Bone Flashcards
1
Q
What are the characteristics of bone?
A
- 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
2
Q
What is the percentage breakdown of subtypes of bone and their characteristics?
A
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.
3
Q
Epiphysis
A
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.
4
Q
Metaphysis
A
Region that contains the growth plate.
Columns of spongy tissue is found
5
Q
Diaphysis
A
Body or shaft of the bone
6
Q
Medullary Cavity
A
The Medullary cavity is also called the Marrow cavity.
Enclosed by cortical bone, this is where the marrow resides.
7
Q
What are the two types of bone marrow?
A
Red Marrow
Yellow Marrow
8
Q
What is red marrow?
A
- 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)
9
Q
What is yellow marrow?
A
- Fat tissue
- May convert to red marrow if blood loss is severe
10
Q
What is the structure of bone?
A
- 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
11
Q
What does the axial skeleton consist of?
A
- Skull,
- Sternum
- Ribs,
- Vertebrae
Think the body’s axis
12
Q
What does the appendicular skeleton consist of?
A
- 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.
13
Q
What are ligaments?
A
Dense regular tissue that connects bone to bone
14
Q
What are tendons?
A
Dense regular tissue that connects bone to muscle
15
Q
What are joints?
A
Areas of contact, or areas near contact between two points
16
Q
What are the types of bone at a microscopic level?
A
Primary bone
Secondary bone
17
Q
What is primary bone?
A
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
18
Q
What is secondary bone
A
At a microscopic level
- Permanent bone
- What most adult bone is
- more ordered collagen arrangement in the extracellular matrix.
19
Q
What is the Haversian System?
A
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.
20
Q
What are Lacunae?
A
- Spaces in bone occupied by bone cells called osteocytes
- One osteocyte occupies each lacuna
21
Q
What are Canaliculi?
A
- Cavities seen within bone matrix, serve as passages for substances and nutrient between the blood vessels and bone cells
22
Q
What are Lamellae?
A
- Concentric rings of matrix surrounding the Haversian canal
23
Q
What is an osteocyte?
A
- 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
24
Q
What is the Haversian Canal?
A
It’s a large canal found in the middle of an osteon (Haversian System)
Nerves, Blood, and lymph vessels travel through here.
25
What are Volkmann's canals?
- 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.
26
What is an osteoblast?
- 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.
27
What is a mesenchymal stem cell?
- 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
28
What is an osteoclast?
- 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
29
What bone cells don't undergo Mitosis?
This is a common DAT question
- Osteoclast
- Osteoblast
- Osteocyte
30
What is an osteoprogenitor cell?
- 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
31
What is coupling?
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.
32
How does coupling differ in young people.
As you're still growing, bone growth exceeds resorption. Once the growth plates ossify then normal coupling proceeds with maintaining homeostasis of Ca++
33
What is Acromegaly?
Excess growth hormone causes an increase in bone deposition without normal breakdown.
Bones become very thick, especially in the face
34
What is Osteoporosis?
- 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
35
How are the thyroid and parathyroid involved in Ca++ homeostasis?
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
36
Describe Cartilage
- 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.
37
What are Chondrocytes?
- They are the cellular unit of cartilage
| - They make collagen and molecules needed by the extracellular matrix
38
What are the three different types of cartilage?
The three types of cartilage are:
- Hyaline Cartilage
- Elastic Cartilage
- Fibrocartilage
39
What is hyaline cartilage?
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
40
What is Elastic Cartilage
- 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
41
What is fibrocartilage?
- Intervertebral discs, pubic symphysis, menisci, and Temporomandibular joint
- Has tons of both Type I and Type II collagen fibers (only type that has both)
42
What is cartilage derived from?
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)
43
What are the arm bones
- Humerus
- Radius
- Ulna
44
What are the leg bones?
- Femur
- Tibia
- Fibula
45
What are the foot and hand bones?
Hand: Carpals
Foot: Tarsals
46
What are the vertebral bones?
Lumbar, Thoracic, Vertebral, Sacrum, coccyx
