Bone

Question 1

What are the characteristics of bone?

Answer 1

• Bone is the most rigid of connective tissues
• It is one of the hardest tissues in the body
• It is a dynamic tissue. It constantly changes shape to deal with the stresses placed on it.
• We have 206 bones. (Enamel = hardest substance in body)
• Functions in support and protection of internal organs
• Is the principle reservoir for Ca++, PO43-, Na+, and Mg++
• Contains homopoietic bone marrow which makes blood cells

Question 2

What is the percentage breakdown of subtypes of bone and their characteristics?

Answer 2

Cortical bone

• 80% of bone mass
• Dense, compact bone
• Outer layer covered by periosteum ( a dense collagenous connective tissue covering diaphysis of many bones)

Cancellous bone

• 20% of bone mass
• Spongy Bone found at the ends of long bones
• Highly vascular
• Inner layer spongy and light
• Provides space for the bone marrow where RBCs, WBCs, and platelets are produced.

NB: All bones contain both types of bone, but differ in percentages.

Question 3

Epiphysis

Answer 3

End segment of a long bone, contains a cartilaginous layer that allow long bones to grow. Once in adulthood the plates close and there is no more growth.

Question 4

Metaphysis

Answer 4

Region that contains the growth plate.

Columns of spongy tissue is found

Question 5

Diaphysis

Answer 5

Body or shaft of the bone

Question 6

Medullary Cavity

Answer 6

The Medullary cavity is also called the Marrow cavity.

Enclosed by cortical bone, this is where the marrow resides.

Question 7

What are the two types of bone marrow?

Answer 7

Red Marrow

Yellow Marrow

Question 8

What is red marrow?

Answer 8

• Virtually all bones at birth have this.
• Tissue that makes blood and blood cells are here (homopoietic)
• At adolescence it’s confined to the axial skeleton (skulls, ribs, vertebrae, and sternum)

Question 9

What is yellow marrow?

Answer 9

• Fat tissue

- May convert to red marrow if blood loss is severe

Question 10

What is the structure of bone?

Answer 10

• Inorganic Matrix
• Calcium Phosphate [Ca3(PO4)2]
• Hydroxyapatite crystals [Ca10(PO4)6 (OH)2]
• 99% of the body’s Ca++ is stored as hydroxyapitite crystals
• Organic Matrix
• Collagen
• Ground Substance (contains many glycoproteins)

Bottom line for DAT:
The distinguishing feature of bone is ground substance and its extracellular matrix of collagen

Question 11

What does the axial skeleton consist of?

Answer 11

• Skull,
• Sternum
• Ribs,
• Vertebrae

Think the body’s axis

Question 12

What does the appendicular skeleton consist of?

Answer 12

• Bones of pelvic and pectoral girdle like arms, legs, feet, etc.

Think the body’s appendages and everything that facilitates the movements of appendages. Pelvis, collar bone, etc.

Question 13

What are ligaments?

Answer 13

Dense regular tissue that connects bone to bone

Question 14

What are tendons?

Answer 14

Dense regular tissue that connects bone to muscle

Question 15

What are joints?

Answer 15

Areas of contact, or areas near contact between two points

Question 16

What are the types of bone at a microscopic level?

Answer 16

Primary bone

Secondary bone

Question 17

What is primary bone?

Answer 17

At a microscopic level

• temporary bone usually replaced in adults
• first bone to form during fetal development and during bone repair
• random collagen arrangement
• present around tooth sutures always

Question 18

What is secondary bone

Answer 18

At a microscopic level

• Permanent bone
• What most adult bone is
• more ordered collagen arrangement in the extracellular matrix.

Question 19

What is the Haversian System?

Answer 19

The Haversian system is also called an Osteon

• Represents the functional unit of much of compact bone.
• Contains
• Osteocytes
• Lacunae
• Canaliculi
• Concentric Lamellae
• Haversian Canal

Pneumonic:
Oysters in the Lagoon: Osteocytes in the Lacunae
Bone canals: Canaliculi
Lamination: Lamellae
Aversion Canal: Haversian Canal is in the center trying to get away from everything.

Question 20

What are Lacunae?

Answer 20

• Spaces in bone occupied by bone cells called osteocytes

- One osteocyte occupies each lacuna

Question 21

What are Canaliculi?

Answer 21

• Cavities seen within bone matrix, serve as passages for substances and nutrient between the blood vessels and bone cells

Question 22

What are Lamellae?

Answer 22

• Concentric rings of matrix surrounding the Haversian canal

Question 23

What is an osteocyte?

Answer 23

• Its a bone cell.
• Formed when an osteoblast becomes embedded in the matrix it secretes.
• Found in a lacuna
• Has projections called canaliculi and can communicate with other osteocytes through these canals via gap junctions
• Does NOT undergo Mitosis

Question 24

What is the Haversian Canal?

Answer 24

It’s a large canal found in the middle of an osteon (Haversian System)

Nerves, Blood, and lymph vessels travel through here.

Question 25

What are Volkmann's canals?

Answer 25

- These are the connecting canals of compact bone. - They connect multiple Haversian canals together and help innervate and bring nutrients throughout compact bone - Filled with nerves, blood, and lymph vessels.

Question 26

What is an osteoblast?

Answer 26

- Found at the surface of bone - Mononucleated cells that build bone - Do NOT undergo Mitosis - They are fibroblasts (They make collagen) - They synthesize much of the organic matrix of the bone, thus exhibit an abundant amount of rough ER and Golgi - Arise from Mesenchymal stem cells - Become an osteocyte when they become trapped in the extracellular matrix they create.

