Slide set 10 - bones Flashcards
What are the 2 qualities of bones that allows them to serve supportive and protective functions?
RIGIDITY
STRENGTH
What are functions of bones?
SUPPORT
- form framework (shape, alignment and positioning)
PROTECTION
- protect the structures they enclose
MOVEMENT
-Bones with joints function as levers that move
MINERAL STORAGE RESERVOIR
- for calcium, phosphorus
HEMATOPOESIS
- Blood cell formation
What are the 4 types of bones ? give example
Long bones (humerus, femur, tibia)
Short bones (tarsals, carpals)
Irregular bones (vertebrea)
Flat bones (skull, shoulder blade)
What material constitutes the majority of ECM?
What is the importance of bones being vascular?
Collagen
Since bone are very VASCULAR, regenerate quite well because of vascularity
What is the part of the bone that is the end of the long bone?
Epiphysis
What is the epiphyseal plate?
Site of bone growth
What is the part that is the shaft of the long bone?
Diaphysis
What are the 2 parts of the bone structre?
- Cancellous (spongy) bone => open space partially filled with needle like structures.
- Compact bone => dense, solid in appearance
What is the function of the daphysis? What is it made of?
Provide strong support without cumbersome weight
Thick and compact bone
What are characteristics of the epiphysis?
- Both ends of a long bone, made of cancellous bone filled with marrow
- Bulbous shape
- Function is to PROVIDE ATTACHMENT for muscles and give stability to joints
What is articular cartilage?
Layer of hyaline cartilage that covers the articular surface of epiphysis
What is hyaline cartilage?
Elastic cartilage, function is to cushion jolts and blows.
Absorbs chocs
What is the periosteum?
- Dense, white, fibrous membrane that covers bone
- Attaches tendons firmly to bones
- Contains cells that form and destroy bone
- Contains blood vessels important in GROWTH AND REPAIR
- Contains blood vessels that send branches into bone
- Essential for bone cell survival and bone formation
What are the 2 layors of bone? What are their characteristics?
Endosteum
-Thin epithelial membrane that lines medullary cavity
Medullary (or marrow cavity)
- Tubelike, hollow space in diaphysis
- Filled with yellow marrow in adult
true or false
There is no red marrow in spaces inside cnacellous bon of irregular and flat bones
False, there are fiew irregular and flat bones that are filled with red marrow
Large amounts of red bone marrow are found in flat bones like those of the ribs, pelvis and skull.
True or false
The extracellular matrix of bones is made up of organic component?
False, organic AND inorganic
What is part of the inorganic salts in the bone matrix?
HYDROXYAPATITE
- Highly specialized chemical crystals of calcium and phosphate
- responsible of the hardness of bones
CALCIUM CARBONATE (10%)
MAGNESIUM AND SODIUM
What is the organic matrix? what secretes it?
Secreted by bone cells (osteoblasts).
- Collagenous fibers and a mixture of protein and polysaccharides which forms a gelatinous material termed GROUND SUBSTANCE
What mineral gives bones mostly their rigidity?
Calcium
Why is gound substance important?
It is important in bone growth, repair and remodeling as it acts as a medium for the diffusion of nutrients, oxygen and metabolic waste
What are the 4 types of structure that make up each osteon? In what type of bone?
In compact bone!
Lacunae - space in which osteocytes are located between hard layers of lamella
Lamella- concentric rings that are, islands of calcified matrix
Canaliculi- ultrasmall canals radiating from the osteocytes and connecting them to each other and to the Haversian canal (part of network that allows excretion and absorbtion of nutrients)
Haversian canal => extends lenghtwise through the center of each osteon and contains blood vessels and lymphatic vessels
Describe the structure of the cancellous bone.
- No osteons
- Contains traveculae-needle
like bony spicules - Nutrients are delivered and waste products removed by diffusion through iny canaliculi (canals radiating from bone cells)
- Bony spicules are arranged along lines of stress enhancinf the bone’s strenght
What is the fait of osteogenic cells?
