Cell

Cell - structural and functional unit of the underlying structure, development and functioning of all living organisms.
Cells exist as independent organisms - celled animals and plants - or as an elementary part of a multicellular organism tissue cells.
The form of some cells, such as amoeba, or leukocytes, volatile form of other more or less constant and characteristic for each type of cells, sperm, ciliates, red blood cells, nerve cells, the majority of plant cells and other
The sizes of cells varies in rather wide limits, most of them are visible only under a microscope. The diameter of the smallest cell of about 4 MK.
The cell is separated from the environment thin cell membrane thickness and structure of which play an important role in the regulation of cell metabolism. The membrane is usually a three-layer consists of protein and lipid metabolism.
The life cycle of each cell consists of two periods: interphase (the period between the two marks) and the actual dividing (see Mitosis, Meiosis).
The length of the life cycle of different cell types varies considerably. For example, the interphase nerve cells lasts for the entire life of the body, and epithelial cells divide very quickly.
The cage consists of two main parts (Fig. 1 and 2) - the cytoplasm (see) and the kernel (see the nucleus of the cell), which can not exist separately, as they are in constant interaction and interdependence.

the scheme of the structure of cells
Fig. 1. The scheme of the structure of cells (microscopy): 1 - the pupil; 2 - core; 3 - the chromatin; 4 - vacuole; 5 - the cytoplasm; 6 - the centrosome.

Fig. 2. The scheme of the structure of cells (electron microscopy): 1 - the cytoplasm; 2 - core; 3 - a kernel; 4 - cell membrane.

The cytoplasm is the most important substrate of cell activity. The main substance of cytoplasm - hyaloplasm - is a colloidal solution of proteins and other organic substances. In hyaloplasm are organelles (education, with different functions), and cell inclusion, appearing and vanishing in the process of metabolism. Mitochondria (or chondriosome), the Golgi apparatus, ribosomes and cellular center (centrosome) are Abdelmonim the organelles, as are present in the cells of all types. In addition obseleting organelles in the cell may attend the special organelles, related to the special function of cells, such as myofibrils muscle cells, cilia mertzatelnogo epithelium , etc.
Cellular inclusion are dependent on the functional state of the cells and differ in their chemical nature (protein, fat, carbohydrate etc)and density (granular and inclusion of liquid content - vacuoles).
The kernel is the second main component of the cell. During the life cycle of a nucleus undergoes a series of complex changes. Chromatin engine components contain DNA, which is missing in the cytoplasm. The kernel has a regulating effect on the growth and development of cells and is the carrier of its hereditary properties.
Cells of plants differs from animal cells rather thick well visible in the light microscope shell. In the cytoplasm of cells of plants there are specific organelles - plastids: chloroplasts carrying out photosynthesis; homoplasty containing yellow and red pigments (carotenoids); colorless leucoplasts and rounded much refracting light bullock - spherosome. In the cytoplasm of plant cells have a more or less developed system vacuoles.
The cell as a living system is able to support and maintain its specific structure thanks to the continuous consumption of energy and substances originating from the environment. The end products of metabolism are excreted into the environment. Every cell, having reached a certain stage of development, is divided into two daughter cells. Division by mitosis, less amitiza, in the first case is a complex restructuring of the nucleus and cytoplasm.


Fig. 1. Smooth muscle cell intestines. Fig. 2. Fat cell from the subcutaneous tissue of rats. Fig. 3. Mitochondria and secretory granules of cells of the pancreas. Fig. 4. The Golgi apparatus in sensitive cell spinal ganglia. Fig. 5. The Golgi apparatus and secretory granules in the cells of the pancreas.

Fig. 6. Polymorphonuclear leukocyte. Fig. 7. Erythrocyte person. Fig. 8. Megakaryocyte from the bone marrow of the person. Fig. 9. Cell liver axolotl. In the cytoplasm red chondriosome and purple protein activation; in the kernel - red oxytelinae the nucleolus and basophilic of glybki chromatin (larger glybki - carisoma). Fig. 10. Chromatophores axolotls filled pigment granules.