CH 6: Skeletal System - Bones and Bone Tissue

Functions of Skeletal System (5)

• SUPPORT

• PROTECTION

• MOVEMENT

• STORAGE

• BLOOD CELL PRODUCTION

Ligament VS Tendons

• TENDONS connect MUSCLES TO BONES

• LIGAMENTS connect BONES TO BONES

Hematopoiesis

The process where BODY PRODUCES ALL TYPES OF BLOOD CELLS

• This involves differentiation of stem cells where it DEVELOPS INTO MATURE BLOOD CELL TYPES

Bone Matrix

BONES ARE COMPOSED OF THIS

• Made of 1/3 (35%) ORGANIC MATERIALS

  • Like… COLLAGEN AND PROTEOGLYCANS

• 2/3 (65%) INORGANIC MATERIALS

  • HYDROXYAPATITE

  • These are the MINERALS of the bone

What happens when minerals (inorganic materials) are removed? If collagen is removed?

• If minerals were removed…BONE BECOMES TOO BENDABLE

• If collagen were removed…BONES BECOME TOO BRITTLE

Osteocytes

• It’s within the lacunae

• It ASSIST WITH NUTRITION OF BONE

• These are MATURE BONE CELLS

Canaliculi

These are LITTLE CANALS/SMALL PASSAGEWAYS for OSTEOCYTES TO COMMUNICATE WITH EACH OTHER

• This is like a hangout road/lounge for other osteocytes to communicate

Lacunae

• This is a SMALL, EMPTY SPACE that the osteocytes would LIVE IN

• These are those UNFINISHED NEW YORK APARTMENTS that the osteocytes would live in

Osteoblasts

These are CELLS that FORM NEW BONES AND GROW + HEAL EXISTING BONES

• The “B” in blasts could mean BUILD

• Would FORM NEW BONE TISSUE ON ALREADY FORMED CARTILAGE

Ossification

This is the PROCESS of FORMATION OF BONES via osteoblasts

Intramembrane ossification

Forms FLAT BONES (like those in the skull and clavicle)

• In the EMBRYONIC CONNECTIVE TISSUE MEMBRANE

• STARTS during the 5TH WEEK OF EMBRYONIC DEVELOPMENT

Endomembrane ossification

Using the CARTILAGE AS A TEMPLATE and is GRADUALLY REPLACED BY BONES

• Forms MAJORITY OF SKELETON

• This TAKES PLACE IN THE CARTILAGE

• Cartilage formation happens at the end of the 4th week of development

Osteoclasts

Cells that BREAK DOWN BONE TISSUE and REABSORB BONES

• Think “C” for CHIP AWAY

• Plays roles in bone remodeling, calcium homeostasis, and repair of bone injuries

• When these BREAK DOWN THE BONES, THEY RELEASE MINERALS WITHIN THE BONES WHICH CAN BE REUSED AGAIN

• PRODUCE COLLAGENASES

Collagenases

group of enzymes that break down collagen, a major protein in animal connective tissues

Osteochondral progenitor cells

These are the TYPE OF CELLS THAT CAN DIFFERENTIATE INTO OSTEOBLASTS OR CHONDROBLASTS

Spongy Bones

These are bones INSIDE THE COMPACT BONE that ALLOWS DISTRIBUTION OF ANY STRESS + PRESSURE

• NO OSTEON inside

Trabeculae

INTERCONNECTIVE RODS/PLATES OF BONE

• Kinda like scaffolding

• GIVES STRUCTURAL SUPPORT AND REDUCE WEIGHT

Compact bone

These are HARD, EXTERNAL BONES that surrounds spongy bones

Osteon

FUNCTIONAL UNIT of the compact bone matrix

Central canal

Canals in the MIDDLE of osteon that HOUSES NERVES + BLOOD VESSELS and GIVES BONES NUTRIENTS

Lamellae (s. lamella)

The LAYER within a compact bone and THE BUILDING BLOCK OF COMPACT BONE

Canaliculi

These are LITTLE CANALS that CONNECT LACUNAE together for OSTEOCYTES TO COMMUNICATE WITH EACH OTHER

Diaphysis

The SHAFT of a LONG BONE

Medullary Cavity

The CENTRAL, HOLLOW SPACE WITHIN THE DIAPHYSIS

Epiphysis

The ENDS of a LONG BONE

• Mostly spongy bone, very little compact bone

Epiphyseal plate

GROWTH PLATE for new bone growth

• This is BETWEEN EPIPHYSIS AND DIAPHYSIS

How do osteoblasts form? What happens after the embedding of osteoblasts in the bone matrix?

