Biology · Excretory Products and Their Elimination · NEET
In healthy adults it is under voluntary control. NCERT says urine is stored in the bladder "till a voluntary signal is given by the central nervous system." So even though the reflex is triggered automatically by bladder filling, the CNS decides when to actually pass urine. This is why you can hold urine for some time before releasing it.
Micturition is the process of releasing urine itself. The micturition reflex is the neural mechanism that causes it. NCERT states clearly: "The process of release of urine is called micturition and the neural mechanism causing it is called the micturition reflex." So one is the event, the other is the nerve pathway behind the event.
The stretching of the urinary bladder as it fills with urine. Stretch receptors on the walls of the bladder detect this filling and send signals to the CNS. The CNS then passes motor messages back to the bladder. So the trigger is bladder stretch, not a full bladder alone.
During micturition the smooth muscles of the bladder wall contract and, at the same time, the urethral sphincter relaxes. Both must happen together: contraction pushes urine out and relaxation opens the exit path. If you only remember one, remember both happen simultaneously, because NEET tests this pairing.
An adult human excretes, on average, 1 to 1.5 litres of urine per day. The urine is a light yellow watery fluid, slightly acidic (pH about 6.0), with a characteristic odour. About 25 to 30 grams of urea is excreted per day. These exact figures are directly from NCERT and are frequently asked.
Match the items given in Column I with those in Column II and select the correct option given below: Column I (Function): a. Ultrafiltration, b. Concentration of urine, c. Transport of urine, d. Storage of urine. Column II (Part): i. Henle's loop, ii. Ureter, iii. Urinary bladder, iv. Malpighian corpuscle, v. Proximal convoluted tubule.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Micturition is the process of releasing stored urine from the urinary bladder to the outside of the body through the urethra.
It is the neural mechanism that causes micturition: bladder stretch is detected by stretch receptors, signals go to the CNS, and the CNS sends motor messages that contract the bladder and relax the urethral sphincter.
On the walls of the urinary bladder. They detect the stretching of the bladder as it fills with urine and start the reflex.
It relaxes (opens) during micturition so that urine can flow out, while the bladder muscle contracts to push the urine.
Urine is slightly acidic with a pH of about 6.0, and an adult passes 1 to 1.5 litres per day, excreting about 25 to 30 grams of urea daily.
