Skeletal System Flashcards
How many bones are in the human body?
206
List the functions of the skeleton
- Support framework for the body
- Forms boundaries (i.e, the skull)
- Attachment for muscles and tendons
- Permits movement (joints)
- Haematopoeisis (production of blood cells in the red bone marrow)
- Mineral homeostasis (mostly calcium & phosphate)
- Triglyceride storage (in yellow bone marrow)
The skeleton accounts for what % of body weight?
18%
What is bone marrow?
A tissue throughout the central cavity of bones, through which we produce all of our blood cells after birth.
This is where we house lots of stem cells, that can specialise as RBC’s, WBC’s or platelets.
99% of the calcium in your body is found where?
In the bones / skeletal system
Where are triglycerides (fats) stored?
In the yellow bone marrow
Why is yellow bone marrow called ‘yellow’?
Because the fat stored within it makes it look yellow.
What are osteogenic cells?
Bone stem cells.
They later specialise to become osteoblasts or osteoclasts.
What are osteoblasts?
Cells that build bone. Immature/juvenile cells.
Which bone cells secrete collagen, ground substance and other components of bony matrix
Osteoblasts
How do osteoblasts become osteocytes?
When they get trapped within their own bony secretions and become stationery and fully mature.
What are osteocytes and what is their function?
Osteocytes are mature bone cells. They maintain the daily metabolism of bone, such as nutrient exchange.
List the 4 types of bone cells.
- Osteogenic cells
- Osteoblasts
- Osteocytes
- Osteoclasts
Which are the biggest bone cells?
Osteoclasts
Osteoclasts are huge cells, derived from the fusion of what?
As many as 50 monocytes (specialised WBC’s)
How do osteoclasts dissolve the surface of bone (resorption)?
By releasing lysosomal enzymes and acids directly onto the bone surface.
What is the difference in function between osteoblasts and osteoclasts?
Osteoblasts build bone matrix, osteoclasts dissolve bone matrix.
Why do osteoclasts have a ‘ruffled border’ on the side of their cell membrane that faces the bone surface?
To increase surface area for enzyme release and reactions, increasing their efficiency at breaking down bone.
What is ‘resorption’?
The breakdown of bone matrix
Which bone cells work together to ‘remodel’ bone throughout life?
Osteoblasts and osteoclasts
What 2 types of bone is the skeleton formed from?
Compact and spongy bone
What % of our skeleton is made of compact bone?
80%
Describe compact bone
Compact bone is found beneath the periosteum, on the outside of bones. It makes up the bulk of the diaphysis of long bones. It contains few spaces and is strong.
What is an osteon?
A small structural sub-unit of compact bone. Osteons look like slices of tree trunks. They are aligned in the same line as stress.
How many parts does an osteon have?
An osteon has 4 parts
List the 4 parts of an osteon
- Haversian canal
- Lamellae
- Canaliculi
- Lacunae
Within an osteon (small, structural, sub-unit of compact bone) what is housed within the Haversian Canal?
Blood vessels and nerves
What are lamellae?
Concentric rings of calcified extracellular matrix, containing minerals and collagen.
Lamellae are found within osteons.
What are canaliculi and where are they found?
Canaliculi are found within osteons. They are a mini system of interconnected canals that provide a route for nutrients and waste within bones.
Why does bone need a rich blood supply?
Because the skeleton is a living structure. Bone is connective tissue and it is alive.
What part of an osteon ensures that we have a blood supply to the bone?
The Haversian canal. It houses blood vessels and nerves.
Why do our bones have nerves running through them?
So that we can feel sensation in them and avoid activity that can break them.
Which part of an osteon gives strength to compact bones?
The lamellae.
They are concentric rings of calcified extracellular matrix, containing minerals and collagen.
Where are osteocytes located within the osteons of compact bone?
Osteocytes are located within the lacunae of osteons, which are essentially small spaces.
Which type of bone does not contain osteons?
Spongy bone doesn’t contain osteons
Describe spongy bone.
Spongy bone is made up of an irregular lattice of thin columns called trabeculae, which are arranged along lines of stress.
Where would you find trabeculae?
In spongy bone
Where would you find spongy bone?
Spongy bone makes up the interior of short, flat and irregular bones, and the ends of long bones.
Spongy bone is always covered with compact bone.
What is spongy bone always covered with?
Compact bone
Why are osteons in compact bone, and trabeculae in spongy bone always arranged along lines of stress?
To ensure that when we’re being active, we are distributing forces in the most efficient and effective way possible, so that our bones can act as shock absorbers.
What is the most abundant mineral in bone?
Calcium phosphate
There is also magnesium, sulphate and potassium
What is the extracellular matrix in bone predominantly made of?
Collagen fibres and minerals.
Collagen is the scaffolding. The minerals contribute to the hardness of the bone.
Define ‘long bones’.
Bones that are longer in length than they are in width.
Define ‘diaphysis’.
The shaft of a long bone
Define ‘epiphysis’.
The end of a long bone
Give 3 examples of long bones
Femur, tibia, humerus
Why are many long bones slightly curved?
