Chapter 6: Bone Tissue Flashcards
The building of new bone tissue and breaking down of old bone tissue
Bone remodeling
Osseus
Bone
This organ is made up of:
- bone (osseus tissue)
- cartilage
- dense connective tissue
- epithelium
- adipose tissue
- nervous tissue
Bones
6 basic functions of the skeletal system
- Support
- Protection
- Assistance in Movement
- Mineral Homeostasis (storage and release)
- Blood cell production
- Triglyceride storage
How do bones SUPPORT the body?
the skeleton serves as the structural framework for the body by supporting soft tissues and providing attachement points for the tendosn and most skeletal muscles
How do bones provide PROTECTION?
The skeleton protects the most important internal organs from injury
How do bones ASSIST IN MOVEMENT?
Bones are pulled by skeletal muscles when they contract, producing movement
How do bones maintain MINERAL HOMEOSTASIS?
Storage and release
- bones store minerals, esp calcium and phorphorous, which contribute to its strength.
- Bone stores about 99% of calcium
- RElease minerals in blood as needed in other parts of the body
How do bones support BLOOD CELL PRODUCTION?
Red bone marrow produces red blood cells, white blood cells and platelets
The process where the red bone marrow produces red blood cells, white blood cells and platelets
Hemopoiesis
What does red bone marrow consist of?
Developing blood cells, adipocytes, fibroblasts, and macrophages within a network of reticular fibres
Where is red bone marrow located?
Developing bones of the fetus
Some adult bones: hip(pevlic) bones, ribs, sternum, vertebra, skull and ends of the humerus and femur
How do bones support TRIGLYCERIDE STORAGE
Yellow bone marrow consists mainly of adipose cells which store triglycerides; these triglycerides contain potential chemical energy
What is a bone that is greater in length than in width?
Long Bone
What are the typical components of a long bone?
- Diaphysis
- Epiphyses
- Metaphyses
- Articular cartilage
- Periosteum
- Medullary Cavity
- Endosteum
This is the bone’s shaft or body - long cylindrical main portion of the bone
Diaphysis
These are the proximal and distal ends of the long bones
Epiphyses
This is the region of a long bone between the diaphysis and the epiphyses. This contains the epiphyseal plate (growth plate)
Metaphyses
This is made of a layer of hyaline cartilage that allows the diaphysis to grow in legnth; it is replaced by a boney structure called the epiphyseal line, once growing is complete
Epiphyseal plate (growth plate)
What is the bone strucutre called that replaces the epiphyseal plate
Epiphyseal line
This part of the long bone is a thin layer of hyaline cartilage covering part of the epiphyses where the bone forms a join
Articular Cartilage
This part of a long bone is a tough connective tissue and its associated blood supply that surrounds the bone surface wherever it is not covered by articular cartilage
Periosteum
The anatomy of the periosteum?
Outer fibrous layer - dense irregular connective tissue
Inner osteogenic layer - consists of cells
How is the periosteum attached to the underlying bones?
Perforating fibres (sharpeys fibres) - thick bundles of collagen that extend from the periosteum into the bone extracellular matrix
What are the functions of the periosteum?
some cells enable rgowth in thickness but not length
protects the bone, assists in fracture repairs, help nourish bone tissue; serves as an attachement point for ligaments and tendons
This part of a long bone is a hollow, cylindrical space within the diaphysis that contains fatty yellow bone marrow and numerous blood vessels in adults
The hollow design increases strength while decreasing weight
Medullary Cavity (marrow cavity)
This structure of the long bone is a thin membrane that lines the medullary cavity
Contains a single layer of bone forming cells and small amount of connective tissue
Endosteum
Describe osseus tissue extracellular matrix
Extracellular matrix is about 15% water, 30% collagen fibres, and 55% crystalized mineral salts
Most abundant mineral salt in osseus tissue
calcium phosphate
Mineral that combines with calcium phosphate to form crystals of HYDROXYAPATITE
Calcium hydroxide
Minerals that combine to compose hydroxyapatite
Calcium phosphate and calcium hydroxide
The process where hydroxyapatite forms into crystals and combines with other mineral salts and ions and is then deposited into framework of collagen fibers of extracellular matrix, crystalize and then harden
Calcification
What cells initiate calcification?
Osteoblasts
What is responsible for the characteristics of bones?
crystallized salts combined with collagen fibres
What does characteristic of bones does collagen fibres contribue to?
