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Structural Embryology

Structural Embryology

Saul Yudelowitz BSc (Hons)

In order to understand embryology, the best place to start is pre embrologey, the fertilization phase, how the menstrual cycle works, as this then is the reason for why certain events occur in embryology. Life is basically the ability to replicate. During a normal 28 day cycle, Estrogen spikes at two different times, this is a result of LH.

LH and FSH come from the anterior patuity, estrogen comes from the ovary. The spikes in estrogen help with the uterus lining, leading to two separate thickenings of the uterus wall. During the fertile period of replication sperm will penetrate the egg. Note that a woman is not fertile during the entire cycle, only for about 8-10 days. Sperm can survive for up to 2 days. You can understand why the male does not live as long as the female by looking at embryology.

Once the egg is fertilized it has a 6 day travel period from the fallopian tubes. The ovaries are separate from the fallopian tube so bacteria canít cross. The ovary is ruptured out; the expansion is related to estrogen. At menopause a women stops releasing her eggs but there are still many left. This is why the duration of fertility is affected by the internal and external environment. While the egg travels down the fallopian tubes it then has a 3 day period that it can embed into the uterus, this occurs during the second estrogen spike.

The uterus lining becomes even more thickened, the method estrogen uses for this is by affecting the coagulation of blood. Sodium reduces coagulation through its ionic charge. In the arteries along the lining is free flowing calcium. As blood leaves in the centre, sodium rich zone and moves to the calcium rich zone as in an injury, it begins to coagulate. The uterus lining thickening of blood is like jellow, there is low sodium and quite high calcium. Estrogen is like a venus fly trap, it folds around and traps calcium.

With regards to endocrine function, the body uses the size of a gland for output. The bigger a gland the more product it will produce. This is why the testis shrinks if oral testosterone is consumed.

After fertilization the cell divides into 2, 4, and 6 cells. At between 6-8 cells it becomes a tight capsule as the egg hasnít expanded from its original size, the cells inside press up onto one another. Ultimately the cell membranes make contact with one another and this is the start of communication. Prior to this occurring a cell can be removed with no affect to the fetus however after this point the fetus will be affected. Up to the 6-8 cell range DNA is the driver however once the cell membranes are pressed together, communication begins and affects growth. This is why dinosaur DNA canít reproduce a dinosaur, cell communication is also required.

In cold temperature the blood flows better, when you heat it up it slows the flow, hence the increase in temperature just before the second estrogen spike.

Once the fertilized egg embeds and reaches about 16 cells it begins to divide into a horse shoe shape. The fertilized egg is the source of the amniotic sack and the placenta. If the fertilized egg doesnít implant the progesterone levels continue to rise. Progesterone has the opposite effect to estrogen on calcium and a miscarriage occurs. This is why during a normal menstrual cycle when the ankles swell and salt is craved, the body is asking for water as the progesterone has affected the miniralcorticosteroids.

Sodium and calcium are highly involved in fertility.

Once the fertilized egg implants it is still at the pre embryonic stage. For a three week period the neural crests and troughs develop as well as the three tissue layers, ectoderm, mesoderm and endoderm. During the 4-8 week period organogenesis occurs, this is a very important time for the correct development of all the organ systems. After 8 weeks everything is formed and the fetus just grows in size. One third of all fertilized eggs are spontaneously aborted during the first third of the first trimester. The internal and external environment also affects this and it could rise as high as 50%.

At 4 weeks the thyroid is under the tongue the thymus is in the cervical canals. This is where the lungs develop from. The ectoderm and mesoderm work together to form the neuroendocrine glands. This combination results in a surface structure with tubes. The ectoderm and mesoderm together also for the lungs and hence the big surface area with tubes and sacks. It is in these structures that high rates of cancer are typically found. They have a big surface with little caves all over them. The endoderm and ectoderm form the gut together early on in the development. The gut needs to physically move food and sense what is inside the gut. Once the food moves into the small intestine, taurine is released.

Taurine puts things to sleep, when released from the gall bladder under strict control of the nervous system; bacteria are put to sleep for up to two hours. This is why the small intestine is small. As soon as the food enters the large intestine, the appendix releases a huge cascade of antigens. As the bacteria arrive at the large intestine they are small compared to human cells. The antigens mark the bacteria for the immune system to direct a response. This is why people why have had their appendix removed tend to become ill easier and more often after the removal of their appendix.

All the threats to the body are things that come into the body so the body separates air and water to allow it to be processed with the thyroid. Lungs develop outside the rib cage as the lungs donít want any calcium. In the digestive tract the high innervations starts early on, this is why a knife to the abdomen is very painful, an area that is very richly innervated with nerves to control digestion. The position of the placenta helps fold the digestive tube through the action of food traveling through. The parathyroids descend from the ear, to the side of the thyroid. They migrate a little late. Itís the same with the kidney and adrenals. The arterial system develops like a railway line. At the top, the horizontal parts for the lungs develop while branching off, below this the next horizontal folds in on its self forming the heart. As do the kidneys. The left side leads the development. This is why it is common to see the left ovary is higher and the left testis slightly lower than the right.

Do remember that the ovaries ascend and the testis descends. This arterial railway line ensures a very early blood supply to the ovaries and testis. The left side develops about a week before the right. The gut and heart are on the left, once developed they release enzymes, which stop duplication of the organs. While the left side develops earlier than the right it is a little clumsier and the right a little more robust be it a little later. The adrenals are close together initially and then descend. From the bladder the kidneys move upward. The urethra is created when the kidneys ascend. The two organs stop moving when they meet, hence the adrenal just above the kidneys.