To allow them to better distribute forces. If our bones were completely straight, they wouldn’t have any ability at all to bow under compression.
Where would you find the epiphyses?
At the proximal and distal ends of long bones.
Which structure separates the diaphysis from the epiphysis in long bones?
The epiphyseal growth plate
What is the epiphyseal growth plate?
A layer of hyaline cartilage that separates the diaphysis from the epiphysis in long bones, and allows the diaphysis to grow in length.
How long are epiphyseal growth plates active for?
Until the age of 18 - 21
They then fuse and become bone (which is why we typically stop growing at this age)
Name 2 long bones that contain some red bone marrow.
Humerus, Femur
What is the periosteum?
The outer layer of bone is covered by the periosteum, with the exception of areas that are covered in cartilage (ie, the ball and socket epiphyseal contacts)
What is the central cavity in the diaphysis of long bones called?
The medullary cavity
What does the medullary cavity in long bones contain?
Red / yellow bone marrow
All bone marrow starts off as red bone marrow. True or false?
True
Following a body trauma, yellow bone marrow can be converted to red bone marrow, to produce more blood cells. True or false?
True
What replaces periosteum on bone joint surfaces?
Hyaline cartilage
How many layers does periosteum have?
- It is a double layered membrane. But it is NOT a serous membrane.
Describe the periosteum
The periosteum is a pain sensitive, highly vascular membrane, that protects bone and serves as an attachment point for ligaments and tendons.
What are the periosteal arteries?
The periosteal arteries are blood vessels that penetrate the periosteum and deliver oxygenated blood into the bone.
Name the 2 layers of the periosteum.
- The tough, outer fibrous layer
2. The inner ‘osteogenic’ layer
What is the purpose of the inner osteogenic layer of the periosteum?
It contains osteoblasts and osteoclasts, assisting in bone growth and repair.
What is the purpose of the outer, fibrous layer of the periosteum?
Muscle attachment and physical bone protection.
List 5 types of bone
Flat, irregular, long, short (cubed-shaped), sesamoid
Where might you find short bones in the body?
Carpals and tarsals in the wrist/hand and ankles/feet
Where might you find flat bones in the body?
Skull, scapula, pelvis
There are 2 ossification pathways used to produce bone. Name them.
- Intramembranous ossification
2. Endochondral ossification
What is the difference between intramembranous ossification and endochondral ossification?
Intramembranous ossification is where bone develops from connective tissue sheets (all flat bones develop in this way).
Endochondral ossification is where bone develops by replacing hyaline cartilage.
When does bone formation begin?
Through foetal development.
Define ‘ossification’
Producing bone
In our early 20’s, the epiphyseal growth plate ossifies. What remains in its place?
The epiphyseal growth line
What is the epiphyseal growth plate and why is it significant?
A layer of hyaline cartilage in the epiphyses, where osteoblasts are produced, ossifying bone matrix. It is what enables bones to grow longer.
At what age do we stop remodelling bone?
We don’t! We are continuously remodelling our bones, in accordance with our environment and daily activities / stresses on the body.
How do bones grow thicker?
Via the osteoblasts within the inner layer of the periosteum.
What are cartilage cells called?
Chondrocytes
Which hormones promote bone formation (osteoblast activity)?
Growth hormone Thyroid hormone Oestrogen Testosterone Calcitonin
Which hormones promote bone break-down (osteoclast activity)?
Parathyroid hormone
Cortisol (and steroid medications)
What does the hormone calcitonin do?
Moves calcium from the blood stream into the bones.
What effect does parathyroid hormone have on bones?
It enhances osteoclast activity, increasing the breakdown of bone and the release of calcium from the bones into the bloodstream.
Why do blood calcium levels have to be tightly controlled?
To ensure proper blood clotting, nerve and muscle function.
Which 2 body systems cannot work without calcium?
Nervous system & muscular system
Calcium exchange is the body is regulated by which glands?
Thyroid and parathyroid glands
What is hypocalcaemia?
Low blood calcium levels
What is hypercalcaemia?
High blood calcium levels
List 3 ways in which parathyroid hormone increases blood calcium.
- Increases osteoclast activity
- Stimulates the kidneys to reabsorb and retain calcium in the blood.
- Increases formation of calcitriol, which promotes calcium uptake from food in the intestines
What is calcitriol?
The final active form of Vitamin D. It pulls calcium from your gut and into your blood.
What form of vitamin D does parathyroid hormone activate?
Calcitriol - the final, active form of Vitamin D
Which organ releases calcitriol?
The kidneys
What is calcitonin?
A hormone that lowers blood calcium levels.
It inhibits osteoclasts and promotes osteoblast deposition of calcium in the bones.
Which gland secretes calcitonin into the blood?
The thyroid gland (para-follicular cells)
With regards to the skeletal system, what very important function does Vitamin D have?
It draws calcium from the intestines and moves it into the blood. It can then go into the bones.
Explain the vitamin D cycle/process in the body
- UV light on the skin creates a Vit D precursor
- It goes to the liver
- It goes to the kidneys
- Finishes as final form of calcitriol (D3)
List some dietary sources of vitamin D
Oily fish (i.e, wild salmon), mushrooms, eggs, supplements (from lichen). But sunshine is best!
