Lecture 4 - ANP1106

Question 1

The Skeletal System

Answer 1

Provides a solid structure to protect & support the body
- Includes bone + cartilage tissue

Question 2

What are the functions of bone tissue ?

Answer 2

Support : Adapts to changes in increased force applied by stimulating remodeling to increase bone strength (denser matrix of calcium & fibers)
- Decreased force (immobilization, limb in a cast, paralysis) is detected & stimulates remodeling to decrease bone strength

Potection of fragile organs : Brain, heart, lungs, etc (encased in bony structure)

Anchorage for muscles : Assists in producing movement

Mineral storage : Drop in blood Ca will trigger parathyroid hormone release which stimulates osteoclasts to degrade bone & release calcium into the blood to restore normal levels
- Ca important for NS function

Blood cell formation : in red bone marrow

Fat storage : in yellow bone marrow

Hormone production : Osteocalcin, involved in bone remodeling + plays critical function in multiple physiological processes (eg. glucose metabolism)

Question 3

What are the functions of cartilage ?

Answer 3

• Providing flexible support – Bends rather than breaks [ Can bend a little unlike bone ]
• Providing a smooth + compressible surface for articulations – Allows joint to “slip” smoothly during flexion / extension / other movements
• Provides a matrix for the development of bone – Some bones produced from matrix of cartilage

Question 4

What are the cells of bone tissue ?

Answer 4

Osteogenic cell (stem cells) – Forms osteoblasts ; give rise to cells that will build & maintain bone
⬇
Osteoblast – Bone growth, development (esp during childhood)
Matrix-synthesizing cell
⬇
Osteocyte – Repair + maintain health of mature bone
- Mature bone cell
- Monitors & maintains mineralized bone matrix
- Deposits bone (change shape)
⬇
Osteoclast – Bone-resorbing cell
Removes bone (change shape) unnecessary for the force being experienced
Remodels mature bone together w/ osteocyte

Question 5

The architecture of all bones includes …

Answer 5

• Outer compact bone
• Spongy (trabecular) bone

Question 6

What are characteristics of the outer bone ?

Answer 6

Forms a dense outer layer of all bones

• Design consists of a structural unit called the osteon (haversian) system
• Formed of elongated cylinders (osteons) oriented parallel to the long axis of bone, containing several hollow tubes of bone matrix arranged like the rings of a tree (each ring is called a lamella)
• Osteocytes (mature bone cells) are between the lamellae in small cavities called lacunae → which are all interconnected by very small canals (canaliculi) which allow the passage of ECF
• Center of an osteon has a larger central canal for passage of larger blood vessels, allows blood supply to flow along the long axis of the bone
• Blood flow perpendicular to haversian canal / long axis is provided by perforating volkmann’s canals (allows blood to reach all parts of the bone)

★ Several osteons are packed together but their cylindrical shape leaves spaces that are filled with interstitial lamellae
★ Entire structure covered by circumferential lamellae which form sheets of bone

Question 7

What are characteristics of the spongy inner (trabecular) bone ?

Answer 7

Forms the inner core of bones

Sponge-like appearance (trabeculae) w/ spaces containing red marrow for forming RBCs + yellow marrow for storing fat

• Bony trabeculae are only a few cell layers thick, irregularly shaped + contain osteocytes in lacuna interconnected by canaliculi
• Nutrients from blood vessels that need to supply osteocytes diffuse into the marrow spaces of the trabeculae & pass through canaliculi to reach all the osteocyte cells throughout bone

Question 8

How does bone strength increase ?

Answer 8

The trabeculae are continually remodeled along lines of stress to give sufficient bone strength

• When new forces applied in new direction → Causes microscopic breaks in bone that cannot be felt / seen on xrays → Detected by osteocytes → Strengthen the bone (adds more bone)
• Exercises (either weight-bearing forces or resistance) → Forces cause microscopic breaks in bone which are repaired by osteocytes to give stronger bones

Question 9

How does bone strength decrease ?

Answer 9

If you immobilize bone, no longer receiving tension / stress → Bone will be reduced in strength to accommodate

Ttrabeculae excessive to force / stress applied will be removed …

• Older adults more sedentary → Bones become more fragile, so slips / falls become forces strong enough to break the bone (Injuries may occur more frequently as a result)

Question 10

What are the connective tissue linings covering the bone ?

Answer 10

Periosteum – Outside, covers bone with an outer fibrous layer and inner osteogenic (bone forming) layer
- Inner layer can regenerate bones so that when bone breaks, there are cells that will form osteoblasts to repair bone

Endosteum – Lines osteon canals of compact bone & trabeculae of spongy bone

Question 11

Bones are classified by ___________

Answer 11

shape

Question 12

Classification of bones

Answer 12

Long bones – Much longer than wide with a shaft (diaphysis), formed mostly of compact bone with a yellow marrow cavity for fat storage
- 2 ends [ epiphyses ] formed of compact and spongy bone covered with hyaline cartilage for joints
- Junction between shaft & end / epiphyses called an epiphyseal line in an adult bone –
- Adolescents have cartilage between end of long bone & shaft which forms epiphyseal growth plate, becomes calcified in adulthood

Irregular bones – Primarily spongy bone containing marrow with a thin covering of compact bone (eg. vertebrae, hip bones)

Flat bones – Thin, flat, sometimes curved bones (eg. skull bones, ribs, breastbone) formed of a compact bone exterior + a spongy bone interior with marrow between trabeculae

Short bones – Roughly cube-shaped (eg. wrist, ankle bones) formed primarily of spongy bone with marrow covered by a thin outer layer of compact bone

Question 13

What is the process of osteogenesis / ossification ?

