We are trying to get the "big picture" of how the urinary system works.
Don't get bogged down in the details or too hung up on the chemistry.
Here are some basic ideas to focus on:

1. What are the structure and function of the following?
Where are they found?
In what order?  ----ureter, urethra, urinary bladder, kidney

2. What are nephrons and where are they found?

3. What is glomerular filtration and where does it happen?

4. What is tubular reabsorption and where does it happen?

5. What is tubular secretion and where does it happen?

6. What is the detrusor muscle and what is the stimulus for urination?
How is the Central Nervous System involved?
What part is voluntary, involuntary?

7. What is the purpose of urination?  What is urine?