6. Trauma, Repair and Recovery

Question 1

What is ‘trauma’?

Answer 1

Any physical injury or severe psychological shock.

To distinguish:

• traumatic injury
• psychological trauma

Question 2

Why do you think the incidence of death and injury from road crashes is rising in low- and middle-income countries such as India and Pakistan, yet falling in high- income countries where there are many more motor vehicles per head of population?

Answer 2

• the rapid increase in the number of vehicles on the roads of developing countries
• the large numbers of pedestrians
• the large number of multi-occupancy vehicles
• the often poor state of repair of roads outside major urban centres and inadequate measures for reducing accidents
• large numbers of unsafe vehicles
• little enforcement of injury prevention measures such as wearing seat belts and crash helmets

Question 3

What happens if blood circulation is impaired by trauma?

Answer 3

The resulting lack of oxygen to the brain will rapidly result in a loss of consciousness as the brain cells can no longer perform their energy-requiring functions.

Question 4

Briefly describe how the blood moves through different parts of the cardiovascular system, referring to the blood vessels involved and any structural features associated with blood movement.

Answer 4

1. Blood is pumped under pressure from the heart into the arteries that carry it to the different parts of the body. The arteries have thick muscular walls to withstand
   the blood pressure created by the pumping of the heart.
2. The arteries branch and eventually become small capillaries which run throughout the tissues, delivering the oxygen and nutrients required by cells. The capillaries have thin walls which facilitate the diffusion of oxygen out of the blood and into the tissues.
3. The blood vessels that lead away from the capillaries in the tissues and carry blood back to the heart are veins. These have thinner less-muscular walls than arteries because they do not need to withstand pressure from the heart. Instead, blood moves through the veins as they are squashed by the movement of surrounding muscles. The blood moves in one direction only (towards the heart) due to the presence of one-way valves in the veins.

Question 5

The flow of blood back to the heart in the veins is known as…

Answer 5

venous return and is achieved by the presence of valves in the veins which only allow blood to flow in one direction, that is, towards the heart.

Question 6

Blood pressure measurements are expressed as two different numbers:

Answer 6

• Systolic pressure (the high pressure in the arteries that occurs during heart contraction and is typically around 120 mmHg)
• Diastolic pressure (the lower pressure in the arteries that occurs between heart contractions and is typically around 80 mmHg)

Question 7

Blood pressure is controlled by both…

Answer 7

1. the rate and size of heart contractions (cardiac output)
2. the constriction and dilation of blood vessels (peripheral resistance).

Signals from the nervous system maintain an effective circulation during different activities (changes in oxygen demand from organs, changes in posture, etc.).

Question 8

What happens if more than 20% of blood is lost through serious bleeding following trauma?

Answer 8

Initial decrease in systolic blood pressure, which triggers a nervous system response.

This response acts to counteract the drop in blood pressure by increasing heart rate and narrowing the capillaries that carry blood to the skin.

This condition is called hypovolaemic shock.

Question 9

Apart from a reduction in blood volume caused by blood loss, what else could lead to an inadequate supply of blood to the tissues (shock)?

Answer 9

Damage to the heart muscle (e.g. through trauma or a heart attack) could also cause shock, because the transport of blood to the tissues would be impaired if the heart failed to pump effectively.

Question 10

How could damage to the nervous system be caused?

Answer 10

This damage could be caused directly to the nervous system, or may be a result of a reduction in the supply of oxygenated blood which would starve the brain cells of the oxygen they need in order to function and survive.

Question 11

Nervous system damage following an injury can be assessed how?

Answer 11

By the level of response that a patient shows to various stimuli.

Question 12

Explain the sequence of events that you would predict to occur in a person who was bleeding uncontrollably from a damaged artery.

Answer 12

• Blood loss of up to 10% not be sufficient to compromise the function of the cardiovascular system, no obvious effects
• Blood loss reached 20%: increasing heart rate and constricted blood vessels to maintain blood pressure, pale skin, reduction of oxygen supply to brain, dizziness
• Blood loss 30%: heart rate very rapid, skin very pale and cold. Signs of lowered levels of consciousness as oxygen supply to the brain would be reduced.
• Blood loss 40%: body no longer able to maintain blood pressure, unconsciousness as the nervous system became starved of oxygen. Lack of oxygen supply to the essential body systems (the muscle of the heart and the muscles involved in lung function and the parts of the nervous system that control them) would rapidly result in death

Question 13

What is a tissue?