Flexibility
What determines a bones hardness?
crystalized inorganic mineral salts
4 types of cells in bone tissue:
- Osteoprogenitor cells
- Osteoblasts
- Osteocytes
- Osteoclasts
Unspecialized bone stem cells that undergo cell division that results in development of osteoblasts
Found along the inner portion of the periosteum, in the endosteum and in the canals within bone that contain blood vessels
Osteoprogenitor cells
These are bone-building cells that synthesize and secrete collagen fibres and other organic componenets needed to build extracellular matrix
Initiate calcification
As they surround themselves with extracellular matrix, they become trapped in their secretions and become osteocytes
DO NOT UNDERGO CELL DIVISION
Osteoblasts
What do -blasts cells do
secrete extracellular matrix
These cells are mature bone cells and maintain daily metabolism (exchange of waste and nutrients with blood)
Do not undergo cell division
Osteocytes
Cell name ending in -cyte do this:
Maintain and monitor tissue
These are huge bone cells derived from the fusion of up to 50 monocytes and are located in the endosteum
Responsible for bone resorption
Osteoclasts
Anatomy and function of an osteoclast
Cell side facing bone surface - plasma membrane is deeply folded into a ruffled border and the cell releases lysosomal enzymes that break down ECmatrix
The term for the release of powerful ezymes and acids that break down proteins and mineral components of extracellular bone matrix
Bone resorption
Two categories of bone that is based on size and distribution of spaces
Spongy or compact
This bone tissue contains few spaces and is the strongest form of bone tissue
Found beneath the periosteum of all bones and makes up most of diaphyses of long bones
Compact Bone
Functions of compact bone
- provides protection and support
- resists stresses produced by weight and movement
The components of compact bone tissue haversion systems (Osteons)
- Osteonic (haversion) canal
- Concentric Lamellae
- Lacunae
- Canaliculi
This part of compact bone haversion system is where small networks of blood and nerce supplies are found
Haversion (Osteonic) canal
This part of the Osteon resembles the ring growth of trees; it is made of circular plates of mineralized ECM of increasing diameter
Form parallell cylinders that run parallel to the long axis of long bones
Concentric Lamellae
This part of an osteon is actually small spaces between the concentric lamellae and contain osteocytes
Lacunae
These narrow channels radiate from the lacunae, contain ECM, and house the long processes of the osteocytes (the processes are able to provide communication between neighboring osteocytes via gap junctions)
canaliculi
What is found in between the osteons in bone tissue?
Interstital lamallae
What is interstitial lamallea formed from?
Fragmens of older osteons that have been partially destroyed during remodeling or growth of the bone
What does interstitial lamellae contain?
Lacunae with osteocystes and canalculi
Where do blood vessels and nerves from the periosteum penetrate compact bone?
Through Interosteonic canals (volkmanns or perforating canals)
The outer and inner circumference of the shaft of a long bone are lined with lamellae called
Circumferential lamellae
Where are these found:
Concentric Lamellae
Interstitial Lamellae
Circumferential Lamellae
- osteons
- between osteons
- the inner and out circumference of long bone shafts
Circumferential lamellae directly deep to the periosteum (outer circumference of bone shaft)
external circumferential lamellae
Circumferential lamellae that line the medullary canal (inner circumference of bone shaft)
internal circumferential lamellae
Fibres that connect periosteum to outer circumferential lamellae
Sharpey’s fibres / perforating fibres
Spongy bone does not have osteons, but rather is composed of:
trabecullae (cancellous bone tissue)
Where is spongy bone always found?
Interior of bones, always protected by a covering of compact bone
What is each trabeculae composed of?
Concentric Lamellae
Osteocytes
Lacunae
Canalucli
What fills the visible spaces we can see between trabeculae of spongy bone?
Red bone marrow in blood cell producing bones; yellow bone marrow in others
Numerous small blood vessels that nourish osteocytes
What area of bones is spongy bone found?
In long bones - found inside epiphyses under a thin layer of compact bone; and in a thin rim bordering the medullary cavity of the diaphysis
Makes most of the interior of short, flat, sesamoid and irregularly shaped bones
2 ways spongy bone tissue is different than compact bone tissue
- Lighter, reducing overall wieght of bones
- Trabecullae support and protect red bone marrow
These are small arteries, accompanied by nerves, that eter the diaphysis through many interosteonic (perforating) canals and supply the periosteum and outer oart of the compact bone
Periosteal Arteries
The hole in compact bone that the nutrient artery passes through in about the middle of the long bone to enter the medullary canal
Nutrient foramen
What does the nutrient artery divide into once it enters the nutrient foramen
Proximal and distal nutrient artery branches that supply the compact bone of diaphysis and the spongy bone tissue and red bone marrow all the way tot he growth plates
How many nutrient arteries are there in long bones?
