TEAS Skeletal System Overview SE

🦴 Skeletal System

1. Why do babies have more bones?

A baby is born with about 270 bones.

An adult has about 206 bones.

Why does the number go DOWN?

👉 Some bones fuse (join together) as you grow.

🧠 Memory trick:

👶 Baby = BONES APART
🧑 Adult = BONES JOINED

So:

270 → fuse → 206

You don't lose bones—you have multiple bones join to become one bone.

🦴 Example: Hipbone

At birth, part of the pelvis has 3 separate bones:

• Ilium

• Ischium

• Pubis

As you grow:

Ilium + Ischium + Pubis → ONE hipbone

🧠 Easy trick:

"I-I-P become ONE hip."

2. Two major divisions of the skeleton

The skeleton is divided into:

🧍 AXIAL🦵 APPENDICULAR

Think:

AXIAL = AXIS = CENTER of your body

APPENDICULAR = APPENDAGES = ARMS & LEGS

---

🧍 AXIAL SKELETON

The axial skeleton is your body's central framework.

It includes:

🧠 Skull
🫀 Rib cage
🦴 Vertebral column (spine)
🫁 Sternum (breastbone)

🧠 Memory trick:

"Axial = Head + Chest + Spine"

Or:

AXIAL = your BODY'S AXIS

🦵 APPENDICULAR SKELETON

Think:

APPENDAGES = things attached to your body

Includes:

💪 Arms
🦵 Legs

• Girdles that attach them to your skeleton

The two major girdles are:

• Shoulder/pectoral girdle → attaches arms

• Pelvic girdle → attaches legs

🧠 Memory:

APPENDICULAR = ARMS + LEGS + THEIR ATTACHMENTS

⭐ SUPER EASY COMPARISON

AXIAL 🧍	APPENDICULAR 🦵
Center of body	Limbs
Skull	Arms
Spine	Legs
Ribs	Shoulder girdle
Sternum	Pelvic girdle
"AXIS = CENTER"	"APPENDAGES = LIMBS"

AXIAL
➡ Center → skull, spine, ribs, sternum

APPENDICULAR
➡ Limbs → arms, legs, girdles

"Which is part of the axial skeleton?"

🧠 HEAD + CHEST + SPINE

"Which is part of the appendicular skeleton?"

💪 ARMS + LEGS + GIRDLES

🦴 1. Vertebral Column

There are 24 pre-sacral vertebrae.

Break them into:

7 Cervical

➡ Neck

12 Thoracic

➡ Chest/back where ribs attach

5 Lumbar

➡ Lower back

So:

7 + 12 + 5 = 24

🧠 BEST TRICK: 7–12–5

Think:

"Breakfast at 7, lunch at 12, home at 5." 😂

7 cervical → 12 thoracic → 5 lumbar

Then come:

Sacrum + Coccyx

So the whole spine is:

7 + 12 + 5 + sacrum + coccyx

🧍 2. AXIAL =

80 bones

Remember:

AXIAL = CENTER of your body

The table breaks the 80 into:

Part	Bones	Easy idea
Inner ear ossicles	6	Tiny ear bones 👂
Skull + hyoid	23	Head/neck 🧠
Sternum + ribs	25	Chest 🫁
Vertebral column	26	Spine 🦴
TOTAL	80

🧠 Don't panic about the numbers!

For TEAS, the big concept is more important:

AXIAL = skull + spine + ribs + sternum

And:

80 = axial

🦵 3. APPENDICULAR =

126 bones

Remember:

APPENDICULAR = ARMS + LEGS + GIRDLES

Part	Bones
Pectoral girdle	4
Upper extremities	60
Pelvic girdle	2
Lower extremities	60
TOTAL	126

⭐ EASY NUMBER TRICK

Notice:

Upper extremities = 60
Lower extremities = 60

So:

ARMS = 60 🖐
LEGS = 60 🦵

Then:

4 + 60 + 2 + 60 = 126

🔥 THE NUMBERS YOU REALLY WANT

Spine:

7 – 12 – 5 = 24

Cervical – Thoracic – Lumbar

Skeleton:

Axial = 80

Appendicular = 126

80 + 126 = 206 total adult bones

🎯 This is a BIG number to know:

🦴 80 + 126 = 206

🧠 SUPER FAST MEMORY CARD

AXIAL = CENTER = 80

APPENDICULAR = LIMBS = 126

80 + 126 = 206

Spine:

C = 7 → Cervical = neck
T = 12 → Thoracic = chest
L = 5 → Lumbar = lower back

7 → 12 → 5 → 24

🔥 One sentence:

"Axial is my center (80), appendicular is my limbs (126), together they make 206."

