What is the structure of the egg - what does it consist of

Birds are dioecious organisms. Males have paired testes, and females - unpaired ovary. Genital ducts open in cloaca. Fertilization internal. After fertilization is formed egg: a fertilized egg, with a large supply of nutrients, is covered with protective egg shells . The embryo has the form of a disk located on the surface of the yolk. The egg cell (germ disk with yolk) is surrounded by several egg shells that perform protective functions. Directly surrounds her protein coat. It performs a protective function and supplies water to the embryo. It has compacted protein formations - cords. They keep the yolk in a constant position - the germinal disc up. Thus, as the egg does not turn over, the germinal disc will always be turned towards the heat source. Material from the site

The protein shell is surrounded by two subshell membranes in the form of thin films that protect the embryo from pathogens. At the stupid pole of the egg, they diverge, forming an air chamber with a reserve of air for the embryo. The shell protects the egg from mechanical damage. In addition, the calcium salts contained in it are used by the embryo to build the skeleton. Gas exchange takes place through the pores in the shell. Above the shell is another thin shell that protects against the penetration of pathogens.

In birds laying eggs in open nests, the coloring of eggs often coincides with the background of the environment, which makes them hardly noticeable. . Eggs laid in closed nests are usually white.

Birds- dioecious animals, they are characterized by internal fertilization, they multiply by laying eggs.

Why does a chicken egg have such a complex structure?

The complex structure of chicken eggs due to the complexity of intrauterine development of the embryo. Conditions created in the chicken egg resemble a simplified and diminished copy of the environment for the development of the mammalian fetus.

The chicken egg is a kind of capsule that allows the baby to form using the mother's heat.

Each component performs important functions:

  • The shell. This is the hardest outer layer of the egg. Most of its composition is calcium carbonate. The shell protects against mechanical damage and the harmful effects of the environment,
  • Lacquer shell. There are two of them in the egg. They are located close to each other and to the shell and cover the protein. Licca membranes disperse at the blunt end of the egg and create an air chamber. They let the gases through, and no liquid passes through them,
  • Cord. By pouring protein onto a plate, you can see thin cords stretching up and down from the yolk. They resemble the umbilical cord, but go to the base of the egg, where the air chamber is located. Chalases allow the yolk to remain in the center of the egg,
  • Yolk sheath. Adjacent to the egg cell membrane. Is the main nutrient medium for the growth and movement of embryo cells during the first 60 hours of incubation,
  • Yolk The main component of chicken eggs, which accumulate all the necessary nutrients to the embryo, amino acids, vitamins, minerals and trace elements,
  • Protein. It consists of four factions. The thinnest layer of gradinous protein closest to the yolk contains chalases holding the yolk in the center. It is surrounded by a thick layer of liquid protein, which the germ needs at the beginning of its development. The protein bag (outer dense protein) nourishes the future chick during the second period of embryonic development, protects the yolk and the body from contact with the shell,
  • Germinal disk. Looking closely at the egg, it shows a speck of red or dark orange color. This is the disk (scar) in which the embryo develops after fertilization. It is always located on top, which allows the germ to get warm under the chicken or in the incubator,
  • Air chamber. Located at the blunt end of the egg, where the protein, moving away from the shell, creates empty space. Thanks to the air chamber, the baby uses the oxygen supply until it hatches out,
  • Cuticle. Formed after the development of eggs in the cloaca, does not allow gases and moisture, protects against infections. If the cuticle is damaged, the shelf life of the egg is greatly reduced.

Why is the structure of the Earth compared to a boiled chicken egg

Often the structure of our planet and boiled eggs called similar. That's because the white, yolk and egg shell can be compared with the core, mantle and crust of the planet. And the Earth, like the egg, is not round.

But such a comparison is not entirely correct. If you reduce the globe to the size of an egg, then it turns out that people live on a very thin shell, which is more fragile than the egg. And under it the red-hot mass boils - magma, while under the shell of the eggs of a hen the life of the chick begins.

