Circulatory system of a turtle. Turtle skeleton: structure (photo)

Skeleton structure of turtles

The axial skeleton (spine) consists of the cervical, thoracic, lumbar, sacral and caudal sections. The cervical spine consists of eight vertebrae, of which the two anterior ones form a movable joint. Trunk section - vertebrae (up to 10) grow with their upper arches to the carapace.

The first few vertebrae are long and attach to the sternum to form the rib cage. The sacral vertebrae bear wide transverse processes to which the pelvis is attached. There are many caudal vertebrae (up to 33), they gradually decrease in size, lose processes and turn into small, relatively smooth bones. The tail section is very mobile. The skull is almost completely ossified and, compared to the skull of amphibians, consists of a larger number of bones. It consists of two sections - cerebral and visceral.

Skeleton of limb girdles. The shoulder girdle is located inside the chest. It consists of three highly elongated bone rays. The scapula stands almost vertically, is rod-shaped and is attached to the carapace by a ligament in the area of the transverse processes of the first thoracic vertebra.

The pelvic girdle of turtles is tightly connected to the spine, and through it to the carapace. The iliac bones of turtles lie strictly vertically, and the pubic and ischial bones lie horizontally. These bones fuse with each other along the midline so that the lower part of the turtles' pelvis bears two foramina.

Swamp turtle skeleton:
1 - acromial process
2 - clavicular element
3 - rib elements
4 - coracoid
5 - chest element
6 - pubisciatic foramen
7 - ilium
8 - ischium
9 - edge elements
10 - neural elements
11 - neck elements
12 - pubic bone
13 - tail element
14 - blade

The skeleton of reptile limbs in turtles is quite typical for terrestrial vertebrates, however, the tubular bones (especially the humerus and femur) are greatly shortened, and the number of bones of the wrist, tarsus, metatarsus and phalanges of the fingers is reduced. Particularly strong changes are expressed in land turtles (due to their walking on their fingers), so that only the claws remain free.

The structure of a turtle's shell

The shell, which serves as a means of passive protection, allows turtles to be accurately distinguished from other animals. The turtle shell is the most important distinguishing feature of all turtles. It protects the turtle from injury, serves as protection from enemies, retains body heat, and gives strength to the turtle skeleton. The shell is so strong that it can withstand 200 times the weight of the owner.
The shell of turtles is a bone formation. It consists of a convex dorsal shield - the carapace, and a flat abdominal shield - the plastron. On average, most turtles have 38 horny scutes covering the carapace and 16 covering the plastron.

The carapace is composed of bone plates of skin origin, with which the ribs and processes of the vertebrae are fused. In total it consists of approximately 50 bones. Skin derivatives participate in the formation of the outer layer, and mesoderm derivatives participate in the formation of the middle layer. Skeletal elements are also attached to the middle layer below: ribs and spinous processes, arches of the trunk vertebrae. The plastron plates were formed from the clavicles and abdominal ribs. Both shields are either movably connected by a tendon ligament or firmly fused by a bone bridge. The top of the shell of most turtles is covered with symmetrical horny scutes. The seams between the plates and scutes do not coincide, which gives the shell special strength (in one group - soft-skinned turtles - the bony shell is covered with soft skin on top). The turtle's shell has holes in the front and back through which the animal extends its limbs. In some species, the moving parts of the shell can tightly close both openings (or one of them) in a moment of danger.

The shape of the shell is associated with the way of life of turtles: in terrestrial species it is high, dome-shaped, often tuberculate, in freshwater species it is low, flattened and smooth, in marine species it is streamlined, teardrop-shaped. The shell can be massive, low, light, narrow, miniature, saddle-shaped. Their shape depends on the environment - the result of adaptation.

A reduction in the plastron, as well as a reduction in the shell in general, occurs in the most aquatic turtles (mud turtles, snapping turtles, three-clawed turtles, sea turtles). In particular, in snapping and mud turtles the plastron is reduced to a small "cross" on the belly. In the most terrestrial aquatic turtles, the plastron is well developed and, moreover, in some genera (Asian hinged turtles and American box turtles) it has movable parts and is capable of closing. The same big-headed turtle, with its strange habits and the attributed ability to climb sloping trees near bodies of water, has a well-developed plastron, compared to snapping and mud turtles. It turns out that mobility is more important in water, and reliable protection on land.