Some, like the tibia, have one; others have several
WHat arteries supply the ends of long bones?
metaphyseal and epiphyseal arteries
Describe the metaphyseal artery
Enters the metaphyses of long bones and suport the nutrient artery to support red bone marrow and teh bone tissues of the metaphyses
Describe the epiphyseal arteries
enter the epiphyses of a long bone and supple the red bone marrow and bone tissue of the epiphyses
Describe the veins of a long bone
- nutrient vein - one or two that exit through diaphesis
- many epiphyseal veins
- many metaphyseal veins
Where do periosteal veins exit?
Through periosteum
Where are the nerves that cause bone related pain?
In the periosteum
Process by which bones form
Ossification or ostogenesis
4 principle situations that bone formation occurs:
- initial formation in an embryo and fetus
- growth of bones during infancy, childhood and adolensence
- Remodelling of bone thorugh life
- the repair of fractures
Two patterns of bone formation in an embryo and fetus
- Intramembraneous ossification
- Endochondral ossification
When bone forms directly within the mesenchyme, which is arranged in sheetlike layers that resemble membranes
Simpler of two methods
Flat bones of skull, mandible, most facial bones, medial part of collar bone are formed this way
Also the way soft spots become bone in newborns
Intramembraneous ossification
When bone forms within hyaline cartilage that develops from the mesenchyme
Endochondral ossification
The process of intermembraneous ossification:
- Development of ossification centre
- calcification
- formation of trabeculae
- development of the periosteum
- Development of ossification centre
where bone will develop, specific chemical messages cause the mesenchyme cells to cluster together and differentiate into osteoprogenitor and then osteoblast cells
Osteoblasts secrete the ECM until they are surrounded
- Calcification
when secretion of ECM stops, the osteocytes are in lacunae and extend their processes into canalculi. In a few days the ECM hardens or calcifies due to deposti of calcium and other mineral salts
- Formation of trabeculae
As ECM forms, it fuses to neighboring trabeculae and therefore spongy bone around the blood vesselin the tissue
Connective tissue associated with the blood vessels in the trabeculae differentiates into bone marrow
- Development of periosteum
Mensenchyme condenses and becomes periosteum
Thin layer of compact bone eventually replaces surface layers of spongy bonen
Endochondrial Ossification Steps
- Development of cartilage model
- growth of cartilage model
- development of primary ossification centre
- development of medullary cavity
- development of secondary ossification centres
- Formation of articular cartilage and the epiphyseal growth plate
- Cartilage Model Development
chemical messages cause mesenchymal cells to gather in shape of future bone and then develop into chondroblasts that secrete cartilage ECM
This produces the cartilage model made of hyaline cartilage
Is covered in a perichondrium
- Growth of the cartilage model
- chondroblasts buried in ECM from step 1 and become chondrocytes
-length grows by continual cells division of chondrocytes and further secretion of the cartilage ECM - known as interstitial growth (endogenous) - thickness growth happens by appositional or exogenous growth in which ecm is depositied on the cartilage surface by new chondroblasts that develop from the perichondrium
As model grows, chondrocytes start to hypertrophy and ECm near them begin to calcify and chondrocytes begin to die, leaving lacunae
- Development of primary ossification centre
Develops inward from the external surface of the bone
nutrient artery penetrates the perichondrium and the cartilage model forming the nutrient foramen which in turn stimulates osteoprogenitor cells in the perichondrium to differentiate into osteoblasts
What is the perichondrium called as soon as it starts to form bone in response to the nutrient artery development
Periosteum
- Development of medullary cavity
Primary ossification centre moves towards bone ends and osteoclasts break down some of the newly formed spongy bone trabeculae
This leaves a cavity in the diaphysis
Eventually diaphysis wall is replaced by compact bone
- Development of secondary ossification centres
develop when epiphyseal arteries enter the epiphyses
happens around the time of birth
Growth proceeds outward and spongy bone remains in the interior
- Articular cartilage formation and the epiphyseal growth plate
hyaline cartilage that covers the epiphyses becomes articular cartilage
hyaline cartilage remains in metaphysis until adulthood and is where length growth occurs
The two major events in growth of length of long bones
- Interstitial growth of cartilage on epiphysis side of growth plate
- Replacement of cartilage on the diaphysis side of the growth plate through endochondrial ossification
4 zones of epiphyseal plate structure
- zone of resting cartilage
- zone of proliferating cartilage
- zone of hypertrophic cartilage
- zone of calcified cartilage
- Zone of resting cartilage
layer nearest epiphysis
small, scattered chondrocytes
anchor epiphyseal plate to the epiphysis of the bone
do not function in bone growth
- Zone of proliferating cartilage
Slightly larger chondrocytes, arranged like stacks of coins
undergo interstitial growth as they divide and secrete ECM
Divide to replace those that die at diaphyseal side of plate
- Zone of hypertrophy
Large, maturing chondrocytes arranged in columns
- Zone of calcified cartilage
Only a few cells thick
mostly chondrocytes that are dead because the ECM has calcified
Osteoclasts discolve the calcified cartilage and osteoblasts and capillaries from the diaphysis invade the area
Osteoblasts produce ECM to replace the calcifed cartilage via endochondral ossification
Epiphyseal line
When adolescence ends (age 18 in girls and 21 in boys), epiphyseal cartilage cells stop dividing and bone replaces all the remaining cartilage
Bone length growth stops completely
What is the only way that bone and cartilage tissue can grow in thickness?
