Wound Healing

Wound Healing• Skin• Haemostasis• Meet the cells• Inflammation• Migration• Proliferation• Maturation

Integumentary system

• What is the integumentary system? Outer covering• What organ(s) are involved?Skin • What structures are involved? Hair, nails, receptors, glands

Integumentary system• Skin structure:3 layers; epidermis, dermis,

hypodermis or subcutaneous.

• Epidermis: Outer layers (4-5) of closely packed cells.• Stratum basale, Stratum spinosum, Stratum

granulosum, Stratum lucidum, Stratum corneum• Contains keratinocytes & melanocytes, Merkel cells

& Langerhans (dendritic) cells.

Epidermis

• Stratum basale is base layer where cells (keratinocytes) multiply. New cells push old cells away from blood supply. They fill with keratin, flatten & die in the corneum. Millions are shed daily.

• Melanocytes are in the stratum basale & produce melanin pigment

• Merkel cells at the epidermis-dermis junction function in touch

• Langerhans (dendritic) cells are phagocytes (immune system cells).

Dermis

• 2 indistinct layers: papillary layer & reticular layer.

• Contain hair follicles, sweat (sudoriferous) glands, oil (sebaceous) glands, touch receptors and a good blood supply.

• Connective tissue with lots of collagen and elastic fibres made by fibroblasts

Hypodermis

• Subcutaneous or superficial fascia anchors skin to underlying muscle.

• contains fat

Integumentary key functions

• Provides external protection• Regulates body temperature• Sensory organ• Excretion• Vitamin D synthesis• Immunity

Functions 1. • Regulation of body temperature primarily by

sweating and changing superficial vein diameter (& blood flow)

• Heat conservation occurs when vasoconstriction of superficial veins re-routes warm blood deeper into the body.

Regulation of body temperature

• Cooling occurs when • (a) Vasodilation of superficial veins brings

blood to the body surface and heat is lost to the environment by radiation convection & conduction.

• (b) An increase in perspiration results in increased evaporation cooling the skin but effectiveness is dependant on the humidity.

Functions

• 2. Protection from mechanical damage (keratin), microbial invasion, dehydration & UV radiation (melanin)

• 3. Excretion for loss of some ions, water & nitrogen containing waste

Functions 4.

• Sensations from sensory receptors• Free nerve endings: temperature, touch, pressure &

pain • Hair receptors : hair movement• Merkels disc: Light pressure• Meissner’s corpuscle: Light pressure • Ruffini’s endings: Deep pressure, stretch • Pacinian corpuscle: Deep pressure, stretch

Functions• 5. Langerhans cells of the epidermis are immune

system cells• 6. Blood reservoir carrying 8-10% of total blood

flow and is highly variable.• 7. Synthesis of Vitamin D when UV rays from sun

promote production of a Vitamin D precursor by the epidermis

• 8. Stores fat & fat soluble vitamins (A, D, E & K)• 9. Cutaneous absorption and secretion• 10. Social interaction

Platelets

Clot Retraction

• Contractile proteins within the platelets pull on the fibrin

• This pulls the edges of the broken blood vessel together

Clot retraction (syneresis)

Clot Destruction (Fibrinolysis)

• Plasminogen is converted to Plasmin

• Plasmin breaks down the fibrin in the clot

Meet the cells

• Labile cells– Regenerate readily, involved in wound repair

• Stable cells– Don’t normally divide in adult, but may

• Permanent cells– Unable to divide, replaced by scar tissue

Neutrophil

Macrophage

Epithelial cells

Fibroblasts

Repair

• Replacement of destroyed tissue by scar tissue• Doesn’t perform original function• Process:– fill in the wound– cover or seal the wound– shrink the wound

• 4 stages:

1) Inflammatory phase

• Haemostasis• Inflammation• Vasodilation & permeability of blood vessels• Phagocytotic cells (neutrophils &

macrophages) eat up cell debris & bacteria• Immediate to 2 - 5 days

2) Migratory phase

• Clot loses fluid and hardens forming a scab• Capillaries grow into damaged area

2) Migratory phase

• Fibroblasts make collagen to fill in the wound

3) Proliferative phase

• 2 days - 3 weeks• Granulation• fibroblasts lay bed of collagen, fills defect (Scar

tissue)• new capillaries, fragile so bleed easily• Epithelialization• Epithelial cells regenerate to form a new

surface layer (under the scab)

Mitosis

4) Maturation phase

• Contraction• Collagen fibres shorten decreasing area of scar • Scab detaches• Epidermis reaches normal thickness• End result is a regenerated epithelial surface

with an underlying area of fibrosis (the scar)

Primary Intention

• minimal tissue loss• e.g. clean, sutured incision

Secondary Intention

• much more tissue replacement• takes longer• e.g. stage IV decubitus ulcer

Primary and secondary intention