Skeletal System #2

Question 1

What is the endochondral ossification?

Answer 1

Bones formed this way: osteoblasts replace chondrocytes (which have died)
- nature of the original support structure: hyaline cartilage model

Question 2

The first step of Endochondral ossification

Answer 2

As the cartilage enlarges, chondrocytes near the center of the shaft increase greatly in size

• The matrix is reduced to a series of small statuses that soon begin to calcify
• the enlarged chondrocytes then die and disintegrate, leaving cavities within the cartilage.

What to look for: enlarging chondrocytes within the calcifying matrix

Question 3

The second step of endochondral ossification

Answer 3

1. Blood vessels grow around the edges of the cartilage, and the cells of the perichondrium convert to osteoblasts.
2. The shaft of the cartilage then becomes ensheathed in a superficial layer of bone

What to look for:
- Epiphysis (the end part of a long bone)
- Diaphysis (the main section of a long bone)
- the bone formation in the diaphysis

Question 4

The three cell types involved in bone formation

Answer 4

• Osteoblasts
• osteocytes
• osteoclasts

Question 5

Step 3 of endochondral ossification

Answer 5

Blood vessels penetrate the cartilage
- osteoblasts begin producing spongy bone at the primary ossification centre

What to look for:
In the Diaphysis,
- medullary cavity
- primary ossification centre
- superficial bone
- spongy bone
- blood vessels

Question 6

Step 4 of endochondral ossificaiton

Answer 6

Remodeling occurs as growth continues, creating a marrow cavity.
- the bone of the shaft becomes thicker & further growth increases length & diameter

Question 7

What is a hematopoietic stem cell

Answer 7

The immune cells derived from the bone marrow produce all blood cells
- more info on the marrow cavity and produce RBCs/ WBCs

Question 8

During the remolding and growing, what does osteoblasts do?

Answer 8

Breaks down trabecular forming medullart cavity

Question 9

During the remolding and growing, what does ostoeclasts do?

Answer 9

continue to add bone at ends of the cavity

Question 10

The step 5 of endochondral ossificaiton

Answer 10

capillaries and osteoblasts migrate into the epiphyses, creating secondary ossification centers
- The epiphyses (at the end of a long bone)
- Hylaline cartilage is located in the epiphyses
- the secondary ossification center are inside the hylaine cartilages

Question 11

The step 6 of endochondral ossificaiton

Answer 11

Soon the epiphyses are filled w/ spongy bones
- an articular cartilage remains exposed to the joint cavity, over time; it will be reduce to a thin superficial layer.
- at each metaphysis, an epiphyseal cartilage separates the epiphysis from the disphysis
= state of most bones at birth

Question 12

5 layers of bones (from superficial to deep)

Answer 12

1) growth plate zones (changes in chondrocytes)
2) reserve zone (matrix production)
3) proliferative zone (mitosis)
4) meturation and hypertrophy (lipids, glycogen, and alkaline phosphatse accumulate; matrix calcifies)
5) Calcified matrix (cell death)

Question 13

How do the condrocytes and osteoblasts work in the growth in length?

Answer 13

In the Growth in length….

1) chondrocytes in epiphyseal place continue to divide and grow, and adding length to bone. chondrocytes closest to cavity die. = “cell division”

2) Ostoblasts migrate towards epiphysis replacing cartilage with bone

Question 14

Where does bone develop from in bone growth?

Answer 14

Bone develops from hyaline cartilage, which become fully ossified shortly after birth

This involves:
- calcification
- deterioration of chondrocytes
- replacement with osseous tissue

Question 15

Which control is bone growth under?

Answer 15

Bone growth is under hormonla control

Question 16

Bone growth during development

Answer 16

bone grows longitudinally through the formation of new cartilage at the epiphyseal plate, however, this process is complete following puberty

Question 17

Lateral bone growth

Answer 17

lateral bone growth is achieved by osteoblasts in the periosteum laying down new bone, and osteoclasts in the medullary cavity breaking down old bone

Question 18

what is the cartilage model?

Answer 18

Endochondral Ossificaiton 1; the number is just for presneting what’s happening during the process (not meaning the steps but are in order tho)

Development of cartilage moel:
mesenchymal cells develop into chondroblasts, which form the cartilage model

Question 19

WHat do chondocyte produce?