Appositional growth
Appositional Growth in Bone tissue:
- Periosteal cells differentiate into osteoblasts
- The ridges fold together and fuse, and the groove becomes a tunnel that encloses the blood vessel
- Osteoblasts in endosteum deposit bone extracellular matrix forming new concentric lamellae and filling in to create a new osteon
- Osteoblasts under periosteum deposist new circumferential lamella , further increasing bone thickness
The ongoing replacement of old bone tissue by new bone tissue
Bone remodelling
What 2 steps does bone remodeling involve?
Bone resorption and Bone deposition
The removal of mineral and collagen fibers from the bone by osteoclasts
bone resortption
the addition of minerals and collagen fibers to bone by osteoblasts
bone deposition
Factors that affect bone growth and bone remodelling
- Minerals
- Vitamins
- HormonesM
How do minerals affect bone growth and resporption?
Large amounts of calcium and phosphorus are needed while bones are growing and bone remodeling. Small amounts of magnesium, fluoride and manganese is also needed.
How do vitamins affect bone growth and remodelling?
Vitamin A - stimulate osteoblast activity
Vitamin C - synthesis of collagen
Vitamin D - increases calcium absorption from foods
Vitamin K and B12 - bone protein synthesis
How do childhood hormones impact bone growth and remodeling?
Insulin-like growth hormone (IGFs)
Growth Hormone (GH)
T3 and T4
Insulin
Childhood - insulin-like growth factors (IGF) - stimulat osteoblasts, promote cell division at growth plate and periosteum, enhance synthesis of proteins
IGFs are secreted in response to growth hormone (HG)
T3 and T4 stimulate osteoblasts
Insulin - increases synthesis of bone proteins
How do adolecent hormones impact bone growth and remodeling?
Sex hormones - estrogens and androgens - adrogens secretred by adrenal glands
- increase osteoblast activity, extracellular matrix production, and responsible for growth spurt in teen years
Estrogen causes female specific changes such as wider pelvis
What hormone in primarily responsible for shutting down the growth plate
sex hormones, especially estrogens in both sexes
What tissue can convert adrogens to estrogens?
adipose
How do adult hormones impact bone growth and remodeling?
sex hormones - contribute to remodelling by slowing resorption of old bone and promoting deposition of new bone
Estrogens slow resporption by promoting apoptosis of osteoclasts
Parathyroid hormone, calciltrol, and calcitonin also affect bone remodelling
What do nerve and muscle cells, blood clotting, and many enzymes require to be stable for their functioning
Ca2+
What role does PTH play in Calcium Ion (Ca2+) exchange
- parathyroid gland cells detect decreased blood calcium levels
- Parathyroid gland cells increase production of cyclic AMP molecules
- Gene for PTH in parathyroid gland cell nucleus, detects increased cyclic AMP leves in cell
- PTH production increases and blood level of PTH rises
- Higher PTH levels in blood increases number and activity of osteoclasts, increasing bone resorption
- This results in increased calcium levels in the blood
How does PTH affect kidneys in response to low calcium levels in blood
Decreases excretion of calcium into urine
How does PTH increase absorption of calcium from foods?
By stimulating formation of calcitrol (active form of vitamin D)
Describe calcitonin (CT) role in reducing blood calcium levels
- Blood calcium level increases
- Parafollicular cells in thyroid secrete calcitonin
- Calcitonin inhibits activity of osteoclasts, speeds up calcium uptake by bone and accelerates calcium deposition into bones
