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 respiration, digestion, blood circulation, excretion and reproduction. This article will consider the system of excretory organs of humans and animals, their structure and functions, as well as their significance in the metabolic reactions of living organisms.
Biological significance of excretory organs
As a result of the metabolism that occurs in every cell of a living organism, a large amount of toxic substances accumulate: carbon dioxide, ammonia, s alts. To remove them, a system is needed that removes toxins into the external environment. The structure and functions of the organs of the excretory system are studied by anatomy and physiology.
For the first time, a separate excretory organ appears in invertebrates with bilateral symmetry. The walls of their body consist of three layers: exomeso- and endoderm. For such organismsinclude flatworms and roundworms, and the excretory system itself is represented by protonephridia.
How the excretory organs function in flatworms and nematodes
Protonephridia are a system of tubular formations extending from the main longitudinal canal. They are formed from the outer germ layer - the exoderm. Toxins and excess ions are removed to the surface of the body of helminths through the pores.
The inner end of the protonephridia is provided with a group of processes - cilia or flagella. Their undulating movements mix the intercellular fluid, which enhances the filtration functions of the excretory ducts.
Progressive complications of excretory organs in annelids
Rings, for example, earthworm, nereis, sandworm, remove metabolic products from their body using metanephridia - the excretory organs of worms. They have the form of tubules, one end of which is leukoidly expanded and equipped with cilia, and the other goes to the integument of the animal and has a hole - a pore. The complication of 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 type of arthropods, the excretory organ has the form of branching tubules, into which dissolved metabolic products and excess water are absorbed 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, except for excretorytubules, there is another organ - the fat body, in which metabolic products accumulate. Malpighian vessels, into which toxic substances have entered, flow into the posterior intestine. From there, the metabolic products are excreted through the anus.
The excretory organ in crustaceans - crayfish, lobsters, spiny lobsters - is represented by green glands, which are modified metanephridia. They are located on the cephalothorax of the animal, behind the base of the antennae. Under the green glands in crustaceans is the bladder, which opens with an excretory pore.
Excretory organ in fish
In representatives of the class of bony fish, there is a further complication of the excretory system. It has the appearance of dark red ribbon-like bodies - trunk kidneys located above the swim bladder. From each of them departs the ureter, through which urine flows into the bladder, and from it - into the urogenital opening. In representatives of 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 bony fish are divided into three groups: those living in fresh water, in s alt water, as well as a group of so-called anadromous living in both s alt and fresh water due to the characteristics of spawning.
Freshwater fish (perch, crucian carp, carp, bream), in order to avoid excess water intake into their body, are forced to remove a large amount of fluid through the renal tubules and Malpighian glomeruli of the kidneys. So, carp releases up to 120 ml of water per 1 kgits mass, and catfish - up to 380-400 ml. To prevent the body from experiencing a shortage of s alts, the gills of freshwater fish act as pumps that pump sodium and chlorine ions from the water. Marine life - 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 s alt. Excess sodium chloride is eliminated through the gills and feces.
In anadromous fish, such as the European eel, there is a "switch" in the way osmoregulation is carried out by the kidneys and gills, depending on what water they are in.
Amphibian excretory system
Being cold-blooded inhabitants of the terrestrial-aquatic environment, amphibians, like fish, remove harmful metabolic products through bare skin and trunk kidneys. In frogs, newts, and the Ceylon fish snake, the excretory organ is represented by paired kidneys located on both sides of the spine, with ureters extending from them, flowing into the cloaca. Partially, gaseous metabolic products are removed from them through segments of the lungs, which, along with the skin, perform an excretory function.
Pelvic kidneys are the main excretory organs of birds and mammals
In the process of evolutionary development, the trunk kidneys are modified into a more progressive form of the excretory organ - the pelvic kidneys. They are located deep in the pelvic cavity, almost next to the cloaca in reptiles and birds,and near the gonads (testes and ovaries) - in mammals. The mass and volume of their kidneys decrease, but the filtration capacity of the renal nephron cells increases significantly, and this leads to the fact that the excretory organs in animals belonging to the classes of birds and mammals much more effectively cleanse the blood of decay products and protect the body from dehydration.
In addition, birds, unlike all other terrestrial vertebrates, do not have a bladder, so urine does not accumulate in them, but from the ureters it immediately enters the cloaca, then out. This is a device that reduces the body weight of birds, which is important, given their ability to fly.
Filtration and adsorption functions of human kidneys
In humans, the excretory organ - 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) biological filter that passes through its cells - nephrons, up to 1500 liters of blood per day. In physiology and medicine, the normal functioning of this organ is of particular importance. And in the Chinese Wu Xing system of he alth, the 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 filtering blood and the formation of primary urine, and convoluted tubules (Henle's loops), providing reabsorption - selective extraction of glucose, vitamins and low molecular weight proteins fromprimary urine, and their return to the bloodstream. As a result of reabsorption, secondary urine is formed. It contains excess water, s alts, urea. It drains into the renal pelvis, and from them into the ureters, and then into the bladder. This is about 2 l / day. From it, she is removed through the urethra to the outside.
Thus, fluid accumulation in the cavity of internal organs is not allowed and intoxication of the body is prevented.
Additional organs excreting metabolic products
In addition to the kidneys, which play a major role in osmoregulation and removal of excess s alts and toxins, the lungs, skin, sweat and digestive glands perform a partial excretory function in the human body. So, as a result of gas exchange carried out by the alveoli, which make up the segments of the lungs, carbon dioxide, water vapor, and toxic substances, such as ethanol decomposition products, are removed. By excretion of sweat glands, urea, excess s alts and water are removed. The liver, in addition to its leading role in the process of digestion, inactivates toxic breakdown products of proteins, drugs, alcohol, cadmium and lead s alts contained in venous blood.
The work of all organs (kidneys, lungs, skin, digestive and sweat glands), which have an excretory function, ensures the normal course of all metabolic reactions and homeostasis.
