Reptiles are a highly organized class of vertebrates, which includes 9400 species, leading a terrestrial, less often semi-aquatic life. In this article we will study the internal structure and life activity of reptiles, and also consider some of their features associated with environmental adaptations.
Skeleton and muscles of reptiles
Unlike amphibians, the spine of reptiles has a more complex structure and consists of cervical, thoracic, lumbar, sacral and caudal divisions. The thoracic vertebrae are connected to the ribs and form a thorax. It is absent in snakes, but their spine contains up to 500 vertebrae. The lizard, in contrast to snakes, is well developed thorax, and the tail section of the spine has its own characteristics: the vertebrae of the caudal region have a layer of cartilaginous tissue and they can easily be destroyed. This process is called autotomy. It has a protective value: the animal is rescued from the teeth of a predator, losing part of the tail. The muscular system in reptiles is quite complicated.
This applies, above all, the pectoral intercostal muscles involved in the process of breathing. Significant development was given to the mandibular muscles, as well as the muscles of the hind limbs in reptiles such as lizards and crocodiles. Anatomically, the rather complex internal structure of the reptiles (the table is shown below) is the result of the aromorphoses and adaptations that have arisen in these organisms in the process of evolution.
Complications in the organization of reptiles have affected the cardiovascular system. Continuing to study the internal and external structure of reptiles, let us dwell on its features and the metabolic processes associated with blood circulation. The metabolism of reptiles is less dependent on the temperature of the environment than in amphibians. Nevertheless, reptiles, like amphibians, are poikilothermic organisms and the temperature optimum in them lies in the interval - + 22 - + 38 degrees. The energy costs of reptiles are lower than those of amphibians. This is due to the complication of the structure of the heart, as well as a partial separation in it of the circulation of arterial and venous blood. Features of the internal structure of reptiles, the table of which is shown below, indicate that reptiles have two circles of circulation. Their circulatory system is closed, in the heart there is an incomplete septum, which completely grows in the crocodiles, keeping the hole between the left and right parts.
The main organ of the circulation consists of two atria and a ventricle. Arterial blood is collected in the upper part of the ventricle, entering it from the left atrium, and the venous blood from the right atrium. Thus, the blood is mixed in the lower right side of the ventricle. During systole, oxygen-enriched blood is pushed into the right arch of the aorta. Mixed blood from the right side of the ventricle enters the left arch of the aorta, and the venous from its lower half into the pulmonary artery. Although, considering the internal structure of reptiles, and talking about the two circles of blood circulation, it must be taken into account that they can not be considered independent, since arterial and venous blood are mixed in the dorsal aorta.
Pelvic kidneys of reptiles
The internal structure of reptiles is characterized by a complication in the structure of one of the leading systems - excretory, consisting in the development of metanephros - pelvic kidney. They are located on the ventral side of the pelvis on either side of the cloaca, connecting with it through the ureters. There is also a bladder. Snakes and crocodiles are anatomically weakly expressed. In the products of reptile exchange, unlike mammals, there is not urea, but uric acid.
How does digestion work?
Most reptiles are carnivorous animals, although reptiles such as the lizard are quick, the steppe turtle, and also feed on plants. Studying the internal structure of reptiles, it becomes clear that the digestive tube has a number of morphological features associated with the overall complexity of the organization. So, they form a secondary palate. It is formed by the bones and divides the oral cavity from the nasopharyngeal passages opening into the pharynx with funnel-shaped formations - secondary choans. In the large intestine, it is for the first time that the reptile has a cecum. Digestive glands: liver and pancreas, produce enzymes, and bile emulsifies lipids. The walls of the esophagus and stomach are muscular and dense, which is especially important for species that swallow food whole (for example, snakes) or large pieces (crocodiles). In the school textbooks of biology studying the internal structure of reptiles (Grade 7), there are many interesting facts concerning the nutrition of reptiles. For example, crocodiles and turtles can last longer than all other vertebrates without food, starving for up to six months. For a normal course of digestion, snakes need an ambient temperature of at least 22-25 ° C, otherwise the digestive glands stop producing enzymes, and the food swallowed whole is not digested, but begins to rot in the stomach, which leads to poisoning and death of the animal.
Continuing to study the internal structure and livelihoods of reptiles, consider the seasonal changes occurring in their ontogeny. They are caused by idioadaptation to temperature fluctuations (diurnal and seasonal cyclicity). For example, in the middle of spring, reptiles lead an active lifestyle from noon, when the soil and air warm up sufficiently.
In July - early August, most animals are most active in the morning or evening hours, and at noon they fall into a state of rest. In winter, reptiles of temperate latitudes fall into hibernation, hiding in cracks in rocks, in burrows or under the roots of trees. Summer hibernation is typical for those species of reptiles that at this time of the year lack food.
Molting in reptiles
Cyclically occurs in animals and the process of molting - a change of dry skin, covered with scutes or horny scales. It also depends on the temperature of the environment. Snakes and lizards complete the molt, in this case the entire skin, called the creep, changes. Crocodiles periodically slough off individual scales - osteoderms. Land tortoises exfoliate skin areas that are not protected by corupaks, and water moults are hardly noticeable.
The cyclic processes in the life of animals include the reproductive function, which is also regulated by the temperature of the external environment. Pay attention to the peculiarities of the internal structure of reptiles. The table below confirms the fact that reptiles are dioecious animals that are characterized by internal fertilization.
Male reproductive system
Female reproductive system
1. Spiny testes are located on both sides of the lumbar spine
1. Paired ovaries located on the mesentery in the lumbar region
2. Attachments of testes
2. Oviducts (Muller's canals) open at the anterior end into the body cavity, and the posterior to the cloaca
4. The seminal vesicle
5. The wolf channel
After it, the females lay eggs covered with lizards, turtles and snakes with a leathery shell, and in crocodiles it is calcareous. Some reptiles, for example, an adder, bear eggs inside the body. The light appears up to 12 cubs, which immediately begin to shed. The sexual system of males is represented by paired testes, vas deferens and a wolf canal flowing into the cloaca. The females have paired ovaries. Eggs that have funnel-shaped openings also enter the cloaca.
Nervous system and sense organs
The internal structure of the reptiles will be incomplete without studying the innervation of the organs and functions of the analyzers. The brain has a complex structure.
Associative centers of the cortex provide the development of a system of conditioned reflexes. The organs of sight, hearing, smell, and touch are sufficiently developed. Snakes and some lizards, for example, hatteria, have a parietal eye, which is a photosensitive organ.