6.1-6.3

(Added 6.4-6.12 -> on 1/27/26)

What does the skeleton do?

they support and protect the organs/inside body

What are the 5 primary functions of Bones?

Support, Storage, Blood cell Production, Protection, Movement

(Support, Store, Produce, Protect, Move)

What does it mean that a Bone’s function is “to storage” ?

• calcium salts of a bone = a mineral reserve which maintains normal concentrations or CALCIUM and PHOSPHATE IONS in body fluid

• ***yellow marrow = stress lipids

How is bone classified?

• Shape

• Internal Structure (Spongy vs Compact)

Bone is also called what Tissue?

OSSEOUS TISSUE

What is part of the Skeletal System

• Bones/Joints

• Connective tissue that stabilize/connect→Cartilage, Ligaments

Why does bone have it’s texture

Deposition of calcium salt in MATRIX

What dominates bones

Calcium Phosphate

Different percentages of what makes up a bone’s weight

• Calcium phosphate = 2/3

• Collagen Fibers = 1/3 (density)

• osteocytes.other cells = 2% of bone mass

Macroscopic features include (other than the 4 shapes)

• 2 types of bone tissue

• Periosteum

• Cellular Endosteum

• Tendon

• Ligaments

What are the 4 shapes of bone

• Short - Carpals, Tarsals

• Long - Femur, Humerus

• Irregular - Vertebrae, Some Skull bones

• Flat - Scapula, Ribs, Sternum, Some Skull bones

Short bones

short and roughly equal dimensions

Flat Bones

thin and relatively broad

Irregular Bones

Complex shape/Doesn’t fit with the rest (it’s giving emo boy)

Long Bones

… long :)

Features of a Long Bone

• Diaphysis (“Central shaft”)

• Epiphysis (Proximal and distal)

• Articular cartilage

• Spongy Bone

• Compact Bone

• Marrow cavity

  • Bone Marrow

• Endosteum

• Periosteum

• Epiphyseal Line

Diaphysis

Aka “Central Shaft” -> its Marrow Cavity is filled with Bone Marrow

Epiphysis (Proximal and Distal)

the wider portions at each end (covered by articular cartilage)

What is cellular Endosteum?

• Covers spongy bone of marrow cavity and over inner surfaces

• ***Active role in bone growth and repair/remodeling

• Lines the inside

Articular Cartilage

Cartilage Covering Joint Ends (Usually in long bones)

Periosteum is what?

• made of fibers and tendons

• provides route for supplies

• Helps bone repair and growth

• Outside layer of bone

Spongy Bone

AKA “Cancellous Bone” : has projections of bone separated by spaces

What are Epiphysis covered by?

• Articular cartilage

  • Each Epiphisis articulates an adjacent bone at a joint

Compact Bone

Densely Packed (forms the Diaphysis)

What does the Marrow cavity do?

• house the bone marrow : a soft fatty tissue

• Has epiphysis = expended portions at the ends

—-

• Red Marrow: Hematopoietic tissue (“hematopoiesis) that produces red blood cells, white blood cells, and platelets.

• Yellow Marrow: Composed mostly of fat cells, it serves as an energy reserve and can convert to red marrow if needed.

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Hallow Part inside of Diaphysis and usually Contains Spongy Bone

• filled with bone marrow

Epiphyseal Line

Marks where Cartilage is Replaced (burial Site for Epiphyseal plate of the bone)

How to spell the long bone part which is the “wider portions at the end”

Epiphysis or Epiphyseal

Central shaft surrounds what?

• Central marrow cavity of long bones

Why immature bone growth?

• problems with junctions between epiphysis and diaphysis

2 types of Bone tissue

• Compact (Dense) vs Sponge (cancellous)

What the the 3 cells in the Bones?

• Osteocytes

• OsteoBlasts

• OsteoClasts

Osteocytes are what?

• in both bone tissue (and are mature bone cells)

• Inside Lacunae (small pockets)

• part of Canaliculi

Osteon

Haversian System (Basic Functional Unit of Compact Bone)

• Osteocytes arranged Concentric Layers around the Haversian Canal (circular formation)

How are nutrients/waste of osteocytes diffused?

• through extracellular fluids surrounding the call and cytoplasmic extensions

How do Osteocytes maintain bone structure?

• recycles calcium salts in bone matrix and assists repairs

Lacunae vs Lamellae

• Lacunae = between sheets of calcified matrix (the gap)

• Lamellae = calcified matrix

What are canalicui?

