Links to the rest:
- Prologue- The Reproductive System
- Part One- Reproduction
- Part Two- Pregnancy
THE STORY SO FAR...
Following puberty, spermatogenesis (sperm production) and oogenesis (ovum production) has begun, creating spermatozoa and ova out of spermatogonia and oogonia. If a guy and a girl do it at the right time of the month, the sperm and the egg get to meet. Thousands of sperm dissolve the acid holding together the cells surrounding the egg, while one lucky sperm gets to penetrate through. Its male pronucleus joins with the female pronucleus in the ovum, resulting in a zygote, which is a diploid cell with 46 chromosomes (as opposed to the ovum and sperm being haploid cells with only 23 chromosomes each).
The zygote then divides until eventually it forms a hollow ball of cells called a blastocyst. This blastocyst implants itself into the uterus, where it gains nourishment while it continues to grow. The embryo and several embryonic membranes form inside the blastocyst- the amnion protects the embryo, the yolk sac and allantois become the umbilical cord and the chorion becomes part of the placenta. Many chorionic villi are formed from the cells of the chorion, providing a large surface area for materials to diffuse back and forth across the placenta. After two months, the embryo becomes a foetus, which continues to grow and grow until it's ready to be born.
THE STORY CONTINUES...
After gestation (i.e. the embryonic and foetal period), a series of events known as labour occurs. This results in parturition, or birth of a newborn baby. Labour has three stages as we shall soon see...
STAGE ONE: THE DILATION OF THE CERVIX
During the final three months of gestation, the uterus begins undergoing contractions which become stronger and more frequent until they occur around every 30 minutes or so. This marks the beginning of the first stage of labour, which lasts around 8-9 hours for the first child and 4 hours for every subsequent child.
Waves of contraction travel from the upper part of the uterus towards the cervix. These contractions are kinda like peristalsis in the alimentary canal, but instead of pushing food along, a baby's being pushed more deeply into the pelvis. During the contractions, the muscle fibres in the uterus shorten slightly, pulling on the cervix, which causes the cervix to shorten and open up (dilate). Eventually, the cervix opens to about 10cm in diameter (wow... that's big...) and the uterus, cervix and vagina form a single, curved passage known as the birth canal.
Once the cervix has opened up (dilated) completely, this stage is complete.
STAGE TWO: EXPULSION
(No, seriously, this stage is called the stage of expulsion.)
Normally, this stage begins with the breaking of the waters- the amniotic membrane bursts and fluid gushes out. However, the breaking of the waters doesn't always occur at this stage- it can occur earlier or later.
The baby is pushed through the fully dilated cervix due to the contractions of the uterus and the woman contracting her abdominal muscles. As this happens, the baby's head turns to face the woman's back. With each contraction, the baby moves outwards. Between contractions, the baby moves back in slightly, but, overall, the baby is pushed out into the world. Once the head has emerged (assuming it's not a breech birth), the baby turns so that it's facing either of the mother's hips, allowing the shoulders and the rest of the body to move through the birth canal more easily. Being born head-first allows the baby to start breathing before it's fully born.
Sometimes the pressure placed on the baby's head may cause it to be pushed slightly out of shape, but not to worry- the bones of the skull are still quite pliable at this point and are separated by joints. The head will resume its normal shape a few days later.
This stage of labour (during which, as my book helpfully states, the woman "is really in labour" due to all the effort required) lasts from 20 minutes to 2 hours. (I feel sorry for the woman. I can't imagine going through all that pain for 20 minutes, let alone 2 hours!)
STAGE THREE: AFTER BIRTH
Right after birth, the baby is still connected to the placenta by the umbilical cord (though it's now able to breathe on its own). The cord is then clamped, tied and cut, and the arteries and vein inside the cord begin to contract. (They may have already begun to contract before the cord was cut.) A few days later, the stump falls away, leaving only the navel, or umbilicus.
The baby comes covered in a protective waxy layer called the vernix. Special cleansing agents are used to wash the baby so that not all of the vernix is removed. This reduces the incidence of skin infections.
Around 5 minutes after the baby is born, all the other stuff in the uterus (i.e. the placenta, umbilical cord, amnion and chorion) are expelled. These are called the afterbirth. Not much blood is lost as the placental vessels constrict and the uterine vessels are squeezed shut due to the contractions of the uterus. Infection can occur due to the large amount of exposed tissue, but modern sanitation methods help to reduce the risk.
CHANGES AT BIRTH
Lots of changes have to occur when the baby is born in order to allow it to function somewhat independently of its mother. Although babies still need a lot of looking after, at least they don't need the mother's help to get oxygen and so on! Some changes also occur in the mother's body.
Perhaps the most dramatic changes occur to the baby. Part of this is due to the baby's circulation system being slightly different before birth and after birth. The main differences include several extra veins and arteries present before birth (including the umbilical arteries, the umbilical vein, the lung bypass and liver bypass) and the presence of an opening between the two chambers of the heart (also generally only present before birth). Let's look at these in more detail:
The liver bypass: After blood returns from the placenta via the umbilical vein, part of the blood will travel through the liver and into the inferior vena cava, though most of it will travel through the liver bypass. The liver bypass is called the ductus venosus, which also flows into the inferior vena cava. Even though not much blood is passing through the liver, it's not a problem since the mother's liver can take care of all of the baby's needs. Blood stops flowing through the ductus venosus after birth, causing it to constrict until it is closed off, forcing all blood to pass through the liver instead.
