Imagine a lumberjack. At first she can handle cutting down a few trees a day, but suddenly her boss wants her to chop down an entire forest by the end of the week! Now she’s stressed out from the increased demand!
Our body is the same; when the demand placed on an organ or tissue is more than it can handle, its called “stress,” and the body can adapt through either hyperplasia or hypertrophy.
Hyperplasia refers to the process where cells in an organ or tissue increase in number, so its like hiring a bigger pack of lumberjacks.
Hypertrophy is when these cells in an organ or tissue increase in size, like if the lumberjack gets really tough so that she can cut down twice as many trees.
So hyperplasia, bigger pack, and hypertrophy, tough lumberjack!
So, a tissue or organ might get stressed by physiological processes or from disease processes.
An example of physiologic hypertrophy is lifting a 10 pound sack of potatoes which puts a bigger functional demand on your skeletal muscles.
In response, the muscle cells produce more proteins or myofilaments and get larger in size, allowing the biceps as a whole to generate more force. As a result your muscles also become bigger and tougher.
An example of pathologic hypertrophy is when the heart undergoes hypertrophy to deal with high blood pressure or hypertension.
In hypertension, the heart has to pump blood against a high resistance and cardiac myocytes once again adapt by increasing the synthesis of myofilaments causing individual cells to get bigger.
In both cases there’s hypertrophy, but the triggers are quite different.
Now, in hyperplasia there’s an increase in the number of cells - a larger pack.
And that can only happen in organs with stem cells that can undergo cellular differentiation to become a mature cell in that organ, like cells in the intestines for example.
So hyperplasia doesn’t occur in relatively permanent tissues without stem cells- like cardiac, nerve, and adult skeletal muscle tissue.
And that’s why those tissues typically only undergo hypertrophy when they face increased stress.
Now there’s compensatory hyperplasia and hormonal hyperplasia.
Compensatory hyperplasia occurs in organs that regenerate, like the skin, lining of the intestines, the liver, and bone marrow.
Hormonal hyperplasia occurs in organs that are regulated by hormones like organs in the endocrine and reproductive system.
Like hypertrophy, hyperplasia can also be physiological or pathological.
