4.6 Tissue Injury and Aging Study Notes
Tissue Injury and Aging
Learning Outcomes
By the end of this section, students will be able to:
Identify the cardinal signs of inflammation.
List the body’s response to tissue injury.
Explain the process of tissue repair.
Discuss the progressive impact of aging on tissue.
Describe cancerous mutations’ effect on tissue.
Introduction
Tissues of all types are vulnerable to injury and aging.
Understanding how tissues respond to damage can guide strategies to aid repair.
Recognizing the impact of aging can assist in diminishing its adverse effects.
Tissue Injury and Repair
Inflammation
Inflammation is the standard, initial response of the body to injury.
Types of injury include biological, chemical, physical, and radiation burns.
All injuries lead to a similar sequence of physiological events.
Functions of inflammation:
Limits the extent of injury.
Partially or fully eliminates the cause of injury.
Initiates repair and regeneration of damaged tissue.
Necrosis (accidental cell death) causes inflammation.
Apoptosis (programmed cell death) is a normal, step-by-step process that destroys cells that are no longer needed.
Apoptosis does not initiate the inflammatory response.
Chronic inflammation occurs if acute inflammation persists, leading to diseased conditions.
Examples include arthritis and tuberculosis.
Cardinal Signs of Inflammation
Four cardinal signs of inflammation (first documented by Cornelius Celsus in the first century AD):
Redness
Swelling
Pain
Local heat
A fifth sign, loss of function, may also accompany inflammation.
Mechanism of Inflammation
Upon tissue injury, damaged cells release inflammatory chemical signals leading to:
Local vasodilation (widening of blood vessels).
Increased blood flow results in apparent redness and heat.
Mast cells present in tissue degranulate to release histamine (a potent vasodilator):
Increased blood flow and inflammatory mediators recruit white blood cells to the site of inflammation.
The endothelium lining local blood vessels becomes “leaky,” allowing neutrophils, macrophages, and fluid to move into the interstitial tissue spaces.
Excess liquid causes swelling, known as edema.
Swollen tissues squeeze pain receptors leading to the sensation of pain.
Prostaglandins released from injured cells activate pain neurons.
Non-steroidal anti-inflammatory drugs (NSAIDs) reduce pain by inhibiting prostaglandin synthesis.
High levels of NSAIDs also reduce inflammation.
Antihistamines decrease allergies by blocking histamine receptors and the resultant histamine response.
Tissue Repair Process
After containing an injury, the tissue repair phase begins:
Removal of toxins and waste products occurs.
Clotting (coagulation) reduces blood loss from damaged blood vessels:
Forms a network of fibrin proteins that trap blood cells and bind the edges of the wound together.
A scab forms when the clot dries, reducing the risk of infection.
At times, a mixture of dead leukocytes and fluid, termed pus, accumulates in the wound.
Healing progress involves fibroblasts from surrounding connective tissues replacing lost collagen and extracellular material.
Angiogenesis (growth of new blood vessels) results in vascularization of new tissue known as granulation tissue.
The clot retracts, pulling the edges of the wound together.
It slowly dissolves as the tissue is repaired.
When a large amount of granulation tissue forms, and capillaries disappear, a pale scar often becomes visible in the healed area.
Primary union describes healing of a wound where edges are close together.
In a gaping wound, the healing takes longer (referred to as secondary union) as edges are pulled together via wound contraction.
For wounds deeper than a quarter inch, sutures (stitches) are recommended to promote primary union and avoid disfiguring scars.
Regeneration is the addition of new cells of the same type as those injured.
Tissue and Aging
Impact of Aging on Tissues
Aging leads to a decline in bodily functions, confirmed biologically.
All cells, tissues, and organs are affected by senescence with noticeable variability among individuals due to genetics and lifestyle.
Outward signs of aging:
Skin and other tissues become thinner and drier, reducing elasticity
Contributes to wrinkles and hypertension.
Hair turns gray due to reduced melanin production in hair follicles.
Facial appearance becomes flabby due to decreased elasticity and collagen fibers in connective tissue.
Joints lose cartilage and become stiff;
The height decreases as bones lose calcium and other minerals.
Internal signs of aging may not be as noticeable:
Increased incidences of heart disease, respiratory syndromes, and type 2 diabetes do not correlate strictly with age.
Wound healing slows in the elderly, with a higher frequency of infections due to declining immune system capacity.
Cellular Aging
Aging is evident at cellular levels:
Telomeres, segments of chromosomes necessary for cell division, shorten with each cell division, limiting renewable capabilities.
Alterations in cell membranes reduce the efficiency of nutrients and oxygen transport into the cell and waste product removal.
Such changes can lead to abnormal cell function and diseases like arthritis and some cancers.
Individual variability in the impact of aging exists:
Studies indicate that exercise and a healthy lifestyle can slow down bodily deterioration associated with aging.
Tissues and Cancer
Understanding Cancer
Cancer is a generic term for diseases where cells avoid regulatory signals leading to:
Uncontrolled growth.
Invasion into adjacent tissues.
Colonization of other organs if untreated.
Tumors compete for blood supply, impacting the health of normal organs.
A mutation is a permanent change in the DNA of a cell.
Epigenetic modifications are changes that do not affect the DNA code but alter its decoding mechanisms, potentially resulting in abnormal cells.
Genetic material alterations may result from environmental agents, infectious agents, or errors during DNA replication that accumulate over time.
Many mutations do not visibly change cell functions; however, mutations impacting key proteins that regulate orderly cell proliferation can lead to abnormal divisions:
Tissues lose their organizational abilities as mutations accumulate, forming tumors.
A tumor is a mass of cells with abnormal architecture:
Many tumors are benign, characterized by non-metastastic behavior.
Tumors become malignant (cancerous) when they breach tissue boundaries, promote angiogenesis, and metastasize to other organs.
Types of Cancer
Cancers derived from epithelial cells are called carcinomas.
Myeloid tissue or blood cell cancers are termed myelomas.
Leukemias refer to cancers of white blood cells.
Sarcomas arise from connective tissue.
Tumor Characteristics
Tumor cells differ in structure and function:
Some are identified as cancer stem cells, which may be responsible for uncontrolled growth.
Modern research shows that tumors possess structured organization rather than appearing as disorganized masses of cells.
Cancer Treatments
Cancer treatment strategies vary based on type and stage:
Traditional methods include:
Surgery: removal of tumors or affected tissues.
Radiation therapy: targeting cancer cells to destroy them.
Chemotherapy: administering drugs to kill rapidly dividing cancer cells.
Hormonal therapy: aims to disrupt hormone-driven cancer cell growth.
Limitations of these treatments:
Difficulty in removing tumors depending on location.
Challenges in radiation and chemotherapy to selectively target only cancer cells.
These treatments often lead to damage in healthy tissues.
Ongoing research is directed towards pharmaceuticals that target specific proteins involved in cancer-related molecular pathways.