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When a human female's egg is fertilized by a male sperm they form a zygote which goes on to develop into three layers: blastocyst, embryoblast and trophoplast. The blastocyst attaches itself to the wall of the uterus and start secretion of the protein Human Chorionic Gonadotrohin (hCG). This protein binds with the LhCG receptor and helps to maintain pregnancy by ensuring that the corpus luteum does not disintegrate during the early stages of pregnancy. It also stimulates the secretion of the hormone progesterone which makes the secretory endometrium stronger and also maintains its strength to sustain the embryo during pregnancy. A minimum level of 10ng/ml of progesterone is needed to sustain the pregnancy throughout its very early stages (http://www.paternityangel.com/Articles_zone/Hormones/Hormones2.htm). A fall below that level during the first 10-12 weeks may cause the secretory endometrium to shed thus resulting in a miscarriage. hCG is also thought to have an immunological role in the survival of the fetus during the first trimester. It causes the destruction of the mothers T-cells (apoptosis) by hCG treated endometrial cells. The T-cells need to be destroyed because the zygote formed also contains antigens from the father which is immunologically different from the mother's which would cause the maternal immune system to recognize it as foreign. This intern causes the activation of T-cells which will proliferate and eradicate the semi-allogenic fetus thus terminating the pregnancy.
The trophoplast forms the placenta which has many roles in the development and survival of the embryo. Its main role and function is to allow the exchange of gases from fetus to mother. It carries oxygen and nutrients from the mother's blood stream into the fetus' and then removes waste such as carbon dioxide. The placenta takes over the production of hCG and progesterone after the first trimester and keeps producing it until birth in order to maintain and sustain the fetus. The placenta also acts as a form of "defense machine" in helping to protect the fetus. It secretes neurokinin B that has phosophocholine molecules and is used to suppress an immune response against the fetus. There are also small lymphocytic suppressor in the fetus that inhibit the maternal cytotoxic T cells by blocking the response to interleukin 2. The placenta helps in the development of the fetus' immune system by allowing the transfer of the antibody immunoglobulin G (IgG). This transfer is made possible by maternal Fc receptor neonatal (FcRn) which actively transport the IgG by picking it up and binding to it in the maternal circulation carrying it across the placenta then releasing it into the fetal circulation.
Apart from passing on valuable nutrients to the fetus, the mother can also transmit diseases and viruses such as HIV. The fetus usually contracts the HIV virus from its mother during the last weeks of pregnancy or delivery if she has advanced HIV or AIDS where her viral load is high or she has a low CD4 count. The fetus is at greater risk of contracting HIV or AIDS if these factors are present: having genital infection such as Chlamydia, water breaking 4 hours before delivery, having vaginal delivery, having a difficult labor that includes the use of forceps or having an episiotomy (http://courses.essex.ac.uk.proxy.essex.ac.uk/bs/bs223/restricted/Mother-to-Baby%20Transmission.htm). Expectant mothers who have the HIV infection or the AIDS virus can take anti HIV drugs such as AZT (zidovuldine) to reduce their chances of transmitting it to their babies. An article from this source (http://courses.essex.ac.uk.proxy.essex.ac.uk/bs/bs223/restricted/Mother-to-Baby%20Transmission.htm) stated that in a study pregnant women who were given AZT tablets in the last 6 months of pregnancy and intravenous AZT during childbirth, along with administering AZT syrup to their babies for the first six weeks of life were much less likely to pass HIV onto their babies. They were also advised not to breast feed their babies as this increases the chances of infection to about 1 in 3.
When a baby is born, it becomes very susceptible to various pathogens as it does not yet have a properly formed immune system. IgG that were passively passed on from the mom through the placenta is present in high amounts in the baby. It is usually equal to or higher than the amounts found in an adult. This provides the baby with passive immunity during the first few months of life.
Breast milk production is synthesized by the hormones prolactin and oxytocin and is usually produced after birth. The milk is made to act as a source of food and nourishment for the baby and also constitutes to the development of the baby's immune system. The "first" milk produced in the breast is known as colostrums. It is considered to be the most important start to lactation/ breast feeding a baby as it is highly rich in immunoglobulins and other substances that are immunologically important. It also contains other vitamins, proteins and nutrients that needed for growth and good health. Colostrum's growth factors stimulate the gut's development while the antibodies provide passive immunity. Colostrum is rich in IgA which coats the gastrointestinal walls of the baby preventing the entry of enteroviruses and bacteria such as E. coli and in addition to the IgG already present, provides protection for the baby until its own immune system is fully developed. Colostrum also contains mild laxatives which causes the passing of meconium which is basically the baby's first stool. This is an important process as it causes the excretion of excess bilirubin which is a waste product of red blood cells and also helps to prevent the development of the condition jaundice.
Breast milk contains many constituents that are of immunological importance to the neonate. It contains "bits" of the mothers (maternal) immune system such as leukocytes, macrophages and neutrophils. Macrophages given to the neonate in breast milk are usually CD14+ which affect the function B and T cell because they show up activation markers such as CD11c, they provide phagocytic activities and causes the secretion of immunoregulatory factors. The macrophages also contain engulfed sIgA, which are in the gut and is released when they come into contact with bacteria.
The main types of lymphocytes found in breast milk are T cells. It is claimed that the maternal activated T cells that are transferred to the neonate, is used to promote the maturation of the neonatal T cells meanwhile compensating of their immature function. it is believed that a the thymus of a breast-fed neonate is two times larger than an infant that is not breast fed. The neutrophils in milk provides maternal protection for the neonate. There are speculations that they tend to have low functions when they are secreted in breast milk.