🦴 Skeletal System = 1-2

5 MAIN JOBS

Think:

Skeletal system = SUPPORT + MOVE + PROTECT + STORE + MAKE

That's your big memory trick. ⭐

1. 🧍 SUPPORT

Bones give your body structure and shape .

Without your skeleton, your body couldn't stay upright.

🧠 Think:

Bones = body's FRAME

Like the frame of a house 🏠.

2. 🏃 MOVEMENT

Bones work with muscles to help you move.

Important:

❌ Bones don't move themselves.

Instead:

Muscles pull on bones → bones move

🧠 Think:

Muscles = pull
Bones = move

---

🦴 Skeletal System = 3-4

3. 🛡 PROTECTION

Bones act like armor around important organs.

Bone	Protects
🧠 Skull	Brain
🦴 Vertebral column	Spinal cord
🫁 Ribs + sternum	Heart & lungs

🧠 Easy phrase:

"Skull protects brain, spine protects spinal cord, ribs protect chest organs."

4. 🧂 MINERAL STORAGE

Bones store important minerals, especially:

Calcium + Phosphorus

Your body can use these minerals when needed.

🧠 Memory:

Bones = mineral bank 🏦

Calcium + phosphorus = stored in bones

5. 🩸 HEMATOPOIESIS

making blood cells

This happens in bone marrow .

🩸 Bone marrow makes:

• Red blood cells

• Other blood cells from stem cells

🧠 Break the word apart:

HEMATO = blood
POIESIS = making

SW:

HEMATOPOIESIS = BLOOD MAKING

🧠 BONUS: What is bone actually made of?

The skeletal system includes:

🦴 Bones + cartilage + ligaments

And bone is a type of:

CONNECTIVE TISSUE

Easy meaning:

Connective tissue = tissue that supports/connects things.

🔥 TEAS CHEAT SHEET

Memorize these 5 words:

🦴 Skeletal System = SMPMH

S → Support
M → Movement
P → Protection
M → Mineral storage
H → Hematopoiesis

Even easier:

"Bones SUPPORT, MOVE, PROTECT, STORE, and MAKE blood."

FRAME → MOVE → ARMOR → BANK → BLOOD
Support → Movement → Protection → Minerals → Hematopoiesis

What mineral is stored in bones?

➡ Calcium + phosphorus

What is hematopoiesis?

➡Blood cell production

What protects the spinal cord?

➡ Vertebral column

What do bones work with to create movement?
➡ Muscles

What type of tissue is bone?
➡ Connective tissue

Where does hematopoiesis occur?
➡ Bone marrow

🦴 Bone Structure

Think of a bone like a house 🏠:

Outside = hard wall
Inside = lighter/spongy area
Outside covering = protective coat

---

1. 🧱 Compact Bone = HARD OUTSIDE

Compact bone is the hard, dense outer layer of the bone.

Think:

COMPACT = HARD + DENSE

It gives the bone strength.

🧠 Memory:

"Compact = Concrete" 🧱

Both are hard!

2. 🧽 Spongy Bone = LIGHT INSIDE

Spongy bone is less dense and has lots of open spaces.

Think of an actual kitchen sponge 🧽.

SPONGY = HOLES + LIGHT

It is usually found inside the bone.

🧠 Memory:

"Spongy = Sponge."

3-4

🦴 3. Osteons = UNITS inside compact bone

Compact bone is organized into little cylinder-shaped units called:

OSTEONS

Think:

Osteons = building blocks of compact bone

🧠 TRICK:

OSTEON = compact bone's unit

You don't need to overcomplicate this.

