(2) unconditional, conditional

(3) water, inorganic salts, reabsorption

Analysis of test questions: (1) In the figure, ① kidney, ② ureter, ③ bladder and ④ urethra constitute the urinary system. ① Kidney is the organ that forms urine and the main organ of urinary system. After urine is formed, it flows into the bladder through two ureters for temporary storage, and finally it is excreted under the control of the nervous system.

(2) From the analysis of reflex types, the phenomenon of "bedwetting" in childhood is a congenital reflex, which belongs to unconditioned reflex, while "holding urine" in adulthood is a conditioned reflex based on unconditioned reflex and involving cerebral cortex after a certain process.

(3) From the analysis, it can be seen that the main component of urine is water, as well as a small amount of inorganic salts and nitrogen-containing waste. A healthy adult forms about l50L of original urine every day, but only 1.5L of urine is excreted, which is due to the reabsorption of renal tubules.