Physiology of the Skeletal System Flashcards
What is the importance of the skeletal system?
One of the major systems of the body
Sometimes grouped with the muscular system as the musculoskeletal system
What is bone material?
A specialised form of extracellular matrix (crystalised)
Maintained and made by living cells
How can bones be used by the body?
Structurally and physiologically
What are the structural roles of the skeleton?
Provides physical support for the body
Attachment points for muscles
Protection of internal structures (Ribcage protects ribs and Skull protects brain)
Is a femur’s role to protect?
No a femur is a limb bone and so has the purpose of attaching muscles
How can a muscle be identified as responsible for protection of internal organs?
If it is close to the skin
How does the ribcage protect the lungs?
Prevents any unnecessary pressure from damaging the lungs as the air pressure increase when a person exhales
How does the skull protect the brain?
The brain has a jelly like consistency and so can be easily damaged, therefore the skull prevents any brain damage from occurring
Are there any bones to protect the blood vessels?
No, blood vessels are unprotected
What how does the general function of bones occur and are there any other roles for bones?
As of joints
They also have physiological roles
What are the physiological roles of bones?
Stores various minerals, particularly calcium and phosphorus
Produces blood (bone marrow)
How does the composition of bone marrow change in adults?
Adults generally have lower quantities of red bone marrow and have more yellow and brown bone marrows
What are the different bone marrows responsible for?
Red bone marrow= red blood cells
Yellow and brown marrow= adipose (fatty) tissues
How long does it take for the entire blood supply to be produced by the boens?
3-4 months; very slow rate of production
Why is calcium needed in the body?
Muscle contractions
Synaptic transmissions
Why is phosphorus needed in the body?
ATP production
DNA/RNA nucleotides
Proteins- proteins activated when phosphorus added to them
Why does bone undergo its own physiological processes?
It is a living tissue and requires maintenance
What are osteogenic cells?
Precursors/makers of osteoblasts (stem cells)
What are osteoblasts?
Cells that build bone
Secrete extracellular matrix
What are osteocytes?
Osteoblasts that are encased in bone (calcified)
Maintain mineral levels, send signals via cell-cell signaling
What are osteoclasts?
Cells that reabsorb bone- cells that digest bone and break it down
How do osteoclasts obtain calcium and phosphorus?
By breaking down bone, as bone material has a limited life span and so wears out
Why do osteoclasts break down bone?
Microscopic changes to proteins and therefore, to change need to break down old bone
Overtime all bone is replaced, osteoclasts renew bone
What can osteoclasts do when a healing a broken bone?
Get rid of the extra sticking out bone as the osteoblasts rebuild bone
What are the two major mechanisms that allow the formation of bone?
Endochondral ossification: bone develops from a precursor made of cartilage (osteoblasts make the bone inside cartilage)
Intramembranous ossification: bone development from general connective tissue (general connective tissue potentially quite tough)
Which bones are made from each mechanism?
Endochondral ossification makes most bones of the limbs- however most of the bones in the face are produced from intramembranous ossification
What occurs in both mechanisms regarding the production of bone?
The bone replaces the cartilage/connective tissue and doesn’t convert it
What are the benefits of cartilage as a precursor?
As a precursor (and with some remaining) the cartilage can act as a shock absorber, and allow for growth
Why do bones fuse together?
The smaller areas fuse together as to allow for the bone to increase and lengthen
What does the increased length (due to cartilage fusing together) benefit?
The fusion of the epiphysis and diaphysis
What does the precursor allow?
Allows developing structure to function
How can muscles develop properly?
By attaching properly
What is osteoid?
The organic component of bone material
How are osteoid, osteoblasts and osteocytes linked together?
Osteoid is produced by the osteoblasts and the osteocytes maintain it
What is osteoid composed of?
Largely composed of collagen (type 1) which is flexible
What is hydroxyapatite and what is its function?
