Class 9 - Bone Tissue pt. 2

Question 1

Ectopic ossification

Answer 1

Abnormal calcification of tissues

Question 2

Calculus

Answer 2

A calcified mass in an otherwise soft organ (e.g. kidney stones).

Question 3

Mineral resorption, where it happens, + 4 steps

Answer 3

Process of dissolving bone. Releases minerals into blood.
Performed by osteoclasts at ruffled border.

1. Hydrogen pumps in membranes secrete hydrogen into space between osteoclast and bone surface
2. Chloride ions follow by electrical attraction
3. Hydrochloric acid (pH 4) dissolves bone minerals
4. Acid-tolerant protease enzyme digests collagen

Question 4

Uses of calcium homeostasis (5) + normal blood plasma calcium concentration

Answer 4

1. Bone structure
2. Neuron communication
3. Muscle contraction
4. Blood clotting
5. Exocytosis

Normal calcium concentration = ~10 mg

Question 5

Hypocalcemia vs hypercalcemia

Answer 5

Hypocalcemia - Calcium deficiency; causes excessive excitability of nervous system/muscles. Variety of causes.

Hypercalcemia - Calcium excess; causes nerve/muscle cells to be less excitable than normal. Rare.

Question 6

3 things calcium homeostasis depends on and 3 hormones

Answer 6

Depends on balance between:
1. Dietary intake (+1000 mg)
2. Urinary/fecal losses (-650 mg, -350 mg)
3. Exchanges between osseous tissue

Hormones involved:
A. Calcitriol
B. Calcitonin
C. Parathyroid hormone (PTH)

Question 7

Calcitriol

Answer 7

Form of vitamin D produced by sequential actions of skin, liver, and kidneys.

RAISES blood calcium; also necessary for bone deposition—helping provide adequate calcium and phosphate

Inadequate Calcitriol results in abnormal bone softens (rickets in children; osteomalacia in adults).

Question 8

3 steps to creating Calcitriol

Answer 8

1. Epidermis keratinocytes use UV radiation to convert 7-dehydrocholesterol to previtamin D3; warm sun on skin converts this to vitamin D3 (cholecalciferol)
2. Liver adds hydroxyl group, creating calcidiol
3. Kidney adds hydroxyl group, creating Calcitriol.

Question 9

3 ways Calcitriol acts to raise blood calcium

Answer 9

1. Increases absorption by small intestine
2. Increases calcium resorption from skeleton (stimulate new osteoclasts)
3. Weakly promotes resorption from kidneys

Question 10

Calcitonin

Answer 10

Produced by parafollicular cells of thyroid gland.

LOWERS blood calcium levels.

Important in children (faster remodeling), weak effect in adults

May inhibit bone loss in pregnant and lactating women

Question 11

2 ways calcitonin lowers blood calcium concentration

Answer 11

1. Osteoclast inhibition, reducing bone absorption
2. Osteoblasts stimulation, deposits calcium into bone

Question 12

Parathyroid hormone

Answer 12

Secreted by parathyroid glands on posterior surface of thyroid.

RAISE calcium levels

Question 13

5 mechanisms by which parathyroid hormone raises calcium blood levels

Answer 13

1. Binds to receptors on osteoblasts, stimulating osteoclasts to resorb bone
2. Promotes calcium resorption by kidneys
3. Promotes final step of Calcitriol synthesis in kidneys
4. Inhibits collagen synthesis by osteoblasts, inhibiting bone deposition
5. Increase urinary phosphate excretion, inhibiting bone formation

Question 14

5 reasons for phosphate homeostasis + normal plasma concentration

Answer 14

1. Bone formation
2. DNA
3. RNA
4. ATP
5. Phospholipids

Normal levels = ~4 mg

Question 15

2 ways of regulating phosphate levels

Answer 15

NOT as tightly regulated as calcium homeostasis.

1. Calcitriol RAISES phosphate levels by promoting its absorption by small intestine
2. Parathyroid hormone LOWERS phosphate levels by promoting its urinary excretion.

Question 16

Ways growth hormones, testosterone, and estrogen impact ossification (3)

Answer 16

1. Stimulate multiplication of osteogenic cells
2. Stimulate matrix deposition by osteoblasts
3. Increase chondrocyte multiplication and hypertrophy in metaphysis

Question 17

Orthopedics

Answer 17

Branch of medicine dealing with prevention and correction of injuries/disorders of bones, joints, and muscles.

Includes design of artificial joints/limbs and treatment of athletic injuries.

Question 18

Stress vs. pathological fracture + 4 kinds of fracture

Answer 18

Stress fracture - Break caused by abnormal trauma to bone.

Pathological fracture - Break caused by bone weakening due to disease

1. Nondisplaced - pieces still in alignment
2. Displaced - pieces not in alignment
3. Comminuted - Shattered; 3+ pieces
4. Greenstick - In children; bone bent and frayed on one end

Question 19

4 Stages of healing for fractures

Answer 19

Uncomplicated healing takes ~8-12 weeks.

1. Hematoma formation - blood clot converted to granulation tissue
2. Soft callus formation - deposition of collagen and fibrocartilage converts granulation tissue to soft callus
3. Hard callus formation - osteoblasts deposit temporary bony collar to unite broken pieces while ossification occurs
4. Bone remodeling - small bone fragments removed by osteoclasts; osteoblasts deposit spongy bone and convert it to compact bone.

Question 20

2 types of treatment for fractures

Answer 20

1. Closed reduction - bone fragments are manipulated into normal positions without surgery
2. Open reduction and internal fixation - surgical exposure of bone and the use of plates, screws, or pins to realign fragments

Question 21

Contributing factors to loss of bone mass (4)

Answer 21

1. Sex - women more affected than men
2. Build - small, light frames more affected
3. Ancestry - white women of Asian and European origin especially vulnerable
4. Age - older individuals more vulnerable

Question 22

Osteopenia vs. osteoperosis

Answer 22

Osteopenia - measurable decline in bone density; may advance to osteoperosis

Osteoperosis - Severe loss of bone density; bones easily fracture

Question 23

Treating osteoporosis (3)

Answer 23

1. Assessed by DEXA scan
2. Drugs can stimulate bone deposition or slow rate of resorption
3. Preventative measures: weight-bearing exercises throughout life