What is the difference between excretion and defecation? Explain the process of excretion in humans.

Excretion is the removal of nitrogenous waste products of metabolism that are formed in the body, such as urine and carbon dioxide through kidneys and lungs. It is a part of excretory system.

Defecation (discharge of faeces) refers to the removal of undigested food and other waste material from the alimentary canal through the anus. It is a part of digestive system. It marks the end of digestion.

Human excretory system

● It consists of a pair of kidneys, a pair of ureters, a urinary bladder and a urethra.

● Urine is produced in the kidneys and passed to the urinary bladder through the ureters.

● It is then excreted out of the urinary bladder via urethra.

● Each kidney possesses about a million nephrons (basic functional unit) that are responsible to filter out blood and produce urine.

● The three processes involved are filtration, re-absorption and secretion.

● Certain substances such as glucose and amino acids are re-absorbed while other waste products are excreted out in the form of urine, which is carried by ureters from the kidney to the urinary bladder.

● Thus, help to concentrate the urine.