These steps of micturition are in the wrong order: the urine is released through the urethra; the…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
These steps of micturition are in the wrong order: the urine is released through the urethra; the bladder muscle contracts and the sphincter relaxes; the wall of the bladder is stretched; stretch receptors send signals to the CNS; the CNS sends motor messages to the bladder.
- Write the steps in the right order.
- What is the name of the neural mechanism?
- Does the urethral sphincter contract or relax at the time of release?
Need a reminder? The key ideaShow
Urine runs from the kidney down the ureter to the bladder. When the bladder is stretched, stretch receptors send signals to the CNS. The CNS sends motor messages: the bladder muscle contracts and the urethral sphincter relaxes. This is micturition. An adult passes to L of urine a day, slightly acidic (pH about ), with to g of urea. Glucose in the urine is glycosuria, and ketone bodies are ketonuria. Both point to diabetes mellitus.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) 1. The wall of the bladder is stretched. 2. Stretch receptors send signals to the CNS. 3. The CNS sends motor messages to the bladder. 4. The bladder muscle contracts and the sphincter relaxes. 5. The urine is released through the urethra.
Step 2. (b) The micturition reflex.
Step 3. (c) It relaxes.
Answer: the order is stretch, signals to the CNS, motor messages, contraction and relaxation, release; the micturition reflex; the sphincter relaxes.
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