Question

"Excretion is a proccess of eliminating waste by-products from the body." Justify this statement. 10 points prize.

Answer 1

Our body works on several processes carried our by different organ systems. These processes can be termed as Life Processes or Metabolic Activities. Without these, our body can't function.

But, it's the law of nature that whenever something is carried out, it eliminates some waste in one form or the other. Thus, these Metabolic Activities also eliminate some Metabolic Wastes.

Now, you might be thinking that you can only see waste elimination through excretion. But let me tell you that all the Activities carried out by our body eliminate undesired products from the body. For example, in the process of Respiration, we exhale carbon dioxide which can be considered a gaseous waste.

But, the main process which is totally about the elimination of unwanted products and nitrogeneous wastes from the body, is none other than Excretion. But how? Let's look into this in detail.

$\textbf{Excretion}$

Excretion can be defined as the biological process by which an organism removes harmful Metabolic Wastes from the body. In unicellular organisms, the process is not very complex because the waste products are diffused into the surroundings through general body surface as in Amoeba and Paramecium. But, in multicellular organisms, the process is complex. Specialised organs perform the function of excretion. For example, flame cells in Planaria, Nephridia in Earthworm, Uric Acid in birds, and Urea in humans. Ammonia is a water soluble waste product excreted by aquatic animals.

So, the main topic here is Humans. The main function of human excretory system is to remove nitrogeneous wastes such as urea from the body. It includes a pair of kidneys, a pair of ureters, a urinary bladder and a urethra.

The main purpose of making urine is to filter out the waste products from the blood. These wastes are removed from blood by kidneys and passed to the urinary bladder by a pair of ureters. The urethra releases it out of the body.

Now, I would like to intimate to you that the process is not so simple as it seems. A lot more is going on inside the kidney. Each kidney is made up of thousands of tiny filtration units or tubules called Nephrons. They are the major structural and functional unit of the kidney. Blood at a very high pressure travels into these tubules by blood capillaries called Glomerulus, whic are surrounded by a cup shaped capsule termed as Bowman's Capsule. This is followed by a long tubular structure. It is convoluted, twisted and known as Loop of Henle or simply, Henle loop. It then finally leads to the collecting duct that collects the filtered urine. 1 - 2 L of urine is produced by the human body in 24 hours.

The formation of urine takes place by the following processes:

⏩Ultrafiltration occurs in the Glomerulus under high pressure forcing many of the substances dissolved in blood into the Bowman's capsule.

⏩The blood then passes through the tubular part of nephron where useful substances such as glucose, amino acids, salts and a major amount of water are reabsorbed. This process is called Selective Reabsoption. The amount of water that is reabsorbed in the body depends on how much excess water is present in the body and the amount of dissolved waste to be excreted.

⏩The urine formed in each kidney then enters a long tube called the ureter, which connects the kidneys with the urinary bladder.

⏩Urine is stored in the urinary bladder until the pressure of the expanded bladder causes the urge to pass it out through the Urethra. As the bladder is muscular, it is under the control of the nervous system. Hence, we can control the urge to urinate.

As we can see, the human body is greatly designed to perform life processes. The process of excretion even engaged selective reabsorption so that non of the nutrients are wasted. By this, we can see that

"Excretion is a process of eliminating waste by - products from the body".


$\textbf{More to note:}$

Keep in mind that Egestion and Excretion are two very different processes. Egestion is the discharge of undigested matter from the digestive tract via the anus in the form of faeces (stools orsolid waste). While, Excretion is the removal of nitrogeneous waste products (urine or liquid waste) from the body.