Introduction to the Skeletal System Flashcards
The Human Skeleton
There are typically 206 bones in the adult human skeleton
The skeleton is divided into two main regions - The axial skeleton + The appendicular skeleton
The appendicular skeleton
Consists predominantly of the bones of the arms and legs (appendages) together with the lateral components of the pelvic girdle
The axial skeleton
consists predominantly of the bones which are located in the central axis of the body.
what does the the axial skeleton include
the skull, spinal column, ribcage and the sacral area of the pelvic girdle
The functions of the skeleton
Support
Movement
Protection
Blood cell production
Fat storage
Calcium storage
two components of bone
Organic component
Inorganic component
Organic component
formed from the protein collagen which is found in the form of fibres which function knit the bone together and prevent fragmentation
Inorganic component
predominantly composed of calcium phosphate which is present in bone in the form of rectangular crystals (hydroxyapatite crystals). This mineral component imparts hardness and rigidity to the bone
Both the organic and inorganic components of bone are required in the correct ratio for bone to maintain its strength
Brittle bone disease (osteogenesis imperfecta)
A genetic disorder usually resulting from abnormalities of the genes that control the production of collagen
Quite rare, occurs in around 1 in 28000 live births
Results in frequent fractures even when the bones are placed under minor stress
Vitamin D and Rickets
Vitamin D deficiency leads to softening of the bones leading to rickets (in children) and osteomalacia (in adults)
This can lead to bones (particularly in the legs) becoming distorted and buckling under the weight of the body
what is Vitamin D
fat soluble vitamin found in liver, oily fish, eggs, dairy products and produced by the skin in sunlight
Essential for the absorption of calcium and phosphate which form the inorganic component of bone that is responsible for imparting hardness and rigidity
Long bones
longer than they are wide (e.g., humerus and femur)
Most long bones are found in the appendicular skeleton within the arms and legs
Long bones function primarily as levers to allow movement
what does each long bone consists of
A diaphysis
The epiphyses
A diaphysis
The shaft of a long bone is composed of incredibly strong compact bone (also known as cortical bone). Running longitudinally through the length of the diaphysis there is usually hollow cavity termed the medullary cavity which is filled with yellow bone marrow (fat)
The epiphyses
Each long bone has a proximal epiphysis (close to the trunk of the body) and a distal epiphysis (away from the trunk of the body).
The epiphyses are the bulbous ends of a long bone and are predominantly composed of softer spongy bone (aka cancellous bone) which may contain small amounts of red bone marrow
Two major types of bone fracture
Simple fractures: only the bone itself is broken with limited damage to the surrounding tissues
Compound fractures: the bone is fractured and penetrates the surrounding tissues and usually out through the skin
pathogens that infect bone
Staphylococcus aureus and Streptococcus pyogenes
what initiates a vigorous inflammatory response
Bacteria can quickly attach to and begin to grow rapidly within the bone tissue initiating a vigorous inflammatory response
osteomyelitis
Infection and inflammation within bones is termed osteomyelitis and is incredibly painful
phagocytic leukocytes (particularly neutrophils) enter the fracture site of the bone and attempt to trap and remove the infecting pathogen. Unfortunately these cells can release enzymes which, as well as killing the pathogen, can cause further bone damage
Infected bone
can act as a reservoir for bacteria (and other pathogens) which may eventually gain access to the blood leading to septicaemia and potentially life-threatening sepsis and septic shock
Flat bones
have a thin, flattened appearance
Most flat bones are located in the axial skeleton where they cover and protect vulnerable areas of the body,
sandwich-like structure
flat bone characteristics
has outer layers of compact bone and an inner core of
spongy (also known as cancellous) bone
This structure is excellent at absorbing physical impacts since the spongy bone at the centre is slightly deformable allowing impact forces to be effectively dissipated
red bone marrow
Within the spongy bone at the core of a flat bone the second type of bone marrow called red bone marrow is located
Red bone marrow is part of the lymphatic system and functions as the primary organ of haematopoiesis (the formation of blood cells)
where is the greatest volume of red bone marrow located
pelvis, ribcage and spinal column
where is adult red bone marrow located
predominantly located in the flat bones of the axial skeleton with smaller amounts found in the epiphyses of some of the larger long bones
what happens during haematopoiesis
the stem cells that reside within the red bone marrow are dividing rapidly to continually produce a steady stream of new blood cells
although this tissue is called red bone marrow - not only responsible for producing red blood cells (erythrocytes) but also all of the white blood cells (leukocytes) and platelets (thrombocytes)
malignancy
Since the stem cells of the red bone marrow are rapidly dividing before differentiating into the different blood cell populations this tissue is prone to malignancy
leukaemia
Diseases such as leukaemia often require bone marrow transplants, this initially involves destroying the existing (malignant) red bone marrow with chemotherapy before matched donor bone marrow is transplanted
Skull fractures
Although flat bones are good at absorbing physical impacts and protecting the tissues which they overlay, when exposed to excessive forces
These irregular types of flat bone fracture can generate splinters of bone which can penetrate into the underlying soft tissues potentially causing extensive damage
Hormonal control of bone density
Bone is a dynamic tissue that is continually being built-up by cells called osteoblasts and broken down by cells called osteoclasts
It has been estimated that it takes around 7 years to “turn over” (replace) an entire bone
calcitonin
When blood calcium levels rise the thyroid gland releases the hormone calcitonin
Calcitonin directs excess calcium into the bones increasing bone density, this explains why dairy products are promoted as being excellent for strong bones and teeth
parathyroid hormone (PTH)
When the blood calcium level is low the parathyroid glands release parathyroid hormone (PTH)
PTH stimulates the release of calcium from the bones and teeth ensuring a stable level of calcium in the blood.
It is essential that calcium levels in the blood are maintained since calcium is a blood clotting factor as well as being essential for muscle contraction, cell division and many other physiological process
Potential loss of calcium from bones and teeth during pregnancy
The presence of increased PTH in the blood is progressively damaging to bones (reducing bone density) and teeth (causing tooth demineralisation)
Since PTH levels may be raised during pregnancy expectant mothers receive free dental care since they are at risk of tooth and gum disease
Low blood calcium often triggers calcium cravings which are particularly apparent during pregnancy where mothers frequently crave calcium-rich foods such as cheese, chocolate and cream cakes.
These cravings can be so intense that some expectant mums may eat things that they would not normally consider eating such as chalk, sand or even coal. This phenomena of craving unusual substances is called pica
