The digestive system of reptiles, like that of other vertebrates, is represented by the digestive tract and glands.
Digestive tract: mouth – pharynx – esophagus – stomach – intestines (small, thick, the rudiment of the cecum appears) – cloaca.
The mouth contains teeth that fuse with bones and a long, muscular tongue.
Snakes have a venom gland that secretes venom. According to their effect, snake venoms are subdivided into blood clotting (for example, in vipers) and affecting the nervous system (for example, in cobras).
Digestive glands – secrete substances (enzymes) necessary for the digestion of food:
- salivary glands – secrete saliva;
- liver – secretes bile;
- pancreas – secretes pancreatic juice.
The respiratory system is represented by light and developed airways – the larynx, trachea, bronchi.
The increase in the area of the respiratory surface due to the folded inner surface of the lungs (the cellular structure of the lungs) led to a more complete saturation of blood with oxygen.
The frequency of respiratory movements in reptiles depends on the ambient temperature (the higher it is, the more often the animal breathes).
In snakes, only one lung is preserved (due to the elongated shape of the body).
The circulatory system is closed and consists of the heart and blood vessels.
Two circles of blood circulation.
Unlike the heart of amphibians, reptiles have a septum in the ventricle of the heart. It is incomplete, and therefore the blood is still mixing in the ventricle.
All reptiles receive mixed blood to the cells of organs and tissues, therefore these animals have a relatively low level of metabolism (reptiles are cold-blooded animals, that is, they do not maintain a constant body temperature).
The heart of most representatives is three-chambered, with an incomplete septum (in crocodiles, the heart is four-chambered).
The reptile brain develops in the direction of an increase in the forebrain (its cerebral hemispheres). The surface of the cerebral hemispheres is absolutely smooth. About 1/4 of the volume of the cerebral hemispheres of the forebrain is occupied by the cerebral cortex, which is responsible for complex forms of behavior. The rest of the volume is striped bodies responsible for instinctive behavior.
Due to this structure of the brain, reptiles have more complex behavior than amphibians.
The movement of reptiles is more complicated than that of amphibians, and therefore, they have a well-developed cerebellum.
The olfactory lobes of the forebrain and the visual hillocks of the midbrain are well developed, which indicates well-developed sense organs.
The sense organs are well developed and adapted to terrestrial existence.
The eyes have two leathery eyelids and a nictitating membrane.
The organ of hearing is the inner and middle ear, protected by the eardrum. The middle ear has only one ossicle. In the inner ear, the cochlea is somewhat isolated.
There are organs of smell, touch and taste.
The organ of touch is most often the tongue.
In snakes, the eyelids are transparent and fused, there is no eardrum (there is an inner and middle ear). They have seismic hearing (they are good at picking up sounds that travel on land or water).
Pythons, vipers, rattlesnakes, and some other snakes have special thermoreceptors that sense heat from warm-blooded animals. That is why the snake, even without seeing, for example, a rodent, feels its presence.
The excretory system is formed by the pelvic kidneys, bladder, and ureters.
In reptiles, it is not liquid urine that is excreted through the cloaca, but uric acid – a clot of filtered metabolic products. Reabsorption of water occurs in the renal tubules. This prevents the animals from losing fluid.
Reproduction and development
Reproduction and development of reptiles takes place on land.
Fertilization is internal.
Most reptiles lay eggs. Outside, the egg is covered with a dense leathery shell, like in many species of lizards and snakes. Or lime shells like turtles and crocodiles. Eggs contain a lot of nutrients necessary for the development of the embryo (its development takes place entirely in the egg).
There are ovoviviparous reptiles (common viper, legless spindle lizard, viviparous lizards), as well as viviparous reptiles with a placenta (sea snakes and some chameleons).