Buck A&p Ch7

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Skeletal system includes

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Bones

Cartilage

Ligaments

Connective tissues

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Bones

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Primary organ of skeletal system

2 types

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Compact bone

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dense connective tissue, appears white, smooth and solid (80% of bone mass)

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Spongy bone

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- internal to compact bone, appears porous (20% of bone mass)

Internal cavity of bone contains either red bone marrow or yellow bone marrow

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Cartilage

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Semi-rigid connective tissue more flexible than bone

2 types found in skeletal system

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Hyaline cartilage

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Costal cartilage (ribs to sternum attachment)

o Articular cartilage (covers ends of bones)

o Epiphyseal plates (found within growing plates)

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Fibrocartilage (weight bearing cartilage, withstands compression)

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o Intervertebral discs (found between vertebrae)

o Pubic symphysis (found between bones of pelvis)

o Menisci (cartilage pads of the knee joints)

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Ligaments

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dense regular connective tissue anchors bone to bone

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Tendons

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dense regular connective tissue anchors muscle to bone

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Functions of the skeletal system

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1. Support and protection

2. Movement

3. Hemopoiesis

4. Storage of mineral and energy reserves

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Support and protection

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structural support, protection of organs and tissue such as the skull (brain) , rib cage (heart and lungs), vertebrae (spinal cord)

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Movement

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skeletal system along with the muscular system allow movement such as sprinting, running, the muscles serve as levers that exert pulls on the bones

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Hemopoiesi

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red bone marrow responsible for the production of blood from stem cells

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Storage of mineral and energy reserves

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calcium and phosphate is stored within bone, calcium is important in many biological processes such as muscle contraction, nervous impulse, blood clotting, phosphate is important for ATP utilization and also for maintaining a resting membrane potential in cell membranes, when the body is in need of calcium or phosphate bone will be broken down and allows release of calcium and phosphate

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Bone Classification by shape

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long, short, flat, irregular

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Long bones

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greater in length than width, most common bone shape, found in limbs

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Short bones

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length nearly equal to width, wrist bones, patella

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Flat bones

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flat, thin surfaces may be slightly curved, skull, sternum, scapulae

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Irregular bones

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elaborate and complex shapes, vertebrae, some skull bones

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Anatomy of Long bones

Regions of long bones

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diaphysis, medullary cavity, epiphysis, proximal epiphysis, distal epiphysis, articular (hyaline) cartilage, metaphysis, periosteum, endosteum

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Diaphysis

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shaft, weight support portion of long bones

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Medullary cavity

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hollow cylindrical spaces

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Epiphysis

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-ends of long bones, composed of outer layer of compact bone and inner layer of spongy bone

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Proximal epiphysis

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end closest to trunk

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Distal epiphysis

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end farthest from trunk

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Articular (hyaline) cartilage

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covers the joint surface of an epiphysis, helps reduce friction and absorb shock in moveable joints

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Metaphysis

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between diaphysis and epiphysis, contains the epiphyseal plate (growing plate) allows for the lengthwise growth of bone

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Periosteum

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outer covering of bone consists of two layers, outer layer (dense fibrous ct anchors blood vessels) inner layer (osteoprogenitor cells, osteoblasts, osteoclasts)

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Endosteum

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internal covering within the medullary cavity (osteoprogenitor cells, osteoblasts, osteoclasts)

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Anatomy of other bones

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Short, flat and irregular bones differ from long bones, outer surface, inner surface,

Bone highly vascularized especially in spongy bone, blood vessels enter bone through periosteum

Bone Marrow (soft connective tissue) 2 types

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Outer surface

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compact bone

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Inner surface

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spongy bone also called diploe (no medullary cavity

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Red bone marrow-

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located in spongy bone of most bones and medullary cavity of long bones

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Red bone marrow compose of

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o Myeloid tissue

o Hemopoietic tissue

o Reticular connective tissue

o Immature blood cells

o Adipose tissue

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Yellow bone marrow

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red bone marrow degenerates and turns in yellow bone marrow

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Adults- red bone marrow found in

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flat bones of skull, vertebrae, ribs, sternum, ossa coxae, proximal epiphyses of humerus, femur

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cells of bone

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osteoprogenitor, osteoblasts, osteocytes, osteoclasts,

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o Osteoprogenitor cells

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bone stem cells, located in periosteum and endosteum

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Osteoblasts

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formed from osteoprogenitor stem cells, abundant RER and golgi, synthesize bone matrix osteoid

