Physiological changes of ageing

Concepts of ageing

• chronologic age and physiologic age are not the same

• vary based on the complex interactions of genetics and the environment

• individuals age at different rates

Effects of ageing on tissues

• affects cells and extracellular matric produced by them

• cells divide more slowly

  • injuries heal more slowly

• rate of RBC synthesis declines

• Extracellular matrix changes important

  • Collagen fibers become irregular – tendons and ligaments become less flexible and more fragile

  • Elastic fibers fragment and bind Ca2+ - making it less elastic

  • Irregular arrangement of fibers and loss of elasticity leads to increased wrinkling and increased risk of bones breaking

• Walls of arteries becomes less elastic because of changes in collagen and elastic fibers

  • Dilation and constriction not as efficient

Integumentary system

• Epidermis thins

• Dermal collagen and elastic fibers decreases leading to wrinkling

• Hypodermal fat decreases – sunken looking cheeks and eyes

• Decrease in sweat gland activity and blood supply to dermis

  • Reduced ability to regulate body temperature

  • Drier skin

• Melanocyte number generally decreases

• Grey / white hair

Muscular System

• Loss of muscle fibers: skeletal, smooth, cardiac

• Surface area of neuromuscular junctions decreases (skeletal muscle)

  • Increased time required for contraction – reaction time and reflexes compromised

• Decrease in motor neurons – less control of muscle – more prone to falling/imbalance

• Decreased density of capillaries (skeletal muscle) therefore reduced blood flow

  • Longer recovery period after exercise

Nervous System

• Decrease in size and weight of brain

  • Loss of motor neurons

  • Loss of cerebellar neurons

• Reflexes slow

  • Action potential generation and conduction and synaptic functions slow

• Structural changes in neurons – decreased function

  • Plasma membrane becomes rigid

  • ER becomes more irregular

  • Neurofibrillar tangles and amyloid plaques form

• Decreased blood supply

• Decreased Short term memory

General stress

• Meissner and pacinian corpuscles decrease

  • Remaining corpuscles become distorted and less functional

  • Become less conscious of something touching, pressing on skin

    • Increased risk of skin injuries

• Difficulty identifying object by touch due to loss of receptor functionality

• Decreased proprioception – i.e. decreased awareness of limb and joint position

  • Affect balance and coordination

Special Senses

• Taste

  • Loss of receptors – taste decreases

• Hearing

  • Hair cells in cochlea decreases – hearing loss

  • Hair cells in other auditory structures decrease – imbalance, less sensitive to gravity, prone to falling

• Smell

  • Smell perception decreases – cause unknown

• Vision

  • Lenses of eyes lose flexibility – rigid (presbyopia)

  • Cataracts

Endocrine System

• Gradual decrease in some endocrine glands

• GH decreases

  • May account for decrease in bone and muscle mass and increase in adipose tissue

  • Greatest in those who do not exercise

  • Decrease may not occur in those who exercise

• Decrease in

  • Melatonin

  • Reproductive hormones: testosterone, progesterone, estrogen

  • Aldosterone, renin

  • Thyroid hormones

  • Parathyroid hormone

  • Insulin

Cardiovascular System: Heart

• Cardiac muscle cells

  • Size and number decrease

• Heart valve become less flexible, thick and rigid

  • Changes in connective tissue

  • Calcium deposits

• Conducting system becomes fibrosed and loss of cells

  • Arrhythmias

• Cardiac output and maximum oxygen consumption reduced

Cardiovascular system: Blood Vessels

• veins:

  • Patchy thickenings – narrowing in those regions

  • Weakening of connective tissue in walls – varicose veins, hemorrhoids

• Arteries

  • Less elastic

  • Deposits of fatty substances, calcium, connective tissue

• Arteriosclerosis

  • Arteries become less elastic

  • Risk of increased BP

• Atherosclerosis

  • Deposition of material in walls – fatlike substance, connective tissue, calcium salts

  • Artery narrows – impairs blood flow

Immune system

• T cells are less functional

• Ability of helper T cells to proliferate in response to antigens decreases

  • Less stimulation of B cells and cytotoxic T cells

• More antigen required to produce an immune response, response is slower

  • Ability to resist infections and develop immunity decreases

• Autoimmune disease occurs

  • Immune responses destroy healthy tissue

Respiratory system

• Pulmonary function decreases with age

  • Calcification of cartilages in the upper respiratory tract

  • Elastic fibers fragment and some calcification

  • Number and size of alveoli reduced and walls thicken – reducing gas exchange across respiratory membranes

  • Vital capacity decreases – reduced ability to fill and empty the lungs

  • Vital capacity = the volume of exhaled air after maximal inspiration.

  • Residual volume increases – alveolar ducts and larger bronchioles increase in diameter – decreasing air available for gas exchang

  • Residual volume = volume of air that remains in the lungs after maximum forceful expiration – i.e. it’s the volume of air that cannot be expelled from the lungs

  • Mucus is more viscous and fewer cilia on epithelium in lungs

    • Cilia cannot efficiently clear viscous mucus out of lungs and into throat. Increases probability of infection. Lung function compromised – viscous mucus reduced gas exchange in alveoli.

Digestive System

• Connective tissue layers of GI tract thins

• Blood supply to GI tract decreases

• Decreased motility of GI tract

  • Smooth muscle cell number deceases in the muscle layers of GI tract

  • Loss of muscle tone and peristalsis – constipation

• Goblet cells in mucosa produce less mucus

  • A major role of mucus – coats the interior surface of the GI tract, lubricates luminal contents and acts as a physical barrier to bacteria and other pathogens. First line of defense against infiltration of microorganisms, digestive enzymes and acids, digested food particles, microbial by-products, and food-associated toxins. These functions compromised by reduced mucus production

• Gastric glands, liver, and pancreas secrete less

  • Reduced secretion of enzymes, buffers etc makes digestion and absorption less efficient

• Tooth loss

  • Decrease in enamel thickness

  • Receding gingiva – exposing dentin

Renal system

• Bladder

  • Loss of urinary sphincter muscle tone – urinary incontinence

  • Less elastic – volume decrease

• Kidney

  • diminished capacity to regulate fluid and electrolyte balance

  • Atrophy of tissue

  • Decrease in nephron number

  • Reduced circulation to remaining nephrons

• Women

  • Shorter urethra because of shrinkage – increased urinary tract infection risk

• Men

  • Prostatic hyperplasia – compresses urethra – difficulty in micturition (urination)

Reproductive System: Women

• menopause most significant

  • Decreased estrogen and progesterone production

  • Uterus size decreases

  • Endometrium thickness decreases

  • Irregular menses, menstruation eventually stops

Reproductive System: Men

• gradual decline

  • Decreased testosterone

  • Benign prostatic enlargement – blockage of prostatic urethra

  • Frequency of prostrate cancer increases

  • Erectile dysfunction

Skeletal system: Bone

• Amount of bone matrix decreases and matrix becomes more brittle (osteoporosis)

  • Decreased collagen production resulting in more mineral

  • Rate of matrix formation by osteoblasts slower than breakdown rate by osteoclasts

• Bone loss from jaws

  • Tooth loss

Skeletal System: Joints

• Joints

  • Greatest effect in synovial joints

  • Wearing down of articular cartilage

  • Matrix replacement declines and matrix becomes more rigid

  • Synovial fluid production decreases

  • Ligaments and tendons around joints shorten and become less flexible

  • Arthritis – inflammatory degeneration of joints