Oocytes (eggs) are, as a rule, the embryonic form of an animal or an egg. Their study is engaged in oology - a special section of zoology.
general information
Their sizes may vary. For example, in a mouse the size of an egg is about 0.06 millimeters, but the diameter of the germinal form of an African ostrich can reach 15-18 centimeters. The shape may also be different. But usually the eggs have a spherical or oval shape. In some living creatures, they can also be elongated, elongated, as, for example, in mule fish, mixins, or insects. Depending on the degree of distribution and the amount of nutrient inside the egg, size and other characteristics are determined. The accumulation of yolk (this substance) is carried out either in the form of a continuous mass, or in the form of granules. Depending on this, experts divide the oocytes into various types. The fertilization process is carried out in the upper part of the oviduct. As the oocyte passes through the channel, crushing occurs. This process proceeds as a discoidal incomplete. Due to the fact that the onset of crushing occurs already in the oviduct, in birds the laid egg can remain at one of the stages of crushing (as, for example, in a pigeon), go gastrulation (as in chicken).
Bird egg
Females of all species of feathered representatives of the fauna lay oocytes. Different species carry eggs of different shapes. This is due to the place where the masonry will be located. For example, if the nest settles in holes or pits, then the eggs will be round. In birds, whose clutch is located on rocky ledges, oocytes will be oblong. Usually, the larger the bird, the larger the egg size. But there are exceptions to this rule. So, for example, brood species whose offspring are adapted immediately for independent feeding carry eggs that are larger in size (compared to the body of the female) than those whose chicks are born helpless. Moreover, the ratio of oocyte mass to body weight in small species is often greater than in larger species. It is believed that the largest eggs are laid by an African ostrich. Regarding the body weight of this feathered representative, its oocyte is 1% of body weight. But the weight of a hummingbird egg is 6% by weight of the bird.
Some structural features of poultry eggs
In birds living in mountainous regions, oocytes have “ribs”, like stiffeners. They are necessary to maintain the integrity of the eggs so that they do not break when the birds land in a nest with a small area. By the way, it should be noted that this rib is able to withstand pressure of the order of 40 kg / sq. cm, and the side where it is absent is not more than 2 kg / sq. see. The surface of the eggs is rough or smooth, shiny or matte. Color can be absolutely anything: from pure white to green and dark lilac. The surface of the eggs of some species is covered with specks, in some cases forming a corolla around the blunt edge. The color will depend on the image and nesting place. So, in many individuals who secretly lay their eggs and house birds, the shell is white. For those who leave masonry on the ground, the color becomes identical to the surrounding conditions: it merges with pebbles or plant rags that line the nest. The egg gets its color even in the birth canal of the female. For example, biliverdin (pigment) in combination with zinc gives a blue or green color to the surface of the egg. Due to protoporphyrin, a red or brown color is obtained, or spots of such shades. Next, we consider in more detail the internal structure of the bird's egg.
Oocyte device
The structure of the bird's egg is appropriate for the purpose. It contains everything necessary for the formation and development of a young organism. The embryo in the egg feeds on the compounds found in the yolk. This mass is presented in two forms - in white and yellow. They are arranged in concentric alternating layers. The yolk lies in the vitellin membrane. He is surrounded by protein. In the early stages of the development of the shell, the eggs of the bird perform a nutritional function. Protein, in addition, provides protection for the new organism from contact with the shell. The contents of the oocyte are surrounded by two subshell layers: the outer and inner. Considering the structure of a bird's egg, it is necessary to say a few words about the shell itself. It consists mainly of calcium carbonate. After masonry, an air chamber is gradually formed on the dull edge of the oocyte.
Yolk
Considering the structure of a bird's egg, the scheme of which is given below, it should be said that deuteroplasma (yolk) is an integral component of the internal contents of the oocyte. The vitelline mass contains all the necessary substances that provide nutrition and normal development of the body. The deuteroplasm is found in the egg cell not only of birds, but also of other animals (and in humans) and is an accumulation of plates or grains that in some cases merge into a continuous mass. The amount of yolk, as well as its distribution, may be different. With a small volume of deuteroplasm, grains or plates are evenly distributed over the cytoplasm. In this case, they speak of "isolecital" eggs. With a large amount of yolk, components accumulate either in the central region of the cytoplasm - near the nucleus or in the vegetative part of the oocyte. In the first case, they talk about centrocytal, and in the second, telolecital eggs. In accordance with the volume and degree of distribution of the vitelline mass, the type of crushing of oocytes is also established. Chemically, the structure of a bird egg provides for three types of deutoplasm. The yolk may be carbohydrate, fatty or protein. But, as a rule, in most individuals, the yolk components include, in addition to these compounds, minerals, pigments, ribonucleic acid, thus having a complex chemical structure. So, for example, in the chicken oocyte that completed growth, the yolk contains neutral fat 23%, protein 16%, 1.5% cholesterol, phospholipids 11% and mineral compounds 3%. Various organoids participate in the accumulation and synthesis of the yolk component: mitochondria, endoplasmic reticulum, Golgi complex. The synthesis of the protein component of the yolk structure in many animals occurs outside the ovary. By pinocytosis, the protein component penetrates the developing egg.
Other elements of the oocyte structure
All shells prevent spreading, drying and damage to the egg. But they do not provide the necessary moisture to the growing body. Extra-germ organs form it . In particular, they include an aqueous (or amniotic) membrane. Due to it, the cavity of the amnion is limited, which is filled with liquid, where, in fact, the body develops. Together with the water, two more layers are formed: vascular and serous (or allantois). In birds and reptiles, this layer is an organ of excretion and respiration. From the ovum to the blunt and sharp edges of the egg, chalases - protein twisted dense strands - leave. They provide a stable core position, preventing displacement from the middle position.
Shell
Studying the structure of a bird's egg, it is necessary to dwell in more detail on the layers surrounding the core. The hardest outer layer is the shell. It is quite dense and performs the function of protecting against mechanical damage and the negative impact of the external environment. Under the shell there are subshell shells. At the blunt end, they diverge and form an air chamber. It contains oxygen, which is necessary for the breathing of a new organism.
Trophic oocytes
There is a type of eggs that in a clutch serves as food for posterity. As a rule, they are unfertilized, and their appearance is practically no different from ordinary ones. The females of some ants and the uterus of the termites lay them down until the colony begins to get enough food. In some cases, unfertilized oocytes of meat-egg and egg chicken breeds are also mistakenly called trophic, since they are not used by birds themselves, but by humans and sometimes by domestic animals.