Differentiale and develop into OSTEOBLASTS
Osteoblasts synthesize and secrete collagen in matrix. They can become trapped in the matrix when it calcifies becomes OSTEOCYTES (mature bone cells)
What cells is not osteogenic? From what is it made?
Osteoclasts stem from macrophages
_______ deposit calcium as they create a new bone matrix. _______ break down bone matrix during bone resorption.
Osteoblasts
Osteoclasts
What organelles do osteoclasts have in large numbers?
- Mitochondria
- Lysosomes
What does the osteoclasts secrete?
- Collagenase
- Matrix mettalloproteinases (MMPS=> destroy ECM such as collagen)
- Lactic and citric acid
How does osteoclasts attach to bone surfaces?
by integrins
What is an osteocyte?
Transformed osteoblast that trapped in the surrounding bone matrix
Final differentiation state for an osteoblast
OPG is an inhibitor/activator or RANK?
inhibitor, by binding to RANKL
What is the process of activation of OC precursor?
RANKL is expressed on surface of osteoblast, and binds its receptor RANK on osteoclast precursor
How does estrogen influence RANKL?
Estrogen limits the amount of RANKL expression by osteoblast
What happens during peri-menopause happen?
- Less estrogen
- Increased expression of RANKL by osteoblasts
- Excess RANKL overwelmes OPG
- Lead to more osteoclasts, increase bone remodeling and increase bone loss
What are stimulator of RANK binding to RANKL?
Parathyroid hormone
What hormone triggers release of calcium? How does it affect blood calcium levels?
Parathyroid triggers calcium release from bones, increases blood calcium levels
What hormones regulate blood calcium levels?
Parathyroid hormone (from parathyroid gland)
Calcitonin (from thyroid gland)
Vitamin D
Why do we need to regulate blood calcium?
- For muscle contraction
- Calcium efflux important in release of neurotransmitters in neurons.
- Crucial for nervous system functions.
What can affect calcium balance?
- Age, disease, medications…
- Children=> usually positive balance that allows bone growth
- Adults input and output should be the same
- Post-menauposal women tend to have a negative calcium balance
- Dietary intake is variable so the body must be able to adapt to raisd or reduced levels
What are the 3 major paths of calcium regulation?
- PTH regulation to increase calcium blood levels by breakdown of bone
- Calcitonin acts to lower blood calcium levels and favour calcium storage in bone
- Vitamin D (calcitriol) regulation of calcium- deposits calcium in bone
What is the action of parathyroid hormrone?
- Releases when plasma Calcium is low
- Mobilizes calcium from bone
- Enhances renal reabsorption of calcium
- Stimulates release of calcitriol
What is the action of calcitriol?
Increases intestinal calcium absorption
what are the 3 pools in which calcium can be found?
- extracellular calcium (0,1% of total)
- Intracellular calcium (0,9% of total)
- Calcium in bone matrix (99% of total)
What is the effect of calcitonin?
- opposite manner than PTH
- Produced in response to high blood calcium
- Decrease bone resorption
- Increases renal calcium excretion
What is the effect of vitamin D on bones?
- Increased calcium reabsorption in the proximal and distal convoluted tubules of the kidney
- Stimulates osteoblast activity to increase bone mass and calcification
- In the intestine, increases the synthesis of calcium binding proteins on intestinal cells
- Disorders of vitamin D can cause weak bones (rickets in children or osteomalacia in adults)
Where does vitamin D come from?
- Vitamin D (calcitriol) is absorbed by the small intestine as part of the diet
OR - is synthesized from exposure of skin to UV light converts
(7-dehydrocholesterol to cholecalciferol in the skin to a preucros of vitamin D)
Aller voir slide 32
go
When skeleton forms in fetus, t is made of ______
cartilage
_______ stimulates osteoblast to secrete more colalgen which makes bones stronger
Exercise
What are the 2 mechanisms for bone formation? What use these mechanisms
Intramembranous: some flat bones, no cartilage (skull).
