Excretion: Excretion is the process of eliminating waste products of metabolism and other non-useful materials.In humans, the two major excretory processes are the formation of urine in the kidneys and the formation of carbon dioxide (a human's abundant metabolic waste) molecules as a result of respiration, which is then exhaled from the lungs. These waste products are eliminated by urinationand exhalation respectively.
Defecation: Defecation is the final act of digestion by which organisms eliminate solid, semisolid or liquid wastematerial (feces) from the digestive tract via the anus. Humans expel feces with a frequency varyingfrom a few times daily to a few times weekly. Waves of muscular contraction known as peristalsis inthe walls of the colon move fecal matter through the digestive tract towards the rectum. Undigestedfood may also be expelled this way; this process is called egestion.
Human excretory system:

1. Kidneys: Kidneys are the main organ of the human excretory system. They are the primary excretory organ in humans.They are divided into three regions- the renal cortex which is the outer layer, the renal medulla which is the inner layer and the renal pelvis which is responsible for carrying the urine from the kidney to the ureter. The functional unit of a kidney is called the nephron.
2. Ureters: There is one ureter that comes out of each kidney as an extension of the renal pelvis. The ureter is a thin muscular tube that carries urine from the kidneys to the bladder.
3. Urinary bladder: It is a sac-like structure that is lined with smooth muscle layer and is responsible for storage of urine till it is expelled from the body by micturition. Micturition is the act of expelling urine from the body. The bladder receives urine from the ureters, one from each kidney. The level of the urinary bladder placement in the body differs in men and women.
4. Urethra: This is a tube that arises from the urinary bladder and functions to expel urine to the outside by micturition.