Answer 13

A collection of similar cells that are grouped together in an organised manner to fulfil a particular function.

Question 14

How can movement of bones be achieved?

Answer 14

By contraction of muscles which are attached to the bones via strong rope-like structures called tendons.

Question 15

Why are muscles referred to as antagonistic pairs?

Answer 15

Because muscles cannot push, they can only pull, they generally work in pairs to achieve controlled limb movement. This is known as antagonism and the muscles are referred to as being antagonistic pairs.

Question 16

What does the

a) flexor
b) extensor

do?

Answer 16

a) flexor: move bones closer together (known as flexion, e.g. bending the arm at the elbow or bending the leg at the knee)
b) extensor: move bones further apart (known as extension, e.g. straightening the arm or leg)

Question 17

What is the extracellular matrix?

Answer 17

The term ‘extracellular’ refers to the fact that this material is outside the cells, whilst ‘matrix’ indicates that this is a substance in which the cells are embedded. Extracellular matrix is mainly made from proteins.

Question 18

Which 4 types of bones can be found in the human body?

Answer 18

1. Long bones (arms, legs)
2. Short bones (wrists, ankles)
3. Irregular bones (vertebrae in the spine)
4. Flat bones (scapula (shoulder blade), most skull bones)

Question 19

There are two distinct types of bone tissue:

Answer 19

1. Along the length of the shaft and all around the ends is compact (sometimes called cortical) bone, which is dense and forms a hollow cylinder;
2. within this is less dense cancellous (can-sell-us) bone, which has a honeycomb appearance and fills the widened areas inside the ends of the bone

Question 20

What is contained in compact bones?

Answer 20

There are canals running through it containing fluid, cells and blood and lymph vessels

Question 21

Which protein is the main component of the bones extracellular matrix?

Answer 21

Collagen, which is the most abundant protein in the body and has a structure that allows it to be formed into long thin fibres.

These fibres are packed together in a very organised manner, which makes the resulting matrix structure very strong

Question 22

Whilst the strength in bone comes from the collagen, the hardness is conferred by…

Answer 22

the mineral component of bone – calcium-containing crystals that are incorporated into the collagen framework.

Question 23

There are two main cell types involved in maintaining the structure of bone:

Answer 23

Osteoblasts: bone- forming cells which secrete collagen and organise the mineralisation of bone

Osteoplasts: disassemble or resorb bone in order to remodel it into an optimal shape

Question 24

What causes osteoporosis?

Answer 24

A disease in which the balance shifts too far towards resorption of bone and an excessive loss of bone structure results

Question 25

What is in the bone marrow?

Answer 25

Specialised cells that make white cells and red blood cells and a variety of other cells. Stem cells!

Question 26

The structure of articular cartilage is that of a smooth resilient coating on the ends of the long bones. What function do you think this performs?

Answer 26

Articular cartilage provides a smooth surface that reduces friction and protects the bones during joint movement.

Question 27

What are calcium ions and how can they be obtained?

Answer 27

• they are in crystals in the bones stems
• mineral element of the bones themselves, but also a vital component of many chemical reactions throughout the body
• if the calcium levels in the blood drop, calcium ions are released from the bones (bone structure becomes weaker)

Question 28

What are the three types of muscles?

Answer 28

• skeletal muscle (part of the musculoskeletal system)
• cardiac muscle (heart muscle tissue)
• smooth muscle (like walls of arteries and the gut)

Question 29

All types of muscle perform the same main function:

Answer 29

Contraction of the muscle changes its shape and moves the structures to which it is attached.

Question 30

What are myofibres?

Answer 30

Myofibres (or muscle fibres) are the contractile cells of the muscle.

They are long and thin (as is suggested by the term fibre) and each cell is multinucleated, i.e. it contains more than one nucleus

Question 31

Inside the myofibres are long organelles. What are they called?

Answer 31

Myofibrils, which run the full length of the cell and contain the proteins that allow contraction.

Question 32

What is a tendon?

Answer 32

Deutsch: Sehne

The structure that forms from the fibres of the extracellular matrix at the ends of the muscle, and joins the muscle to the bone

Question 33

Describe the structure etc. of a tendon.

