Musculoskeletal System Flashcards
What are the two meanings of bone?
1) Bone the organ
- organs are made up of different types of tissue
2) Bone the tissue
- One of the tissues found in the bones of the skeleton.
What are the 6 functions of the skeletal system?
1) support
2) protection of vital organs
3) movement - muscle must pull on bone
4) Calcium and phosphorous reserve
5) Haemopoiesis
6) Fat storage
Why must calcium be tightly regulated?
It is used for many things, e.g. muscle contraction of heart, hormone and enzyme production.
What percentage of calcium is stored in the bones?
99% in the bones
What is the function of haemopoietic tissue? What colour is it?
Makes RBC’s, WBC’s and platelets.
Red
What are the two components of bone marrow?
Haemopoietic tissue and fat storage tissue
What is the phosphorous found in bone used for?
To build many substances e.g. ATP
Describe the bone marrow at birth compared to that of an adult.
All bone marrow is red at birth.
In adults, red bone marrow tends to be in the axial skeleton.
What are the two components of the adult skeleton?
Axial and Appendicular
How many bones are in the axial and appendicular skeleton?
80 (some paired)
126 (all paired)
What are the differences in function between the axial and appendicular skeleton?
Axial: support/protection and haemopoiesis
Appendicular: movement and fat storage
Describe the overall sections of a long bone in order.
Epiphysis, metaphysis, diaphysis, metaphysis, epiphysis
Relate the type of forces to the requirement for plates, rods and beams in the epiphysis and diaphysis.
Epiphysis: Forces perpendicular so plates, rods, and beams are needed for support.
Diaphysis: Forces are parallel so no need for plates, rods, and beams.
What are plates, rods and beams formed by?
Trabeculae
What are trabeculae covered by?
Endosteum
List the layers of the epiphysis from outside to inside.
Articular cartilage, compact bone, spongy bone
What is another name for spongy bone?
Trabecular bone
Why is there no periosteum covering the articular cartilage?
It would just be sheared off by the other bone.
What is found between trabeculae?
Medullary cavity with bone marrow inside.
Where are blood vessels found in the epiphysis? What is their function?
Inside compact bone and between trabeculae.
RBC’s, WBC’s and platelets can enter blood.
Give the layers of the diaphysis from outside in.
Periosteum, compact bone, endosteum, medullary cavity
What is the periosteum?
Outer fibro-cellular sheath surrounding the bone. Made up of dense irregular connective tissue, rich with blood vessels and nerves.
Describe the compact bone of the diaphysis.
Forms a cylinder
Very light and strong
How does the compact bone of the diaphysis compare to that of the epiphysis?
D: thick
E: thin
Describe the endosteum of the diaphysis.
Thin, inner fibro-cellular layer lining medullary cavity.
What does the medullary cavity of the diaphysis contain in the appendicular skeleton vs the axial skeleton vs the front of the face?
Appendicular: yellow bone marrow
Axial: red bone marrow
Front of face: air (must be lighter)
What is another name for the perforating fibres between the periosteum and the compact bone? What are they produced by?
Sharpey’s fibers - very strong
Collagen produced by periosteum blends with the collagen on the bone.
Where are the blood vessels found in the diaphysis?
In the periosteum and compact bone.
Bone is a type of __________ _________ tissue
Specialised connective
What are the two components of connective tissue?
ECM and cells
What is ECM made up of?
Fibres (organic): 1/3 of the dry weight Ground substance (inorganic): 2/3 of the dry weight
In bone, what fibres are present? What is their purpose?
Collagen fibres type I and IV. Resists tension (stretching and pulling)
What is found in the ground substance?
Water and long chain carbs Hydroxyapatite Ca10(PO4)6OH Resists compression (squeezing and crushing)
What type of cells are found in bones? What are the functions of each type?
Osteogenic: cell reserve
Osteoblast: bone formation
Osteocyte: bone maintenance
Osteoclast: bone destruction
What does tension plus compression add up to?
Torsion (twisting)
What are osteogenic cells also known as? What is the precursor, location, and function?
Osteoprogenitor cells.
