The excretory system is a passive biological system that removes excess, unnecessary materials from the body fluids of an organism, to help maintain internal chemical homeostasis and prevent damage to the body. The function of excretory systems is the elimination of the waste products of metabolism and to drain the body of used up and broken down components in a liquid and gaseous state. These substances leave the body as urine, exhalation, and also through sweating.
Kidneys are bean-shaped organs of a reddish brown color that are found in the sides of the vertebral column. Once the body has extracted what it needs from food and drink, it sends the wastes to the kidneys. The kidneys filter the wastes, including urea, salt and excess water, which are flushed out of the body as urine.
The skin performs its excretory function via the sweat glands. These glands produce sweat that contains salt, excess oils, water, and other unnecessary substances which are then excreted out of the body through small pores. Sweating also helps to cool the body during evaporation.
The lungs are very important excretory organs as they expel carbon dioxide from the body via exhalation. The lungs use cells known as alveoli to remove the carbon dioxide from our blood. Otherwise, the carbon dioxide would accumulate and have a detrimental effect to our body.
- Accessary Excretory System Organs
Although considered a secondary, or accessary excretory system organ, the liver plays a vital part in keeping the body clean. Harmful poisons and chemicals that are either produced in the body or consumed are broken down and detoxified by the liver. For example, a bi-product of the metabolic process within the body is ammonia and the liver processes this into urea, a less harmful substance which continues to be filtered and excreted by the kidneys as urine.
Although the gallbladder does not have a highly significant role to play in the excretory system, it does have a function that assists the overall process. Bile, a liquid produced by the liver to break down waste, is first stored in the gallbladder. When needed, it is discharged into the small intestine whose role is to break down fats, ethanol and other acidic wastes.
3. Urinary Bladder
The waste fluid that is created in the liver and collected in the kidney is transferred into the urinary bladder where it is temporarily stored until the individual urinates. The urinary bladder provides a short term solution for storing urine in the body until it is ultimately discharged.
The ureters tubes of smooth muscle fiber transfer liquid waste from the kidneys into the urinary bladder. The urine is moved with peristaltic movements which force the urine away from the kidneys. The ureters also have ureterovesical valves which ensure the waste fluid does not travel back into the kidney.
The urethra runs through the penis in males, and serves as a carrier of semen as well as urine for their ultimate discharge out of the body. The urethra tube is shorter in females and is just above the vaginal opening.
- Large Intestine
Food particles are absorbed into the blood stream via the small intestine. The undigested substances are transferred to the large intestine which essentially serves as a storage organ for the excretory products. The descending, ascending and transverse colons also facilitate the absorption of leftover vitamins, water and salt. The distal straight section (known as the rectum) is used for the storage of waste products (feces) before they are excreted from the body via the anal canal with the help of internal and external sphincters.