Oxygen demand

[ed34]

I know that when muslce tissue requires a higher flow of Oxygen, the arteries supplying the tissue dilate to allow this. Does anyone know how this process actually works? What is the feedback system between muscle and arteries?
If I begin jogging, my leg muscles will obviously draw more oxygen from the blood being supplied and so the ratio of oxygen/carbon dioxide in that area will be very low. The muscles will struggle because the oxygen level is insufficient.
I always thought there was a sensor at the base of the brain somewhere which reacts to the acidity level of blood, giving an idea of whether we should breathe faster or slower. But what actually tells arteries to dilate and in particular areas of the body?

[kenkeith]

Thanks for the questions, its a learning process for everyone!.

[ed34]

yes thanks very much for that.

[kenkeith]

" In a psychological response to fear, the brain sends out hormones to reduce blood flow to non essential organs and increase blood flow to muscles and the brain. This is the 'fight or flee' condition."  

>>>>>I agree, but some exceptions to the underlying role of the body responses you have stated.  For review. the fundamental physiologic response to ft and frt forms the foundation of modern day stress medicine and occurs under excessive stress. This response is hard-wired into our brains and represents a genetic wisdom designed to protect us from bodily harm. This response actually corresponds to an area of our brain called the hypothalamus, which—when stimulated—initiates a sequence of nerve cell firing and chemical release that prepares our body for running or fighting....I'm not sure of the chemicals, but I believe it is adrenaline and the lungs may be the focus not the brain (sometimes the brain doesn't work very well under stress). My source: "The term "fight or flight" is often used to characterize the circumstances under which adrenaline is released into the body. It is an early evolutionary adaptation to allow better coping with dangerous and unexpected situations. With dilated blood vessels and air passages, the body is able to pass more blood to the muscles and get more oxygen into the lungs in a timely manner, increasing physical performance for short bursts of time.

QUOTE: " If we exercise, such as running a marathon. we need extra blood flow to the leg muscles and the heart/lungs etc. Just the same as the fight/flee condition. However, the brain will not activate the alarms simply because we start to run a marathon. So, the missing information is 'what causes the non essential systems to be lowered in blood supply when we simply exercise'. The arteries supplying the legs dilating would cause a shortage of blood and a huge pressure drop, so what triggers blood to be re-routed from the digestive system etc."

>>>First we drop the adrenaline and any chemical release from hypothalamus (if normal). Replace with the sympathetic nervous system, a part of the automatic or autonomic nervous system (that is, the brainstem and spinal cord) stimulates the nerves to the heart and blood vessels. This nervous stimulation causes those blood vessels (arteries and veins) to contract or constrict (vasoconstriction).  

This vasoconstriction reduces blood When you begin to exercise, a remarkable diversion happens. Blood that would have gone to the stomach or the kidneys goes instead to the muscles, and the way that happens shows how the body's processes can sometimes override one another. As your muscles begin to work,flow to tissues. Your muscles also get the command for vasoconstriction, but the METABOLIC BYPRODUCTS (ie ATP) produced within the muscle override this command and cause vasodilation. Because the rest of the body gets the message to constrict the blood vessels and the muscles dilate their blood vessels, blood flow from nonessential organs (for example, stomach, intestines and kidney, obviously some is drawn from the heart and that would explain angina) is diverted to working muscle. This helps increase the delivery of oxygenated blood to working muscle further.

Does that help?
.

[ed34]

"I'm reading what you write, I read my response, and I am at a loss to understand what my response is missing"

1. In a psychological response to fear, the brain sends out hormones to reduce blood flow to non essential organs and increase blood flow to muscles and the brain. This is the 'fight or flee' condition.

2. If we exercise, such as running a marathon. we need extra blood flow to the leg muscles and the heart/lungs etc. Just the same as the fight/flee condition. However, the brain will not activate the alarms simply because we start to run a marathon. So, the missing information is 'what causes the non essential systems to be lowered in blood supply when we simply exercise'. The arteries supplying the legs dilating would cause a shortage of blood and a huge pressure drop, so what triggers blood to be re-routed from the digestive system etc.

[kenkeith]

I'm reading what you write, I read my response, and I am at a loss to understand what my response is missing.  There are only two processes that facilitate an increase of blood flow, and I believe I both have been given...may be not enough detail?

[ed34]

Thank you for your explanation, it makes perfect sense, but if I could put down how I understand this, I hope you can find time to comment on whether I have it right or not.

When we experience an emotional response, such as fear for example, our brain will put our body into 'fight or flee' mode. It will lower blood flow to less essential systems and increase flow to muscles needed to run or fight. It sends out relevant hormones such as adrenaline to get the heart racing and dilate the coronary arteries and increase our breathing rate. Extra oxygen is supplied to the brain giving us the ability to make decisions much faster which would be an advantage in a life threatening situation.

When we simply exercise, such as cycling or jogging, the brain is not put into stress mode so the same processes are not activated. However, they need to be activated in the same way, somehow, so we gain endurance. The Arteries to muscle tissue are sensitive to the waste (byproducts) produced by muscle cells as they produce energy. As these products increase, the arteries dilate further to give more supply.

I wonder what causes the blood supply to non essential systems to be reduced? Maybe as the flow decreases in those areas the arteries automatically contract? Like a built in mechanism to enable us to use our muscles more effectively?

[kenkeith]

You have identified the process of getting oxygenated blood to the skeletal muscles and extracting the oxygen in exchange for carbon dioxide, etc. The feed backback can be how brain reacts to the message sent by the endothelium cells to dilate vessels as you have alluded.

To the point when one exercises, the blood vessels in the muscles dilate and the blood flow is greater. The body has an interesting way of making those vessels expand. As **ATP (biochemical for energy) gets used up in working muscle, the muscle produces several metabolic byproducts (such as adenosine, hydrogen ions and carbon dioxide). These byproducts leave the muscle cells and caus the capillaries within the muscle to expand or dilate. The increased blood flow delivers more oxygenated blood to the working muscle.

**Adenosine triphosphate: An important carrier of energy in cells in the body and a compound that is important in the synthesis (the making) of RNA. Adenosine triphosphate (ATP) is a nucleotide (a building block of a nucleic acid such as RNA). The body produces ATP from food and then ATP produces energy as needed by the body.
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"When you begin to exercise, a remarkable diversion happens. Blood that would have gone to the stomach or the kidneys goes instead to the muscles, and the way that happens shows how the body's processes can sometimes override one another. As your muscles begin to work, the sympathetic nervous system, a part of the automatic or autonomic nervous system (that is, the brainstem and spinal cord) stimulates the nerves to the heart and blood vessels. This nervous stimulation causes those blood vessels (arteries and veins) to contract or constrict (vasoconstriction). This vasoconstriction reduces blood flow to tissues. Your muscles also get the command for vasoconstriction, but the metabolic byproducts produced within the muscle override this command and cause vasodilation, as we discussed above. Because the rest of the body gets the message to constrict the blood vessels and the muscles dilate their blood vessels, blood flow from nonessential organs (for example, stomach, intestines and kidney) is diverted to working muscle. This helps increase the delivery of oxygenated blood to working muscle further".