Anatomy: Endochondral Ossification and Bone Remodeling

Question 1

What is Endochondrial Ossification and how is it different from Intermembranous?

Answer 1

It forms the rest of the skeleton (post cranial skeleton) while the intemembranous forms the skull (cranial).

Question 2

How does bone FORM INITIALLY from Cartilage in the process of Endochondrial Ossification?
How does it form later within the process?

Answer 2

It forms from Hyaline Cartilage (Glassy cartilage at the ends of bones)

Later in the process, it forms from dead calcified chondrocytes through OSSIFICATION.

Question 3

What are the 5 steps of Endochondrial Ossification? (Explain the process)

Answer 3

1. Bone Starts to form around Hyaline Cartilage Model
2. The cartilage in the CENTER of the Diaphysis starts to calcify and develop Cavities.
3. Pereosteal Bud invades cavities and Spongey Bone starts to form.
4. Diaphysis elongates and Medullary (marrow) cavity starts to form. Secondary Ossification Centers start to form in the epiphyses for the 5th and last step.
5. The epiphyses ossify. When completed, hyaline cartilage
   remains only in the epiphyseal plates and articular cartilages.

Question 3

What are the bones formed from Endochondrial Ossification RELIANT on?

Answer 3

The growth & destruction of Hyaline Cartilage

Question 4

What are the Key/Primary Cell types in Endochondrial Ossification & What do they do? (3 types of Cells)

Answer 4

Chondrocytes: Cells that produce and maintain cartilage.
Osteoblasts: Cells responsible for bone formation.
Osteoclasts: Cells that resorb bone tissue.

Question 5

What are some things that regulate Endochondrial Ossification?

Answer 5

Hormones such as sex & growth hormones and signal pathways.

Question 6

Where does Endochondrial Ossification primarily occur in?

Answer 6

Post-cranial Skeleton, in primarily long bones

Question 7

What Are the consequences of abnormalities in Endochondrial Ossification?

Answer 7

Primarily Growth-related disorders

Question 8

What are the 5 Primary Types of Bones?

Answer 8

Short, Flat, Long, Sesamoid, Irregular

Question 9

How do Long bones LENGTHEN?

Answer 9

Through the division of Chondrocytes at the epiphyseal plates.

Question 10

Where does Bone Growth occur?

Answer 10

At the Epiphysis on the side closest to the diaphysis.

Question 11

5 Different Zones of the Epiphyseal Plate: Zone of Reserve Cartilage

Answer 11

This zone contains small, scattered chondrocytes that are not actively involved in growth. It anchors the epiphyseal plate to the bone of the epiphysis.
Provides stability and a supply of cells for future growth.

Question 12

5 Different Zones of the Epiphyseal Plate: Zone of Proliferation

Answer 12

In this zone, chondrocytes rapidly divide and form columns of stacked cells.
Results in the production of new cartilage.

Question 13

5 Different Zones of the Epiphyseal Plate: Zone of hypertrophy and maturation

Answer 13

Chondrocytes in this zone enlarge (hypertrophy) and begin to mature

Question 14

5 Different Zones of the Epiphyseal Plate: Zone of calcification

Answer 14

dead chondrocytes; some calcified.

Question 15

Which of the zones is NOT involved in Longitudinal growth of the bone?

Answer 15

Zone of reserved Cartilage

Question 16

5 Different Zones of the Epiphyseal Plate: Zone of ossification

Answer 16

Chondrocytes are calcified and osteoblasts invade and produce bone matrix.

Question 17

Why do Chondrocytes that reach the Zone of Calcification Die?

Answer 17

They are FAR from the Blood Supply.

Question 18

What happens to the Calcified Cartilage in the Zone of Ossification?

Answer 18

It’s replaced with Bone.

Question 19

What’s Appositional Growth?

Answer 19

Bones growing WIDER

Question 20

What is the process of Appositional Growth?

Answer 20

NEW Lamellae are formed/added, which results in old Lamellae turning into OSTEONS.

Question 21

What is Growth Hormone and where is it Secreted?

