A&P Chapter 07
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Transcript of A&P Chapter 07
Ivyanatomy.com
Chapter 7
Osteology is the science of bones
Bones are a living dynamic tissue: constantly remodeled through life
Functions of Bone:
• Protection – brain is protected by the skull & heart and lungs by the thoracic cage
• Support & Movement – muscles attach to the skeleton
• Calcium and Phosphate storage
• Blood Cell Production – blood cells are produced by red bone marrow
Red Bone Marrow – site of blood cell production
• Locations of Red Bone Marrow:
• Infant – all bones are filled with red bone marrow
• Adult – red bone marrow is limited to
• flat bones (sternum, ribs, skull, hips) and
• irregular bones (vertebrae)
Yellow Bone Marrow – Adipose tissue
The cells associated with bones include:
• Osteocytes = cells that maintain bone.
o Osteocytes reside within chambers, called lacunae
• Osteoblasts = cells that deposit new bone. Once mature, osteoblasts
become osteocytes.
• Osteoclasts = cells that dissolve bone.
• Osteoclasts originate from white blood cells
• and they secrete an acid that dissolves the inorganic salts of bone.
The extracellular matrix of bones is composed of
• hydroxyapatite – a calcium phosphate salt that provides the hardness of bones
• collagen fibers – provides bone with some pliability
1. Long bones = elongated diaphysis
• Humerus radius ulna metacarpals phalanges
• Femur tibia fibula metatarsals phalanges
2. Short Bones = cube-shaped
• carpals
• tarsals
3. Flat Bones = plate-like
• Sternum, ribs, scapula
• parietal and frontal bones
4. Irregular bones = variety of shapes
• vertebrae
• mandible
• maxilla
• ethmoid bone
• sphenoid bone
5. sesamoid (or round) bone = develops
within tendons
• patella
Parts of a long bone
Epiphysis = expanded end of bone
• Filled with spongy (cancellous) bone
• Proximal epiphysis & distal epiphysis
• Sites of articulation (joint)
Diaphysis = shaft of long bone
• Lined with compact bone
Articular cartilage = covers epiphyses
• Composed of Hyaline cartilage
Epiphyseal line = remnant of bone growth (epiphyseal plate)
Parts of a long bone
Medullary Cavity = chamber within diaphysis
• Filled with bone marrow, blood vessels and nerves
• Yellow Bone Marrow in adults• Red Bone Marrow in children
Endosteum = Membrane that lines medullary cavity
• Contains dense connective tissue
• Blood vessels and nerves• osteoblasts
Periosteum = Tough membrane covering the bone
• Composed of Dense Connective Tissue
• Blood Vessels, Nerves, Osteoblasts
• Continuous with tendons and ligaments
Parts of a long bone
Compact bone
• Lines the Diaphysis and a thin layer
surrounds the epiphyses
• Composed of osteons
Spongy bone
• Fills the epiphyses and a thin layer
lines the medullary cavity
• Trabiculae = thin bony plates
• Osteocytes lie within trabiculae
Compact Bone
Osteon = Structural & functional unit of compact bone
Lamella = concentric rings of bone around a central canal
Central Canal (Haversian Canal)
• Contains blood supply and nerve
• Aligned parallel to diaphysis
Lacunae = bony chamber that contains an osteocyte
Osteocyte = maintains the bone
Canaliculi = canals connecting osteocytes to the central canal
• Canaliculi are filled with cellular processes
• Pathway for nutrient and waste diffusion
Osteon continued
Perforating Canal (Volkmann’s Canal)
• conveys blood from periosteum
towards the central canal
• Aligned perpendicular to diaphysis
Compact bone is composed of osteons cemented together by bone matrix.
Bone Development and Growth
Parts of the skeletal system begin to develop during the first
few weeks of prenatal development
Bone formation = ossification
Bones replace existing connective tissue in one of two ways:
As intramembranous bones
As endchondral bones
Intramembranous Ossification
Intramembranous Ossification
Forms broad, flat bones of the skull
Formed by replacing layers of embryonic connective
tissue (mesenchyme) with bone
Osteoblasts within mesenchyme
deposit bony matrix in all directions
Osteoblasts become osteocytes
once surrounded by bone
Intramembranous Ossification
Intramembranous ossification follows four steps.
(a) Mesenchymal cells group into clusters, and ossification centers form.
(b) Secreted osteoid traps osteoblasts, which then become osteocytes.
(c) Trabecular matrix and periosteum form.
(d) Compact bone develops superficial to the trabecular bone, and crowded blood vessels condense into red marrow.
Endochondral Bones
Endochondral Bones
Most of the bones in the skeleton are endochondral
Bone formation begins with a hyaline cartilage model
Cartilage decomposes and is replaced by bone.