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Osteocytes

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mature bone cells, derived from osteoblasts, maintain bone matrix and detect mechanical stress

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Osteoclasts-

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large multinuclear, phagocytic cells, derived from bone marrow cells, involved in breaking down through the process of bone resorption

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Organic component- osteoid

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collagen proteins plus semisolid ground substance of proteoglycans)

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Inorganic component

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salt crystals calcium phosphate and calcium hydroxide interact to form hydroxyapatite, also present calcium carbonate, sodium, magnesium, sulfate, fluoride, crystals formed provide the rigidity of bone

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Bone formation

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o osteoblasts secrete osteoid

o calcification (hydroxyapatite crystals deposited in bone matrix)

o vitamin D and Vitamin C critical for bone formation

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Bone resorption (bone matrix destroyed)

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o osteoclasts release of proteolytic enzymes digest organic components (collagen fibers, proteoglycans)

o HCl dissolves mineral parts (calcium and phosphate)

o Calcium and phosphate ions enter blood

o Occurs when blood calcium levels are low

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Compact bone anatomy

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osteon, central canal, concentric lamellae, osteocytes, lacunae, canaliculi, perforating canals,

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Osteon

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functional and structural unit of bone

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Central canal

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center of osteon, houses blood vessels and nerves

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Concentric lamellae

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rings of bone connective tissue, contains collagen fibers

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Osteocytes

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mature bone cells found between concentric lamellae, help maintain matix

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Lacunae

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small spaces that house an osteocyte

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Canaliculi-

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channels within bone, house osteoclast cytoplasmic extensions

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Perforating canals

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canals that contain blood vessels and nerves

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Spongy bone anatomy

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o No osteons

o Trabeculae- narrow rods and plates of bone (bone marrow can be deposited here

o Parallel lamellae- made of bone matrix

o Osteocytes

o lacunae

o Caniliculi

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Hyaline cartilage anatomy

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o 60-70% water

o no calcium allows for flexibility

o ground substance gel like

o chondroblasts- produce cartilage matrix

o chondrocytes- derived from chondroblasts, housed in lacunae

o perichondrium- dense irregular connective tissue

o avascular

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Cartilage growth

Cartilage growth in length

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initiated during embryogenesis

interstitial growth

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Cartilage growth in length interstitial growth

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1. chondrocytes undergo mitosis

2. two chondroblasts occupy lacunae

3. chondroblasts secrete and synthesize cartilage matrix which pushes and separates them into their own lacunae à chondrocytes

4. cycle repeats as along as chondrocytes continue to produce more matrix

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Cartilage growth in width- appositional growth

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1. stem cells residing in perichondrium undergo cell division

2. new stem cells differentiate into chondroblasts which will produce and secrete new cartilage matrix

3. chondroblasts secrete and synthesize cartilage matrix which pushes and separates them into their own lacunae à chondrocytes

4. cycle repeats as along as chondrocytes continue to produce more matrix

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matrix

embryonic development cartilage grows in length and width, later interstitial growth ceases as cartilage matures and growth only occurs at periphery of tissue

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appositional growth will continue

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Osteogenesis or ossification

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formation and development of bone, begins during embryogenesis and continues during childhood and adolescence

Bone begins to form either via intramembranous ossification or endochondral ossification

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Intramembranous ossification (originates from mesenchyme

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Produces following bones

o flat bones of skull

o facial bones (zygomatic, maxilla)

o mandible

o central part of clavicle

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Steps for intramembranous ossification

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o mesenchyme thickens and condenses with dense supply of vascularization

o ossification center formation within the thickened region of mesenchyme, mesenchymal cells divide and give rise to osteoprogenitor cells-->osteoblasts -->secrete osteoid

o calcification of osteoid- calcification traps osteoblasts within lacunae--> osteocytes

o woven bone and periosteum formation, woven bone replaced by lamellar bone, continual division of mesenchymal cells to produce osteoblasts

o lamellar bone replaces woven bone , lamellar bone composed of compact and spongy bone

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Endochondral ossification (originates from hyaline cartilage)

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Produces following bones:

o most all bones of body

o upper and lower limbs

o pelvis

o vertebrae

o ends of clavicle

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Steps for endochondral ossification

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o fetal hyaline cartilage develops from chondroblasts secreting matrix, chondrocytes trapped within lacunae and perichondrium surrounds cartilage

o cartilage calcifies and periosteal bone collar forms

o primary ossification center forms in diaphysis

o secondary ossification centers form in epiphyses

o bone replaces all cartilage except articular and epiphyseal cartilage

o lengthwise growth continues until the epiphyseal plates ossify and form epiphyseal lines

