Cell (cellula) is a microscopic formation, elementary particle of a living organism, but is a complex system that contains the nucleus and cytoplasm. The sizes of the cells are from a few micrometers to 200 micrometers. Cell shape is different (spherical, spindle-shaped, flat, cubic, prismatic, cylindrical, star-shaped, with spikes). Cell structure is difficult. Externally, every cell has a membrane - cytolemma (plasmolema). Cytolemma - is a semi-permeable membrane through which performes the transport of substances and the interaction of cells with neighboring cells and intercellular substance. In the cell is contained nucleus, which is involved in protein synthesis and keeps genetic information. The core is covered with shell - cariolema. The core filled nucleoplasm (carioplasma), which have 1-2 nucleolus and chromatin. Around the core is placed cytoplasm. The composition of the cytoplasm included cytosol, organelles and cytoplasmic inclusions. Cytosol - is free of organelles substance of cytoplasm semi-liquid, semi-transparent, is involved in the metabolism. Organelles - constant part of cells that perform specific functions.
Organelles include:
- Mitochondria - the energy cell organelles are involved in the processes of oxidation, phosphorylation;
- Internal mesh apparatus (lamellar complex or Golgi apparatus), which consists of vesicles, plates, tubes, synthesize polysaccharides is involved in removing of products of its life to outside of the cell;
- Cytoplasmic (endoplasmic) grid - formed by tubes and plates. Non-granular cytoplasmic grid involved in the metabolism of lipids and polysaccharides. Granular cytoplasmic grid contains spherical granules - ribosomes and their clusters - polysomes (polyribosomes). Granular cytoplasmic grid is involved in protein synthesis. Cytoplasmic inclusion - is the accumulation of various substances (protein, fat, pigment and others creations).
Cell functions:
- metabolism;
- multiplication by separation;
- motion reactions.
The cells are part of the tissues.
Tissue - is community of the cells and the extracellular substances united by origin, structure and function. Epithelial tissue or epithelium - the layer of cells that lie on the basement membraneunder which is a loose connective tissue. The epithelium covers the body surface (skin), lined with mucous membranesby separating the body from the environment and performing coating and protective functions and also forms the tissue of endocrine glands and glands of external secretion.
Connective tissue consists of a small number of cells and a significant amount of intercellular substance (collagen, elastic, reticular fibers, the main substance). Connective tissue performs a supporting and protective functions (bone, cartilage, dense fibrous connective tissue) and trophic function (blood, lymph, quaggy fibrous and reticular connective tissue).
Muscular tissue performs movements of the body; contains special structure - myofibrils.
Smooth muscle tissue is composed of spindle mononuclear cells. With such tissue formed the walls of blood vessels, viscera.
The skeletal (striated) muscle tissue is composed of striated muscle fibers and forming the skeletal muscles, the muscles of the tongue, throat, larynx.
Cardiac muscle tissue consists of muscle cells (heart myocytes), has stripes.
The nervous tissue consists of nerve cells (neurons) and neuroglia. Neuroglia performs supporting, trophic, protective, borderline function. Neuroglia cells form a cavities of the brain, central channel of spinal cord and form a base of the central nervous system the bodies surrounding neurons and their spines, carry out phagocytosis (glial macrophages).
With tissues built organs.
Organ (organum) - is part of the body that has a shape, internal structure, occupies a special place in the organism and performs a specific function. In the formation of every organ participate various tissues, but a major is one (for the brain - nervous, for muscle - muscular, for glands - epithelial), and others - auxiliaries.
System of organs - the organs that perform joint function and have a common origin (digestive system, respiratory system, cardiovascular system, nervous system, etc.).
The organs apparatus - the organs that perform joint function but have different origins (musculoskeletal system, endocrine system).
