How does insulin resistance develop, making people diabetic?
Great question. This concept can often be difficult to wrap your head around. Insulin is released from the Beta cells in your pancreas in response to carbohydrates and sugar. When your body is digesting food, it needs to either use the carbohydrates for energy or store them in your body's cells for later. It does so using insulin. Insulin has many actions, including opening glucose transporters on cell membranes that allow glucose into the cell, signaling the liver store glucose as glycogen and to stop the process of making glucose, as well as signaling an array of enzymes that allow the body to break down and store glucose. (We can get into the specific actions later). If you overload your body with carbohydrates and sugar without using any of it for energy (by exercising and being active), the Beta cells in your pancreas are constantly stimulated to release more insulin to deal with all those carbs. Eventually, the system gets totally overloaded. The receptors that insulin binds to on the cell membranes are all taken up, so there is too much extra insulin in your body with no where to go. This is where insulin resistance kicks in. Insulin is there, but your body stops using it appropriately. Like when you listen to the same song over and over again and you always hear it and all of a sudden it's overplayed and you're totally sick of it and don't want to hear it anymore. Now it's important to note- this is not diabetes. This is what happens before you become a diabetic. Eventually, your Beta cells get tired of releasing all this insulin and they start to shut down. (Just like when you study for too long and feel like you're not understanding something and you just get tired and want to give up). Now, your body goes from having too much extra insulin to not enough insulin. This is where diabetes kicks in. When your Beta cells don't work well any more, there is nothing to help the carbohydrates and sugar get into the appropriate cells for use and storage, and it starts binding to other cells (nerves and red blood cells) it's not supposed to, and wreak havoc.
One of the first medications you give someone with high blood pressure is an ACE-inhibitor, which works on the kidneys. But I thought high blood pressure had to do with the heart and blood vessels. So why is that medication used?
You are right! High blood pressure, or hypertension, is mainly caused by problems with the blood vessels. When plaque builds up on the walls of your arteries, the pressure the blood exerts on those arteries increases because the tank that the blood is in has become smaller. This causes a lot of harm and potential problems, but we can get to that later. If we can treat the hypertension by lowering the pressure, hopefully those problems can be avoided. So how do we treat it? The two best ways to decrease the pressure within your blood vessels are to either make the vessels bigger, or take some of the fluid inside out. We always want to try life style modifications first- good nutrition and exercise can help reduce the amount of plaque to make the vessels bigger again. If that doesn't work, there are medications that will make the vessels bigger, but those tend to be more dangerous and have more side effects. Instead, we typically try to take some of the fluid out. How do you get rid of extra fluid in your body? You pee it out- think about what happens when you drink a ton of water during the day... you end up running to the bathroom every hour because your kidneys are filtering out all that extra fluid. ACE-inhibitors work through the Renin-Angiontensin-Aldosterone System (RAAS) that is responsible for how much fluid is delivered to your kidneys. We can get into the specific pharmacologic/ physiologic actions of the medications if you'd like, but for now it is just important to know that ACE-inhibitors allow more fluid from your blood stream to go into your kidneys, which in turns allows your kidney to excrete, or get rid of, more fluid through urine. This "empties the tank" that is your blood vessels- as I said before... less fluid in the vessels equals less pressure. And just like that, your high blood pressure is lowered!
How can I best remember the pathway that blood travels through the heart?
There are a few key concepts to remember when trying to figuring out the pathway of blood through the heart. For starters, try to remember these things: 1) the heart collects used up blood from the body on one side, and sends off newly oxygenated blood to the body on the other. 2) ARTERIES (with an A) take blood AWAY (with an A) from the heart. Veins, then, carry blood into the heart. 3) The LEFT (with an L) side of the heart collects blood from the LUNGS, while the right side of the heart collects blood from the body. 4) An atrium is an entrance way. So the blood must always enter through the atrium before going into a ventricle. Ok, so keeping these things in mind, lets piece together the pathway: Used up blood with very little oxygen travels from the body back to the heart through the Vena Cave (a Vein = into the heart) --> Right atrium --> right ventricle --> pulmonary Artery (Artery = Away from the heart to the lungs) --> lungs (to replace that oxygen) --> pulmonary Vein (a Vein = into the heart from the lungs) --> Left atrium (collects from the Lungs) --> left ventricle --> Aorta (an Artery = Away from the heart to the body). Now lets look at a picture of blood flow through the heart so you can picture this pathway. Remember, anything blue represents blood without oxygen, anything red represents blood with oxygen in it.