• Small channels in the matrix

• Connect lacunae to blood vessels

• Contains cytoplasmic extensions of osteocytes

Trabeculae

Lamellae Rod formation

• (“3 strands is not easily broken…” bible verse)

OsteoCLASTS

• Bigguh cells (50 or more nuclei)

• Secrete acids and enzymes

• “Osteolysis”/Resorption Release store minerals

• DISSOLVES bony matrix

• regulates calcium and phosphate concentrations

OsteoBLASTS

• CREATES new bone and matrix (“ossification”)

• promotes deposition of calcium salts in organic matrix

• surrounded by calcified matris = becomes a osteoclast (like jedi becoming sith)

Compact Bone

• Has Osteon (“Haversian System”).. basic functional unit

  • Osteocytes arrange in a CONCENTRIC pattern/in concentric layers around a central canal/”Haversian canal'“ (Big circle, circle, circle)

    • Has 1/more vessels

• Lamellae = cylindrical = parallel to long axis of central canal

• Perforating canals = passage ways which links vessels of central canals with periosteum and marrow cavity

• Covers every bone except joint capsules (articular cartilage go there)

• ** Covers area with limited direction stress … Stronk

  • Ex: Limb Bones

Spongy Bone

• No osteon

• Lamallae = rods/plates formation; branching, open networks

  • The trabecular netowrk = supports/protects cells of red bone marrow

• Canaliculi from LACUNAE = at the end of the bone, exposed surface of trabeculae

  • Nutrients/waste diffuses between marrow and osteocytes

• LIGHTER than compact bones (muscles move bone easier)

• Covers interior of bone

• Stress from many directions : weakuh (not heavy stress)

Growth of bone stars from when a embryo is

6 weeks after fertilization

• skeleton = all cartilage

• Bone = keeps growing till usually 25

Ossification is what?

Process of replacing other tissues with bone (Making new bone)

Calcification is what?

Deposition/accumulation of calcium Salts

• usually during ossification (can happen in non-bone tissue)

2 types of ossification are what?

Intramembranous and Endochondridal

Intramembranous Ossification is what?

• bone develops in sheets/membranes of connective tissue

• usually in deep dermis layers

• * Looks like sponge but changes later

Steps for Intramembranous Ossification are what?

1. OSTEOBLASTS differentiate in ebryonic/fetal fibrous connective tissue

2. Matrix is secrete by stem cells (stem cells become calcified) … Osteoblasts differentiate from connective tissue stem cells

   • 1 and 2 happen ins the ossification center

3. new bone grows outward ; osteoblasts get trapped in calcified matric and turn to osteocytes (NOT CLASTS)

4. Blood vessels grow ; supply osteocytes and also get trapped in the bone too

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the intarmembranous bone looks spongy but remodeling around vessels = osteons are created (ONLY SEEN IN COMPOUND BONE)

Example of Intramembranous Ossification processes bones

• Flat bones of skull, mandible, and clavicles

Endochondia Ossification is what?

forms in hyaline cartilage and covers it up laterz (more common than intra.)

• cartilage into true bone

• ---

  ONLY FORMS IN HYALINE CARTILAGE

Steps of Endochondia Ossification are what?

1. Chondrocytes (in cartilage) enlarge; surrounding matrix calcifies

   • Chondrocytes die, matrix slows its nutrient diffusion

2. Bone forms thin layer around shaft area; blood vessels invade perichondrium

   • Cells in inner layer differentiate into OSTEOBLASTS (starts making bone matrix)

3. Blood vessels invades inner region of cartilage

   • Migrating fibroblasts differentiate into OSTEOBLASTS

   • new osteoblasts form spongy bone in center shaft in. a PRIMARY OSSIFICATION CENTER

4. Bone enlarges; OSTEOCLASTS breakdown spongy bone = makes a marrow cavity

   • Cartilage dont fill bone bcauz epiphysisal cartilage/”plates” on the ends are growing/enlarging

   • Bone length increases

   • ** osteoclasts break, and osteoblasts create (ying and yang motion)

5. Center of Epiphysis starts calcifying; blood vessels and osteoblasts fo into the Epiphysis

   • ** Make a SECONDARY ossification center; Epiphysis is filled with spongy

   • ** cap of of cartilage is exposed to joint cavities = “ARTICULAR CARTILAGE”

   • SHAFT Bone and Epiphysis = separated by cartilage

6. Osteoblasts produce more than the epiphysis cartilage expands = cartilage narrows till diaapears

7. END OF GROWTH = “epiphyseal closure”

   1. **Time it is done varies by person, and bone type (plus sex hormones too)

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sex hormones = speed up growth —- puberty (some boys say their bones/GROWING hurt)

• this is why

IN adults = marks of former locations of epiphysial cartilage is marked by a line (like the berlin wall)

Appositional growth is what?

• Diameter of bone increases

Why does Appositional growth happens?

• Cells of periosteum become OSTEOBLASTS and more bony matrix (outer)

• Osteoclasts erode inner surface; marrow cavity enlarges

  • One must decrease so the other increases

What are the requirements for regular bone health?

• Calcium (salts)

• Phosphorus

• Vitamin A, C

• Vitamin D 3

• HORMONES

Phosphate and calcium help with what?

