What is the external and internal structure of the birds? How do they differ from other classes of animals? What signs are peculiar only to birds? You will find answers to these questions in this article.
General characteristics of birds
Birds are a class of animals whose body is covered with feathers. They have a constant and high body temperature and are active at any time of the year. The ability to fly is characteristic of most representatives of this class. The external and internal structure of birds is subject to this feature.
Birds can easily change their place of residence depending on conditions. Due to the ability to fly, the class is widespread, it is found in a wide variety of conditions around the planet. There are about 9,000 species of birds.
Birds also have a pronounced concern for their own offspring. Reproduction occurs with large, calcareous eggs.
The external structure of birds
The body of a bird consists of a head, a movable neck, a teardrop-shaped body and limbs. The skin is thin and dry due to the absence of skin glands. Most birds have iron, which is used to lubricate feathers - coccygeal. It is especially well developed in waterfowl. The secret secreted by the gland serves to maintain the elasticity of the feathers and prevents them from getting wet. In some species (ostriches, parrots, pigeons, bustards), the function of lubrication is carried out by special powder feathers, which, when broken off, form a powder.
In birds, various growths can be present on the beak, legs, head. In some species of birds (for example, carnivores and parrots), the base of the beak is covered with a soft wax. On the legs there may be plates, fringes, membranes.
The external and internal structure of birds directly depends on the lifestyle. The shape of the body, head, paws and tail, wings can be very diverse. It all depends on the habitat and method of obtaining food.
The external structure of birds. Plumage
Feather cover is inherent only to a class of birds, therefore they are also called feathered. The plumage fits snugly to the body and gives it a streamlined shape. The cover is light and retains heat well, which helps to incubate eggs. Some feathers, due to their structure, provide the ability to fly (tail and fly).
Feathers themselves are derivatives of the skin, akin to the scales of reptiles. The structure of the pen is as follows: its trunk consists of a dense shaft, ending in the back (hollow end). A fan is attached to the rod. They consist of horn plates - barbs. Barbs with branches called barbs extend from the rod. Part of them is strewn with hooks, with which they connect to neighboring barbs without hooks. A large feather may consist of a million barbs.
This structure provides the density of the fan. During the flight, quite a bit of air can pass through the feather. If the barbs are disconnected, then the bird will correct them with its beak when cleaning feathers.
By functionality, feathers can be divided into two groups: down and contour. The feathery feathers smelled loose. There is also just fluff - feathers, consisting almost of the same beards, with an undeveloped shaft. There are also bristle feathers, which, on the contrary, consist of rods, practically without barbs. There are also hairy feathers on which the function of touch is vested. Contour feathers can be divided into fly, steering, covering and coverslips. Each type of pen performs its function. The diverse color of the feathers is due to the presence of pigments.
Musculoskeletal system
Features of the internal structure of birds are associated with a characteristic inherent only in birds - the ability to fly. The skeleton of a bird is light, but at the same time it has great strength, consists of thin hollow bones. It includes the skull, spine, belt of limbs and bones of the limbs. The skeleton protects the internal organs.
The internal structure of the birds suggests a large volume of the skull. The orbits are enlarged, the jaws form a beak, and teeth are missing. The spine is divided into 5 sections: cervical, thoracic, lumbar, sacral, caudal. The vertebrae of the cervical spine have a special structure, thanks to which the bird can turn its head 180 degrees.
The thoracic vertebrae fuse together and form a single bone, to which the ribs are attached. Flying bird species have a keel on their sternum . This is a large outgrowth on which powerful wing muscles are attached. The vertebrae of the lumbar and sacral regions also fuse together to serve as a reliable support for the pelvis, while the tail vertebrae fuse into a single coccyx bone to become a support for the tail feathers.
The humeral girdle is made up of three pairs of bones: the clavicle, scapula and crow's bones. The wing consists of the humerus, forearm, and hand bones. The pelvic bones fuse with the vertebrae and serve as a support for the lower extremities. The leg consists of the thigh, lower leg, foregut (several fused foot bones) and fingers.
Muscles of the bird, located from the keel to the shoulder, provide the wings. In flying birds, the muscles in this part are especially well developed. The neck muscles provide movement of the head. The internal structure of the birds is interesting in the field of the structure of muscles and tendons of the lower extremities. Tendons extend through the joints of the legs, ending in the fingers. When the bird sits on a tree and bends its legs, the tendons stretch and fingers grab the branch. Due to this feature, birds can sleep on branches, their fingers do not open.
Digestive system
We continue to study the internal structure of birds. The general characteristic begins with the first section of the digestive system - the beak. It represents the bones of the jaws, covered with horn covers. The shape of the beak depends on the method of obtaining food. No birds have teeth. Food is swallowed whole, with a beak, a bird can tear off suitable pieces from a large piece.
The feathered esophagus can stretch significantly. Some species of birds can fill it with food and not feel discomfort. At the end of the esophagus, there may be goiter - a special extension adapted to store food.