Answer 21

It enhances cell division and protein synthesis in all tissues and they are secreted by anterior pituitary gland.

Affects both Longitudinal & Appositional Growth.
DIRECTLY stimulates Osteoblasts in the Periosteum.

Question 22

Where are hormones primarily Secreted?

Answer 22

Endocrine Gland

Question 23

What conditions result from excess growth hormone, and what causes them?

Answer 23

1. Gigantism (in childhood): Caused by a tumor that secretes growth hormone; leads to excessive longitudinal and appositional bone growth before epiphyseal plates close.
2. Acromegaly (in adulthood): Also caused by a tumor; results in enlargement of bones and soft tissues after epiphyseal plates have CLOSED.

Question 24

What are the effects of Acromegaly and potential health issues?

Answer 24

No increase in height, enlargement of bones, cartilage, and soft tissues.
Affects skull, facial bones, hands, feet, and tongue.
Can lead to heart and kidney malfunction.

Question 25

What is Bone Remodeling?

Answer 25

Continuous process of bone formation throughout one’s life
growth in length is finished
New bone formed by Osteoblasts, while old ones are resorbed by Osteoclasts.

Question 26

Why does Bone Remodeling Occur within our bodies?

Answer 26

-Calcium Homeostasis
-Replacement of primary bone with secondary bone
-Bone repair
-Replacement of old brittle bone with newer bone
-Adaptation to tension and stress

Question 27

How does Testosterone & Estrogen play a role on Bone Remodeling?

Answer 27

Testosterone PROMOTES Osteoblast activity while Estrogen INHIBITS Osteoclast activity.

Question 28

What extraneous factors play a role in Bone Deposition, remodeling, and/or repair?

Answer 28

-Calcium ion intake – (diet) must be adequate to support bone deposition
-Vitamin D intake – (diet) must be adequate to promote calcium ion absorption from gut and prevent calcium ion loss in urine
-Vitamin C intake – (diet) must be adequate for synthesis of collagen
-Vitamin K intake – (diet) must be adequate for synthesis of glycoproteins
-Protein intake – (diet) must be adequate for osteoblasts to synthesize collagen fibers in organic matrix

Question 29

What maintains Calcium Ion Homeostasis in our blood?

Answer 29

Negative Feedback Loops

Question 30

Explain Negative Feedback Loops in the context of Calcium Ions in blood.

Answer 30

Calcium Ion levels drop in the blood and is detected by the Parathyroid Cells (receptor). The parathyroid cell then secrete parathyroid hormone to regulates and increases Calcium levels. (Control Center & Effector).

The effector process also leads to Osteoclasts breaking down the inorganic matrix by/in order to release Calcium Ions.

Question 31

What is Calcitonin?

Answer 31

Opposite effects of parathyroid hormone. Pulls calcium ions out of blood to manufacture inorganic matrix of bone. (bone deposition).

Question 32

What are Simple Fractures?

Answer 32

Skin and tissue around fracture remain intact but bone is broken.

Question 33

What are Compound Fractures?

Answer 33

Bone is broken & skin and tissue around fracture are damaged.

Question 34

What is Hematoma?

Answer 34

Type of Blood Clot Involved in Fracture Healing; Fills in the gap between bone fragments.

Question 35

Explain the body’s reaction to a Fracture

Answer 35

The Hematoma acts as an inflammatory response to fill in the gap between the broken bone fragments.
The Fibroblasts produces collagen and extracellular matrix in order to create/provide structural support through INFILTRATING the Hematoma.
The Chondrocytes then produce collagen so there of fracture can have support and strength to withstand other pressures, or pulling forces. The Chondrocytes also starts producing Hyaline Cartilage.
The combination of Chondrocytes and Fibroblasts create Soft Callus which turns into Hard Callus over time with the help of Osteoblasts.
Then Bone Callus is remodeled and replaced with Secondary Bone.

Question 36

What are Glucocorticoids?

Answer 36

Can inhibit osteoblast function and promote osteoclast activity.

Ex: Cortisol