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Once the wound is free of debris and new blood vessels have begun to form, repair cells called fibroblasts lay down a scaffolding of collagen. This collagen network matures into granulation tissue, which forms the foundation of scars. The granulation tissue matures as the collagen fibers become increasingly interlinked. Externally, the scar can be seen to contract and close the wound, and this process of collagen maturation and remodeling continues for a lifetime.
The response is characterised by an acute catabolic reaction, which precedes the metabolic process of recovery and repair. This metabolic response to trauma was divided into an ebb and flow phase by Cuthbertson.
The ebb phase corresponds to the period of severe shock characterised by depression of enzymatic activity and oxygen consumption. Cardiac output is below normal, core temperature may be subnormal, and a lactic acidosis is present.
The flow phase can be divided into
- a catabolic phase with fat and protein mobilisation associated with increased urinary nitrogen excretion and weight loss, and
- An anabolic phase with restoration of fat and protein stores, and weight gain.
In the flow phase, the body is hypermetabolic, cardiac output and oxygen consumption are increased, and there is increased glucose production. Lactic acid may be normal.
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Phase
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Duration
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Role
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Physiological
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Hormones
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Ebb
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<24hrs
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maintenance of blood volume; catecholamines
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decreased BMR, decr. Temp, decreased O2 consumption; vasoconstriction; increased CO, increased HR; acute phase proteins
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Catecholamines, Cortisol, Aldosterone
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Flow
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Catabolic
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3-10 days
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maintenance of energy
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incr. BMR, incr. Temp., incr. O2 consumption, negative nitrogen balance
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Incr. glucagon, insulin, cortisol, catecholamines - but insulin resistance
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Anabolic
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10-60 days
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replacement of lost tissue
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positive nitrogen balance
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Growth hormone, IGF
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Participants