Question 27

What is a mesenchymal stem cell?

Answer 27

- It is an embryonic connective tissue cell derived from mesoderm. - It is a stem cell that gives rise to a lot of different cell types including: * Osteoblasts * Myocytes (muscle cells) * Chondrocytes (cartilage cells) * Adipocytes (fat cells) - They also make growth factors

Question 28

What is an osteoclast?

Answer 28

- A member of the monocyte / macrophage family. - They break down bone (bone resorption) - Once they are finished they often die by apoptosis - These multinucleated cells have abundant lysosomes and mitochondria and are very large and motile - They occupy shallow depressions called Howship's lacunae that identify areas of bone reabsorption - Lysosomal enzymes such as gelatinase and collagenase are secreted by these cells which degrade the bone. - Does NOT undergo Mitosis

Question 29

What bone cells don't undergo Mitosis?

Answer 29

This is a common DAT question - Osteoclast - Osteoblast - Osteocyte

Question 30

What is an osteoprogenitor cell?

Answer 30

- It is derived from a primitive stem cell (mesenchymal) and differentiates into osteoblasts and osteocytes. - Found in the marrow, periosteum, and within the marrow cavity

Question 31

What is coupling?

Answer 31

An important DAT concept to understand - Osteoclasts break down some bone to "excavate" the area to form an absorption cavity. - Bone resorption stops - Osteoblasts now take over and build new bone. - This process of bone breakdown and rebuilding is called coupling - The process is important to help maintain calcium homeostasis as well as building adaptations to mechanical pressures exerted on bones.

Question 32

How does coupling differ in young people.

Answer 32

As you're still growing, bone growth exceeds resorption. Once the growth plates ossify then normal coupling proceeds with maintaining homeostasis of Ca++

Question 33

What is Acromegaly?

Answer 33

Excess growth hormone causes an increase in bone deposition without normal breakdown. Bones become very thick, especially in the face

Question 34

What is Osteoporosis?

Answer 34

- Osteporosis is a decrease in bone mass, which gets worse as estrogen levels decline. - Estrogen therapy could help this. - Bones become very fragile as osteoclastic activity exceeds bone deposition, thus making bones easy to break - Not getting enough calcium contributes to this issue, because bone is broken down for Ca++ and not built back up properly

Question 35

How are the thyroid and parathyroid involved in Ca++ homeostasis?

Answer 35

Decrease in Ca++ - When Ca++ levels decrease, the parathyroid gland releases parathyroid hormone which binds to hormone receptors on osteoblasts and causes them to stop building bone. - The Osteoblasts then secrete Osteoclast-Stimulating Factor, which induces Osteoclast formation and they start breaking down bone and releasing Ca++ into the body. Increase in Ca++ - When Ca++ levels increase, the thyroid gland secretes calcitonin which binds to hormone receptors on osteoclasts, inhibiting them from breaking down any more bone. - Osteoblasts start using the Ca++ to build more bone mass Summary: Low Ca++: Parathyroid -> Parathyroid Hormone -> Osteoblast Stop -> Osteoclast Stimulating Factor from Osteoblast -> Osteoclast GO! High Ca++: Thyroid -> Calcitonin -> Osteoclast stop

Question 36

Describe Cartilage

Answer 36

- Cartilage is a specialized connective tissue - Does not contain blood vessels, nerves, or lymphatics, but gets its nourishment from blood vessels of surrounding tissues by diffusion through the extracellular matrix. - Inorganic phase is like bone. It contains hydroxyapatite - Organic structure is very different from bone. It contains 80% water and the other 20% collagen and proteoglycans. - Cells called chondrocytes occupy small cavities called lacunae. - It's surrounded by a dense fibrous connective tissue called the perichondrium (around cartilage). - Since it has no blood supply, it has a very slow rate of mitotic activity, and if damaged, heals slowly and with difficulty.

Question 37

What are Chondrocytes?

Answer 37

- They are the cellular unit of cartilage | - They make collagen and molecules needed by the extracellular matrix

Question 38

What are the three different types of cartilage?

Answer 38

The three types of cartilage are: - Hyaline Cartilage - Elastic Cartilage - Fibrocartilage

Question 39

What is hyaline cartilage?

Answer 39

Hyaline cartilage is the most abundant type of cartilage - We find it in the: * Nose * Larynx * Part of the ribs * Trachea * Bronchi * Epiphyseal Plate - Reduces friction - Shock Absorber - Aids in Bone Movement

Question 40

What is Elastic Cartilage

Answer 40

- Elastic Cartilage is found in the pinna of the ear (outer ear) and the epiglottis (part of the larynx) - Principle protein is elastin - Allows for repeated bending

Question 41

What is fibrocartilage?

Answer 41

- Intervertebral discs, pubic symphysis, menisci, and Temporomandibular joint - Has tons of both Type I and Type II collagen fibers (only type that has both)

Question 42

What is cartilage derived from?

Answer 42

It's derived from mesenchyme, a stem cell that also can turn in to osteocytes and many other things. It's growth is dependent on somatotropin (growth hormone)

Question 43

What are the arm bones

Answer 43

- Humerus - Radius - Ulna

Question 44

What are the leg bones?

Answer 44

- Femur - Tibia - Fibula

Question 45

What are the foot and hand bones?

Answer 45

Hand: Carpals Foot: Tarsals

Question 46

What are the vertebral bones?

Answer 46

Lumbar, Thoracic, Vertebral, Sacrum, coccyx