Answer 33

• like ropes that attach muscles to bones (or sometimes to other muscles)
• high tensile strength (they can withstand being pulled on with great force without breaking) and often have to be flexible enough to bend around joints
• made from collagen fibres and some elastic fibres

Question 34

What are ligaments?

Answer 34

Deutsch: Bänder

Similar in structure to tendons, but instead of connecting muscle to bone they connect bones to each other.

Question 35

What are Schwann cells?

Answer 35

The cells associated with peripheral neurons that wrap themselves around the axons, this enables faster more efficient transmission of action potentials along the axon.

Question 36

How is the skin structured?

Answer 36

Skin contains two main layers:

1. the epidermis, which is the outermost layer,
2. and the underlying dermis.

Beneath the dermis there is a layer of subcutaneous fat (subcutaneous therefore means under the skin).

Question 37

What happens in the epidermis?

Answer 37

Keratinocytes (living cells) are gradually pushed towards the surface as more new cells are formed beneath them. As they move outwards, a fibrous protein called keratin is made inside the cells. When keratinocytes reach the outer layers they die, so these outer layers are made from lots of flat thin dead cells packed full of keratin.

The base layer of the epidermis also contains other cell types including those that give the skin its colour (pigment) and provide chemicals to protect the skin from the harmful effects of the sun.

Question 38

There are a number of different cell types present in the dermis:

Answer 38

• Fibroblasts produce and maintain the extracellular matrix proteins
• Immune system cells ready to respond to damage
• Capillaries and sensory nerve endings
• Fat cells which store energy in the form of fat but also serve to cushion and insulate the body
• Sweat glands and hairs, both of which are involved in the temperature regulation function of the skin

Question 39

How do sweat glands work?

Answer 39

Sweat glands are ducts lined with epithelial cells which originate in the subcutaneous tissue and open onto the surface of the skin or into the hair follicles.

Sweat is a salty fluid that is released by the sweat glands in response to nerve signals (triggered by fear or excessive heat) – the sweat evaporates from the surface of the skin using heat energy, thus helping to cool the body down.

Question 40

What is tissue fluid?

Answer 40

Tissue fluid comes from the capillaries, which have a very thin wall that allows some of the inner fluid to leak out of the blood into the surrounding tissues.

Red blood cells and large dissolved blood plasma proteins remain inside the capillaries, but the tissue fluid allows dissolved nutrients and oxygen to reach the tissue cells via diffusion. All of the cells within a tissue are bathed in the tissue fluid, and the network of capillaries ensures that all cells are close to a supply of oxygen and nutrients.

Question 41

The leakage of water into the tissues will leave the blood in the capillaries with a reduced water content. Can you suggest how this imbalance might be redressed?

Answer 41

Tissue fluid moves back into the capillaries, redressing the balance. This means that there is a continuous exchange of fluid between the inside of the capillaries and the surrounding tissue cells.

Question 42

What are endothelial cells?

Answer 42

The flat cells that line the cardiovascular system, like the tiles on the inside wall of a tunnel.

Question 43

What is vasodilation and vasoconstriction?

Answer 43

Vasodilation: blood flow to the dermis increases and
the skin turns red = cooling the body

Vasoconstriction: the blood flow to the dermis decreases and the skin turns pale = conserving body heat by reducing blood flow through the skin

Question 44

Briefly describe which structures in skin are related to the functions of (a) protection, (b) sensation and (c) temperature regulation.

Answer 44

(a) Protection: epidermis (waterproof, keratinocytes, thicker at sites where most protection is needed, pigments for sun
(b) Sensation: sensory nerve endings in the dermis

(c) Temperature: hairs which sprout from
the dermis, subcutaneous fat, blood vessels in dermis, sweat from sweat glands in dermis

Question 45

Since tendons are made predominantly of similar extracellular matrix fibres (collagen) to those found in muscles and bones, why are they not stiff like bones or contractile like muscles?

Answer 45

The stiffness and compressive strength of bones are largely due to the mineral components which are not present in tendons. The contractility of muscles is due to the myofibres, which are not present in tendons.

Question 46

Which 4 types of fractures are there?

