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Figure

Cells vary considerably in size. This illustration shows the relative sizes of four types of cells. (a) Red blood cell, 7.5 ^m in diameter; (b) white blood cell, 10-12 ^m in diameter; (c) human egg cell, 140 ^m in diameter; (d) smooth muscle cell, 20-500 ^m in length.

Blood Vessels Figures

Figure 3.2

Cells vary in shape and function. (a) A nerve cell transmits impulses from one body part to another. (b) Epithelial cells protect underlying cells. (c) Muscle cells pull structures closer.

Figure 3.2

Cells vary in shape and function. (a) A nerve cell transmits impulses from one body part to another. (b) Epithelial cells protect underlying cells. (c) Muscle cells pull structures closer.

Figure

A composite cell. Organelles are not drawn to scale.

Figure

A transmission electron microscope.

Figure

A transmission electron microscope.

flexible and somewhat elastic. It typically has complex surface features with many outpouch-ings and infoldings that increase surface area. The cell membrane quickly seals tiny breaks, but if it is extensively damaged, cell contents escape, and the cell dies.

The maximum effective magnification possible using a light microscope is about 1,200x. A transmission electron microscope (TEM) provides an effective magnification of nearly 1,000,000x, whereas a scanning electron microscope (SEM), can provide about 50,000x. Photographs of microscopic objects (micrographs) produced using the light microscope and the transmission electron microscope are typically two-dimensional, but those obtained with the scanning electron microscope have a three-dimensional quality (fig. 3.5).

In addition to maintaining the integrity of the cell, the membrane controls the entrance and exit of substances, allowing some in while excluding others. A membrane that functions in this manner is selectively permeable (percme-ah-bl). The cell membrane is crucial because it is a conduit between the cell and the extracellular fluids in the body's internal environment. It even allows the cell to receive and respond to incoming messages, a process called signal transduction. (Signal transduction is described in more detail in chapter 13.)

Blood Vessels Figures

Figure 3.5

Figure 3.5

Human red blood cells as viewed using (a) a light microscope (1,200x), (b) a transmission electron microscope (2,500x), and (c) a scanning electron microscope (1,900x).

Shier-Butler-Lewis: I I. Levels of Organization I 3. Cells I I © The McGraw-Hill

Human Anatomy and Companies, 2001

Physiology, Ninth Edition

Fetal Neck Vessels

Figure 3.6

Cell membrane

"Tails" of phospholipid

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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