The shell of turtles is a bone formation and only on the outside is it covered with horny plates. The structure of the carapace plates resembles a large horny shield. Each scute has its own growth zone and grows throughout life. In turtles of temperate latitudes, growth occurs more rapidly in the warm season. New portions of keratin form “growth rings”. In young turtles, and especially in those bred in captivity, during the first few years of life, keratin is deposited in the form of many thin rings (this does not correspond to the age of the turtle). Often, the “growth rings” can provide information about the age of the turtle, the time when it came into captivity, the onset of a chronic disease associated with impaired growth, the correctness of the conditions of detention, etc.

“Pyramidal” shell growth is a pathological process, sometimes observed when young land turtles are kept improperly in captivity, and is also associated with a violation of keratin deposition and with a discrepancy in the growth rate of the bone and horny plates of the shell.

Names of carapace scutes:

Carapace:
1 - nape (cervical, central)
2 - marginal cervical
3 - marginal fore and hind limbs (peripheral)
4 - vertebral (central, dorsal)
5 - edge lateral (literal edge)
6 - costal (lateral)
7 - supra-caudal (anal, caudal)
8 - movable joint

Plastron:
1 - interthroat
2 - throat
3 - shoulder
4 - axillary
5 - chest
6 - abdominal
7 - femoral
8 - anal (anal)
9 - inguinal
10 - movable joints

Skeleton of carapace and plastron:
1 - occipital (neck) plate
2 - proneural plate
2" - neural plate
3 - supracaudal (metaneural) plate
4 - caudal (sacral) plate
5 - edge plates
6 - atrial plate
6" - rib plates
7 - entoplastron
8 - epiplastron
9 - gioplastron
10 - mesoplastron
11 - hypoplastron
12 - xiphiplastron
13 - preplastron
14 - gioplastron

In young turtles, wide gaps (lacunae) remain between the bone plates. During the growth process (the first 1-2 years of life), the bone plates quickly grow towards each other and zigzag sutures form between them. After this, growth noticeably slows down and shifts to the periphery of the plates. In some species of turtles, cartilaginous tissue develops at the junction of the plates and a semi-movable joint is formed. In turtles of the genus Cuora and Terrapene, the plastron can close in front and behind - along the boundaries of the middle plates of the plastron. In the turtles Pyxis arachnoides and Kinosternon, the plastron is closed only in the anterior part. In Kinixis, the posterior part of the carapace is capable of closing.

The ancestors of turtles are believed to have appeared in the Triassic period of the Mesozoic era, i.e. about 220 million years ago. Their shell developed from ribs, which, over the course of evolution, gradually expanded and fused together to form a hard shell.

The most famous ancestor of modern turtles, Odontochelys semitestacea, living in the Late Triassic, was found in southwestern China. This turtle, about 20 cm long, had teeth on the upper and lower jaws. Its shell was not fully developed - Odontochelys had only the hard lower part of the shell - the plastron, while its carapace was not developed and consisted of expanded ribs. It also had a long tail and elongated preorbital (preorbital) skull bones. It is believed that Odontochelys was a marine inhabitant.

Distinctive features of the order Turtles (TESTUDINES) are the following:

The body is enclosed in a bony shell, covered on top with horny scutes or skin (in the Far Eastern). The head on a long, movable neck, like the legs, can usually be retracted under the shell. There are no teeth, but the jaws have sharp horny edges. Eggs with a hard, calcareous shell.

Skin of turtles

Turtle skin consists of two main layers: the epidermis and the dermis. The epidermis completely covers the entire surface of the body, including the carapace. In turtles, molting occurs gradually and the epidermis changes in certain areas as it wears out. In this case, a new stratum corneum is formed, lying under the old one. Lymph begins to flow between them and fibrin-like proteins begin to flow. Then lytic processes increase, which leads to the formation of a cavity between the old and new stratum corneum and their separation. Land turtles normally shed only their skin. Large scutes on the head, paws and shell scutes should not shed.

The head is located on a long, movable neck and can usually be retracted under the shell in whole or in part, or placed on its side under the shell. The roof of the skull does not have temporal pits and zygomatic arches, that is, it is of the anapsid type. The large orbits are separated along the midline by a thin interorbital septum. At the back, the ear notch protrudes into the roof of the skull.

The turtle's mouth contains a thick, fleshy tongue.

Cardiovascular system of turtles

The cardiovascular system is typical for reptiles: the heart is three-chambered, large arteries and veins are connected. The amount of under-oxidized blood entering the systemic circulation increases with increasing external pressure (for example, during diving). The heart rate decreases, despite the increase in carbon dioxide concentration.

