause can be urethra blockage nerve problem and weak bladder muscles.
Your bladder does not empty entirely or at all when you urinate. Urinary retention is the medical term for this condition. Urinary retention is classified as either acute (sudden) or chronic (long-term) (long-term). Acute refers to something that happens quickly and can be dangerous. You've had chronic Urine retention for a long time if you have it.
Spinal Cord Trauma
Urinary incontinence or overactivity of the bladder can be caused by spinal cord injuries, particularly those to the tenth thoracic vertebra (T10).
Stroke, Alzheimer's disease, and other conditions in which nerve pathways to and from the spine and brain are blocked or injured are examples of neurological disorders. Acetylcholine (ACh), a neurotransmitter, is involved in the relaying of nerve signals during Micturition. ACh can be blocked with the drug atropine, causing the detrusor muscle to contract and Urine retention.
Incontinence due to stress can occur at any age. It happens when the abdominal pressure rises, such as when sneezing or coughing. When abdominal pressure rises slightly, the normally acute angle between the bladder and urethra is lost, causing pressure in the bladder to rise.
Incontinence occurs as a result of muscle laxity and weakness at the bladder neck, around the urethra, and in the pelvic floor, with relatively minor pressure changes. Stress incontinence can occur in men after a prostatectomy, as well as in women after childbirth and during menopause due to reduced oestrogen secretions (McLaren, 1996).
Urine flow can be obstructed by renal stones, inflammation, or an enlarged prostate gland, resulting in frequent Micturition and Urine retention. Bladder tumours and pregnancy both reduce normal bladder capacity.
Micturition Problem Management
The factors in the environment that inhibit the Micturition should be absent.
For a normal Micturition the coordination of the parasympathetic, sympathetic, and somatic nerve as they help in the Micturition process
The capacity of the bladder to hold Urine should remain the same and regular.
Sphincters, detrusor, and pelvic muscles should have normal muscle tone and functioning.
In any region of the urinary bladder and urinary tract, there should be no obstruction.
Key Points in Micturition
Urine is created and collected in nephron or uriniferous tubule (in the kidney) and flows into the ureter
Ureter muscle facilitation of the smooth muscle contraction
The Urine is stored in a hollow, elastic, and muscular organ of the urinary bladder
The Urine flows out through the urethra
The Urine carries out waste from the body(mainly nitrogenous wastes if stored in the body may be very harmful and may even cause death )
FAQs on Micturition Process in Humans
1. What is the micturition process?
The micturition process is the physiological mechanism by which urine is expelled from the urinary bladder through the urethra. It involves coordinated activity of the bladder muscles and sphincters to store and then release urine.
- Urine is produced in the kidneys and transported to the bladder via the ureters.
- The urinary bladder stores urine temporarily.
- Urine is expelled through the urethra during urination.
2. How does the micturition reflex work?
The micturition reflex is a spinal reflex that triggers bladder contraction when it becomes filled with urine. It is initiated by stretch receptors in the bladder wall.
- As the bladder fills, stretch receptors in the wall are activated.
- Sensory impulses travel to the sacral spinal cord (S2–S4).
- Motor signals return via parasympathetic nerves.
- The detrusor muscle contracts and the internal sphincter relaxes.
3. What is the role of the detrusor muscle in micturition?
The detrusor muscle is the smooth muscle of the urinary bladder responsible for contracting to expel urine. Its coordinated contraction increases bladder pressure during urination.
- It remains relaxed during urine storage.
- It contracts under parasympathetic stimulation during voiding.
- Its contraction pushes urine toward the urethra.
4. What is the difference between voluntary and involuntary control of micturition?
Voluntary control of micturition involves conscious regulation of urination, while involuntary control is governed by spinal reflexes. Both systems work together for normal bladder function.
- Involuntary control: Mediated by the spinal micturition reflex and parasympathetic nerves.
- Voluntary control: Controlled by the cerebral cortex and external urethral sphincter.
- The external urethral sphincter is made of skeletal muscle and can be consciously controlled.
5. What are the stages of the micturition process?
The micturition process occurs in two main stages: urine storage and urine voiding. These stages involve coordinated muscular and neural mechanisms.
- 1. Storage phase: The bladder relaxes, and both sphincters remain contracted.
- 2. Voiding phase: The detrusor muscle contracts, and sphincters relax.
6. Which nerves are involved in the control of micturition?
Micturition is controlled by parasympathetic, sympathetic, and somatic nerves that regulate bladder and sphincter activity. These nerves coordinate storage and release of urine.
- Parasympathetic nerves (S2–S4): Stimulate detrusor contraction.
- Sympathetic nerves (T11–L2): Promote bladder relaxation and internal sphincter contraction.
- Pudendal nerve: Controls the external urethral sphincter voluntarily.
7. What is the function of the urinary bladder in micturition?
The urinary bladder functions as a temporary reservoir that stores urine until it is expelled during micturition. It is a hollow, muscular organ located in the pelvic cavity.
- It can expand due to its elastic walls.
- It contains the detrusor muscle for contraction.
- It signals fullness through stretch receptors.
8. What is the role of the urethral sphincters in urination?
The urethral sphincters regulate the release of urine by controlling the opening of the urethra. There are two sphincters with different control mechanisms.
- Internal urethral sphincter: Smooth muscle, involuntary control.
- External urethral sphincter: Skeletal muscle, voluntary control.
9. At what bladder volume does the urge to urinate begin?
The urge to urinate usually begins when the bladder contains about 150–200 mL of urine. This sensation is caused by activation of stretch receptors in the bladder wall.
- Mild urge: Around 150–200 mL.
- Strong urge: Around 300–400 mL.
- Maximum capacity: About 400–600 mL in adults.
10. Why is micturition important for the body?
Micturition is important because it eliminates metabolic wastes and helps maintain fluid and electrolyte balance in the body. It is the final step of the urinary system function.
- Removes urea, creatinine, and excess salts.
- Maintains osmotic balance and blood volume.
- Prevents overdistension and damage to the bladder.
