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Summary Reviewer in Skeletal System
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Reviewer for Chapter 6 of Anatomy and Physiology
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Seeleys Anatomy and Physiology, 12th Edition (VanPutte, 2020), Chapter 1-29
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SKELETAL SYSTEM Lamellar Bone – mature boneLamellae – thin, concentric sheets or layers in bone
Component of Skeletal System
- Bones Spongy Bone
- Cartilages - less bone matrix and more space
- Tendons - consists trabeculae
- Ligaments
Trabeculae - interconnecting rods or plates of bone
Functions of the Skeletal System - have spaces filled with bone marrow and
1. Body support blood vessels
2. Protect organs - surfaces are covered with single layer of
3. Movement osteoblast and few osteoclasts
4. Mineral storage Compact Bone
5. Blood cell production - more bone matrix and less space
- can also be called cortical bone
Bone Histology - solid, outer layer of bones
- Bone, cartilage, tendons, ligaments are
connective tissues Osteon – functional unit of compact bone
- Determined by large composition of ECM
- composed of lamellae
- ECM – contains collagen, ground substance,
water, minerals, other molecules Central Canal/Haversian Canal – provide passageway for
blood vessels and nerves
Collagen
- lined with endosteum
- provides flexibility, strength, support
- resist pulling Lamellae – concentric rings bone matrix which surround
- most abundant the central canal
- osteocytes are located in spaces called
Ground substance – contains proteoglycans that traps
lacunae between the lamellar rings
water which help cartilage to be smooth and resilient
Canaliculi – small tunnels radiate between lacunae across
ECM of tendons and ligaments – contains large amount of
lamellae
collagen fibers (making it very tough)
- connect osteocytes to one another
Bone Matrix - provide transport of nutrients and remove
- 35% organic, 65% inorganic wastes
- Organic – collagen & proteoglycans
Structure of Long Bone
- Inorganic – hydroxyapatite (Ca10 (PO4)6
Diaphysis – center portion of the bone which is composed
(OH)2 -calcium phosphate crystal
of compact bone
- The mineral component gives bone
Medullary Cavity – hollow center of bone that contains
compression strength
bone marrow
Bone Cells
Epiphyses – ends of a long bone; contain mostly spongy
Osteoblasts – responsible for the formation of bone, repair,
bone with an outer layer of compact bone
and remodeling
Osteoblasts – produce collagen and proteoglycans Articular Cartilage – hyaline cartilage that covers the end
of long bone; within joints
- Secrete high concentration of calcium and
phosphate that forms hydroxyapatite Epiphyseal Plate – located between epiphysis and
diaphysis
Osteocytes – maintain bone matrix and form osteoclast
- where growth in bone length occurs
after matrix has surrounded it; long-lived
Epiphyseal line – occurs when bone stops growing in
Lacunae – spaces which houses osteocytes
length and epiphyseal plate becomes ossified
Canaliculi – long, narrow spaces that house cell extensions
Bone Marrow – soft tissue inside the cavities in spongy
Osteoclasts – bone-resorbing cells / bone-destroying cells bone and medullary cavity
Bone Reabsorption – bone repair and remodeling by Red Bone Marrow – produce blood cells
removing existing bone
Yellow Bone Marrow – stores fat
Bone Breakdown – important for mobilizing crucial
Calcium; when it’s broken down, it goes into the blood
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, o In the fetus, the spaces within bones are filled with - occurs at the surface of the bone
red bone marrow. Just before birth, the red bone (endosteum/periosteum)
marrow starts to get converted to yellow marrow. - Appositional Growth – as osteoblasts deposit
o In adults, most red bone marrow is in the flat new bone matrix, the bone increases in width,
bones. The long bones of the femur and humerus or diameter
contain yellow marrow.
Bone Growth in Length
Periosteum – connective tissue membrane that covers the - major source of increased height of an
outer surface of a bone individual
o Outer layer – blood vessels - occurs in epiphyseal plate
o Inner layer – single layer of bone cells - occurs through endochondral ossification
- chondrocytes increase in number on the
Endosteum – single layer of connective tissue that lines the epiphyseal side of the plate
internal surfaces of all cavities within bones - chondrocytes enlarge and die
- cartilage matrix becomes calcified
Ossification – formation of new bone - osteoclasts remove cartilage that forms
around enlarged cells
Bone Formation – can result in compact or spongy bone
- dying chondrocytes are replaced by
2 processes in fetus: osteoblasts
1. Intramembranous ossification - osteoblasts start forming bone by depositing
- osteoblasts begin to produce bone within bone lamellae on the surface of the calcified
embryonic connective tissue membranes cartilage; this process produce bone on the
- occurs primarily in the bones of the skull diaphyseal side of the epiphyseal plate
- Ossification centers – where the ossification
begins Bone Remodeling
- 2 or more ossification centers exist in each - removal of existing bone by osteoclasts
flat skull bone and mature skull bones result - deposition of new bone by osteoblasts
from fusion of these centers and they grow - occurs in all bones
- responsible for changes in bone shape, repair,
Steps: 1. Osteoblasts produce bone matrix. adjustment of bone to stress, and calcium ion
Osteocytes become osteocytes. regulation
Trabeculae develop.
2. Osteoblasts gather on the surface of Bone Repair
trabeculae. Trabeculae grows larger. 1. broken bone causes bleeding and a
Spongy bone forms. hematoma form
3. Red bone marrow forms. Periosteum 2. callus forms
forms. Bone matrix form outer surface of
Callus – bone cartilage network between and
compact bone.
around the bone fragments
2. Endochondral ossification
- Bone formation within a cartilage model 3. woven, spongy bone replaces the callus
- cartilage model is replaced by bone 4. compact bone replaces the spongy bone
- primary ossification center – forms bone in
the diaphysis Bone and Calcium Homeostasis
- secondary ossification center – forms bone in
Calcium – critical nutrient involved in many physiological
the epiphysis
processes
Steps: 1. Chondrocytes build cartilage model, it o stimulation and regulation of skeletal and
become chondrocytes. cardiac muscle contraction
2. Cartilage model hardens. o exocytosis of cellular molecules (neural
3. Osteoblasts invade calcified cartilage signal)
and primary ossification center forms o Bone is a major site for calcium.
diaphysis. o Movement of calcium in and out the bones
4. Secondary ossification centers form help determine blood levels of calcium.
epiphysis. o Calcium → bone; osteoblasts build new bone
5. Almost completely ossified and o Calcium ← bone; osteoclasts breakdown
remaining cartilage is articular cartilage. bone
o Calcium homeostasis is maintained by
Bone Growth in Width parathyroid hormone (PTH) and calcitonin
- occurs by the deposition of new bone lamellae
onto existing bone or other c.t. Parathyroid Hormone (PTH)
o secreted by parathyroid gland
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