Some embryonic mesenchymal cells in the connective tissue DIFFERENTIATE INTO OSTEOCHONDRAL PROGENITOR CELLS which THEN FORMS OSTEOBLASTS

• After EMBEDDING IN THE BONE MATRIX, OSTEOBLASTS TURN INTO OSTEOCYTES

  • The embedding happens when they get stuck within the lacunae after building new bone structures

How do spongy bone form?

Osteoblasts form on the surface of trabeculae + produce more bones → the trabeculae grows bigger/longer + remodels (because it’s getting added on) → trabeculae joins together in interconnected networks to form spongy bone

How does compact bones form?

specialized cells within the spongy bone forms red bone marrow while cell surrounding the developing bone becomes the periosteum → osteoblast in the periosteum create the outer compact bone layer

What are the steps to bone repair when someone fractures their bone? (A LOT of steps)

1. Hematoma Formation (Inflammatory Stage)

   1. This MAKES BLOOD CLOT which HELPS STOP BLEEDING and give foundation for healing

      1. Hematoma = Blood Clot

   2. INFLAMMATION OCCURS

      1. This happens because the hematoma attracted cells relating to inflammation to help repair the bone

2. Callus Formation occurs with fibro/chondroblasts (Soft Callus Formation)

   1. This is after inflammation where MESENCHYMAL STEM CELLS DIFFERENTIATE INTO CHONDRO AND FIBROBLASTS

   2. Creates SOFT CALLUS which HELPS TEMP. STABILIZE FRACTURED BONE and GIVE FRAMEWORK for hard callus

3. Callus Ossification (Hard Callus Formation)

   1. OSTEOBLASTS invade soft callus and DEPOSIT MINERALS (hydroxyapatite) which HARDENS SOFT CALLUS AND INCREASE STABILITY

4. Bone Remodelling occurs with osteoclasts (Bone remodelling)

   1. The HARD CALLUS IS RESHAPED

      1. OsteoCLASTS REMOVE EXCESS BONE TISSUE

      2. OsteoBLAST BUILD NEW BONES

What are the roles of calcium for the bone? (3)

• STIMULATE MUSCLE CONTRACTION

• STIMULATE + REGULATION OF CARDIAC MUSCLE

• EXOCYTOSIS FOR NEURAL SIGNALING

How does the body go back into homeostasis when there’s LOW BLOOD CALCIUM LEVELS?

1. Parathyroid hormones are going to secrete which MAKES MORE OSTEOCLASTS

2. The osteoclasts are going to BREAK DOWN/CHIP AWAY FROM REGULAR BONES TO RECEIVE MORE CALCIUM

3. Since there’s more calcium, homeostasis is restore

Having LOW BLOOD CA LVLS are bad because if parathyroid hormones keep making osteoclasts which break down the bones, the BONES BECOME REALLY BRITTLE

How does the body go back into homeostasis when there’s HIGH BLOOD CALCIUM LEVELS?

1. CALCITONIN hormones are RELEASED from thyroid to DECREASE ACTIVITY OF OSTEOCLASTS

2. REDUCE PTH (parathyroid hormones) which are responsible for making osteoclasts

   1. This helps with lowering blood calcium because osteoclasts can’t break down bone for calcium

3. OSTEOBLASTS are STIMULATED to USE EXCESS CALCIUM TO MAKE NEW BONE TISSUE

Osteoporosis

It’s a condition with A LOSS OF BONE MATRIX and DECREASED BONE MASS/DENSITY

• Makes bones fragile

• Could occur because of decreased blood calcium

  • WHY? This is because the parathyroid stimulates creation of osteoclasts which chips away the bones for calcium, making the bones more fragile and delicate

The primary function of osteoblasts is to…

A. stimulate bone growth.

B. Inhibit the growth of bone.

C. Resorb bone along the epiphyseal plate

D. Prevent osteocytes from forming.

E. Lay down bone matrix.

E. Lay down bone matrix

Explain:

A (stimulate bone growth) would NOT be the correct answer because, although that is the job of osteoblasts, it’s a very BORAD DESCRIPTION of their job whenever there are other answers that are more specific (e.g, lay down the bone matrix)

Match the following

Sort the Following into Endochondral and Intramembranous Ossification

Label the Bone Structure