A living organism is a whole system of interconnected organs and tissues. Thanks to their coordinated work, the animal can function normally. And it doesn’t matter what stage of development the organism is at. The only difference is that representatives of the fauna can be at different stages of evolution, which means that animal organs and organ systems also differ in terms of structure and work. The principle of phylogenesis is based on this.
The structure of the animal organs
Most organs have a general structural structure: connective tissue membrane, muscle layer and inner layer. Depending on the work and functions, these layers can be well developed, absent or supplemented by other areas.
Not all animals form organs. For example, intestinal and sponges, flatworms remained at the tissue level of organization.
Biology. Animal organ systems
Initially, the body of organisms consisted of differentiated cells. In the process of evolution, animal organs, organ systems were formed. They vary in function, but their work is aimed only at one thing - maintaining a constant internal environment of the body and normal life.
The following organ systems are distinguished:
1. Circulatory.
2. Digestive.
3. Musculoskeletal.
4. Excretory.
5. Respiratory.
6. Endocrine.
7. Nervous.
8. Sexual.
9. The sensory system.
Animal circulatory system
The circulatory system first appears in annelids, and in them it is of a closed type. The two main vessels are the dorsal and ventral. They are connected in the front part of the worm’s body by powerful channels, which are trivially called “hearts”, but these are not separate organs, but ordinary vessels, the walls of which contain a thick layer of muscle tissue.
Further, the evolution of organs was as follows:
- in all types of animals up to mollusks inclusive circulatory system of the open type;
- the cephalic chordate system is closed, but the heart is not yet;
- starting with cyclostomes (myxines, lampreys), a two-chambered heart appears;
- in amphibians and reptiles, the heart is three-chambered, the blood mixes;
- birds and mammals have a 4-chamber heart, due to which they can maintain a constant body temperature (homeothermic organisms).
Digestive system
The digestive system was first described in flatworms (in the form of closed channels). There is no anus. Subsequently, the internal organs of animals evolved as follows:
- in roundworms , a through intestinal tube appears: the posterior intestine and the anus (in the flat ones, there were only two sections of the intestine);
- in annelids, calcium salivary glands are formed, the task of which is the decomposition of detritus;
- in arthropods, the anterior and middle intestines are lined with chitinous integuments;
- at a lancelet appears hepatic outgrowth;
- in cartilaginous fish - a spiral valve in the small intestine, its function is to increase the suction surface;
- Further, evolution went to lengthen the intestines, and, accordingly, to increase the absorption area.
Musculoskeletal system
The musculoskeletal system consists of two systems: the skeleton and muscles. The skeleton plays the role of support, and the muscles are responsible for movement in space. The evolution of the latter went to greater differentiation and reduction of the metameric arrangement.
- The skeleton appears in cyclostomes.
- In cartilaginous fish, it is cartilaginous; in most bone fish, it is bone.
- With access to land, amphibians have five-fingered limbs, bones of free limbs develop and new sections of the spine appear.
- Reptiles form a chest.
- In birds, there are many changes in the structure of the skeleton in connection with adaptation to flight.
- In mammals, there is a final differentiation of bones.
Excretory system
What animal organs exist? Organ systems also include an excretory system, which is responsible for the removal of metabolic products, toxins and poisons from the body.
- In flatworms, the excretory system is represented by protonephridia.
- In annelids, this is already metanephridia.
- Arthropods have green glands, malpighian vessels.
“The mollusks have a kidney.”
- All subsequent types (before fish) have head kidneys.
- In fish and amphibians, trunk kidneys.
In all, from reptiles to mammals, these functions are performed by the pelvic kidneys.
Respiratory system
It performs the function of assimilating oxygen from the environment. First appears in arthropods.
- In crustaceans, the respiratory system is represented by gills.
- In insects - trachea.
- In mollusks - a lung formed by a mantle cavity.
- In all animals, up to and including fish, the respiratory organs are gills.
- Frogs have bag-shaped lungs.
“Reptiles have honeycombs.”
- In birds - spongy.
- In mammals - alveolar lungs.
Nervous system
The nervous system connects the remaining organ systems into a single organism, giving signals and regulating the work of each site.
The diffuse-type nervous system appears in the intestinal cavity.
“Flatworms have orthogons, or the staircase nervous system.”
- In roundworms, the near-pharyngeal nerve ring and nerve trunks.
- In annelid worms, the periopharyngeal nerve ring and abdominal nerve chain.
- In arthropods, the head ganglion appears and the abdominal nerve chain remains.
- The mollusks have a nerve system.
- In the cephalic chords, an extension of the neural tube appears on the front end of the body.
- In fish, all parts of the brain are isolated.
Further, the reptiles appear rudiments of the cerebral cortex.
In mammals, convolutions of the brain appear.
Reproductive system
The function of the reproductive system is to reproduce its own kind. The reproductive system can be female or male, hermaphrodites (annelids, mollusks) are found. The female system developed gradually. The main organs are the uterus, fallopian tubes, ovaries. Many parasitic worms also have an ootype and additional glands: protein, vitelline.
The male reproductive system consists of the testes and the vas deferens. Next, sperm are thrown out through the copulative organ to the outside or into the female genital organs.
Conclusion
We examined what are the organs of animals. Organ systems play an important role in maintaining the normal functioning of absolutely any individual, be it worms or humans. If each of the systems works correctly, homeostasis of the body is maintained.
Children in biology classes study the structure of living organisms. Visual material allows you to better remember how the organs of animals look. Tables of different systems can be found in almost any biology cabinet.