Introduction to the Skeletal System

Question 1

The Human Skeleton

Answer 1

There are typically 206 bones in the adult human skeleton

The skeleton is divided into two main regions - The axial skeleton + The appendicular skeleton

Question 2

The appendicular skeleton

Answer 2

Consists predominantly of the bones of the arms and legs (appendages) together with the lateral components of the pelvic girdle

Question 3

The axial skeleton

Answer 3

consists predominantly of the bones which are located in the central axis of the body.

Question 4

what does the the axial skeleton include

Answer 4

the skull, spinal column, ribcage and the sacral area of the pelvic girdle

Question 5

The functions of the skeleton

Answer 5

Support

Movement

Protection

Blood cell production

Fat storage

Calcium storage

Question 6

two components of bone

Answer 6

Organic component

Inorganic component

Question 7

Organic component

Answer 7

formed from the protein collagen which is found in the form of fibres which function knit the bone together and prevent fragmentation

Question 8

Inorganic component

Answer 8

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

Question 9

Brittle bone disease (osteogenesis imperfecta)

Answer 9

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

Question 10

Vitamin D and Rickets

Answer 10

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

Question 11

what is Vitamin D

Answer 11

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

Question 12

Long bones

Answer 12

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

Question 13

what does each long bone consists of

Answer 13

A diaphysis

The epiphyses

Question 14

A diaphysis

Answer 14

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)

Question 15

The epiphyses

Answer 15

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

Question 16

Two major types of bone fracture

Answer 16

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

Question 17

pathogens that infect bone

Answer 17

Staphylococcus aureus and Streptococcus pyogenes

Question 18

what initiates a vigorous inflammatory response

Answer 18

Bacteria can quickly attach to and begin to grow rapidly within the bone tissue initiating a vigorous inflammatory response

Question 19

osteomyelitis

Answer 19

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

Question 20

Infected bone

Answer 20

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

Question 21

Flat bones

Answer 21

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

Question 22

flat bone characteristics

Answer 22

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

Question 23

red bone marrow

Answer 23

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)

Question 24

where is the greatest volume of red bone marrow located

Answer 24

pelvis, ribcage and spinal column

Question 25

where is adult red bone marrow located

Answer 25

predominantly located in the flat bones of the axial skeleton with smaller amounts found in the epiphyses of some of the larger long bones

Question 26

what happens during haematopoiesis

Answer 26

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)

Question 27

malignancy

Answer 27

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

Question 28

leukaemia

Answer 28

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

Question 29

Skull fractures

Answer 29

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

Question 30

Hormonal control of bone density

Answer 30

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

Question 31

calcitonin

Answer 31

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

Question 32

parathyroid hormone (PTH)

Answer 32

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

Question 33

Potential loss of calcium from bones and teeth during pregnancy

Answer 33

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