A&P Lecture 1.5: Endoplasmic Reticulum

This is an in depth  explanation of the Endoplasmic Reticulum as a part of the cell. This lecture note is linked to A&P Lecture 1: The Cell

ANATOMY AND PHYSIOLOGY LECTURE 1.4

ENDOPLASMIC RETICULUM

The endoplasmic reticulum is a continuous a series of membranes distributed throughout the cytoplasm of

the cell located at the he outer membrane of the nuclear envelope. It is consists of broad, flattened, interconnecting sacs and tubules. The interior spaces of those sacs and tubules are called cisternae and are

isolated from the rest of the cytoplasm.

Most cells contain a system of membranes known as the endoplasmic reticulum, or ER. The ER may be either of two types: (1) a granular, or rough, endoplasmic reticulum or (2) an agranular, or smooth, endoplasmic reticulum. A granular endoplasmic reticulum bears ribosomes on its surface, whereas an agranular endoplasmic reticulum does not. The agranular endoplasmic reticulum serves a variety

of purposes in different cells; it provides a site for enzyme reactions in steroid hormone production and inactivation, for example, and a site for the storage of Ca 2 + in striated muscle cells. The granular endoplasmic reticulum is abundant in cells that are active in protein synthesis and secretion, such as

those of many exocrine and endocrine glands.

The rough endoplasmic reticulum is called “rough” because it has ribosomes attached to it. The ribosomes of the rough endoplasmic reticulum are sites where proteins are produced and modified for secretion and for internal use. The amount and configuration of the endoplasmic reticulum within the cytoplasm depend on the cell type and function. Cells with abundant rough endoplasmic reticulum synthesize large amounts of protein that are secreted for use outside the cell.

Smooth endoplasmic reticulum, which is endoplasmic reticulum without attached ribosomes, manufactures lipids, such as phospholipids, cholesterol, steroid hormones, and carbohydrates. Many phospholipids produced in the smooth endoplasmic reticulum help form vesicles within the cell and contribute to the plasma membrane. Cells that synthesize large amounts of lipid contain dense accumulations of smooth endoplasmic reticulum. Enzymes required for lipid synthesis are associated with the membranes of the smooth endoplasmic reticulum. Smooth endoplasmic reticulum also participates in the detoxification processes by which enzymes act on chemicals and drugs to change their structure and reduce their toxicity. The smooth endoplasmic reticulum of skeletal muscle stores calcium ions that function in muscle contraction.