Week 11 - Bone Biology

Question 1

What are the 6 important functions of bone

Answer 1

1. Provides support
2. Protects the internal organs (brain, heart, ect)
3. Assists body movements (in conjunction with muscles)
4. Stores and releases salts of calcium and phosphorus
5. Participates in blood cell production (haemopoiesis)
6. Stores triglycerides in adipose cells of yellow marrow

Question 2

What are the typical features of long bone

Answer 2

• Diaphysis (bone shaft)
• 2 epiphyses (both ends of the bone at the joints)
• 2 metaphysis (region between diaphysis and epiphysis)
• Articular cartilage covering both epiphyses
• Periosteum (connective tissue surrounding the diaphysis)
• Medullary cavity (hollow space within diaphysis)
• Endosteum (thin membrane lining the medullar cavity)

Question 3

What is the diaphysis

Answer 3

bone shaft

Question 4

what are epiphyses

Answer 4

the ends of the bone at the joint

Question 5

what is the metaphysis

Answer 5

region between diaphysis and epiphysis

Question 6

what is periosteum

Answer 6

connective tissue surrounding the diaphysis

Question 7

what is medullary cavity

Answer 7

hollow space within diaphysis

Question 8

what is endosteum

Answer 8

thin membrane lining the medullar cavity

Question 9

What are the different bone cells

Answer 9

• Osteoprogenitor cells:
• Osteoblasts
• Osteocytes:
• Osteoclasts:

Question 10

what are osteoprogenitor cells

Answer 10

bone stem cells able to differentiate into other types of cells

Question 11

what are osteoblasts

Answer 11

cells which build bone by secreting matrix

• B for building

Question 12

what are osteocytes

Answer 12

mature bone cells which maintain bone tissue

Question 13

what are osteoclasts

Answer 13

cells which resorb bone by secreting acids and enzymes to dissolve bone matrix promoting bone resorption (normal part of bone homeostasis)

c for carving bone

Question 14

what is the process of bone formation called

Answer 14

ossification

Question 15

what are the 2 forms of ossification

Answer 15

1. intramembranous ossification
2. endochondral ossification

Question 16

what is intramembranous ossification

Answer 16

• Occurs in flat bones (e.g., skull) when a connective tissue membrane is replaced by bone
• Bone forms directly from mesenchymal tissue.

Question 17

What is endochondral ossification

Answer 17

• Replaces cartilage with bone in embryos and fetuses.
• Also occurs at epiphyseal plates of long bones during growth.

Question 18

what is bone formation like in childhood/adolescence

Answer 18

Bone formation > resorption.

Question 19

what is bone formation like in adulthood

Answer 19

balanced bone formation and resorption

Question 20

what is bone formation like in aging/postmenopause

Answer 20

Resorption > deposition → ↓ bone mass.

Question 21

What are the 2 main physiological processes which regulate bone remodeling

Answer 21

o Calcium homeostasis
o Mechanical and gravitational stress

Question 22

what secretes parathyroid hormone (PTH)

Answer 22

chief cells in the parathyroid gland

Question 23

when does the parathyroid gland secrete parathyroid hormone (PTH)

Answer 23

when calcium drops

Question 24

What is the function of parathyroid hormone (PTH)

Answer 24

increases osteoclasts activity which releases calcium as bone is broken down (bone in 99% calcium)

o Stimulates kidney to produce calcitriol → boosts Ca²⁺ absorption in intestines

Question 25

what is hypercalcemia

Answer 25

high levels of Ca2+ in the blood

Question 26

what is hypocalcemia

Answer 26

low levels of Ca2+ in the blood

Question 27

what does prolonged low Ca2+ causes

Answer 27

parathyroid hypertrophy (e.g., rickets).

Question 28

What is the chemical composition of bone

Answer 28

* 70% mineral (hydroxyapatite): Ca₁₀(PO₄)₆(OH)₂ * 30% organic matrix: o 90–95% collagen o Rest is ground substance

Question 29

what is the average daily intake of calcium

Answer 29

* Average daily intake: ~1000 mg from diet (mostly dairy) – 1L of milk (approx. same for phosphorus)

Question 30

where is calcium lost

Answer 30

in intestinal cells (~250 mg).

Question 31

What is the function of vitamin D (calcitriol)

Answer 31

* Increases Ca²⁺ absorption from gut. * Enhances bone deposition and resorption. * Stimulates calbindin synthesis in intestinal cells. * Also: o Increases phosphate absorption. o Decreases renal excretion of Ca²⁺ and phosphate.

Question 32

what is the effect of vitamin D (calcitriol) on bone

Answer 32

Bone resorption - Absence of Vit D causes role of PTH to be greatly diminished or even prevented Bone deposition - Smaller quantities of Vit D promotes bone calcification. Intestinal effect but also enhances mineralization of bone

Question 33

where is vitamin D (calcitriol) produced

Answer 33

* Produced in kidneys under control of PTH. * Without PTH or kidney function → no calcitriol synthesis.

Question 34

what is the function of medication bisphosphonates

Answer 34

o Enzyme-resistant analogues of pyrophosphate. o Inhibit osteoclast attachment to bone. o Prevent resorption; used in osteoporosis and cancers.

Question 35

What is the function of medication denosumab

Answer 35

o Human monoclonal antibody to RANKL. o Inhibits osteoclast formation.

Question 36

how does the process of bone resorption occur

Answer 36

- PTH binds to osteoblasts which then release key signaling molecules - releases RANKL which binds to RANK receptor on pre-osteoclasts stimulating their differentiation into active osteoclasts which causes bone resorption - also releases M-CSF which helps osteoclasts precursors survive and multiply

Question 37

what does osteoblasts release when PTH binds

Answer 37

RANKL M-CSF

Question 38

Function of RANKL

Answer 38

Stimulates osteoclast differentiation into active osteoclasts

Question 39

what is the function of M-CSF

Answer 39

Promotes osteoclast precursor survival.

Question 40

what is OPG (osteoprotegerin)

Answer 40

- decoy receptor made by osteoblasts - it binds to RANKL preventing it from activating RANK - inhibits osteoclast formation protecting bone from excessive breakdown

Question 41

Function of calcitonin

Answer 41

- inhibits osteoclast activity - works in opposition to PTH - lowers Ca2+ levels in blood

Question 42

what releases calcitonin

Answer 42

thyroid gland

Question 43

What is osteonecrosis of the jaw (ONJ)

Answer 43

bone death due to lack of blood supply. In ONJ, this happens specifically in the jawbone. * Rare complication. * Risk factors: o High-dose IV bisphosphonates (used in cancer treatment). o Radiation therapy. o Bone infection (osteomyelitis).

Question 44

What regulates calcium in the body

Answer 44

* Regulated by PTH, calcitriol, and calcitonin. * Involves coordinated actions of: o Bone (resorption/deposition) o Kidneys (reabsorption/excretion) o Intestines (absorption)

Question 45

What controls the formation of calcitriol

Answer 45

concentration of Ca2+ - inverse relationship