Answer 13

Includes formation of the bony skeleton in embryos, growth of bones to maturity & remodelling or repair of bones in adults, 2 types :
- Intramembranous ossification
- Endochondral ossification

Question 14

Intramembranous ossification

Answer 14

Ossification occurring within a membrane

• At about 8 weeks of embryonic development the flat bones of the skull (cranium) + clavicles develop from a fibrous CT membrane containing mesenchymal cells which differentiate into bone forming cells (osteoblasts)
• Bone gradually consumes all CT to form compact & spongy bone

Question 15

Endochondral ossification

Answer 15

For all bones below the skull except the clavicle

• Starts at 2nd month of development via replacement of hyaline cartilage

Question 16

T/F : Some facial bones (nose, lower jaw, etc) will continuously grow throughout life

Answer 16

TRUE

Does not grow at same pace (otherwise have very long noses / chins)

Question 17

During infancy and adolescence or early adulthood, long bones lengthen by ________________ which occurs entirely by growth from the ___________________

Answer 17

interstitial growth, epiphyseal plates

• Longitudinal growth ends when bone tissue of the epiphysis and diaphysis fuses (epiphyseal plate closure) to form the epiphyseal line which occurs about age 18 in females or age 21 in males because the chondroblasts reproduce more slowly and get replaced by bones

Question 18

Appositional Growth

Answer 18

• All bones grow in width by appositional growth where osteoblasts on the periosteal side of periosteum secrete bone matrix to make bone wider while osteoclasts on the endosteal side will remove bone matrix (becomes wider but NOT thicker, inner part being removed by osteoclasts)

Question 19

What are the steps of a fracture repair ?

Answer 19

1. Bleeding stimulates the formation of a hematoma, death of oxygen-deprived bone cells (no circulation, no oxygen being delivered to cells so they die), & inflammation which causes pain
2. The hematoma is transformed into a soft fibrocartilaginous callus that is invaded by blood vessels bringing macrophages to clean up the area (remove some soft dead cells) then osteoclasts resorb damaged bone while fibroblasts release fibrous tissues, chondroblasts form cartilage, and osteoblasts convert cartilage → bone tissue –> get busy laying down tissue components to span the break
3. Conversion of the fibrocartilaginous callus into a trabecular bone callus (usually requires 2 months to stabilize bone in a hard / soft cast)
4. Bone remodelling to regain original shape by removal of any extra bony material & converting trabecular bone callus into original compact bone (process can take a few years to completely regain original shape, but already gets very strong after 2 months)

Question 20

What is osteoporosis ?

Answer 20

When bone resorption outpaces bone formation so the bone becomes porous (much weaker, may ore easily break)

• Occurs mostly in the neck of the femur + bones of the spine
• Such loss of bone occurs with insufficient exercise (reduced stress to bones promoting bone remodeling → removal of excess strength not needed), a diet poor in calcium and protein, abnormal vitamin D receptors, and smoking (reduces estrogen levels which normally inhibits bone resorption)
• Age reduces estrogen & testosterone levels so there is less restraint on osteoclast bone resorption and less promotion of osteoblast / osteocyte bone deposition
• Can be countered by increasing stress to the bone (exercise)

Question 21

What is cartilage ?

Answer 21

Strong + flexible with properties in between CT & bone

• Composition includes ground substance (all components of the extracellular matrix except for fibrous materials) with lots of glycosaminoglycans, chondroitin sulfate, and hyaluronic acid held together with chondronectin (adhesive protein). The matrix also includes collagen fibers (can have some elastic fibers as for the ear to increase flexibility)

Cartilage is 80% water but is devoid of blood vessels & nerves – Results in poor repair, no nociceptors to sense pain

Cartilage is covered by perichondrium – Dense layer of fibrous CT that can form scar tissue following damage to cartilage, 2 types
- Chondroblasts – Immature cartilage cells that actively form cartilage, correspond to osteoblasts
- Chondrocytes – Mature cartilage cells found in lacunae that maintain cartilage, correspond to osteocytes

Question 22

What are the 3 types of cartilage ?

Answer 22

• Hyaline cartilage
• Elastic cartilage
• Fibrocartilage

Question 23

Hyaline Cartilage

Answer 23

Most abundant

• Glassy blue-white appearance, has chondrocytes in the center forming only 1-10% of the volume, and is firm but pliable because of the collagen fibers
• Found in embryonic skeleton, articular ends of long bones (also epiphyseal plates in growing children), costal cartilages of ribs, cartilages of nose, trachea, and larynx
• Its role is to provide support + cushioning during compressive stress

Question 24

Elastic Cartilage

Answer 24

Like hyaline cartilage but with more elastic fibers
- Found in the external ear and epiglottis
- Role is to allow bending & the return to its original shape (elastic fibers allow more flexing than hyaline)

Question 25

Fibrocartilage

Answer 25

• Appears as rows of chondrocytes & lacunae alternating with rows of thick collagen fibers producing a structure intermediate between hyaline cartilage and dense regular CT
• Found in the intervertebral discs, pubic symphysis, and discs of knee joints where hyaline cartilage meets a ligament or a tendon
• Role is to provide tensile strength (resist pulling/pushing) with the ability to absorb stress (resist compression) much more than hyaline