2. Skeletal System Flashcards
The anatomical position
Describes the body position from which directional terms always refer to:
- Person stands erect, palms forward
- Feet parallel, flat on the floor
- Arms are at the sides of the body
Supine position
Describes the body lying face up
Prone position
Describes the body lying face down
Directional terms: Medial
Nearer to the midline
Directional terms: Lateral
Away from the midline
Directional terms: Bilateral
Both sides
Directional terms: Unilateral
One side
Directional terms: Ipsilateral
On the same side
Directional terms: Contralateral
On the opposite side
Directional terms: Proximal
Nearer to the trunk
Directional terms: Distal
Further from the trunk
Directional terms: Anterior (ventral)
Nearer the front
Directional terms: Posterior (dorsal)
Nearer the back
Directional terms: Superior
Towards the top
Directional terms: Inferior
Towards the bottom
Body planes
- Coronal / frontal plane: Separating the body FRONT & BACK
- Sagittal plane: Separating the body LEFT & RIGHT
- Horizontal / transverse: Separating the body TOP & BOTTOM
How may bones in the human body and % of body weight
206 bones in the human body
Accounts for 18% of body weight
Functions of the human skeleton
- Supports framework for the body
- Forms boundaries (skull)
- Attachment for muscles & tendons
- Permits movement (joints)
- Haematopoiesis - formation & development of blood cells from red bone marrow
- Mineral homeostasis (mostly calcium & phosphate)
- Triglyceride storage (yellow bone marrow)
Name the bone cells
- Osteogenic cells
- Osteoblasts
- Osteocytes
- Osteoclasts
Osteogenic cells
Bone stem cells
They are the only bone cells to undergo division (producing osteoblasts)
Osteoblasts
The bone-building cells
They synthesise and secrete collagen and other components of bony matrix
They are trapped and become osteocytes
Osteocytes
Mature bone cells
They maintain the daily metabolism of bone e.g. nutrient exchange
Osteoclasts
Huge cells derived from the fusion of as many as 50 WBC’s (monocytes)
On the side facing the bone surface, cell membrane is folded into a ruffled boarder, where the cell releases powerful lysosomal enzymes & acids which digest bone matrix
Resorption is the breakdown of bone matrix
Osteoblasts & osteoclasts work together to remodel bone throughout life. Excess osteoclasts activity leads to bone density loss.
The two types of bone
Compact & spongy
Compact bone
80% of the skeleton is compact bone
Contains few spaces and is strong
Found beneath the periosteum of all bones and makes up the bulk of the diaphysis of long bones
A structural unit of compact bone is an ‘Osteon’ (aligned in the same lines as stress)
Four parts of an Osteon
- Haversian canal: contains blood vessels & nerves
- Lamellae: concentric rings of calcified extracellular matrix (minerals & collagen)
- Canaliculi: a mini system of interconnected canals that provide a route for nutrients/waste
- Lacunae: small spaces called lacunae with osteocytes
Spongy bone
Does not contain osteons, instead has trabeculae (irregular lattice of thin columns) that are arranged along line of stress
Microscopic spaces between trabeculae help make the bone lighter & can be filled with bone marrow
makes up the interior of short, flat, and irregularly-shaped bones & the ends of long bones
Spongy bone is always covered with compact bone
Bone matrix
An extracellular matrix that surrounds separated cells made up of collagen and minerals (calcium phosphate as well as magnesium, sulphate and potassium).
long bone two parts
Diaphysis (shaft)
Epiphyses (two heads)
Long bones
Bones that have a greater length than width
contain a diaphysis (shaft) & epiphyses (two heads)
Slightly curved for force distribution
Contain mostly compact bone in the diaphysis & spongy bone in the epiphysis
Examples include: femur, humerus & tibia
Epiphysis
Ends of long bones (proximal and distal) Contains spongy bones with red bone marrow surrounded by compact bone and hyaline cartilage
Epiphyses are separated from the diaphysis by the epiphysis growth plate (a layer of hyaline cartilage that allows the diaphysis to grow in length)
Diaphysis
The shaft of long bones
Contains mostly compact bone
Outer compact bone is covered by ‘periosteum’
Contains a central ‘medullary cavity’ that contains red/yellow bone marrow
All marrow starts off as what?
Red marrow
Periosteum
Surrounds the external surface of bone when it’s not covered by cartilage (joint surfaces)
The periosteum is a pain-sensitive, highly-vascular membrane that protects bone & serves as a attachment for ligaments/tendons
Where do the periosteal arteries enter
The periosteal arteries enter the diaphysis through many perforating canals, delivering oxygenated blood
The periosteum is a double layered membrane containing what?
