cells of the human body essays

cells of the human body essays Cells are the basic living units of all plants and animals. The cell is the structural and functional unit of all living organisms. There are a wide variety of cell types, such as nerve, muscle, bone, fat, and blood cells. Each cell type has many characteristics, which are important to the normal function of the body as a whole. One of the important reasons for maintaining hemostasis is to keep the trillions of cells that form the body functioning normally. An averaged size cell is one-fifth the size of the smallest dot you can make on a sheet of paper with a sharp pencil. Although cells may have quite different structures and functions, all cells share some common characteristics. The plasma, or cell membrane, forms the outer boundary of the cell through which the cells interacts with its external environment. The nucleus is usually located centrally and functions to direct cell activities, most of which take place in the cytoplasm, located between the plasma membrane and the nucleus. The plasma membrane is the outer part of a cell. The plasma membrane is made up of 45% - 50% lipids, 45% - 50% proteins, and 4% - 8% carbohydrates. The main lipids are phospholipids and cholesterol. Phospholipids easily come together to form a lipid bilayer, a double layer of lipid molecules, because they have a polar head and a nonpolar tail. The charged water-loving heads are exposed to water inside and outside the cell, whereas the uncharged water-fearing tails face one another in the interior of the plasma membrane. The other major lipid in the plasma membrane is cholesterol, which is mixed among the phospholipids and makes up about a third of the total lipids in the plasma membrane. Cholesterol is too hydrophobic to extend to the hydrophilic surface of the membrane but lies within the hydrophobic region of the phospholipids. The amount of cholesterol in a given membrane is a major factor in determining the fluid nature of the m...