Lecture 13 - Bone Flashcards
What is ossification?
The formation of bone
How many types of ossification are there?
2
What are the 2 types of ossification?
Endochondral ossification
Intra-membranous ossification
What is EndoCHONDRAL Ossification?
Formation of LONG BONES from a Hyaline CARTILAGE TEMPLATE
CHONDRAL = Cartilage
Continued growth and lengthening at epiphyseal plate (appositional growth)
So what is Appositional Growth and therefore Endochondral Ossification?
Chondrocytes at epiphyseal plate secrete new bone matrix/tissue at the surface of the bone.
Bone gets added to existing surface
This causes the bone to grow outwards expanding and widening
What is Intra-membranous ossification?
Formation of bone from clusters of Mesenchymal Stem Cells (MSC) in the centre of the bone
Interstitial growth (growth in middle)
What Bones does Endochondral Ossification form?
Long Bones (E.g):
Tibia, fibula, femur, metatarsals and phalanges of LOWER LIMB
Humerus, radius, ulna, metacarpals and phalanges of UPPER LIMB
What bones does Intra-membranous ossification form?
Flat Bones of the skull and face
Most Cranial Bones (Part of Skull)
Clavicle
How many bones in the body?
206
Bone functions
Support body
Protect Organs
Storage/reserviour of inorganic substances (CALCIUM and PHOSPHORUS)
Haemopoiesis
Fat storage (yellow marrow)
Acid-base homeostasis (Calcium is alkali)
What type of tissue is Bone?
CONNECTIVE Tissue
If Bone is a connective tissue what is it made up of?
Cells (Osteoblasts, osteocytes and osteoclasts)
Collagenous fibres
Hard calcified matrix (only other body parts with a hard matrix is teeth
So the extracellular matrix = Collagenous fibres and calcified matrix
What 2 parts are the skeleton split into?
Axial Skeleton
Appendicular Skeleton
How many bones in Axial skeleton and what is its function?
80
The main supporting/foundation bones
The bones down the middle
Examples of bones in the Axial skeleton
Bones of skull
RIbs
Vertebrae
How many bones in the Apendicular Skeleton and its function
126
All other bones not in Axial Skeleton
Needed to help movement
Examples of Appendicular Skeleton bones
Upper Limbs
Lower LImbs
Pelvic Girdle
What are the 2 forms of Bone?
Compact/dense (Cortical Bone)
Spongy (Cancellous or medullary Bone)
Where is Compact/Cortical bone found?
Shafts of long bones
Forms plates of flat bones
Where is spongy bone found?
Ends of long bones (In epiphyses)
Centre of flat bones
Centre of Irregular Bones
What is found in central cavity and in spaces of spongy bone in Long Bones?
Red bone marrow (Haemopoiesis)
Yellow bone marrow ( Adipose tissue for energy source)
What is special about yellow bone marrow?
It can convert to red bone marrow in times of severe stress
What is Periosteum?
The tough DENSE vascular fibrous connective tissue layer that surrounds the bone.
It supplies blood (nutrients),lymphatic vessels and nerves to the Osteons via the Haversian canal
What is the Endosteum?
Thin cellular layer lining the inside of the marrow cavity of the bone
What is the function of Cortical bone?
Provides mechanical strength and protects organs
Spongy Bone function and where is it found?
End of long bones and centre of flat and irregular bones
Gives space for red marrow to grow and develop
What is the strucutre and function of the Central cavity of long bones?
Has spaces of spongy bone (yellow marrow can be here)
What is the Epiphyses in long bone?
The ends of the bone containing Cancellous or spongy bone
What is the diaphyses in long bone?
The hollow region of bone made up of cortical bone found between the 2 epiphyses, contains Bone marrow
What is an osteoblast?
Bone producing cell
It lays down substance called osteoid
What is osteoid?
Collagen 1
Enzymes
Ground substance
What is an Osteocyte?
An osteoblast which has been surrounded in MINERALISED OSTEOID = BONE SUBSTANCE
What is an osteoclast?
Multinucleated cell that contains macrophages which breaks down bone.
What is an Osteon/Haversian system?
Osteon and Haversian system are interchangeable terms
The Functional Unit of the Cortical Bone
The Structures that cortical bone is composed of
What is Lacunae?
Spaces which contain osteocytes
What is lamellae in the Osteon?
The concentric rings of matrix which surround the Haversian Canal
What is the Haversian Canal?
The central part of the Osteon that contains:
-Nutrient Providing Blood Vessels
-Lymphatic Vessels
-Nerves
These supply the osteocytes with blood nutrients from the periosteum.
What are Volkmann’s Canals?
Haversian canals that branch horizontally to adjacent Osteons.
They help blood to flow from the periosteum to all of the Osteons
What is found within the lamellae?
Lacunae (Contain osteocytes)
What are canaliculi in Osteons?
Small channels running between all of the lacunae, supply the osteocytes with substances and nervous impulses
What is Spongy (cancellous bone) made up of?
Network of Beams of Bone called Trabeculae
Cancellous bone has gaps between its Trabeculae.
What is found here?
Red Bone Marrow
How does Osteoid become mineralised?
Calcium and phosphate deposited into osteoid forms strong crystals called hydroxyapatite
Why is vitamin D important for bones?
