Bones

Question 1

What are the 2 main roles of the skeleton

Answer 1

Structural

Homeostasis

Question 2

How does the skeleton provide structrual support

Answer 2

Enables movement

Support/form structure

Protection for internal organs

Question 3

How does the skeleton help with homeostasis

Answer 3

Acts as a storehouse for essential minerals (85% of phosphorous, 99% of calcium)

Site of energy metabolism

Endocrine function

Uses bone marrow

The skeletal system helps maintain mineral homeostasis by regulating the level of calcium and other minerals in the blood by storing or releasing them from bones as needed. This process also helps maintain homeostasis in blood pH because the minerals are basic.

Question 4

What are the two components of bone ?

Answer 4

Cortical and cancellous bone

Question 5

Explain the components of cortical bone and what it does

Answer 5

It is also called the compact/dense bone, and makes up 80% of total bone mass, and is 10% porous. Its function is to provide strength to the structure, and this exists as the outer layer of the bone

Question 6

Explain the components of cancellous bone and what it does

Answer 6

Makes up ~20% of total bone mass. It is highly porous, with 50-90% of it being porous.

It provides a network of thin trabeculae in all directions which allow for stress shock absorption

Provides a large bone surface for mineral exchange.

This is the inside part of the bone

Question 7

What is the bone matrix

Answer 7

Bone matrix constitutes a complex and organized framework that provides mechanical support and exerts essential role in the bone homeostasis.

It provides mechanical support and assists in homeostasis

Question 8

What is the bone matrix composed of

Answer 8

Collagen cross links

Collagen 1 (provides elasticity)

Hydroxyapatite crystals (provides rigidity)

Collagen makes up 90% of the bone matrix

Question 9

Is a balance of collagen and hydroxyapatite crystals necessary? WHy?

Answer 9

Yes it is necessary, because bones need to be balanced between hard, strong and flexible. To achieve this, there has to be a balance in collagen and hydroxyapatite crystals in the bone matrix.

Question 10

What is the cause of brittle bones

Answer 10

Occur when there are too many hydroxyapatite crystals but not enough collagen

Question 11

What is the cause of bendy bones

Answer 11

Occurs when there is too much collagen compared to hydroxapatite crystals

Question 12

What is the function of bone remodelling

Answer 12

Repair damage to skeleton

Prevent accumulation of aged tissue/micro damage in the bones

Supply calcium and phosphorous for mineral homeostasis

Question 13

Name the key cells involved in bone remodelling

Answer 13

Osteoblasts

Osteoclasts

Osteocytes

Question 14

What is the function of osteoblasts

Answer 14

Osteoblasts FORM BONE. They are responsible for forming organic collagen matrix, osteoid and then mineralise it. It can terminally differentiate into an osteocyte or returnn to resting bone lining cell when it is done

Question 15

What is the function of osteoclasts

Answer 15

Osteoclasts RESORB/DEGRADE BONE. They are responsible for resorbing bone matrix by secreting acid to break down the collagen matrix. Also has lots of lysosomes which helps dissolve bones. It then liberates these minerals into circulation (i.e. allows for calcium to be released into circulation)

Question 16

What is the function of osteocytes

Answer 16

These regulate local mineral deposition and chemistry of bone matrix level, controlling extracellular concentration of Ca2+ and phosphate ions in bone tissue over time

These are terminally differentiated osteoblasts which are embedded into the bone.

It can release various molecules which increase (RANKL) or decrease (OPG) osteoclast formation and activity

These are mechano-sensing cells which responds to load in tissue

Question 17

Why might we want to resorb bones

Answer 17

As some parts of the body has microdamage or is old –> allows for the process of remodelling

Question 18

Explain the bone remodelling cycle

Answer 18

Basically the osteoclasts come and resorb/degrade bone, and then it is followed by the osteoblasts which place down collagen matrix which later on solidifies into bone. Some osteoblasts than become osteocytes and the cycle continues.

Question 19

What is ossification

Answer 19

Process in which the bone forms i.e. osteoblasts lie down materials which induces calcification which is process of hardening of the bone

Question 20

What is intramembranous ossification

Answer 20

Bone directly replacing mesenchymal skeleton

Question 21

What is the mesenchymal skeleton

Answer 21

It is embryonic connective tissue framework from which the skeleton of vertebraes develop

Question 22

What is endochondral ossification

Answer 22

Where the mesenchymal skeleton is replaced by cartilage model first, before it is replaced by bones

Question 23

What bones form via intramembranous ossification

Answer 23

Flat bones

Question 24

What bones form via endochondral
ossification

Answer 24

Long bones

Question 25

How does intramembranous ossification work

Answer 25

Intramembranous ossification is a process by which bone tissue is formed directly from mesenchymal tissue, without a prior cartilage stage. It is one of the two primary methods of bone formation, the other being endochondral ossification. This process is responsible for forming the flat bones of the skull, the clavicles, and other flat bones in the body. Here’s a step-by-step explanation of intramembranous ossification:

Development of Ossification Centers:

The process begins in the mesenchymal tissue, where certain mesenchymal cells cluster together and differentiate into osteoblasts. This cluster of osteoblasts forms an ossification center.
Secretion of Osteoid:

The osteoblasts begin to secrete the organic components of the bone matrix, known as osteoid, which includes collagen and other proteins. The osteoid is not yet mineralized and is softer than the mature bone.
Calcification:

The osteoid matrix soon becomes mineralized through the deposition of calcium phosphate, which hardens the matrix. This process transforms the osteoid into a hard, mineralized bone tissue.
Formation of Woven Bone and Periosteum:

