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!


The Urinary System – Filtration

Last week, we talked about the basics of the urinary system, including the organs involved. This week, let’s take a closer look at what happens in the kidney, starting with filtration. The posts will be segmented because there will be a lot of new terms coming your way, and I would hate for you to get overwhelmed! So let’s learn how our bodies makes our pee, step by step.

Parts of the kidney

The basic functional unit within the kidneys is known as the nephron. This consists of all of the numbered portions, starting at the glomerulus (5) and ending at the distal tubule (6). 

The main components involved in filtration are the arteries, and the glomerulus.


It is at the Bowman’s capsule where the filtration of blood occurs. The blood from the renal artery (renal means ‘kidney’) flows into a smaller version of an artery, known as the afferent arteriole. The name sounds weird, but ‘afferent’ basically means ‘towards something’. So this arteriole is moving blood towards the glomerulus. So this arteriole can also be referred to as the afferent glomerular arteriole.

The afferent arteriole then branches to form tiny blood vessels known as capillaries. These capillaries form a ball-like structure, which is part of the glomerulus (5). The capillaries are therefore called the glomerular capillaries.

The blood from the capillaries continues to flow into the next vessel, which is another arteriole, named the efferent arteriole. ‘Efferent’ means ‘away from something’, so the blood is moving away from the glomerulus. So this arteriole can also be referred to as the efferent glomerular arteriole.

This movement of the blood increases the amount of pressure within the capillaries, causing fluids to leak out. These fluids pass through a filter-like membrane, known as the glomerular basement membrane. Some substances are too large to pass through the basement membrane and, therefore, continue to circulate through the bloodstream.

The filtrate that goes through the glomerular basement membrane enters the Bowman’s capsule. The space inside the Bowman’s capsule is continuous with the rest of the tubule, which includes the proximal tubule, the loop of Henle and the distal tubule. The filtrate is concentrated and modified within these components of the tubule, which will be discussed next week.

And that is, thankfully, all there is to the filtration process for the urinary system! Next week, we’ll learn about what happens to the filtrate in the tubule.

Alcohol – Effects on the Body

I’m a university student and you can bet that I’ve seen a lot of people under the influence of alcohol. They can be loud, giggly, emotional, and sometimes really tired.

I wanted to see just what effects alcohol has on our bodies, so posts about the different effects of alcohol will be popping up every now and then. For now, I thought it would be cool to see the list of effects alcohol has been found to have on our bodies.

Some of these effects are real extremes, so take them lightly. 🙂

List of the effects of alcohol on our body

Short-term effects

  • Nausea
  • Diarrhea
  • Makes you urinate more frequently (stay tuned, we’ll be talking about this one shortly!)
  • Flushed appearance
  • Reduced cognitive and motor skills(which is why you shouldn’t drink and drive!)
  • Loss of inhibitions and more confidence
  • Blurred vision (aka beer goggles) and slurred speech
  • Intense moods, e.g. aggression, elation, depression
  • Headache
  • Blackouts
  • Alcohol poisoning, which is really lethal

Diseases/conditions (in extreme cases!!!)

  • Can lead to the development of heart disease after long-term excessive use.
  • Potential cancer developing effects
  • May cause pancreatitis, which can lead to the development of diabetes
  • Liver disease
  • High blood pressure
  • Depression and/or anxiety
  • Weakened immune system
  • Anemia

Effects on our reproductive systems?!

  • Linked to damaging fertility (extreme case)
  • Small amounts of alcohol can affect a woman’s menstrual cycle
  • Alcohol can reduce the amount of testosterone a man produces
  • May affect the quality of a man’s sperm

And this is just a sampling of all of the effects of alcohol. In a couple of weeks, we’ll be talking about urination so that we can get to explore the effects of alcohol on it the week after :).

So, take it easy with eggnog for now, ladies and gents. No need to binge drink, it may just lead to some unhealthy effects!

I will be on hiatus until the first week of January, due to the holidays but Happy holidays and Happy New Year 🙂 Stay safe!