The heart consists of two atria (left and right) and a ventricle with an incomplete septum. The atria communicate with the ventricle through a bifid canal. A partial interventricular septum develops in the ventricle, due to which a difference in the amount of oxygen in the blood is established around it.

In front of the thymus gland is the unpaired thyroid gland. Its hormones play a very important role in the regulation of general tissue metabolism, influence the development of the nervous system and behavior, the functions of the reproductive system and growth progress. In turtles, thyroid function increases during wintering. The thyroid gland also produces the hormone calcitonin, which slows down the resorption (absorption) of calcium from bone tissue.

All turtles breathe through their nostrils. Open mouth breathing is abnormal.

The external nostrils are located at the front end of the head and look like small round holes.

The internal nostrils (choanae) are larger and oval in shape. They are located in the anterior third of the palate. When the mouth is closed, the choanae are closely adjacent to the laryngeal fissure. At rest, the laryngeal fissure is closed and opens only during inhalation and exhalation with the help of the dilator muscle. The short trachea is formed by closed cartilaginous rings and at its base is divided into two bronchi. This allows turtles to breathe with their heads pulled inward.

Digestive system of turtles

Most land turtles are herbivores, most aquatic turtles are carnivores, and terrestrial turtles are omnivores. Exceptions occur in all groups.

All modern turtles have completely reduced teeth. The upper and lower jaws are covered with horny sheaths - rhamphotheca. In addition to them, the front paws can be involved in grinding and fixing food.

Vision turtles

The main structure of the eye is an almost spherical eyeball, located in the recess of the skull - the orbit and connected to the brain by the optic nerve. It extends from the inside of the eyeball and is enclosed in a sheath. Accommodation of the lens is carried out by contraction of the ciliary muscle, which in turtles is striated, and not smooth like in mammals.

A characteristic feature of turtles is the presence of a shell, the upper part of which is called the carapace, and the lower part is called the plastron, they are connected to each other by bony bridges. The carapace consists of approximately 50 bones, developed from the ribs, spine and skin elements. The plastron is formed from the clavicles, interclavicular bones and abdominal ribs.
The bone carapace is covered with a layer of keratin sheets called scutes, the pattern of which does not follow the pattern of the underlying bones, that is, the junctions of the scutes do not correspond to the bone sutures. Both the bones of the shell and the scutes are able to recover (regenerate). New scutes appear in turtles during a period of intensive growth. In some species, the scutes form ring-shaped growth zones, from which the age of the animal can be approximately determined. This method is not absolutely reliable, requires experience and gives the most reliable results in turtles of temperate climate zones. In aquatic species, for example, the scutes may molt several times during one year, which also leads to the formation of rings, but cannot be an indicator of age. Constant growth in captivity is a common phenomenon; growth zones may become smoother. Thus, contrary to popular belief, it is impossible to accurately determine the age of a turtle by the number of so-called “annual rings”.
There are different types of shells. The shell bones of leatherback, soft-bodied and two-clawed turtles are reduced and the scutes are replaced by tough skin. Most newborn turtles have holes between the carapace bones, which close with age in most but remain in some species, such as the elastic turtle.
Many species of turtles have hinged shells, such as those of box turtles.
When calculating drug doses, some doctors subtract 33-66% of body weight, attributing it to the shell. However, since bones are metabolically active, this practice is not justified from a physiological point of view.
Another characteristic feature of turtles is that the girdles of the thoracic and pelvic limbs are located inside the rib cage. The vertical arrangement of the limb girdles strengthens the armor and provides a strong foundation for the femur and humerus.
With few exceptions, the bones of the limbs themselves are similar to those of other vertebrates. The elongated fingers of some marine and freshwater species help them when swimming.
Retraction of the head and neck is ensured by powerful muscles. The muscles running from the shoulder and pelvic girdles to the plastron are also well developed; they are even visible on x-rays.

Turtle skin

The skin of turtles can be ironed or covered with scales. Representatives of the family of land turtles (Testudinidae) have the thickest skin. The thickness of the skin is taken into account when choosing the injection site; usually they try to choose places with the least amount of scales. Like all reptiles, turtles' skin sheds periodically, coming off in pieces, which is especially noticeable in aquatic turtles.

