Write a short and clear response to the question:
 
Mention one distinct role of each of the following structures involved in the excretory system of human beings:

i. Renal Artery
ii. Urethra
iii. Glomerulus
iv. Tubular part of nephron
 
i. Renal Artery -
ii. Urethra -
iii. Glomerulus -
iv. Tubular part of nephron -