Hyperplasia and hypertrophy

Definitions & Key takeaways

Hyperplasia and hypertrophy are two ways that the size of cells can increase. Hyperplasia is an increase in the number of cells, while hypertrophy is an increase in the size of cells. During hypertrophy, the cells enlarge as they fill with more cytoplasm. This can lead to an increase in the strength or function of the tissue. During hyperplasia, new cells are formed as existing cells divide. This can lead to an increase in the number of cells and the overall size of the tissue.

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Introduction0:00–0:57

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.

Hypertrophy0:57–1:54

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 pressures 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.

Hyperplasia1:54–5:04

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 occur in organs that are regulated by hormones like organs in the endocrine and reproductive system.
Like hypertrophy, hyperplasia can also be physiological or pathological. An example of physiologic hyperplasia is enlargement of the female breast during pregnancy.
In preparation for breastfeeding, hormones like prolactin, progesterone, and human placental lactogen stimulate the growth of glandular tissue in the breast causing them to enlarge.
An example of pathologic hyperplasia is having excessive hormonal stimulation. For example, normally, during a menstrual cycle, the endometrium, which forms the inner lining of the uterus, grows and proliferates when exposed to estrogen.
But if there is an overproduction of estrogen by an ovarian tumor, it can lead to excessive endometrial growth - also called endometrial hyperplasia.
Now, one problem with hyperplasia is that it’s sometimes associated with cancer. Normally, hyperplasia is an adaptive response to stress, so it’s a tightly regulated process, meaning the tissue doesn’t grow out of control.
And in hyperplasia the process stops if the stress factors are eliminated. That’s different from cancer where there’s uncontrolled cell division.
Now, the thing is that as cells divide in hyperplasia some can mutate and that’s how hyperplasia can slip into dysplasia and eventually into malignancy.
While cells from hyperplasia are normal and healthy, cells from dysplasia can have an abnormal shape and function. And malignant cells might not only be abnormal, but also replicate uncontrollably, causing cancer.
And that’s why individuals with endometrial hyperplasia that’s left untreated, can develop endometrial cancer. Finally, it’s important to remember that in tissues that have stem cells, hyperplasia and hypertrophy usually occur together when there’s increased stress.
For example, in pregnancy, the uterus gets stimulated by estrogen, which lead to hypertrophy and hyperplasia of the smooth muscle cells in the uterine wall.
Meaning that the cells get tougher and the pack of cells gets more numerous. Alright, as a quick recap, whenever an organ encounters any sort of physiological or pathological stress, it adapts by hyperplasia or hypertrophy.

Review5:04–5:39

You can remember that as - hyperplasia, bigger pack, and hypertrophy, tough lumberjack! In general, hyperplasia and hypertrophy occur together in organs with stem cells like the skin, liver, bone marrow or uterus.
Organs that lack stem cell like the heart, skeletal muscle, and nerve can only undergo hypertrophy.