Respiratory system of turtles

Due to their hard shell, the breathing process in turtles proceeds differently than in other vertebrates that have a movable chest. Turtles inhale and exhale through their nostrils; mouth breathing is a sign of pathology. The glottis is located at the root of the tongue. In cryptonecked turtles, the trachea is relatively short and quickly branches into two main bronchi, which open into the lungs. The location of the tracheal bifurcation close to the head allows turtles to breathe freely with their heads pulled inside the shell. The lungs are attached dorsally (above) to the carapace, and ventrally (below) to a membrane associated with the liver, stomach and intestines. Turtles do not have a true diaphragm separating the lungs from the abdominal organs. The lungs are large, segmented sac-like structures that resemble a sponge in appearance. The surface of the lungs is dotted with stripes of smooth muscle and connective tissue. Despite the fact that the volume of the lungs is large, their respiratory surface is much smaller than that of mammals. The large volume of the lungs allows aquatic turtles to use them as a buoyancy organ.
Breathing involves many structures. Antagonist muscles significantly increase or decrease the volume of the body cavity, and therefore the lungs. This is done through movements of the limbs and head. Turtles, like amphibians, are able to inflate their throats, but unlike the latter, they do this not while breathing, but for the purpose of smell.
In submerged snapping turtles, inhalation is an active process and exhalation is a passive process, resulting from hydrostatic pressure. On land, the opposite happens. Turtles do not have negative pressure in the chest, so open fractures of the shell, even if the lungs are visible in the fracture, do not lead to respiratory depression. Evacuation of foreign bodies from the lungs naturally is more difficult in turtles compared to mammals. Thus, they lack ciliated epithelium in the lungs, the bronchi drain poorly, they are segmented and have large cavities, and the absence of a muscular diaphragm makes coughing impossible. As a result, pneumonia in turtles is difficult to treat and often leads to death. In pond, snapping and side-necked turtles, the cloacal bursa provides respiration during hibernation under water. The Nile softshell turtle (Tryonyx triunguis) receives 30% of its oxygen through vascularized papillae in the pharynx and the rest through the skin.
Many Australian species are able to consume oxygen using the cloacal bursa, which allows them to remain under water for a long time, which is important during hibernation. The record holder for cloaca breathing is the Fitzroy's turtle (Rheodytes leukops), which can draw in and expel water from the cloaca 15-60 times per minute. This breathing supports the life of turtles during the resting period, however, in the active stage they need oxygen from the air. Turtles are capable of holding their breath for long periods of time, which makes gas anesthesia impossible without premedication and intubation.

Gastrointestinal tract of turtles

The tongue of turtles is large, thick and does not extend out of the mouth, like that of snakes and turtles. Most land turtles are herbivores; among aquatic turtles there are herbivores and carnivores.
Turtles do not have teeth; they tear off pieces of food using a scissor-shaped beak, or rhamphotheca. In captivity, rhamphotheca must be periodically pruned, and a lack of calcium in the diet can cause its irreversible deformation. The salivary glands produce mucus, which helps swallow food, but does not contain digestive enzymes. Aquatic species eat underwater. The esophagus runs along the neck. It is easier to probe the esophagus of large turtles with the head fully extended from the shell, but in this position it will be more difficult to open the mouth, so when probing, when possible, place a plastic tube into the esophagus without pulling the head out of the shell.
The stomach lies on the lower left and has the esophageal and pyloric sphincters. The small intestine is relatively short (compared to mammals), weakly contracts, and absorbs nutrients and water. Digestive enzymes are produced in the stomach, small intestine, pancreas and liver. The pancreas is a pale orange-pink organ that may be associated with the spleen and is connected to the duodenum by a short duct and has endocrine and exocrine functions similar to those of mammals.
The liver of turtles is a large, saddle-shaped organ that is located directly under the lungs. It consists of two main lobes, between which the gallbladder is located, and also has recesses for the heart and stomach. The liver is dark red in color, and in some species it is pigmented with melanin. A pale yellowish-brown hue is not normal. The small and large intestines are connected by the ileocercal valve. The cecum is poorly developed. The large intestine is the primary site of microbial digestion in herbivorous turtles. The rectum ends in the cloaca.
The time it takes for food to pass through the gastrointestinal tract depends on many factors, including temperature, frequency of feedings, and the percentage of water and fiber in the diet. Under natural conditions, the transit time is longer than in captivity. Metoclopramide, cisapride and erythromycin do not affect the rate of passage of food through the gastrointestinal tract of turtles.