- A tough outer ‘fibrous layer’ that protects bone
- An inner ‘osteogenic layer’ that contains osteoblasts and osteoclasts, assisting in bone growth and repair
Types of bone
- Short bone (cubed shaped) - e.g. carpals, tarsals
- Irregular bones (complex shapes) - e.g. vertebrae
- Flat bones (two plates of compact bone) - e.g. skull, scapula
- Sesamoid bone - e.g. patella
- Long bone - e.g. femur, tibia
Bone formation
Bone formation begins during foetal development, before continuing into childhood and then into adult life
There are two ossification pathways used to produce bone; these are:
- Intramembranous ossification:
- bone develops from connective tissue sheets
- all flat bones (i.e. skull) and the clavicles develop this way - Endochondral ossification
- bone develops by replacing hyaline cartilage
Bone growth
Long bones elongate from the epiphyseal growth plate
In the early 20’s, the epiphyseal growth plate ossifies so that only a thin ‘epiphyseal line’ remains
If a bone fracture damages the epiphyseal plate during childhood, the bone may grow shorter (stunt growth)
Bones may also grow in thickness using osteoblasts in the periosteum
Bone hormones
Many hormones affect bone growth and density by altering the ratio of osteoblast to osteoclast activity
- Promote ‘osteoblast’ activity (bone formation)
- growth hormone & thyroid hormone
- oestrogen & testosterone
- calcitonin - Promote ‘osteoclast’ activity (bone loss)
- parathyroid hormone
- cortisol & steroid medications
Bone homeostasis
Bones are an important mineral reservoir, mostly calcium
Blood calcium levels have to be tightly controlled to ensure proper blood clotting, nerve & muscle function
If blood calcium levels are low (hypocalcaemia) osteoclasts will breakdown bone and release calcium into the blood
If calcium levels are high (hypercalcaemia) there will be an increase in osteoblast activity (take calcium back into the bone)
calcium exchange is regulated by the parathyroid glands & thyroid glands
Parathyroid hormone
Increases blood calcium
Increases the activity of osteoclasts (resorption)
Stimulates the kidneys to reabsorb & retain calcium in the blood
Increases formation of calcitriol which promotes calcium uptake from food in the intestines
Calcitonin
Calcitonin is a hormone that lowers blood calcium levels
Secreted by para-follicular cells of the thyroid gland
Inhibits osteoclasts & promotes osteoblast deposition of calcium in the bones
The overall result is increased bone formation & decreased blood calcium
Vitamin D
Facilitates calcium absorption in the intestines and is directly involved in bone turnover
Vitamin D3 works closely with K2.
Vitamin D3 assists the absorption of calcium into the blood, whilst K2 activates a protein called ‘osteocalcin’ which controls utilisation of the calcium in the body (depositing into bones)
What happens to vitamin D levels with age
decrease
Low vitamin D factors
- Low sun exposure
- reduced dietary absorption
- reduced ability to produce an active form of vitamin D through it’s processes in the skin, liver & kidneys
- High alcohol intake
- Magnesium deficient
Exercise
Within limits, bone can become stronger in response to mechanical stress
Mechanical stress leads to increased mineral deposition & increased collagen production
Lack of stress on bones can cause bone mass loss of up to 1% per week
The skeleton is divided into what section?
The axial & appendicular sections
The axial skeleton
The ‘central skeleton’
Contains 80 bones
Serves to protect the body’s most vital organs
The axial skeleton contains the: skull, inner ear bones, hyoid, thoracic cage and vertebral column
Skull
Forms the cranium (upper head), the face and encapsulates the brain
The skull bones are joined with fibrous joints (‘sutures’)
‘Sinuses’ are air-filled cavities in the skull that:
- give resonance to the voice
- lighten bones of face & cranium
Fontanelles
- fibrous structures (soft spots) on a baby’s head joining the skull bones together. (ossify at 12-18 months)
- allows the baby’s head through birth canal
The vertebral column consists of 24 movable vertebrae, what are they?
Cervical (7) C1-C7
Thoracic (12) T1-T12
Lumbar (5) L1-L5
Sacrum & coccyx (fused bone)
How are neighbouring vertebrae connected?