The surface of the egg is hard and smooth, and the surface of the planet is relief, and most of it is under water. They differ in form - the Earth is more like a ball or sphere.


Birds live in all regions of our planet, including in remote areas of Antarctica.

At present, scientists number 10,640 species of birds and almost twice the number of their subspecies. Many of which so far have not been practically studied, including their structure.

In addition, in the remote corners of our planet, unknown species of bird are still found. The study of which is difficult due to the remoteness of their habitat. Birds are perfectly adapted to their habitat.

There are land and waterfowl. The structure of some species of birds is slightly different from the structure of their relatives. In addition, there are flightless species. The most famous of them are ostriches and penguins. Despite the fact that the structure of the body of these birds does not allow them to rise into the air, they are perfectly adapted to their environment.

For example, penguins swim and dive perfectly, and ostriches are unsurpassed runners. Birds are important in human life. Meat and eggs of domestic birds are a source of protein and make up a significant part of the human diet.

External structure

The body of the birds has a streamlined shape and is covered with feathers. Most birds have a light and very durable skeleton. The lightness of the bird's bones is achieved due to their special tubular structure. Each bone has a cavity filled with air.

The spine of birds has five sections:

Exactly the same structure of the spine have all mammals. However, unlike them, the spine of birds is practically immobile with the exception of the cervical region. The forelimbs of birds have transformed into wings. And this they have preserved all the bones of mammals. The extremity of the bird consists of the humeral, elbow and radius bones. However, birds have only three fingers.

The pectoral muscles are best developed. The hind limbs are very powerful and muscular. This makes it possible to make a good start from the ground during takeoff. The most developed leg muscles in non-flying birds.

Internal structure

Compared to other warm-blooded wild animals, birds have a very unusual respiratory system. The lungs are very small. The bronchi are connected to a large number of air sacs that protect the internal organs of the bird from overheating.

The temperature of the bird's body ranges from 38-44 degrees Celsius. When the ambient temperature decreases, they do not hibernate, but make long flights to warm countries. The internal structure of the birds makes them most adapted to flight. So they have no bladder and the rectum is very short. The organs of excretion are a pair of kidney shaped beans.

The structure of the skull of birds most closely resembles the structure of the skull of lizards and snakes. At the same time, the skull is very light, with large eye sockets and a brain box. In addition, all birds have a beak. Birds have excellent eyesight and hearing, which help them navigate in space.

The structure of the heart of birds

Like all other living creatures on our planet, the heart is the central organ of blood circulation in birds. The structure of the heart of birds largely repeats the structure of this organ in other animals. The heart has the shape of a rounded cone and consists of two atria and two ventricles.

The main function of the heart is to provide blood circulation through the vessels and arteries of birds. Arterial blood passes through the left half of the heart, and venous blood flows through the right half of the heart. Blood circulates in a closed circuit. In all birds, the heart is slightly more to the right than in mammals. The rhythmic work of the heart is responsible for the neuromuscular system present in it.

Poultry egg structure

The bird's egg is oval.

  1. Yolk,
  2. protein,
  3. under the shell,
  4. shell.

The yolk is ball-shaped and takes up almost 1.3 the weight of the whole egg. The yolk is 30% fat and 17% protein. The rest of its volume is water. In the yolks of birds there are many vitamins, minerals and trace elements. Such as: potassium, calcium, phosphorus, iron, sulfur.

The bird's egg protein is 89% water. In addition, it has 10% protein and the minimum amount of carbohydrates (only 1%). Protein consists of the same substances as the yolk. Differences only in the proportions of these substances. In addition, the protein is completely absent fats.

The eggs of ostriches, penguins and large birds of prey are the most dense in their shells. The surface of the eggs is penetrated by the pores through which the embryo breathes. A freshly laid egg is covered with a thin layer of mucus, which facilitates the passage of the egg from the oviduct to the outside.

Pen structure

Birds have several species of feathers. Each of which performs its inherent functions. Flying birds have contour, flight, and tail feathers. In addition, all birds have a down playing the role of warming their undercoat.

