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 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