Chapter 6: The Skeletal System

Question 1

Functions of bones

Answer 1

• provide support points for soft body tissue
• protect organs
• store calcium
• produce blood cells in red bone marrow
• store fat in yellow bone tissue

Question 2

What are bones made up of?

Answer 2

Each individual bone is an organ that is made up of all 4 types of tissue working together. It is known as a connective tissue though since it has cells, fibres, and ground substance.

Each bone has components of both compact and spongy bone.

Question 3

What constitutes the skeletal system?

Answer 3

Bones, joints, cartilage, tendons, ligaments

Question 4

Long bone

Answer 4

A bone longer than it is wide, includes all limb bones (besides ankle/wrist).

• contains a diaphysis (middle) and widened ends called epiphyses
• a metaphysis is between diaphysis and epiphyses, it holds the epiphyseal plate for growing bones.
• there is a connective tissue layer that covers the diaphysis of the bone, and hyaline cartilage covers the epiphyses.

Question 5

What are the 4 cells present in bone tissue?

Answer 5

1. Osteoprogenitor cells - small unit that will develop into an osteoblast.
2. Osteoblasts- forms the bones extracellular matrix.
3. Osteocytes - maintains the bone tissue but doesn’t make new matrix.
4. Osteoclasts - cells that break down the bone and reabsorbs it

Question 6

Compact bone

Answer 6

The outer layer of all bones (and is most of the diaphysis)

-contains osteon (or haversian) systems which consist of layers called lamellae. The lamellae encircle a Haversian canal
- volkmann canals run horizontally through the bone and join osteons together.
- lacunae in lamellae hold osteocytes with allow for canaliculi to connect lacunaes to the central canal.

Question 7

Spongy bone

Answer 7

• does NOT contain osteons.
• lamellae arranged in columns called trabeculae (which have lacunae and canaliculi).
• bone marrow forms between trabeculae.

Question 8

How is blood supplied to a bone?

Answer 8

• the nutrient artery enters compact bone near the middle of diaphysis and branches into the marrow cavity.
• other arteries enter the epiphyses and branch to support blood
• periosteal arteries supply the periosteum and outer part of compact bone.

Question 9

Ossification

Answer 9

The process by which bone in formed

Occurs in 3 situations:
1. In a fetus/embryo to form a bony skeleton
2. Into early adulthood to lengthen bones
3. Throughout life to remodel/repair fractures

Question 10

Intramembranous ossification

Answer 10

Bone develops from sheets of embryonic mesenchyme connective tissue

Occurs in the formation of flat bones of the skull, mandible, and clavicles

Question 11

Endochondral ossification

Answer 11

Bones develop from existing hyaline cartilage.

Most bones of the body are formed this way.

Question 12

Interstitial growth

Answer 12

How the cartilage model grows in length

Question 13

Appositional growth

Answer 13

How the cartilage model grows in thickness

Question 14

Bone widening

Answer 14

Bone grow in thickness (appositional growth) to keep up with the growth in length (interstitial growth).

Osteoblasts will secrete bone matrix and osteoclasts increase the size of the marrow cavity -> make the bone grow outward

Question 15

Bone remodeling

Answer 15

Bone undergoes, constant remodeling, replacing old bone tissue with new bone tissue in order to repair any fractures.

Question 16

Calcium homeostasis

Answer 16

Bones and blood need stable amounts of calcium. Since the bones store calcium, it can contain/release calcium when necessary. (It acts as a buffer in this way)

Calcitonin inhibits bone resorption and more calcium salts are deposited into the matrix

Question 17

Periosteum

Answer 17

A connective tissue layer filled with blood vessels and nerve that wrap around bone

Question 18

Endosteum

Answer 18

A membrane lining the marrow cavity in the diaphysis.

Question 19

Medullary cavity

Answer 19

aka the bone marrow cavity

Found in the diaphysis on the long bone and lined by a layer of endosteum.
It contains yellow bone marrow which stores fat

Question 20

Step 1 of intramembranous ossification

Answer 20

Ossification centre forms

Mesenchymal cells develop into osteoprogenitor cells, then into osteoblasts

The osteoblasts will secrete the organic extracellular matrix to form the ossification centre

Question 21

Step 2 of intramembranous ossification

Answer 21

Calcification

Osteoblasts become osteocytes

Osteocytes deposit mineral salts into the matrix which calcifies it (hardens it)

Question 22

Step 3 of intramembranous ossification

Answer 22

Trabeculae form

The matrix hardens into trabeculae that fuse with one another to form the spongy bone.

In the spongy bone, red bone marrow forms which fills the gaps between the trabeculae.

Question 23

Step 4 of intramembranous ossification

Answer 23

Periosteum develops

The mesenchyme cells outside of the ossification center condense to form the periosteum.

A thin layer of compact bone forms under the periosteum

Question 24

Step 1 of endochondral ossification

Answer 24

Cartilage model develops

Mesenchymal cells crowd to form what the future bone will look like. After that they become chondroblasts and secrete cartilage extracellular matrix. This produces a hyaline cartilage model.

A perichondrium develops around the cartilage model

Question 25

Step 2 of endochondral ossification

Answer 25

Growth of the cartilage model

The cartilage model grows in length (interstitial growth) and in thickness (appositional growth).

Chondroblasts become chondrocytes which enlarge to calcify (harden) the matrix.

The Chondroblasts die and lacunae form around them

Question 26

Step 3 of endochondral ossification

Answer 26

Primary ossification centre

The nutrient artery penetrates the perichondrium.

There are osteoprogenitor cells in the perichondrium that become osteoblasts. Then the perichondrium becomes periosteum. Because of the nutrient artery, capillaries grow and help produce the primary ossification centre.

Osteoblasts deposit bone extracellular matrix over the calcified cartilage remains, this forms the trabeculae that spread to the ends of the model.

Question 27

Step 4 in endochondral ossification

Answer 27

Marrow cavity forms

Osteoclasts break down part of the trabeculae to form a marrow cavity in the diaphysis.

The diaphysis wall is replaced by compact bone

Question 28

Step 5 of endochondral ossification

Answer 28

Secondary ossification centre

An artery grows into the epipyhsis and secondary ossification centre forms (around the time of birth)

Spongy bone begins to form

Question 29

Step 6 of endochondral ossification

Answer 29

Cartilage remains

Any remaining hyaline cartilage at the joint surface (ends) become articular cartilage.

Some hyaline cartilage remains between diaphysis and epiphyses which is the epipyseal (growth) plate.

The bone continues to grow in length by adding new chondrocytes and replacing them with bone.