Endochondral (cartilage, vascular): vascular, long and float bones.
What is the intramembranous bone formation mechanism? what happens?
Occurs when membranes are replaced by bone tissue.
Occurs within a connective tissue membrane.
Flat bones, like the bones of the skull, sternum and clavicle.
- Does not begin with a cartilage model, instead, dense areas of mesenchymal cells (multipotent stem cells) differentiate and begin to lay down bone around themselves, forming early spicules.
What are the 2 major steps of intramembranous bone formation?
- spongy bone tissue begins to develop at sites within the membranes called CENTERS OF OSSIFICATION
- Red bone marrow forms within the spongy bone tissue, followed by the formation of compact bone on the outside.
Go see slide 35
go
What are characterisitcs of endochondral bone development? How is it different from intramemebranous bone formation?
Difference=> it begins as a cartilage model, with bone formation spreading essentially form the center to the ends.
What are the steps of cartilage formation in endochondral bone formation?
- Mesenchymal stem cell migrate to the site of eventual bone development
- These cell are induced to become chondrocytes (cartilage cells)
- Chondrocytes differentiate into very dense avascular mass
- Cartilage forms in the shape of the bone
What are the steps of endochondrial ossification?
- Cartilage is surrounded by periosteum (envelope of connective tissue)
- Develops and enlarges
- Osteoblasts which differentiate from the inner surface of the periosteum produce a collar of bone
- Primary ossification center forms
- Blood vessel enters the cartilage at the midpoint of the diaphysis
ALLER VOIR VIDEO
https://www.youtube.com/watch?v=xXgZap0AvL0
What are the 4 layers of the epiphyseal plate? Describe them
- Zone of PROLIFERATION: Chondrocytes (cartilage cells) undergoing active mitosis causing thickening of the the layer, and epiphyseal plate to increase in lenght
- Zone of HYPERTROPHY: older enlarged cells undergoing degenerative changes associated with calcium deposition
- Zone of CALCIFICATION: Dead or dying cartilage cells undergoing rapid calcification
- OSSIFICATION zone: matrix undergoes calcification
Epipheseal plate is the site of bone _______.
Growth
When does epiphyseal plate fuse?
Around puberty
- Epiphyseal plate remains between diaphysis until bone growth in length is complete
How does closing of the epiphyseal plates vary?
- Varies from person to person (mostly due to different sex hormones)
- Varies from bone to bone ( digits close early, arm, leg and pelvis bones close later)
How does bone grow in diameter?
- Bones grow in diameter by the combined action of osteoclasts and osteoblasts
- Osteoclasts enlarge the diameter of the medullary cavity by eroding the inner surface
- Periosteum cells develop into osteoblasts
- Osteoblasts from the periosteum build new bone around the outside of the bone
What are symptoms of osteoporosis ?
- Fractures of the vertebrae, wrists or hips
- Lowe back pain, neck pain, bone pain or tenderness
- Loss of height over time
- Stooped posture
What medication can be prescribed in osteoporosis? What else then medication?
Raloxifene
Calcitonin
Estrogen replacement therapy
Or else=> exercise => cause increase in bone density
How does estrogen acts on osteoblast?
- Estrogen acts on osteoblast to stimulate the production of TGF-Beta
- TGF-Beta causes the osteoblasts cells to make osteoprotegerin (OPG)
- OPG binds to RANKL and prevents it from binding to RANK receptors on the preosteoclasts. This prevents them from becoming osteoclasts and thus limits bone resorption
- When there are low levels of estrogen, levels of OPG decline, lets RANK bind to RANKL, more osteoclasts.
What is the difference in remodeling between adults and young adults ?
Adults:
- Osteocytes in lacunae continuously remove and replace surrounding calcium salts
- MAintain surrounding matrix
- Osteoblasts and osteoclasts remain active
- Remodeling bone, especially spongy bone
In young adults:
- Remodeling is so rapid that about one-fifth of the skeletal mass is replaced each year
