Blood-brain barrier story

Let me tell you a story about nutrients travelling up the bloodstream heading towards the head. Because there is a lots of toxic and harmful substances in the blood normally, those nutrients in it get to the point, where only the smallest of them can actually get after that point. That point is simply called the blood-brain barrier (BBB), and it protects the brain from any of those harmful substances.

One of those nutrients, which actually can get through it quite easily is glucose (simple sugar), the main or almost the only food for the brain and whole nervous system. Moreover, the brain does not have any storage room for glucose, so the steady supply of it is necessary for continuous functioning of basically whole body.

But this story of travelling of glucose into the brain get even more interesting. Before actually getting in, there is a "sort of" a middle ground, where it needs to get first. That middle ground is called cerebrospinal fluid (CSF). In an average adult person, there is around 800-1500ml of that fluid in the whole body. And as a proper middle ground, it has very exact boundaries, so it can be only at certain places.

Four small cavities inside of the brain called ventricles (2 lateral, third, and fourth) are filled with it, and the inner side  of them contains special cells, which produce this fluid. From there, they travel or flow through ducts into so-called subarachnoid space, which covers the whole brain and the spine. Hence the word cerebro (brain) - spinal fluid. Because rates of its production and reabsorbtion into the bloodstream are the same, its volume and pressure stays normally constant.

Ever heard about the fact that our brains are basically floating in the fluid? Well, this is it. It literally floats in this CSF tightly packed in that small subarachnoid space. It helps to absorb any physical blows to the head, along with already mentioned supplying the brain with nutrients. Nice flow diagram shows clearly how and where this CSF travel.

This flow diagram is actually quite clever, because on the left side you can see the names of the spaces or cavities, and on the right side you can see the names of the ducts and other structures involved. Plus, within the subarachnoid space, there is a mixing of blood with CSF going on. So when you sometimes feel like scratching your head, it's probably useful to do it for enhancing this mixing and helping some glucose to get into the brain.

Doctors have been pondering and trying to figure out how to deliver certain substances past the BBB, and they came up with the solution. They created highly concentrated glucose solution containing some desirable substance, and the brain will suck it in all thinking it's all the glucose. This way certain drugs can be administered directly to the brain tissue, which would otherwise never be able to cross the BBB.

Also, the alcohol and certain anesthetics seem to have the same capacity, along with some very small molecules like ions of Na, Cl, K, Ca, Mg, carbon dioxide, and mainly the oxygen. Because despite of the brain being only about 2% of total body weight (about 1300g), it consumes about 20% of oxygen supply by lungs. Pretty busy in there, right?

Only 1-2 minutes of the blood flow interruption into the brain can impair a function of nervous system, and 4 minutes would lead to a pernament damage of the brain. I will close this post with another flow diagram, displaying nicely how the blood and CSF interract. It very simple, so there's no need to explain much in there. Enjoy studying.

Ode to the water - the life giving fluid

This post is a collection of arguments about why is the water so important for life, health, beauty, and many other things. So let's start with the starters. The water is a medium in which nearly all chemical reactions of the body occur. It's essential to health and life, mainly because of the ability to form solutions and suspensions. Because it participate as both the reactant and the product, it is really the ideal medium for metabolic reactions inside the body.

When it comes to heat, the water can absorb or release a large amount of it with only a modest change of its own temperature. A characteristic that's called the high heat capacity. Plus the water is a major part of mucus and other lubricating fluids in the body. Let me name just a few of them: saliva, blood, milk, lymph, urine, bile, semen, sweat, tears, vaginal fluids, digestive juices, cerebrospinal fluid in your spine, and synovial fluid in your joints.

Now some more technical details of the body:

For the newborn, the water content of the body is about 75%. This will get down to about 55-60% by the second year of life, and stays roughly the same for the rest of the life. Otherwise, the adipose (fat) tissue is the only tissue in body without the water in it, so fatter people has logically less proportion of water in the body than lean people.

The kidneys are the organs that take care of filtrating the blood. Each day, they filtrate about 150 litres of it in women, and about 180 litres in men. That is about 65 times the whole volume of the blood in the body, even if  99% of it goes back to the bloodstream. Which redirects the rest of  1-2% into the urine, making about 1-2 litres of urine every day.

Mass of the kidneys is changing with the age as well, so for 20 years old person it weight about 260g, but in 80 years old person, it weights only about 200g. And the filtration rate decline by 50% between ages 40-70 too. Speaking of filtration rate, it is the quickness by which kidneys can filtrate, and it is 125 ml per minute for men, and 105 ml per minute for women.

Think of it as something over one liter in about 10 minutes. That brings me to my first flow diagram, which describe the situation, where you would about to drink one liter of water, and wait less than 10 minutes, and keep on drinking. The state that your body is going to get in is called the water intoxication.

To understand this flow diagram, it's good to mention one important rule: "The water follows the salt (NaCl), and the salt follows the water". Or in other words: "Where the salt goes, the water follows". So in the first stage sweating, vomiting, and diarrhea support the loss of the salt from the body. Moreover, any further drinking the plain water, is another factor contributing to that loss. This results in the decrease of Na concentration in the plasma (liquid portion of blood), and interstitial fluid, which is the fluid in the space outside of cells (or between cells if you like).


Decreased osmolarity means that because there is less salt, then there has to be less water as well (in the same space). So then cells compensate this event by taking up the water inside of them through the process called osmosis, and they become swelled. The state of swelled cells is basically defined as the water intoxication. If the intake of water was too large at the beginning, or it is continuing, then the convulsions, coma, and possible death can occur.


Water and the sea

Now, let's go back in the evolution and make clear about how really important the water is. By the definition, most of the life forms share the marine origin, meaning that all life basically comes from the sea. Moreover, the conditions inside of cells of most organisms living on the planet, are remarkably uniform.

Or, to put it another way, the fluids inside the most of our cells have the concentration of salt highly comparable with the salt water in the sea. Because the ocean presents itself as the very stable environment for development of organisms, those organisms living outside of the sea are quite sensitive to even slight changes in the salt concentration within their cells.

Basically, the biggest problem of any organism living outside the ocean, is to maintain this salt concentration inside of cells, which is achieved only by regular intake of water and salt. Ideally, the sea salt of course. Technically, kidneys can function on as little as 0.5 litre of water for a day or so, which they keep circulating over and over. By the end of the day, however, the urine can be as much as 1000 times more acidic than the blood.

Also, the fluid balance depends highly on electrolyte balance. Electrolytes are minerals, or inorganic compounds, which dissociate into ions - atoms, molecules, or compounds with the positive or negative charge. So the regular intake of those electrolytes with the water is essential, because normally, the water loss equals the water gain during the day. This way the body fluid volume remains constant and stable. The flow diagram bellow shows clearly how the body deals with the differences in input and output of the water during the day.

Generally, the recommended intake of water is about 1 liter for every 1000 calories of solid food. So it would mean that for recommended 2500 calories a day, you need to drink about two and half of liters of water. I know I'm getting my fair share of water everyday, and especially during the exercise, where you lose additional water through sweating and increased metabolic rate of the body. That increase can be even up to 20 times higher than the metabolic rate of the body during the rest. Along with up to 20 times higher of the oxygen consumption, but that's another topic for another post.