Adolescence, Adulthood and Old Age

This is my third and final post (for now) on growth and development! The first, on factors influencing development, can be found here; the second, on infancy and childhood, can be found here.

Adolescence and Adulthood

Adolescence is the period of transition from childhood to adulthood.

Many physical changes occur during adolescence. First of all, adolescents rapidly grow taller, during what is known as an adolescent growth spurt. Girls normally get their growth spurts at around 11-14 years old, while boys normally get theirs at 13-16 years old. Since boys' growth spurts are towards the end of their growth period rather than in the middle of it, they normally end up being taller than girls.

Growth spurts often begin with a gain in weight, with fat deposited on the legs, arms, buttocks and abdomen. The fat then becomes redistributed or used as a source of energy as the rapid growth in height occurs. Nearly all of the bones in the body increase in size, but not at the same time, which sometimes results in "unusual" proportions (like having really long, skinny legs relative to the rest of your body). Normally the legs grow first, followed by the vertebrae, and then the shoulders and hips. Boys' shoulders broaden while girls' hips widen.

The face also changes during adolescence. The head grows in length and breadth, and the forehead becomes higher and broader. The nose, jaw and chin grow, the mouth widens and the lips become fuller. The head doesn't grow as much as the body does, though, so the head becomes smaller in relation to overall body size.

Internal organs, such as the heart and lungs grow, providing greater physical endurance. Cartilage and fibrous tissue also disappear as bones grow. Muscles also grow due to an increase in the amount of protein in the muscle cells. Normally, muscle growth occurs after bone growth. Once the bones have stopped growing, other changes to the skeleton continue to take place: the plates fuse where elongation of the bones used to take place, preventing further growth.

The reproductive system also changes. As you well know, puberty is the time during which sexual maturity (physically, that is) is attained. The organs of the reproductive system begin to grow and start producing their respective gametes, or sex cells. (More info on these gametes can be found here and here.) In females, the first menstrual period indicates that sexual maturity has been attained; in males, the first ejaculation indicates this.

Other secondary sexual characteristics, which are characteristics associated with a person's gender but aren't related to sexual reproduction, also develop during puberty. These are due to the secretion of sex hormones. In females, these include breast growth and broadening of the hips, while in boys it includes an increase in the size of the larynx, which gives them deeper voices. Both genders also have to put up with hair growing in annoying places.

Aside from just physical growth, adolescents also have to grow mentally and emotionally. They have to learn many different skills to be able to take on adult life. (Don't ask me, though, I can't say I've mastered any of these skills.) Spending more time with friends is one way in which many adolescents learn independence, but this can sometimes create conflict with parents. Actually, quite a lot of factors can cause adolescents to have frequent conflicts with their parents. I probably don't have to say- you probably all know. Adolescence is also the time when many people start to become interested in members of the opposite sex- or the same sex, for that matter. So yeah, all kinds of relationship stuff going on all around.

Ageing

The study of ageing is called gerontology, which is concerned with minimising the disabilities and handicaps of old age. The area of medicine that deals with prevention and treatment of disease in older people is called geriatrics.

Ageing occurs on several levels. It occurs on the cellular level, the tissue level, the system level and so on.

Here are some changes that happen on the cellular level:

• Mitochondria become swollen
• Endoplasmic reticulum becomes more sac-like
• Cellular respiration is reduced as some types of cells get older
• Reduced ability to metabolise fats
• Increase in the number of breaks in the DNA molecule and in chromosomal abnormalities. However, DNA content remains the same
• Enzyme activity changes- some increase activity with age and some decrease activity with age, while others appear to stay the same.
• Number of cells dividing at any one time appears to decrease with age. However, this may be due more to how many times the cell has divided, rather than age of the cell. Eventually, cell division may cease altogether.

Ageing also comes with a decline in the performance of all the organ systems. This is called senescence. These changes lead to a decrease in homeostatic capacity, which is the ability to maintain a constant internal environment while other environmental factors, such as temperature, might be changing. This can then lead to a decrease in the ability to cope with physical and emotional stress, and the increased risk of disease. Chronic diseases, such as high blood pressure, cardiovascular diseases, cancer and so on, become more common, while acute diseases (diseases which quickly reach a peak) become less common.

Here are some changes that happen on the tissue and system level:

• Skeletal system: Bone tissue becomes lighter and more brittle. Joints lose elasticity, and cartilage becomes thinner.
• Muscles: Muscles become smaller and weaker. This loss of muscle strength is more obvious in activities requiring more coordination.
• Respiratory system: Breathing efficiency is reduced due to the loss of elasticity in the alveoli and increased rigidity of the chest wall.
• Circulatory system: Blood vessel walls lose their elasticity, causing the heart to work harder to overcome the increased resistance. This then causes blood pressure to rise.
• Urinary system: Kidney filtration is reduced due to the reduction in blood flow.
• Digestive system: The alimentary canal produces less of the digestive juices and peristalsis becomes slower.
• Skin: The skin becomes wrinkled, dry and occasionally scaly. Underlying layers of fat decrease, causing skin to sag. The number and activity of hair follicles, sweat glands, sebaceous glands and pigments results in greying hair, a loss of hair, mottling of the skin, reduced sweating and decreased oil production.
• Nervous system: Efficiency of the nervous system decreases. This may be due to a decrease in nervous system capacity, blood flow, tissue permeability and sensitivity of sense organs.
• Endocrine system: Production of hormones responsible for immune responses decreases.
• Reproductive system: Women generally undergo menopause between 45-55 years. This period of change is known as the climacteric. The gradual decrease in hormones causes periods to become less regular before stopping totally, as well as a decrease in the size of the reproductive organs (uterus, ovaries, etc.). Men eventually become unable to maintain an erection. Eventually these changes lead to a loss of fertility.

Other psychological and intellectual changes occur with ageing. While research suggests that intellectual functioning (i.e. the ability to perform numerical skills, verbal skills etc.) doesn't decline with age, the capacity to learn and memorise does. As people age, they are less efficient at recalling recently learned material and entering material into long-term memory. However, their long-term memory is often quite good.

Death

Unfortunately, eventually we're all going to die some day. Let's take a quick look at the process:

There are several stages that people go through as they die: 

1. This stage is called the "stress response syndrome." The person breathes rapidly (hyperventilates), their heart beats faster and their muscles contract. Eventually their heart stops beating, and they lose consciousness.
2. The hairs on the skin become erect, the pupils dilate and the bladder and bowel empty.
3. The temperature on the skin falls. Internal organs lose heat. Body organs then cease functioning at different rates. The first to cease functioning is the brain- the time that this happens is the official time of death. Many other organs can still function for a short time after the brain has "died," and can thus be transplanted into other people.

Aside from these physical stages, there are several psychological stages that people go through while dying (independent of the physical stages above):

1. Denial- The person tries to deny that they are dying (although aware of the fact). They may withdraw from social activities so that they don't have to discuss death with anyone.
2. Depression
3. Acceptance- The individual realises that death is inevitable. Many try to approach death with dignity.

Wow, this is a rather grim place to end a post... Well, I suppose it did end with "many try to approach death with dignity," so maybe not so grim after all! I don't know. I just feel like anything else I say right now might end up sounding insulting to those who have lost relatives, so I'm just going to shut up and leave you all to sleep or do whatever you need to do.