Posted in Psychology & Medicine

From Cell To Birth: A Man And A Woman

Organisms have the amazing ability to beget new life. In bacteria, this can be as simple as splitting itself in two. In humans, however, this process is much more complex.
As a sexually reproducing animal, both a man and a woman are required for the creation of a new person. The process, as complex as is it, is so intricately designed by nature that it could possibly be considered as one of the greatest abilities of the human body.

A man contributes sperm, providing half of the genetic material the future baby. The sperm also decides the sex, depending on whether it carries the X or Y chromosome. Note that gametes only carry half the number of chromosomes (which are usually paired) of a normal cell.
Sperm is made in the testes. Here, under the guidance of hormones such as testosterone and nurturing cells, they grow from a small stem cell, into a plump, round spermatocyte, until it is streamlined to become the sleek spermatozoa that people are more familiar with. All of this occurs as the cell journeys from the outside of the seminiferous tubule to the centre where it is released altogether with its fellow batch.
The sperm is still immature, the equivalent of a high-school graduate. It is expelled into the epididymis, a 4-metre-long tube packed full of concentrated sperm, acting as the “boot camp”. Here, the sperm is drained of extra baggage it is carrying, while learning how to swim effectively. It is stored until the time comes.

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A woman contributes an egg, carrying the other half of the genetic material required. It is significantly bigger than a sperm, and as such is produced in much fewer numbers. A woman, unlike a man, has a limit to how many eggs she can produce, and the moment her reservoir runs out is called menopause. Until then, she produces one (or more sometimes) egg every month according to her menstrual cycle.
An egg is developed within a follicle, that acts as a house and oestrogen factory until the egg is released. To get to this stage, it needs to defeat its competitors first. To prevent multiple pregnancies, the ovaries kill all secondary follicles except one dominant follicle. The follicle then ovulates, wherein the oocyte (egg) is expelled almost explosively, caught by the finger-like fimbriae, and then transported towards the uterus via the fallopian tube.
If the egg is not fertilised within a day, it dies and is later expelled with the endometrium, in what every woman knows as a period.

This is only the beginning of the long journey until the miraculous birth of a child.

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Posted in Science & Nature

From Cell To Birth: Sex

The two copulatory organs are the penis and the vagina. Both are designed to maximise the chance of a new life being conceived.

The penis is normally flaccid, but when stimulated through touch or erotic images and thoughts, it can become stiffened to eight times its original size. Contrary to certain slang words, the penis contains no bones – it is merely a sponge.
When the brain signals the penis to become erect, the sponge is relaxed, letting blood flood in, filling it like a balloon. This combined with two muscles and the sheath enclosing the penis achieves the erection which is critical in sex.

The vagina is shaped to perfectly accommodate an erect penis, and receives the sperm that will eventually fertilise the egg. As sex involves the piston movement of the erect penis within the vagina, it is bound to suffer chafing. So nature developed Bartholin’s glands that produce a lubricant, smoothing the process.
The clitoris actually shares its origin with the penis, and thus swells when sexually excited. It is also extremely sensitive.

The goal of sex is simple – excite the penis enough for the man to achieve an orgasm (note that female orgasm is optional, but ideal, for conception). When a threshold is reached, the brain sends out strong signals to squeeze sperm out from the epididymis, and seminal fluid from the prostate and seminal vesicles. The combined fluid (semen) shoots through over half a metre of tube until it is ejaculated out.
The semen collects in the vagina, where the cervix laps up the semen and transports it into the uterus. From here, the sperm’s adventure begins, facing many troubles to conceive the egg at the end of the line.

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Posted in Science & Nature

From Cell To Birth: Fertilisation

Once the sperm enters the vagina, the real battle begins. The vagina is highly acidic, an environment in which sperm can only survive 2~3 hours. It is crucial for the sperm to enter the uterus through the cervix, but only 1% of the 200~300 million sperm make it through.

Even within the uterus, they must brace harsh conditions as they travel against gravity. After about 5 hours of intense swimming, the sperm reach the top of the uterus. Here they face a choice: go left or go right. Half the sperm make the wrong choice and head down the eggless fallopian tube and ultimately die. The rest navigate their way through the maze of folds in the fallopian tube, often getting lost or sticking to the wall thinking that it is an egg.

About 200 sperm finally make it to the egg, which sits in the ampulla of the fallopian tube. But as always, there is competition even at this final moment. Only one sperm can win the race, and the fastest one will ultimately produce a new life.

When the first sperm touches the egg, a series of chemical reactions occur, essentially “priming” the sperm. This causes it to start the acrosome reaction, where it releases a hoard of enzymes from its head, digesting away the covering shell (zona pellucida) of the egg. It then becomes supercharged, using all of its energy to drive itself inwards until it reaches the oocyte within. As soon as this happens, the tail breaks off, and one final chemical reaction as the calcium level spikes occurs to release more enzymes that prevent the acrosome reaction in other sperm. It also solidifies the zona, forming an impenetrable shield to prevent other sperm coming in (polyspermy can lead to a failed pregnancy).

The calcium spike that causes the above cortical reaction also triggers the egg to divide, so that it reaches the most mature stage. The winning sperm can then combine its nucleus with the oocyte, forming the 46 chromosomes that will set the genetic basis of the new zygote (first stage of a baby).

To reach the egg, the sperm must travel over 20cm – beating its tail over 20,000 times. The probability that a certain sperm will fertilise the egg is 1 in 500,000,000.
Life starts under a near-zero probability condition.


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Posted in Science & Nature

From Cell To Birth: Implantation

When an egg is fertilised by the sperm, it is called a zygote. This zygote immediately starts to divide at an exponential rate, to achieve the feat of transforming from a single cell to a 3kg baby. The division and growth happens as the zygote slowly drifts towards the uterus, where it can secure itself.

