1 N5315 Advanced Pathophysiology Cellular Adaptation and Injury Cellular Adaptation Overview Individual cells have a well defined function and structure as programmed by their genetic makeup. They are able to maintain homeostasis with minimal difficulties; however, when the stressors become severe or chronic, that is when adaptation responses occur. Adaptation is a process that cells undergo to adapt to their environment and to protect themselves from injury. Adaptation patterns can be physiologic or pathologic. Physiologic adaptation patterns are a normal and expected process. Uterine enlargement during pregnancy is an example of a physiologic adaptation pattern. A pathologic adaptation is a cellular response that is not considered normal but is necessary because of the harsh environment in which the cell is living. Left ventricular hypertrophy is an example of a pathologic cellular adaptation to chronically elevated blood pressure. There are five main types of cellular adaptation and they are as listed on your screen. (Atrophy, Hypertrophy, Hyperplasia, Dysplasia, Metaplasia) Atrophy is a decrease or shrinkage in the size of the cell. As more cells of the affected organ undergo this process, the entire organ will shrink as well. The shrinking of the thymus gland during childhood is an example of a physiologic atrophy. Pathologic atrophy occurs as a result of decrease in work load, pressure, use, blood supply, nutrition, hormonal stimulation, or nervous stimulation. Disuse Atrophy is skeletal muscle atrophy that occurs from a person being immobilized for a prolonged period of time. This is what happens in persons who are paralyzed. The mechanism of atrophy is not completely understood but it is believed to be an imbalance between protein synthesis and degradation. Essentially there is an increase in the catabolism of the intracellular organelles. The end result is a reduction of the structural components of the cell such as less mitochondria, myofilaments, and endoplasmic reticulum. This reduction of the intracellular contents is what causes atrophy. Once the cell has decreased in size, it has now compensated for the decreased blood supply, nerve supply, nutrient supply, hormonal supply, etc. and has achieved a new homeostasis to survive. The cells are still alive but have diminished function. This may lead to cellular death. Hypertrophy is an increase in the size of cells which will ultimately increase the size of the organ. Think of this as the opposite of cellular atrophy. It is caused by hormonal stimulation or increased functional demand, which increases the cellular protein in the plasma membrane, endoplasmic reticulum, myofilaments, and mitochondria (not cellular fluid). This ultimately leads to the increased cell size. Skeletal muscle hypertrophy is a physiologic adaptation pattern in those persons who do heavy work or weight lifting exercises. When a kidney is surgically removed, the other kidney will increase in size to accommodate for the increased work load. This too is a physiologic adaptation pattern. Cardiomegaly (enlarged heart) is an example of a
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- Fall '15
- cells, Hypoxic Cellular Injury