WEEK 2 - Osseous Tissue

Question 1

important functions of bones

Answer 1

1. support: for body and soft organs
2. protection: protects the brain, spinal cord, and vital organs
3. movement: levers for muscle action
4. storage: calcium and phosphorus, and growth factors
5. blood cell formation: hematopoiesis: occurs in red marrow cavities of certain bones
6. hormone production: osteocalcin: is secreted by bones and helps regulate insulin secretion, glucose levels and metabolism

Question 2

types of bone cells
1. osteoprogenitor

Answer 2

• a stem cell and lives in the periosteum (membrane that covers the bone) and endosteum (inside the bone, lines marrow cavity)

Question 3

2. osteoblast

Answer 3

• make the ECM and all of collagen, they can divide
  gets trapped in matrix to form osteocyte

Question 4

3. osteocyte

Answer 4

• a mature bone cell that monitors and maintains the bone matrix

Question 5

4. osteoclast (like a macrophage)

Answer 5

• cell that breaks down tissue and releases Ca2+
  multi-nucleated

Question 6

inorganic component of bones

Answer 6

hydroxyapatite/mineral salts: calcium phosphate crystals sticks to collagen and makes bone hard and resists compression, lasts long after death due to mineral composition

Question 7

bone development

Answer 7

ossification (osteogenesis) process of bone tissue formation, begins in month 2 of development, before that is all cartilage

Question 8

intramembranous ossification

Answer 8

• skull, jaw and clavicle are not cartilage, grow from CT

Question 9

endochondral ossification

Answer 9

everything else, start off as hyaline cartilage

Question 10

endochondral ossification in a long bone (week 9)

Answer 10

bone collar formed around the diaphysis because osteoblasts secrete the matrix
chondrocytes in the middle of this bone collar die, it is called the primary ossification centre, hole is formed and tissue calcifies
cartilage calcifies in the centre, cavity develops

Question 11

cont.

Answer 11

periosteal bud (hole) enters the cavity and spongy bone is formed in the middle
secondary ossification centres appear in the epiphysis (growth on ends), same events except the hole is not made

Question 12

at birth

Answer 12

hyaline cartilage remains in two places: epiphyseal plate and articular cartilages

Question 13

post natal bone growth

Answer 13

the epiphyseal plate does not change sizes because new cartilage forms on the epiphyseal side and then chondrocytes become bone or die on the diaphysis side

Question 14

epiphyseal growth plate

Answer 14

resting zone:
- chondrocytes are resting

proliferation zone:
- cartilage cells undergo mitosis
- fresh chondrocytes, estrogen stimulates

hypertrophic zone:
- older cartilage cells enlarge

calcification zone:
- matrix becomes calcified, cartilage cells die, the matrix begins to deteriorate

ossification zone:
- blood vessels bring osteoclasts and degrade the calcified matrix and osteoblasts secrete new bone matrix, medullary cavity grows

Question 15

when does it stop?

Answer 15

puberty: low levels of oestrogen activate growth spurt
near the end of adolescence: chondroblasts divide less often
epiphyseal plate thins
high levels of estrogen causes epiphyseal plate closure: epiphysis and diaphysis fuse
bone lengthening ceases
females: 18 yrs
males: 21 yrs

Question 16

bone remodelling occurs

Answer 16

• bone resorption (breakdown) done by osteoclasts
• osteoclasts bind bone and seal edge, secrete H+ and lysosomal enzymes and the material is endocytose and absorbed by blood, then osteoclast dies
• bone deposition (production) done by osteoblasts
• osteoblasts secrete the ECM called osteoid (collagen)
• collagen binds calcium and phosphate ions and forms crystals thus more minerals/hydroxyapatites
• osteoblasts get trapped thus osteocytes form

Question 17

bone disorders

Answer 17

• Imbalances between bone deposit and bone resorption underlie nearly every disease that affects the human skeleton.

Three major bone diseases:
- Osteomalacia and rickets
- Osteoporosis
- Paget’s disease

Question 18

osteomalacia (called this in adults)

Answer 18

• Bones are poorly mineralised
• Osteoid is produced, but calcium salts are not adequately deposited
• Results in soft, weak bones
• Pain upon bearing weight

Question 19

rickets (osteomalacia of children)

Answer 19

• Results in bowed legs and other bone deformities because bone ends are enlarged and abnormally long
• Cause: vitamin D deficiency or insufficient dietary calcium

Question 20

osteoporosis

Answer 20

• is a group of diseases in which bone resorption exceeds deposition
• Matrix remains normal, but bone mass declines
• Bones become porous and light to due the absence of density

Question 21

osteoporosis risk factors

Answer 21

• most often aged, postmenopausal women, affect 30% of women aged 60–70 years and 70% by age 80
• estrogen plays a role in bone density, so when levels drop at menopause, women run a higher risk
• men are less prone due to protection from the effects of testosterone

Question 22

osteoporosis treatment

Answer 22

Traditional treatments include:
- Calcium
- Vitamin D supplements
- Weight-bearing exercise

• Hormone replacement therapy: slows bone loss but does not reverse it and is controversial because of the increased risk of heart attack, stroke, and breast cancer