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Bone growth

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interstitial growth (length) appositional growth (width),

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Interstitial growth (length

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Zone of resting cartilage, zone of proliferating cartilage, zone of hypertropic cartilage, zone of calcified cartilage, zone of ossification

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Zone of resting cartilage

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nearest to epiphysis and farthest to diaphysis, chondrocytes within cartilage, secures epiphysis to epiphyseal plate

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Zone of proliferating cartilage

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chondrocytes undergoing rapid cell division which leads to columns of flattened lacunae are parallel to diaphysis

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Zone of hypertropic cartilage

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chondrocytes cease cell division and begin to enlarge in size (hypertrophy), lacunae walls thin out

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Zone of calcified cartilage

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2-3 layers of chonrdrocytes, minerals deposited and destroying chondrocytes

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Zone of ossification

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lacunae walls break down forming longitudinal channels, paces invaded by capillaries and osteoprogenitor cells

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Growth in bone length occurs between zone 2 and zone 3 , thus growth in bone is due to growth in hyaline cartilage

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Upon adulthood rate of epiphyseal cartilage slows down and osteoblast activity increases resulting in epiphyseal plate narrowing and ultimately disappearing

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Appositional growth (width)

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Occurs within periosteum, osteoblasts produce and deposit bone matrix into circumferential lamellae (resemble tree rings) Osteoclasts resorb bone matrix leads to expansion of medullary cavity

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Bone remodeling

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Bone is very dynamic in there is continuous bone deposition and bone resorption this is called bone remodeling and occurs at the periosteal and endosteal surfaces of bone

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Bone remodeling dependent on

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coordinated activities of osteoblasts, osteocytes, osteoclasts , influenced by hormones and mechanical stress to bone

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Mechanical stress occurs

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through weight bearing movement and exercise, osteocytes detect mechanical stess and communicate to osteoblast to increase osteoid production followed by deposition of mineral salts

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Athletes tend to have thicker bones due to

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the excessive mechanical stress

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Lack of weight-bearing activities can lead to

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weakening of bone due to lack of mechanical stress

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Growth hormone

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stimulates production of somatomedin à cartilage proliferation at epiphyseal plateà bone elongation

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Thyroid hormone

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stimulates metabolic rate of osteoblasts

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Parathyroid hormone

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increases blood calcium levels by encouraging bone resorption by osteoclasts

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Estrogen and testosterone

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stimulate osteoblasts, promote epiphyseal plate growth and closure

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Glucocorticoids

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increase bone loss and impair bone growth

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Serotonin

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inhibits osteoprogenitor cells from differentiating into osteoblasts

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Regulation of calcium is critical several important physiological processes (skeletal muscle contraction, nerve impulses) require

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CALCIUM

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Calcitriol and parathyroid hormone important for the regulation of

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blood calcium levels

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Through a series of enzymatic reactions Vitamin D is converted to calcitriol which circulates in the blood, an increase in parathyroid hormone leads to increase production of

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CALCITRIOL

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cALCITRIOL STIMULATES WHAT

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absorption of calcium ions from small intestine to blood

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Parathyroid hormone production is stimulated by what

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a decrease inb lood calcium levels, working together with calcitriol they increase the release of calcium from bone by increasing osteoclast activity, also stim kidneys to excrete less calcium and stim the small intestine to increase absorption of calcium into the blood.

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Calcitonin hormones also plays a role in

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Regulated bloodc alcium levels, however it is stiumulated when there is an excess of calcium circulating. it inhibits osteoclast activity and stimulates the kidneys to excrete more calcium

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Osteoporosis

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decreased bone mass and weak bones, linked with menopause due to decreased production of estrogen which stimulates bone growth, essentially with age bone resorption outpaces bone production leading to weak and brittle bones fractures of bones increases due to the weakening of bones

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stress fracture

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thin break due to increased physical activity

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pathologic fracture

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occurs in bone weakened by disease

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simple fracture

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bone does not penetrate skin

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compound fracture

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broken bone pierces through skin

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bone Repair

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1. Fracture hematoma forms- formed from the tearing of blood vessels

2. A fibrocartilaginous callus forms- originates from hematoma (lasts 3 weeks)

3. A hard bony callus forms- osteoprogenitor cells form osteoblasts which in turn produce primary bone (persists for 3-4 months)

4. Bone remodeled- compact bone replaces primary bone