30 hours after fertilisation, the zygote is now 2 cells.
72 hours, the zygote is now 16 cells.
96 hours, the zygote is now a ball of over 60 cells, and now called a morula.
108 hours, the morula has a cavity inside, and is called a blastocyst.
The blastocyst, essentially a shell of cells with a mass of cells at one point, hatches out of the zona pellucida as it is now much bigger.
To gain the massive amount of energy required for development, the zygote eats up simple sugars in the fallopian tube during its travel.

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As mentioned before, when pregnancy does not happen, the endometrium is shed and flushed out. To prevent this, the blastocyst secretes something called βhCG, keeping the corpus luteum alive, which secretes progesterone to maintain the endometrium. As the endometrium is the fertile “soil” where the embryo will grow, this is a vital step (βhCG is the hormone tested in a pregnancy test).
When the blastocyst reaches the uterus, it finds a safe spot on the endometrium, with the inner cell mass facing the wall. This is where implantation begins.

After clinging tightly to the endometrial cells, the blastocyst fuses some of its cells into a digging tool that can eat away at the endometrium. As it digests away the cells, the blastocyst slowly burrows in until it is completely embedded inside. Cells invade the hollowed space, firmly securing the blastocyst while destroying blood vessels and glands to release nutrients, securing a supply line. Now, it can start its rapid development into an embryo as it leeches away the mother’s nutrients.

A foreign body latching on to the host’s cells, digesting away tissue and leeching blood and nutrients – an embryo acts exactly like a parasite, to ensure that it can safely survive the 40-week gestation. In fact, an embryo can implant itself almost anywhere in the body, such as the fallopian tubes, ovaries or even the gut, as long as there is a secure blood supply. This is called an ectopic pregnancy, and can be an extremely dangerous scenario to both the mother and developing fetus.

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Posted in Science & Nature

From Cell To Birth: Growth

After implantation, the embryo quickly grows from a ball of cells into what will be a fully-formed baby. However, it first needs a way to feed: the placenta.
It is an organ that actively takes nutrients and oxygen from the mother’s blood, exchanging it for the embryo’s waste products. It is extremely effective in keeping the fetus alive and protects it from infections or the mother’s immune system.
The blood is carried by the umbilical cord, which plugs into the belly button. This cord is the lifeline throughout term, and disrupting the blood supply will lead to permanent brain damage or even death.

In the first 10 weeks, the blastocyst develops into a very primitive disk-like object that shares no resemblance to a person. It keeps growing and differentiating at a rapid rate (almost doubling in size per week) until it forms an embryo that is more familiar, roughly about week 6. Interestingly, a human embryo looks almost identical to embryos of rabbits, chickens, turtles and fish, showing how all animals shared a common ancestor in the course of evolution. At this stage, the embryo has features such as gills, a tail and a fish-like appearance.

After 10 weeks, the embryo has grown to about 5~8cm (almost 10~20 times the size at week 6), and is now called a fetus. It begins to properly grow organs, and resembles a miniature baby with primitive features.
It continues to grow for the next 30 weeks, continuously relying on the mother for nutrition and life support.

Many different factors contribute to premature birth and IUGR (intrauterine growth restriction), which leads to the birth of a small baby. This may result in less developed organs (especially the lungs) and may affect the health of the newborn throughout its life. There are also many poisons known to harm the development of the embryo/fetus, such as alcohol, nicotine, cocaine, heroin and much more. These should be avoided from a few weeks before conception onwards (even after birth while breastfeeding).

By about 38 weeks, the lungs (the last organs to fully mature) are ready and the fetus is upside down. It is ready to leave the womb, and thus sends a signal to the mother, known as labour. This is when the arduous process of childbirth begins.

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Posted in Science & Nature

From Cell To Birth: Childbirth

The onset of labour signals that the birth of the child is imminent. Strong contractions of the uterus under the influence of oxytocin cause intense pain for the mother. This escalates as oxytocin creates a vicious cycle for more and more powerful contractions. Other signs include a bloody show, where blood and mucus leaks out, and the water breaking, where amniotic fluid bursts out as the membranes rupture.
When the cervix has fully dilated to 10cm wide, the baby is ready to come out, and this is the end of the first stage. It may take over 24 hours for this stage to be over – all the while the mother is in extreme pain as her body transforms for the process.

The second stage concerns the delivery of the baby, and follows a precise series of steps.

  1. The baby, oriented head-down, facing either right or left, leans against the pelvis.
  2. The baby begins to descend, passing through the pelvis.
  3. It flexes its head as it comes through the cervix, turning towards the mother’s back as it does so.
  4. As the head crowns, the baby turns back to its side-facing position so the shoulders can come out.
  5. The rest of the body comes out with the shoulder. Forceps may be used to help.

The passage of such a large head and body is only possible through the massive dilation of the cervix, the stretch of the vagina, and the soft, malleable skull of the baby (a newborn’s head often looks conical and alien-shaped). Quite often, the opening of the vagina is not wide enough, and the opening may be cut open more to ensure it does not rip.

After the baby is safely delivered, the umbilical cord and the placenta are also delivered, thus ending the third stage (afterbirth). The cord is clamped and cut, and the baby is then thoroughly checked to ensure it is healthy and has no developmental issues.

Although in the past childbirth was extremely risky and often led to the death of the mother and/or baby in the process, nowadays protocols and health professionals ensure that both survive the procedure, thus ending the incredible 40-week journey until the birth of a new life. Only after understanding the arduous steps and the risks a mother takes to give birth to her child can one truly appreciate the value of life.

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