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The Skeletal System · Chapter 3 of 7
1986, age 11: a new town, a school with concrete floors, and feet, shins and back that hurt by the last bell. This chapter goes under the periosteum: compact boneDense, strong bone tissue forming the outer layer of bones. built as osteonsThe structural unit of compact bone, consisting of concentric lamellae around a central canal. — weight-bearing pillars with a twist — and spongy boneA porous bone tissue found inside bones, providing lightweight support. as trabeculae — trusses for stress from every direction — plus the lamellae, lacunae and canaliculiTiny channels that connect osteocytes, allowing communication and nutrient exchange. that keep a buried cell alive, and the ground-bone slide where you can see it all.
The question you will answer
Compact and spongy bone are the same tissue arranged two ways. What is an osteon, why does its collagenA structural protein in the dermis that provides strength and elasticity. spiral, how is a cell twenty layers deepAway from the surface of the body. fed, why do trabeculae look like a bridge — and what does a day on concrete ask of each?
Opener · Standing on Concrete · about 1¾ minutes
The opener is the same narrated animation you will watch in Scene 1.
Watch the opener first. It sets the question; the chapter answers it.
1
Read the chart
Patient chart · Stina
1986 · age 11 · the new town
1985–86 · 10–11
The move. A Tuesday/Thursday clinic and a hospital forty minutes away; no Dr. Gonzalez (Module 5).
1986 · 11
New school: concrete floors, no gym mats, desks too tall. Feet, shins and low back hurt by the last bell most days; worst on fever weeks.
The nurse
“Flat feet? Get better shoes.”
Told
Insoles. “Everyone’s feet hurt.”
Chart clues this module: 6 · this chapter
Before you go on · your prediction
Feet, shins and back aching by the end of a day standing and sitting on concrete, worse on fever weeks. What is the load actually landing on?
Open the one you lean toward. Nothing is recorded and nothing is revealed — you come back to it at the end.
Flat feet — the arches are collapsing under the load
Ask whether flat feet produce shin and back pain that tracks fever weeks.
The muscles, tired from standing
Ask why the same day of standing hurts more on a fever week, and what in bone itself bears a standing load.
Bone built as pillars and trusses, carrying the load through a periosteum that is already inflamed
Ask how compact and spongy bone each carry stress, and what an inflamed tissue under load reports.
From Stina’s diary
2
The story
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 · The new town
They moved the summer she turned eleven, to a town where the clinic ran Tuesdays and Thursdays and the hospital was forty minutes away. The new school had concrete floors under thin tile and desks built for someone taller. By the last bell her feet, shins and low back hurt, and on the weeks the fevers came — nobody was counting them — all three hurt more. The nurse looked at her feet, said flat, and suggested better shoes; Mom bought insoles. ‘Everyone’s feet hurt’ was true and useless. A day on concrete loads the skeleton in two ways, and the skeleton has two kinds of bone to meet them: the compact bone of a tibial shaft, which takes stress along one axisSecond cervical vertebra; has the odontoid process (dens) for pivoting head (“no” motion). and is built as pillars, and the spongy bone of a heel and a vertebral body, which takes stress from every direction and is built as trusses. Both were being loaded through a periosteum that Chapters 1 and 2 have already shown could be inflamed. The load was ordinary. The tissue was not.
See it move: Scene 1 · Standing on Concrete · Scene 2 · The Osteon
II · The osteon
Compact bone is very dense and takes stress mainly from one direction; its unit is the osteon, or Haversian system — the packet calls it the functional unit of strength, found only in compact bone. Picture a stack of tubes, each inside the next: the lamellae, tubes of matrix, four to twenty of them around a central (Haversian) canal that carries blood vessels and nerve fibers. In each lamella the collagen fibers run in a spiral, and the spiral reverses direction in the next lamella — the packet’s ‘twister resistor’, the site’s sacrificial bonds Molecular bonds in bone collagen that break to absorb impact and reduce fracture risk.. A twisting load that would shear one lamella is caught by the next. Osteons run along the bone’s long axis like pillars in a colonnade. Between pillars are interstitial lamellaeLayers of bone matrix found between osteons., leftovers of older osteons that remodeling cut through; under the periosteum and lining the cavity run circumferential lamellae, hoops around the shaft. Perforating (Volkmann’s) canals cross from the periosteum to join the central canalsA hollow canal in an osteon containing blood vessels and nerves.. A shaft is a bundle of twisted pillars inside a set of hoops.
