From birth to death, all of us undergo change. While our appearance, abilities and perspectives change, to name a few, the structural and functional changes that occur in the body of a healthy person during his lifetime are called ‘physiological changes’.

These physiological changes make the different systems in the human body such as the circulatory system to operate not only efficiently but also to capacity.

The physiological changes in the different phases of life serve special purposes which are unique to these phases. Children are not ‘little adults’ and older people are simply not ‘older adults’.

Here are four important phases of life in a healthy adult. These phases are early childhood, adolescence, adulthood under which pregnancy is dealt with and old age.

Early childhood (birth to eight years of age)

The main physiological changes during childhood are growth and development of skills. From the time a baby is born, he grows not only in weight and height but also in mental, social and physical abilities. These changes are measured in ‘milestones’. A child needs to be nurtured with appropriate nutrients in adequate amounts and have adequate exercise for the physical growth to be optimum.

However, what is not considered is that the child also needs love, attention and emotional support for his physical growth. He needs constant stimulation of his brain and the nervous system to develop intelligence, language skills and coordination.
Genetic factors allow for maximum growth only when the environmental conditions are met fully.

Key physiological changes

Growth — From birth to three years, a child typically doubles in height and quadruples in weight. The body proportions change to assume a more adult like appearance. After the age of three, physical growth slows down, while the brain reaches 95% of its adult volume by five years. The number and size of brain cells (neurons) increase, with many chemical changes too. The major difference between the brain development in a child and an adult is that the brain is far more impressionable (neuroscientists use the term “plastic”) in early life than in maturity.

This plasticity has both a positive and a negative side. While on the positive side, it means that a young child’s brain is more open to learning and enriching influences, on the negative side, the brain is more vulnerable to developmental problems, should the environment be impoverished or un-nurturing.

Development of skills — Physical changes in early childhood are accompanied by rapid changes in cognitive and language development. The child learns to respond to the environment using all his senses. Other skills such as eating with his fingers or using cutlery, writing, drawing and toilet training also develop very fast.

What can be done to optimise growth and development of skills?

Exclusive breast feeding during infancy has been shown to promote growth and prevent diseases even later in life.
Balanced, nutritious meals which include food rich in micronutrients such as iron, calcium, iodine, zinc etc., are needed for physical growth and prevention of disease.

Adequate sleep is essential, with infants and young children needing more hours than adults to improve learning, information processing and memory.

Physical exercise should be encouraged, with a wealth of scientific evidence showing that it is extremely beneficial for physical, emotional and mental growth. Swimming is an excellent form of exercise for young children.

Watching TV and computer games should be discouraged, as it has been found that young children who spend a lot of time in front of the screen lack focus and attention. Opportunities should be provided for outdoor games as much as possible.
Talking and reading are important, with the child being encouraged to question and discuss, while adults listen actively while giving an opportunity to the child to observe and practise. These activities improve coordination between fingers and eyes and ears as well as language skills.

Adolescence (from puberty to about 18 years)

The physiological changes are mostly controlled by the secretion of hormones such as testosterone in males and oestrogen in females by the pituitary gland. Rapid changes in hormone levels are mostly seen in early adolescence, with environmental influences too playing a major role in emotional and sexual maturity later on.

Key physiological changes

Physical growth — There is a rapid increase in height, while the reproductive system achieves full maturity. By the age of 17, the adolescents may be bigger than their parents and capable of having children themselves.

Emotional and cognitive development — Although the brain reaches 95% of its adult volume by the time a child is five years old, it continues to develop substantially in adolescence and even early adulthood.

Some changes during this period make the brain more efficient. Nerve cells transmit impulses faster and brain functions become more localized on either the right or the left hemispheres. These changes are reflected in the abilities of adolescents with regard to greater memory and problem-solving.

However, as the brain’s efficiency increases, it loses the ability to take on new functions easily. An example being that although most secondary language instruction is during adolescence, the brain would actually be more receptive to learning this material earlier in life.

Changes in levels of some neurotransmitters (chemical messengers) in the brain influence the way that adolescents respond to and interpret emotional events. These changes make adolescents more emotional and responsive to stress but less responsive to rewards. This may result in feelings of boredom, a desire to seek out novelty and take risks.

Adolescents have rapid mood swings and are general moody. Hormones are thought to be partially responsible for these emotional changes, especially among younger adolescents. Beyond early adolescence, however, the direct link between hormones and moods is relatively weak. Stressful changes in the environment of an adolescent may play an equal role as biological factors in influencing their moods.

Sexual maturity (Please see table below)

How to get the best out of these changes Provide balanced, nutritious meals at home.

Encourage physical exercise.

Recognise both the physical and psychological changes as normal. Help them to get over the awkwardness that is associated with sudden changes in their body. Be confident to discuss issues related to sex and sexuality. Respect their search for an identity and independence and their need for privacy.

