musculoskeletal system Flashcards
What are the functions of bones and cartilage ?
Protecting vital structures
Providing levers to bring about movements and resist effects of gravity
Storage of minerals (e.g. Calcium deposition)
Which cells secrete the ECM of cartilage ?
Chondrocytes, then become embedded in it
What is the main component of the ECM of cartilage ?
Chondroitin sulfate (protein) strengthened by collagen, elastic fivers and other proteins
What are the three types of cartilage ?
Hyaline, Elastic and Fibrocartilage
What are the 3 main features of hyaline cartilage (where found, function, and ossification) ?
- Forms laryngeal cartilages, tracheal rings, bronchi and costal cartilages
- Cushions (articular) surfaces of bones in synovial joints
- Forms temporary skeleton of developing fetus (replaced by ossification)
What are the 2 main features (where found, and ossification) of elastic cartilage ?
- Forms in ears, tip of nose, epiglottis
- Never ossifies
What are the 2 main features (where found and function) of fibrocartilage ?
Forms tough shock-absorbing discs (intervertebral discs which are prone to slip) between the symphyses in midline of body
How does calcitonin affect bone ?
Inhibits osteoclast activity, causing decreased Calcium concentration in the blood
How does parathormone (parathyroid hormone, PTH) affect bone ?
Increases osteoclast activity, cause release of Calcium in blood
Which cells make the ECM of bone ?
Osteoblasts, before they become embedded in it
How do osteoclasts maintain contact with other cells and their blood supply after they become embedded in the ECM ?
Via microscopically small channels
What is the ECM of bone made of ?
Calcium hydroxyapatite (crystallised mineral salts) bound to osteoid (mixture of collagen and other organic protein fibres) and water
Where on the bone is most of the bone tissue found ?
On the periosteum
What is the periosteum ?
A dense, fibrous, layer of vascular (rich blood and nerve supply) connective tissue envelope outer surface of the bone EXCEPT articular surfaces.
What are the functions of bone?
Protection Movement Support Storage of minerals Blood cell formation (hematopoiesis)
Know how to draw the structure of a long bone
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What is the epiphysis of a long bone?
The head, has an articular surface and is covered by hyaline cartilage
What is the diaphysis of a long bone ?
The shaft, hollow cylinder containing bone marrow (it’s a nutrient foramen)
Describe how the anatomy of a long bone is different in childhood.
Ends of long bone separated from diaphysis by players of hyaline cartilage (epiphyseal plate). In that plate, columns of cartilage cells undergo division (hence growth) and are eventually removed by osteoclasts. The space is then invaded by osteoblasts and a new bone is laid down.
Why do girls stop growing before lads ?
Girls produce oestrogen (puberty) before lads produce sufficient testosterone so girls cease to grow before lads.
What is the significance of the medullar cavity ?
Contains bone marrow (which is a site of hematopoiesis).
What are the walls of the medullar cavity made of ?
Cancellous bone
Which cells make up the peritoneum ?
Osteoblasts, osteoclasts, fibroblasts and mesenchymal cells.
Which cells are present in bone and what are their functions ?
Fibroblasts- Synthesise collagen and other fibres
Osteoprogenitor cells- stem cell population lining the surface of the bone, give rise to osteoblasts in bone growth and repair
Mesenchymal cells- May differentiate into osteoblasts and chondroblasts
Osteoblasts- Cuboidal cells responsible for bone formation, cover surface of bone (secrete bone matrix so abundant RER and Golgi, then become embedded in it, becoming osteocytes) by 1. Depositing organic matrix then 2. causing mineralisation
Osteocytes- Mature osteoblasts (not all osteoblasts become embedded and become osteocytes). Embedded in lacunae, relatively inactive. Still connected through cytoplasmic processes in canaliculi. Maintain bone matrix through cell to cell communication and influence bone remodelling. They are mechanosensing (response to mechanical stimuli)
Osteoclasts- Release H+ and hydrolytic enzymes to dissolve the mineral, liberate Calcium and break down extracellular matrix.
Osteoclasts- Multinucleated, derived from heamatopoietic cells. In respond to mechanical stresses and physiological demand they resorb bone matrix though demineralisation. They are found in fractures, at epiphyses during growth and in remodelling sites.
What is the Endosteum?
Tissue lining medullar cavity of the bone.
- In cortical bone, lines cortical bone and delimits medullar cavity.
- In trabecular bone, coats interior surface of taberculae
What are other names for spongy bone ?
Cancellous bone and trabecular bone
What is the function of compact bone ?
Supporting body weight, protecting organs, storing and releasing Calcium, provision levers for movement
What is the function of spongy bone ?
Metabolic activity (such as exchange of Calcium, enabled by its large SA)
What are the units of compact bone ?
Closely packed osteons (=Haversian systems), which are basically a central canal (osteonic/Haversian canal) surrounded by concentric rings (lamellae) of matrix.
What are osteocytes and where are they in compact bone ?
Osteocytes are “mature osteoblasts that have become trapped within the very bone matrix they produced” .They are found in spaces between lamellae called lacunae.
