During exercise, the endocrine system and various hormones released by various glands are going to have a massive effect on metabolism. So some of those glands are going to be the anterior pituitary gland, the thyroid gland, the adrenal glands, and the pancreas, all of which are going to release hormones that are going to help us regulate metabolism and fuel that exercise session. Depending on the specific session, these are going to help to control how much carbohydrates and how much... that our body's using for metabolism in order to fuel the exercise itself. One of those hormone and hormone glands that are really important for controlling exercise metabolism is the anterior pituitary gland.
You can see the pituitary gland right there in that red and that skull that's rotating. The anterior pituitary gland is going to be secreting its hormones based on hypothalamic stimulating and inhibitory hormones that are released. With this...
Exercise is typically going to increase the secretion of all anterior pituitary hormones. So it's going to be mostly stimulation during exercise. One of the hormones that are really important that the anterior pituitary gland is going to release is growth hormone. Growth hormone is going to build tissues and organs.
It promotes muscle hypertrophy. It increases fat metabolism and increases blood-free fatty acid. This allows us to have higher amounts of fat utilization.
to spare glucose because we have a much more limited supply of glucose in our body. Regardless if you're doing aerobic or resistance exercise, the amount of growth hormone being released is going to be proportional to the intensity of that exercise session. Another important gland for controlling the metabolism through the endocrine system is the thyroid gland, which we can see right here is this white mass in the circulating skeleton. The thyroid gland releases tri-idothyronine, which is T3, and thyroxine, which is T4. Both at rest, but also in response to acute exercise.
These hormones are going to increase metabolic rates of all tissues of the body. They're going to increase protein synthesis, glucose uptake by the cells, glycolysis, and gluconeogenesis, so increasing the utilization of that glucose that is being uptake, and it's going to increase the amount of new glucose being created from non-glucose original molecules. It's going to increase free fatty acid availability, which is going to help with aero...
metabolism and also help in sparing that glucose because again we don't have a ton of glucose in our body. It's going to increase over time. It's going to increase the number and the size of the mitochondria within our body and within our cells so that we become better with aerobic metabolism. The adrenal medulla, which is the intersection of the adrenal glands that sit on top of the kidneys. We can see a cross section of the adrenal glands here in the medulla is this center part.
The outside here is the cortex. But the adrenal medulla is going to be important for increasing norepinephrine and epinephrine release during exercise. Exercise is going to be stimulating the sympathetic nervous system.
The sympathetic nervous system is going to be controlling the adrenal medulla, and it's going to be going directly to it with sympathetic neurons that are going to increase the endocrine release of that adrenal medulla, increasing epinephrine release and norepinephrine release, mostly epinephrine though. So about 80% of what it releases is epinephrine, the other 20% being norepinephrine. These hormones, which are basically the exact same chemicals as the neurotransmitters released by the sympathetic nervous system, are going to act just like those neurotransmitters from the sympathetic neurons, except for because they're going into the bloodstream and floating around a little bit before ending on a cell, a target cell or a target receptor, they take a little longer to degrade so they have a longer action.
With this, they're going to have all the same actions though. So they're going to increase all the following heart rate, contractility of the heart, blood pressure, respiration, metabolism, glycogenolysis, so the breakdown of glycogen to release glucose, blood glucose, and free fatty acid availability. So again, glycogenolysis increasing the amount of glucose available.
We're also going to be increasing fatty acid availability though, so fats. And we see this aiding in the redistribution of blood flow to the active skeletal muscle. It's going to be doing this by helping to vasoconstrict a lot of the blood vessels around the body in the less active tissues. It is not just the adrenal medulla that's going to have an impact on metabolism during exercise. The adrenal cortex is also going to be involved.
The adrenal cortex releases corticohormones. Think cortico meaning the cortex and steroidal hormones, corticosteroid hormones. The three types are going to be glucocorticoids, which we'll talk about here in a second. mineral corticoids, and gonadocorticoids.
The ones we're going to focus on right now is the glucocorticoid steroids, which as you would guess from the name is going to be impacting how we handle glucose. In general though, this has direct effect on metabolism throughout the body. The main glucocorticoid steroid that's being released is cortisol. It is 95% of all of the glucocorticoid steroid activity within the body.
And the effects of cortisol is going to be increased gluconeogenesis, so the creation of glucose from non-glucose substrates, increased free fatty acid availability, increased protein catabolism, decreased glycolysis to spare glucose for the brain. Remember, cortisol gets released typically around 30 minutes in a moderate to intense bout of aerobic exercise. So we're at this point trying to spare glucose a little bit. Cortisol is also going to decrease immune reactions. by being an anti-inflammatory agent, which is okay during exercise, not so okay on a sort of constant basis at rest though.
All these are acting to try to preserve glucose availability for the brain, and so it's going to increase our uses of fats and increase our uses of proteins, and also increase the availability of glucose in order to do that. The pancreas as a gland is a really important organ. You can see a picture of it right here.
It is going to be what controls blood glucose at rest and during exercise. It's the major controller of blood glucose. It's going to do this by releasing two different hormones in different situations.
It releases insulin when blood glucose is very high, which is going to bring glucose into the cells and clear blood glucose. And it releases glucagon when blood glucose is low to help boost up glucose levels. So let's go through each of these. Again, insulin is released when blood glucose is high.
decreasing the amount of blood glucose by facilitating the transport of glucose into the cells. So it clears the glucose from the bloodstream and pushes it into the cells. It's going to increase synthesis of glycogen, which is the storage form of glucose.
Remember, we have too much glucose when we are releasing insulin. It's going to increase protein and fat synthesis as well. It decreases lipolysis, which is the breakdown of fat releasing fatty acids. Remember, we have too much glucose. glucose.
We probably want to be using glucose rather than fat at this point in time. And it decreases gluconeogenesis, which is the creation of new glucose. Again, we have too much glucose. We don't want to create more. Glucagon, the opposite hormone released by the pancreas, is going to respond again to low blood glucose.
So it's going to increase blood glucose, increasing the release of glucose from the liver into the bloodstream. It's going to increase glycogenolysis, which is that breakdown of the storage form of glucose in the liver as well as it works on the skeletal muscle and it's going to increase gluconeogenesis so the creation of new glucose from non-glucose substrates so all this is going to increase glucose availability and glucose that gets into the bloodstream clearly blood glucose is really important for the body during exercise i'm going to have a whole other video where i talk about how we get the blood glucose into the the muscle cells because we actually decrease insulin during exercise. And so come back and make sure that you watch that video as well to help understand that.