Endoplasmic Reticulum

Endoplasmic reticulum (ER) literally means "little network within the cytoplasm." It is a system of interconnected channels called cisternae34 (sis-TUR-nee) enclosed by a unit membrane (fig. 3.26). In areas called rough endo-

33chromat = color

34cistern = reservoir

Tem Nuclear Envelope

Figure 3.25 The nucleus. (a) TEM micrograph showing the nuclear envelope and internal structure. (b) TEM micrograph of the nuclear surface showing the high density of nuclear pores. Why do these nuclear pores have to be larger in diameter than the channels in the cell's plasma membrane? (See table 3.1.)

Figure 3.25 The nucleus. (a) TEM micrograph showing the nuclear envelope and internal structure. (b) TEM micrograph of the nuclear surface showing the high density of nuclear pores. Why do these nuclear pores have to be larger in diameter than the channels in the cell's plasma membrane? (See table 3.1.)

plasmic reticulum, the network is composed of parallel, flattened sacs covered with granules called ribosomes. The rough ER is continuous with the outer membrane of the nuclear envelope, and adjacent cisternae are often connected by perpendicular bridges. In areas called smooth endoplasmic reticulum, the membrane lacks ribosomes, the cisternae are more tubular in shape, and they branch

Saladin: Anatomy & I 3. Cellular Form and I Text I © The McGraw-Hill

Physiology: The Unity of Function Companies, 2003 Form and Function, Third Edition

Chapter 3 Cellular Form and Function 117

Rough Endoplasmic Reticulum Micrograph

Rough endoplasmic reticulum

Chapter 3 Cellular Form and Function 117

Rough Endoplasmic Reticulum

Rough endoplasmic reticulum

Smooth Endoplasmic Reticulum
Cisternae

Smooth endoplasmic reticulum y

Figure 3.26 Endoplasmic Reticulum (ER). (a) Rough ER. (b) Smooth ER and an inclusion (oil droplet). (c) Structure of the endoplasmic reticulum, with rough and smooth regions.

more extensively. The cisternae of the smooth ER are thought to be continuous with those of the rough ER, so the two are functionally different parts of the same network.

The ER synthesizes steroids and other lipids, detoxifies alcohol and other drugs, and manufactures all of the membranes of the cell. Rough ER produces the phospho-lipids and proteins of the plasma membrane, and synthesizes proteins that are either packaged in other organelles such as lysosomes or secreted from the cell. Rough ER is most abundant in cells that synthesize large amounts of protein, such as antibody-producing cells and cells of the digestive glands. This role is discussed further in chapter 4.

Most cells have only a scanty smooth ER, but it is relatively abundant in cells that engage extensively in detoxification, such as liver and kidney cells. Long-term abuse

Saladin: Anatomy & I 3. Cellular Form and I Text I © The McGraw-Hill

Physiology: The Unity of Function Companies, 2003 Form and Function, Third Edition

118 Part One Organization of the Body of alcohol, barbiturates, and other drugs leads to tolerance partly because the smooth ER proliferates and detoxifies the drugs more quickly. Smooth ER is also abundant in cells of the testes and ovaries that synthesize steroid hormones. Skeletal muscle and cardiac muscle contain extensive networks of smooth ER that store calcium and release it to trigger muscle contraction.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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