Endoplasmic Reticulum

The most extensive cytoplasmic organelle is the network of membranes that forms the endoplasmic reticulum (Figure 3-12). These membranes enclose a space that is continuous throughout the network. (The continuity of the endoplasmic reticulum is not obvious when examining a single electron micrograph because only a portion of the network is present in any one section.)

Two forms of endoplasmic reticulum can be distinguished: granular (rough-surfaced) and agranular (smooth-surfaced). As noted on the next page, the

Vander et al.: Human Physiology: The Mechanism of Body Function, Eighth Edition

I. Basic Cell Functions

3. Cell Structure

© The McGraw-Hill Companies, 2001

Cell Structure CHAPTER THREE

Cell Structure CHAPTER THREE

Lysosome

Granular endoplasmic reticulum

Mitochondria

Agranular endoplasmic reticulum

Granular endoplasmic reticulum

Agranular endoplasmic reticulum

Ribosomes

Granular endoplasmic reticulum

Structure: Extensive membranous network of flattened sacs. Encloses a space that is continuous throughout the organelle and with the space between the two nuclear-envelope membranes. Has ribosomal particles attached to its cytosolic surface

Function: Proteins synthesized on the attached ribosomes enter the lumen of the reticulum from which they are ultimately distributed to other organelles or secreted from cell.

Agranular endoplasmic reticulum

Structure: Highly branched tubular network that does not have attached ribosomes but may be continuous with the granular endoplasmic reticulum.

Function: Contains enzymes for fatty acid and steroid synthesis. Stores and releases calcium, which controls various cell activities.

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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