Be aware of the risks of this phase such as violence, sexual issues, eating disorders, psychological disorders such as schizophrenia and mood disorders

Recognize the need for sleep. Growth and development use a lot of energy which may be why teenagers often seem to need much sleep. Getting up late may be irritating, but may not be just laziness.

Adulthood (18 -65 years)

This is a period of many years during which the body may not change much but continue to function in a regular manner. As this has been dealt with on Page 1, here the focus is on pregnancy.

Pregnancy (any age from puberty to menopause)

The physiological changes during this period are due to various hormone secretion patterns and growth of the gravid uterus (the womb with the foetus).

Key physiological changes

Changes occur in all the systems.

Some effects are directly linked to the hormones and others to hormonal effects on organ systems.

Gastrointestinal system — Morning sickness due to effects of maternal hormones; heartburn due to flow of stomach acid into the oesophagus (gullet); and constipation due to the slowing of intestinal movements.

Cardiovascular system — Feeling faint and dizzy due to a reduction in blood pressure and ankle swelling due to water retention.
Musculoskeletal system – Backache due to changes in the curvature of the lumbar spine.

Genitourinary system — Urinary frequency due to pressure on the urinary bladder by the enlarging uterus.
Other — Weight gain due to the enlarging uterus, baby and placenta, maternal fat and protein stores and water retention.

How to get the best out of these changes

Recognize the normal symptoms of pregnancy as they mean that the body is adapting well to sustain the baby and make the woman ready for childbirth and breastfeeding.

Pregnancy does not mean that the woman is ill. These are symptoms of wellness rather than of disease.
Nutritious food in small quantities should be eaten several times a day. When sleeping, the upper half of body should be slightly raised than the lower, to keep the acid in the stomach.

Green leaves and high-fibre vegetables and fruits should be eaten to prevent constipation.Vitamins and iron should be taken according to prescribed doses to meet the increased requirements of pregnancy.

Strenuous exercise should be avoided, as the uterus now has a big blood supply and during exercise it will be diverted to muscles, making the expectant mother unduly tired and dizzy. Short bursts of light, regular exercise are beneficial.
There should be proper sleep at night and several naps during the day. Frequent urination is not a disease but comes about due to the growing uterus putting pressure on the bladder. Lots of fluids should be taken during the pregnancy.
The weight gain should be slow and even, with the help of both the doctor and the nutritionist.

The feet should be kept up as much as possible to facilitate blood flow to the placenta.

Old age (above 65 years of age)

Key physiological changes

The gradual decline in the functioning of the organ systems and slowing down of activities.
Changes in the appearance.

Reduction in adaptability.

The gradual failure of the cells to repair or replace themselves causes the physical changes of ageing and occurs in every organ or tissue of the body

Even though the ageing process cannot be stopped, being aware of these changes and adopting a healthy lifestyle can reduce the impact on overall health.

With the production of collagen and natural oils reducing, the skin becomes drier, weaker and less elastic, leading to wrinkles and increased risk of injury. The hair turns grey. Muscle bulk and strength fail and staying upright and mobile become a challenge. Muscle loss accelerates after menopause in women and then after about 60.

Metabolism starts to slow in young adulthood, making weight gain more likely and setting the scene for the ‘middle-aged spread’ and an increased risk of type 2 diabetes later in life.

In women, menopause brings enormous physical change, usually from the late 40s, as the natural production of the oestrogen hormone reduces, leading to thinning of the skin and bones and an increasing risk of cardiovascular disease.
Reduced motility of the large bowel results in constipation.

The reduction in cortical function leads to memory impairment and reduced motor and sensory peripheral nerve function in the nervous system.

Changes occur in autonomic function which includes temperature regulation resulting in the failure of normal response mechanisms to hot and cold.

How to get the best out of these changes 

Appearance — Using moisturizing creams, lotions to decrease skin wrinkling and dryness. Keeping to good oral hygiene and having regular oral health checks.

Physical strength and mental benefits — Exercise is beneficial for strength, mobility and balance and may reduce the risk of falls. This applies even to frail older people. Indirectly, physical activity may also increase wellbeing, social activity and mental health.

How much exercise?

• The goal is to work towards 30 minutes of at least moderate-intensity physical activity at least five days of the week.
• Two 15-minute periods of moderate activity daily may be a good way to start. If that is too much, take a ‘little and often’ approach, starting with just three minutes and gradually increasing the time.
• The ideal is a combination of endurance exercises, strength exercises and stretching/balance/co-ordination exercises.
• It is never too late to start and any activity is better than none.
• Adequate warm-up is important and safe exercises/movement patterns should be chosen.

Nutrition–Elderly people have relatively more body fat and less lean body mass, resulting in lower metabolic rates. Therefore, calorie needs are reduced, so the diet needs proportionately more protein, essential fats and micronutrients.
Improving cognition (memory, attention, focus)

‘Brain-boosting exercises’ such as crosswords, sudoku, chess or even computer games.

Listening to classical music.

Learning new tasks such as using a computer.

(The writer is a Senior Lecturer in Physiology at the Department of Physiology, Faculty of Medicine, University of Colombo

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