Intervertebral discs
Vertebral column functions
- Protection for spinal cord
- Movement e.g. side bending
- Support of skull
- Forms axis of the trunk
Intervertebral discs
Discs are shock-absorbing structures
23 discs are present in the spine
They bind vertebral bodies and separate individual vertebrae
Discs are most hydrated in the morning and aged 30-40
In 2 parts: Annalulus fibroses & nucleus pulposes
What does the thoracic cage and ribs consist of?
- sternum
2. Ribs (12 pairs)
Thoracic cage and ribs
The ribs attach to the sternum via costal cartilage
Ribs 11 & 12 are ‘floating ribs’
Appendicular skeleton
The appendicular skeleton is the distal skeleton - consisting of the limbs
Consists of 126 bones
Functions: movement & organ protection
What does the appendicular skeleton consist of
- Shoulder girdle, arm and hand
- Pelvic girdle, leg and foot
Shoulder girdle contains:
- Clavicle (anteriorly)
- Scapula (posteriorly)
- Humerus (upper arm)
- Ulna (medial forearm bone)
- Radius (lateral elbow bone)
- Carpals (wrist bone)
- Metacarpals (bones in between carpals and digits/fingers)
- Phalanges (fingers, divided into: proximal, intermediate and distal)
Pelvic girdle contains:
- Femur (the longest & strongest bone in the body)
- Tibia (shin bone)
- Fibular (bone in lateral lower leg)
- Patella (sesamoid bone, anterior knee)
- Tarsals (ankle bones)
- Metatarsal bones (bones connecting middle section of foot)
- Phalanges (toes)
Muscles that attach to the bone and move joints are called what?
Skeletal muscles
Skeletal muscles
Skeletal muscles attach to sites of the human skeleton (via tough fibrous structures called tendons)
Their subsequent contracture (shortening) generates movement
How many joints are in the human body
187
What are joints
Joints connect two bony structures and permit movement
What are the three types of joints
- Fibrous
- Cartilaginous
- Synovial
Explain fibrous joints
Bones are held tightly together, permitting limited movement (sutures in the skull)
Explain Cartilaginous joints
Articulating bones tightly connected by cartilage; permit little to no movement (epiphyseal growth plate, intervertebral discs)
Explain synovial joints
Synovial joints permit the most movement
Bones at the joints are covered by a layer of hyaline cartilage (articular cartilage) that reduces friction & acts as sock absorber
They contain synovial fluid, which consists mostly of hyaluronic acid & interstitial fluid filtered from the blood. (they have no direct blood supply)
The obtain nutrients from diffusion (joint movement is essential for this to happen)
e.g. ‘ball & socket’ (shoulder & hip) and ‘hinge’ (elbow & knee)
What is bursae
Bursae are closed, fluid filled sac-like structures that are strategically located to reduce friction.
The inside of a bursae contains connective tissue fluid similar to synovial fluid
These ‘sacs’ cushion areas where bone would otherwise rub on muscle, tendons or skin
located between: skin & bone, tendons & bone, muscle & bone, ligament & bone
Flexion (Angular movements)
Decrease in joint angle
Extension (Angular movements)
Increase in joint angle
Rotation (Angular movements)
Movement around it’s longitudinal axis. in the limbs it can be medial or lateral (away from the midline)
Lateral flexion (Angular movements)
Movement of trunk away from midline
Abduction (Angular movements)
Movement away from midline
Adduction
Movement towards midline
Circumduction (Angular movements)
Circular (flexion, abduction, extension, hyperextension, adduction in succession)
Elevation (special movements)
Superior movement (up)
Depression (special movements)
Inferior movement (down)
Protraction (special movements)
Anterior movement (forward)
Retraction (special movements)
Posterior movement (backward)
Inversion (special movements)
Medial movement of sole (turn in)
Eversion (special movements)
Lateral movement of sole (turn out)
Dorsiflexion (special movements)
Bending foot up
Plantar flexion (special movements)
Bending foot down
Supination (special movements)
Movement of forearm to turn palm up
Pronation (special movements)
Movement of forearm to turn palm posteriorly
Opposition (special movements)
Movement of thumb across palm to touch fingertips
X-rays
Used to visualise the skeletal system, lungs, heart and teeth
They pass through less dense matter (air, fat, muscle, and other tissues) & absorbed by denser materials (bones, tumours, lungs affected by severe pneumonia), appearing white
Blood clots can also be detected due to accumulation of RBC’s
Adverse effects: Cancer (DNA damage / genetic mutations) X-rays are mutagenic agents
