S&F Exam 2

Bones

Osseus tissue

Bone that is hardened

Compact bone

• Outside of bone

• Looks smooth

• Contains osteons

Trabecular bone

“Spongy bone”

• Inside of the bone

• Made of trabeculate

Osteogenic cells

Stem cells

• Inside and outside of cells

• Wait to receive signal to be made

What do osteogenic cells do

Form osteoblasts

Types of cells in bone

1. Osteogenic cells

2. Osteoblasts

3. Osteocytes

4. Osteoclasts

Osteoblasts

Matrix-synthesizing cell responsible for bone growth

• Builds bone

• Produces extracellular matrix

• Deposition

Extracellular matrix

Things outside the cell

• Cause the deposition of calcium and phosphate

Depletion of calcium and phosphate

• Makes bones hard (osseus tissue)

• Removed from blood stream and deposited onto osteoid

What goes on in osteocytes

Osteoblasts that are trapped in osseus tissue

Function of osteocytes

• Monitor and maintain mineralized bone matrix

• “Strain sensors” in bones to send alerts to increase bone density

Osteoclasts

Break down bone

• Dissolve ECM of bone to release calcium and phosphate in bloodstream

• Resorption

• Squirt acid

Osteoblast ECM org/inorg

• 1/3 organic

• 2/3 inorganic

Organic Osteoblast ECM

Proteins

• Collagen

• Proteoglycan

Inorganic Osteoblast ECM

Minerals

• Calcium and Phosphate as hydroxyapatite

Removal of organic matrix

• Bones become brittle and break

• Causes osteogenesis imperfecta

Osteogenesis imperfecta

“Brittle bone disease”

Born with this

Removal of inorganic matrix

• Cannot resist compression

• Bendy

• Causes rickets and osteomalacia

Osteomalacia

In adults

• removal or inorganic matrix of bone

Compact bones features

• Haversian system

• Central canal

• Periosteum

• Endosteum

Haversian system

Rings that look like a tree trunk

Central canal

Empty space in the middle of a bone

• Has an artery, vein, and nerve

Periosteum

Lines the outside of bones

Endosteum

Lines the inside of bones

Collagen arrangement in osteons

Runs in different directions in each layer

• lets bone withstand forces in all directions

Artery in osteon

delivers oxygen and nutrients

Vein in osteon

Collect waste and carbon dioxide to heart

Canaliculi

• Little canals that connect osteocytes to artery, vein, nerve, and each other

• Has small amount of ISF

Osteon

• Made up of osteocytes

• Load‑bearing units of compact bone

Purpose of canaliculi

1. Delivery of oxygen and nutrients & removal of waste

2. Detection of mechanical strain and signals are sent in response

Trabeculae

Spongy-like part of the bone

Anatomy of trabecular bone

1. Trabeculae

2. Bone marrow

3. No central canals needed

4. Center are hollows

Functions of trabecular bone

• Strong, but lightweight

• Important in calcium and phosphate homeostasis

• Structure is based on mechanical stress

• Shock absorption

Where is red bone marrow located

In spaces among trabeculae spongy bone

Where is red bone marrow in children

• In medullary cavities

• Skull, vertebrae, ribs, sternum, hip, bones of upper and lower limbs

Where is red bone marrow in adults

Skull, vertebrae, ribs, sternum, hip, proximal head of femur and humerus

• Turns yellow between 20-25 years old

Medullary cavity

Central, hollow space in shaft of long bones, where bone marrow and blood vessels are stored

Epiphysis

Head of long bones

Diaphysis

Long part of long bone, hollow

Articular cartilage

Hyaline cartilage on the outside of bone at joint

Epiphyseal plate

• Hyaline cartilage

• Growth plate

• Between epiphysis and diaphysis

• Can only grow in length here

Ossification

Bone formation

Types of ossification

• Intramembranous

• Endochondrial

Intramembranous ossification

Deposit of bone from mesenchymal tissue without a cartilage intermediate

Endochondrial ossification

• Osteoblast deposit bone on cartilage, replaces cartilage

• Forms majority of the skeleton

Chond

Cartilage

Embryonic skeleton

Forms flat bones of skull, facial bones, clavicle, and mandible

Endochondrial ossification order of events

1. Start as cartilage shaped as how the bone will look

2. Primary ossification center develops in center of diaphysis

3. Repeat going up and down diaphysis

4. Secondary ossification develops in epiphysis

5. All cartilage has been replaced with bone other than articular surfaces and epiphyseal plate- ends 12 weeks of fetal period

