Physiological Aspects of Ageing

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Physiological Aspects of Ageing

• Age-Related Changes

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General Characteristics of Physical Ageing

• Ageing is not a simple, single process, but a
  series of interrelated events that accumulate
  until a change becomes noticeable and permanent.
• Research in ageing is beginning to find out the
  reasons for these changes and the genetic and
  environmental factors that control them
• All of the changes that occur in the human body
  during senescence eventually result in impaired
  function and reduced efficiency of function.

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• The ageing process depends on a combination of
  both genetic and environmental factors.
• Recognizing that every individual has his or her
  own unique genetic makeup and environment, which
  interact with each other, helps us understand why
  the ageing process can occur at such different
  rates in different people.
• Overall, genetic factors seem to be more powerful
  than environmental factors in determining large
  differences among people in ageing and lifespan.
• There are even some specific genetic disorders
  that speed up the ageing process, such as
  Hutchinson-Gilford, Werners, and Down syndromes.
• However, many environmental conditions, such as
  the quality of health care that you receive, have
  a substantial effect on ageing.

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• Biological changes associated with
• maturity and ageing
• Brain weight 85
• BMR 80
• Liver blood flow 50
• Liver weight 63
• Cardiac output at rest 65
• Respiratory capacity of lungs 55
• Kidney mass 65
• Conduction velocity of 85
• nerve fibre

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• Collagen fibres in the dermis of the skin become
  thicker and lose their elasticity and adipose
  tissue in the hypodermis also decreases. What
  does this contribute to?
• There are also a decreased number of hair
  follicles and reduced number of sweat glands.
  What problems may this cause?
• In general, physical changes occur throughout the
  body, including reduced metabolic rate, reduced
  nerve conduction velocity and reduced strength
  of skeletal muscle contraction.

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Physiological Theories of Ageing

• The genetic theory there are believed to be
  pleitropic genes that promote survival in the
  early stages of life and ageing later in life.
  Our cells may be pre-programmed to age and to
  self-destruct at particular times. These genes
  may stimulate the production of molecules that
  eventually cause or accelerate the ageing
  process.
• DNA theory- the genetic material in our cells, is
  damaged by internal and external toxins. Our
  bodies have developed intricate repair systems
  that maintain the integrity of this code and of
  our cells and their function. Over time, our DNA
  repair systems falter. Some scientists believe
  the accumulation of uncorrected DNA damage over
  years is a major cause of aging.

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• The disposable soma theory- DNA is kept in good
  repair until the time of reproduction, after
  which efforts are transferred to nurturing of
  infants, rather than for tissue repair processes.
  According to the Hayflick limit, cells can
  undergo a limited number of cell divisions. This
  is greater for foetal cells than for cells from
  elderly individuals.
• The Telomeric theory- Inside the nucleus of
  virtually all of our cells are chromosomes, 46 in
  all. At the tips of these chromosomes are
  telomeres, repeating sequences of genetic
  material that shorten each time a cell divides.
  Cell division important because many cells in our
  body (e.g., those that line our digestive tract)
  must be replaced over time. When a cell's
  telomeres reach a critically short length,
  however, that cell can no longer replicate.

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• Its structure and function begin to fail as it
  enters this state of growth arrest, called
  replicative senescence.
• Some have likened the process of telomere
  shortening to a genetic biological clock that
  winds down over time.
• Today, researchers continue to probe the
  telomeric "timepiece," hoping to better
  understand the aging process and fight diseases,
  particularly cancer.

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• 5. The endocrine theory secretion and
  effectiveness of particular hormones are believed
  to decline in older age.
• 6. The immunological theory progressive failure
  of the immune system reduces the ability to fight
  disease and increases the risk of autoimmune
  diseases and cancers.
• 7. The free radical theory the free radicals
  that are produced as a by-product of metabolic
  processes in cells react with proteins, DNA and
  enzymes to cause damage to cells and tissues.
  Pollution and exposure to cigarette smoke can
  increase production of free radicals.
• 8. Accumulation of waste over time accumulation
  occurs as removal is not as efficient.
  Accumulated waste interferes with normal
  functioning of cells which can result in
  structural changes/mutations

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• Cellular Changes Associated with Ageing
• Ageing causes functional changes in cells.
• Rate at which cells multiply slows down with
  ageing.
• Certain cells important for functioning of immune
  system (T-cell lymphocytes) also decrease with
  age.
• In addition, age causes changes in our responses
  to environmental stresses or exposures, such as
  ultraviolet light, heat, not enough oxygen, poor
  nutrition, and toxins (poisons) among others.

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• Age interferes with apoptosis.
• This programs cells to self-destruct or die at
  appropriate times.
• Process is necessary for tissues to remain
  healthy
• It is especially important in slowing down immune
  responses once an infection has been cleared from
  body.
• Different diseases that are common in elderly
  people can affect this process in different ways.
• Cancer results in a loss of apoptosis.
• Cancer cells continue to multiply and invade or
  take over surrounding tissue, instead of dying as
  originally programmed.

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• Other diseases may cause cells to die too early.
• In Alzheimers disease, a substance called
  amyloid builds up and causes the early death of
  brain cells, which results in a progressive loss
  of memory and other brain functions.
• Toxins produced as by-products of nerve-cell
  transmissions are also thought to be involved in
  the death of nerve cells in Parkinsons disease.