Urogenital system of turtles

The kidneys in turtles are metanephric, located in the posterior part of the body behind the acetabulum (in most marine species - in front of the acetabulum).
Reptiles are unable to concentrate urine, presumably as a result of the absence of the Petit of Henle. Soluble nitrogen breakdown products such as ammonia and urea require large amounts of water for excretion, which can only be easily achieved in aquatic and semi-aquatic species. Land turtles do not produce as many water-soluble nitrogenous wastes, replacing them with insoluble ones such as uric acid and urate. This complicates the diagnosis of kidney diseases in turtles using standard methods for mammals, based on the determination of urea nitrogen and creatinine in the blood. Serum uric acid levels may increase with kidney disease in turtles, but may remain unchanged.
Unlike other reptiles, turtles' urogenital tracts open into the bladder neck rather than into the urodeum of the cloaca. The bladder is bilobed with a very thin wall. Land turtles use the bladder as a reservoir for water. Water can be absorbed in the cloaca, rectum and bladder, which must be taken into account when prescribing drugs excreted through the kidneys.
The paired gonads are located in front of the kidneys. Fertilization is internal. The upper part of the oviduct secretes the protein for the egg, and the lower part secretes the membrane. Male turtles have an unpaired, large, pigmented penis. In a calm state, it lies in the lower part of the cloaca and does not participate in the excretion of urine. In an excited state, it is removed from the cloaca, and on it you can see a groove intended for the transport of sperm. The penis of turtles does not screw in like those of snakes and lizards.

Circulatory system of turtles

The heart of turtles is three-chambered with two atria and one ventricle. Although this design may involve mixing of oxygen-rich blood from the lungs and oxygen-poor blood from the internal organs, in fact, the rows of muscle ridges and the periodicity of ventricular contractions prevent this.
The right atrium receives oxygen-poor blood from the systemic circulation through the sinus venosus, a large vascular chamber on the dorsal (carapace-facing) surface of the atrium. The wall of the venous sinus is muscular, but not as thick as that of the atrium. Blood enters the venous sinus from four veins:

right anterior vena cava
left anterior vena cava
posterior vena cava
left hepatic vein

The ventricle itself is divided into three subchambers: pulmonary, venous and arterial. The pulmonary chamber is the lowest part of the ventricle of the heart of turtles, it reaches the opening of the pulmonary artery. The arterial and venous cavities are located above it and receive blood from the left and right atrium, respectively. The left and right aortic arches extend from the venous cavity in front and behind.
The muscular crest to some extent separates the pulmonary cavity from the arterial and venous ones. The arterial and venous cavities are connected by the intraventricular canal.
Single-leaflet atrioventricular valves partially cover the intraventricular canal during atrial systole, and during ventricular systole they prevent the reflux of blood from the ventricle into the atria.
Functionally, the circulatory system of turtles is dual in nature, which is achieved by a series of muscle contractions and successive changes in pressure. Contraction (systole) of the atria directs blood into the ventricle. The position of the atrioventricular valves in the intraventricular canal leads to the fact that blood from the systemic circle is directed through the right atrium into the pulmonary and venous cavities. At the same time, blood from the lungs from the left atrium enters the arterial cavity. Ventricular systole is caused by contraction of the venous cavity. Successive contractions of the venous and pulmonary cavities cause blood to flow from them into the pulmonary circulation, which is an area of low pressure.
After systole, the arterial cavity begins to contract. Blood enters through the partially contracted venous cavity into the systemic circulation through the right and left aortic arches. Blood does not enter the pulmonary cavity, since as a result of contraction of the ventricle, the muscle crest comes into contact with its ventral wall, thereby creating a barrier. The right and left atrioventricular valves prevent the flow of blood from the ventricle into the atria.
The described mechanism occurs only during normal breathing, when a left-to-right shunt is created based on the pressure difference in the chambers of the turtles’ heart. During diving, when the pressure in the lungs increases, the shunt operates from right to left. Thus, during normal breathing in red-eared turtles, 60% of the blood ejected by the heart enters the lungs and only 40% enters the systemic circulation. When diving, pulmonary circulation is reduced and most of the blood enters the systemic circulation.
Like other reptiles, a renal portal system is present. Its significance for drug pharmacokinetics has not been studied, however, it is recommended that potentially nephrotoxic substances be administered into the anterior half of the body.

The structure of a turtle is very complex. This knowledge can be useful when keeping these reptiles at home. Let us begin, perhaps, with an excursion into the anatomy of turtles from the axial skeleton, namely the spine.

Spine

It has cervical, thoracic, lumbar, sacral and caudal sections. Cervical, has eight vertebrae, several anterior ones are connected to form a movable joint. The vertebrae of the body are connected to the ribs. The upper vertebrae, together with the sternum, actually form the chest and cavity, which contains important internal organs. The pelvic bones are attached to the sacral vertebrae. The caudal vertebrae are represented in large numbers; they do not bear any special functional load. The turtle's skull is represented by a large number of bones. It has two sections, cerebral and visceral.