See it move: Scene 2 · The Osteon · Scene 3 · Lamellae Three Ways
III · Feeding a buried cell, and building a bridge
Matrix does not let nutrients diffuse through it — the mineral sees to that. So every osteocyte, in its lacunaSmall spaces in bone tissue where osteocytes reside., reaches out through canaliculi, hair-thin channelsProtein passages in the cell membrane that allow specific molecules to pass through. that connect lacuna to lacuna and, at the innermost ring, to the central canal. Nutrients leave the capillary, enter the fluid in the canaliculi and pass cell to cell outward, a relay; wastes come back the same way. The osteocytes also use the network to sense strain — fluid shifting in the canaliculi as the bone bends — and to signal to the surface cellsThe basic structural and functional units of life. whether to build or resorb. Spongy bone has no osteons. Its trabeculae are thin plates and struts of lamellar bone, each only a few cells thick, fed from the marrow around them, so no central canals are needed. They are not random: they line up along the lines of stress like the trusses of a bridge — Wolff’s law, which Chapter 6 returns to. Spongy bone is lightweight, takes stress from all directions, holds red marrowBone marrow that produces blood cells. in its spaces, and is the first bone lost when remodeling tips toward resorption. On the site’s ground-bone slide — compact bone, unstained, 40X — you can see the osteons as targets, the lacunae as dark lentils, and the canaliculi as the fine cracks that join them.
See it move: Scene 4 · Feeding the Buried Cell · Scene 5 · Ground Bone Under the Microscope
3
Watch · explore · think · check
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.
How to read the scenes
- Animation (dark teal) — a short animated explainer, one idea each
- Slide (dark teal) — a still to study: a micrograph, a diagram or a map
- Explore (purple) — something to push on while you watch
- Game (purple) — a quick challenge
- Think (gold) — reason it out, then spot-check yourself with a few true/false questions; not graded
- Check (gold) — a quick H5P that scores itself
Scene 1 of 5
Standing on Concrete
Two textures, two kinds of load — and one periosteum between the floor and the bone.
Animation · in production · 1 min 40 s
Standing on Concrete
A child standing on a tiled concrete floor, the load drawn as arrows into the heels, the tibial shafts, the vertebral bodies. The tibiaShinbone; large, weight-bearing medial bone of the lower leg. splits: compact bone as pillars, arrows along one axis. The calcaneusHeel bone; largest tarsal; attachment site for Achilles tendon. and a vertebra split: spongy bone as a lattice, arrows from every direction. Fever week: the periosteum drawn inflamed, the same arrows now hurting. Caption: the load was ordinary; the tissue was not.
Prefer the full lecture? Spongy and Compact Bone (original video on the site)
Explore · in production
Which bone takes which load?
Six load cases — a tibial shaft, a heel landing, a vertebral body in sitting, a skull blow, a femoral neckNarrow region just below the head; common fracture site. in a stumble, a rib in a breath. For each, predict whether the stress comes from one direction or many, and drag “compact / osteons” or “spongy / trabeculae” to the part that bears it. Then the fever-week slider: predict how an inflamed periosteum changes what the same load feels like. Last: say why insoles could not fix this.
Think · not graded
A tibial shaft and a heel bone take a standing load very differently. Explain the two textures as two engineering answers, and then say what changes about a day on concrete when the wrapper around both is already inflamed.
The true/false spot-check for this prompt is in production.
Check · Mark the Words
Mark the features of compact bone; leave the spongy-bone features unmarked.
This self-scoring check is in production.
Evidence card 1
Add it to your evidence board
Feet (spongy heels), shins (compact shafts) and low back (spongy vertebral bodies) — three loads, two textures, one inflamed wrapper, worse on fever weeks.
Scene 2 of 5
The Osteon
Tubes within tubes, a spiral that reverses every layer, and a canal of vessels down the middle.
Animation · in production · 1 min 50 s
The Osteon
A pillar pulled from a femurThigh bone; longest and strongest bone in the body; has a large round head and prominent trochanters. It telescopes into its lamellae; the collagen in each is drawn as a spiral, and the next spiral runs the other way. A twisting load: one layer starts to shear, the next catches it. The central canal fills with an artery, a vein, a nerve. Zoom out: a colonnade of osteons along the shaft, interstitial scraps between, circumferential hoops around. Caption: the functional unit of strength — only in compact bone.
Prefer the full lecture? The Osteon (original video on the site)
Explore · in production
Build an osteon
A central canal. Add lamellae one at a time and set the collagen spiral direction in each before the twist test; predict what happens when every layer spirals the same way, then when they alternate. Then drag the three lamella types — concentric, interstitial, circumferential — to where they sit on a cross-section of the shaft. Last: predict what runs in the central canal and what runs in a perforating canalCanals that connect central canals, allowing blood flow between osteons..
