Anatomy and Physiology Resource Site

GLOSSARY

1 - Anatomy and Physiology Basics

2 - Cells and Tissues

3 - Cell Physiology

4 - Skin and Membranes

5 - Skeletal System

6 - Muscular System

7 - Nervous System (Part I)

8 - Nervous System (Part II)

9 - Endocrine System

10 - Reproductive Systems

11 - Circulatory System

12 - Respiratory System

13 - Digestive System

14 - Urinary System

15 - Microbiology

16 - Lymphatic System and Immunity

Video Tutorials

2.8 - The Inflammatory Response

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 and function, 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.

Wound healing and the inflammatory response occur simultaneously, but can be examined as two separate processes.

Inflammatory Response

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.

Histamine released by mast cells causes nearby blood vessels to dilate and causes capillaries in the area to become “leaky”, increasing circulation in the area
White blood cells to enter the area to help prevent infection

Circulation increases in the area and fluid begins to build up

Platelets and clotting factors in the fluid help temporarily seal the injury and prevent the spread of infection. This begins the process of wound healing.
White blood cell macrophages begin consuming bacteria and viruses in the area, guided by the concentration gradient of chemokine alarm chemicals coming from injured cells.

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.

Wound Healing

Click here to see a tutorial about wound healing

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.

Epithelial tissues 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 (brain, spinal cord) do not regenerate easily and instead form scar tissue when injured.

The process of wound healing has three stages:

Capillary permeability increases around the injury site.

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.

Granulation tissue forms.

Granulation tissue is a delicate pink tissue rich in tiny capillaries (small blood vessels) that bring cells of the immune system to the injury site to clean up the initial clot and any invading bacteria. It also contains fibroblasts, which begin to form collagen fibers to fill in the injury site.

Regeneration of the epithelial tissue and scar tissue formation.

In tissues that regenerate easily, new cells form to replace the cells lost by injury. The cells form underneath the scab, growing from the outer edges towards the center.
Underneath the newly formed tissue, fibroblasts form dense connective tissue called a fibrosis (scar tissue). The amount of scar tissue is greater if the injury is in a tissue that does not regenerate easily.