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Blood is always red, actually. Veins look blue because light has to penetrate the skin to illuminate them, blue and red light (being of different wavelengths) penetrate with different degrees of success. What makes it back to your eye is the blue light.

Meanwhile, here's what happens to the blood in your body:

The heart pumps blood to your lungs to pick up oxygen. The oxygen-rich blood is then pumped out to your body through your arteries. It's bright red at this point.

From your arteries, the blood flows through tiny blood vessels called capillaries, where it gives up its oxygen to the body's tissues. Your lips have a lot of these capillaries, which is why they're red.

Your blood, now exhausted of its oxygen, is dark red as it now returns to your heart through your veins.

This article has been corrected from the original version.

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Blood is always red, actually. Veins look blue because light has to penetrate the skin to illuminate them, blue and red light (being of different wavelengths) penetrate with different degrees of success. What makes it back to your eye is the blue light.

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How many different systems does the circulatory system connect with?

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Yes

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How many functions are in the circulatory systems?

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Why do our veins bulge?

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Why does the blood change color?

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Why are you veins different colors?

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Your body vomits when it senses various different threats. These threats can take the form of toxic chemicals or stress hormones in the blood, swaying motions, or an upset stomach. Chemicals and hormones are detected by the brain's chemoreceptor trigger zone (CTZ), swaying motions are detected by the inner ear, while an upset stomach is identified by the vagus nerve. Once the signal for a need to vomit arrives at the CTZ, it sets off a chain reaction.

1. Brainstem

The chemoreceptor trigger zone (CTZ) receives a stimulus that might warrant vomiting. The vomiting centre begins a choreographed sequence of actions.

2. Salivary glands

Your mouth suddenly begins producing extra saliva. This is slightly alkaline and forms a buffer to protect your mouth and teeth from incoming stomach acid.

3. Diaphragm

You take a deep breath to avoid getting vomit in your lungs, then the diaphragm contracts in a few short pulses, squeezing the stomach to create pressure.

4. Glottis

The glottis closes, sealing the airway. Nothing enters or leaves the lungs. Diaphragm contractions without vomiting cause dry heaves.

5. Abdominal muscles

The abdominal muscles contract to further increase pressure. The pyloric sphincter at the bottom of the stomach is held closed. The only way out is upwards.

6. Skin

The sympathetic nervous system raises your heart rate and makes you sweat across your whole body, to shed the heat from this sudden exertion.
Read more: Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun facts.

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Your body vomits when it senses various different threats. These threats can take the form of toxic chemicals or stress hormones in the blood, swaying motions, or an upset stomach. Chemicals and hormones are detected by the brain's chemoreceptor trigger zone (CTZ), swaying motions are detected by the inner ear, while an upset stomach is identified by the vagus nerve.

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If they do. how do new cells grow back?

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Do cells in the Lungs die off

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How does bone marrow create blood exactly?

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Water is important because your body uses water in all its cells, organs, and tissues to help adjust its temperature and maintain other body functions.

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Yes they do.

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Mouth, epiglottis, esophagus, liver, stomach, gallbladder, small intestine, large intestine, rectum, anus

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You get dehydrated

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Yes

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What other foods help your bone grow?

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How does calcium get to your bones?

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How many parts are in the digestive system.

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What happens in your body when you throw up?

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Yes, you can drink water upside down as long as your esophagus is working properly.

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The skeletal system works to protect the muscular system. Without the skeletal system or muscles would be seriously damaged.

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The skeletal system works to protect the muscular system. Without the skeletal system or muscles would be seriously damaged.

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How do your bones come back together when they break?

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Is it possible for your digestive system to stop working? And what would happen?

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What happens if you don't drink enough water?

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Why is water so important?

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If you drink stomach acid will your stomach acid digest the stomach acid?

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They ether take longer to turn into chyme in the stomach or something like a Lego with just grind by the system and maybe hurt the system

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It takes about 24 hours to digest the average sandwich

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Since you can eat upside down, can you drink something upside down?

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Since you can eat upside down, can you drink something upside down?

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How many bones are specifically protecting the heart?

# data[].attributes.subject
How many bones are specifically protecting the heart?

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How does your body digest  things that aren't food, what happens to them.
ex. gum

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Do cells exit the body?

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How do cells exit the body?

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Is hair dead cells?

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What are the different parts of the digestive system.

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How do they these systems work together?

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How do they these systems work together?

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How many nevers are there?

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Do unicelled organisms eat or are they a producer?

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Is there a max number that unicellular cells can "make"?

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Is there a max number that unicellular cells can "make"?

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Can different types of cells come together to make one thing.

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When cells die does your body make new ones?

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Are different cells different colors.

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Do cells die?

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What produces more cells, or are they all already there?

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What produces more cells, or are they all already there?

# data[].attributes.body
How many different types of cells are there?

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What does calcium do to make your bones stronger.

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How long does it take for our food to digest.

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Why does calcium help our bones?

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How many cells are in the average human body?