4. 🩸 Haversian Canal

Inside each osteon is a:

Haversian canal

It contains:

🩸 Blood vessels
⚡ Nerves

So the canal is basically the bone's supply line.

🧠 Memory:

HAVERSIAN = HIGHWAY 🚗

Blood vessels and nerves travel through it.

5. 🧥 Periosteum =

OUTER COVERING

The periosteum is a fibrous membrane that covers the outside of the bone.

It contains:

🩸 Blood vessels
⚡ Nerves
💧 Lymphatic vessels

🧠 BIG TRICK:

PERI = around

So:

PERIOSTEUM = around the bone

Think of it like a jacket around the bone 🧥

⭐ Put it all together

Imagine cutting a bone in half:

🧥 PERIOSTEUM
⬇
🧱 COMPACT BONE
⬇
🧽 SPONGY BONE

Inside the compact bone:

OSTEONS → HAVERSIAN CANALS → blood vessels + nerves

🔥 Super-fast memory:

PERIOSTEUM = COVER
COMPACT = HARD
SPONGY = HOLES
OSTEON = UNIT
HAVERSIAN = BLOOD + NERVE HIGHWAY

🦴 6. Five Types of Bones

There are 5 types:

1. Long

2. Short

3. Flat

4. Irregular

5. Sesamoid

🧠 Initials:

L S F I S

You can remember:

"Long Short Flat Irregular Sesamoid"

The shape/name usually gives you a clue about the bone.

Examples worth knowing:

Type	Easy example
Long	Femur, humerus
Short	Wrist/ankle bones
Flat	Skull, sternum, ribs
Irregular	Vertebrae
Sesamoid	Patella (kneecap)

🧠 BEST TRICK:

LONG → limbs 💪
SHORT → wrist/ankle ✋🦶
FLAT → protection 🛡
IRREGULAR → weird shapes 😂
SESAMOID → inside tendons → patella

🎯 TEAS QUICK REVIEW

Know these 7 things:

Compact → hard outer bone 🧱

Spongy → lighter, porous bone 🧽

Osteon → basic unit of compact bone

Haversian canal → blood vessels + nerves 🩸⚡

Periosteum → outer covering of bone 🧥

Long/Short/Flat/Irregular/Sesamoid → 5 bone types

Patella → sesamoid bone

🔥 ONE-LINE MEMORY:

"Cover → Hard → Sponge → Units → Highway."

Periosteum → Compact → Spongy → Osteons → Haversian canals

🦴 LONG BONE

Picture a femur (thigh bone):

END 🟢 — MIDDLE 🟡 — END 🟢

That's basically the whole thing!

---

1. 🟢 EPIPHYSIS = THE ENDS

There are 2 epiphyses:

• Proximal epiphysis = end closer to the body

• Distal epiphysis = end farther from the body

What's inside?

Mostly spongy bone 🧽

What happens here?

Bone growth occurs here (more precisely, at the growth plate associated with the epiphysis).

🧠 TRICK:

EPIPHYSIS = ENDS

E = Ends ⭐

2. 🧊 ARTICULAR CARTILAGE = SMOOTH COVER

This covers the ends of the bone where it forms a joint.

Its main job:

REDUCE FRICTION

Think:

🦴 ↔ 🦴
Instead of bones rubbing directly against each other, cartilage helps them move smoothly.

🧠 TRICK:

ARTICULAR = ANTI-FRICTION

long bone pt.2

3. 🟡 DIAPHYSIS = THE LONG MIDDLE

This is the long shaft/middle part of the bone.

It is mostly:

COMPACT BONE 🧱

🧠 TRICK:

DIA = LONG SHAFT

Think "diaphysis = diameter-long middle".

---

4. 🕳 MEDULLARY CAVITY = THE INSIDE SPACE

Inside the diaphysis is a hollow space called the:

Medullary cavity

It contains bone marrow.

There are two important types:

🔴 Red marrow

➡ Makes blood cells

This is hematopoiesis.

