0:00 Cellular adaptation is the ability of cells to respond to various types of 0:11 stimuli and 0:12 adverse environmental changes. 0:14 These adaptations include hyperplasia, hypertrophy, atrophy and metoplasia. 0:22 These adaptations can be physiologic or pathologic, depending upon whether the 0:28 stimulus is normal 0:29 or abnormal. 0:31 A cell can adapt to a certain point, but if the stimulus continues beyond that 0:36 point, 0:37 failure of the cell and hence the organ can result. 0:40 If cells cannot adapt to the pathologic stimulus, they can die. 0:46 So let us discuss the four basic types of cellular adaptation. 0:51 Hyperplasia, hypertrophy, atrophy and metoplasia. 0:57 We will also explore the physiologic and pathologic stimuli in each of these 1:02 cellular adaptations, 1:04 beginning with hyperplasia. 1:11 Hyperplasia is an increase in the number of cells. 1:16 Physiologic hyperplasia occurs due to normal stresses, for example, an increase 1:21 in the 1:21 size of breasts during pregnancy, an increase in the thickness of the endomet 1:27 rium during 1:28 the menstrual cycle and liver growth after partial resection. 1:34 Pathologic hyperplasia occurs due to an abnormal stressor, for example, growth 1:41 of the adrenal 1:41 glands due to production of adrenal corticotropin hormone by the pituitary aden 1:48 oma, and proliferation 1:49 of the endometrium due to prolonged estrogen stimulus. 1:55 Important point regarding hyperplasia is that only cells that can divide will 2:01 undergo hyperplasia. 2:03 And these cells include the epidermis, the intestinal cells, liver cells, bone 2:08 marrow 2:09 cells and fibroblasts. 2:12 Hyperplasia does not occur in myocytes of the heart and the neurons of the 2:17 brain because 2:18 these cells do not undergo cell mitosis or cell division. 2:29 The second cell adaptation is hypertrophy, which is an increase in the size of 2:36 the cell. 2:37 Physiologic hypertrophy occurs due to a normal stressor, for example, enlarg 2:42 ement of skeletal 2:43 muscle with exercise. The myocytes cannot divide, but they can increase in size 2:51 . 2:51 Pathologic hypertrophy occurs due to an abnormal stressor, for example, 2:56 increase in the size 2:58 of the heart due to aortic stenosis. 3:01 Aortic stenosis is due to a change in the aortic valve which obstructs the or 3:06 ifice resulting 3:07 in the left ventricle, working harder to pump blood into the aorta, and so this 3:13 undergoes 3:14 hypertrophy. 3:17 Morphologically hyperplasia and hypertrophy can look similar. They both result 3:24 in actually 3:24 an increase in organ size. Therefore, they cannot always be distinguished 3:31 grossly, and microscopic examination is required to distinguish the two. 3:42 The third type of cellular adaptation is atrophy, which is the decrease in the 3:49 size of a cell 3:50 that has at one time been a normal size. 3:56 Physiologic atrophy occurs due to a normal stressor, for example, the decrease 4:00 in the 4:00 size of the uterus after pregnancy. 4:04 Pathologic atrophy occurs due to an abnormal stressor. In general, atrophy is 4:10 due to the 4:10 loss of the stimulus to that organ. Specific types of loss of stimulus include 4:17 when the 4:18 cell has loss of blood supply or innervation, loss of endocrine stimulus, dis 4:25 use, mechanical 4:26 compression, decrease workload or aging. Here is an example of atrophy of 4:33 skeletal muscle 4:34 because of misuse or aging. 4:43 The final type of cellular adaptation is metoplasia, and metoplasia is the 4:48 change of the epithelium 4:51 at a site or location, from one type of epithelium to another type. In metopl 4:58 asia the epithelium 4:59 is normal in appearance, but in an abnormal location. 5:06 How metoplasia occurs is that the epithelium, the cell that is normally present 5:13 at the site 5:14 cannot handle the new environment, the stimulus, and so it converts to a type 5:20 of epithelium 5:21 that can adapt to these changes. 5:25 Metoplasia is more often than not pathologic. A good example is seen in Barrett 5:31 's esophagus 5:32 and Metoplasia in the lungs. Barrett's esophagus is due to reflux of gastric 5:39 contents into the 5:39 esophagus, which causes the epithelium type to convert from squamous to gland 5:49 ular. 5:49 Squamous metoplasia in the lungs is due to exposure of respiratory epithelium 5:54 to toxin 5:55 and cigarette smoke. 5:59 Most forms of metoplasia are reversible if the stimulus is removed, whereas a 6:05 few, such 6:05 as Barrett's esophagus, tends to be permanent once they are established. Metopl 6:12 asia can 6:12 progress to dysplasia. Dysplasia is not a true cellular adaptive response. It 6:19 is where 6:19 the cells divide and become abnormal in structure and function. It may progress 6:24 to become cancers. 6:31 So those are the four important cellular responses, adaptations. But what 6:37 happens when the cells 6:38 cannot adapt to their new environment? 6:42 When cells cannot adapt to certain stimuli, they become injured, which can lead 6:47 to cell 6:48 death, if not reversed. Some causes of cell injury include hypoxia, decreased 6:54 oxygen, 6:55 ischemia, decreased blood flow to that cell, physical or chemical agents, 7:01 trauma, infectious 7:02 agents, aging and nutritional imbalances. 7:09 Cellular injury can be divided into two types, reversible cellular injury or 7:16 irreversible 7:16 cellular injury. Reversible cellular injury, as the name suggests, can be 7:22 reversed if 7:23 the stimulus is removed and the cell can return to normal function. E-re 7:28 versible cellular 7:29 injury means the cell is damaged and dies in an uncontrolled process termed 7:36 cellular necrosis. 7:38 The other form of cellular death is apoptosis, which is programmed cell death. 7:50 In summary, we discussed the four cellular adaptations, hyperplasia, hypertro 7:56 phy, atrophy 7:57 and metoplasia. We also discussed cellular injury, when the cells cannot adapt 8:04 to their 8:04 new environment, and the consequences of this, which includes necrosis. 8:20 You
