Types of Nephridia

Excretory system unit found in many primitive invertebrates, as well as the amphioxus, is responsible for removing waste products from the body cavity and disposing of them in the environment. The development of nephridia, which eliminated the necessity for all cells of an organism to be in touch with saltwater for the diffusion of metabolic wastes, facilitated tissue specialisation.

There are two types of nephridia. More primitive protonephridia can be found in flatworms (such as the Ribbon Worm), as well as in rotifers (like the Ribbon Worm). Metanephridia are found in more sophisticated segmented invertebrates, such as earthworms, and are frequently arranged in pairs.

In the protonephridium, a body cavity is filled with a hollow cell, which is connected to a nephridiopore, an external entrance. If it has cilia or a flagellum, the hollow cell is referred to as a flame bulb (or flame cell). If it doesn’t, it’s referred to as a solenocyte. Filtered urine is pumped out of the body through the cilia or flagella in either form.

In the metanephridium, the tubule does not have a flame cell, and it opens directly into the body. Cilia on the tubule’s surface take up fluids from the cavity and route them to the outside; tubule cells actively reabsorb necessary nutrients as they pass through. To distinguish them from other organisms, nematodes have two similar structures: the renette and the lateral canal.

Depending on where they’re located in the body, earthworms can be divided into three categories: First, septal nephridia; then, integumentary nephridia An infection of the pharynx.

Protonephridia and Metanephridia

In contrast to protonephridia, metanephridia are a form of excretory glands with ciliated funnels that open into the human body’s interior cavity.

Septal Nephridia

Nephrostome, nephridium body, neck and the terminal duct comprise each septal nephridium.

Nephrostome

It is also known as a ciliated funnel or nephridiostome. Flattened funnel-shaped nephridium structure in the coelom proximal flattened funnel structure There’s an elliptical mouth-like hole that leads into the giant central cell’s intracellular canal, and a large upper and smaller lower lip surround the aperture’s borders. Several rows of tiny ciliated cells line the lip margins, and the central canal is ciliated too.

Neck

Ciliated canals create the neck of the urinary tract. It connects the nephrostome to the nephridium’s main body.

Body of Nephridium

This animal’s body is divided into two sections, one short and straight, the other long, twisted. The proximal and distal limbs come together to form a loop in the ear canal. Both of these limbs have nine to thirteen twists in a spiral around each other. While the distal limb of the twisted loop is now the straight lobe, the proximal limb of the nephridium neck connects to the terminal duct and remains attached to it. Nephridial loops are made up of long, coiled connective tissue that is found inside the nephridium. Twisted loop has four canals, three on its bottom half and two on its upper half of the lobe’s limbs. Two of the straight lobe’s four canals, like the ciliated canal of the neck, are ciliated.

Terminal Duct

An excretory duct at the extremity completes the short and narrow design. The nephridium and septal excretory canal are connected by this canal.

Integumentary Nephridia

Nephridia can be found in every segment of a person’s torso, beginning at segment 7 and continuing until the last segment. These are known as integumentary nephridia, and they number between 200 and 250 in each segment, except for the clitellar region, where they number between 2,000 and 2,500 in each segment. There is no nephrostome or coelom opening in these little nephridia. As a result, they are known as closed nephridia. Rather than having a single ciliated canal, each integumentary nephridium contains two, one on each side of the V-shaped lumen. Each nephridium is accessed by a nephridiopore on the skin’s outer surface. Exonephric nephridia are integumentary nephridia because excretory wastes are discharged directly into the environment.

Pharyngeal Nephridia

• There are three paired tufts of nephridia in segments 4, 5, and 6, one on each side of the anterior part of the alimentary canal. 
• Nephridia in the pharynx also contain blood glands
• When it comes to mouth organs, the size and shape of each pharyngeal nephridia are comparable to those of the septum.  
• it has two ciliated canals in its lumen as well as two straight lobes
• Each segment has a single thick-walled duct that emerges from each nephridium. 
• Segment 6th nephridia ducts open into the buccal cavity in segment 2nd, while segment 4th nephridia ducts open into the upper pharynx in segment 4th.
• Enteronephric nephridia that open into the buccal cavity and pharynx are known as protonephridia because they may have taken over the role of digestive glands
• Nephridia of P. posthuma have recently been found to generate a number of enzymes, such as amylase, chymosin, prolinase and prolidase. These enzymes hydrolyze a wide range of food products. As a result, these nephridia function similarly to the salivary glands.

Conclusion

The nephridium (plural nephridia) is an invertebrate organ that is found in pairs and that performs a function that is comparable to that of the vertebrate kidney (which originated from the chordate nephridia). Nephridia are parasites that remove metabolic waste from the body of an animal. Nephridia are divided into two fundamental categories: metanephridia and protonephridia. Metanephridia are the more common of the two.