I am just coming down from that finals rush that us university students are all so accustomed to. Those long nights of studying and early mornings to keep studying – it gets tiring. A lot of students have a particular molecule to thank for getting them through those long days: caffeine. Whether it’s coffee, or energy drinks, students can be seen anywhere on campus chugging down these caffeinated substances. But how does this particular substance work to keep the students active and awake?

What is Caffeine?

Caffeine is a purine alkaloid, which is a particular type of chemical compound. It is found organically in Coffea arabica and Camellia sinsensis.

Coffea arabicaCamellia sinsensis

Coffea arabica is the source of coffee, while Camellia sinsensis is the source of tea.

How does caffeine affect our systems?

Caffeine can be completely absorbed by the stomach and small intestine within 45 minutes, and it takes around 3 to 4 hours just to remove half of the consumed caffeine from your system.

Caffeine stimulates our central nervous system (CNS), which is composed of our brain and spinal cord. By stimulating the CNS, the caffeine molecules fight against drowsiness and helps keep you alert. It does all of this by preventing a nucleoside, named adenosine (which is found in our DNA!), from binding to its receptors in the brain.

Adenosine usually suppresses the CNS when it binds to its receptors; this leads to general drowsiness. When caffeine binds these receptors, adenosine can no longer interact with the brain receptors which leads to a decrease in drowsiness (or increase in alertness!). Another result of caffeine binding these receptors is the stimulation of other neurotransmitters that also lead to an increase in your ability to concentrate and stay awake. These neurotransmitters include: norepinephrine, dopamine, acetylcholine and serotonin (which will be explored later).

An interesting fact about caffeine is that its half life,which is the time it takes to remove half of the consumed substance from your system, can be shortened by one’s smoking. So if you’re smoking, you’re going to need more caffeine than the average person to get relatively the same jolt of energy.

And that’s a brief summary of caffeine and its effects! Now you know how exactly caffeine works to become your savior through those long nights. Thanks caffeine, on behalf of all of us sleep-deprived students.

The Urinary System – Concentration and Dilution

Last time, we talked about how the urinary system allows for our bodies to selectively reabsorbs things that were filtered out of our circulatory system. One of the molecules that can be reabsorbed is water, which is an important molecule for several reasons. In terms of the urinary system, water is important for the concentration and dilution of our urine.

The concentration and the dilution of urine is regulated by 2 hormones: Anti-diuretic hormone and Aldosterone.

The anti-diuretic hormone is released if you’re dehydrated, and literally translates to “against the passing of urine”. In situations where you are dehydrated, your blood volume will be low due to the lack of a sufficient amount of water, resulting in a lower blood pressure. To counteract this, the anti-diuretic acts to reduce the amount of water lost by the body and minimizes how much urine you make and release. This will result in a more concentrated urine that has a less water than usual and is a deeper yellow due to the higher concentration of urea.

Aldosterone is also released when you’re dehydrated. This hormone is responsible for the increase in thirst while also helping your body retain water by increasing the amount of sodium in your body. The more solute there is in your body, the more likely water is to stay with the solute (rules of osmosis, hurray!).

These hormones exert their effects primarily on the distal tubule of the nephron (after the loop of Henle), so that is where the water is reabsorbed!

So when these hormones are released, your urine will be more concentrated because water is retained by your body! Amazing, right?

Next week: We will finally get to talking about the effect of Alcohol on Urine!

Is there something you’d like to learn about? Tell me about it here and I may just do a post about it 🙂

The Urinary System – Selective Reabsorption

Last week, we learned about the general filtration process that occurs in our kidneys. This week, we’ll learn just how our kidneys modify the filtrate to produce urine.

The filtrate that is in the renal tubule consists of water as well as other small molecules, like sugars and urea. Some of these molecules, like sugars, can return to the bloodstream in a ‘process’ known as selective reabsorption. It’s called ‘selective’ reabsorption because the bloodstream is picky as to what it absorbs from the tubule. The molecules that leave the tubule enter tiny blood vessels next to the tubule, which are called peritubular capillaries. The molecules can then be carried through the rest of the circulatory system, to provide our body cells with nutrients (if they’re sugars).

Parts of the Kidney

Selective reabsorption mainly occurs in the proximal tubule, which is the beginning of the tubule. The proximal tubule is just after the Bowman’s capsule. Whenever a molecule leaves, it is accompanies by water, which means a lot of water is reabsorbed by the bloodstream in this process.

By returning the molecules to the bloodstream, the remaining filtrate’s composition changes. As water leaves, the concentration of particles in the tubule increases.

Hormones can affect what is reabsorbed in the distal tubule. These hormones are the anitidiuretic hormone (ADH), which is also known as vasopressin, and aldosterone. They’ll be discussed next week when we talk about Concentration and Dilution!