Structure and Function of Bones Flashcards
What mind of tissue is bone comprised of?
Connective tissue
From which germ layer is bone derived?
Mesoderm
What are the three names of the outer layer of bone?
Compact
Lamellar
Cortical
What are the three names of the bone which is deep to the cortical bone?
Spongy
Trabecular
Cancellous
What are Haversian rings/osteons?
Haversian systems make up the compact bone. Rings of concentric lamellae of bone tissue surrounding the central (Haversian) canal which contains blood vessels and nerves.
What is the name of the canal which lies perpendicular to the Haversian canal in bone and what is it’s function?
Perforating / Volkmann’s canals serve to connect the blood and nerve supply of the periosteum to the neurovascular supply of the central canals and medullary cavity.
What is the main function of compact bone?
To provide structure /strength to the bone
Cancellous bone does not contain osteons but instead has…?
An irregular lattice of thin columns called trabeculae which are arranged along the lines of stress.
What is the name for the macroscopic spaces between trabeculae?
Medullary cavities
What feature of the compact bone allows it to withstand torsion pressures?
All the collagen fibres in one lamella run in a single direction but adjacent lamella will have collagen fibres running in opposite directions.
What are lacunae?
Tiny cavities located between lamellae that contain osteocytes
What are canaliculi?
Hair-like canals which are filled with extracellular fluid that radiate from the lacunae and serve to connect lacunae so as to provide nutrients and oxygen to osteocytes within the lacunae
What is the main protein of the bone matrix?
Collagen type I
Which molecules assist in the cross-linking of collagen in the bone?
Pyridinium
Give examples of non-collagen proteins which exist in the matrix of bone?
Osteopontin
Osteocalcin
Fibroconnectin
Bone has calcium and phosphate minerals. In what form do these exist within the bone?
Calcium and phosphate exist in bone in the form of hydroxyapatite
Why is mineralisation of bone important?
To maintain the rigidity of the bone
What are the three types of cell in the bone?
Osteoblast
Osteocyte
Osteoclast
What is the origin of osteoblasts?
Osteoblasts are of mesenchymal origin and differentiate from osteoprogenitor cells
Osteoblasts are multi-nucleated whilst osteoclasts are mononuclear. T/F?
False - the opposite is true
What is the function of an osteoblast?
Osteoblasts form bone. They synthesise the matrix and regulate its mineralisation and synthesise collagen and other organic components. They are also important in allowing calcification of bone
From what cells are osteocytes derived?
Osteocytes are derived from osteoblasts
What is the function of osteoclasts?
Osteoclasts are responsible for bone resorption (break down of bone)
The edge of an osteoclast cells which is closest to the bone has a highly infolded surface called a ruffled border. What is the function of this?
It contains powerful enzymes and acids which are released and digest the protein and mineral components of the extracellular matrix
What is the function of an osteocyte?
Osteocytes sense and respond to mechanical loading of the skeleton and regulate bone formation and resorption (bone remodelling)
From what cells are osteoclasts derived?
Osteoclasts are of the monocyte-macrophage lineage
What is the periosteum of a bone?
It is the fibrous connective tissue which surrounds the external bone in all areas other than the area of a joint.
Where on a bone are sensory nerve fibres found?
In the periosteum
A bone cannot survive without its periosteum. Why?
Because the periosteum is supplied with blood vessels, lymphatic vessels and sensory nerve fibres,
What are the functions of the periosteum?
Help with fracture repair
Nourish and protect bone
Act as an attachment point for tendons and liagments
How is the periosteum secured to the underlying bone?
By thick bundles of collagen fibres (perforating/Sharpey’s fibres) which extend from the periosteum to the extracellular bone matrix
What is the purpose of the nutrient artery in bones?
To supply the cancellous bone and bone marrow with oxygen and nutrients. (It also sometimes supplies the very inner layers of compact bone too)
Hoe does blood reach the cells of the compact bone?
Through Haversian canals
How does the nutrient artery get into the bone?
Through a hole in the bone called the nutrient foramina
How do periosteal arteries enter the shaft of the bones?
Through Volkmann’s canals
What is the function of epiphyseal arteries?
To deliver oxygen and nutrients to cells in the red bone marrow and bone tissue of the epiphyses
What kind of nerves cause constriction or dilation of the blood vessels within bone?
Vasomotor nerves
What is the endosteum?
This is the thin layer of cells which covers the internal bone surfaces facing the medullary cavities such as the trabecullae of spongy bone and the canals which pass through the cortical bone
What kind of cells are contained within the endosteum?
Osteoblasts and osteoclasts
What are the functions of bone?
Provide support and structure to the body
To protect vital organs
To hold reservoirs of calcium and phosphate (important in maintaining homeostasis)
Contains blood producing cells (therefore important in haemopoiesis)
Storage of triglycerides (fat) in yellow bone marrow
Works as a lever on which muscles act to produce movement
Describe, briefly, the composition of bone.
Around 30% of bone is composed of osteoid - an organic ECM primarily composed of collagen type I
Around 70% of bone is composed of inorganic minerals in the form of hydroxyapatite crystals
Only a tiny portion of bone is composed of the bone cells
Spongy bone reduces the weight of the skeleton. Why is this useful?
So that muscles do not have to work as hard to act upon the skeleton
Why is the shaft of long bones narrow?
To accommodate the belly of muscles. The epiphysis do not need to be narrow because here there are only the smaller, tendonous attachments of muscles
How do osteoblasts assist in the calcification of the bone matrix?
They secrete alkaline phosphatase (ALP) which dephosphorylates molecules in the osteoid to allow calcification of the matrix by laying down calcium phosphate
The ruffled border of microvilli exists on osteoclasts. What is its function?
These microvilli infiltrate the disintegrating bone surface and it is at these sites that lysosomal enzymes are release in order to resorb the bone
Why is it possible to tie a bone in a knot (as seen in the bone structure lab) if the bone is left in a beaker of acid?
Because the acid dissolves the mineral crystals leaving only the organic component of bone behind. The mineral component is responsible for the hardness of the bone whilst the organic component - particularly collagen - is responsible for the tensile strength. Without the mineral component the bone is less rigid and so can be bent into different shapes
Osteoclasts use hydrogen ions from acid to dissolve the mineral component of bone. Where do these hydrogen ions come from?
Carbonic anhydrase catalyses the formation of carbonic acid which acts as a source of hydrogen ions
What is the composition of bone?
70% mineral matrix
30% osteoid
Tiny percentage cells
What is the name of old haversian systems which have nit yet been resorbed?
Interstitial lamella
Why do adjacent lamellae of compact bone run in opposite directions?
To provide resistance to torsion forces
What are the two types of trabeculae?
Compression - upon which weight acts directly
Tensile - which lie more horizontally
Cancellous bone has a higher rate of turnover than compact bone so responds to changing stresses upon it faster than compact bone and is consequently more affected by osteoporosis. T/F?
True
What kind of bone marrow mainly exists in the medullary cavity of adult bones?
Yellow marrow
Which of the bone cells has an extensive rough ER, golgi apparatus and many ribosomes?
Osteoblasts as these produce many proteins
What is the name of the enzyme which is secreted by osteoblasts and dephosphorylates components of osteoid to allow calcification of the matrix?
Alkaline phosphatase
Which bone cell contains numerous lysosomes?
Osteoclasts