Answer 19

Endochondral ossification 2;

chondrocytes produce a substance that inhibits the formation of blood vessels limiting O2 & nutrient delivery

Question 20

does chondrocytes in shaft enlarge or reduce?

Answer 20

endochondral ossificaiton 3;

chondrocytes in shaft enlarge

Question 21

What happens after chondrocytes in shaft enlarged?

Answer 21

endochondral ossificaiton 4;

Chondrocytes in the primary ossification site enlarge & stop secreting collagen & other proteoglycans & begin secreting alkaline phosphates and enzymes required for mineral deposition

endochondral ossificaiton 5;
calcification of the matrix occurs

Question 22

Where do blood vessels grow into?

Answer 22

endochondral ossificaiton 6;
Blood vessels grow into perichondrium transforming it into periosteum-containing osteoprogenitor cells which become osteoblasts.

Question 23

how is the Collar of bone generated?

Answer 23

endochondral ossificaiton 7;
Osteoblasts secrete osteoid against the shaft of the cartilage model => generate collar of bone

Question 24

Mature chondrocytes in the endochondral ossification

Answer 24

endochondral ossification 8;
Mature chondrocytes can not divide and die leaving cavities

Question 25

the process osteoblast in ossification turn into osteocytes

Answer 25

Osteoblast in ossification sites produce osteoid &turn into osteocytes as mineral deposits surround & harden around them

Question 26

How are new osteons & central canals formed during appositional growth

Answer 26

1. ridges in the periosteum create a groove for periosteal blood vessels (Periosteal ridges)
2. periosteal ridges fuse, forming an endosteum-lined tunnel
   (endosteum and tunnel/ periosteum )
3. osteoblasts in the endosteum build new concentric lamellae inward toward the center of the tunnel, forming a new osteon
   (endosteum)
4. bone grows outward as osteoblasts in the periosteum build new circumferential lamellae. Osteon formation repeats as new periosteal ridges fold over blood vessels.
   (NEW osteon with a central cannel)

Question 27

The direction of growth that Appositional growth works into

Answer 27

Growth in width by appositional growth
- enlargement of the medullary cavity with increased bone diameter resulting from appositional growth
(the bone matrix is removed by osteoclasts/ bone deposited by superficial osteoblasts)

Question 28

Osteoblasts and osteoclasts in appositional growth

Answer 28

osteoblasts under the periosteum lay down bone
meanwhile, osteoclasts break down bone on the inside of medullary cavity
=> bone increases in diameter, cavity enlarges

Question 29

THE BONE GROWTH AT PUVERTY

Answer 29

Under the influence of sex hormones (testosterone), growth hormone and thyroid hormone
=> cartilage in epiphyseal plate is replaced with bone
=> epiphyseal plate where the line shows that NO further growth in length

Question 30

What does having epiphyseal cartilage mean?

Answer 30

the bone is still growing

Question 31

What does having epiphyseal lines mean?

Answer 31

the bone growth is over
=> adult

Question 32

what is Bone remodeling?

Answer 32

Bone remodelling occurs throughout life and involves the resorption of old bone and deposition of new bone where it is needed
=> Remodeling occurs in response to:
- bone growth (to maintain proper thickness and bone shape)
- blood C++ levels
- mechanical stress on the bone

Question 33

Why do sharks have a skeletons made of cartilage instead of bone?

Answer 33

b/c cartilage is weightless (lighter) and ever beared

Question 34

Blood supply to Bone

Answer 34

=> living (vascularized)
The top of a long bone
- epiphyseal artery and vein
- metaphyseal artery and vein

the middle of a long bone
- nutrient artery and vein
- periosteal artreis and veins

Question 35

Nerve supply in bone

Answer 35

periosteum, endosteum and bone itself is richly supplied with sensory nerve endings

Question 36

WHat is Osteoblast activity

Answer 36

Osteoblast activity = bone growth

Question 37

Hormonal and Nutritional Requirement for Normal Bone Growth

Answer 37

hormonal:
1. growth hormone: from the pituitary gland, promotes Osteoblast activity

