Histology of Bone and Cartilage

Question 1

_ is a flexible, deformable material that serves as resilient, smooth-gliding surface for the movement of our joints; cushions places where bone might rub against bone

Answer 1

Cartilage is a flexible, deformable material that serves as resilient, smooth-gliding surface for the movement of our joints; cushions places where bone might rub against bone

Question 2

Bone is the rigid structural framework of our body but also serves to _, _ , _, _

Answer 2

Bone is the rigid structural framework of our body but also serves to
1. Store calcium
2. House bone marrow
3. Synthesize blood cells
4. Aid in the removal of toxins

Question 3

Bones are divided into three regions:

Answer 3

1. Diaphysis: center component
2. Epiphysis: outer components
3. Metaphysis: boarders the diaphysis

Question 4

The _ functions as the main shaft of the bone; it is hollow and contains _ and _

Answer 4

The diaphysis functions as the main shaft of the bone
* It is hollow and contains nutrient arteries and yellow bone marrow (within the medullary cavity)

Question 5

We have a distal and proximal _ at each end of the bone; the articular surface of these is covered with cartilage

Answer 5

We have a distal and proximal epiphysis at each end of the bone; the articular surface of these is covered with cartilage

Question 6

The _ section of bone contains the cartilage growth plate in children, where bones will lengthen through adolescence

Answer 6

The metaphysis section of bone contains the cartilage growth plate in children, where bones will lengthen through adolescence
* The metaphysis is the interphase btwn epiphyses and diaphysis

Question 7

The _ and _ regions of bone contain extensive networks of spongy bone

Answer 7

The epiphysis and metaphysis regions of bone contain extensive networks of spongy bone

Question 8

The hard outer surface of the bone is covered by a dense membrane called _

Answer 8

The hard outer surface of the bone is covered by a dense membrane called periosteum

Question 9

The interior surface of the bone is covered by a thin vascular layer called _

Answer 9

The interior surface of the bone is covered by a thin vascular layer called endosteum

Question 10

Red bone marrow is the location of _

Answer 10

Red bone marrow is the location of blood cell production

Question 11

Yellow bone marrow is the site for _

Answer 11

Yellow bone marrow is the site for fat storage and mesenchymal cells
* Mesenchymal cells are the precursors to bone, fat, cartilage, muscle cells

Question 12

At birth, the whole skeleton is filled with only _ marrow

Answer 12

At birth, the whole skeleton is filled with only red bone marrow; as we age some of this gets converted to yellow marrow

Question 13

In adults the red bone marrow is in _ and the yellow marrow is in _

Answer 13

In adults:
* Red marrow: epiphysis and metaphysis
* Yellow marrow: diaphysis

By the time we turn 25, red marrow is mostly in the axial skeleton and yellow marrow is in the diaphysis of long bones like the femur

Question 14

Cartilage has a low metabolic rate and diminished healing ability; why?

Answer 14

Cartilage is avascular and receives most of its nutrients through diffusion

Question 15

How is cartilage formed?

Answer 15

Mesenchymal cells differentiate into chondroblasts –> chondroblasts secrete the cartilage matrix and get trapped in lucunae –> once trapped they are now chondrocytes

Question 16

What is the perichondrium?

Answer 16

Perichondrium is a dense outer layer surrounding the cartilage; it contains collagen and gives cartilage the ability to grow/repair

Question 17

Recall that the three types of cartilage are _, _ , _

Answer 17

Recall that the three types of cartilage are hyaline, elastic, fibrocartilage
* Hyaline cartilage is most abundant

Question 18

Hyaline cartilage is strong; its matrix consists of _ and _

Answer 18

Hyaline cartilage is strong; its matrix consists of chondroitin sulfate and type II collagen

Question 19

Where do we find hyaline cartilage?

Answer 19

Hyaline cartilage
* Articular surfaces of joints = articular cartilage
* Trachea
* Bronchi

Question 20

What does hyaline cartilage look like?

Answer 20

Hyaline cartilage has a glassy, smooth appearance

Question 21

The matrix of elastic cartilage is composed of _ and _

Answer 21

The matrix of elastic cartilage is composed of type II collagen and chondroitin sulfate
* (Like hyaline cartilage) but also contains elastic fibers!
* Give it elasticity

Question 22

Where do we find elastic cartilage?