Think · not graded
The packet calls the alternating spirals a “twister resistor”. Explain what load that resists, why the same arrangement with every spiral running one way would fail, and why spongy bone can skip osteons altogether.
The true/false spot-check for this prompt is in production.
Check · Summary
Choose the true statement about the osteon in each set.
This self-scoring check is in production.
Evidence card 2
Add it to your evidence board
A shaft built as twisted pillars does not fail under a day of standing — the load on her shins was never the problem.
Scene 3 of 5
Lamellae Three Ways
Concentric, interstitial, circumferential — rings, scraps and hoops on one cross-section.
Slide · in production
A Shaft in Cross-Section
Rings around a canal, scraps between the rings, hoops around the whole — three kinds of lamella and one word for all of them: sheets of matrix.
Prefer the full lecture? Spongy and Compact Bone (original video on the site)
Explore · in production
Label the section
The packet’s transverse-section sketch redrawn: drag periosteum, circumferential lamellae, osteon, concentric lamellae, interstitial lamellae, central canal, perforating canal, endosteumA thin connective tissue lining the marrow cavity., spongy bone and marrow cavityThe hollow space inside bones that contains bone marrow. onto it before the key. Then a remodeling replay: watch an osteoclastBone-resorbing cells that break down bone matrix. tunnel through two old osteons and an osteoblast Bone-forming cells that secrete osteoid. line the tunnel with a new one — predict what the leftover pieces are called. Last: on the microscopic square, mark one lacuna and the canaliculi that join it to the canal.
Think · not graded
Interstitial lamellae are the scars of remodeling — pieces of osteons that a tunneling osteoclast cut through. Explain how a shaft that is five to seven percent recycled a week ends up looking like this, and what a bone with no interstitial lamellae would tell you.
The true/false spot-check for this prompt is in production.
Check · Image Hotspots
On the osteon diagram, find the central canal, a concentric lamellaRings of bone matrix surrounding the central canal in an osteon., a lacuna, canaliculi, an interstitial lamella, the circumferential lamellae and a perforating canal.
This self-scoring check is in production.
Evidence card 3
Add it to your evidence board
The packet’s own sketch, labeled — the architecture the chart never pictured when it wrote “flat feet”.
Scene 4 of 5
Feeding the Buried Cell
A relay through hair-thin canals — and the same network as a strain gauge.
Animation · in production · 1 min 30 s
Feeding the Buried Cell
A capillary in the central canal. Glucose and oxygen cross into the fluid of the innermost canaliculi, reach an osteocyte, pass arm to arm outward ring by ring; waste travels back. The bone bends under a step; fluid shifts in the canaliculi; the osteocytes signal to the surface — build here, resorb there. Caption: a relay for food, and a nervous systemThe organ system that controls body functions using electrical and chemical signals. for strain.
Prefer the full lecture? The Osteon (original video on the site)
Explore · in production
How far can food travel?
An osteon with a capillary at the center. Predict before the simulation how many lamellae out a cell could survive by diffusionPassive movement of molecules from areas of high to low concentration. through solid matrix alone (none), then switch the canaliculi on and watch the relay reach the outer ring. Then break a canaliculus and predict which cells die. Last: bend the bone with a slider and watch the fluid shift — predict what the osteocytes tell the surface cells, and what a bone that is never loaded tells them.
Think · not graded
Mineralized matrix blocks diffusion, yet an osteocyte twenty layers deep lives for decades. Explain the relay, say why spongy trabeculae need none of it, and then say what the same network does when the bone bends.
The true/false spot-check for this prompt is in production.
Check · Single Choice
How does an osteocyte buried in compact bone get its nutrients?
This self-scoring check is in production.
Evidence card 4
Add it to your evidence board
OsteocytesMature bone cells that maintain bone tissue. that sense strain and signal the surface are the cells Wolff’s law runs on — Chapter 6 loads them with a backpack.
Scene 5 of 5
Ground Bone Under the Microscope
Unstained, ground thin: targets, lentils and cracks — the whole architecture on one slide.
Slide · in production
Ground Compact Bone, Slide 093-B
Grind the bone instead of dissolving it and the architecture survives: every ring, chamber and crack of the packet’s page 6-4A.
Prefer the full lecture? Captain Concrete — Compact Bone (original video on the site) · histology page: Bone · Captain Concrete · The Lattice
Explore · in production
Read the ground slide
Slide 093-B at 40X with hidden hotspots. Before the labels, click an osteon, its central canal, a lacuna, a canaliculus and an interstitial lamella; then explain why the lacunae look black. Toggle to slide 048b and find trabeculae and marrow, and predict why no targets appear. Last: the two hero cards — Captain Concrete and the Lattice — drag each ID hint to the slide it belongs to.