Precursor: unspecialised stem cells (mesenchyme = embryonic connective tissue)
Location: surface of bone in the periosteum and endosteum.
Function: normally dormant, but can divide and supply developing bone with bone-forming cells.
What is the precursor for osteoblasts? What are they located? What is their function?
Osteogenic cell
Location: usually in a layer, under the peri or endosteum. Wherever new bone is being formed.
Function: synthesis, deposition and mineralisation of osteoid.
What is osteoid?
Not a cell.
The organic extracellular matrix (mainly collagen) of bone, synthesised by osteoblasts prior to mineral deposition. Collagen accounts for 70% of osteoid with the remainder consisting of proteoglycans and other proteins.
This precursor matrix is eventually infiltrated with bone salts (hydroxyapatite) and this process is called calcification. Water is displaced gradually, so it becomes difficult for full calcification.
This makes the bone strong but also dense, thus nutritive fluids cannot diffuse freely through it.
What is the precursor to osteocytes? Where are they located? What is their function?
Osteoblast
Location: trapped within lacunae inside bone. Osteocytes can communicate with neighbouring cells through their long cellular processes and canaliculi.
Function: bone tissue maintenance.
How do osteoclasts come about? Where are they found? What is thei function?
Fusion of monocyte (WBC) progenitor cells forming a syncitium.
Location: at sites where bone resorption is occurring.
Function: secretes acid and hydrolytic enzymes to dissolve the mineral and organic components of bone. Exposes collagen using acid and breaks down protein with enzymes.
What is the function of the clear zone?
Stops acids and enzymes from getting out from under the bone.
What must happen for a child’s bone to grow into an adult’s bone?
Appositional growth: the bone has to be remodelled. This involves appositional growth and bone resorption. We don’t want the bone to get too thick and heavy.
How does appositional growth occur? Give an example of when this might occur? What does it occur in response to?
Bone is put down onto an existing layer.
A long bone growing in diameter.
In response to mechanical damage.
Describe the process of bone resorption.
Monocyte precursor cells leave blood vessel and start to fuse on bone surface. Osteoclasts form on surface and start dissolving. A tight seal is formed between the osteoclast and the surface of the bone. Osteoclasts eventually die by apoptosis and resorption stops. They have a short life. Blood vessels grow into new space.
What is Howship’s lacuna?
A pit formed when an osteoclast dissolves bone.
What happens when growth of the bone stops?
Osteoblasts can convert back into osteogenic cells or die. Osteoid becomes fully calcified.
Why can’t the tissue bone grow by interstitial growth?
It is too rigid
Where does interstitial growth occur? What occurs during interstitial growth?
In softer tissues that can deform.
Involves cells dividing, secreting more extracellular matrix, and growing the tissue from within.
What is appositional growth? Why is this the only way bone can grow?
Adding new bone onto an existing surface.
Bone is designed to resist deformity.
What does bone-remodelling involve?
The two processes, appositional growth and bone resorption, which occur throughout the skeletal system, often completely independent of each other.
What process do long bones grow by?
Endochondral ossification
How does oestrogen affect bones? Why does osteoporosis occur?
It is needed for osteoclast regulation.
Osteoporosis occurs at menopause because of decline in oestrogen. Affects spongy bone first.
As osteoblasts deposit new bone onto a surface, they do so in ________ or _______.
Describe the placement of collagen fibres. What effect does this have?
Layers or sheets
The collagen fibres are typically put down in the same direction within a layer, but can alternate up to 90 degrees out of phase between the layers. This enables bone to withstand forces from different directions, making it significantly stronger. Increases strength without increase of volume.
What are the two forms of lamellar bone?
Spongy and compact
What is another name for mature bone?
What is another name for immature bone?
M: Lamellar bone
I: Woven bone
Describe woven bone.
Wavey collagen, low density, random arrangement, not very strong. Most turns into lamellar bone after 3 years. The only place it is found in the adult skeleton is when a bone is broken.
What is another name for spongy bone?
Cancellous or trabecular bone
What percentage of the skeleton is spongy bone? What does this change depend on?
20%
Changes depending on loads placed on bones throughout the skeleton.