The stomach of the bird consists of the glandular and muscular sections. In the first case, gastric juice is released, which softens the food, and in the second there is its grinding. The pebbles swallowed by the birds contribute to this process. The stomach is followed by an intestine ending in a cesspool. The ureters and excretory tracts of the reproductive organs also open into the cesspool.
Respiratory system
We continue to study the internal organs of birds. The internal structure of the birds is subject to the need to ensure flight. This also applies to the respiratory system, which is represented not only by the lungs, but also by the air sacs located in the free space between the internal organs. These bags are connected to the lungs and have an important function of providing breathing during the flight. At rest, the bird breathes lungs, working with the chest.
In flight, due to the work of the wings, the air sacs increase and contract, supplying air to the lungs. The faster the bird flaps its wings, the more often there is a reduction in air sacs. For example, a dove alone takes 26 breaths, and in flight - up to 400. Thanks to the active circulation of air, the bird's body cools. Air enriched with oxygen from the respiratory bags enters the lungs, which prevents the bird from suffocating.
Circulatory system of birds
Features of the internal structure of birds can be found by studying the circulatory system, which is represented by two circles of blood circulation and a four-chambered heart. The large and small circles of blood circulation are completely disconnected, that is, arterial and venous blood do not mix. The heart consists of two atria and two ventricles.
The heart muscle is able to accelerate its work tenfold, for example, at rest, the heart of a pigeon contracts 165 times per minute, and during flight - 550 times. Features of the structure of the circulatory system of birds caused by a high level of metabolism. The heart has a large volume, the pulse is frequent, the blood is saturated with oxygen and sugars - all this provides both an intensive supply of all organs with necessary substances and a quick removal of metabolic products.
Sensory organs
The sense of smell in the birds is poorly developed. Most birds are unable to distinguish odors. The internal structure of birds, especially hearing organs, is more developed than that of reptiles. Hearing organs are represented by the inner, middle and outer ear. The latter consists of a deep external auditory meatus framed by skin folds and special feathers.
Birds have well developed organs of vision. Eyes of large size and complex structure, good sensitivity. Color vision is better developed than many other animals. Birds distinguish a large number of shades. At a high speed of movement during the flight, vision allows you to evaluate the situation from a great distance, but the bird sees clearly also objects located in a few centimeters.
Nervous system
In flight, birds make complex movements, so the cerebellum, which is responsible for coordination, is large. Visual tubercles are also well developed. The forebrain hemispheres are enlarged. The internal structure of birds, their brain and nervous system is associated with the complex behavior of birds.
Most actions are instinctive - building a nest, pairing, caring for offspring. But with age, birds are able to learn. If the chicks do not feel fear of humans, then adults are afraid of people. They can distinguish a hunter from an unarmed one, and crows can understand what exactly in a person’s hand is a stick or a gun.
Some species of birds recognize people who often feed them, can be trained and can imitate various sounds, including human speech.
Excretory and reproductive systems
Consider the excretory and reproductive systems, their internal structure and breeding of birds. Since the metabolism in birds is accelerated, the kidneys are large. These paired metanephric organs are divided into three lobes and are located under the dorsal walls of the pelvis. The ureters that leave them open in the cesspool. Feathered no bladder. Vital waste, consisting mainly of uric acid, is rapidly excreted from the body.
Most birds do not have a copulative organ . The testes, increasing in size during the breeding season, remove the contents through the channel into the seminal vesicle located in the cesspool.
The internal structure of birds, or rather, the reproductive organs of females, has interesting features. They have developed only the left ovary and oviduct, the right ones are usually rudimentary. Most likely this is due to the lack of space for the simultaneous formation of large eggs. The oviduct departs from the ovary, which is divided into several sections: a long fallopian tube, a thin-walled and wide uterus, and a narrow vagina that opens into the cloaca. To carry out fertilization, the male presses his cloaca to the cloaca of the female.
Reproduction and care for offspring
We examined the internal structure of birds. Biology not only studies anatomy, but also analyzes the behavior of animals. Let's talk about such a complex process as reproduction and care for offspring in birds.
The breeding season begins when enough food appears. Our birds - in the spring and summer. But reproduction in birds held in captivity, for example decorative, stimulate at any time of the year, increasing the amount and nutrition of the feed.
Most small and medium-sized birds form pairs for the season; large ones often have long-term unions. They can form flocks where temporary pairs are formed. The choice of a partner is not accidental. The males flow to attract the attention of females: they open feathers, make special sounds, enter into fights.
Most species lay their eggs in a nest, which can be located on the ground, on trees, bushes, in hollows, minks. The eggs are protected by a strong shell, often masked in color.
In brood species (poultry, ducks, geese, black grouses, swans), chicks appear from an egg with open eyes and covered with down. Very quickly, they begin to eat on their own and leave the nest. In nesting birds (pigeons, crows, tits, sparrows, rooks, parrots, birds of prey), the cubs appear blind and naked, completely helpless.
Birds are characterized by long-term care for offspring. The birds heat and feed their chicks, protect them.