• reliable source for minerals; during prenatal/embryo… baby absorbs calcium and could absorb mass of mom (done through absorbing minerals in mom’s blood stream)

Viamin D3

• Calcium metabolism role

• Goes into liver and kindey to turn into CALCITROL

  • Calcitrol = hormones; stimulates absorption of calcium and phosphate ions

Vitamin A/C

• Essential for bone growth and maintenance

• Vitamin C deficiency = scurvy; reduced osteoblast # ; brittle/weak bones

Rickets

• Flexible bones

• - as a result of lack of Vitamin D 3

• soft/bending of bones (usually during kids years it shows)

  • BOW LEGGED STANCE… bros couldn’t win against gravity frfr (too soft)

What are the 3 things that bone growth and development need to be in balance?

1. Mineral supply : Especially calcium salts

2. Vitamins

   •  D₃ : helps calcium metabolism 

     • Deficiency in D₃ = RICKETS

   • A and C : supports osteoblasts functions

3. Growth, sex, thyroid, and calcium-balancing  HORMONES

Two items that maintain the bone MATRIX are…

• Osteoblasts

• OsteoClasts

What is the Turn over rate for Bone?

1/5 is remodeled every year (20%)

Influenced by…

• Age

• Mechanical Stress

• Hormonal Balance

Is every part of the bone remodeled? Explain

1. Yes however, the amount of time it takes differs from…

   1. person to person

   2. bone type

   3. location of the bone

What allows bones the ability to adapt to new stresses:?

Remodeling

If bone is heavily stressed, what happens to it?

Could Fracture/break

What happens if bone isn’t subjected ot daily stresses?

Becomes weaker and brittle

What does regular exercise do for bones?

Maintains Normal Bone Structure and strength

What happens to a bone when someone wears a cast (and now removes it)

lose up to 1/3 of bone mass (work out to strengthen it)

What is the Most Abundant Mineral in the Human Body?

• Calcium (salts)

Explain what happens in the body to certain physiological processes if calcium ion concentrations increase and if they decrease.

1. Increase : Muscle and neurons shut down/become unresponsive

   1. Above 5% -> unusual 

   2. 30% -> unresponsive

2. Decrease : Become energetic/excited… they convulse… 

   1. 35% -> convulse

   2. 50% -> death

How can calcium levels in body fluids become elevated?

1. Parathyroid Hormone (PTH) ; Parathyroid Glands

2. Calcitrol ; Kindeys

How can calcium levels in body fluids become lowered?

Calcitonin : THYROID GLANDS 

What are 3 main causes of bone fractures mentioned in the text?

1. Weak bones

2. Overstress/ repetitive stress

3. Injuries/Trauma/Falls

In order for bones to heal on their own, what do they need?

1. Blood vessels/Supply remains 

2. Cellular Parts of the Endosteum & Periosteum are intact

How long can the Healing of Bones take?

4 months to a year

Explain the 4 steps in the repair of a fracture.

1. Blood clot : Fracture Hematoma 

   1. Closes off blood supply

   2. KIlls osteocytes

   3. Results in dead bones on either side of the fracture

2. Cells of Periosteum and Endosteum go to fracture

   1. Makes an external and internal Callus

   2. ** external callus = develops hyaline cartilage

3. Osteoblasts replace cartilage with spongy bone

4. Spongy bone is replaced by compact bone

   1. Leave a slightly thicker bone patch at the fracture site

Explain what happens to bones as we age.

Weakens and gets more brittle 

Why is osteoporosis more common in older women than in older men?

Their sex hormone keeps being produced till 60 (androgens)

Where do elevations and projections form on bones and what are they used for?

Form where ligaments and tendons attach or where adjacent bone articulate at joints

Depressions, grooves, and Openings

Shows where blood vessels and nerves run along and/or penetrate bone

Process

Any Projection or bump

Trochanter

A large, rough projection

Tuberosity

A smaller, rough Projection

Tubercle

A small, rounded projection

Spine

a pointed process

Head

The expanded articular end of an Epiphysis, separated form the shaft by a neck

Neck

a narrow connection between Epiphysis and Diaphysis

Condyle (median and Lateral)

A smooth, rounded articular process

Trochlea

A smooth Grooved articular process shaped like a pulley

Crest

A prominent ridge

Foramen

A rounded passageway for blood vessels/nerves

Canal

A duct or Channel

Fissure

An Elongated cleft/slit

Sinus

A chamber within a bone, normally filled with mucus

What are the two Skeletal Divisions and their subdivisions?

1. Appendicular (126)

   1. Limbs

      • 32 Upper (each limb)

      • 31 Lower (each limb)

2. Axial (80)

   1. Skull (22)

      • 7 Associated (includes 1 Hyoid Bone)

      • 8 Cranial Bones 

      • 14 Facial Bones

   2. Thoracic Cage (25)

      • 24 ribs

      • 1 Sternum

   3. Vertebral Column  (26)

Partial Fracture

A break that doesn’t go through the bone completely

Complete Fracture

A break that goes Completely through the Bone

Open Fracture

AKA Compound fracture

Fracture goes through the skin and can be seen externally

Closed Fracture

AKA simple fracture

Fracture does not pierce though the skin (all internal)

Non-Displaced Fracture

two broken ends of the bones are still lined up (not moved)

Displaced Fracture

two broken ends of the bones are not lined up (moved out of place and it needs to be set)