When I was reading over the sections that Matheus had written for me to look over, the issue of growth plate senescence would come up over and over again.
He would mention how senescence is from two factors, oxidative stress and free radicals. Also, Matheus suggested that free radicals and homocysteine would cause oxidative stress. A quick check with google search seems to validate his point that oxidative stress is caused by homocysteine (source: Homocysteine and oxidative stress)
It made me wonder just what types of factors would cause increased senescence. Matheus actually disagrees with Tyler’s opinion that the replication possibility of the chondrocytes from the resting zone is finite, but limitless.
One point which is very interesting he made which made me rethink how the growth plate really work is when he made the point that the speed at which the physeal chondrocytes proliferation and replicate is much faster than all other types of cells in the body. This is why these types of cells, the growth plate cells are the first types of cells that really go completely extinct, because the speed or rate at which they divide and go through their life is much faster than other cells.
While I am not a real biologist, the reasoning makes some sense. The chondrocytes do seem to be proliferating, which is just mitosis, at a much faster rate than the other types of cells. If the other types of cells like neurons, adipocytes, and others were proliferating at the same speed, we as a species would have a much shorter lifespan.
I would think about my chemical engineering days and realized that one of the easiest to identify and quantify factors which would probably effect growth plate senescence, and thus adult height is temperature.
From elementary chemistry, based on the Arrhenius equation,
Arrhenius’ equation gives the dependence of the rate constant k of a chemical reaction on the absolute temperature T (in kelvin), where A is the pre-exponential factor (or simply the prefactor), Ea is theactivation energy, and R is the Universal gas constant.
k = A*exp ( -Ea / R*T )
Under the factors that influence chemical reaction…
- Temperature: Usually conducting a reaction at a higher temperature delivers more energy into the system and increases the reaction rate by causing more collisions between particles, as explained by collision theory. However, the main reason that temperature increases the rate of reaction is that more of the colliding particles will have the necessary activation energy resulting in more successful collisions (when bonds are formed between reactants). The influence of temperature is described by the Arrhenius equation. As a rule of thumb, reaction rates for many reactions double for every 10 degrees Celsius increase in temperature, though the effect of temperature may be very much larger or smaller than this.
If we then just imagine the process of any type of cell mitosis as a chemical reaction, then clearly the rate of chondrocyte proliferation would be increased with increased Temperature.
Let’s also remember how reaction rates are actually written and set up (source: Wikipedia article on reaction rates).
Then if we assume that the mesenchymes which differentiate into the chondrocytes in the resting zone are substrates in a chemical reaction as well as the rate limiting factor, then the most simplified way to describe the height increase growth in humans is just
r = k(T) * A^(n) where A is the only element that is the substrate and n is the number of moles in the system we are analyzing.
the r would just be the loss over time of the one reactant, so r = – dA/dt
is -dA/dt = k(T) *A
So from just a simple explanation of chemical kinetics, it is very reasonable to assume that increased Temperature can increase the rate at which the growth plates reach senescence.
Then I would evidence from an old study I found entitled “Stimulation Of Bone Growth by Short-Wave Diathermy”
I am also reminded of the evolutionary-ecological heuristic rule of thumb called Bergmann’s Rule, which state that on average, people further away from the equator, in colder climates are bigger in size than people closer to the equation. This hypothesis has been challenged a lot and some people have proved that Bergmann’s Rule is actually wrong.
However the implications and hypothesis for me is very interesting. I would actually write quite extensively about this idea in multiple posts including “Bergmann’s Rule, Application On The Human Species”
I would post even further this idea that colder temperatures would be better for increased final adult height in the post “A Study Of Temperature Variation On Sea Slugs Can Explain Why People Are Taller In Colder Environments”
Interestingly, the same studies on deep sea gigantism in shellfish or crustaceans lead to the same conclusion. The specific study was “Bergmann’s Principle and Deep-Water Gigantism in Marine Crustaceans”. From the Wikipedia article on Bergmann’s Rule…
“…In marine crustaceans, it has been proposed that an increase in size with latitude is observed because decreasing temperature results in increased cell size and increased life span, both of which lead to an increase in maximum body size (continued growth throughout life is characteristic of crustaceans).”
There was even an extension to Bergmann’s Rule called Hesse’s Rule which states…
“…species inhabiting colder climates have a larger heart in relation to body weight than closely related species inhabiting warmer climates”
This rule, which I just discovered may explain why bergmann’s rule may be valid for humans.
Larger hearts, if they are not due to a disorder or pathology, means that more nutrients can be pumped to all of the regions in a person’s body. The larger heart, means higher pumping rates of the blood to all the cells, so the cells manage to live longer.
The leap in logic then is to assume that from the extra rates of blood nutrients being pumped to the growth plate region, there would be more progenitor mesenchyme cells in the epiphysis region for eventual differentiation. We already know that some compounds like Niacin do increase the proliferation of stem cells, as long as the blood flow rate is increased,leading to blood vessel dilation, which causes niacin to increase the cells.
I had mentioned the hypothesis that the recent Chinese Olympic Swimmer Ye Shiwen’s performance can be explained by two thing, her puberty induced 4 inch growth spurt, and an above average sized heart in the post “Personal Theory: Ye Shiwen Olympic Performance Of Increased Swimming Performance Can Be Explained By A Massive Growth Spurt And A Physical Abnormality” There might even be a correlation between height and heart size.
Growth plates can be actually modulated and controlled by two factors which is related to temperature, which are heart size and rate at which the chondrocyte proliferate.
The two things that happen to a person’s body when that person is born in a colder environment are…
- Their heart becomes bigger from prenatal growing process in the mother’s womb.
- The rate at which the resting zone mesenchyme are depleted/differentiated into chondrocytes into the proliferation zone is slowed down.