🧠 RED = BLOOD

🟡 Yellow marrow

➡ Mostly fat cells

🧠 YELLOW = FAT

⭐ PUT THE WHOLE BONE TOGETHER

Think:

🟢 END — 🟡 LONG MIDDLE — 🟢 END

EPIPHYSIS → DIAPHYSIS → EPIPHYSIS

Then remember:

Ends → mostly spongy
Middle → mostly compact
Inside middle → medullary cavity
Red marrow → blood cells
Yellow marrow → fat
Articular cartilage → reduces friction

---

🧠🔥 BEST MEMORY TRICK E-D-E

Epiphysis = Ends
Diaphysis = Diaphysis = long middle
Epiphysis = End

And:

🔴 RED = BLOOD
🟡 YELLOW = FAT
🧊 CARTILAGE = LESS FRICTION

Where is the long shaft of a bone?

➡ Diaphysis

What are the ends called?
➡ Epiphyses

What reduces friction at joints?
➡ Articular cartilage

Where does hematopoiesis occur?
➡ Red bone marrow

What is yellow marrow mostly made of?
➡ Fat cells

Which part is mostly compact bone?

➡ Diaphysis

Which part is mostly spongy bone?
➡ Epiphysis

⭐ Memorize this:

“ENDS are EPI,

MIDDLE is DIA,

RED makes BLOOD,

YELLOW stores FAT, CARTILAGE stops FRICTION.”

🦴 LONG BONE

Has the classic:

EPIPHYSIS → DIAPHYSIS → EPIPHYSIS

• Epiphysis = ends

• Diaphysis = long shaft/middle

• Medullary cavity = inside the shaft

• Articular cartilage = covers joint surfaces

Examples: femur, humerus

What about other bones?

Other bone types don't have this same long-bone layout.

For example:

• Short bones → wrist/ankle bones

• Flat bones → skull, ribs, sternum

• Irregular bones → vertebrae

• Sesamoid bones → patella

⭐ TEAS trick

If you see:

Epiphysis + diaphysis + medullary cavity

Think:

LONG BONE ONLY 🦴

But things like compact bone, spongy bone, periosteum, and bone marrow can be found in other bones too.

So don't memorize the epiphysis/diaphysis layout for every bone type.

🦴 OSSIFICATION =

MAKING BONE

First, what does ossification mean?

Ossification = the process of making bone.

Your body takes soft cartilage and gradually turns it into hard bone.

🧠 Memory trick:

OSSI = BONE
Ossification = Bone formation

🧸 How does it happen?

Think of it like this:

🧽 Soft cartilage

⬇

🧂 Calcium + phosphorus are deposited

⬇

🦴 Hard bone

So:

CARTILAGE → MINERALS → BONE

The important minerals are:

Calcium + phosphorus ⭐

👶 What happens when you're a baby?

Babies have more cartilage in their skeleton than adults.

Especially in their long bones.

As the child grows, cartilage is gradually replaced by bone.

📏 Growth plates =

HOW LONG BONES GROW

This is the BIG TEAS point.

At the ends of long bones are areas called:

Growth plates

They are made of cartilage.

As you grow:

Growth plate cartilage → ossification → more bone → longer bone

That's how your long bones get longer, helping you grow taller.

🧠 BEST MEMORY:

Growth plate = Growth! 📏

If you see growth plate, immediately think:

LONG BONE GETTING LONGER

🔥 SUPER EASY PICTURE

Imagine a long bone:

🦴 ← end | middle | end → 🦴

At the ends:

Growth plate = cartilage

As you grow:

cartilage → bone

➡ Bone gets longer
➡ You get taller

⭐ ONE BIG THING TO REMEMBER

Ossification

= cartilage becomes bone

Growth plate

= cartilage at the end of a growing long bone

Calcium + phosphorus

= minerals deposited to make the bone hard

🧠 TEAS MEMORY TRICK

Remember:

“GROW → PLATE → CALCIUM → BONE”

Growth plate
⬇
Cartilage
⬇
Calcium + phosphorus
⬇
Ossification
⬇
Longer bone

🎯 If TEAS asks:

What is ossification?
➡ Bone formation.

What happens to cartilage during ossification?
➡ It is replaced by hard bone/mineralized tissue.

What is the growth plate?
➡ A cartilage region where a growing long bone lengthens.

