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!

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Scabs

Ouchy, that’s a boo boo!

It can hurt like no tomorrow whenever you scrape your skin deeply or get a nasty cut and you start to bleed. Eventually, you’ll notice that in place of the bloody cut or scrape, there’s a scab. But what are scabs made of and how do scabs form?

As soon as your skin and blood vessels are damaged, your blood interacts with collagen. This is a protein that is found in your skin. When this is detected, specialized blood cells called platelets, or thrombocytes, rush to the area and secrete inflammatory factors. At the same time, these platelets stick together; they aggregate to form a clot.

Two other proteins, fibrin and fibronectin, then form a net-like structure to prevent further blood loss. Platelets attach to this net and acts as a temporary skin layer until the entirety of the net structure is replaced by collagen.

The platelets release growth factors, which stimulate the rate of cellular division, to help regenerate the lost or damaged skin cells. It releases a lot of other proinflammatory factors that help in the healing process, like serotonin and histamine, to dilate blood vessels and increase cell proliferation.

scab is basically the net structure intermediate of fibrin, fibronectin and platelets that acts as a shield for your body against any external infectious particles.

So, it’s good that our bodies scab in response to blood vessel damage because, otherwise, we would be exposed to several infectious particles and contract diseases with every paper cut that drew blood. And that could lead to much more pain than a little boo boo.

Nosebleeds aka Epistaxis

My roommate had a nosebleed a while ago, and I thought that it might be a good idea to go into why people get nosebleeds and how to properly take care of one.

What are the common causes for nosebleeds?

Picking your nose or Minor injuries

When you pick your nose, you might scratch against a blood vessel that lines the inside of your nose, which leads to blood escaping the vessel and your nose. Minor injuries like bashing your nose against a table or being punched in the nose can lead to the breaking of the blood vessels too.

Colds or Allergies or Dry, heated air or Blowing your nose

The inside of your nostrils are usually lined with mucous, which makes it a moist environment. On the other hand, these situations, excluding blowing your nose, cause your blood vessels to dry out and and become crusty, which can lead to the breaking of the vessels. Blowing your nose while having a cold or an allergic reaction can further irritate the vessel lining of your nose, which can eventually lead to a nosebleed too.

How to take care of a nosebleed

If your nose is bleeding because of a sustained injury, make sure to go see your doctor to ensure that everything is okay. If your nose starts bleeding on its own, likely due to the other reasons, then here are some things you should do:

  • Do not lie down
  • Damp washcloths usually work best to catch blood
  • Do not tip your head back
  • Pinch the part of your nose just below the bony part and breathe through your mouth for 10 minutes or so. If you do this for 20 minutes and your nose is still bleeding, talk to your doctor.
  • If you have a room with dry air, getting a humidifier helps to prevent future nosebleeds.

Both of the italicized points are things you should not do. They both lead to the blood going down, into your throat, which can lead to you choking on your blood. So please remember to sit up or stand with your head leaned forward, not back!

See your doctor if: you feel like you might pass out, you look like you’re losing too much blood or you just started taking a new prescription.

So, all you nose-pickers, watch out because winter might be the worst time for you to do your thing; the dry air will make your nose lining less moist and picking your nose is basically like begging for a nosebleed.

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Bruises

Whenever you run into something or take a bad fall, you’ll find a bruise in the place that hurts (so long as your skin didn’t tear!). But what causes bruising and is there a way to treat it?

What is bruising?

Bruises, also known as contusions or ecchymosis, are the localized pooling of blood outside of blood vessels. So a bruise is simply when your blood escapes your blood vessels in a tissue yet remains in a certain area.

Why do we bruise?

When a part of your body is struck, the impact causes your blood vessels (more specifically capillaries, though sometimes it’s venules) in that area to rupture. This releases blood cells close to the skin’s surface, which spread out under the skin giving it a reddish colour.

The Colour changes of a Bruise

  1. This reddish colour changes over the period of healing for a bruise. At the beginning, your bruise will be red because it will have an iron-oxygen complex.
  2. After a couple days, however, your bruise will change to a deep purple or a blue colour; this is because the oxygen will have been used up by the surrounding tissues, resulting in the loss of an iron-oxygen complex (which gave the blood its red colour).
  3. Then you bruise will slowly begin to heal; at around 5 days, your bruise may turn a green colour which is the result of hemoglobin, the protein found in our blood cells that contains iron to attract oxygen, breaking down in the blood cells that escaped.
  4. The final colour stage is a yellow or brown colour, where the body is reabsorbing the lost blood and in its last stretch of healing itself. This usually occurs after 9 or 10 days.

How to help your bruise heal

When your bruise is healing, the blood that remains in the blood vessels needs to clot to prevent the further loss of blood. To help with the clotting process, it is recommended that you rest the affected area to ensure that there is no additional stress on the tissue.

Also, apply something to cool the area, perhaps a bag of ice or an ice pack. By cooling the area, you help influence the blood vessels to constrict. By constricting, the blood vessels reduce blood flow which means that there will be less blood that is lost through the rupture. Icing the area will also help calm down any swelling that occurs, but make sure to only apply ice intermittently for a maximum duration of 20 minutes. For the first day, it’s recommended that you ice the bruise for 20 minutes, take a break from the cooling for 20 minutes, and then repeat.

Both of these methods will help prevent the spread of blood underneath the skin but outside of the blood vessels; in other words, it helps contain the blood that escaped from the blood vessel in one area.

If you don’t rest the tissue after its blood vessel ruptures, it is likely that blood will spread to other areas in the vicinity of the impacted area. This is why you will sometimes find that there is a new bruise near the original one a day or two later.

Your blood vessels will heal themselves over the roughly 9 day period and your skin should go back to normal; just remember, rest and ice up! If you don’t, it can take a lot longer for the tissue to heal.

 

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