Answer 22

Elastic cartilage:
* Pinnae of ear
* Epiglottis
* Nose

Question 23

Fibrocartilage is specialized to resist _ and _ forces

Answer 23

Fibrocartilage is specialized to resist compressive and pulling forces
* Found in the meniscus, annulus fibrosis, pubic symphysis

Question 24

What does fibrocartilage look like?

Answer 24

Fibrocartilage has abundant type I collagen –> fibrous appearance
* The chondrocytes in their lucunae seem to line up in distinct rows, interspersed with fibers

Question 25

Our compact bone is known as _

Answer 25

Our compact bone is known as **cortical bone**

Question 26

Our spongy or cancellous bone is known as _

Answer 26

Our spongy or cancellous bone is known as **trabecular bone**

Question 27

Cortical bone lies in _ region of the bone

Answer 27

Cortical bone lies in **outer regions and surface** of the bone * Makes up about 80% of bone mass

Question 28

Trabecular bone can be found in _ region

Answer 28

Trabecular bone can be found as **porous network of bone in the interior** * 20% bone mass * Larger surface area than cortical bone * Specialized functions; bone marrow occupies the spae between porous network

Question 29

Where do we find osteoblasts, the cells that synthesize and mineralize bone?

Answer 29

**Osteoblasts** line the *surface of bony trabeculae* ; they are here to synthesize and mineralize bone *They also signal to the osteocytes to break down bone*

Question 30

Osteoblasts secrete components of the bony matrix, including _, _, _

Answer 30

Osteoblasts secrete components of the bony matrix, including: 1. **Type I collagen** 2. **Osteopontin** 3. **Osteocalcin**

Question 31

When osteoblasts become entrapped in the bony matrix, they become _

Answer 31

When osteoblasts become entrapped in the bony matrix, they become **osteocytes** * Osteocytes are the most numerous cell type * They sit in the **lacunae** within bone * Involved in the **maintanance of bone**

Question 32

The osteoclasts break down and digest the bony matrix; they are found in _ region

Answer 32

The **osteoclasts** break down and digest the bony matrix; they are found **on the surface of bone** in little indentations called **Howship lacunae**

Question 33

Howship lacunae house _ type cells

Answer 33

**Howship lacunae** house the **osteoclasts**

Question 34

What do osteoclasts look like?

Answer 34

**Osteoclasts** are huge, multi-nucleated cells, found on the surface of bone * Look for howship lacunae

Question 35

After osteoclasts move around inside the bone and get stimulated to resorb bone by the osteoblasts, what do they do next?

Answer 35

1. After osteoclasts move around inside the bone and get stimulated to resorb bone by the osteoblasts 2. They **seal off an area of bone surface --> secrete enzymes to dissolve that bone --> ingest remnants by phagocytosis**

Question 36

The functional unit of cortical bone is called the _

Answer 36

The functional unit of cortical bone is called the **osteon**

Question 37

Osteons are several layers of _

Answer 37

**Osteons** are several layers of **osteocytes** that form a tree ring-like structure with intervening layers of bone matrix called **lamellae**

Question 38

Lamellae wrap around the _ , a central canal that contains one-two capillaries

Answer 38

Lamellae wrap around the **Haversian canal** , a central canal that contains one-two capillaries

Question 39

Haversian canals communicate with periosteal vessels via a perforating channel called _

Answer 39

Haversian canals communicate with *periosteal vessels* via a perforating channel called **Volkmann canals**

Question 40

The bone matrix gets its tensile strength from _ It gets compressive strength through _

Answer 40

* The bone matrix gets its tensile strength from **type I collagen** (organic) * It gets compressive strength through **inorganic compounds like hydroxyapatite**

Question 41

_ are tiny "canals" where the cytoplasmic extensions of the osteocytes spread; they allow osteocytes to send chemical messages to each other

Answer 41

**Canaliculi** are tiny "canals" where the cytoplasmic extensions of the osteocytes spread; they allow osteocytes to send chemical messages to each other

Question 42

What role do canaliculi play during remodeling?