What minerals are important?
➡ Calcium + phosphorus.

Why are growth plates important?
➡ They allow long bones to grow longer.

🔥 FINAL CHEAT:
OSSIFICATION = CARTILAGE → BONE
GROWTH PLATE = LONG BONE GROWTH
CALCIUM + PHOSPHORUS = HARD BONE

🦴 1. Does cartilage turn into bone?

Yes, during bone development and growth, cartilage is gradually replaced by bone through ossification.

Think:

🧽 Cartilage → 🦴 Bone

But not all cartilage in your body turns into bone . For example, cartilage remains in places like your joints because it helps provide smooth movement.

📏 2. Do adults still have growth plates?

No — not open growth plates.

When you're growing up:

Growth plate = cartilage → allows long bones to get longer

When growth is finished:

Growth plate closes → becomes bone

SW:

👶 Child: growth plate = cartilage + active growth
🧑 Adult: growth plate = closed/fused bone

🧠 TEAS trick:

GROWING = growth plate OPEN
ADULT = growth plate CLOSED

🧂 3. What is phosphorus?

… is a mineral that your body needs.

For your TEAS, think of it as one of the building materials for strong bones and teeth.

🦴 Calcium + Phosphorus = strong/mineralized bone

Think of them like a construction team :

🧱 Calcium + phosphorus → help build/harden bone

You get phosphorus from foods such as meat, dairy, eggs, beans, nuts, and whole grains.

🧠 Super easy memory:

CALCIUM + PHOSPHORUS = BONE BUILDERS 🦴

⭐ Remember these 3 things:

Ossification = cartilage is replaced by bone

Growth plate = cartilage area that lets long bones grow longer

Phosphorus = mineral that works with calcium for bone formation/mineralization

TEAS one-liner:

🦴 “Growing bones use growth plates; calcium + phosphorus help make them strong.”

🦴 Bone Remodeling =

CONSTANT REPAIR

Your bones aren't just sitting there forever. Your body is constantly:

🧹 removing old bone → 🏗 making new bone

This is called bone remodeling.

Think of a house:

🧹 Old bone gets removed
⬇
🏗 New bone gets built

This helps keep bones healthy and also releases minerals like calcium when your body needs them.

⭐ The 3 Bone Cells

This is the MOST IMPORTANT part.

🏗 1. Osteoblast = BUILDS

OsteoBLAST = BUILD

Osteoblasts make new bone.

🧠 Memory:

BLAST = BUILD 💥🏗

---

🧹 2. Osteoclast = BREAKS DOWN

OsteoCLAST = CLEARS/CUTS bone

Osteoclasts break down/resorb old bone.

This is called:

Bone resorption

🧠 Memory:

CLAST = CRASH/CRUSH 🧹

So:

Osteoclast → breaks down bone

---

🦴 3. Osteocyte = MATURE BONE CELL

An osteocyte is a mature bone cell that lives in bone tissue and helps maintain it.

Think:

CYTE = CELL

🧠 Memory:

OsteoCYTE = bone CELL

🔥 THE BEST TRICK EVER

Just memorize:

BLAST = BUILD

CLAST = CRASH

CYTE = CELL

Cell	Job
🏗 Osteoblast	Builds new bone
🧹 Osteoclast	Breaks down old bone
🦴 Osteocyte	Mature bone cell / maintains bone

🦴 What is bone resorption?

Don't let the word scare you.

Bone resorption = breaking down old bone

The osteoclast does it.

When bone is broken down, calcium and other minerals can be released into the blood for the body to use.

🧠 Think:

RESORPTION = REMOVE

🔄 BONE REMODELING

Put it all together:

Osteoclast 🧹
⬇
Breaks down old bone
⬇
Osteoblast 🏗
⬇
Builds new bone

That's bone remodeling.

🧠 SUPER EASY PHRASE:

“CLAST cleans, BLAST builds.”

And:

“Bone is constantly being broken down and rebuilt.”

🎯 TEAS QUICK CHECK

Which cell builds bone?

