Key Functions of Skin, Lungs, and Liver in Human Excretory System
The liver is the largest and the busiest organ of the body. It performs a number of functions including the formation of urea. This area is actually excreted by the kidney in the form of urine. The process by which liver forms urea is called an Ornithine cycle. Through this process, more toxic waste ammonia is converted into less toxic urea. The liver also removes bile pigments like biliverdin and bilirubin from the body. These bile pigments are the breakdown products of the hemoglobin of the dead RBCs. The liver also removes excess cholesterol, vitamins to an extent. Thus the liver plays an important role in excretion.
Order of toxicity of nitrogenous waste -
uric acid < urea < ammonia
A Brief on What is Excretion
In order to understand what are the roles of different organs in excretion, we must first know what is excretion.
Excretion is a biological process by which the body removes unwanted substances which are present in excess and the metabolic wastes produced during various biochemical reactions from itself.
In the human body, excretion is performed, by the excretory system. This excretory system in addition to the removal of wastes also helps in maintaining the osmoregulation of our body in order to maintain homeostasis.
There are two types of organs involved in excretion. These are -
Accessory organs
Necessary organs
Role of Kidney in Excretion
A pair of kidneys, a pair of ureters, a urinary bladder, and urethra forms the urinary system and are the necessary organs of excretion. Kidneys are bean-shaped the d structures present near the dorsal body wall between the 11th and 12th thoracic vertebra and 1st and 2nd lumbar vertebra. The function of the kidney is to remove the nitrogenous waste urea, from the body in the form of urine. Nephron is the structural and functional unit of the kidney.
Other Excretory Organs of the Body
There are organs other than the kidney which performs the role of excretion and such organs are called the accessory organs of excretion. They are meant to perform some other function of the body and in addition to those functions, they perform excretion also.
Liver, Lungs, Skin are some of the accessory organs of excretion.
Role of Lungs in Excretion
It is already mentioned that excretion refers to the removal of unwanted substances that are undesirable and are present in excess amounts in the body. Lungs perform the function of removing the carbon dioxide from the body which is a gaseous waste.
All the cells of our body are constantly involved in metabolic reactions. Due to this certain wastes like carbon dioxide are continuously formed and are collectively brought to the lungs through blood and are released out by the expiration process. Thus lungs play an important role in excretion.
Role of Skin in Excretion
Glands of skin (soft epidermal derivatives of skin) are also involved in excretion. There are different glands present in the skin. The following are some glands involved in the excretion process.
Sweat Glands
These are simple coiled tubular glands. They maintain the temperature of the body by releasing sweat which causes a cooling effect. Sweat has a small amount of urea in addition to the extra water thus in a way sweat glands are also involved in excretion.
Sebaceous Glands
These are the glands that are played in the hair follicle and their secretion is called sebum, which is not a watery secretion. Some of the lipid wastes are released in sebum from these glands of the skin.
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Importance of Other Excretory Organs
Salivary Glands
These glands are present in the buccal cavity. There are 3 salivary glands present at different places in the mouth. Together they all release a secretion called ‘saliva’.This saliva has water, mucous, and also a little amount of urea in it. So salivary glands are also excretory to an extent.
Tear Glands
They are also known as lacrimal glands and are found in the eyes. Their secretions are called tears which are watery and absorb amounts of urea waste in it. Thus tear glands also help in the removal of the waste.
FAQs on How Do Other Organs Help in Excretion?
1. What is the role of the lungs in excretion?
The lungs are crucial for excreting metabolic waste in the form of gases. Their primary excretory function is the removal of carbon dioxide (CO₂), a major waste product of cellular respiration. Every day, our lungs expel a significant amount of CO₂, approximately 18 litres, along with a considerable quantity of water vapour.
2. How does the skin function as an excretory organ?
The skin contains two types of glands that assist in excretion:
- Sweat Glands: These glands produce sweat, a watery fluid containing NaCl, small amounts of urea, and lactic acid. While the primary function of sweat is to cool the body, it also helps eliminate these metabolic wastes.
- Sebaceous Glands: These glands secrete sebum, an oily substance that eliminates wastes like sterols, hydrocarbons, and waxes. Sebum's main role is to provide a protective, oily layer on the skin.
3. What is the importance of the liver in the body's excretory process?
The liver is the largest gland in the body and plays a vital, though indirect, role in excretion. It processes metabolic byproducts, converting toxic substances into less harmful ones. Its key excretory-related functions include:
- Converting highly toxic ammonia into urea through the urea cycle, which is then transported to the kidneys for removal.
- Metabolising and excreting substances like bilirubin, biliverdin, cholesterol, degraded steroid hormones, vitamins, and drugs into the bile. This bile is then released into the small intestine and eliminated with faeces.
4. Why are the lungs, liver, and skin considered accessory excretory organs and not primary ones?
The lungs, liver, and skin are termed accessory or secondary excretory organs because excretion is not their primary physiological function. Their main roles are respiration (lungs), metabolism (liver), and protection/thermoregulation (skin). They contribute to eliminating waste as a byproduct of these functions. In contrast, the kidneys are considered the primary excretory organs because their principal role is to filter blood, remove nitrogenous wastes, and maintain the body's salt and water balance (osmoregulation).
5. Does the large intestine participate in excretion in the same way as the kidneys?
No, the large intestine's role is different from the kidneys'. The process of eliminating undigested food as faeces is called egestion, not excretion. Excretion specifically refers to the removal of metabolic waste products from the body's cells. While the large intestine does eliminate certain substances like excess salts of calcium and iron, its primary function is to remove solid food waste, not the nitrogenous wastes filtered by the kidneys.
6. What specific metabolic wastes are eliminated through sweat and sebum?
Sweat and sebum eliminate different types of waste materials.
- Sweat, produced by sweat glands, primarily eliminates water and salts (like NaCl) but also contains small quantities of metabolic wastes such as urea and lactic acid.
- Sebum, secreted by sebaceous glands, is an oily substance that helps excrete lipids like sterols, hydrocarbons, and waxes.
7. Can other glands, besides those in the skin, help eliminate waste from the body?
Yes, a small amount of metabolic waste can be eliminated through other glands. For example, the salivary glands can secrete trace amounts of nitrogenous wastes like urea into saliva. Similarly, lacrimal glands (tear glands) release a salty fluid that can contain small amounts of waste products, although this contribution to overall excretion is minimal.
