How do bones avoid veins?

Gawdzilla Sama

Gawdzilla Sama

Valued Senior Member
Short version for subject line. Expanded it would be "I saw a triceratopsian shield* that had grooves in it for veins. I'm wondering how the bone shaped itself to provide that channel?"

The groove would provide protection for the veins on three sides, and if deep enough the vein wouldn't protrude above the general level of the skin on the shield.

*Rather like an elephant ear with a bone plate in it. Just wondering. I'm sure Jack Horner could explain it, but I don't like him much.
 
You're thinking on too large a scale - as if the shield is a single large growth. Think in terms of cell growth.

The artery came first (otherwise there would be no nutrients for the cartilage/bone to grow).
Then cartilage forms in interstitial areas between arteries.
Then cartilage calcifies into bone.

Bones don't "grow" in the way trees grow out of the ground. They "fill" into defined areas. Those defined areas are bounded by and constrained by the structure and chemistry of adjacent organs.

(They do get larger - in concert with other tissues, such as arteries.)



But sure, as SG suggests, protruding arteries would surely be selected against, after a few generations of bleeding out every time they squoze through a dense forest.
 
But the bone is smooth on either side of the vein. The bone doesn't grow "normally" under the vein. Just curious.
 
Gawdzilla Sama said:
But the bone is smooth on either side of the vein. The bone doesn't grow "normally" under the vein. Just curious.
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You're thinking of the bone as one monolithic structure that's shaping itself at a macro scale.

Think of it at the cellular level. No given cell knows what the other 99% of the "shield" structure is doing. All it knows is what it's neighbour cells are doing and the structures immediately around it. It grows according to what is immediately around it including other organs, such as arteries.

And remember, this was established while still an embryo. The arteries developed in-place, and the "organ" that will develop into a cartilaginous mass, eventually to become bone, also developed in-place.

How does a given cell "know" it is next to an artery so it does not split and grow more cells into that space? I think the answer is that the cells are constrained by the boundary of the "sac" that will harden into cartilage. Being soft tissue, that sac has an indent where the artery is.
 
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Gawdzilla Sama said:
Yeah, but the "knows" part escapes me.
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Chemical messages between the blood vessel and osteoblasts.

Angiogenesis is one of the more important processes in higher animals, and we have had a _very_ long time to evolve ways to get blood cells into organs and other structures. (In fact, angiogenesis works so well that cancer stimulates blood vessel growth; in effect, the cancer mass "asks" for blood vessels and your body supplies them.)
 
billvon said:
Chemical messages between the blood vessel and osteoblasts.

Angiogenesis is one of the more important processes in higher animals, and we have had a _very_ long time to evolve ways to get blood cells into organs and other structures. (In fact, angiogenesis works so well that cancer stimulates blood vessel growth; in effect, the cancer mass "asks" for blood vessels and your body supplies them.)
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Ah, that makes sense. Very intelligent design.
 
check out what happens when a baby is born with coarctation of the aorta.
In brief, there is a narrowing in the passage of blood through the aorta, so in some cases blood supply to the lower body can be impaired. What can happen is the phenomenon of notching of the ribs,which means that new collateral vessels develop to supply the rib cage directly from the aorta and the ribs are notched as new vessels pass through them....
 
That's what happens. I'm exploring how it happens, if you get the distinction. Just curiosity based on viewing a college student working on a five-foot wide shield from a topsian.
 
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