2. Thyroid hormone (stimulates epithermal cells) = thyroxine
   : stimulates cell metabolism, promotes osteoblast activity
3. Calcitriol
   : produced by kidneys; derived from vitamin D3 allows normal absorption of Ca++ and PO4 ion from the digestive tract
4. sex hormones: estrogen & testosterone
   : promote growth, cause osteoblast to produce bone faster

pretty similar to skin-maintaining hormones

Question 38

Nutritional Requirements for bone growths

Answer 38

1. calcium and phosphate salts
   - needed to prevent rickets (children and osteomalacia (adults))
2. Vitamin C: required for collagen synthesis stimulates osteoblast differentiation (from citrus fruits)
   - lack of Vit C = loss of bone density/ volume
3. Vitamin A: stimulates osteoblast activity
   - maintaining bones
4. Vitamin K (in green vegies) and B12 (mostly in cereals): required for synthesis of proteins in normal bone

Question 39

What is Scurvy and its effect?

Answer 39

• teeth fall out
• fatigue
• bleeding or swollen gums
• reddish spots on the skin or petechiae
• swollen muscles or joints
• open wounds that take time to heal

Question 40

Regulation of bone remodelling

Answer 40

Hormonal
Functions: maintain calcium ion in blood and interstitial fluid at 9-11 mg/ 100ml blood

Two organs monitor calcium levels
: para(side) thyroid gland and thyroid gland
- right under the thyroid cartilage

Question 41

The parathyroid glands

Answer 41

they release parathyroid hormone in response to lower than normal Ca++ in blood

Effect of the parathyroid hormone:
a) stimulates osteoclast activity
: dissolves bone to release calcium into the blood

b) increases the rate of absorption of Can++ from the intestine
c) decreases the rate of excretion by the kidney
(decreasing the rate of calcium in the urinary system)
=> have to keep them in the body

Question 42

The thyroid gland

Answer 42

releases the hormone calcitonin (calcium is too high: we have to tone it down)

in response to higher than normal Ca++ in blood

Effect of Calcitonin:
a) inhibit the activity of osteoclasts
- keep them in the body; we don’t need them anymore

b) increase rate kidneys excrete Ca++
- increasing the rates of calcium in excretion

Question 43

What happens if there’s too low calcium in body

Answer 43

the parathyroid gland releases parathyroid hormone

(bone) the hormone binds to the osteoblast and stimulates the osteoclast to differentiate into mature osteoclasts.
- these mature osteoclasts erode the bone matrix, thereby releasing stored calcium => calcium released; the calcium level in the blood increases

(intestinal response) The PTH enhances the calcium-absorbing effects of calcitriol on the intestines
=> The rate of intestinal calcium absorption increases and calcium is absorbed quickly - the calcium level in the blood increases

(Kidney response) The PTH increases renal production of the hormone calcitriol. Calcitriol stimulates calcium reabsorption by the kidneys and calcium absorption in the intestines. - sending more calcitriol to the intestines => calcium conserved - the calcium level in the blood increases

Question 44

What happens if there’s too high calcium in body

Answer 44

C cells in the thyroid gland secrete calcitonin

(Bone) Calcitonin decreases osteoclast activity but does not affect osteoblasts which continue to deposit calcium ions within the bone matrix. (But there’s a limit)
- calcium release slowed => Ca2+ level in blood decreases
(not dissolving bone anymore but still building the bones)

(intestinal) Decreasing PTH or calcitriol level results in a decrease in the rate of calcium ion absorption by the intestines. - calcium absorbed slowly => Ca2+ level in blood decreases

(kidney) increased calcitonin level has an inhibitory effect on the kidneys and suppresses calcium ion reabsorption - less calcitriol to intestines and more calcium excreted (more calcium lost in urine)
=> Ca2+ level in blood decreases

Question 45

What happens if C2+ levels drop by 35%?

Answer 45

Too less C2+ = it over excites nerves

Question 46

What if blood Ca2+ levels are more than 30%?