Answer 46

Open fracture: This is where the overlying skin has been broken and the broken bone is exposed to the outside world

Closed fracture: The skin remains intact

Greenstick fracture: An incomplete fracture that often occurs in children whose bones tend to bend rather than break completely

Insufficiency fracture: This is damage caused by ‘normal’ forces acting on osteoporotic bone

Question 47

If the broken parts of the bone are in the correct position, what is it called?

Answer 47

Undisplaced - little intervention is required other than immobilising and protecting the damaged area.

Displaced: then an operation will often be required in order to realign the broken parts of the bone.

Question 48

What means splinting the bone?

Answer 48

For small bones like fingers and toes, immobilising it with a piece of rigid material or by taping it to the neighbouring finger or toe

(Bone adopts the mechanical function that the intact bone normally plays, immobilising the damaged area and shielding the repair site from mechanical forces until such time as it has fully repaired)

Question 49

What can be done to immobilie a larger bone?

Answer 49

In larger bones, such as those in the arm and the lower part of the leg, a cast fulfils a similar function to a splint.

This hard shell provides protection to the repair site and immobilises the area so that the damaged ends of the fractured bone can fuse.

Question 50

Two of the nastiest infections that can result in limb loss and death are gas gangrene and tetanus. What happens then?

Answer 50

Gas gangrene: caused by the Clostridium perfringens bacterium, release toxins (poisons). Damage can spread rapidly. One of the toxins produced by this bacterium is a collagenase enzyme which breaks down collagen in the tissues with disastrous consequences.

Tetanus: caused by bacterium called Clostridium tetani which releases a toxin that causes paralysis of muscles and can therefore lead to breathing (ventilation) failure and death. Rare in affluent countries due to immunisation.

Question 51

‘Greenstick’ fractures are so named because…

Answer 51

they resemble the fracture that occurs when someone tries to break a fresh green stick from a tree. When an old dry stick is broken, it snaps cleanly into two separate parts, whereas the green stick will bend, then fracture on one side only.

Greenstick fractures are often seen in children. This is because their bones have the ability to bend more without breaking than the bones of adults

Question 52

Can you suggest what components of the bone determine whether it snaps or bends when force is applied?

Answer 52

The composition of the extracellular matrix, in particular the relative amounts of collagen (strength) and minerals (hardness).

Question 53

What do you think are the main factors that cause falls in older people?

Answer 53

External factors: uneven surfaces, poor lighting, poor design of housing, lack of handrails, uneven stairs;

Poor physical health: sight and hearing deficits, balance impairment, muscle weakness or gait (way of walking) problems;

Poor mental health: confusion, cognitive (processing and understanding) and memory difficulties, inappropriate doses of medication

Question 54

Why is the exact location of a hip fracture so important?

Answer 54

Because in some positions a fracture will damage the blood supply to the head of the femur.

Broken hips may be repaired or replaced depending on the location of the fracture and the patient’s age, medical fitness and resources available.

Question 55

Describe some tests that would be undertaken in hospital when assessing a patient with a fractured limb.

Answer 55

• X-ray image of the damaged area would be taken in order to assess the location and severity of the fracture (and whether it was displaced).
• Damage to other tissues would also be assessed, in particular checking for a pulse at the end of the damaged limb (a check for blood vessel damage) and for sensation
  (a check for nerve damage).

Question 56

Briefly explain the main reason for the variation of the seriousness of the outcome and level of survival, assuming that there are no immediate life-threatening problems such as severe blood loss.

Answer 56

The main reason is the availability of expert medical care and facilities. If there is a delay in treating serious injuries such as these, then the risk of severe infection causing further damage or even death is greatly increased.

Question 57

Hip fractures can occur as a result of various incidents including traffic accidents, sporting injuries, and falls in older people. Describe the main factors that would influence the choice of treatment that might be given for a hip fracture.

Answer 57

Precise position of the fracture and the age, medical fitness of the patient and the resources available

Question 58

The word repair suggests that…

Answer 58

something is being mended, and that the finished product will always ‘have been repaired’ rather than be the same as when it was new/regenerated.

Question 59

What is the sequence of actions when skin is damaged?

