Organ of excretion: structure and function. Selection organs in animals: description, meaning

Maintaining a normal level of metabolism in the body, called homeostasis, is carried out with the help of neuro-humoral regulation of the processes of breathing, digestion, circulation, secretion and reproduction. In this article, we will consider the system of organs for the isolation of humans and animals, their structure and functions, as well as their significance in the metabolic reactions of living organisms.

Biological significance of organs of excretion

As a result of the metabolism that occurs in every cell of a living organism, a large number of toxic substances accumulate: carbon dioxide, ammonia, salts. To remove them, you need a system that removes toxins into the external environment. The structure and functions of the excretory organs are studied by anatomy and physiology.

For the first time, an isolated organ of excretion appears in invertebrate animals with bilateral symmetry. The walls of their body consist of three layers: exomezo and endoderm. Such organisms include flat and round worms, and the excretory system in them is represented by protonephridia.

How the excretory organs function in flat worms and nematodes

Protonephridia is a system of tubular formations extending from the main longitudinal canal. They are formed from an external embryonic leaf - exoderm. Toxins and excess ions are released to the surface of the helminth body through the pores.

The inner end of protonephridia is provided with a group of processes - cilia or flagella. Their undulating movements intermix the intercellular fluid, which enhances the filtration functions of the excretory tubules.

Progressive complications of the discharge organs in annelids

Kolchetsy, for example, earthworm, neresis, sand-grass, remove from their body metabolic products, using metanephridia - the organs of secretion of worms. They have the appearance of tubules, one end of which is leukically expanded and equipped with cilia, and the other goes to the covers of the animal and has a pore opening. The complication of the excretory organs in earthworms is explained by the appearance of a secondary body cavity - the coelom.

Features of the structure and function of Malpighian vessels

In representatives of the arthropod type, the excretory organ has the form of branching tubules into which dissolved metabolites and excess water are sucked from the hemolymph-intracavitary fluid. They are called Malpighian vessels and are characteristic of representatives of the classes of arachnids and insects. In the latter, in addition to the excretory ducts, there is another organ, the fat body, in which the metabolic products accumulate. Malpighian vessels, which received toxic substances, flow into the back of the intestine. From there, the products of metabolism are released through the anus.

The organ of excretion in crustaceans - crayfish, lobsters, lobsters - is represented by green glands, which are modified metanephridia. They are located on the cephalothorax of the animal, behind the base of the antennas. Under the green glands of the crustaceans is located the bladder, which opens with excretory at times.

Organ of fish secretion

Representatives of the class of osseous fishes have a further complication of the excretory system. It has the appearance of dark red ribbon-like bodies - the trunk kidneys located above the swim bladder. Each of them leaves the ureter, through which the urine flows into the bladder, and already from it - into the genitourinary opening. In the class of cartilaginous fish (sharks, rays), the ureters flow into the cloaca, and the bladder is absent.

Based on the structure of the excretory system, all bone fish are divided into three groups: living in fresh water, in saline reservoirs, as well as a group of so-called checkpoints living in salt and fresh water in connection with the characteristics of spawning.

Freshwater fish (perch, crucian carp, carp, bream) to avoid excess water in their body, are forced to remove a large volume of fluid through the renal tubules and Malpighian glomerulus of the kidneys. So, carp secrete up to 120 ml of water per 1 kg of its mass, and the catfish - up to 380-400 ml. To ensure that the body does not lack salt, the gills of freshwater fish serve as pumps that pump sodium and chlorine ions out of the water. Sea inhabitants - cod, flounder, mackerel, - on the contrary, suffer from a lack of water in the body. To avoid dehydration and maintain normal osmotic pressure inside the body, they are forced to drink sea water, which, filtered in the kidneys, is cleared of salt. Excess sodium chloride is removed through the gills and with excrement.

In transitional fish, for example, the European eel, "switching" of the methods of osmoregulation carried out by the kidneys and gills occurs, depending on what water they are in.

Excretory system in amphibians

Being cold-blooded inhabitants of the terrestrial-aquatic environment, amphibians, like fish, remove harmful products of metabolism through naked skin and trunk kidneys. In frogs, newts, Ceylon fish, the organ of excretion is represented by paired kidneys located on both sides of the spine, with the ureters that flow from them flowing into the cloaca. Partially gaseous metabolic products are removed from them through the segments of the lungs, which along with the skin perform the excretory function.

Pelvic kidneys are the main organs of allocation of birds and mammals

In the process of evolutionary development, the trunk kidneys are modified into a more progressive form of the excretory organ - pelvic kidneys. They are located deep in the pelvic cavity, near the cloaca in reptiles and birds, and near the gonads (testes and ovaries) - in mammals. The mass and volume of the kidneys decrease, but the filtration capacity of renal nephron cells increases significantly, and this leads to the fact that the organs of excretion in animals belonging to classes of birds and mammals are much more effective in purifying blood from decay products and protect the body from dehydration.

In addition, in birds, unlike all other terrestrial vertebrates, there is no bladder, so urine does not accumulate, and from the ureters comes immediately to the cloaca, then outward. This is an adaptation that reduces the body weight of birds, which is important, given their ability to fly.

Filtration and adsorption function of human kidneys

In humans, the organ of excretion - the kidneys - reaches its highest development and specialization. It can be considered as a very compact (the weight of both kidneys of an adult does not exceed 300 g), a biological filter that passes through its nephron cells, up to 1500 liters of blood per day. In physiology and medicine, the normal work of this body is given special significance. And in the Chinese health system, the U-Sin kidneys are the main life-supporting element.

The renal parenchyma contains about 2 million nephrons consisting of Bowman-Shumlyansky capsules, in which the process of blood filtration and formation of primary urine occurs, and convoluted tubules (Henle loops), providing reabsorption - selective extraction of glucose, vitamins and low-molecular proteins from the primary urine, and Returning them to the bloodstream. As a result of reabsorption, secondary urine is formed. It contains excess water, salts, urea. It drains into the renal pelvis, and from them into the ureters, and further into the bladder. This is about 2 liters / day. From it, it is removed through the urethra to the outside.

Thus, the accumulation of fluid in the cavity of internal organs is not allowed and organism intoxication is prevented.

Additional organs for the release of metabolic products

In addition to the kidneys that play the main role in osmoregulation and removal of excess salts and toxins, the lungs, skin, sweat and digestive glands are partially excretory in the human body. So, as a result of gas exchange, carried out by the alveoli, of which the lung segments are composed, carbon dioxide, water vapor, toxic substances, for example, decomposition products of ethanol, are released. By excretion of the sweat glands, urea, an excess of salts and water is removed. The liver, in addition to the leading role in the process of digestion, inactivates the toxic products of the breakdown of proteins, drugs, alcohol, cadmium salts and lead contained in venous blood.

The work of all organs (kidneys, lungs, skin, digestive and sweat glands), which is characterized by excretory function, ensures the normal course of all metabolic reactions and homeostasis.