➡ Osteoblast

Which cell breaks down bone?
➡ Osteoclast

What is bone resorption?
➡ Breaking down/removing old bone

What is bone remodeling?
➡ Old bone is removed and new bone is built

Which cell is a mature bone cell?
➡ Osteocyte

What can bone resorption release?
➡ Calcium and other minerals

⭐ Memorize this:BLAST = BUILD

🏗CLAST = CRASH 🧹

CYTE = CELL 🦴

🦴 1. First: What is an osteon?

OSTEON = basic unit of COMPACT bone

Think of an osteon like a tiny bone cylinder/building block.

The first picture is basically showing you one osteon cut in half.

---

🟠 2. What are all those orange rings?

Those rings are called lamellae.

They're layers of bone matrix arranged in circles around the center.

Think:

🧅 Osteon = like an onion

The rings = lamellae

You don't need to stress over this one for the TEAS. Just recognize:

Lamellae = layers/rings of an osteon.

🦴 4. Where are the osteocytes?

Look at the little cells between the rings.

Those are:

OSTEOCYTES

Remember from before:

OSTEOCYTE = mature bone cell

They live inside the bone matrix of the osteon.

🧠 Think:

🏠 Osteocytes LIVE inside the bone.

🏗 5. What about osteoblasts?

Look at the surface of the bone in the picture.

The cells sitting along the outside are osteoblasts.

Remember:

OSTEOBLAST = BUILDS bone 🏗

They're on the surface because they're involved in making new bone.

---

🧹 6. What about osteoclasts?

Also found on the bone surface.

Remember:

OSTEOCLAST = BREAKS DOWN bone 🧹

So:

OSTEOBLAST → buildsOSTEOCLAST → breaks down

🔥 BLAST = BUILD
🔥 CLAST = CRASH

🖼 NOW LOOK AT THE SECOND PICTURE

This picture is zoomed out.

You're looking at a long bone.

🧥 Periosteum

The outside covering.

PERI = around

🧱 Compact bone

The hard outer bone.

COMPACT = HARD

🧽 Spongy bone

The lighter, porous bone inside the ends.

SPONGY = SPONGE

🟡 Yellow bone marrow

Inside the medullary cavity.

YELLOW = FAT

🦴 Osteon

A tiny structural unit inside the compact bone.

🔬 THE LAST PICTURES = THE 3 CELLS

🏗 Osteoblast

BUILDING bone

🦴 Osteocyte

MATURE bone cell living in bone

🧹 Osteoclast

BREAKING DOWN bone

⭐ THE MOST IMPORTANT THING

Don't mix up WHERE they are:

Osteocytes

➡ INSIDE the bone matrix/osteon

Osteoblasts

➡ SURFACE of bone
➡ BUILD

Osteoclasts

➡ SURFACE of bone
➡ BREAK DOWN

🧠 Easy phrase:

“CYTES live INSIDE; BLASTS build; CLASTS clear.”

🔥 SUPER FAST TEAS CHEAT SHEET

osteon

Term	Think
Osteon	Unit of compact bone
Lamellae	Rings/layers
Central canal	Blood vessels + nerves + lymphatic vessels
Osteocyte	Mature cell inside bone
Osteoblast	BUILD bone
Osteoclast	BREAK DOWN bone
Periosteum	Covering around bone
Compact bone	Hard/dense
Spongy bone	Porous/light

“Osteon is the house. Osteocytes LIVE inside. Osteoblasts BUILD. Osteoclasts BREAK.”

🦴 SKELETAL SYSTEM — SUPER EASY1.

🦴 What does the skeletal system DO?

Remember S-M-P-M-B:

S = Support

Keeps your body upright and gives it shape.

M = Movement

Works with muscles to help you move.

P = Protection

Protects organs.

M = Minerals

Stores calcium + phosphorus.

B = Blood

Bone marrow helps make blood cells.

🧠 Easy phrase:

“Bones Support, Move, Protect, Store, and Make.”

