Although our external and internal body defenses are designed to protect us from injury, invading pathogens
and harmful substances, they are made of tissues
that can be injured. Tissues
are varied in their structure
, but the way tissues
inflame (swell) and repair themselves after injury is very similar.
The inflammation and repair of tissues
involves several systems
in the body. The circulatory and immune systems
work in conjunction with the damaged tissues
themselves to respond to injury in a non-specific way.
and the inflammatory response
occur simultaneously, but can be examined as two separate processes.
Click here to see a tutorial about the inflammatory response
Any time body tissues
are injured, the inflammatory response
is triggered. It is often uncomfortable and even painful when tissues
are inflamed, but inflammation helps to prevent further injury and brings substances and cells
important in wound repair to the injury site.
The inflammatory response
occurs in a few stages:
Injured cells release alarm chemicals, stimulating mast cells.
Circulation increases in the area and fluid begins to build up
Swelling decreases once tissue repair is complete.
- Once the cells surrounding the injury are no longer damaged or under attack by pathogens, they stop releasing alarm signals.
- Circulation around the injury site returns to normal, and the lymphatic system returns the excess fluid to the circulatory system, decreasing swelling.
Click here to see a tutorial about wound healing
(also called tissue repair
) is the process by which injured tissues
are repaired, and begins almost immediately after injury in an attempt to prevent further damage.
such as the skin and mucous membranes
replace their cells
regularly as they become worn out and damaged, giving them a remarkable ability to regenerate
when injured. Connective tissues
including bone are also prone to regenerating instead of developing large amounts of scar tissue (fibrosis)
when injured. Other tissues
such as skeletal muscle
, cardiac muscle
, many organs
including those of the nervous system
, spinal cord
) do not regenerate easily and instead form scar tissue
The process of wound healing
has three stages:
Capillary permeability increases around the injury site.
Granulation tissue forms.
Regeneration of the epithelial tissue and scar tissue formation.
- This allows circulatory fluid containing clotting factors to enter the injury site, stopping blood loss and temporarily holding the injury site closed.
- A scab forms when the clotting factors bind together and the clot is exposed to air.