Читать книгу Understanding Anatomy and Physiology in Nursing - John Knight - Страница 16

The cytoplasm is the region between the plasma membrane and the nuclear membrane. It is predominantly composed of the endoplasmic reticulum (ER) which consists of a system of interconnected flattened membranes. In diagrams of the cell (see Figure 1.1) only small portions of the ER are usually shown, but in reality this complex labyrinth-like system occupies a large proportion of the cell. The ER is split into two distinct types: the rough ER has a multitude of tiny specialised organelles termed ribosomes embedded within its membranes, which are responsible for its characteristic rough, uneven appearance. Ribosomes are the organelles where amino acids are linked together to form proteins according to the instructions encoded in DNA (Chapter 14); for this reason the rough ER is referred to as a region of protein synthesis within cells. The second type of ER is termed smooth ER since it lacks ribosomes; smooth ER is primarily involved in lipid (fat) synthesis. Fats have a multitude of functions within the body including: synthesis of cell membranes, storage of energy, insulation and cushioning and protecting fragile organs such as the kidneys.

The cytoplasm is an aqueous environment and is filled with a watery fluid called the cytosol. The cytosol functions as a transport medium within cells containing dissolved sugars for energy, amino acids for protein synthesis and a variety of intracellular chemical signals and growth factors which are involved in coordinating the internal biochemistry and physical activities of the cell.