In the human body, several chemical reactions take place every second. These reactions are known as metabolic reactions. The metabolic reaction can be classified as anabolic and catabolic. Anabolic reactions create something new that will be useful for the body whereas catabolic reactions break or burn something so that energy is produced.
All these reactions produce waste material. Some waste materials are toxic and the human body converts them to non-toxic forms. At some point, these excretory products need to be removed from the body. The organs that support this function are called excretory organs.
Here in respiration reaction, the main result is gaining energy for cell function by using glucose. Water and carbon dioxide are waste products of this reaction.
In simple excretion is the process that eliminates waste products from the human body.
Excretory products and excretory organs in humans
Excretory products or else the waste products from cellular reactions are carbon dioxide, water, urea, uric acid, salts, and water vapor.
Feces are not considered excretory products because they are not made from a chemical reaction inside cells. Feces are the remainder of the process of digestion. Therefore, feces are not considered in excretion.
Excretory products are excreted by using the excretory organs.
The main excretory organs in the human body are;
Lungs excrete carbon dioxide and water vapor by exhaled air.
Kidneys excrete nitrogenous waste like urea and uric acid as well as excess water and salts by urine.
Sweat from the skin removes a little amount of nitrogenous waste like urea along with water vapor and salts.
Here the list of excretory products is summarized with their respective excretory organ.
The human urinary system is responsible for excreting nitrogenous toxic waste from the human body. This is discussed further in the next paragraphs.
Human Urinary System
The human urinary system consists of kidneys, ureters, bladder, and urethra. Kidneys filter metabolic waste and produce urine. Ureters transport urine from the kidneys to the urinary bladder. The urinary bladder stores urine until it is passed. The urethra acts as a passage for passing urine.
Renal blood supply is from renal arteries. They are direct branches from the aorta.
Renal veins carry deoxygenated blood from the kidneys. They open into the IVC (inferior vena cava).
So the main functions of each part of the urinary system can be listed as follows;
- Kidneys – filter metabolic waste the from blood
- Ureters – transport urine from the two kidneys to the urinary bladder
- Bladder – store urine until it is passed
- Urethra – acts as a passage for passing urine
Process of human excretion
In this dia, gram the process of human excretion is presented visually.
More about kidneys
Humans have a pair of kidneys. They resemble the shape of a bean.
In the upper part of the abdomen, kidneys are found lying on the back muscles towards the abdominal cavity. They lie on either side of the spine facing each other. Because of the larger liver, the right kidney is pushed downward than the left kidney. Kidneys slightly move up and down with respiratory movements.
On the outer surface, the kidney is seen with its blood vessels, the renal artery, and the renal vein. The ureter is the tube that arises from the kidney, that carries urine from the kidney to the urinary bladder.
Renal arteries supply the blood with oxygen to the kidney. Metabolic waste made from cellular reactions is also found in blood from renal arteries. The renal artery is divided into several branches inside the kidney. Each kidney has its own renal artery. So there are two renal arteries as right renal artery and the left renal artery.
After filtration of waste products, renal veins bring the remaining deoxygenated blood back into circulation. Just like the renal arteries, there is a pair of renal veins named the right renal vein and the left renal vein.
Urine is made inside the kidneys by means of glomerular filtration, secretion, and reabsorption. The complex mechanism of urine formation will be discussed in a separate article.
The ureter carries urine made in the kidney. The ureter arises from the renal pelvis. Two kidneys make two separate ureters.
Urine and its components
One is the most widely discussed excretory products of humans is urine. Urine contains water, salts such as sodium chloride, urea, and minimum amounts of uric acid.
Usually, glucose is not found in urine, but in diabetes mellitus where blood glucose levels are high, glucose is found in urine as a constituent.