Name: how blood clots support wound healing
Uploaded: 2023-04-30T12:17:39.000Z
Duration: 1 min 28 s
Channel: JoVE

K12 Standards

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NC K-12 Science Standard Course of Study

9-12

Biology

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms- Structures and Processes

LS.Bio.2.1

Phases of Wound Repair

Wound repair occurs in four phases in animal tissue.
The first phase, hemostasis, starts immediately after an injury. Damaged blood vessels constrict, leading to reduced blood flow and hypoxia at the injury site. This attracts platelets and activates the clotting mechanism to help seal the wound. A blood clot further helps control bleeding and prevent infection.
The damaged cells at the wound site then signal immune cells to initiate the second phase, inflammation. Neutrophils and macrophages are recruited through the bloodstream to kill bacteria and remove debris. These cells release growth factors to begin the third phase, proliferation, and facilitate fibroblast migration from the surrounding tissue.
Fibroblasts divide, secrete collagen-rich extracellular matrix, and promote the reestablishment of the blood vessel network, leading to the formation of granulation tissue.
In the final phase of repair, remodeling, the wound contracts and most fibroblasts die. Then, the collagen fibers are rearranged into an organized and rigid structure, providing strength to the newly formed tissues.
The granulation tissue is gradually transformed into scar tissue that mimics normal tissue structu

phases of wound repair

Following injury, the integrity of the injured tissues must be reestablished. For example, in skin tissue, wound repair involves coordination among resident skin cells, blood mononuclear cells, extracellular matrix, growth factors, and cytokines to complete the healing cascade.
Formation of Blood Clot 
In case of deep injuries, trauma to blood vessels results in blood loss. In the meantime, phospholipids released from the ruptured endothelial cellular membrane are converted into arachidonic acid and metabolites like thromboxane A2 and prostaglandin 2&#945;. These factors promote vasoconstriction at the site of injury, generally lasting up to 5-10 minutes and resulting in brief hypoxia. Due to a lack of oxygen, cells and tissues surrounding the injury site shift ATP production via the anaerobic glycolysis pathway. The lactic acid produced at the end of anaerobic glycolysis reduces the pH in the adjoining tissues and cells. Blood vessel trauma and reduced pH significantly induce platelet activation, adhesion, and aggregation. Next, the blood clot is formed, sealing the injury site from external infection and establishing the temporary matrix composed of thrombin, collagen, fibronectin, and platelets. This matrix induces several cytokines and growth factors that are needed during the repair process.
Chemotaxis and Activation
Once the clot is formed, damaged cells at the injury site send a distress signal to immune cells in the body. This is followed by the recruitment of the neutrophils at the injury site. Prostaglandins E2 have a central role in the inflammatory response. They promote vasodilation and increase the blood flow to allow the movement of neutrophils. The neutrophils inhibit the growth of bacteria by releasing proteolytic enzymes. Even macrophages play a critical role in all the phases of wound repair, such as secretion of cytokines and growth factors like interleukin and tumor necrosis growth factor. They also promote fibroblast proliferation and angiogenesis at the wound site.
Extracellular Matrix Reorganization
Collagen is the major fibrous protein in the extracellular matrix (ECM) that imparts tensile strength and regulates cell adhesion to the tissues. The damage caused to ECM is restored in the remodeling phase of the wound repair. In the granulation tissue, ECM produced by fibroblasts is composed of type III collagen &#8212; a weaker structural protein. To cope with higher collagen demand, fibroblasts prefer to secrete type III collagen, and the rate of collagen production is highest. It is in the remodeling phase of the healing cascade that the matrix metalloproteinases (released by fibroblasts) remodel type III collagen into type I collagen that is stronger and has higher tensile strength. The arrangement of type I collagen into parallel bundles helps wound contraction and provides rigidity to newly formed tissues.

Following injury, the integrity of the injured tissues must be reestablished. For example, in skin tissue, wound repair involves coordination among ...

Education

JoVE Core

Cell Biology

Unit 1

Regeneration and Repair

KEY TERMS AND CONCEPTS

how blood clots support wound healing

Wound healing begins when injured tissue works to restore its normal structure. In skin, this repair process depends on resident skin cells, blood mononuclear cells, the extracellular matrix, growth factors, and cytokines. Together, these signals guide the healing cascade.

Deep injuries can damage blood vessels and cause blood loss. Endothelial cells release phospholipids from their ruptured membrane, which are converted into arachidonic acid and metabolites such as thromboxane A2 and prostaglandin 2α. These factors cause vasoconstriction at the injury site for about 5 to 10 minutes and lead to brief hypoxia, or low oxygen.

When oxygen is limited, nearby cells shift ATP production to anaerobic glycolysis, which does not use oxygen. Lactic acid forms at the end of this pathway and lowers the pH in nearby tissues. Blood vessel injury and the lower pH help trigger platelet activation, adhesion, and aggregation, which leads to clot formation.

The blood clot seals the wound and helps protect it from external infection. It also creates a temporary matrix made of thrombin, collagen, fibronectin, and platelets. This matrix supports the cytokines and growth factors needed for repair.

After the clot forms, damaged cells send distress signals to immune cells. Neutrophils are recruited to the wound site next. Prostaglandin E2 helps drive the inflammatory response by causing vasodilation and increasing blood flow so neutrophils can move in. Neutrophils slow bacterial growth by releasing proteolytic enzymes, and macrophages also help by releasing cytokines and growth factors such as interleukin and tumor necrosis growth factor. Macrophages further support fibroblast proliferation and angiogenesis, which is the formation of new blood vessels.

The final stage is extracellular matrix reorganization. Collagen is the main fibrous protein in the extracellular matrix and gives tissues tensile strength and cell adhesion. In granulation tissue, fibroblasts produce type III collagen, which is a weaker structural protein, and collagen production is highest at this stage. During remodeling, matrix metalloproteinases released by fibroblasts convert type III collagen into stronger type I collagen. The type I collagen then forms parallel bundles that help wound contraction and give new tissue rigidity.

How Blood Clots Support Wound Healing

overview of regeneration and repair

How Tissues Regrow and Heal After Injury

Regeneration and repair are two ways the body responds to injury, disease, and aging. Regeneration replaces damaged tissue with new growth that restores the original structure and function. Repair usually leaves a fixed tissue pattern and forms a scar. Scars do not usually bring back full tissue function, and the injured area may still look or act abnormal. Animals show very different levels of regeneration. Some, like salamanders, have specialized stem cells that help them regrow fully...

Wound healing begins when injured tissue works to restore its normal structure. In skin, this repair process depends on resident skin cells, blood mononuclear cells, the extracellular matrix, growth factors, and cytokines. Together, these signals guide the healing cascade. Deep injuries can damage blood vessels and cause blood loss. Endothelial cells release phospholipids from their ruptured membrane, which are converted into arachidonic acid and metabolites such as thromboxane A2 and...

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Stem Cell Repair in Blood and Tissues

Stem cell therapy is used in regenerative medicine to repair damaged tissues and organs and help restore function. Stem cells can multiply and change into different tissue types, which makes them useful for tissue repair. One common example is hematopoietic stem cell transplantation, which is used in blood cancer treatment to replace damaged bone marrow and rebuild healthy blood cells. Two main stem cell types are used in stem cell therapy: adult stem cells and embryonic stem cells, or ESCs.

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Nuclear Reprogramming in Cloning and Stem Cells

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key terms and concepts

Learn how clot formation, immune cell signals, and collagen remodeling help skin repair after injury, from platelet activation to stronger new tissue.

How Blood Clots Support Wound Healing | JoVE K12

cell biology

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How Blood Clots Support Wound Healing

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