Tag: structures and functions related to the excretory system

Amphioxus or Branchiostoma is a peculiar chordate animal, which does not have excretory organs in the form of mesodermal kidneys but are in the form of protonephridia. They are similar to protonephridia of flat worms or polychaete, annelids and they are ectodermal in origin. In Amphioxus there are 90 to 100 pairs of protonephridia present segmentally on dorso-lateral pharyngeal wall one above each gill slit on either side. Simply, they are ciliated, thin walled, closed ectodermal tubules like structures.

The original nephrostomes remain in the adult frog on the ventral face of the kidney as ciliated peritoneal funnels. These convey coelomic fluids directly into the blood sinuses of the kidney. They are regarded as accessory excretory structures.

The excretory organs of earthworm are coiled tubular structures, known as nephridia. A nephridium consists of a ciliated nephridial canal, that opens into the coelom by nephrostome and to the exterior or in the gut by nephridiopore. The walls of nephridia are glandular and richly supplied with blood vessels, they extract solutes and water from the blood by ultra filtration, and discharge the filtrate into the nephridial canal. 

In most of the invertebrates, the excretory structures are simple tubular forms whereas vertebrates have complex tubular organs called kidneys. Shark is a vertebrate and has kidneys as excretory structures.
Protonephridia or flame cells are the excretory structures in Platyhelminthes (Flatworms, e.g., Planaria), rotifers, some annelids and the cephalochordate Amphioxus. Protonephridia are primarily concerned with ionic and fluid volume regulation, i.e., osmoregulation.
Nephridia are the tubular excretory structures of earthworms and other annelids like Leech. Nephridia help to remove nitrogenous wastes and maintain a fluid and ionic balance.
Malpighian tubules are the excretory structures of most of the insects including cockroaches. Malpighian tubules help in the removal of nitrogenous wastes and osmoregulation.

Nephridial organs, or nephridia, are excretory structures that evolved in many invertebrates, including flatworms, nemerteans, rotifers, annelids, mollusks, and lancelets. Each nephridial organ consists of simple or branching tubes that typically open to the outside of the body through excretory pores, called nephridiopores. Two types of nephridial organs are protonephridia and metanephridia. The excretory system of insects and spiders consists of several hundred Malpighian tubules. Malpighian tubules are slender extensions of the gut wall. Their blind ends lie in the hemocoel (blood cavity) and are bathed in hemolymph. The mammalian urinary system consists of the kidneys, the urinary bladder, and associated ducts. Each kidney has more than 1 million functional units called nephrons. A nephron consists of a cuplike Bowmans capsule connected to a long, partially coiled renal tubule.
In option A typhlosole is an intestinal fold for absorption but contractile vacuole is meant for osmoregulation. In option C antennae of cockroach are sensory but clitellum of earth worm forms cocoon. In option D tube feet of starfish are meant for locomotion and not related to other structures mentioned which have a role in digestion of food.

'Green Gland' is one of the pair of excretory organs in each side of the head region of decapod crustaceans, emptying at the base of the antennae. Prawns have green glands for excretion.

Solenocytes are a type of long, narrow, flagellated cell that functions in excretion of nitrogenous wastes and occurs in a variety of organisms, including certain annelids and molluscs.

Wolffian duct is also called as archinephric duct, is a pair of tubes that carry urine from primitive or embryonic kidneys to the exterior or to a primitive bladder. 

Various animals of animal kingdom presents a variety of excretory structures. In most of the invertebrates, these structures are simple tubular forms. Protonephridia or flame cells are the excretory structures in Platyhelminthes (Flatworms, e.g., Planaria), rotifers, some annelids and the cephalochordate Amphioxus. Protonephridia are primarily concerned with ionic and fluid volume regulation, i.e., osmoregulation. Nephridia are the tubular excretory structures of earthworms and other annelids. Nephridia help to remove nitrogenous wastes and maintain a fluid and ionic balance. Malpighian tubules are the excretory structures of most of the insects including cockroaches. Malpighian tubules help in the removal of nitrogenous wastes and osmoregulation. Antennal glands or green glands perform the excretory function in crustaceans like prawns. Vertebrates have complex tubular organs called kidneys as primary excretory organ. Towards the centre of the inner concave surface of the kidney is a notch called hilum through which ureter, blood vessels and nerves enter. Inner to the hilum is a broad funnel shaped space called the renal pelvis with projections called calyces. The outer layer of kidney is a tough capsule. Inside the kidney, there are two zones, an outer cortex and an inner medulla. The medulla is divided into a few conical masses (medullary pyramids) projecting into the calyces (sing.: calyx). The cortex extends in between the medullary pyramids as renal columns called Columns of Bertini.

Mammals like humans and rabbit, many terrestrial amphibians and marine fishes mainly excrete urea and are called ureotelic animals. Ammonia produced by metabolism is converted into urea in the liver of these animals and released into the blood, which is filtered and excreted out by the kidneys. Some amount of urea may be retained in the kidney matrix of some of these animals to maintain a desired osmolarity.