Answer 46

Too much Ca2+ = muscles and nerves become unresponsive

Question 47

Normal Ca2+ level in blood

Answer 47

(bone) within the skeleton, osteoblasts continuously deposit new bone matrix.
- at the same time osteoclasts erode the existing matrix, releasing calcium and phosphate ions into the circulation
=> The balance between osteoblast and osteoclast activity is hormonally regulated

(intestine) calcium and phosphate ions are absorbed from the diet => the absorption rate is hormonally regulated

(kidney) the levels of calcium and phosphate ions lost in the urine are hormonally regulated

Question 48

Bone remodelling (Wolff’s law)

Answer 48

Response to mechanical stress Wolff’s law:
- bones are remodelled in response to forces placed on them

how does it work?
- stress generates electrical currents in bone
- osteocytes are mechanosensor & secrete chemicals that “alter the activities of osteoblasts and osteoclasts”

Question 49

What is the trabeculae?

Answer 49

Trabeculae are the thin columns and plates of bone that create a spongy structure in a cancellous bone, which is located at the ends of long bones and in the pelvis, ribs, skull, and vertebrae.

Question 50

Net effect of Wolff’s Law:

Answer 50

1) bones that are used (stressed) become stronger
- the trabeculae is reshaped to cope with the stress
2) Unstressed bones are remodelled to become weaker

Question 51

Repair of fractures

Answer 51

treatment
- realign bone pieces = reduction of movement (e.g. immobilize)

the healing time
kids: 2-3 months
adults: 6 months

Question 52

The step for the repair of bone fracture

Answer 52

1st step: fracture hematoma Formation
- immediately after the fracture, extensive bleeding occurs.
- over a period of several hours, a large blood clot, or fracture hematoma, develops
= a hematoma fills the gap between the bone fragments

2nd step: Callus formation
- an internal callus forms as a network of spongy bone unites the inner edges, and an external callus of cartilage and bone stabilizes the outer edges
= Fibroblasts and chondroblasts infiltrate the hematoma and a soft callus forms

3rd step: Spongy bone formation
- the cartilage of the external callus has been replaced by bone and struts of spongy bone now unite the broken ends
- fragments of dead bone and the areas of bone close to the break have been removed and replaced
= Osteoblasts build a bone callus

4th step: compact bone formation
- a swelling initially marks the location of the fracture
- over time, this region will be remodelled and little evidence of the fracture will remain
= the bone callus is remodelled and primary bone is replaced with secondary bone

Question 53

Effects of aging on the skeletal system

Answer 53

starting age 30-40 (a normal part of the aging process)
- bones become thinner & weaker (osteoblasts slowed down)
- “Osteopenia” = reduction in bone mass

Cause: due to inadequate ossification
- decreased osteoblast activity
- osteoclasts continue at a normal rate (dissolving bones)

after 40 years of age:
women - lose ~ 8% bone mass/ 10 years
men - lose ~ 3% bone mass/ 10 years

Question 54

Bones most affected by osteopenia

Answer 54

Epiphyses, vertebrae, jaws
- resulting in fragile limbs, height reduction and loss of teeth

Osteoporosis = loss of bone mass sufficient to compromise function

contributing factors include:
- osteocytes slow down & start dying after 50+ years!
- less stimulation of osteoblast activity due to declining hormonal levels, for example:
Estrogen levels decrease in women after 35, especially after menopause (age 50)
Testosterone levels decrease in men more gradually after 35

• over age 45, 29% of women and 18% of men have osteoporosis

Question 55

Prevention of Osteoporosis

Answer 55

• develop good bone mass when young
  (vit C, B12, A)
• maintain diet and exercise through the aging process
• other contributing factors are:
  1) smoking
  2) uncontrolled diabetes
  3) hormone disorders
  4) physical inactivity
  5) low blood flow (low O2)

Question 56

What sorts of clues might bones provide as to the lifestyles of those individuals?

Answer 56

Age = teeth
Age = joint breakdown
Age = bone density
Biological sex = pelvic bone
Biological sex = skull

Question 57

Bone marrow:

Answer 57

Red (myeloid) and Yellow (fat)

Red bone marrow:
- hip, breast, skull, ribs, sternum, vertebrae, shoulder blades
- in the spongy material at the proximal ends of the femur and humerus

Hematopoietic stem cells in the red marrow produce:
- Red blood cell(RBC)
- platelets
- most white blood cells

• there’s a difference between ones in adult and infant

The papers only mention the red but…
Yellow marrow produces cartilage, fat and bone