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• Free radicals and antioxidants
• During aerobic respiration, our bodies produce
  toxins called "free radicals.
• These molecules can cause damage to cells and
  DNA, but are generally "mopped up" by substances
  called antioxidants before they cause damage.
• As we age, this process becomes more inefficient.
• Free radical or oxidative damage has been
  implicated in several age-associated diseases,
  from cancer to Alzheimer's.
• Some researchers suggest that this damage may be
  a central cause of the aging process itself.
• Scientists are now investigating how diets rich
  in antioxidants (Vitamins C and E are two of the
  most common) can limit the harm caused by
  oxidative damage and perhaps even slow aging.

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• Mitochondria and free radicals
• Mitochondria, cells' energy converters.
• Involved in cellular respiration
• Mitochondria also produce damaging oxidantsfree
  radical molecules produced by the metabolism of
  oxygen
• Wreak havoc on cells and their DNA.
• As the source of these toxic products,
  mitochondria are also their first potential
  victims.
• Their proximity to the free radicals they
  produce, combined with their exceedingly
  intricate structure, make them particularly
  vulnerable to injury over time.
• Researchers are seeking to understand this injury
  as a critical part of the aging process, and
  perhaps a cause of a host of age-related diseases.

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• Changes in Height
• Height is lost as we age
• The reasons for height loss include the
  following
• - changes in posture
• - changes in the growth of vertebrae (the bones
  that make up the spine)
• - a forward bending of the spine
• - compression of the discs between the
  vertebrae
• - increased curvature of the hips and knees
• - decreased joint space in the trunk and
  extremities
• - joint changes in the feet
• - flattening of the arches
• The length of the bones in our legs does not
  change much.

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Changes in Heart Function with Age

• Heart weight increases and collagen (most common
  protein in body) stiffens.
• Stroke volume does not change with age, but
  ability to increase it becomes reduced
• The cardiac conduction system becomes less
  sensitive (SAN cells replaced by fibrous tissue)
  to autonomic stimulation and the effects of
  adrenaline. What will happen to heart rate?
• The baroreceptor reflex response to alterations
  in arterial blood pressure is reduced. This may
  increase the risk of orthostatic hypotension.
• The combination of altered cardiac output and
  impaired ventilatory capacity tends to reduce
  oxygen delivery to respiring tissues.

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Changes in the Blood Vessels with Age

• Most significant alterations in structure occur
  in the large elasticated arteries.
• Decreased aortic compliance, loss of elasticity
• Arterial disease increases resistance to blood
  flow. Narrowing of lumen. What effect will this
  have on arterial blood pressure?
• What factors may promote arterial disease?
• How does arterial disease increase the risk of
  myocardial infarctions (heart attacks) and
  cerberovasuclar accidents (strokes)?

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Consequences of CVA

• What functional changes may occur if the cerebral
  arteries are occluded?
• Reduced or impaired cerebral blood flow cause
  cerebral ischaemia that induces death of neurones
  by necrosis within a few hours.
• An area of dead neural tissue is referred to as
  an infarct. For several days following a CVA,
  cells surrounding the infarcted area may
  degenerate as a consequence of apoptosis
  (programmed cell death).
• Increased production of lactic acid and increased
  release of neurotransmitters, including glutamate
  facilitate death of neurones following CVA.

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• Respiratory function
• Alveolar function unchanged with age
• Noticable change is reduction in lung compliance
• Also loss of elasticity and reduction in strength
  of muscles of rib cage reduces usable lung
  capacity to 82 maximum value by age 45 62 at
  age 65 and 50 at age 85
• Over time some alveoli replaced by fibrous tissue
• Gas exchange reduced
• Main problems arise with increased demand
  (exercise)

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• Renal function
• Vessels supplying nephrons can become
  atherosclerotic
• Fall in GFR may occur
• Affect kidneys ability to excrete metabolites and
  drugs
• At age 80, reduced to 50
• Consequences on homeostasis (eg)
• Main problem is reduced ability to respond to
  salt load or depletion
• Acid base balance
• Urinary incontinence

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General Characteristics of the Ageing Brain

• Brain volume may be reduced by as much as 10 of
  that of a young adult. Associated with this are
  enlargement of the ventricles, deepening of the
  sulci and prominence of the gyri.
• The areas of the brain that show most age-related
  loss of neurones are the cerebral cortex, the
  cerebellum and the basal ganglia.
• Short-term memory loss becomes more apparent with
  ageing in some individuals and may be associated
  with neural loss and dysfunction in the temporal
  lobes, hippocampus and thalamus.
• The incidence of Parkinsons disease is increased
  in old age. Neurones in the substantia nigra of
  the midbrain degenerate. This impairs the
  ability of the basal ganglia to control movement.
• What are the symptoms of Parkinsons disease?

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Changes in Auditory and Visual Function with Age

• The sensorineural hearing loss that occurs in
  older age is presbycusis. Explain how this
  hearing loss occurs.
• Conductive hearing loss may also occur. Identify
  factors that may contribute to conductive hearing
  loss.
• In the eyes, the lens decreases its elasticity
  and becomes less mobile. What is the function of
  the lens?
• Cataracts may develop as a build-up of proteins
  causes an opacity that impairs vision.
• Loss of fat in the eyelids and reduced tone of
  the levator muscle causes drooping (ptosis) of
  the eyelid.
• A reduction in neurones is evident in the primary
  visual cortex.