2. 🧍 AXIAL vs 🦵 APPENDICULAR

🧍 AXIAL = CENTER

Includes:

• Skull 🧠

• Sternum

• Ribs

• Vertebral column/spine

🧠 Trick:

AXIAL = AXIS = CENTER

---

🦵 APPENDICULAR = LIMBS

Includes:

• Arms 💪

• Legs 🦵

• Their girdles/attachments

🧠 Trick:

APPENDICULAR = APPENDAGES = ARMS + LEGS

---

3. 🦴 Five bone types

L S F I S

Long → femur, humerus
Short → wrist/ankle
Flat → skull, ribs, sternum
Irregular → vertebrae
Sesamoid → patella

🧠 Quick trick:

Long limbs, Short wrists/ankles, Flat protection, Irregular shapes, Sesamoid = kneecap

4. 🏗 Ossification

This big word simply means:

OSSIFICATION = BONE FORMATION

Cartilage is gradually replaced by harder, mineralized bone during development.

🧠 Think:

Cartilage → minerals → 🦴 BONE

5. 🔄 Bone remodeling and more

Your bones are constantly being repaired and renewed.

Old bone 🧹

⬇
removed
⬇

New bone 🏗

replaces it

That's bone remodeling.

🧠 Trick:

REMODELING = RENOVATING your bones 🏠

---

6. 🔬 Osteon

This sentence in your notes needs a small correction:

❌ Osteon is NOT a bone cell.

✅ Osteon = structural unit of compact bone.

Think of an osteon as a tiny cylinder/building block of compact bone.

Inside it is the:

Haversian (central) canal

It contains:

🩸 Blood vessels
⚡ Nerves
💧 Lymphatic vessels

🧠 Trick:

OSTEON = compact bone UNIT
CENTRAL CANAL = supply HIGHWAY

7. 🏗 Osteoblast

OSTEOBLAST = BUILDS bone

🧠 BLAST = BUILD

🏗 Osteoblast → new bone

---

8. 🧹 Osteoclast

OSTEOCLAST = BREAKS DOWN bone

This is called bone resorption.

🧠 CLAST = CRASH

🧹 Osteoclast → removes old bone

---

9. 🦴 Osteocyte

OSTEOCYTE = mature bone cell

These are found within the bone tissue and help maintain it.

🧠 CYTE = CELL

So:

OsteoCYTE = bone CELL

🔥 THE 5-SECOND BONE CELL TRICK

This is the one I'd REALLY memorize:

🏗 BLAST = BUILD🧹 CLAST = CRASH

🦴 CYTE = CELL

And:

“CYTES live inside, BLASTS build, CLASTS clear.”

🎯 FINAL TEAS CHEAT SHEET

Topic	Remember
Skeletal system	Support, Movement, Protection, Minerals, Blood
Axial	Center
Appendicular	Arms + legs
5 bone types	Long, Short, Flat, Irregular, Sesamoid
Ossification	Bone formation
Remodeling	Old bone → new bone
Osteon	Unit of compact bone
Haversian canal	Blood vessels + nerves
Osteoblast	BUILD 🏗
Osteoclast	BREAK DOWN 🧹
Osteocyte	Mature bone cell 🦴

⭐ If you only memorize 6 things:

AXIAL = CENTER
APPENDICULAR = LIMBS
OSSIFICATION = BONE FORMATION
OSTEON = COMPACT BONE UNIT
BLAST = BUILD
CLAST = CRASH

What makes up the framework of the skeletal system?

Bones, cartilage, and ligaments

Medullary Cavity

Found inside the long bone and contains both red and yellow marrow

Hollow space inside a long bone

Think of a long bone like a hollow tube:

🦴 Bone wall → 🕳 Medullary cavity → 🦴 Bone wall

The medullary cavity is the space inside the shaft (diaphysis) of a long bone.

What's inside? 🩸

It contains bone marrow:

• 🔴 Red marrow → makes blood cells

• 🟡 Yellow marrow → mostly stores fat

“Bone has a hollow middle filled with marrow.”

🎯 TEAS one-liner:

Medullary cavity = hollow space inside the diaphysis of a long bone that contains bone marrow.

⭐ DIAPHYSIS = shaft
⭐ MEDULLARY CAVITY = hollow inside the shaft
⭐ RED MARROW = blood
⭐ YELLOW MARROW = fat

Describe the general structure of a bone

Compact bone surrounds spongy bone