Answer 42

During remodeling *canaliculi* enable the chemical messages from damaged tissue to lead osteoclasts to the site of damage

Question 43

The general scheme of bone formation is an initial formation of _ , which forms the network for the deposition of _ to form the final bone

Answer 43

The general scheme of bone formation is an initial formation of **extracellular matrix** , which forms the network for the deposition of **minerals (calcium, phosphate, magnesium)** to form the final bone * The ECM is made of type I collagen + other proteins like sialoprotein, osteocalcin, decorin * Noncollagen proteins are essential for mineralization

Question 44

Endochondral ossification is _

Answer 44

**Endochondral ossification** is **formation of bone within cartilage** * It is how most long bones form

Question 45

Intramembranous ossification is _

Answer 45

**Intramembranous ossification** is formation of bone directly from *mesenchymal tissue* * How most cranial and flat bones form

Question 46

What are the general steps of endochondral ossification?

Answer 46

**Endochondral ossification**: 1. Blood vessels in the *perichondrium* surround the cartilage model --> they bring osteoblasts in --> **osteoblasts deposit the bone collar** 2. The bone collar causes the **chondrocytes to die** (nutrients can't diffuse) --> blood vessels penetrate the space + osteoblasts to **form the primary ossification center**; the perichondrium is now the periosteum 3. Bone invades the diaphysis --> **cartilage between the diaphysis and epiphysis lengthens the bone** 4. **Secondary ossification centers** form on the epiphyses 5. Remaining cartilage becomes *articular cartilage*; **epiphyseal growth plate closes** eventually (late adolescence)

Question 47

Achondroplasia is an autosomal dominant inherited disorder that leads to abnormal _

Answer 47

Achondroplasia is an autosomal dominant inherited disorder that leads to abnormal **endochondral ossification** * Long bones don't develop properly * Intramembranous ossification is normal --> head normal size

Question 48

The primary ossification center forms in the _ region

Answer 48

The primary ossification center forms in the **diaphysis** region

Question 49

The secondary ossification center forms in the _ region

Answer 49

The secondary ossification center forms in the **epiphyses**

Question 50

_ are multipotent cells that can differentiate into several connective tissue types (osteoblasts, chondrocytes, myocytes, adipocytes)

Answer 50

**Mesenchymal stem cells** are multipotent cells that can differentiate into several connective tissue types (osteoblasts, chondrocytes, myocytes, adipocytes)

Question 51

Most mesenchymal cells in adults are found in the _

Answer 51

Most mesenchymal cells in adults are found in the **bone marrow** and **adipose tissue**

Question 52

What are the steps of intramembranous ossification?

Answer 52

**Intramembranous ossification** 1. Some mesenchymal cells differentiate into osteogenic cells (and capillaries) --> differentiate into osteoblasts and form clusters called **ossification centers** 2. Osteoblasts **secrete osteoid** and become entrapped --> now they are **osteocytes** 3. Clusters of **osteoid unite to form a trabecular network around the capillaries**; the superficial surface of trabecular bone forms periosteal layer containing osteoblasts 4. Periosteal layer creates **compact bone layer**

Question 53

Osteoclasts come in to remodel bone; they will attach to the _ and secrete a variety of _

Answer 53

Osteoclasts come in to remodel bone; they will attach to the **osteon** and secrete a variety of **collagenases** * Collagenases release calcium, phosphate, magnesium into the blood

Question 54

_ is the hormone regulating osteoclast activity

Answer 54

**Parathyroid hormone** is the hormone regulating osteoclast activity * Main stimulator of bone resorption * Indirect stimulation (through osteoblasts)

Question 55

PTH first stimulates _ to release signaling molecules called _ that will stimulate osteoclast activity

Answer 55

PTH first stimulates **osteoblasts** to release signaling molecules called **RANK ligand** that will stimulate osteoclast activity

Question 56

Aside from RANK ligand, osteoclasts are also directly stimulated by _

Answer 56

Aside from RANK ligand, osteoclasts are also directly stimulated by **interleukin 6 (IL-6)** * Important in osteoporosis pathology in women

Question 57

Osteoclasts are repressed by _ and _

Answer 57

Osteoclasts are repressed by **calcitonin** and **calcitriol**

Question 58

Primary hyperparathyroidism can lead to _

Answer 58

**Primary hyperthyroidism** is caused by *overactive parathyroid gland* that can lead to * Hypercalcemia * Bone fractures