Answer 59

1. Blood from damaged blood vessels in the skin fills the wound area and starts to clot
2. Proteins dissolved in the blood respond to damage by becoming insoluble, forming fibres (like extracellular matrix) made of the protein fibrin (temporary barrier)
3. Inflammation
4. Fibrin clot dries, fibroblasts in dermis populate in the fibrin clot and replace it with collagen; contract and pull the sides of the wounded dermis together
5. Epidermal cells divide and migrate to cover the healing dermis
6. New blood vessels disappear, collagen fibres ressemble normal skin architecture in dermis

Question 60

How do scars form?

Answer 60

By fibrosis, in which the fibroblasts which formed the temporary granulation tissue go on to produce large amounts of more permanent collagen fibres

Question 61

In larger wounds, or those in places where the skin is under a lot of tension, it is often necessary to hold the wound closed using…

Answer 61

sutures (Wundnaht)

Question 62

What happens during the repair stage after bone injury?

Answer 62

1. Bone breaks ⇒ blood leaks out and fills the area of damage
2. Blood starts to clot to form a fibrin scaffold
3. Stem cells migrate, making new osteoblasts
4. Osteoblasts secrete collagen and organise the mineralisation of the
   extracellular matrix
5. Clot (or callus) becomes vascularised, means new capillaries arise

Question 63

What happens during the remodelling stage after a bone injury?

Answer 63

• Remodelling by osteoblasts and osteoclasts
• Collagen that forms fibres and gives the bone tissue strength gets moved around until it is positioned in the optimal orientation

Question 64

Why might elevation of a limb with a damaged muscle help reduce inflammation?

Answer 64

Elevation will encourage blood flow back towards the heart due to the effects of gravity, helping to relieve the build-up of fluid at the site of injury.

Question 65

What are fibroblasts?

Answer 65

A type of cell that can migrate into wound sites and make new extracellular matrix proteins such as collagen.

Question 66

Consider the structure of tendon tissue and suggest a feature that might be responsible for poor healing.

Answer 66

• Poor blood supply compared with muscles and bones
• So supply of oxygen and nutrients thus number of cells limited
• Cells responsible for debris and building new tissue

Question 67

Which two types of grafts exist?

Answer 67

• Autograft: From the person herself

- Allograft: From another person

Question 68

What would be the advantage of repairing a tendon with a graft that still has a piece of bone attached?

Answer 68

The new attachment would be bone to bone rather than tendon to bone, so would exploit the good healing properties of bone to achieve the repair.

Question 69

What is an adhesion?

Answer 69

The joining of tissues to each other that may occur abnormally during repair.

(med. Anwachsen)

Question 70

Explain the repair process of tendons after surgery.

Answer 70

1. Inflammation, fibrin scaffold forms
2. Fibroblasts lay down new collagen, forming temporary granulation tissue
3. Gradually replaced with permanent collagen and other extracellular matrix proteins

Biggest problem: Adhesion of tendons to their surroundings caused by fibrosis

Question 71

What happens if the nerve connection between the CNS and a muscle is damaged?

Answer 71

Then the muscle cannot contract and will deteriorate

Question 72

Explain the repair process of nerves.

Answer 72

1. If an injury cuts through an axon then the part of the axon that has been detached from the cell body disintegrates,
2. The debris is cleared away by other (immune) cells.
3. The Schwann cells that were surrounding the part of the axon that disintegrated now form a pathway that can guide axonal re-growth from the end of the remaining axon.
4. Eventually this process can result in growth of the axon
   all the way to the target and a oration of function.

Question 73

What are the problems with the repair of nerves?

Answer 73

• Takes very long (muscles can deteriorate)
• Big gaps
• Forming synapses with tissues
• Adhesion

Question 74

How can the problems caused by the natural repair process of nerves be solved?

Answer 74

Nerve grafts - even without living axons, they supply a scaffold for guiding and supporting repair, made from the extracellular matrix proteins and the Schwann cells in the donor nerve.

Question 75

What problems might be caused by adhesions between a nerve running through the leg and its surrounding muscle tissue?

Answer 75

Peripheral nerves need to be able to move independently of the surrounding tissue, slipping over muscles that are contracting and bending and stretching around joints.

If adhesions form, parts of the nerve will be anchored to the surrounding tissue and tension pulling on the nerve could result in nerve damage or pain during movement.

Question 76

What do you think is the main purpose of rapidly building a capillary network at the site of a repair?

Answer 76

Repair involves division, migration and action by cells, which need a source of oxygen and nutrients from the blood in order to survive and carry out their function.

