Blood is a liquid tissue that performs essential functions. However, in different organisms, its elements differ in structure, which is reflected in their physiology. In our article, we will dwell on the features of red blood cells and compare human and frog erythrocytes.
Diversity of blood cells
Blood is formed by a liquid intercellular substance called plasma and formed elements. These include leukocytes, erythrocytes and platelets. The first are colorless cells that do not have a permanent shape and move independently in the bloodstream. They are able to recognize and digest particles foreign to the body by phagocytosis, therefore they form immunity. This is the ability of the body to resist various diseases. Leukocytes are very diverse, have immunological memory and protect living organisms from the moment they are born.
Platelets also perform a protective function. They provide blood clotting. This process is based on the enzymatic reaction of the transformation of proteins with the formation of their insoluble form. As a resulta blood clot forms, which is called a thrombus.
Features and functions of red blood cells
Erythrocytes, or red blood cells, are structures containing respiratory enzymes. Their shape and internal contents may vary in different animals. However, there are a number of common features. On average, red blood cells live up to 4 months, after which they are destroyed in the spleen and liver. The place of their formation is the red bone marrow. Red blood cells are formed from universal stem cells. Moreover, in newborns, all types of bones have hematopoietic tissue, while in adults - only in flat ones.
In the animal body, these cells perform a number of important functions. The main one is respiratory. Its implementation is possible due to the presence of special pigments in the cytoplasm of erythrocytes. These substances also determine the color of the blood of animals. For example, in molluscs it can be lilac, and in polychaete worms it can be green. The red blood cells of the frog provide its pink color, while in humans it is bright red. Combining with oxygen in the lungs, they carry it to every cell of the body, where they give it away and add carbon dioxide. The latter comes in the opposite direction and is exhaled.
RBCs also transport amino acids, performing a nutritional function. These cells are carriers of various enzymes that can influence the rate of chemical reactions. Antibodies are located on the surface of red blood cells. Thanks to these substances of a protein nature, red blood cells bind andneutralize toxins, protecting the body from their harmful effects.
Evolution of red blood cells
Frog blood erythrocytes are a vivid example of an intermediate result of evolutionary transformations. For the first time, such cells appear in protostomes, which include nemertine tapeworms, echinoderms, and mollusks. In their most ancient representatives, hemoglobin was located directly in the blood plasma. With development, the need of animals for oxygen increased. As a result, the amount of hemoglobin in the blood increased, which made the blood more viscous and made it difficult to breathe. The way out of this was the emergence of red blood cells. The first red blood cells were rather large structures, most of which were occupied by the nucleus. Naturally, the content of the respiratory pigment with such a structure is insignificant, because there is simply not enough space for it.
Further evolutionary metamorphoses developed towards a decrease in the size of erythrocytes, an increase in concentration and the disappearance of the nucleus in them. At the moment, the biconcave shape of red blood cells is the most effective. Scientists have proven that hemoglobin is one of the most ancient pigments. It is even found in the cells of primitive ciliates. In the modern organic world, hemoglobin has retained its dominant position along with the existence of other respiratory pigments, since it carries the largest amount of oxygen.
Oxygen capacityblood
In the arterial blood, only a certain amount of gases can be in a bound state at the same time. This indicator is called oxygen capacity. It depends on a number of factors. First of all, this is the amount of hemoglobin. Frog erythrocytes in this regard are significantly inferior to human red blood cells. They contain a small amount of respiratory pigment and their concentration is low. For comparison: amphibian hemoglobin, contained in 100 ml of their blood, binds an amount of oxygen equal to 11 ml, while in humans this figure reaches 25.
Factors that increase the ability of hemoglobin to attach oxygen include an increase in body temperature, pH of the internal environment, the concentration of intracellular organic phosphate.
Structure of frog erythrocytes
When examining frog erythrocytes under a microscope, it is easy to see that these cells are eukaryotic. All of them have a large decorated core in the center. It occupies a fairly large space compared to respiratory pigments. As a result, the amount of oxygen they can carry is greatly reduced.
Comparison of human and frog erythrocytes
Red blood cells of humans and amphibians have a number of significant differences. They significantly affect the performance of functions. Thus, human erythrocytes do not have a nucleus, which significantly increases the concentration of respiratory pigments and the amount of oxygen carried. Inside them isspecial substance - hemoglobin. It consists of a protein and an iron-containing part - heme. Frog erythrocytes also contain this respiratory pigment, but in much smaller quantities. The efficiency of gas exchange is also increased due to the biconcave shape of human erythrocytes. They are quite small in size, so their concentration is greater. The main similarity between human and frog erythrocytes lies in the implementation of a single function - respiratory.
RBC size
The structure of frog erythrocytes is characterized by rather large sizes, which reach a diameter of up to 23 microns. In humans, this figure is much less. His red blood cells are 7-8 microns in size.
Concentration
Due to their large size, frog blood erythrocytes are also characterized by a low concentration. So, in 1 cubic mm of blood of amphibians there are 0.38 million of them. For comparison, in humans this number reaches 5 million, which increases the respiratory capacity of his blood.
RBC shape
When examining frog erythrocytes under a microscope, one can clearly determine their rounded shape. It is less beneficial than biconcave human red blood cell discs because it does not increase the respiratory surface and occupies a large volume in the bloodstream. The correct oval shape of the frog erythrocyte completely repeats that of the nucleus. It contains strands of chromatin containing genetic information.
Cold-blooded animals
The shape of the frog erythrocyte, as well as its internal structure, allows it to carry only a limited amount of oxygen. This is due to the fact that amphibians do not need as much of this gas as mammals. It is very easy to explain this. In amphibians, breathing is carried out not only through the lungs, but also through the skin.
This group of animals is cold-blooded. This means that their body temperature depends on changes in this indicator in the environment. This sign directly depends on the structure of their circulatory system. So, between the chambers of the heart of amphibians there is no partition. Therefore, in their right atrium, venous and arterial blood mixes and in this form enters the tissues and organs. Along with the structural features of erythrocytes, this makes their gas exchange system not as perfect as in warm-blooded animals.
Warm-blooded animals
Warm-blooded organisms have a constant body temperature. These include birds and mammals, including humans. In their body, there is no mixing of venous and arterial blood. This is the result of having a complete septum between the chambers of their heart. As a result, all tissues and organs, except for the lungs, receive pure arterial blood saturated with oxygen. Along with better thermoregulation, this contributes to an increase in the intensity of gas exchange.
So, in our article we examined what features human and frog erythrocytes have. Their main differences relate to size, the presence of a nucleus and the level of concentration in the blood. Frog erythrocytes are eukaryotic cells, they are larger in size, and their concentration is low. Due to this structure, they contain a smaller amount of respiratory pigment, so pulmonary gas exchange in amphibians is less efficient. This is compensated with the help of an additional system of skin respiration. The structural features of erythrocytes, the circulatory system and the mechanisms of thermoregulation determine the cold-bloodedness of amphibians.
The structural features of these cells in humans are more progressive. The biconcave shape, small size and lack of a core significantly increase the amount of oxygen carried and the rate of gas exchange. Human erythrocytes perform the respiratory function more efficiently, quickly saturating all the cells of the body with oxygen and releasing carbon dioxide.
