Physiology of Micturition
Linda Cardozo, Staskin David in Textbook of Female Urology and Urogynecology - Two-Volume Set, 2017
Micturition describes a dynamic process that alternates between phases of storage and expulsion of urine stored in the urinary bladder. The storage phase typically extends for hours, whereas the expulsion phase lasts for a few seconds. Reciprocal contraction and relaxation of smooth muscle in the bladder and urethra is required for these two phases of different duration to happen, which is accomplished by the complex interactions among smooth muscle, connective tissue, urothelium, and supportive structures with innervation. The relay of afferent input from the bladder to the neural circuitry in the brainstem, in particular the periaqueductal gray (pag) and the pontine micturition center (pmc), switches on the periodic transformation of the lower urinary tract from the mode of bladder filling to voiding [1–3] (figure 23.1). The volitional control over this dynamic process is lacking in infants, but is gained through learning by the age of 5 in most individuals. The micturition in both sexes is influenced by neural, biomechanical, biochemical, and morphologic properties of the bladder and urethra, as well as the hormonal influences and unique pelvic and perineal anatomy [4].
Neurogenic bladder in the neonate
Prem Puri in Newborn Surgery, 2017
In the newborn and infant, voiding occurs as a result of a spinal reflex secondary to bladder distention, which stimulates the efferent limb of the reflex arc, resulting in spontaneous detrusor contraction. Initially, as the bladder fills, the periurethral striated muscles make the external urinary sphincter contract to prevent urine loss. The act of micturition occurs with subsequent relaxation of the external sphincter, resulting in the bladder emptying at low pressure. During the first year of life, the number of voiding episodes per day remains constant at about 20, occurring both during sleep and while awake; with increased age, there is a reduction in the voiding frequency that relates to the relative increase in bladder volume and decreasing proportion of the caloric intake associated with fluid.
The Urinary System and Its Disorders
Walter F. Stanaszek, Mary J. Stanaszek, Robert J. Holt, Steven Strauss in Understanding Medical Terms, 2020
Since stasis allows bacterial invasion through the urinary tract, urinary stasis is frequently implicated in acute pyelonephritis, and it may arise from such underlying disorders as ureteral or urethral strictures, renal calculi ("kidney stones" formed through the process of nephrolithiasis), tumors, prostatic hypertrophy, or neurogenic bladder. Symptoms of acute pyelonephritis include fever and chills, vomiting, and bladder irritation from infected urine, causing urgency and frequency of urination (also called miction or micturition). A more descriptive term for acute pyelonephritis, although one that is less frequently used, is acute infective tubulointerstitial nephritis because it describes the infective nature of the disease and the involvement of the tubules and their interstitial spaces. The term pyelonephritis should only be applied to diseases with documented urinary tract infection (UTI).
Pharmacological treatments available for the management of underactive bladder in neurological conditions
Published in Expert Review of Clinical Pharmacology, 2018
Seyedeh-Sanam Ladi-Seyedian, Behnam Nabavizadeh, Lida Sharifi-Rad, Abdol-Mohammad Kajbafzadeh
In the normal situation, micturition reflex initiates after maximal filling of bladder and consequent stretch in bladder wall. Afterwards, afferent nerves, brain circuits, and efferent nerves conduct the impulse, respectively, which leads to an effective and sustainable detrusor contraction. Sacral parasympathetic nucleus and pontine micturition center (PMC) facilitate this reflex [13]. PMC is normally inhibited by limbic system and in turn receives inputs from higher cortical centers. During the storage phase, afferent fibers are responsible for bladder volume monitoring. Intact bladder sensation is fundamental to initiate micturition reflex and efferent system action [21]. Magnitude of detrusor contraction during voiding is also regulated by afferent system [22]. Efferent pathway provides contraction of bladder detrusor and adjusts speed, magnitude, and duration of contraction [21]. It is intuitive that interruption of signaling in aforementioned pathways and regulatory centers could result in diminished, absent, or ineffective detrusor contractility. Therefore, a variety of neurogenic diseases and injuries could result in UAB. Among them brain strokes, multiple sclerosis, Parkinson’s disease, diabetes mellitus, and spinal cord injuries are the well-known neurogenic causes of UAB. There is also evidence that diminution of response occurs in brain regions (responsible for interpretation of sensory inputs from the bladder) as age increases [18].
Effect of udenafil administration on postmicturition dribbling in men: a prospective, multicenter, double-blind, placebo-controlled, randomized clinical study
Published in The Aging Male, 2020
Kyungtae Ko, Won Ki Lee, Sung Tae Cho, Young Gu Lee, Tae Young Shin, Min Soo Choo, Jun Hyun Han, Seong Ho Lee, Cheol Young Oh, Jin Seon Cho, Hyun Cheol Jeong, Dae Yul Yang
Studies on PMD have mostly been performed in the field of nursing care [9,10]. The major cause of PMD identified in these studies is weakening of the bulbocavernosus muscle in the pelvic floor. At the end of the micturition process, the bulbocavernosus muscle should contract and milk out the residual urine trapped in the bulbar urethra. However, weakening of this muscle causes residual urine to be retained, leading to PMD. Weakening of the bulbocavernosus muscle, similar to urinary incontinence in females, is thought to be caused by several factors, including constipation, being overweight, lack of physical exercise, chronic cough, neurological disorders, and damaged autonomic nerves due to pelvic surgeries [8,14]. PFMT has been widely used for PMD, because the exercise was the only method known to address these factors [10,11]. However, PFMT did not show immediate treatment effectiveness in males, and patients had difficulty learning the technique without appropriate supervision. Although squeezing or swiping the perineum after urination to remove residual urine is easy to perform, this by itself does not provide satisfactory results.
Association between dietary inflammatory index and urinary flow rate: a nationwide study, NHANES 2009–2016
Published in The Aging Male, 2023
Yifan Li, Shi Qiu, Xianghong Zhou, Boyu Cai, Sheng Wang, Xingyu Xiong, Kun Jin, Lu Yang, Qiang Wei
The mechanism of the urination reflex is complex, which is affected by nerve conduction, detrusor function, and the bladder outlet. In neuromodulation, related studies have found that when the expression of inflammatory factors in cell micro-environment is up-regulated, it can activate nuclear factorκB (NF-κB) pathway and induce cell apoptosis; on the other hand, inflammatory factors can stimulate nerve cells to start self-protection and repair mechanism, among which TNF -αand IL-6 can cause degeneration and demyelination of peripheral nerve axis, causing nerve conduction dysfunction [27,28]. In terms of muscle control, detrusor and pelvic floor muscles, which are the main muscles affecting urination. It has been reported that IL-1 can inhibit glucose transport and lactic acid production in muscle tissue, resulting in muscle metabolic disorders and inhibition of myoblast proliferation, fusion, and regeneration, finally leading to myasthenia [29]. Meanwhile, a recent study found that the weak urination strongly associated with the presence of lower muscle strength, which including both smooth muscle and skeletal muscle [24].
Related Knowledge Centers
- Autonomic Nervous System
- Bladder
- Central Nervous System
- Excretion
- Reflex
- Somatic Nervous System
- Urine
- Urethra
- Urinary System
- Pontine Micturition Center