Reddit reviews Guyton and Hall Textbook of Medical Physiology, 12e

Several things happen:

First the capacitance vessels (mostly veins in your legs) contract, forcing more blood into the rest of the circulation.

Next: Extracellular fluid flows from the extracellular space into capillaries and "refill" the circulation. This is not blood, but has a similar basic composition without the cellular components. If effectively dilutes your blood, restoring volume but with fewer active components (Red and white blood cells, platelets, coagulation factors etc).

At the same time hormonal signals make the kidneys retain water and salt as well as excrete EPO (erythropoietin) into the circulation. The first bit helps restore total body fluid levels to normal, and the second bit speeds up red blood cell production.

(This is kind of rough from my memory from pre-clinical physiology. If you are really interested in things like this, have a basic understanding of chemistry and physics and have a masochistic streak you could pick up a used copy of a previous version of this http://www.amazon.com/Guyton-Hall-Textbook-Medical-Physiology/dp/1416045740)

It's nice, but that's not exactly how things work irl. Most of the oxygen in the body is consumed in cellular respiration in order to create ATP through oxidative phosphorylation. Basically, the only thing which would substantially lower the oxygen consumption is lowering of the core body temperature, since that slows down the cellular metabolism substantially. The main reason people die in stroke is due to lack of oxygen due to impaired blood flow, and lowering the body temperature helps lower the cells' oxygen requirement.

Also, but this is nitpicking, oxygen actually has negligible effect on breathing and heart rate if the arterial pO2 is higher than 8-10.5 kPa, whereas the main blood gas which controls breathing and heart rate at sea level is CO2, since it can pass the blood brain barrier and through CO2+H2O<->H2CO3<->H+ + HCO3- the H+ ion lowers the pH in hypercapnia, which stimulates the central chemoreceptors and the respiration center in the brain, leading to increased respiration and heart rate. Source



tldr Carbon dioxide controls heart rate, not oxygen.

This is the classic text:

http://www.amazon.com/Guyton-Hall-Textbook-Medical-Physiology/dp/1416045740

Ditto! I decided on this one for my lady: Guyton Hall Textbook - Medical Physiology.

https://www.amazon.com/Guyton-Hall-Textbook-Medical-Physiology/dp/1416045740

Alright, this kind of made me run back to my textbooks just so I can speak from science that I have learned, here are the sources from the textbook I used.

Cholesterol is not innately good or bad, this someone has already mentioned and is true. Our body makes cholesterol as a handy way to break down larger fats our body intakes from food into usable ones that our body needs to function. Cholesterol is transported through our body using Lipoproteins, there are many classes to this lipoprotein, VLDL, LDL, HDL. For the sake of simplicity lets talk about LDL and HDL because this are often used clinically.

LDL stores a massive amount of cholesterol, and HDL in comparison stores a poor amount of cholesterol. Now LDL has been shown to be responsible in making plaques inside the lining of blood vessels which causes plaques which inturn causes coronary heart disease. Several important points; We make a fixed amount of lipoproteins (HDL, LDL) based on our blood plasma concentration of cholesterol, the formula is here. Now based on this when there is an excess amount of LDL floating in the blood and injury occurs, macrophages (immune cells, which get activated to the area when injury occurs) eat up LDL and make foam cells which release growth factors that further perpetuate the inflammation in the intima (middle of) the blood vessels. Handy picture incase you don't wanna read.

Now this being said, there is a clinical evidence to suggest that those who have risk factors (physical inactivity and obesity, diabetes mellitus, hypertension, hyperlipidemia, and cigarette smoking.) that aid themselves atherosclerosis (the whole plaque thing by LDL) should try to reduce their cholesterol (since we already said that amount of cholesterol influences amount of LDL).

Things that can be done to reduce cholesterol, is increasing bile acid production (which reuptakes cholesterol) by eating things like oat bran, which binds bile acids and is a constituent of many breakfast cereals, increases the proportion of liver cholesterol that forms new bile acids rather than forming new LDLs and atherogenic plaques. Or by taking statins which competitively
inhibits hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase, a rate-limiting enzyme in the synthesis of cholesterol. This inhibition decreases cholesterol synthesis and increases LDL receptors in the liver, usually causing a 25 to 50 percent reduction in plasma levels of LDLs.

Key points of what was said here, not everyone needs statins. Only those who have the above risk factors should take them. And statins have been long shown to help reduce the production of LDL through stopping the production of cholesterol via a basic biochemical pathway.


Now I don't know everything and I'm sure statins aren't a panacea and some do cause harm I know for example (talked about in one of my textbooks) that they have a ton of unintended side effects and these are the ones we know about. Granted looking at basic profit loss I'm sure big pharma doesn't wanna do more research in order to find stuff that they know will scare people. But what is a doctor supposed to do when he knows that the patient has bad genes (Indians have a nasty problem with this, well published and researched) that put him in the risk factors, the patient doesn't want to exercise or eat right. Is he supposed to let them die? or put them on statins and logic a risk/reward argument (doing more good than harm).