TeachableMedicalNews article 02222020

Teachable moment in classrooms:

  1. Autonomic nervous system chapter —  examples for sympathetic and parasympathetic activities
  2. Autonomic nervous system chapter —  neurotransmitters acetylcholine and norepinephrine and their receptors
  3. urinary system chapter – layers and tissues of the urinary bladder wall
  4. urinary system chapter – nerve pathways for the micturition reflex

The news item:  A recent news item informs us that a drug to treat overactive bladder is effective in men as well:

Men Get Overactive Bladder, Too

Don’t always blame the prostate.

 

The article mentions the symptoms of overactive bladder, the fact that men get this disorder as much as women, and that one treatment, Myrbetriq, is acting through  beta 3 adrenoceptor agonists.

So, Why Do I Care??    An overactive bladder will make you go to the bathroom frequently, and leak urine (this is called urge incontinence) even though the bladder is not full. That may severely disrupt the lives of the people with the syndrome.  27% of men over age 40 has overactive bladder symptoms at some time during their lives.  That translates into tens of million men in the USA.  The symptoms are severe enough that many of the affected men seek medical help.

Plain English, Please!!!  First, let’s talk about voiding the urinary bladder. A full bladder activates stretch sensing neurons, and those send nerve impulses to our spinal cord, and from there nerve impulses excite the muscle of the bladder. When the excited bladder muscles contract, they act like when you clutch you cupped palms together, and squeeze water from it. The overactive bladder has a muscle that get excited on its own, and squeezes urine before the bladder is full.  That premature squeezing causes the urge incontinence, and the urge to go to the bathroom.

Second, let’s talk about what excites the muscles of the urinary bladder.  When the smooth muscle of the bladder receives nerve impulses that excite contraction, the nerve endings release the chemical acetylcholine.  The smooth muscle cells have receptors for this chemical. Picture acetylcholine as your car keys, and the lock in your car door as the receptor.  Other keys don’t open your car, so acetylcholine is the chemical signal that starts muscle contraction.

Third, let’s talk about how the bladder muscles can be made to relax. As the bladder is regulated by our autonomic nervous system, there are activating and inhibiting nerve impulses going to the bladder.  In addition to the green light-type of nerve impulses that make the bladder muscles contract, we also have the red light-type of nerve impulses that make the bladder muscles relax.  The nerve endings that relax the bladder release the chemical called norepinephrine.  The norepinephrine “key” fits into the “lock” called adrenoceptor. The drug Myrbetriq is and artificial key for that lock called beta 3 adrenoceptor, so Myrbetriq turns on and enhances the red light-type relaxing signals to the bladder muscle.  As the result the bladder relaxes, and the patient no longer has the urge to go to the bathroom, and no longer has incontinence (urine leakage).