Cytokines and chemokines are also present in breast milk. They include: IL-1Î², IL-4, IL-5, IL-6, IL-8,IL-10, IL-12, IL-13, TNF Î±, TGF Î² (transforming growth factor), INF Î³, granulocyte- colony stimulating factor, RANTES and monocytes chemotactic protein 1. Cytokines in general influences the development and maturation of immune cells in the neonate. Maternal cytokins TGFÎ², IL-10 and IL-6 helps with the maturation of the "naÃ¯ve" intestinal immune system and also help IgA producing cells to develop and differentiate.
Breast milk helps with microbial colonization and immune development by using bacterial agents from microflora to promote the maturation of their immune system. The mechanism by which this is done is not yet defined. Having a good (optimum) flora in the early stages of life that encourages Th2 response is important for neonates to produce the cytotoxic response that s needed to eliminate intestinal pathogens. This is called the bifidus factor. Nucleotides promote lymphocytic proliferation, activation of macrophage, NK activity and the production of a range of immunomodulatory factors.
Breast milk also contains anti-inflammatory components that reduces the chances of it having exaggerated inflammatory response which can cause gut damage and other illnesses. IL-10 is an immunosuppressive cytokine that is produced by the mammary cells and present n breast milk. IL-10 inhibits the release of pro-inflammatory cytokine which in turn dampens Th1 response. TGFÎ² (1 and 2) is taken up by the neonates gut at a high rate and is used in immune regulation to lessen inflammation and heal cells that were damaged by cytokines or infection in the intestines.
Immunoglobulins such as IgG, IgA, IgM and IgD are present in breast milk. These immunoglobulins are passively passed from mother to baby and helps the baby's immune system by making antibodies agans foreign antigens that enter their bodies.
All the listed components in breast milk helps to "kick-start" the development of the neonates' immune system where it can recognize self from non self and fight off any foreign pathogens. If there is a failure to this then and is thought to cause problems such as having inflammatory bowel disorders, allergy to some kinds of food related allergies and displaying autoimmunity.
Even though it is stated that "breast is best", it may not always be possible for a mother to breast feed their child. In some cases supplementary foods are used to provide nutrients for the neonate. Mothers who have infections such as HIV and other conditions that can be transmitted via breast milk are not advised to breastfeed as they can transfer it to their neonate. Mothers who are also on certain medications are not meant to breast feed. Rarely, some women are not able to breast feed as they are not producing enough milk. In these cases formula milk is the alternative used. It has its pros and cons.
Some parents chose to give their babies water to drink as part of their feed, weather before or after breast or bottle feeding. It is thought to be beneficial in countries that have hot climates as it keeps the baby hydrated and it is also said to be used to aid in digestion of milk after a feed. It is used to calm the discomfort of hiccups and helps with the teething stage as water has a high fluoride concentration, thus providing fluoride to help with the growth of teeth.
There are disadvantages of giving babies water to drink at too early age. Babies under 6 months of age have strong sucking reflexes and immature kidneys .Too much water can be taken in and can alter the sodium level in the neonate enough to affect brain activity and also cause fluctuating body temperatures, bloating, imbalanced electrolytes and weight loss. It is also thought that feeding a baby may result in them having a condition known as jaundice. This condition is more likely to occur in neonates who are being bottle fed as they received no colostrum to help them pass out the excess bilirubin. Water from the tab or from other sources may contain dangerous microbes and pathogens such as cholera which is quite frequent in parts of Africa where there isn't clean water. Contracting diseases like this poses a great health risk to a newborn neonate as its immune system is very weak and may not be able to fight off the bacteria. This disease causes diarrhea and vomiting and can sometimes be fatal for young babies.
Some mothers prefer to bottle feed their neonate from birth. Formula milk is tried to be made as identically similar to breast milk as possible. It provides babies with essential elements such as vitamins and minerals, fat, carbohydrates and proteins. Most formula milk is made from cow's milk and contains added vitamin k. There are benefits to bottle feeding one's neonate such avoiding any discomfort if breast feeding is difficult, it is easily accessible i.e. it can be done anywhere at any time, it is slowly digested as it has synthetic nutrients thus making the baby fuller for longer, so longer time between feeds, it reduces the chances of the baby having Haemorrhagic Disease of the Newborn (HDN) as there is added vitamin K. Pre-term formula is fed to babies who are born premature. It is specially deigned to help their immature systems develop. It has a high calorie content to help with weight gain. Some babies that are lactose intolerant ( cannot break down and digest lactose) can be bottle fed with soya milk as an alternative to breast and cows milk.
There can also disadvantages of bottle feeding a neonate with formula milk. They can become anemic because there isn't enough iron, fatty acids and vitamin E in the milk, they may have excess strain on their immature kidneys as there are excess amounts of sodium, protein and potassium. It also tend to cause gas, constipation, diarrhea, urine and ear infections and digestive problems. The major and most important disadvantage of giving formula milk is that is has no antibodies as it is synthetically made. It also lacks growth hormones and other constituents important in immunity. Therefore neonates who are formula fed are more susceptible to infections and illnesses as their immune system is not properly build up and their resistance to pathogens is low. Premature babies who are bottle fed can develop Necrotizing Enterocolitis (NEC) which is a condition where poor blood supply and infection causes damage to the intestines. There is a greater chance of bottle fed babies becoming obese than a breast fed baby. Tooth decay may also result from formula feeding. "Bottle mouth" occurs when a baby usually falls asleep with its bottle in its mouth and the natural sugars have continuous contact with the baby's teeth causing decay.
In conclusion, for a healthy mom, "breast is best" for her baby. She passively passes on antibodies through the placenta and through her breast milk that helps in the development of her neonates immune system. Babies that are breast fed for the first 6 months of life are more healthier and has reduced chances of contracting any form of pathogenic condition.