Feathers are very important for birds and help them stay in the air. Tail feathers are attached to the tail and help make turns in the air. Fly feathers form the plane of the wings.

Reproduction as reproductive organs in birds are testicles in males and ovaries in females that have only one ovary. The embryo develops in the fertilized egg, which is pushed out by the oviduct, after which the bird incubates the eggs, warming them with its warmth.

Birds have a lot of enemies. In addition to humans, most predatory mammals are enemies of birds, many of which feed on eggs and bird meat. In addition, birds of prey often kill individuals of smaller subspecies.

Destroy their nests and eat chicks. In addition, large reptiles and some predatory fish hunt birds. However, despite such a large number of enemies, the number of birds does not decrease.


The longest live large birds with low fertility and a long development cycle. The maximum duration of small birds, sparrows, tits, swallows) does not exceed 7-8 years. However, to achieve such an old age in the wild is not everyone can. Many birds die at an early age. Becoming a victim of various predators.

The life of large birds is comparable to the life expectancy of large mammals and humans. For example, an ostrich can live 45-50 years, and an eagle up to 70-80 years. The longest birds in captivity live. Where they are protected from a variety of adverse factors that shorten the lives of their tribesmen.

Interesting Facts

  1. The endurance and adaptability of the birds has no equal.
  2. During periods of migration, they are able to make multi-day flights with little or no rest and food.
  3. Equally hardy and not flying birds. For example, the Patagonian penguins make swims lasting 2-3 weeks. Overcoming during this time the distance is 1200-1500 km.
  4. Among the flying birds the highest speed of the swifts. They are able to reach speeds of 100-115 km / h

Detailed structure of chicken eggs

The shell covers the outside of the egg and is important because it maintains its physical integrity and is a bacteriological barrier. It consists mostly of a calcium matrix with an organic impurity, that is, calcium is the most representative and important element in the shell. It also contains other minerals and trace elements, albeit with a lower concentration:

The structure of the shell is as follows: it is permeated with many pores that form the tunnels between the crystals of minerals. These tunnels provide gas exchange between the inside of the egg and the outside atmosphere. The number of pores varies from 7,000 to 15,000. A large concentration of pores is located in the lower obtuse part of the product, where the gas chamber is located under the shell.

The color of the shell can be white or brown, depending on the breed of hens, on the concentration of pigments, called porphyrins, and located in the calcium matrix of the shell. These pigments do not affect the quality and nutritional properties of the product. Different shades of shell color also depend on the individual state of each chicken. The type of food and the bird breeding system do not affect the color of the shell, nor the intensity of this color.

The quality and strength of the shell depends mainly on the mineral metabolism of the chicken and, as a result, on its proper feeding. Other factors affecting the strength of the shell are as follows:

  • genetics,
  • sanitary conditions of poultry,
  • ambient temperature

The entire surface of the shell, including the pores, is covered with a special film - organic cuticlewhich consists mainly of proteins (90%) and a small amount of lipids and hydrocarbons. The main function of the cuticle is to close the pores and thus form a physical barrier against the entry of microorganisms into them. The cuticle also avoids large water loss during evaporation and gives the product a brilliant look. After the chicken laid an egg, this film is wet, then it dries out and degrades gradually. After 2-4 days, the cuticle completely disappears.if the product is washed, or grind, then the film disappears ahead of this period.

Two membranes cover the shell from the inside, they are called nanticyric inner and outer membranes. Both surround the protein and counteract the penetration of bacteria into it.

When a chicken carries an egg, the membranes in it are firmly connected to each other. Some time after the appearance of the egg, due to the decrease in its internal volume during cooling (the temperature of the chicken’s body is 39 ºC and equal to the temperature of the freshly laid egg), air from the atmosphere penetrates into the thick pole of the product, since it is the bottom of the shell that contains the maximum number of pores. In this lower zone of chicken eggs, the membranes as a result of this process are separated and form gas chamber.