The lung bypass: The foetus' lungs are collapsed and still not functioning, resulting in a high resistance to blood flow. Therefore, little blood passes through the lungs- most blood from the right ventricle passes through the ductus arteriosus, or lung bypass, instead. This takes the blood from the pulmonary artery to the aorta. When the baby is born, the lungs begin to function and no longer offer so much resistance to blood flow. This results in less blood flowing through the ductus arteriosus, resulting in it turning into fibrous tissue within a few weeks. Normally, the baby will start breathing at the shock of birth, but if not, the increase in carbon dioxide levels in the blood following clamping of the umbilical cord stimulates the respiratory system.
The foramen ovale: The foramen ovale is an oval opening between the two chambers of the heart. It allows blood to flow directly from the right atrium to the left atrium. This helps the highly oxygenated blood get to the foetal tissues faster, and anyway, the right side of the heart isn't needed as much at this point (as the lungs aren't functioning yet). Once blood starts flowing to the lungs, more blood enters the left atrium, causing the pressure to increase. This increased pressure forces the flap of the foramen ovale to close off. If this fails to close, the baby ends up with a "hole in the heart" and a lack of oxygen in the blood. This can be fixed via surgery.
Other changes in the circulatory system after birth include an increase in the number of red blood cells to carry around oxygen. Meanwhile, the number of white blood cells begins to decrease. The baby's heart also pumps quite quickly after birth- 125 to 130 beats per minute- in order to keep the baby warm outside the uterus and to provide enough oxygen for increased muscular activity. Another way oxygen levels increase is through rapid breathing- newborns breathe at around 45 breaths per minute for the first two weeks, though that eventually begins to slow down.
Changes also occur to the mother after birth. After birth, the mother undergoes a period known as puerperium, when the organs return to their non-pregnant state. The uterus continues to contract, normally painlessly, though some women may find these contractions painful too. These contractions, as well as the gradual shrivelling of the muscle fibres, cause the uterus to shrink, flattening the abdomen. As the uterus shrinks, it discharges a mixture of blood and the breakdown of tissues. This discharge can last for 3-6 weeks. Other changes that occur after pregnancy include the blood quantity returning to normal (after increasing during pregnancy) and a variety of emotional changes. The reproductive system is fully back to normal when the periods come back- this can be 10 weeks after birth (if the woman isn't breastfeeding) or 20 weeks or so after birth (if the woman is breastfeeding).
A BIT MORE ABOUT THE BABY...
Postnatal care is the care that needs to be given to the newborn baby. Newborns are small, and their surface area is quite large compared to their mass. This means that they can lose or gain heat and lose water relatively quickly, so care needs to be taken to keep the baby hydrated and warm- but not too warm! As for diet- breast milk is ideal for human babies. However, the mother needs to make sure that she's eating a healthy, balanced diet so that there are plenty of nutrients in her breast milk.
WAYS OF GIVING BIRTH
Aside from an all-natural birth, there are several ways to help a mother give birth to babies that just don't want to be born, for whatever reason (e.g. the foetus is positioned weirdly- I'll get to this later- or the woman's pelvis is too small). These include:
- Forceps and ventouse delivery- The forceps are like a kind of "pincer" that's used to grab onto the baby's head and pull the baby out (probably not as violent as it sounds). This can cause damage to the mother's tissues, so some doctors prefer using a ventouse, or vacuum extractor, that consists of a flat suction cup which fits against the foetus' head. The doctor can then pull the baby out this way.
- Caesarean section (a.k.a. C-section)- An incision is made in the lower part of the woman's abdomen, through the abdominal wall and the lower part of the uterus. The baby is then removed, and the openings are repaired with stitches.
- Induced labour- The doctor may decide to induce labour for a variety of reasons, including incompatibility of blood groups between foetus and mother, high blood pressure, bleeding, or a pregnancy that has gone on for over 42 weeks. There are several methods of inducing labour- one is to cut the amnion, and another is to give intravenous oxytocin, which stimulates contraction of the uterus. These methods, sometimes used together, generally result in delivery of the baby within 24 hours.
Oh, and about the foetus being positioned weirdly- 3% of babies are in the breech presentation (buttocks down rather than head down) at birth. If the baby is still in this position by the 34th week, the doctor will try to turn it around via external manipulation. If this doesn't work, then a caesarean section may be used to deliver the baby.
OTHER STUFF ABOUT BIRTH
There are many places to give birth. Some women give birth in a place they'd originally planned to give birth at (e.g. a hospital, at home etc.) while some end up giving birth in a less-than-desirable place (like in a car on the way to the hospital). Although some women prefer the warm, friendly environment of a home birth with the presence of a midwife, hospital births have the advantage of the availability of doctors and specialised equipment if needed.
And that, my friends, ends my little "mini-series" thingymabob about birth! Next up: growth and development!
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