Question 77

This process of building new blood vessels is known as…

Answer 77

angiogenesis

Question 78

Explain the repair process of new blood vessels (angiogenesis).

Answer 78

1. In response to chemical signals, endothelial cells lining existing vessels become active
2. The endothelial cells divide to make more cells and modifying their extracellular matrix = able to sprout new branches of vessels into the new tissue

Question 79

Can you think of any factors, other than extent of injury and quality of care, which might influence how well a person recovers?

Answer 79

Age is an important variable in recovery from injury, as is the overall health of the person, their psychological state and their level of expectation.

Question 80

What processes occur during repair that might increase the demands placed on the body?

Answer 80

Tissue repair involves

• increased cell division,
• increased cellular activity (e.g. migration and matrix remodelling)
• increased production of tissue components (e.g. proteins such as collagen)

Question 81

What happens when a person is not really healthy and gets injured?

Answer 81

the body will not be able to meet this extra demand for tissue repair then the repair will be impaired.

Question 82

Why is vitamin C (ascorbic acid) so important in terms of tissue repair?

Answer 82

Because it is required for the assembly of amino acids (the individual building blocks of proteins) into large fibres that provide structural support for the tissues thus collagen production by cells.

Insufficient vitamin C in the diet causes scurvy.

Question 83

What does it mean when a cell is ‘differentiated’?

Answer 83

Cells can be identified by the way they behave or by the molecules they make. If cells divide, the daughter cells are identical to the parent cell.

These properties make these cells differentiated, i.e. they have adopted a particular identity.

Question 84

What is the difference between differentiated cells and stem cells?

Answer 84

Stem cells are not differentiated. They can divide to give rise to daughter cells that can develop into a variety of different types of differentiated cells.

Question 85

The sequence of events that occurs in tissues follows a general pattern:

Answer 85

Formation of a fibrin clot, then infiltration of the fibrin scaffold with cells and blood vessels (formation of granulation tissue), then replacement of granulation tissue with new tissue or scar tissue.

Question 86

Fibrin, which forms a fibrous mesh during blood clotting, is often referred to as a ‘temporary extracellular matrix’. Explain why.

Answer 86

• The extracellular matrix in undamaged tissue is made from proteins such as collagen which provides much of the structure and function for the tissue and supports the cells within it.
• Fibrin is sometimes referred to as temporary extracellular matrix since it functions to support the cells that migrate into a damaged area (just like the cell support function of normal extracellular matrix), but it is then replaced with more appropriate ‘permanent’ extracellular matrix proteins.
• Fibrin is therefore like the scaffolding on a building site – it provides a temporary support while the final building blocks are being arranged.

Question 87

What advantages might stem cell therapies have over autograft and allograft approaches?

Answer 87

The potential advantages include the ability of stem cells to replenish themselves. This would overcome limitations in the amount of donor tissue available for grafting and if a person’s own stem cells were used they would not trigger an immune response. It may also be possible for regeneration rather than repair to be achieved.

Question 88

What is PTSD?

Answer 88

Post-traumatic stress disorder.

Following a life-threatening situation, even though the person may be physically unharmed, there is a possibility that they may suffer post-traumatic stress disorder and suffer from flashbacks – recurring memories of the trauma, which are far more vivid than normal memories.

Question 89

Why do trauma memories may differ from memories for other events?

Answer 89

Because the amygdala plays a greater role in their storage (normal memories involve the hippocampus).

Question 90

Why is the amygdala so important for PTSD?

Answer 90

Memories that have been stored under the influence of the amygdala are far less amenable to inhibition. There are numerous connections between the amygdala and the prefrontal cortex, so the amygdala may be able to act on the prefrontal areas so as to reduce their usual inhibitory activity.

That leaves the memories liable to pop into consciousness with the least provocation, and a PTSD sufferer is forced to try to avoid anything that might trigger the flashbacks.

Question 91

What factors would need to be taken into account when estimating the financial cost of traffic accidents?

Answer 91

• Damage to vehicles and infrastructure
• Lost economic output from those involved in the crash
• Medical and other healthcare costs
• The cost of police time, emergency services and legal expenses

Question 92

What is the GDP?

Answer 92

Gross domestic product - all the wealth generated within a country, so it takes no account of wealth brought in from outside.