THE IN-BETWEENERS ◆ ISSUE #12 ◆ SERIES II: THE ROOKIE
The Shapeshifter
The epiphyseal (growthAn increase in size and number of cells.) plate · they / them
“I make you taller. Then I quit.”
POWER: Turns cartilageA flexible connective tissue found in joints, the ear, nose, and rib cage. Cartilage can be of three into bone while you watch.
WEAKNESS: They run out. At puberty the plate seals into a line and never works again.
FIBERS: Collagen, changing state as you watch.
SECRET IDENTITY: The growth plate at the end of a long bone.
The epiphyseal plateA growth plate in developing bones made of cartilage. is a band of hyaline cartilageThe most abundant cartilage type, found in joints, ribs, and the nose. between the epiphysisThe expanded ends of a long bone. and diaphysisThe shaft of a long bone. of a growing long bone. ChondrocytesMature cartilage cells housed in lacunae. keep building cartilage on one side while osteoblasts replace it with bone on the other. “The osteoblasts chase the chondrocytes.”
Growth Spurt Era. It Won’t Last.
Where they live, what they do, and the one thing they can’t do
Where they live
- Between the epiphysis and the diaphysis of growing long bones
- The femurThigh bone; longest and strongest bone in the body; has a large round head and prominent trochanters and humerusLong bone of the upper arm; articulates with scapula at shoulder and radius/ulna at elbow., and also the metacarpalsPalm bones numbered thumb (1) to pinky (5); heads form knuckles., metatarsalsLong bones of the foot; numbered big toe (1) to pinky toe (5)., and every phalanx
- On an X-ray, an open plate looks like a gap in the bone
Their powers
- Lengthens bones through appositional growthThe process of bone widening and thickening by adding layers to the surface. at the edge of the plate
- Every time the chondrocytes divide, they push the epiphysis farther from the diaphysis
- Osteoblasts Bone-forming cells that secrete osteoid. follow and ossify the cartilage left behind
Their weakness
They have an expirationThe process of exhaling, which can be passive (relaxation of respiratory muscles) or active (involvi date. Estrogen and testosterone at puberty help close the plate.
Once the chondrocytes stop, the plate becomes an epiphyseal lineA remnant of the epiphyseal plate, marking where growth stopped., all bone, and growth in length is over.
Every weakness is the structure.
Going Through a Phase (Five, Actually)
Read the zones from cartilage to bone
The crew: cells
Chondrocytes go from resting, to dividing in stacked columns, to swelling up, to dying. Osteoblasts move in behind them and lay down bone; osteoclasts remodel it.
The fibers
Collagen throughout: type II in the cartilage end, type I in the new bone.
The matrix
Glassy hyaline cartilage at one edge, calcifying in the middle, solid bone at the other. Firm gel at one end, rock at the other.
Before and After, in One Picture
Real slides. Find them in every one.
ID HINT: Hyaline cartilage at the top; then a band of dividing chondrocytes stacked like coins; then swollen cellsThe basic structural and functional units of life.; then pink bone below. Read it top to bottom.
Exhibit A
Exhibit B
Exhibit C
Micrographs: University of Michigan Histology, licensed under CC BY-NC-SA 3.0.
Prove You Were Actually Paying Attention
Prove you can spot them
Mission 1: Coming soon
Open slot for a new H5P. Replace this block with a shortcode such as [h5p id="000"], for example a hotspot activity built from one of the Evidence Board slides.
Videos Nobody Asked You to Watch (Watch Them)
The Origin Story They Won’t Stop Telling
How a cartilage model becomes a bone (endochondral ossificationBone formation replacing a cartilage model, common in long bones)
1. A cartilage model
Chondrocytes build a hyaline cartilage model of the bone. Cartilage has no blood vessels, so they are on their own.
2. The bone collar
Osteoblasts form a collar of compact boneDense, strong bone tissue forming the outer layer of bones. around the shaft, like a starched shirt collar, and start the periosteum.
3. Primary ossification center
Blood vessels move in. Osteoblasts replace the cartilage of the diaphysis with bone; osteoclasts hollow out the medullary cavityThe hollow space inside bones that contains bone marrow., which fills with marrow.
4. Secondary ossification centers
Vascularization reaches the epiphyses. Chondrocytes die, osteoblasts replace the cartilage, and only the plate between epiphysis and diaphysis stays cartilage.
5. The plate closes
After puberty, chondrocyte activity stops and the plate becomes the epiphyseal line.
Used to Be One of Them. Now Becoming the Other.
Students confuse them with these two. Here’s how to tell.
The Glider
Hyaline cartilage. The Shapeshifter starts as the Glider. Look for the stacked columns of dividing cells: plain hyaline doesn’t line up.
The Lattice
Spongy bone. What the Shapeshifter leaves behind. Pink struts and marrow, with no cartilage zones.
List of terms
- growth
- cartilage
- epiphyseal plate
- hyaline cartilage
- epiphysis
- diaphysis
- Chondrocytes
- femur
- humerus
- metacarpals
- metatarsals
- appositional growth
- Osteoblasts
- expiration
- epiphyseal line
- cells
- endochondral ossification
- compact bone
- medullary cavity