Lecture 6: Bone Physiology

Primarily made of collagen and hydroxyapatite - Ca10(PO4)6(OH)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.

Calcium & Phosphates Parathyroid hormone (PTH). Cholecalciferol and Calcitriol (Vit.D3). Estrogen and other Sex hormones. Calcitonin. Bisphosphonate ( anti resorptive agents)

1) the osteoblasts 2) bone lining cells, and 3) osteocytes.

Osteocytes = mature bone cells In lacunae Connected by canaliculi Osteoblasts synthesize new matrix Osteogenesis Osteoclasts dissolve bone matrix Osteolysis

Calcitonin decreases blood calcium levels PTH increases blood calcium levels

Kidney Bone GI tract

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.

Production of bone on soft tissue

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

1)Changes in bone structure occur on existing bone structure and 2) Bone structure alterations occur by independent action of osteoblasts and osteoclasts.

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

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

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

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

Serum immunoassays for osteocalcin. Alkaline phosphatase – both types

Immunoassays for the type I collagen pyridinoline crosslink

• 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.

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.

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.

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.

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.

• 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.

• 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.