The eyes are located on the side of the head, looking down. These animals eat with the help of a hard beak, which has irregularities similar to teeth. The turtle's head has a fairly streamlined shape, which gives it speed to the marine species.

The turtle's brain has two sections, the head and the dorsal. Despite the fact that the brain is very small in size. Most of the functional load is borne by the spinal cord.

Carapace

The structure of a turtle's shell has a number of features unique to this amphibian. The shell is a distinctive feature of this amphibian from all other species inhabiting our planet. It also serves as protection for reptiles. Functions of the shell:

Protection from injury;
Preservation of heat generated by the body;
Protection of internal organs, axial skeleton.

This structure is very strong, supporting a mass much greater than the weight of the turtle. Components of the shell:

Carapace - dorsal shield;
Plastron - abdominal shield.

The carapace is represented by many bone plates that are firmly connected to the ribs and vertebrae. It consists of half stone, bone plates. The lower shield is formed by ribs. These two shields are connected to each other by ligaments or immovably by bone structures. At the top of the shell there are horny scutes. There are seams between the shields and the plates, but they go in different directions, this gives reinforcement to the frame. In front and behind the shields there are holes for limbs, which the animal can hide inside in case of danger. The shell of different species of turtles has a different shape in its structure. These distinctive features appeared during the process of evolution. They are an adaptive mechanism associated with the living conditions of the reptile.

Bone plates and scutes tend to grow throughout the life of the animal. The intensity of growth is related to climatic conditions; in warm weather they grow faster. Keratin deposited in the plates gives them a ring-shaped shape. Scientists can use these formations to judge the age of the reptile, its health, the presence of diseases, and whether it was kept in captivity.

Young turtles have very large distances between the plates. With intensive growth, the plates grow towards each other, thereby forming a different number of seams.

Leather

The skin has two layers: the epidermis and the dermis. The entire surface of a turtle's body is covered with epidermis; as it ages, it peels off and the animal sheds. The skin is very strong, elastic, and does not contain glands. Moisture does not evaporate through it, so if a sea creature gets on land, the skin will not dry out. But it is capable of absorbing warm liquid. Using this mechanism, the animal controls the balance of water in the body.

Claws

Claws come from the epidermis. They have five toes on their paws and a claw at the distal end. Their number may vary, depending on the type of turtle. At home, it is imperative to take care of them on time, trim or file them. If care is not taken in a timely manner, a blood network is formed inside them, which is then injured and bleeding occurs. Claws grow slowly; their rapid growth indicates pathology. Requires specialist consultation.

The cardiovascular system

The circulatory system forms two closed circles. The heart has three chambers, consisting of two atria and one ventricle, which has an incomplete septum. The right part of the ventricle contains venous blood, which gives it to the pulmonary artery. The middle part, containing mixed blood, leaves the left part of the aortic arch. The left side of the ventricle carries pure arterial blood through the right side of the aorta. Both arches communicate into one aorta, which makes an internal turn around the food tube. The descending aorta carries arteriovenous blood. How is blood enriched with oxygen? Venous blood flows through the pulmonary arteries into the lungs, where it exchanges carbon dioxide, and itself is enriched with oxygen and turns into arterial blood. Through the pulmonary veins it returns to the heart, entering it through the left atrium.

Very important arterial trunks that supply the brain, spinal cord and upper limbs of turtles depart from the aorta. These are the carotid and subclavian arteries. The descending aorta gives off many branches supplying blood to the internal organs, stomach, entire intestinal tract, gonads and lower extremities.

Blood from the head leaves through the jugular veins, first collecting in the sinuses. The paired jugular veins flow into the cava; this is the main vein that collects venous blood from all organs. It flows into the right atrium. The entire cardiovascular system of this reptile is very similar to other amphibians.

Offspring

These reptiles lay eggs. Animals do not hatch them, but put them in a secluded sunny place. The process of babies maturing takes place under the sun. To break through the strong shell, babies have a growth on their head, with which they make their way out. This growth is vestigial. In appearance, these reptiles are an exact copy of adult individuals, only hundreds of times smaller. From birth they are independent, looking for their own food.

