How Does the Micturition Reflex Work? Steps & Regulation
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: Complete Guide for Biology Students
1. What is the micturition process?
Micturition is the biological process of expelling urine from the urinary bladder through the urethra to the outside of the body. This entire action is controlled by the central nervous system (CNS) and is also commonly known as urination or voiding. The process involves both involuntary and voluntary muscle contractions to effectively release the stored urine. For more details on the micturition process, you can refer to our guide on the Micturition Process.
2. What are the main steps involved in the micturition process?
The micturition process generally follows a sequence of steps involving the nervous system and bladder muscles. The key steps are:
Bladder Filling: As urine produced by the kidneys fills the urinary bladder, its walls, made of the detrusor muscle, begin to stretch.
Signalling the Brain: Specialised stretch receptors in the bladder wall detect this stretching. They send nerve impulses to the spinal cord and then to the brain, creating the sensation or urge to urinate.
Voluntary Control: The brain's higher centres, specifically the cerebral cortex, allow for conscious control. A person can choose to either delay urination by keeping the external urethral sphincter contracted or initiate it.
Voiding (Urination): When urination is initiated, the brain sends signals for the detrusor muscle to contract and the internal and external urethral sphincters to relax, allowing urine to flow out through the urethra. You can find a detailed breakdown in our NCERT Solutions for Class 11 Biology Ch 16.
3. Why is micturition considered a reflex action?
Micturition is fundamentally a reflex action because the initial trigger is involuntary. This is known as the micturition reflex. When the bladder stretches to a certain point, nerve signals are sent to the sacral region of the spinal cord. The spinal cord responds by sending back signals via parasympathetic nerves that cause the bladder's detrusor muscle to contract and the internal sphincter to relax. While this basic reflex is involuntary, it is overlaid with voluntary control from the brain, which allows us to consciously decide when and where to urinate. For more on this, check our Class 11 Excretory Products and Their Elimination Notes.
4. What is the role of the central nervous system (CNS) in regulating urination?
The CNS plays a crucial dual role in regulating micturition. The process is managed by different levels of the nervous system:
Spinal Cord: Contains the basic reflex centre that can trigger urination involuntarily when the bladder is full.
Pons (in the brainstem): Houses the pontine micturition centre, which coordinates the contraction of the bladder muscle and the relaxation of the sphincter, ensuring smooth and efficient voiding.
Cerebral Cortex (in the brain): Provides conscious, voluntary control. It allows an individual to inhibit the micturition reflex, enabling them to delay urination until it is socially acceptable. This involves sending inhibitory signals to the pons. The signals are transmitted by specialised cells called neurons.
5. How does the body know when it's time to urinate?
The body knows it's time to urinate thanks to stretch receptors embedded in the muscular wall of the urinary bladder. As the bladder gradually fills with urine (typically around 200-400 mL), these receptors are activated. They send increasingly frequent signals to the brain via the nervous system. The brain interprets these signals as the sensation of bladder fullness and the urge to urinate. The stronger the signals, the more urgent the sensation becomes. This mechanism is a key part of the larger Human Excretory System.
6. How can emotions like stress or nervousness affect the micturition process?
Emotions like stress or nervousness activate the body's 'fight-or-flight' response, which is controlled by the sympathetic nervous system. This system can override the normal, relaxed state required for bladder filling. It can cause involuntary contractions of the bladder's detrusor muscle. This creates a sudden, strong urge to urinate, even if the bladder isn't particularly full, a phenomenon many people experience before an exam or a public speaking event.
7. What is the importance of having voluntary control over micturition?
While micturition is a natural reflex, the ability to exert voluntary control over it is crucial for social continence. This control, learned during toilet training in early childhood, allows individuals to consciously inhibit the urination reflex and keep the external urethral sphincter contracted. This enables us to delay urination until a socially appropriate time and place is available. The loss of this control, a condition known as urinary incontinence, highlights the functional importance of this higher brain function in daily life. Answering such conceptual questions is crucial, as highlighted in our Important Questions for CBSE Class 11 Biology.