What are canaliculi ?
They are small channels from the lacunae to osteonic canals for passage through the matrix. Very strong light cylinder resisting compressive forces.
How is the density and SA of cancellous/spongy bone compared to compact bone ?
Higher SA but lower density.
Where is cancellous bone usually found ?
Proximal to joints (at the end of bones) and within interior of vertebrae
What are the units of spongy bone ?
Trabeculae and bars of bone adjacent to irregular small cavities with red marrow (hematopoietic cells in there). Canaliculi connect to the cavities to receive blood supply
How are the trabeculae of spongy bone alligned ?
They are aligned along lines of stress for support. They CAN realign if the direction of stress changes.
What is another name for compact bone ?
Cortical bone
Which type of bone is more affected in osteoporosis ?
Cancellous bone
Who are osteoclasts regulated by ?
Osteoblasts and hormones
What is a sealing zone ?
“The attachment of the osteoclast’s plasma membrane to the underlying bone”
What are symptoms of Van Buchem disease ?
Bone overgrowth, increased osteoblastic formation and decreased osteoclastic resorption
What is hypertrophy (give an example) ?
Increase in volume of organ or tissue through growth in size of its cells (in the case of bone, when bone formation > bone resorption, e.g. Van Buchem disease)
What is atrophy (give an example) ?
Wasting away of organ or tissue, especially due to degeneration of cells (in the case of bone, when bone resorption > bone formation).
How long does a remodelling cycle of bone take ?
3 months
Which are the steps of the remodelling cycle ?
- Quiescence
- Resorption (osteoclasts remove portion of bone to be replaced later)
- Reversal
- Formation (osteoblasts lay down collagen and minerals deposit over area previously remodelling by osteoclasts)
What is the closing cone?
Where the osteoblasts are doing the refilling
What is the cutting cone ?
Where the osteoclasts are doing the tunnelling
What are potential causes of hypertrophy ?
Physical stress, traction and pressure (muscular forces through attachment of muscle to bone through tendons causes formation of bone markings such as tubercles and lines)
What are potential causes of atrophy ?
Non-weight bearing/immobility, sex hormone deficiency (e.g. menopause, decreased oestrogen, often results in osteoporosis), endocrine/nutritional disorders (e.g. vitamin D deficiency
What is Wolff’s law?
Bone adopts to load under which it is placed
Which factors affect healing time for fractures ?
Age + severity + position of fracture
What are the steps of fracture healing ?
1) Callus formation- Osteoblasts quickly form woven bone, to bridge gap. Woven bone is weak since the collagen fibres are irregular
2) Lamellar bone laid down- collagen is organised in regular sheets to give strength and resilience
3) Remodelling by osteoclasts to restore original bone shape
What is the first step of bone growth from foetus to adult and which cells are present in this stage ?
1) Cartilage model- Made of 3 main types of cells:
Chondroblasts (type of mesenchymal progenitor cell)- Immature, actively dividing cells which give rise to chondrocytes and components of the ECM
Chondrocytes- Specialised cells (differentiated cells of chondroblasts) which synthesise, maintain and remodel ECM of cartilage. Found in the lacunae of the cartilage matrix. Have a low capacity to regenerate.
ECM- Made of collagen fibrils and proteoglycans
What is the second step of bone growth from foetus to adult ?
Ossification
What are the two types of ossification ?
Endochondrial ossification and intermembraneous ossification
What is endochondrial ossification (for long bones) ?
Bone is formed onto temporary cartilage model
Cartilage model grows then chondrocytes mature and hypertrophy and growing cartilage model starts to calcify
Chondrocytes far from blood vessels less able to gain nutrients so start to died. Fragmented calified bone matrix left behind acts as structural framework for bony material
Osteoprogenitor cells and blood vessels from periosteum invade the area, proliferate and differentiate into osteoblasts which start to lay down bone matrix
What is intermembraneous ossification (for flat bones) ?
Cartilage is not present.
Bone formed by direct replacement of mesenchyma
What is mesenchyma ?
Type of Animal Tissue made of loose cells embedded in ECM (fluid nature allows cells to migrate easily, hence role in development of morphological structures in fetal/embryonic stages)
What is the primary ossification centre, why? Is it active before birth ?
Diaphysis , since that’s where bone growth starts during fetal life in endochondrial ossification. It is active before birth.
What is the secondary ossification centre, why ?
Epiphysis, since after birth bone begins to develop in ends of bone (hence at birth many bones consist of bony diaphysis and cartilaginous epiphysis)
What is the last remainder of cartilaginous model ?
The epiphyseal plates of bones (before it fuses)
Where does growth behind within the epiphyseal plate ?
At epiphyseal side and cells move towards diaphysis arranged in stacks.
Where is the resting zone ?
On the epiphyseal side of plate (reserve cells)
What is the growth zone ?
Cells undergoing mitosis
What is the transformation zone ?
Cartilage cells are transforming, enlarging and matrix is calcifying
What is the osteogenic zone ?
Calcified cells removed by osteoclasts and replaced by bone secreted by osteoblasts