Respiratory system

The upper respiratory tract, and in general the entire respiratory system, begins with the nostrils, which conduct incoming air to the choanae. From the choanae, air is thrown into the mouth and moves further along the larynx. The body of the larynx has three cartilages. After the larynx comes the trachea, which consists of half rings giving it a round shape. Next, this tube divides into the right and left bronchus, which flow into the lungs. The chest of these animals is immobile, so the act of breathing is carried out only by expanding the lungs themselves. Accessory muscles help them do this. The volume of lung tissue is quite large, which allows turtles to stay under water for a long time.

Digestive tract

Through the oral cavity, food enters the wide esophagus, which smoothly passes into the stomach. On the left side of the stomach is the spleen, which produces various blood elements. Then the stomach continues with the horseshoe-shaped duodenum, which seems to envelop the pancreas. The pancreas is an organ that produces enzymes necessary for the process of digesting food. The small intestine passes into the large intestine, which ends in the cloaca. It is located outside the tail. Their gastrointestinal tract is quite long. This is necessary for longer digestion of consumed plant foods. The digestive organs also include the liver and gall bladder, the duct of which opens in the thickness of the duodenum.

Urinary system

Turtles have kidneys as an organ for producing and excreting urine. The kidneys are a paired organ located above the pelvic cavity closer to the upper shield. The ureters emerge from the kidneys and open into the cloaca.

The genital organs are represented by the testes and vas deferens, which also open on the cloaca. The mating organ is hidden deep in the cloaca.

The female reproductive organs are represented by ovaries, which do not communicate with the oviducts. The oviduct opens on the anterior abdominal wall with a large funnel. When eggs mature, they fall into the body cavity and then move along the oviduct to the exit.

The turtle will never be able to leave its shell, because it has become fused with it;
The cervical vertebrae are so elastic that they allow you to rotate your head, stick it out or hide it in moments of danger;
The reptile is able to completely hide all parts of its body inside its shell;
Although the shell is protection, it can also be subject to damage;
The turtles were in orbit, from where they returned alive;
They do not have vocal cords, but are capable of making sounds, this occurs by quickly squeezing out a stream of air;
The glands present in the cloaca secrete pheromones, which the male can hear at a distance of several kilometers;
Good blood supply to the cloaca allows gas exchange through it;
These reptiles can live up to hundreds of years;
Not all of these animals are herbivores; they can even eat their own kind, killing them with their massive beak and tearing them apart with their powerful paws.

The turtle has a very interesting body structure. Her body has nothing superfluous, all formations perform a specific function. More detailed information about the structure of the turtle body can be found by reading specialized literature. By the way, it can be purchased in bookstores. Studying the structure of reptiles helps to better understand its habits and food preferences. Create the most favorable conditions for their maintenance.

In the fauna of our planet, reptiles, numbering about 6 thousand species, are represented by several biological groups. One of them is the Turtle squad. Contains 328 species, grouped into 14 families. This article will study the structure and features associated with the aquatic-terrestrial lifestyle of this animal.

Anatomical structure

Representatives of the order live in the steppes, foothills of Pakistan and India, in the deserts of Turkmenistan, Syria and Libya. Like other animals belonging to the reptile family, a number of idioadaptations to a dry and hot climate can be found in the structure of their body, as well as in their life processes. Among such adaptations are dense leathery integuments, the absence of mucous glands, and the presence of horny scales and scutes. These formations consist of fibrillar proteins - keratins. Their function is to increase the mechanical strength of the outer integument.

Since land turtles, for example the steppe and Central Asian turtles, feed on fairly tough plant foods, they have a beak on their heads - a kind of appendage that has sharp edges with teeth. Turtles use it to tear off parts of plants and grind them with tuberous protrusions. The eyes are also located on the head. They are limited to three eyelids: lower, upper and third. Presented in the form of a leathery film that covers only half of the eye. All turtles have well-developed binocular vision and are perfectly oriented in their environment.

Sections of the turtle skeleton

To answer the question whether a turtle has a skeleton, remember that the body of a reptile is anatomically divided into 4 parts. It consists of a head, neck, torso and tail. Let's look at the cross-sectional structure of a turtle. So, its spine consists of 5 sections: cervical, thoracic, lumbar, sacral and caudal. The skeleton of the head is completely bony. It is connected to the neck through two movable vertebrae. In total, the turtle has 8 cervical vertebrae. At the moment of danger, the head is pulled inside the shell due to the presence of a hole in it. Land reptiles perceive low frequency sounds. Turtles are considered “silent” animals because their vocal cords are anatomically poorly developed. That's why they make a hissing or squeaking sound.