Think · not graded
On a ground section A cut or slice of the body or an organ for study. the lacunae are black and the cells are gone; on a decalcified section the cells are there and the rings are faint. Say what each preparation sacrifices, which one shows an osteoclast at work, and which one shows a twister resistorA term describing bone’s ability to resist twisting forces..
The true/false spot-check for this prompt is in production.
Check · Image Hotspots
On slide 093-B, find an osteon, a central canal, a lacuna, canaliculi and an interstitial lamella.
This self-scoring check is in production.
Evidence card 5
Add it to your evidence board
Architecture built to carry a child across a concrete floor for decades — nothing about the load explains why it hurt, and nothing about the slide can show the cytokine that did.
4
Your evidence board
Every scene gave you an evidence card, and the chart adds more. Sort each card into the column it supports: Ordinary loads on bone whose wrapper is inflamed, Neither on its own, or Flat feet, bad shoes, tired muscles. Some cards can honestly go in more than one place — that’s allowed, and the feedback tells you which cards decide the case.
Evidence board · drag and drop · in production
The sorting board for this chapter’s cards is being built. Until it arrives, sort your evidence cards on paper into the three columns above.
5
Your verdict
Time to decide. Look back at your bet, then build your verdict from statements that hold up — no writing needed.
Look back at your prediction
Feet, shins and back that ache by the end of a day on concrete, worse on fever weeks — the reading that fits best is…
Find the one you chose at the top. Does the evidence support it, refute it, or revise it?
- Flat feet — the arches are collapsing under the load
- The muscles, tired from standing
- Bone built as pillars and trusses, carrying the load through a periosteum that is already inflamed
Build your verdict · no writing
Choose the statement that holds in each set. The ones you keep become your argument.
This activity is in production.
6
The finding
Finding · the concrete
Ordinary Load, Inflamed Tissue
1986, age 11: feet, shins and low back ache by the end of every day on concrete, worse on fever weeks; “flat feet”, insoles. Chart entry: compact bone is twisted pillars and spongy bone is trusses, each built for its load and fed through canaliculi — a normal skeleton carries a school day without complaint, and pain that tracks fever weeks is about the tissue, not the floor. Held open: what “she’ll grow out of it” was betting on — the plates that build a child’s bones, and whether they had anything to do with the pain.
Next · Chapter 4
She’ll Grow Out of It
Too short for the desks at eleven, four inches taller at thirteen. Every adult who said “growing pains” was betting on the growthAn increase in size and number of cells. plate. This chapter builds bone from nothing — a membrane, a cartilageA flexible connective tissue found in joints, the ear, nose, and rib cage. Cartilage can be of three model, five zones — and asks when the bet would have paid.
Reliable information on rare diseases
NORD · NIH GARD · Orphanet · MedlinePlus Genetics: FMF · FMF & AID Global Association · Autoinflammatory Alliance · Global Genes · Amyloidosis Foundation
Stina has one rare disease. In the United States, about 1 in 10 people live with one of the more than 7,000 known rare diseases. These organizations are where patients, families and clinicians go for trustworthy information.
Hop to:
← Familial Mediterranean Fever — case home
All pages for Module 6 — The Skeletal System
6.0 Module Overview
6.1 Growing Pains
6.2 The Fitness Test
6.3 Pillars and Trusses
6.4 She’ll Grow Out of It
6.5 The Joint That Swelled With the Fever
6.6 Five Percent a Week
6.7 Broken, Mended, Read Whole
6.8 Conclusion and Assessment
6.9 The Evidence Behind the Case
All Modules
- Anatomical Language, Membranes & Homeostasis
- Just Enough Chemistry
- The Cell & Its Transport
- Making Cells & Proteins
- The Integumentary System
- The Skeletal System
- The Muscular System
- Nervous Tissue & the Senses
- The Spinal Cord
- The Brain & the Blood–Brain Barrier
- The Autonomic Nervous System
- Special Senses (in developmentThe process of growth and differentiation.)
- The Endocrine System
- Blood
- The Heart
- Blood Vessels
- The Digestive System
- The Respiratory System
- The Urinary System
- Fluids, Electrolytes & Acid–Base Balance
- The Reproductive System
- The Immune System
List of terms
- compact bone
- osteons
- spongy bone
- canaliculi
- collagen
- deep
- anatomy
- physiology
- axis
- sacrificial bonds
- interstitial lamellae
- central canals
- lacuna
- channels
- cells
- red marrow
- tibia
- calcaneus
- neck
- femur
- perforating canal
- endosteum
- marrow cavity
- osteoclast
- osteoblast
- concentric lamella
- nervous system
- diffusion
- Osteocytes
- section
- twister resistor
- growth
- cartilage
- development