Ch. 7 – Bone tissueCh. 7 – Bone tissue

• Skeletal system – composed of bone, cartilages, ligaments

• Functions: support, protection, movement, mineral storage, blood formation

Bone tissueBone tissue

• Fig. 7.1: bone shapes (long, short, flat, irregular)

Fig. 7.2: Fig. 7.2: anatomy of a long anatomy of a long bonebone

– Compact bone, spongy (cancellous) bone

Fig. 7.2: Fig. 7.2: anatomy of a long anatomy of a long bonebone

– Compact bone, spongy (cancellous) bone

– Diaphysis, epiphysis, marrow cavity (in the diaphysis; filled with yellow bone marrow)

– Articular cartilage (hyaline cartilage covering the epiphyses)

Fig. 7.2: Fig. 7.2: anatomy of a long anatomy of a long bonebone

– Periosteum (serous membrane around the outside of the bone), endosteum (lines the cavities inside bones)

– Epiphyseal plate – hyaline cartilage; the site of long bone growth (in length) – found only in children

– Epiphyseal line – when long bone growth is completed, the plate turns into bone; full height has been achieved

Fig. 7.4: Fig. 7.4: bone cellsbone cells

• Osteogenic cells – stem cells that give rise to other bone cells

• Osteoblasts – bone-forming cells; make the boney matrix

Fig. 7.4: Fig. 7.4: bone cellsbone cells

• Osteocytes – Former osteoblasts that are trapped inside the

matrix they deposited– Lie in lacunae, which are connected by

canaliculi

Fig. 7.4: Fig. 7.4: bone cellsbone cells

• Osteocytes – Former osteoblasts that are trapped inside the

matrix they deposited– Lie in lacunae, which are connected by

canaliculi • Neighboring osteocytes are connected to each

other via gap junctions in these canaliculi; this is how they pass nutrients and wastes to each other since they are far from blood vessels

Fig. 7.4: Fig. 7.4: bone cellsbone cells

• Osteocytes – Former osteoblasts that are trapped inside the

matrix they deposited– Lie in lacunae, which are connected by canaliculi

• Neighboring osteocytes are connected to each other via gap junctions in these canaliculi; this is how they pass nutrients and wastes to each other since they are far from blood vessels

• Osteoclasts – Dissolve bone– They contain lots of lysosomes (digestive enzymes)

Compact boneCompact bone

• Fig. 7.5: osteon (the structural unit of compact bone)

• Concentric lamellae (layers of matrix)

Compact boneCompact bone

• Fig. 7.5: osteon (the structural unit of compact bone)

• Concentric lamellae (layers of matrix)

• Central canal (contains blood vessels and nerves)

• Perforating canals (horizontal passageways that connect central canals)

Compact boneCompact bone

• Fig. 7.5: osteon (the structural unit of compact bone)

• Concentric lamellae (layers of matrix)• Central canal (contains blood vessels and

nerves)• Perforating canals (horizontal passageways

that connect central canals)• Boney matrix is made of mineral salts (calcium

and phosphate) crystallized onto collagen fibers

Spongy boneSpongy bone

• Trabeculae form along stress lines

Bone marrowBone marrow

• Is located in the marrow cavity of long bones and in the spaces of spongy bone

• Two kinds:

Bone marrowBone marrow

• Is located in the marrow cavity of long bones and in the spaces of spongy bone

• Two kinds:– Red bone marrow makes blood cells

• Located in spongy bone

– Yellow bone marrow stores fat• Located in the marrow cavity of long bones

Bone developmentBone development

• Ossification, or osteogenesis – formation of bone

• Fig. 7.10: – The fetal skeleton is made of hyaline

cartilage; it ossifies during development (isn’t done until mid-20’s)

Bone developmentBone development

• Ossification, or osteogenesis – formation of bone

• Fig. 7.10: – The fetal skeleton is made of hyaline

cartilage; it ossifies during development (isn’t done until mid-20’s)

– (Also see fig. 7.12 on your own) Fig. 7.2: the epiphyseal plate is the site of long bone growth (in length)

• When this (hyaline) cartilage is depleted, becomes an epiphyseal line and growth has ended

Insight 7.2: Insight 7.2: achondroplastic achondroplastic dwarfismdwarfism

– Growth of long bones in length ends early (the epiphyseal plate closes very early)

• Long bone growth is stunted (in length)

– Pituitary dwarfism – deficiency in growth hormone, so all bones are affected, not just long bones

Bone remodelingBone remodeling

• Continual remodeling throughout life

• Stresses on bone create microscopic fractures, which stimulate osteoblast activity

Bone remodelingBone remodeling

• Continual remodeling throughout life

• Stresses on bone create microscopic fractures, which stimulate osteoblast activity

• Also, osteoclasts release minerals into the blood when needed

• This process reshapes bones in response to current needs/activities

Bone remodelingBone remodeling

• Continual remodeling throughout life• Stresses on bone create microscopic fractures,

which stimulate osteoblast activity • Also, osteoclasts release minerals into the blood

when needed• This process reshapes bones in response to

current needs/activities• If a stress is repeatedly applied to a particular

area, osteoblasts will deposit more bone there, creating a bump or ridge

• If excess bone is not needed, osteoclasts will remove it

Disorders Disorders

• Insight 7.4: osteoporosis– Brittle bones from loss of matrix, particularly in

spongy bone– Bones fracture easily

Disorders Disorders

• Insight 7.4: osteoporosis– Brittle bones from loss of matrix, particularly in

spongy bone– Bones fracture easily– Highest risk in postmenopausal white women;

other risk factors: smoking, diabetes, poor diet, lack of weight-bearing exercise

– Osteoclasts are more active than osteoblasts

Disorders Disorders

• (See table 7.3): – Rickets – softening of the bones; caused by

insufficient sunlight or vit. D in children• Vit. D increases the absorption of calcium from

food (in the digestive tract)