Biology of Ageing - Lecture 22

Biology of Ageing - Lecture 22

• Ageing is defined by methods using functional status, rather than chronological age
• Methods include the Katz ADL scale, used to measure daily living activities and independence
• The Katz ADL scale assesses abilities such as bathing, dressing, toileting, transferring, continence, and feeding
• Scores range from 0 (very dependent) to 6 (high independent)
• Defining old age, there's no universally agreed-upon age; ranges and categories exist (e.g., 51-70 years, >70 years, 65 years (Medicare eligibility), 60 years, World Health Organization categories) but functional and various other assessments are important
• The US Census Bureau uses different age categories (young old: 65-74 years, aged: 75-84 years, oldest old: 85+)
• Life expectancy is the average number of years a person is expected to live in a population cohort. It's typically reported as life expectancy from birth
• Life span is the maximum number of years a person can live. Human life span is projected between 110-120 years
• Improvements in life expectancy are largely due to fewer deaths from cardiovascular diseases (CVD), stroke, and accidents. The same is true as someone ages but mortality rates associated with different diseases are important to distinguish
• Physiological changes with ageing include changes in body composition, leading to a loss of physical resilience. Fat-free mass (bone, muscle, water) decreases, with muscle loss being the most prominent (sarcopenia)
• A rise in body fat mass, and a decrease in overall body weight, are also common
• Factors that influence body composition changes with ageing include physical activity, hormones, food intake, and lower metabolism
• Sensual awareness, such as taste and smell, can be affected by ageing; declining taste and smell can also be present due to disease or medication
• Oral health alongside changes in taste and smell can also include issues with teeth loss caused by factors unrelated to aging (GI secretions, skeletal system, mucosal membrane, muscle in the mouth), olfactory neurons and taste buds
• Appetite and thirst regulation mechanisms weaken with age, leading to potential undernutrition and an increase in the likelihood of dehydration
• Tools like the Mini Nutritional Assessment (MNA) are used in clinical contexts to screen and assess nutritional status in older adults
• Cellular senescence is the process of cells accumulating changes in structure and disrupting metabolism, thus leading to deterioration over time
• Hayflick Limit: normal somatic cells have a limited number of cell divisions. Cells stop dividing after about 50-60 divisions in vitro
• Telomeres, repetitive nucleotide sequences at the ends of chromosomes, protect the chromosome from deterioration but shorten with each cell division, thus making an important factor in cell aging

Theories of Aging

• Programmed aging (e.g., Hayflick Limit, Cellular senescence, Molecular Clock Theory - Telomere shortening)
  • Hayflick Limit: All cells have a limited number of divisions
  • Cellular senescence: Cells stop dividing after a certain number of divisions
  • Telomere shortening: Telomeres shorten upon each cell division leading to cellular ageing
• Wear and tear theory (e.g., Free Radical Theory)
  • Free radical theory: Build-up of unstable oxygen compounds (ROS) leading to damage in tissues and cells over time, leading to cellular ageing