Hardens the osteoid
Is a form of calcium phosphate, and is modified with added calcium carbonate
What is the significance of the terms “hard” and “malleable”?
If a material is hard, it is relatively weak and so when it is hit it will break
If a material is malleable, it is relatively strong as it will dent and not break easily
How can osteoid be described?
As malleable and holds well together; the minerals are hard but brittle
In combination the bones are hard but brittle, and malleable, and both characteristics decrease the risk of fractures
What is calcification?
When osteoid has hydroxyapatite added to it
How does bone production occur?
Osteoblasts produce a special form of extracellular matrix
This matrix becomes calcified (a process known as mineralisation), making bone which surrounds and encases the osteoblast
The encased osteoblast then becomes an osteocyte, the most common form of bone cell
What happens to the old bone material?
The osteoclasts break it down
What is the purpose of bone turnover?
Allows for maintenance and reshaping of the bone
Why do bones undergo reshaping?
In response to damage
To adapt to the demands of the bone
How can bones take into account any missing muscle?
Grow towards the missing muscle and so then allow the muscle to move
How can it be identified if muscles require more support?
Muscle attachments are all different shapes, and so the more outgrown they are shows how strong the muscle is
More support is required for stronger muscles
How are force and bone recycling linked?
The less force that is on a bone shows that they are apparently weaker, and so their resources can be recycled
What does the microstructure of bone contain?
Osteon (rings of lamellae)
Periosteum
Central canal (also at the centre of osteon)
Lacunae (tiny cavities containing osteocytes)
(Yellow) Marrow
What is the importance of the central canals in bones?
Contain blood vessels and so supply nutrients to osteocytes
When the bone is broken down the minerals are returned to the blood
What is the position of osteons is spongy bone?
Branching out
What is the appearance of the osteon?
Constrained (twisted around) bone
What is the composition of bone marrow in adults and why?
Adults have mostly yellow or brown bone marrow, with little re bone marrow, due to a slower rate of blood component development
Why are the tiny channels (lacunae) important?
Allow for communication
Why is the bone important in regards to minerals?
When phosphorus and calcium levels are low in the blood they can be extracted from the bone
The bones hold 99% of the body’s calcium supply
The bones hold 80% of the body’s phosphorus supply
What is the importance of the parathyroid gland?
Can secrete parathyroid hormone (PTH) to trigger osteoclasts to break down the bone matrix and release minerals into the bloodstream
Where are the parathyroid glands located?
Small structures on the back of the thyroid
What is the significance of parathyroid hormone (PTH) in response to calcium?
It is released in response to low blood serum Ca2+ ions
PTH triggers the activity of osteoclasts, which break down the bone matrix and therefore release its component calcium into the bloodstream
Ca2+ increases and results in less PTH being released.
Negative feedback (as part of homeostasis)
What occurs during hypercalcemia?
Higher levels of Ca2+ in the blood (than normal) leads to the thyroid releasing calcitonin
Calcitonin triggers osteoblast activity to increase (more bone is made and Ca2+ levels in blood decrease as is being used up)
Ca2+ reabsorption in the kidney decreases
Ca2+ levels are brought down to normal
What occurs during hypocalcemia?
Lower levels of Ca2+ in the blood (than normal) leads to the parathyroid gland releasing parathyroid hormone
This leads to increased osteoclast activity in the bone, and increased Ca2+ reabsorption in the kidney
This then causes calcitriol to be triggered and increases Ca2+ absorption from the gut
Ca2+ levels are brought up to normal
What is hematopoiesis?
The process of producing blood cells
Where are haemopoietic stem cells (HSCs) found and what is their function?
Found in the bone marrow and produce all forms of blood cells including red blood cells (erythrocytes) and white blood cells (lymphocytes and other immune cells)
What is the link between blood cell production and bone marrow?
Blood cell production specifically occurs in red bone marrow. However, in hypoxic conditions, blood cell production can occur in yellow bone marrow which can become red bone marrow, but is usually a store of fat
