Physiological Changes During Old Age
The physiological decline in body functions during aging is not uniform. It varies among different organs. The capacity of the system may not decline but their ability to respond to a challenge or to maintain homeostasis is lowered. The physiological changes that occur in various systems are as follows.
a. Taste and smell
There is a decrease in the number of taste buds and papillae on the tongue. The ability to taste salt is very much decreased whereas that to sugar in less altered. Besides there is a reduction in olfactory sensitivity which decreases the ability to detect the flavour. This decreases the palatability of the food resulting in poor intake. Diminished taste and smell decreases the sensory stimulation that may impair metabolic processes.
b. Salivary Glands
Decrease in salivary secretion or lack of salivation (xerostomia) causes a feeling of dry mouth, which makes chewing and swallowing difficult. Hence crunchy, dry and sticky foods are avoided by old people.
They may lose teeth or have ill fitting dentures which makes chewing difficult. They may omit fresh vegetables and fruits. This may lead to vitamin and mineral deficiency accompanied by decreased gastrointestinal motility and problems in elimination like constipation.
d. Gastrointestinal function
The secretion of digestive enzymes and digestive juices decline. This results in incomplete digestion, or food remaining longer in stomach for digestion. The secretion of hydrochloric acid, intrinsic factor and pepsin decreases which affects absorption of calcium, protein, iron and vitamin B12.
Above 60 years of age the rate of emptying of liquids is rapid which again leads to decreased absorption of nutrients.
The pH of proximal small bowel increases and there is bacterial over growth in the bowel.
In the small intestine there is decreased secretion of enzyme lactase, which can be a risk factor for developing osteoporosis. Thinning of gastrointestinal layer decreases gastric motility and prolonged transit through the colon leading to constipation.
e. Liver and biliary function
There is a decrease in blood flow to the liver. This may lead to minor structural and biochemical changes. Gall bladder becomes sluggish in releasing bile, which impairs fat metabolism and increases susceptibility to gall stones. The activity of drug metabolising enzymes decrease and therefore lower drug doses need to be prescribed during old age.
f. Metabolic Function
There is a decrease in metabolic rate and impaired glucose tolerance, which necessitate dietary modifications. The body protein levels also decrease.
g. Neurological Function
There is a decrease in neuromuscular coordination. They may develop a state of confusion. There is a decreased synthesis of seratonin. Carnitine derived from the aminoacids lysine and methionine may be effective in slowing down mental deterioration. Carotenoids play a protective role related to aging and cognitive function.
h. Cardiovascular function
Changes in blood vessels such as narrowing of the lumen, thickening of the arterial walls and replacement of elastic muscle fibres with non elastic fibres lead to increased rigidity of vessels (atherosclerotic changes) which reduces their capacity to carry nutrients to the cells. There is decreased myocardial contractibility and increased peripheral resistance, increasing the prevalence of hypertension.
i. Renal function
There is a decrease in Glomerular Filtration Rate (GFR) affecting the elimination of waste products and reabsorption of electrolytes. Moreover, the body's ability to regenerate nephrons ceases after 40 years of age. Hence increased solute load on each nephron may lead to necrosis and kidney damage.
j. Skeletal tissue
Demineralisation of bones is more rapid than mineralisation. The bones become increasingly vulnerable to fractures and the vertebrae may collapse. This results in decline in height and a stooped or bowed posture. This posture may affect respiratory function.
k. Pulmonary function
Pulmonary capacity declines by about 40 percent throughout life. Among elderly this may not have an impact on health but may impose restriction on energetic exercise.
l. Harmonal changes
Activity of various glands like thyroid, adrenal cortex, islets of langerhans is decreased resulting in changes in metabolism and metabolic functions. The hormonal imbalance affects the calcium metabolism leading to osteoporosis and bone loss. Menopause in women decreases their iron requirements.