The position of the ovaries and testis relative to cortisol (which is produced from the adrenals) affects how the pelvis develops.

The thyroid sits under the tongue initially. Thyroid has C cells that produce calcitonin. This regulates the laying down and taking away of calcium. This is why under the jaw no calcium is deposited. If the thyroid stays under the tongue for too long this typically results in a cleft pallet as there is not enough calcium for normal formation. As the thyroid descends to the trachea, it controls the calcium deposits. This is why there is very little calcium along this path. The cervical canals where the lungs develop and where the thymus slides in are connective tissue and therefore have no calcium. The thyroid slides down into its final position, the parathyroid sits on the side of the thyroid, the thymus slides down and rests on the bronchial tubes. The thymus ends up connecting to the thyroid. This is how the thymus and thyroid communicate through adult life. This is part of the respiratory tree for keeping the lungs healthy, free from calcium and bacteria. The thymus conditions the cells from the bone marrow as well. This is why in AIDS the CD3 and CD5 cause problems. The thymus goes all the way down to contact the liver. If you place food under the tongue the liver will sense it immediately. There is therefore a direct communication from under the tongue to the gut.

The liver begins development near the umbilical cord, it also stops calcium. The adult the liver has the first choice on vitamin K, which also traps calcium. Vitamin K is highly concentrated in the liver. The kidneys begin functioning early on and this is where the urea comes from. The gut and liver develop from similar tissue and donít migrate much. The fetus processes food from the umbilical vein, this is also how it learns to process food and so what the mother eats will have a significant affect on what the child can process in the future.

Nerves to muscle communication is late, after 9 weeks, this suggests that the peripheral nerves can regenerate. There are about 8 crests in the neck area, which develop into different organs like the tongue and lungs etc. The organs that develop from here have very little calcium or no calcium. The neural tube at the end of the neural cord stretches quite a bit. Similar to a piano string at full stretch, when they come back towards each other they can expand. The head side grows more. The tail begins to disintegrate.

At about the 8th week the curvature of the spine opens up, this is when it looks like a fetus. Time laps photography shows the cells moving around like an anthill. A cell will migrate from one hip and the opposite shoulder, where they migrate forms a trail of nerves and arteries. Where these two migrating cells meet an ear forms. This is also how our fingerprints form along with many others functions. With these migrations the whole structure shifts and moves around.

Part of the reason for the testis descending and the ovaries ascending is, the testis produce a lot of testosterone. This attracts calcium, while this occurs it thickens the pelvic girdle. Testosterone as a hormone is the most potent at regenerating nerves. Testosterone causes the tailbone to curve inward and thicken. In the female, the ovary sits right near the main source of cortisol, the adrenals. Cortisol releases calcium, this is what initiates the menstrual cycle. Since the ovary is near this cortisol and cortisol also cuts off testosterone, the female pelvis calcifies slower. Puberty in women typically occur at about 19, in men this occurs at 17. Testosterone causes calcification faster; this is why men reach puberty before women.

We are born mostly with cartilage and lay down calcium until puberty. When a bone grows, the body lays down calcium from the center. The part that is calcified stops growing, as this process progresses to the joint, it leaves the cartilage with no calcium. As estrogen causes calcification slower the female pelvis grows larger. The male pelvis also has a much poorer blood flow compared to the female pelvis. Because of the location of the prostate the male pubic symphasis is calcified by puberty. As the ovaries ascend in the female the prostate doesnít develop. A female has the reminisce of the prostate in the vagina which is a rough ending with very little nerve endings. This area is commonly referred to as the G spot. As erection and ejaculation is a highly neutrally involved process the testosterones ability to develop nerves is well used here. This also explains the main differences of stimulation to the male and female. When a male has had spinal surgery that affects ejaculation, this function can still be evoked by electrical stimulation of the prostate. The prostate could be considered as the little brain in the male as there are so many nerves in it. This is why erectile function can be lost if the prostate is damaged during surgery. When comparing the male and female pelvis, the female pelvis has less nerves with a better blood supply while the male has more nerves with lower blood supply.

The head of the penis become the clitoris in the female. The foreskin becomes the hood. The inner labia is developed from the same place that the under part of the penis comes from. The folds of the testis are the outer labia in the female. All the male and female reproductive structures arise from the same tissue. There are estrogen receptors in the breast, which attract calcium via estrogen and this grows the breasts, the penis has testosterone receptors and this has a similar affect. Calcium is also needed for bigger muscles.

The lack of fluidity in males compared to females is in part due to the calcium levels. This is the reason women are target at having low calcium by the pharmaceutical industry. So the question women should ask: do you want more calcium and the affects of what males have?

The thyroid each time we eat and swallow releases a little iodine and calcitonin. This goes with food to block calcium absorption. The thymus blocks calcium from the ribs, so the lungs can stay flexible. The liver is a very effective calcium blocker, so during our adult life calcium is constantly being blocked from foods that we eat. There is no doubt that we need calcium however its best form for us is in the from of animal bones. If you eat sardines, eat the bones, however taking calcium supplements is working against your body. As the left side develops first the right has a more robust development, especially with the nerves, this is why most people are right side dominant. The musculoskeletal system is layered down but its main development comes from movement. The heart really looks after the brain and lungs; it is less concerned with the peripheral. Every muscle has one-way valves. You could look at a muscle as a one-way heart valve. Sitting and holding the muscles tight reduces blood flow. Think next time you have tight neck and shoulder, see what works better, exercise or stretching?

Please do note that this is a simplified version of embryology.


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