How does vitamin D3 work closely with vitamin K2?
D3 assists the absorption of calcium into the blood
K2 activates a protein called osteocalcin, which controls utilisation of calcium in the body (depositing it in bones)
What role does vitamin K2 play in the skeletal system?
K2 activates a protein called osteocalcin, which controls the depositing of calcium from the blood into the bones.
What is osteocalcin?
A protein activated by vitamin K2, which moves calcium from the blood into the bones.
Where can we get Vitamin K2?
From fermented foods (ie, natto), and from our own gut bacteria.
Weight bearing exercise can help stimulate osteoblasts and bone growth/density. True or false?
True
Explain 3 roles of the periosteum
- To protect the bone
- To help the bones grow in width
- To deliver blood supply to the bone (via periosteal arteries)
The skeleton is divided into 2 sections, what are these called?
- Axial skeleton
2. Appendicular skeleton
How many bones are in the axial skeleton?
80
What is the role of the axial skeleton?
To protect the body’s most vital organs
What does the appendicular skeleton consist of?
The bones supporting the extremities / limbs
Which bone does the tongue attach to?
The hyoid bone
What type of joints are the skull bones joined together with?
Fibrous joints (“sutures”)
What are the sinuses and what do they do?
The sinuses are air-filled cavities in the skull.
They give resonance to the voice, and lighten the face and cranium
What are fontanelles?
Soft spots on a baby’s head at the junctions between the fibrous sutures. Fontanelles assist in childbirth.
How many moveable vertebrae are in the spinal column?
24
How many vertebrae are in each section of the spinal column?
Cervical = 7
Thoracic = 12
Lumbar = 5
Sacrum & Coccyx (fused bones)
List 3 functions of the vertebral column.
- Protection of the spinal cord
- Movement (i.e, side bending)
- Supporting the skull
- Axis of the trunk
What structure connects neighbouring spinal vertebrae with one another?
Invertebral discs
Each thoracic vertebrae (T1 - T12) attaches to a corresponding rib (rib 1 - 12). True or false?
True
Which lumbar vertebrae is the most vulnerable to injury and why?
L5 (the lowest). This is purely mechanical. All of the weight of the upper body is sat on it.
How many intervertebral discs are there and what is their function?
23
They act as shock absorbers and separate individual vertebrae.
When are vertebral discs most hydrated?
In the morning.
Also at age 30 - 40 (this is why prolapsed discs are most common at this age)
Vertebral discs are comprised of 2 parts. Name them.
- Annulus fibrosis (tough outer)
2. Nucleus pulposus (a gel-like inner pad)
What is the thoracic cage comprised of?
The ribs (12 pairs), sternum, thoracic vertebrae (posteriorly)
Which ribs are not attached to the sternum?
Ribs 11 and 12 (‘floating ribs’). They have no anterior bony attachments.
How many bones make up the appendicular skeleton?
126 bones
Where are the carpal bones found?
In the wrist
Where are the phalanges found?
In the fingers. They are the finger bones.
What are skeletal muscles?
Muscles that attach to bone and move joints
Generally speaking, which tough, fibrous structure attaches muscle to bone (via the periosteum)?
Tendons
How many joints are in the human body?
187
What are the 3 types of joints?
- Fibrous joints (i.e, sutures in the skull)
- Cartiliginous joints (i.e, epiphyseal growth plate, intervertebral discs)
- Synovial joints
Which type of joint permits the most movement?
Synovial joints
What are the opposing joints of synovial joints covered by, and why?
A layer of articular cartilage.
This reduces friction and acts to shock absorb
What does synovial fluid mostly consist of?
Hyaluronic acid and interstitial fluid
Do synovial joints have a direct blood supply?
No
What are bursa?
Sac-like, fluid-filled structures that are strategically located to reduce friction in the body.
What type of fluid is found inside bursae?
Connective tissue fluid
Where are bursae located?
Between skin and bone, tendon & bone, muscle & bone, or ligament & bone
i.e, shoulder, hip, knee
Define ‘flexion’
Decrease in joint angle
Define ‘extension’
Increase in joint angle
Define ‘rotation’
Movement around a longitudinal axis (twisting).
In limbs it can be medial or lateral.
Define ‘lateral flexion’
Side bending. Movement of the trunk away from the midline
Define ‘abduction’
Movement away from the midline
i.e, hip or shoulder/arm
Define ‘adduction’
Movement towards the midline
i.e, hip or shoulder/arm
Define ‘circumduction’
Circular movement, multiple combinations of other movements.
Define ‘protraction’ and ‘retraction’
Protraction = Anterior movement (forwards) Retraction = Posterior movement (backwards)
i.e, protract and retract the shoulders
Define ‘inversion’ and ‘eversion’.
Inversion = medial movement of sole (turn in) Eversion = lateral movement of sole (turn out)
Define ‘supination’ and ‘pronation’
Supination = turning the palm upwards Pronation = turning the palm downwards
Define ‘opposition’
Movement of thumb across the palm to touch fingertips
