6.4 She’ll Grow Out of It

Three short movements: the case, the anatomyThe study of the structure of the human body. and physiologyThe study of how the body functions., then the tie back to Stina. Each links to the scene where you’ll see it move.

I · Four inches

In September 1986 she was too short for the desks and sat on a cushion; by spring she had grown four inches and gone through two pairs of shoes. The clinic, visited once that year for something else, offered the growth spurt as the explanation for everything: the bones are stretching, it will settle when she stops growing. It was a precise, testable claim, and nobody tested it. Her pain was along the shins and in the feet and back, not at the ends of the bones where growth happens; it was there before the spurt and unchanged through it; and benign growing pains, when studied, do not track growth spurts at all. She stopped growing at sixteen, when her plates closed. The pain did not close with them. To see why the bet was wrong you need to know how a bone is made and what the plate does while a child sleeps.

See it move: Scene 1 · Outgrow It · Scene 2 · Calcify Is Not Ossify

II · Calcify is not ossify; a bone from a membrane

Two words the site itself muddles. Calcification is the deposit of calcium salts into a tissue — it hardens whatever it lands in, cartilage, a vessel or a kidney, and it does not make bone. Ossification, osteogenesis, is bone replacing an existing tissue; it begins at about week eight and runs two ways. Intramembranous ossification makes the flat bones of the skull and the clavicles from a fibrous membrane, in four steps. One: mesenchymal cellsThe basic structural and functional units of life. cluster and become osteoblasts — an ossification center. Two: they secrete osteoid, it calcifies, and the trapped cells become osteocytes. Three: osteoid accumulates in a random weave around the vessels — woven bone — and the mesenchyme outside condenses into periosteum. Four: the woven bone under the periosteum is replaced by lamellar compact boneDense, strong bone tissue forming the outer layer of bones. while the trabeculae inside become the diploëThe spongy bone layer sandwiched between compact bone in flat bones. with its red marrowBone marrow that produces blood cells.. Woven first, lamellar after — the order every bone follows, including a healing fractureBreaks in bones due to stress or injury..

See it move: Scene 2 · Calcify Is Not Ossify · Scene 3 · Bone From a Membrane

III · A bone from a cartilage model, and the five zones

Everything below the skull — long, short and irregular bones — forms by endochondral ossificationBone formation replacing a cartilage model, common in long bones: bone replacing a hyaline cartilageThe most abundant cartilage type, found in joints, ribs, and the nose. model, in five steps. One: osteoblasts from the new periosteum lay a bone collar around the shaft — the primary ossification centerAn area where bone formation begins in the diaphysis of a long bone.. Two: the cartilage inside calcifies and its chondrocytes die, while the model lengthens at its ends. Three, month three: a periosteal bud — vessels, osteogenic cells, osteoclasts — invades, and spongy boneA porous bone tissue found inside bones, providing lightweight support. forms on the calcified scaffold. Four: osteoclasts hollow the medullary cavityThe hollow space inside bones that contains bone marrow.. Five, around birth: secondary centers appear in the epiphyses, leaving hyaline cartilage only at the joint surface and in a disc between end and shaft — the epiphyseal plateA growth plate in developing bones made of cartilage.. The plate is a conveyor. From the epiphysisThe expanded ends of a long bone. toward the shaft: a resting zone anchoring the plate; a proliferation zone where chondrocytes divide in stacks like coins, pushing the epiphysis away; a hypertrophic zone where they swell; a calcification zone where the matrix calcifies and the cells die; an ossification zone where osteoblasts arrive on the vessels and lay bone on the calcified cartilage. Cartilage lengthens one face, bone eats the other, the plate stays the same thickness and the bone gets longer — interstitial growthBone growth from within, increasing bone length., which cartilage can do and bone cannot. Width is appositional: periosteal osteoblasts build outside while osteoclasts widen the cavity. At puberty the sex hormones speed the plate and then close it — around sixteen in girls — and the plate becomes the line.

See it move: Scene 4 · Bone From a Cartilage Model · Scene 5 · The Five Zones and the Width

5 scenes. Each one has a short animation or a slide, something to explore, a true/false spot-check of your thinking, and a quick check. Every scene gives you an evidence card for your board.

Every scene gave you an evidence card, and the chart adds more. Sort each card into the column it supports: A pain unrelated to growth — a living tissue inflamed, Neither on its own, or Growing pains: the plates stretching, over when growth ends. Some cards can honestly go in more than one place — that’s allowed, and the feedback tells you which cards decide the case.

Time to decide. Look back at your bet, then build your verdict from statements that hold up — no writing needed.