What do osteogenic cells form during endochondrial ossification

Form osteoblasts in periosteum

What do osteoblasts do during endochondrial ossification

Form bone collar- ring of bone

What do chondrocytes do during endochondrial ossification

Hypertrophy and die- the matrix hardens around them

What do osteoclasts do during endochondrial ossification

Remove dead chondrocytes and hollow out medullary cavity

What happens during secondary ossification

Osteoblast replace calcified cartilage with spongy bone, but not medullary cavity in epiphysis

Types of bone growth

• Interstitial

• Appositional

Interstitial bone growth

Growth in length of bones

• Only occurs of epiphyseal plate

Appositional bone growth

Growth in width and density of bones

Location of young chondrocytes

On the epiphyseal side of the plate

Location of older chondrocytes

Closer to diaphysis

Longitudinal bone growth after birth order

1. Chondrocytes on epiphyseal side produce new cartilage, which pushes away from diaphysis

2. Chondrocytes on diaphysis side hypertrophy, ECM calcifies and die

3. Osteoclasts remove dead chondrocytes and osteoblasts replace it with new bone

4. Chondrocytes eventually stop producing new ones and plate closes

What happens once chondrocytes stop producing new cartilage

• Formation will continue until all cartilage is replaced with bone

• Epiphyseal plate turns into epiphyseal line to mark the end on longitudinal bone growth

Achondroplastic dwarfism

• Normal sized head

• Normal sized body

• Short bones and limbs

How does Achondroplastic dwarfism occur

• Cartilage does not divide like it should

• Bone deposits too fast

• Growth plates close too soon

Wolfe’s Law

Structure of bone is based on the stress applied to it and the bone adapts to these stresses

Wolfe’s law in bones order of events

Osteocytes detect activity → alerts osteogenic cells that become osteoblasts → osteoblast build more bone

Remodeling

Process of resorption and deposition

Resorption

Osteoclasts

Deposition

Osteoblasts

Ectopic ossification

Mineralization gone wrong

• deposits calcium and phosphate in soft tissue

Ex of mineral resorption/ deposition

Braces

Where does calcium and phosphate homeostasis take place

In the bloodstream

Calcium in blood normal range

9.2-10.4

Normal PTH levels

10-65

Normal vitamin D levels

18-64

Normal calcitriol level

18-64

How to increase calcium in blood stream

Get it from bones

Calcium is necessary for many cellular functions

Hypocalcemia

Not enough calcium in blood

• increase in neuromuscular activity

• Muscle tremors/ spasms

Increase in neuromuscular activity meaning

• Muscles contract too quickly

• Nervous system fires signals too easily

6 mg/dL calcium in blood meaning

Muscles cannot relax

4 mg/dL calcium in blood meaning

Larynx contracts, which causes suffocation

Hypercalcemia

Too much calcium in blood

• Decrease in neuromuscular activity

12 mg/dL calcium in blood meaning

• Depression of nervous system

• Muscle weakness

• Impaired reflexes

• Cardiac arrest

Calcitonin

Released from “C” cells of thyroid glands

• lowers blood calcium

• in response to increase in calcium

Parathyroid hormone

Released from parathyroid glands

• raises blood calcium

• released in response to decreased calcium

Vitamin D function

Calcitriol

• Raises blood calcium by simulating absorption of dietary calcium

Calcitonin role in osteoblasts/clast

Deposition

• simulates osteoblats

• inhibits osteoclasts

PTH role in osteoblasts/clast

Resorption

• stimulates osteoclasts

• inhibits osteoblasts

Rickets

• Due to vitamin D and calcium deficiency

• Not enough inorganic matrix

• Legs bend

Osteoporosis

Loss of bone density

How to maintain healthy bone density

Osteoclast activity= osteoblast activity

How to build healthy bone density

Osteoblast activity> osteoclast activity

How to decrease bone density

Osteoclast activity> osteoblast activity

Osteoporist target

Targets spongy bone

Osteopenia

• Bone mass decreases too much

• Occurs after age 40

Osteopenia in women

Bone density decreases 8% per decade

Osteopenia in men

Bone density decreases 3% per decade

What happens in osteoporosis

Spongy bone is vulnerable → greater surface area for osteoclast activity

How loss of bone mass and strength occurs

Bone resorption > bone deposition

What happens to women at age 70

Women lose 30% of bone tissue

Black women and bone density

• Have denser bones

• Less affected by menopause-related bone loss