4.6 Tissue Injury and Aging

Tissue injury and repair are crucial processes in the body's response to damage. From inflammation to healing, these mechanisms work together to restore function and protect against further harm. Understanding these processes is essential for grasping how the body maintains homeostasis.

As we age, our tissues undergo significant changes that affect their structure and function. These alterations can lead to slower healing, increased susceptibility to disease, and the development of cancerous growths. Recognizing these age-related changes is key to comprehending overall health and longevity.

Tissue Injury and Repair

Signs of tissue inflammation

Top images from around the web for Signs of tissue inflammation

• 

  4.1 Types of Tissues – Douglas College Human Anatomy and Physiology I (1st ed.) View original

  Is this image relevant?

• 

  Inflammation & Tissue Injury - Phytecs View original

  Is this image relevant?

• 

  Anatomy/Immune System - Wiki - Scioly.org View original

  Is this image relevant?

• 

  4.1 Types of Tissues – Douglas College Human Anatomy and Physiology I (1st ed.) View original

  Is this image relevant?

• 

  Inflammation & Tissue Injury - Phytecs View original

  Is this image relevant?

1 of 3

Top images from around the web for Signs of tissue inflammation

• 

  4.1 Types of Tissues – Douglas College Human Anatomy and Physiology I (1st ed.) View original

  Is this image relevant?

• 

  Inflammation & Tissue Injury - Phytecs View original

  Is this image relevant?

• 

  Anatomy/Immune System - Wiki - Scioly.org View original

  Is this image relevant?

• 

  4.1 Types of Tissues – Douglas College Human Anatomy and Physiology I (1st ed.) View original

  Is this image relevant?

• 

  Inflammation & Tissue Injury - Phytecs View original

  Is this image relevant?

1 of 3

• Redness (rubor) occurs due to vasodilation and increased blood flow to the injured area, delivering more oxygen and nutrients to support healing
• Swelling (tumor) results from increased vascular permeability and fluid accumulation in the interstitial space, causing visible enlargement of the affected tissue
• Heat (calor) is generated by increased blood flow and metabolic activity in the affected tissue, as cells work to repair the damage
• Pain (dolor) is caused by the release of inflammatory mediators (prostaglandins, bradykinin) and stimulation of pain receptors, serving as a protective mechanism to prevent further injury
• Loss of function (functio laesa) occurs due to tissue damage and the inflammatory process, limiting the ability to use the affected area until healing progresses

Sequential responses to tissue damage

1. Hemostasis initiates the healing process by stopping blood loss through vasoconstriction, platelet aggregation and activation, and the coagulation cascade forming a fibrin clot
2. Inflammation follows, characterized by vasodilation and increased vascular permeability, allowing leukocytes (neutrophils and monocytes) to migrate to the injury site for phagocytosis and debris removal, while inflammatory mediators (histamine, prostaglandins, cytokines) are released
3. Proliferation and repair involve angiogenesis forming new blood vessels, fibroblast activation and collagen synthesis to rebuild the extracellular matrix, and epithelialization as epithelial cells migrate and proliferate to cover the wound
4. Remodeling is the final stage, featuring collagen maturation and organization, scar tissue formation to strengthen the repaired area, and gradual restoration of tissue strength and function over time

Stages of tissue repair

• The inflammatory phase occurs immediately after injury and lasts up to 72 hours, characterized by inflammation, hemostasis, and debris removal to prepare the site for repair
• The proliferative phase begins around 72 hours post-injury and lasts for several weeks, involving angiogenesis, collagen synthesis, and epithelialization to rebuild the damaged tissue
• The remodeling phase starts after the proliferative phase and can last for months to years, characterized by collagen maturation, scar tissue formation, and gradual restoration of tissue function as the repair process finalizes

Aging and Tissue Alterations

Effects of aging on tissue

• Decreased cell proliferation and regenerative capacity lead to slower healing and reduced ability to replace damaged cells over time
• Accumulation of cellular and molecular damage from oxidative stress, DNA mutations, and protein misfolding and aggregation contributes to tissue dysfunction and increased risk of age-related diseases
• Altered extracellular matrix composition, with decreased collagen synthesis and elasticity and increased cross-linking of collagen fibers, results in stiffer, less resilient tissues
• Impaired tissue healing and repair mechanisms, combined with increased susceptibility to degenerative diseases (osteoarthritis, osteoporosis) and infections, compromise tissue function and overall health in older individuals

Cellular and molecular changes in aging

• Cellular senescence occurs when cells lose their ability to divide and enter a state of permanent growth arrest, contributing to tissue dysfunction and inflammation
• Telomere shortening, the progressive loss of protective DNA sequences at chromosome ends, limits cell division capacity and is associated with aging and age-related diseases
• Accumulation of free radicals, highly reactive molecules that damage cellular components, leads to oxidative stress and accelerated aging
• Mitochondrial dysfunction, characterized by decreased energy production and increased oxidative damage, contributes to cellular aging and tissue decline
• Stem cell exhaustion, the gradual depletion and functional decline of tissue-specific stem cells, impairs tissue regeneration and homeostasis in aging organisms

Cancerous alterations in tissue

• Uncontrolled cell division and growth occur due to mutations in proto-oncogenes and tumor suppressor genes (p53, BRCA1), along with evasion of apoptosis, leading to the formation of tumors
• Altered cell morphology and differentiation cause a loss of normal tissue architecture and function, as cancerous cells no longer perform their intended roles effectively
• Angiogenesis and neovascularization involve the formation of new blood vessels to support tumor growth, providing oxygen and nutrients to rapidly dividing cancer cells
• Invasion and metastasis enable cancer cells to penetrate basement membranes and migrate to distant sites, establishing secondary tumors in other organs (lungs, liver, bones) and compromising their function
• Evasion of immune surveillance through various mechanisms allows cancer cells to avoid detection and elimination by the immune system, facilitating their continued growth and spread