The key difference between nephridia and malpighian tubules depends on their occurrence in organisms. Nephridia are present in lower organisms such as worms and mollusks while the malpighian tubules are present in the posterior regions of insects and terrestrial arthropods.
Excretion is an important aspect of living organisms. Metabolic pathways generate various excretory products as by-products. However, accumulation of waste within a living body system is toxic and harmful. Therefore, the presence of a mechanism to remove metabolic waste from the body through a system of excretion is a must. Hence, different types of excretory organs are present in different groups of organisms. Nephridia and malpighian tubules are two examples of such excretory organs.
CONTENTS
1. Overview and Key Difference
2. What are Nephridia
3. What are Malpighian Tubules
4. Similarities Between Nephridia and Malpighian Tubules
5. Side by Side Comparison – Nephridia vs Malpighian Tubules in Tabular Form
6. Summary
What are Nephridia?
A nephridium is an excretory organ present in invertebrates or lower organisms. It occurs as a pair, and its function similar to that of a vertebrate kidney. Accordingly, the main function of the nephridia is to remove metabolic waste from the body. Nephridia are present in two forms namely protonephridia and metanephridia. Protonephridia are primitive and simpler in structure and found scattered in the body cells. It is mostly present in Platyhelminthes, rotifers, memertea, lancelets etc.
A hollow cell is present in the body cavity of protonephridium where a duct is a lead from it to the exterior opening of the organism. These exterior openings are known as nephridiopores. Usually, fluids filter from the body cavity into these hollow cells. We call these hollow cells as flame cells if they contain cilia. Otherwise, we call them solenocytes if they contain flagella. These flagella or cilia function to wave the filtered urine through the tube to the external environment.
Figure 01: Metanephridium
Moreover, metanephridia are more advanced and are in pairs. It is present in organisms such as annelids, arthropods, mollusks etc. The metanephridia lack hollow cells. Thus, it opens directly into the body cavity. Cilia are present inside the tubules of metanephridia to wave the fluids into the external environment from the body cavity. Many nutrients reabsorb from the cells of tubules as they pass on along the tubules.
What are Malpighian Tubules?
Malpighian tubules are thin tubules present in the alimentary canals of arthropods. They usually occur in pairs, and variable numbers of tubules are present in the different species of organisms. Moreover, malpighian tubules are lined with microvilli and found convoluted in order to increase the surface area for reabsorption and to maintain the osmotic balance. These tubules work together with specialised glands that line the wall of the rectum.
When compared with nephridia, there is no filtration takes place in tubules. Thus, the urine production takes place by tubular secretion. The cells lining the tubules and bathing in the hemolymph employ the tubular secretion. Hence, the diffusion of metabolic wastes such as uric acid occurs freely between the cells and the malpighian tubules. Furthermore, there are ion exchange pumps present in the lining of the tubules. These ions pump actively transport H+ ions into the cells and Na+ and K+ ions out of the cells.
Figure 02: Malpighian Tubules
Water diffuses passively during the formation of urine. Hence, the exchange of ions in and out of the cells drawing electrolytes, water and uric acid into the tubules balances the osmotic pressure. When organisms are in contact with low water environments, water and electrolytes are reabsorbed while uric acid is excreted when in contact with a thick liquid or powder.
What are the Similarities Between Nephridia and Malpighian Tubules?
- Nephridia and Malpighian Tubules are excretory system structures.
- Both types appear as tubules.
- Also, they are not present in chordates.
What is the Difference Between Nephridia and Malpighian Tubules?
Nephridia and Malpighian tubules are two excretory organs present in the organisms that are not chordates. Nephridia are present in lower organisms such as worms and mollusks while the Malpighian tubules are present in insects and terrestrial arthropods. Therefore, this is the key difference between nephridia and Malpighian tubules. A further difference between nephridia and Malpighian tubules is that the nephridia occur mainly in pairs while Malpighian tubules occur in bunches. Also, though both organs fulfil the excretory function, Malpighian tubules have another important function. That is; other than the excretion, Malpighian tubules maintain the osmotic balance in insects and terrestrial arthropods. However, nephridia do not involve in maintaining the osmotic balance. Thus, this is also another difference between nephridia and Malpighian tubules.
The below infographic presents more facts regarding the difference between nephridia and Malpighian tubules.
Summary – Nephridia vs Malpighian Tubules
Living organisms must possess a mechanism to remove metabolic waste from their body through a system of excretion. Excretory systems comprise a main excretory organ. Nephridia and malpighian tubules are two excretory organs present in two different groups of organisms. Nephridia are present in invertebrates or lower organisms. They function to remove the metabolic waste of worms and mollusks. Furthermore, there are two types of nephridia namely, protonephridia and metanephridia.
On the other hand, Malpighian tubules are thin tubules which are found in the alimentary canals of arthropods. Malphigian tubules perform the excretory function through tubular secretion, unlike nephridia. Furthermore, Malpighian tubules are important for the balance of osmotic pressure since they possess ion pumps on their walls. Thus, this summarises the difference between nephridia and Malpighian tubules.
Reference:
1.Britannica, The Editors of Encyclopaedia. “Nephridium.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 20 July 1998. Available here
2.Kelley, Fenton Crosland, and James Arthur Ramsay. “Excretion.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 20 Sept. 2018. Available here
Image Courtesy:
1.”Metanephridium”By KDS4444 – Own work, (CC BY-SA 4.0) via Commons Wikimedia
2.”Internal morphology of Lepidoptera”By Bugboy52.40 – Own work (CC BY-SA 3.0) via Commons Wikimedia