State the importance of the following in the human excretory system:
$(1)$ Nephron
$(2)$ Antidiuretic hormone $(ADH)$

(N/A) $(1)$ Nephron: It is the structural and functional unit of the kidney,responsible for the process of urine formation through filtration,reabsorption,and secretion.
$(2)$ Antidiuretic hormone $(ADH)$: It is released from the posterior pituitary gland and facilitates the reabsorption of water from the distal convoluted tubule and collecting duct,thereby concentrating the urine and preventing water loss.