Lecture 6: Bone Physiology

Question 1

What are bones made from

Answer 1

Primarily made of collagen and hydroxyapatite -

Ca10(PO4)6(OH)2

Question 2

Skeletal function

Answer 2

Structural integrity+strength to body
Protect vital organs
Blood cell formation
Storage of essential minerals
particularly “Calcium”, phosphate,
magnesium, and sodium. 
10%cardiacout-put.

Question 3

Key players in skeletal system

Answer 3

Calcium & Phosphates

Parathyroid hormone (PTH).

Cholecalciferol and Calcitriol (Vit.D3).

Estrogen and other Sex hormones.

Calcitonin.

Bisphosphonate ( anti resorptive agents)

Question 4

three different sub-categories of bone cells related to osteoblasts:

Answer 4

1) the osteoblasts

2) bone lining cells, and 3) osteocytes.

Question 5

Function of osteoblasts and osteocytes and osteoclasts

Answer 5

Osteocytes = mature bone cells
In lacunae
Connected by canaliculi

Osteoblasts synthesize new matrix
Osteogenesis

Osteoclasts dissolve bone matrix
Osteolysis

Question 6

Role of PTH and Calcitonin in blood ca level regulation

Answer 6

Calcitonin decreases blood calcium levels

PTH increases blood calcium levels

Question 7

Target organs for Ca homeostasis

Answer 7

Kidney
Bone
GI tract

Question 8

How does the kidney, GI tract and bone aid in homestasis

Answer 8

PTH causes kidneys to retain ca ions

PTH causes osteoclasts to increased release of calcium ions from bone matrix

PTH and calcitriol causes intestine to increase rate of absorption of calcium.

Question 9

Define osteogenesis

Answer 9

Production of bone on soft tissue

Question 10

What can osteogenesis be divided into

Answer 10

1.intramembranous ossification
process by which flat bones like the skull, mandible and clavicle are formed.

2.endochondral ossification
process is different from intramembranous ossification in that it occurs with a cartilage base. Endochondral ossification is responsible for a good deal of formation of the long bones and vertebrae

Question 11

Bone modeling characteristics

Answer 11

1)Changes in bone structure occur on existing bone structure
and

2) Bone structure alterations occur by independent action of
osteoblasts and osteoclasts.

Question 12

Define bone remodeling

Answer 12

osteoblasts and osteoblasts do not act independently but are coupled and bone resorption and formation occur at the same spot on a bone surface.

Question 13

Bone remodeling process

Answer 13

1. Quiescence refers to the resting state of the bone surface. This includes all of the bone surfaces.
2. Activation is the recruitment of osteoclasts to a bone surface and signal coupling of osteoblasts.
3. Resorption is the removal of bone by osteoclasts.
4. Reversal is the process by which osteoclasts stop removing bone and osteoblasts fill the defect.
5. Formation is the laying down of bone by osteoblasts

Question 14

Biochemical markers of bone turnover: Resorption

Answer 14

• Pyridinoline (Pyr)
• Deoxypyridinoline (dPyr)
• Amino terminal telopeptide of
type I collagen (NTX)
• Carboxyl terminal telopeptide of
type I collagen (CTX)

Question 15

Biochemical markers of bone turnover: Formation

Answer 15

Osteocalcin (OC)
• Bone-specific alkaline
phosphatase (BAP)
• Amino terminal propeptide of
type I collagen (PINP)
• Carboxyl terminal propeptide of
type I collagen (PICP)

Question 16

How to asses bone formation

Answer 16

Serum immunoassays for osteocalcin.

Alkaline phosphatase – both types

Question 17

How to assess boen resorption

Answer 17

Immunoassays for the type I collagen pyridinoline crosslink

Question 18

What causes Osteoporosis

Answer 18

• Lack of estrogen in women or androgen in men
• Lack of exercise to stress the bones.
• Inadequate intake of calcium and phosphorus. •Abnormalities of vitamin D metabolism.
• Loss of muscle mass.

Question 19

Define Osteoporosis

Answer 19

More bone removal than bone formation

Osteoporosis is defined as a disease in the bone in which the bone mineral density is reduced, bone microarchitecture is disrupted, and the amount and variety of non-collagenous proteins in the bone is altered. Osteoporotic bones are more at risk of fracture.

Question 20

Role of estrogen

Answer 20

Plays an important role in the growth and maturation of bone as well as in the regulation of bone turnover in adult bone.

Regulate cell death (apoptosis).

Accelerates the death of osteoclasts, while prolonging the life of osteoblasts.

Increase intestinal absorption of calcium

Increase reabsorption of calcium from the renal tubule.

Question 21

What is Osteopenia and difference to osteoporosis

Answer 21

is a condition that begins as you lose bone mass and your bones get weaker. This happens when the inside of your bones become brittle from a loss of calcium.

The difference between osteopenia is midway point of osteoporosis and bone loss is not as severe as
in osteoporosis. (bone density is lower but not severe).

That means someone with osteopenia is more likely to fracture a bone than someone with a normal bone density but is less likely to fracture a bone than someone
with osteoporosis.

Question 22

Primary vs Secondary Osteoporosis

Answer 22

Primary osteoporosis is bone loss that occurs during the normal human aging process.

Type 1 primary osteoporosis typically occurs
in postmenopausal women. It is caused by increased activity of osteoclasts, related to decreased levels of estrogen in the circulation.

Type 2 primary osteoporosis, affects both men and women. Bone loss is not related to an increased osteoclastic activity, and the cause of bone loss is obscure. This is SENILE osteoporosis (bone loss that results from aging)

Secondary osteoporosis is defined as bone loss that results from specific, well-defined clinical disorders.

Question 23

What is Rickets

Answer 23

• Skeletal disorder that’s caused by a lack of vitamin D, calcium, or phosphate.
• Calcium is not deposited in bones.
• Bones become soft.
• Bowing of the bones, and other deformities occur.

Question 24

Define Osteomalacia

Answer 24

• Disease characterised by the softening of the bones caused by impaired bone metabolism.
• Primarily due to inadequate levels of available phosphate, calcium, and vitamin D, or because of resorption of calcium.

Question 25

Rickets and osteomalacia may be caused by

Answer 25

u A deficiency or abnormal metabolism of vitamin D

A decrease in serum phosphate and calcium

An increase of ALP and PTH

Question 26

What causes Vit D deficiency?

Answer 26

a dietary lack of the vitamin

insufficient ultraviolet exposure to form endogenous vitamin D

most commonly, malabsorption interfering with the intestinal absorption of fats and fat-soluble vitamin D.

Question 27

Define Pagets Disease

Answer 27

is a localized, although sometimes multifocal, skeletal disorder of unknown cause and is characterized by abnormal bone remodeling brought about by waves of bone resorption and defective reformation (forms dense bone).

Question 28

How does loss of muscle mass AND lack of exercise/stress to bones cause osteoporosis?

Answer 28

lack of exercise/stress to bones:
If you are not causing stress or use of bones, then the body does not see a major use for them. Therefore the body will start to degrade the bones due to lack of use. Therefore major resorption, major bone loss and thus osteoporosis.

loss of muscle mass:
muscle atrophy appears to contribute directly to bone loss primarily via increased bone resorption by osteoclasts, although decreases in irisin levels with disuse may also suppress osteogenesis