Structure and functions of the carapace

Continuing to study the turtle's skeleton, let's look at the upper part of its shell. It has a bulge that looks like a small bell. In land turtles it is especially tall and massive, in aquatic turtles it is flatter and streamlined. The carapace consists of two layers. The outer one contains keratin scales - scutes, and the lower one has a completely bone structure. The vertebral arches of the lumbar-thoracic region and ribs are attached to it. Taxonomists use the color and pattern of the horny scutes of the carapace to determine the species of animals. It is because of this that they were and remain the object of fishing. Glass frames, cases, and knife handles are made from it. The shell has several holes into which the animal retracts its head, limbs and tail in times of danger.

Plastron and its meaning

The lower part of the shell is called the plastron. Between it and the carapace is the soft body of the animal. Both halves of it are united by a bone shell. The plastron itself is an anatomical derivative of the girdle of the forelimbs and ribs. It is as if “soldered” into the body of the turtle. Terrestrial forms have a massive plastron. And in marine inhabitants it is reduced to cruciform plates located on the abdominal part of the body. Due to growth, concentric lines are formed on the scutes of the shell. From them, herpetologists can determine the age of the turtle and its state of health.

Characteristics of the skeleton of the front and hind limbs of a turtle

The skeleton of a turtle, the diagram of which is given below, indicates that animals of this species belong to reptiles. They have the bones of the forelimb girdle attached to their spine: the scapula, the clavicle and the crow's formation. They are located in the middle of the chest. The scapula is connected to the carapace by a muscular fold at the location of the first vertebra. The hind limb girdle consists of the pubis, ilium and ischium. They form the pelvis. The tail section consists of many small vertebrae, so it is very mobile.

Features of the structure of the limbs of land turtles

The forelimbs of reptiles consist of the shoulder, forearm, wrist, metacarpus and phalanges, which is similar to the skeleton of other classes of land animals. However, there are differences in the structure of the bones of the forelimb. For example, the arms are short, and their number forming the carpus is less than in mammals. The hind limbs also have anatomical features. The femur is very short, and their number in the foot is also reduced. This is especially noticeable in land turtles: box turtles, red-eared turtles, and steppe turtles. Since they move along the surface of the earth, the bones of the phalanges of their fingers experience constant mechanical stress. Thus, the skeleton of a turtle has the necessary idioadaptations that contribute to its adaptation to its habitat.

Red-eared turtle: structure and features of life

Among all other species, this animal is the most popular as a pet. The structure is typical of freshwater forms. Its head is well mobile, its neck is long, its carapace is green, and its plastron is yellow. Because of this, the turtle is often called the yellow-bellied turtle. The limbs are massive, covered with horny scutes, ending in claws. In nature, they feed on insects that live in abundance along river banks, fish larvae and fry, as well as algae. The female is easy to distinguish from the male: she is more massive and longer, and her lower jaws are larger. These animals breed from late February to May, laying from 4 to 10 eggs in sandy holes. Baby turtles usually hatch in July or August.

Land species of turtles

This group of reptiles is represented by such animals as the Central Asian tortoise, listed in the Red Book, the Balkan tortoise, and the panther. There are only about 40 species. turtles - shell. It is very massive, with a highly raised plastron. The animals themselves are quite sedentary. The Central Asian turtle depends little on water sources. She can do without it for a long time, feeding on succulent leaves or shoots of herbaceous plants. Since the animal has to adapt to the dry climate of the steppe or semi-desert, its annual activity is strictly regulated. It lasts only 2-3 months, and the rest of the year the turtle spends in semi-torpor or hibernates in burrows dug in the sand. This happens twice a year - in summer and winter.

The structure of the land turtle is characterized by a number of adaptations associated with life on land. These are columnar, massive limbs, the phalanges of which are completely fused, leaving short claws free. The body is covered with horny scales, which prevent excess evaporation and ensure the conservation of water in the tissues of the animal. Thus, the animals are reliably protected by a super-strong bone-horny shell. In addition, they can scare away potential enemies with sharp hissing sounds or very rapid emptying of a large bladder. All types of land turtles are long-lived. They can live from 50 to 180 years. In addition, they are highly adaptable and resilient.

However, let's not forget that 228 species of turtles need protection and are on the verge of extinction. For example, the range of the green turtle is rapidly decreasing. It serves as a commercial object, as people eat its meat. Due to urbanization and a decrease in the area of natural habitat, the number of animals is decreasing every year. The question of the advisability of keeping turtles in human dwellings, even if they are localized in specially equipped terrarium conditions, remains controversial. A negligible number of these animals survive to their biological age in captivity. The majority die from a person’s ignorant and irresponsible attitude towards them.