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Does blood eventually end up as poo?

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weavero | 16:11 Wed 22nd Nov 2006 | Science
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Despite the question looking juvenile, I'd like to know if blood, and indeed, other parts of the body that decay, end up coming out t'other end? I always thought it did, and there I was at work going "blah blah blah" until someone doubted me, and my education! Whooooopsy. Mustn't look silly now dears. Cheers!
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Good old wikipedia
http://en.wikipedia.org/wiki/Red_blood_cell

About half way down click on the 'bilirubin' link, or go here
http://en.wikipedia.org/wiki/Bilirubin
You are partly correct in that when old red blood cells are broken down, the red pigment, haemoglobin, is converted into a bile pigment called bilirubin. The bile is then secreted into the digestive tract just after the stomach and the bilirubin therefore gives faeces some of their colour.

Other cells that die in the body are broken down by enzymes into small soluble molecules that are either recycled, stored for later reuse, or removed by the kidneys and excreted in the urine.
Red blood cells (erythrocytes) survive for around four months in the human body. The reason for their relatively short life is that although they can make their own energy without using the oxygen they carry, they cannot make protein. Without protein they cannot repair themselves.

Following some biochemical changes to the cell wall, water is soon able to pass into the red blood cell, transforming their shape from a disc to a sphere. The speed with which they travel through the blood vessels is then greatly reduced.

Another type of cell within the blood called a phagocyte then engulfs these slow-moving spherical erythrocytes in a similar way to an amoeba. A larger form of phagocyte called a macrophage which is present in the circulation, lymph nodes, spleen, red bone marrow and certain other places then mop up the phagocytes.

Once this absorbtion has taken place, the old fragile erythrocytes are broken down. The erythrocyte proteins are broken down into their constituent amino acids and are stored ready to be used for the manufacture of new proteins. The iron from the haemoglobin is removed and sent for storage in the bone marrow, where eventually it will be turned into new haemoglobin although a small proportion is stored in specialised cells within the circulatory system for immediate use to correct such things as iron levels in the bloodstream.

Now although the protein and iron from the red blood cells is constantly recycled in this way with hardly any loss, the same cannot be said of the what's left of the haemoglobin.

(continued)
Haemoglobin contains a red pigmented chemical structure called a porphyrin. This looks like four connected rings arranged in a square with a haem (iron) component sitting in the centre. A chemical change then occurs to this haem structure turning it into the orange/yellow pigment called bilirubin.

The toxic, fat-soluble bilirubin is "locked" together with albumen in the blood to minimise toxicity in the body and then transported via the blood plasma to the liver. Here more changes occur to its chemical structure via an enzyme turning it water-soluble in order for it to become part of bile. The bile is released into the duodenum via the gall bladder.

As the bilirubin product moves through the intestines, enzymes of specialised bacteria get to work on it converting it into urobilinogen from where its excreted via the faeces. A related substance called stercobilinogen is turned into stercobilin, which gives faeces their distinctive colour.

Sometimes the urobilinogen gets back into the circulation where it's removed through urine via the kidneys or excreted again via bile.

A very fine balance is kept by the body with this haemoglobin destruction/bilirubin production pathway. When it goes wrong, the bilirubin accumulates in the blood which in turn, leads to jaundice. The newborn often suffer from jaundice because the system is not up and running correctly immediately after birth.
Finally, yes, following cellular degradation, most parts of the body end up coming out of either the urinary tract or the bowel.
Question Author
Wow! Incredible answer from 'theprof'. And thanks for all the other answers, good work!

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