Infancy and Childhood

This is my second post about growth and development. The first, about factors affecting development, can be found here.

Feeding Babies

I'm going to start off with how babies are fed via breastfeeding. How exactly do breasts produce milk, anyway? There's probably quite a long, complicated process to it but for now we'll just simplify it to one word: hormones.

At around age 10 or 11, the breasts start to develop due to the influence of oestrogens and progesterone. During pregnancy, the breasts develop further due to greater concentrations of oestrogens and progesterone: the lobes (sections of the breast- I'll get to them later) become bigger, the nipple darkens, and oil-secreting glands around the nipple enlarge in order to prevent the nipple from drying out. Towards the end of pregnancy, a hormone called prolactin (lactogenic hormone) is also produced by the pituitary gland. The action of this hormone is initially inhibited by the oestrogens and progesterone, but once the baby is born, the loss of the placenta causes a decline in levels of these hormones, allowing prolactin to kick in a day or two after birth, sometimes even earlier. Prolactin promotes growth and development of the breast as well as the secretion of milk.

What exactly is in the breasts? Well, each breast consists of 15-25 sections called lobes, which are then subdivided into a number of lobules. Lobes and lobules are surrounded by fatty connective tissue. The walls of lobules are made up of lots of glandular alveoli, which secrete milk. The lobules then lead into ducts, which open up into milk spaces, which then lead into short, straight ducts to the nipple. Each lobe has its own milk space, so there are 15-25 openings on the nipple for secretion of milk.

The first secretion is a watery, yellowish-white fluid called colostrum, which has a similar composition to milk. However, colostrum contains little to no fat, and has a high content of the mother's antibodies, which are then absorbed by the infant's intestine to give the baby temporary immunity to certain diseases.

Milk remains stored in the breast until the baby starts suckling. Suckling triggers an automatic response called a milk let-down. Nerves in the nipple are stimulated, sending messages to the brain, which in turn instructs the pituitary gland to release the hormone oxytocin. Oxytocin causes the small muscles around the milk-filled lobules in the breast to contract, pushing milk through the openings on the nipple into the baby's waiting mouth. Suckling also stimulates secretion of prolactin, which causes more hormones to be released and more milk to be produced. Hence, babies can control their own milk supply. At the height of lactation, up to 1.5L can be produced each day. The nutritious quality of the milk depends on the mother's diet, so mothers should take care to eat a healthy, balanced diet, both for themselves and for their babies.

Breastfeeding has a lot of advantages. It's sterile, always at the right temperature and generally meets all the nutritional needs of the baby (I say "generally" because it might not if the mother is malnourished). Additionally, there is no artificial alternative to colostrum. Benefits to the mother include decreased risk of ovarian cancer, breast cancer and bone loss.

Babies grow very quickly during their first few years of life. Over the first year alone, their body length increases by over a third, while their weight almost triples. (Thankfully they eventually learn how to walk so their parents don't need to carry them everywhere!) Their proportions also change too- babies have large heads in proportion to their bodies, but during the course of their lives their heads grow much slower than the rest of their bodies, so that when they are adults their heads are only around 10% of body height.

Intellectual and Emotional Needs

Aside from physical needs such as nutrition, all of us, including little babies, have various intellectual and emotional needs.

Babies have loads of stuff they need to learn. They need to learn how to adapt to life outside of the womb, motor skills, speech, how to socialise, and so on. Thankfully, their brains grow really fast- by the age of 6, the brain is already around 90% of the adult size!

Babies learn through watching, listening, touching, smelling, tasting and copying others. Their senses need to be stimulated to pick up information, but they can get tired from being overstimulated. They can learn speech by first "babbling" before copying words that they hear and having their pronunciation corrected by others. (Probably a gross oversimplification :P)

Motor skills are learned largely by practice and trial and error. (Again, probably a massive oversimplification.) There are three patterns involved in motor development: the cephalocaudal pattern, in which movements of upper parts of the body develop before those of the lower parts of the body (e.g. being able to reach for an object before being able to walk); the proximodistal pattern, in which parts of limbs closer to the body are able to be controlled first (e.g. upper arm can be controlled before forearm, which can be controlled before the hand and fingers); and the gross to specific pattern, in which larger muscle movements are learned before finer movements like picking up objects with the fingers.

Bonding is important for the social and emotional development of the child. It refers to the love and affection between parent and child. Aside from forming close relationships with parents, it is also important for babies and children to form close relationships with others.

For the first month or two of life, babies cannot tell the difference between people and objects. At around the third month they start to tell the difference, and respond to people with smiles, sounds, smiling, kicking or waving their hands. These actions are called social smiles. As children grow, they begin to learn acceptable social behaviours from their parents and other influential people in their environment.

Next up: Adolescence, adulthood and old age!