Growth & Death
Molecules and Signalling
Protein Synthesis
ATP Production
Electrolytes
Cell Structures
Tissue Structure
Cardiac Output
Cardiac Cycle
Circulation
Special Circulations
Pulmonary Ventilation
Gas Exchange
Regulation of Respiration
Mouth
Stomach
Small Intestine
Large Intestine
Liver
Vitamins
Other
Nephron
Micturition
Regulation
Embryology
Hormones and Regulation
Fetal Physiology
Pregnancy
Components
Synapses
Sensory System
Motor System
Ocular Physiology
Thyroid and Parathyroid Glands
Adrenal Glands
The Pancreas
Hypothalamus and Pituitary
Cells of the Immune System
Innate Immune System
Adaptive Immune System
Immune Responses
Infections
Haematology
Micturition (urination) is the process of urine excretion from the urinary bladder. Micturition has two discrete phases: thestorage/continence phase, when urine is stored in the bladder; and the voiding phase, where urine is released through the urethra. These phases require coordinated contraction/relaxation of the bladder and urethral sphincters, which are all under control of the sympathetic, parasympathetic and somatic nervous systems.
Storage of urine requires relaxation of the detrusor muscle and contraction of both the internal and external urethral sphincters. This is controlled by the sympathetic nervous system in the case of the detrusor and internal urethral sphincter, and the somatic nervous system for the external urethral sphincter.
As the bladder fills rugae distend and a constant pressure in the bladder (intra-vesicular pressure) is maintained. This is known as the stress-relaxation phenomenon and is responsible for signalling the need to urinate. The voiding phase of micturition is mainly controlled by the parasympathetic nervous system and also requires voluntary relaxation of the external urethral sphincter to allow passage of urine.
by Namita Anand
by Oliver Jones and Omar Haque
by Farhana Patel
Please enter your username or email address below. You will receive a link to create a new password via emai and please check that the email hasn't been delivered into your spam folder.
We use cookies to improve your experience on our site and to show you relevant advertising. To find out more, read our privacy policy.