Vitamin D is necessary to absorb calcium
Low Vit D = low calcium = poor bone mineralisation = weak bones
What is an osteoblast called that is trapped in bone lamellae?
Osteocyte
Which cells produce alkaline phosphatase?
Osteoblasts
What is the function of alkaline phosphatase?
MAKES HYDROXYAPATITE
Changes the osteoid pH by adding hydroxide and bicarbonate ions to calcium phosphate leading to the deposition of hydroxyapatite (mineralisation)
What is the cement line?
The boundary between newly formed bone tissue and non bone tissue
How is the periosteum connected to the bone?
Via collagen fibres called Sharpeys fibres
What is the function of the inner layer of sharpeys fibres?
Contains Osteoprogenitor cells that differentiate into Osteoblasts
What are the cavities called which osteocytes occupy?
Lacunae
How is bone lamellae arranged in cortical bone to form an Osteon?
In concentric rings running 45º to each other
Protects against torsion damage
How are the collagen fibres arranged in a bone lamellae?
Running in same direction
What is bone resorption?
When osteoclasts release collagen digesting enzyme and acidic mixture to dissolve Calcium phosphate in the bone returning it to the blood
What is bone remodelling?
Constant formation, breakdown and replacement of bone
What is Osteomyelitis?
Infection within bone
What is osteopathy?
Disease of the bone
What is Osteoporosois?
Weak bone
What is Osteosarcoma?
Cancer originating from bone forming cells
What is the middle of a bone called?
Diaphyses
What are the 2 ends of a bone called?
Epiphyses
What are the 2 steps to bone remodelling?
Osteoclasts cut large cutting cone
Osteoblasts make smaller tunnel of cortical bone called the closing cone
What can affect the activity of osteoblasts?
Simulated by:
-calcitonin
-GH
-Thyroid hormones
-Vit A
-OESTTROGEN AND TESTOSTERONE
What can affect the activity of osteoclasts?
Increased activity by PTH - so more Ca2+ released into blood
Decreased by calcitonin (block action of PTH at PTH receptor)
What nutrients affect bone stability and why?
Vitamin D (makes Calcitriol needed for Ca2+ absorption so poor mineralisation of bone if deficient)
Vitamin C (synthesising strong collagen, is a cofactor for prolyl hydroxylase needed to hydroxylate proline so many strong hydrogen bonds can form)
Vitamins K and B12 - needed to make bone proteins
What does a decrease in bone mass of trabecular bone leave patients vulnerable to?
Increased susceptibility to fracture
What is Osteogenesis imperfecta?
Brittlel bone disease to a gene mutation
What gene is mutated in Osteogenesis imperfecta?
COL1A1
What is the affect of the mutated COL1A gene in Osteogenesis imperfecta?
Incorrect Collagen 1 production
Not enough made or collagen made does not knit together well
What are the signs and symptoms of Osteogenesis imperfecta?
BLUE SCLERA
Short stature
Weak bones (fractures)
Poor teeth development
Loose joints and flat or arched feet
What are the 2 bone diseases that occur as a result of Vitamin D deficiency?
Rickets
Osteomalacia
Which of the Vitamin D deficiencies affects children?
Rickets
What are the signs and symptoms of Rickets in children?
BOWED LEGS
Soft bones
Painful to walk
Short height and stature
How does a lack of vitamin D cause weak soft bones?
Vitamin D needed to make Calcitriol
Calcitriol needed to absorb calcium
Lack of calcium leads to reduced formation of Hydroxyapatite so reduced/ineffective bone mineralisation
What is Osteomalacia?
Rickets in adults
Vitamin D deficiency
What are the 2 types of Primary Osteoporosis?
Type 1 = post menopausal women
Type 2 = older men and women (senile osteoporosis)
How does Primary Type 1 osteoporosis occur in post menopausal women?
Decreased oestrogen levels causes decreased activity of OSTEOBLASTS and INCREASED amounts of OSTEOCLASTS
What happens in Primary Type 2 osteoporosis?
As people get older, osteoblasts lose their function
What is secondary Osteoporosis?
Caused by drug therapy, malnutrition, prolonged immobilisation, metabolic bone diseases
In terms of bone strength and amounts, what happens in osteoporosis?
Loss of bone matrix
Loss of structural density
Demineralisation
How can poor bone strength/demineralisation be detected?
Measure bone density
In terms of resorption bays, what happens in osteoporosis associated with aging?
INcomplete filling of the bays
How can osteoporosis be prevented/delayed?
Sufficient calcium intake
Exercise
Not smoking
Which type of bone is affected most by osteoporosis?
Trabecular/cancellous bone
What type of mutation causes Achondroplasia?
Autosomal dominant POINT mutation
Which gene is affected in Achondroplasia?
FGFR3
What is the function of the FGFR3 gene?
Prodces fibroblast growth factor
This stimulates Chondrocytes to lay down new cartilage
What happens when the FGFR3 gene is mutated?
FGF is not made
Reduced Endochondral ossification
What are the signs of achondroplasia?
Short stature (normal head and torso)
Long bones cant form properly (Endochondral ossification affected since cartilage affected, Intramembranous ossification normal)