The inner membrane has fine fibrous structureand consists of keratin. In the presence of lysozyme in the protein matrix, the membrane slows down the penetration of some types of microorganisms into the product, and prevents the penetration of others. The outer membrane is more porous than the inner membrane, and serves as the point of attachment of the shell to the rest of the egg. Both membranes form around the edible part of the product the isthmus, which is part of the oviduct, which is located between the egg shell, which, as its name suggests, is the site of shell formation.

As the product loses its freshness, it also loses water evaporating through the pores in the shell, as a result of which the gas chamber at its lower pole increases in volume. Product stored at high temperatures, aging faster. The height of the air chamber in the egg is one of the main signs of its freshness and, as a result, quality, regardless of the number of days elapsed after the appearance of the product. Category A product must have air chamber less than 6 mm high.

The integrity and purity of the shell are factors that determine whether an egg is suitable for human consumption as fresh or unsuitable. When the shell is dirty or damaged, it is possible that the organisms have penetrated into the center of the product.

For this reason, the product, whose shell is dirty, has cracks and other signs of violation of its integrity, cannot be supplied for sale.

It is widely believed that eating crushed shell will allow you to use a large amount of calcium contained in it. Nevertheless, the chemical state in which calcium is in the shell makes it impossible for it to be absorbed by our body.

As mentioned above, the egg protein consists of two distinct parts: viscous and current.

The viscous part of the protein surrounds the yolk and is the main source of riboflavin and egg protein. The less viscous or fluid part of the protein is closer to the shell. When you peel a fresh egg from the shell, you can clearly see the difference between these two parts, since the yolk, surrounded by a viscous protein, floats in its center. As the egg loses its freshness, the viscous protein loses its texture and eventually merges with the fluid part.

В своей основе состав белка яйца следующий: вода 88%, протеины 12%. Наиболее важным протеином (54% от массы всех остальных протеинов яйца) является овальбумин, чьи свойства интересны с питательной и кулинарной точек зрения. Качества белка связано с его текучестью и может быть оценено по вязкости его внешней оболочки.

The richness of essential amino acids of egg protein proteins and their harmonious combination led to the use of egg protein as a standard, with which the quality of proteins of other nutrients is compared and assessed. In the kitchen, ovalbumin is interesting in the preparation of many dishes due to its gelatinous structure, which it acquires after heat exposure. Protein contains more than half of all egg proteins, and is also rich in lipids. Vitamin B2 is found in protein in greater quantities than in the yolk.

The protein is transparent, however, in some cases whitish "clouds" may appear in it, which do not imply any problem for its use as a food product and are associated only with the freshness of the egg.

The yolk does not just float freely in the egg white, it is held on both sides by woven protein threads, which are connected to its poles by their second ends.

The yolk is the central yellowish part of the egg, which is surrounded by a membrane that separates it from the protein and provides the shape of the yolk itself. When this membrane breaks, the yolk flows out and mixes with the protein.

In the yolk are the main vitamins, lipids and minerals of the egg, so from a nutritional point of view, this is the most valuable part. The water content in the yolk is approximately 50%.

The solid or dry part of the yolk is equally divided between proteins and lipids, leaving a small part of the vitamins, minerals and carotinoids. The latter are responsible for the yellowish color of the yolk, which may have different colors and shades depending on the feeding of the birds, and have antioxidant properties. Note that the color of the yolk is of commercial interest.

Inside the yolk, there is a germinal disc, a small transparent disc, which is where the embryonic cell division begins in the case of a fertilized egg.

In rare cases, you can find eggs with two yolks. This situation is possible when a chicken produces two eggs instead of one in the process of ovulation. This situation is often observed at the beginning of laying, when the chicken begins to trot.

Reddish or brown spots that sometimes appear inside the egg should not be confused with the development of the embryo. These spots are the epithelial cells of the oviduct, which separated from it during egg formation. These cells do not pose any problems in the use of the product in food, and they can be easily removed with the tip of a clean knife. When packing a product, if these spots are visible in the transmitted light of a special camera, then such an egg is no longer considered to belong to quality category A.