Apoptosis

Stimuli

Low O2, toxins, ATP depletion, damage

Specific, genetically programmed physiological signals

ATP required

No

Yes

Cellular pattern

Swelling, organelle disruption, tissue death

Chromatin condensation, membrane blebbing, single-cell death

DNA breakdown

Random fragments

Nucleosome-sized fragments

Plasma membrane

Burst

Blebbed (see Figure 9.19)

Fate of dead cells

Ingested by phagocytes

Ingested by neighboring cells

Reaction in tissue

Inflammation

No inflammation

Like the cell division cycle, the cell death cycle is controlled by signals, which may come either from inside or outside the cell. These signals include the lack of a mitotic signal (such as a growth factor), and the recognition of DNA damage. As we will see in Chapter 17, many of the drugs used to treat diseases of excess cell proliferation, such as cancer, work through these signals.

The events of apoptosis are very similar in most organisms. The cell becomes isolated from its neighbors, chops up its chromatin into nucleosome-sized pieces, and then fragments itself (Figure 9.19). In a remarkable example of the economy of nature, the surrounding living cells usually ingest the remains of the dead cell. The genetic signals that lead to apoptosis are also common to many organisms.

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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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