{"id":4867,"date":"2025-11-22T17:33:59","date_gmt":"2025-11-22T22:33:59","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/?post_type=chapter&p=4867"},"modified":"2025-12-07T23:11:14","modified_gmt":"2025-12-08T04:11:14","slug":"micturition-urination-process-overview-and-control","status":"web-only","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/chapter\/micturition-urination-process-overview-and-control\/","title":{"raw":"8p3 Micturition (Urination) Process \u2013 Overview and Control","rendered":"8p3 Micturition (Urination) Process \u2013 Overview and Control"},"content":{"raw":"Micturition (Urination) Process \u2013 Overview and Control<\/strong>\r\n
    \r\n \t
  1. \r\n

    Allowing Bladder to Fill<\/strong>:<\/h1>\r\n
      \r\n \t
    • Sympathetic Nervous System (SNS<\/strong>) uses neurotransmitters Epinephrine<\/strong>, E & Norepinephrine<\/strong>, NE) to create a sympathetic tone on both detrusor muscle and internal sphincter, so that:\r\n
        \r\n \t
      • o SNS relaxes<\/strong> the detrusor<\/strong> smooth muscle of the bladder (allows filling) and<\/li>\r\n \t
      • o SNS contracts<\/strong> the internal<\/strong> smooth muscle sphincter around urethra (preventing urination).<\/li>\r\n \t
      • o Cerebrum contracts the<\/strong> voluntary external sphincter (skeletal muscle) around urethra (preventing urination).<\/li>\r\n<\/ul>\r\n<\/li>\r\n \t
      • The\u00a0bladder <\/strong>contains\u00a0300-400 mL<\/strong>\u00a0of urine before the urge to urinate occurs. Adult bladder can hold more than 500mL.<\/li>\r\n \t
      • Pelvic Floor Muscles:<\/strong> provide support and control over the bladder as they contract during increases in intra-abdominal pressure (e.g., coughing, lifting) to prevent involuntary urination.<\/li>\r\n<\/ul>\r\n<\/li>\r\n<\/ol>\r\n \r\n
          \r\n \t
        1. \r\n

          Urination<\/strong>:<\/h1>\r\n
            \r\n \t
          • The micturition sacral reflex is initiated when:\r\n
              \r\n \t
            • 1) Stretch receptors<\/strong> in the bladder are activated & the signal is transmitted via sensory afferent neurons to the spinal cord, cerebrum & pons. The L1 sensory nerve sends fullness information to the pons<\/strong> (pontine micturition center).<\/li>\r\n \t
            • 2) Parasympathetic Nervous System (PSNS) nerves<\/strong> are stimulated by the bladder stretching and release Acetylcholine (ACh) which cause bladder detrusor muscle to contract. However, urination is prevented as sphincters remain closed, though pressure in bladder builds.<\/li>\r\n \t
            • 3) Cerebrum<\/strong> determines if location is appropriate, then stimulates pons<\/strong> to inhibit SNS output to detrusor<\/strong> & internal sphincter<\/strong>, so that detrusor no longer relaxes and internal sphincter no longer contracts. PSNS<\/strong> is allowed to continue contracting the detrusor.<\/li>\r\n \t
            • 4) Voluntary motor neuron <\/strong>to external sphincter<\/strong> stops firing so external sphincter relaxes. Urination occurs.<\/li>\r\n<\/ul>\r\n<\/li>\r\n<\/ul>\r\n<\/li>\r\n<\/ol>","rendered":"

              Micturition (Urination) Process \u2013 Overview and Control<\/strong><\/p>\n

                \n
              1. \n

                Allowing Bladder to Fill<\/strong>:<\/h1>\n
                  \n
                • Sympathetic Nervous System (SNS<\/strong>) uses neurotransmitters Epinephrine<\/strong>, E & Norepinephrine<\/strong>, NE) to create a sympathetic tone on both detrusor muscle and internal sphincter, so that:\n
                    \n
                  • o SNS relaxes<\/strong> the detrusor<\/strong> smooth muscle of the bladder (allows filling) and<\/li>\n
                  • o SNS contracts<\/strong> the internal<\/strong> smooth muscle sphincter around urethra (preventing urination).<\/li>\n
                  • o Cerebrum contracts the<\/strong> voluntary external sphincter (skeletal muscle) around urethra (preventing urination).<\/li>\n<\/ul>\n<\/li>\n
                  • The\u00a0bladder <\/strong>contains\u00a0300-400 mL<\/strong>\u00a0of urine before the urge to urinate occurs. Adult bladder can hold more than 500mL.<\/li>\n
                  • Pelvic Floor Muscles:<\/strong> provide support and control over the bladder as they contract during increases in intra-abdominal pressure (e.g., coughing, lifting) to prevent involuntary urination.<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n

                     <\/p>\n

                      \n
                    1. \n

                      Urination<\/strong>:<\/h1>\n
                        \n
                      • The micturition sacral reflex is initiated when:\n
                          \n
                        • 1) Stretch receptors<\/strong> in the bladder are activated & the signal is transmitted via sensory afferent neurons to the spinal cord, cerebrum & pons. The L1 sensory nerve sends fullness information to the pons<\/strong> (pontine micturition center).<\/li>\n
                        • 2) Parasympathetic Nervous System (PSNS) nerves<\/strong> are stimulated by the bladder stretching and release Acetylcholine (ACh) which cause bladder detrusor muscle to contract. However, urination is prevented as sphincters remain closed, though pressure in bladder builds.<\/li>\n
                        • 3) Cerebrum<\/strong> determines if location is appropriate, then stimulates pons<\/strong> to inhibit SNS output to detrusor<\/strong> & internal sphincter<\/strong>, so that detrusor no longer relaxes and internal sphincter no longer contracts. PSNS<\/strong> is allowed to continue contracting the detrusor.<\/li>\n
                        • 4) Voluntary motor neuron <\/strong>to external sphincter<\/strong> stops firing so external sphincter relaxes. Urination occurs.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n","protected":false},"author":1370,"menu_order":6,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":["zoe-soon"],"pb_section_license":"cc-by-nc-sa"},"chapter-type":[],"contributor":[60],"license":[57],"class_list":["post-4867","chapter","type-chapter","status-web-only","hentry","contributor-zoe-soon","license-cc-by-nc-sa"],"part":59,"_links":{"self":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapters\/4867","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/wp\/v2\/users\/1370"}],"version-history":[{"count":3,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapters\/4867\/revisions"}],"predecessor-version":[{"id":5263,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapters\/4867\/revisions\/5263"}],"part":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/parts\/59"}],"metadata":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapters\/4867\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/wp\/v2\/media?parent=4867"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/pressbooks\/v2\/chapter-type?post=4867"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/wp\/v2\/contributor?post=4867"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.bccampus.ca\/pathophysiology\/wp-json\/wp\/v2\/license?post=4867"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}