Endochondral Ossification
1. Hyaline cartilage forms model of
future bone
2. Cartilage degenerates and
periosteum surrounds bone
3. Osteoblasts from periosteum invade
the degenerating tissue
4. Osteoblasts beneath periosteum
form compact bone at diaphysis =
primary ossification center
5. Later, Osteoblasts form spongy bone
at epiphyses = secondary ossification
center
Endochondral Ossification
Intramembranous ossification follows four steps.
(a)Hyaline cartilage forms model of future bone
(b)Cartilage degenerates and periosteum forms around
bone
(c) Primary ossification center forms compact bone within
the diaphysis
(e) Secondary ossification centers form spongy bone within
the epiphyses
(f) Some cartilage remains at the epiphyseal plates & as
articular cartilage at the end of bones
Endochondral Ossification
Two areas of endochondral bone retain
cartilage after ossification.
1. Articular cartilage
• surrounds the epiphyses for joints
2. Epiphyseal plates
• retain cartilage for bone growth
Growth at the Epiphyseal Plate
Epiphyseal Plate
• Band of hyaline cartilage that remains
between the two ossification centers
• Bone growth continues at epiphyseal
plates until adulthood.
• New cartilage is added towards the epiphysis
and cartilage is ossified towards diaphysis
• Once the epiphyseal plates ossify the
bones can no longer be lengthened
4 Layers (zones) of growth at
epiphyseal Plate
1. Zone of resting cartilage (reserve zone)
• Cartilage cells near epiphysis
• Do not participate in bone growth
• Anchor epiphyseal plate to epiphysis
2. Zone of proliferating cartilage
• Young chondrocytes undergoing
mitosis
• Adds new cartilage to plate
(b)
4 Layers (zones) of growth at
epiphyseal Plate
3. Zone of hypertrophic cartilage
• Older cells enlarge and thicken the
epiphyseal plate
• Osteoblasts invade and calcify the
cartilaginous matrix.
4. Zone of calcified cartilage
• Dead cells & calcium matrix
Ossified bone (zone of ossification)• Osteoclasts dissolve and phagocytize the matrix• Osteoblasts invade the region and deposit new bone.
Age Occurrence
3rd month prenatal development
Ossification begins in long bones4
4th month prenatal development
Most primary ossification centers have appeared in diaphysis of long bones.
Birth to 5 years Secondary ossification centers appear in the epiphyses of long bones.
5 to 12 years (females)
5 to 14 years (males)
Ossification rapidly spreads from the ossification centers
15 to 18 years (females)
17 to 20 years (males)
Bones of the upper limbs and scapulae completely ossified.
16 to 21 years (females)
18 to 23 years (males)
Bones of the lower limbs and hip bones completely ossified
21 to 23 years (females)
23 to 25 years (males)
Bones of the sternum, clavicles, and vertebrae completely ossified.
By 23 (females)
By 25 (males)
Nearly all bones completely ossified.
Bone Remodeling
Calcium is constantly exchanged between the blood and bone.
Bone resorption = Osteoclasts breakdown bone releasing
calcium into the blood.
• Bone resorption occurs when blood [Ca2+] is low and it’s
stimulated by parathyroid hormone (PTH).
Bone deposition = Osteoblasts deposit new bone from
calcium in the blood stream.
• Bone deposition occurs when blood [Ca2+] is high and it’s
stimulated by the hormone calcitonin.
Vitamin D – promotes Ca2+ absorption in small intestine
• Vitamin D deficiency = softened and deformed bones
• Osteomalacia in adults
• Rickets in children
Vitamin A – balances bone resorption and deposition
• Vitamin A deficiency = retards bone development
Vitamin C – is required for collagen synthesis.
• Vitamin C deficiency = results in fragile bones
Nutrients that effect bone homeostasis
Growth Hormone (GH)
• Secreted from pituitary gland
• Promotes bone growth at epiphyseal plates
Pituitary Gigantism
over secretion of GH during childhood
Pituitary Dwarfism
insufficient GH during childhood
Acromegaly
• Over secretion of GH as an adult
• Occurs after epiphyseal plates have sealed
• Enlargement of hands, feet, nose
Hormones that affect bone homeostasis
Calcitonin
• Secreted from thyroid gland
• Promotes bone deposition
• Stimulates Osteoblast activity
• Inhibits Osteoclast activity
Parathyroid Hormone (PTH)
• Secreted from parathyroid glands
• Promotes bone resorption
• Stimulates Osteoclast activity
• Inhibits Osteoblast activity
Hormones that affect bone homeostasis
Thyroid Gland
Blood CalciumNormal Range
Increased blood calcium detected by cells in
thyroid gland
Thyroid Gland secretes Calcitonin
Osteoblasts deposit calcium into bones
Blood calcium returns to normal
Blood calcium level increases
Blood calcium level decreases
Decreased blood calcium detected by cells in parathyroid
gland
Parathyroid glands secrete PTH
Osteoclasts resorb boneto release Calcium into
the blood
Sex Hormones (testosterone & estrogen)
• Promotes long bone growth at puberty
• Sex hormones also stimulate ossification at
epiphyseal plates*
*Estrogen has a stronger effect than testosterone on
bone ossification, which is why ossification of the
epiphyseal plates occurs earlier in development in
females than in males.
