Tissue Shrinkage and Death

The shrinkage of a tissue through a loss in cell size or number is called atrophy43 (AT-ruh-fee). Atrophy results from both normal aging (senile atrophy) and lack of use of an organ (disuse atrophy). Muscles that are not exercised exhibit disuse atrophy as their cells become smaller. This was a serious problem for the first astronauts who participated in prolonged microgravity space flights. Upon return to normal gravity, they were sometimes too weak from muscular atrophy to walk. Space stations and shuttles now include exercise equipment to maintain the crews' muscular condition. Disuse atrophy also occurs when a limb is immobilized, as in a cast.

Necrosis44 (neh-CRO-sis) is the premature, pathological death of tissue due to trauma, toxins, infection, and so forth. Gangrene is any tissue necrosis resulting from an insufficient blood supply. Gas gangrene is necrosis of a

40hyper = excessive + plas = growth

41 trophy = nourishment

43a = without

44necr = death + osis = process

Saladin: Anatomy & Physiology: The Unity of Form and Function, Third Edition

5. Histology

Text

184 Part One Organization of the Body

Gas GangreneScab Formation

-Scab

Macrophages

Fibroblasts

Leukocytes

-Scab

Macrophages

Fibroblasts

Leukocytes

1. Bleeding into the wound

2. Scab formation and macrophage activity

Scab Formation

Scab

■ Fibroblast

Macrophage

Blood capillary

Figure 5.34 Stages in the Healing of a Wound to the Skin.

Scab

■ Fibroblast

Macrophage

Blood capillary

Epithelial Tissue Wound Bed
- Epidermal growth

Scar tissue (fibrosis)

3. Formation of granulation tissue

4. Epithelial regeneration and connective tissue fibrosis

Figure 5.34 Stages in the Healing of a Wound to the Skin.

Saladin: Anatomy & I 5. Histology I Text I I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition wound resulting from infection with certain bacteria. Infarction is the sudden death of tissue, such as heart muscle (myocardial infarction), which occurs when its blood supply is cut off. A decubitus ulcer (bed sore) is tissue necrosis that occurs when immobilized persons, such as those confined to a hospital bed or wheelchair, are unable to move, and continual pressure on the skin cuts off blood flow to an area. Cells dying by necrosis usually swell, exhibit blebbing (bubbling) of their plasma membranes, and then rupture. The cell contents released into the tissues trigger an inflammatory response in which macrophages phagocytize the cellular debris.

Apoptosis45 (AP-oh-TOE-sis), or programmed cell death, is the normal death of cells that have completed their function and best serve the body by dying and getting out of the way. Cells undergoing apoptosis shrink and are quickly phagocytized by macrophages and other cells. The cell contents never escape the cell, so there is no inflammatory response. Although billions of cells die every hour by apoptosis, they are engulfed so quickly that they are almost never seen except within macrophages. For this reason, apoptosis was not discovered until recently.

Apparently every cell has a built-in "suicide program" that enables the body to dispose of it when necessary. In some cases, a receptor protein in the plasma membrane called Fas binds to an extracellular suicide signal. Fas then activates intracellular enzymes that destroy the cell, including an endonuclease that chops up its DNA and a protease that destroys cellular proteins. In other cases, cells seem to undergo apoptosis automatically if they stop receiving growth factors from other cells. For example, in embryonic development we produce about twice as many neurons as we need. Those that make connections with target cells survive, while the excess 50% die for lack of nerve growth factor. Apoptosis also "dissolves" the webbing between the fingers and toes during embryonic development; it frees the earlobe from the side of the head in people with the genotype for detached ear-lobes (see chapter 4); and it causes shrinkage of the uterus after pregnancy and of the breasts after lactation ceases.

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Responses

  • hannele
    Is atrophy the premature, pathalogical death of tissue?
    7 years ago
  • Nieve
    What is premature, pathalogical death of a tossue due to trauma, toxins, or in fections?
    5 years ago

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