As the calcification continues, the osteoblasts become trapped within the bone matrix and differentiate into osteocytes, the mature bone cells. The bone matrix forms a network of woven bone, which is less organized than mature lamellar bone.
Simultaneously, the mesenchymal tissue surrounding the developing bone condenses to form the periosteum, a fibrous membrane covering the outer surface of the bone.
Development of Lamellar Bone:

Over time, the woven bone is replaced by lamellar bone, which is more organized and structurally stronger. This remodeling process involves the resorption of woven bone by osteoclasts (bone-resorbing cells) and the deposition of new lamellar bone by osteoblasts.
The lamellar bone is arranged in concentric layers known as lamellae, which form the mature structure of flat bones.
Formation of Compact and Spongy Bone:

Depending on the location within the bone, the lamellar bone may organize into two types: compact bone and spongy bone.
Compact bone forms the dense outer layer of bones, providing strength and protection.
Spongy bone, also known as cancellous bone, consists of a network of trabeculae (bony struts) and contains spaces filled with bone marrow, making it lighter and more flexible than compact bone.
Throughout intramembranous ossification, blood vessels infiltrate the developing bone, providing essential nutrients and removing waste products. This vascularization is crucial for the continued growth and development of the bone tissue.

In summary, intramembranous ossification is a direct bone formation process that transforms mesenchymal tissue into bone without a cartilage intermediate, resulting in the formation of flat bones such as those in the skull and clavicles.

Question 26

How does endochondral ossification work

Answer 26

Formation of the Cartilage Model:

The process begins with mesenchymal cells differentiating into chondrocytes (cartilage cells), which form a hyaline cartilage model that resembles the shape of the future bone.
Growth of the Cartilage Model:

The cartilage model grows in size through two mechanisms: interstitial growth (chondrocytes dividing and producing more cartilage matrix from within) and appositional growth (new chondrocytes and matrix being added to the surface).
Development of the Primary Ossification Center:

As the cartilage model enlarges, chondrocytes in the center begin to hypertrophy (increase in size) and the surrounding cartilage matrix calcifies, causing the chondrocytes to die due to lack of nutrients.
This calcified area forms the primary ossification center. Meanwhile, the perichondrium (the connective tissue around the cartilage model) transitions into a periosteum as osteoblasts form a bone collar around the diaphysis (shaft) of the cartilage model.
Invasion of the Periosteal Bud:

Blood vessels, along with osteoblasts and osteoclasts, invade the calcified cartilage through the nutrient foramen, forming the periosteal bud.
The invading cells break down the calcified cartilage matrix and begin to form spongy bone (trabecular bone).
Formation of the Medullary Cavity:

Osteoclasts resorb the newly formed spongy bone in the center of the diaphysis, creating a medullary (marrow) cavity.
This cavity eventually fills with bone marrow and the process of bone formation continues outward from the primary ossification center.
Development of Secondary Ossification Centers:

After birth, secondary ossification centers form in the epiphyses (ends) of the bone. Similar to the primary ossification center, chondrocytes in the epiphyses hypertrophy, the matrix calcifies, and blood vessels invade, bringing in osteoblasts and osteoclasts.
Secondary ossification centers result in the formation of spongy bone in the epiphyses, but unlike in the diaphysis, no medullary cavity forms.
Formation of Articular Cartilage and Epiphyseal Plate:

The hyaline cartilage that remains on the surface of the epiphyses becomes the articular cartilage, which reduces friction and absorbs shock in joints.
A layer of hyaline cartilage, known as the epiphyseal plate (growth plate), remains between the diaphysis and each epiphysis. This plate is responsible for the lengthwise growth of long bones during childhood and adolescence.
Chondrocytes in the epiphyseal plate continue to divide and produce new cartilage, which is then ossified, allowing the bone to lengthen.
Closure of the Epiphyseal Plate:

When growth in length is complete, typically after puberty, the chondrocytes in the epiphyseal plate stop dividing, and the remaining cartilage is replaced by bone. This process is known as epiphyseal plate closure, resulting in the formation of the epiphyseal line.

Question 27

What is osteoporosis

Answer 27

It is characterised by compromised bone structure and strength, predisposing an increased risk of fracture

a medical condition in which the bones become brittle and fragile from loss of tissue, typically as a result of hormonal changes, or deficiency of calcium or vitamin D.

Question 28

What are the stats of getting osteoporosis

Answer 28

1/3 for women and 1/5 for men over 50 years old

Question 29

What are the primary risk factors for osteporosis

Answer 29

Age - older is higher

Gender - female is higher risk (especially post menopausal)

Height/BMI - short and frail have higher risks

Genetics

Question 30

What are the lifestyle risk factors for osteoporosis

Answer 30

Little calcium intake

Unhealthy diet

Lack of sunlight

Lack of exercise

Sedentary lifestyle

Smoking/medications

Question 31

Explain the role of exercise in improving osteoporosis

Answer 31

Increased exercise such as weight bearing exercise stimulates greater fractures in the bone, however, this stimulates greater bone remodelling which thus reduces the chances of devloping osteoporosis

When you exercise regularly, your bone adapts by building more bone and becoming denser.

Question 32

What are the causes of osteoporosis

Answer 32

An imbalanced bone remodelling (more osteoclasts compared to osteoblasts). As a result of this, more bone is degraded compared to created

Question 33

How can estrogen influence osteoporosis

Answer 33

Because it acts on both osteoclasts and osteoblasts to decrease bone resorption and increase bone formation. Thus, a decrease in estrogen during menopause –> increased bone resorption but less bone formation

Question 34

How can testosterone influence osteoporosis

Answer 34

It increases bone formation, and is a source of estrogen. Reduces with age –> bone loss and fracture