Hormones that affect bone homeostasis
Impacts of Exercise and Sunlight on Bone Homeostasis
Exercise – especially resistance or strength exercise strengthens bones. Muscles pull on bones, and bones thicken in response.
Sunlight – UV rays promote the release of Vitamin D from skin. Circulating vitamin D is activated in the liver, then it promotes the absorption of Calcium from the intestines.
Greenstick fracture
One side of the bone bends,
the other side breaks.
Most common in children,
because their bones are
more pliable than adults.
Fissured fracture
Longitudinal break on the bone.
Transverse fracture
Complete break perpendicular
to the diaphysis
Oblique fracture
Complete break at any other
angle not perpendicular to
diaphysis
Comminuted fracture
Results in several bony
fragments
Spiral fracture
Results from twisting
the bone
(a) Hematoma Formation Blood vessels rupture causing severe bleeding.The blood clots, forming a hematoma
(b) Cartilaginous Callus Formation
Fibroblasts deposit a mass of fibrocartilage
(c) Bony Callus Formation
Osteoblasts replace the cartilaginous callus with a bony callus
(d) Bone RemodelingOsteoclasts and
macrophages remove excess bone and debris
Repair of a fracture
Osteopenia “low bone mass”
• Progresses towards osteoporosis
Osteoporosis “porous bone”
• Bones develop spaces and canals
• Bones are fragile and easily broken
• Common in menopausal women
(from the low estrogen levels)
Over time, osteoclasts outnumber osteoblasts, and
more bone is resorbed than can be deposited. Bone
mass decreases as a result.
Healthy Bone Osteoporosis Bone
Ways to delay or prevent osteoporosis:
1. Exercise daily.
2. Consume enough calcium and
vitamin D every day.
3. Do not smoke.
Attribution
• Skeleton illustration Pixabay CC0 Public Domain https://pixabay.com/p-30160/?no_redirect• Classification of bone by shape By BruceBlaus (Own work) [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia
Commons https://upload.wikimedia.org/wikipedia/commons/7/77/Blausen_0229_ClassificationofBones.png• Parts of a long bone By OpenStax College [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons
https://upload.wikimedia.org/wikipedia/commons/2/23/603_Anatomy_of_Long_Bone.jpg• Diagram of Compact Bone By OpenStax College [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons
https://upload.wikimedia.org/wikipedia/commons/5/58/624_Diagram_of_Compact_Bone-new.jpg• Diagram of Osteon By BDB [CC BY-SA 2.5 (http://creativecommons.org/licenses/by-sa/2.5)], via Wikimedia Commons
https://upload.wikimedia.org/wikipedia/commons/7/75/Transverse_Section_Of_Bone.png• Intramembranous ossification By OpenStax College [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons
https://upload.wikimedia.org/wikipedia/commons/a/a9/611_Intramembraneous_Ossification.jpg• Endochondral Ossification By OpenStax College [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons
https://upload.wikimedia.org/wikipedia/commons/9/97/608_Endochrondal_Ossification.jpg• Epiphyseal Plate By OpenStax College [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons
https://upload.wikimedia.org/wikipedia/commons/1/15/622_Longitudinal_Bone_Growth.jpg• Bone Remodeling By Cancer Research UK (Original email from CRUK) [CC BY-SA 4.0 (http://creativecommons.org/licenses/by-sa/4.0)],
via Wikimedia Commons https://upload.wikimedia.org/wikipedia/commons/d/dd/Diagram_showing_bone_remodelling_Fig_CRUK_112.svg
• Types of Fractures By OpenStax College [CC BY 4.0 (http://creativecommons.org/licenses/by/4.0)], via Wikimedia Commons https://upload.wikimedia.org/wikipedia/commons/3/35/612_Types_of_Fractures.jpg
• Repair of Bone Fracture By OpenStax College [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons https://upload.wikimedia.org/wikipedia/commons/1/12/613_Stages_of_Fracture_Repair.jpg
• Normal and Degraded Bone By Gtirouflet (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons https://upload.wikimedia.org/wikipedia/commons/8/8e/Bone_normal_and_degraded_micro_structure.jpg