Copyright © 2017 John Wiley & Sons, Inc. All rights reserved.

Bone Bone is an organ made up of several different tissues (bone, cartilage, dense connective tissue, adipose, and nervous tissue) working together The entire framework of bones and their cartilages constitute the skeletal system Copyright © 2017 John Wiley & Sons, Inc. All rights reserved.

Functions of the Skeletal System
Provides support Protects the internal organs (brain, heart, etc.) Assists body movements (in conjunction with muscles) Mineral homeostasis - stores and releases calcium and phosphorus Participates in blood cell production (hemopoiesis) Stores triglycerides in adipose cells of yellow marrow Copyright © 2017 John Wiley & Sons, Inc. All rights reserved.

Structure of Bone A long bone consists of several parts: Diaphysis (bone shaft) 2 epiphyses (both ends of the bone at the joints) 2 metaphyses (region between diaphysis and epiphysis) Articular cartilage covering both epiphyses Periosteum (connective tissue surrounding the diaphysis) Medullary cavity (hollow space within diaphysis) Endosteum (thin membrane lining the medulary cavity) Copyright © 2017 John Wiley & Sons, Inc. All rights reserved.

Histology of Bone Bone contains an abundant extracellular matrix that surrounds widely separated cells The extracellular matrix is about 15% water, 30% collagen, and 55% crystalized mineral salts Copyright © 2017 John Wiley & Sons, Inc. All rights reserved.

Histology of Bone Bone contains 4 types of cells: Osteoprogenitor cells (bone stem cells able to differentiate into the other types of cells) Osteoblasts (bone-building cells that secrete matrix) Osteocytes (mature bone cells) Osteoclasts (remodel bones and cause them to release calcium) Copyright © 2017 John Wiley & Sons, Inc. All rights reserved.

Blood and Nerve Supply of Bone
Periosteal arteries (accompanied by nerves) enter the diaphysis through Volkmann’s canals. They are accompanied by periosteal veins. A nutrient artery enters the center of the diaphysis through a nutrient foramen. Nutrient veins exit via the same canal. The metaphyses and epiphyses also have their own arteries and veins. Copyright © 2017 John Wiley & Sons, Inc. All rights reserved.

Blood and Nerve Supply of Bone
The periosteum is only found on areas where there is no articular cartilage Copyright © 2017 John Wiley & Sons, Inc. All rights reserved.

Bone Formation Ossification (osteogenesis) is the process of bone formation. Bones form in 4 situations: During embryological and fetal development When bones grow before adulthood When bones remodel When fractures heal Copyright © 2017 John Wiley & Sons, Inc. All rights reserved.

Bone Formation Ossification takes place in 2 forms: Intramembranous and endochondral. Intramembranous ossification occurs in flat bones when a connective tissue membrane is replaced by bone. See text: 15e – p. 178, 14e – p. 176, 13e - 189 Copyright © 2017 John Wiley & Sons, Inc. All rights reserved.

Bone Formation- Intramembranous
Copyright © 2017 John Wiley & Sons, Inc. All rights reserved.

Bone Formation Bones thicken thanks to the cooperative action of osteoblasts and osteoclasts Discuss only a typical long bone at this point. Later, other bone types will be discussed. Copyright © 2017 John Wiley & Sons, Inc. All rights reserved.

Bone Formation As osteoblasts deposit bone on the outer surface osteoclasts widen the medullary cavity from within Discuss only a typical long bone at this point. Later, other bone types will be discussed. Copyright © 2017 John Wiley & Sons, Inc. All rights reserved.

Bone Growth and Remodeling Interactions Animation:
Bone Growth and Remodeling – necessary nutrients Bone Growth and Remodeling – maintenance of bone thickness Copyright © 2017 John Wiley & Sons, Inc. All rights reserved.

Bone’s Role in Calcium Homeostasis
Bones store 99% of the body’s calcium. The parathyroid gland secretes parathyroid hormone (PTH) when calcium levels drop. Osteoclasts are stimulated to increase bone resorption and calcium is released. PTH also stimulates the production of calcitriol by the kidneys to increase calcium absorption in the intestines. Copyright © 2017 John Wiley & Sons, Inc. All rights reserved.

Bone’s Role in Calcium Homeostasis

Calcium Homeostasis Interactions Animation:

Exercise and Bone Tissue Interactions Animation:
Effect of Exercise on Bone Copyright © 2017 John Wiley & Sons, Inc. All rights reserved.

Aging and Bone Tissue From birth through adolescence, more bone is produced than is lost during remodeling. In adults, the rates are the same. Older individuals, especially post-menopausal women, experience a decrease in bone mass when resorption outpaces deposition. Copyright © 2017 John Wiley & Sons, Inc. All rights reserved.

Osteoporosis Decreased bone mass resulting in porous bones
Those at risk white, thin menopausal, smoking, drinking female with family history athletes who are not menstruating due to decreased body fat & decreased estrogen levels people allergic to milk or with eating disorders whose intake of calcium is too low Prevention or decrease in severity adequate diet, weight-bearing exercise, & estrogen replacement therapy (for menopausal women) behavior when young may be most important factor

Effects of Osteoporosis

Matrix of Bone Inorganic mineral salts provide bone’s hardness
the most abundant salt is calcium phosphate. It combines with calcium hydroxide to form hydroxyapatite which combines with calcium carbonate and crystalize and the tissue hardens. Organic collagen fibers provide bone’s flexibility their tensile strength resists being stretched or torn remove minerals with acid & rubbery structure results Mineralization (calcification) is hardening of tissue when mineral crystals deposit around collagen fibers Bone is not completely solid since it has small spaces for vessels and red bone marrow spongy bone has many such spaces compact bone has very few

Role of Collagen & Minerals

Interstitial and Appositional Growth
Interstitial growth demands an elastic matrix (can occur in cartilage, but not in bone tissue). The cell or tissue grows uniformly throughout its mass. Appositional growth occurs when new material (cells, matrix) are added to the surface of the existing substance. Occurs in both cartilage and bone tissue. See text (Tortora 14e) p. 128 & 170.

Bone Formation or Ossification
All embryonic connective tissue begins as mesenchyme. Intramembranous bone formation = formation of bone directly from mesenchymal cells. Endochondral ossification = formation of bone within a hyaline cartilage model.

Calcification vs. Ossification
The process of bone tissue formation is called ossification. The process of calcification, the deposition of calcium salts, occurs during ossification, but it can also occur in other tissues. (The result is a calcified tissue, such as calcified cartilage).

Spongy Bone Structure and Stress

The Fetal Skeleton at 12 Weeks

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Copyright © 2017 John Wiley & Sons, Inc. All rights reserved.

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