7 weeks old human embryo from Anatomy & Physiology, Connexions Web site.
Have you ever wondered how a single cell can turn into a complex human?
Embryology is a branch of science that studies the formation, growth, and development of embryos. It deals with the stages of prenatal development, starting with the formation of gametes, fertilization, formation of the zygote, development of the embryo and fetus, and ending with the birth of a new person. The two main procedures involved are growth and differentiation. Embryology can also be seen as the road to the formation of various tissues and organs in the body that are specialized to perform certain functions.
Embryology is the steps by which an organism develops from a unicellular zygote into a multicellular organism. Embryo development is complex and well-regulated. The development of the human embryo is divided into the following progressive phases:
organogenesis (formation of organs)
The human embryo is regarded as a fetus nine weeks after fertilization. There is no unique feature that differentiates the embryo from the fetus. The term fetus suggests that the embryo can be perceived as a human. The embryo is pink on a red background. The embryo has a slightly rounded part at one end with an extended tail-like piece that is bent in a C-shape. Two small bumps are visible on the sides, where the limbs will later form.
Read on why this can be a daunting topic for teachers and students, five suggestions for improving the learning experience, and thoughts on why virtual labs make things easier.
There are three reasons why embryology can be difficult for even the most academically sound students.
Before the popular use of the microscope and the birth of cell biology in the 19th century, embryology was based on descriptive and comparative studies. Not being able to visualize the process can frustrate learning and make it difficult for students to stay excited.
Each cell contains the whole genome (a perfect genetic blueprint), but only a specific set of genes is expressed at any given time. The set of expressed genes gives the cell its traits, functions and, if necessary, specialization. It is an ever-changing process in which gene expression is turned on and off in response to internal and external stimuli. A gene is said to be expressed when it is transcribed and a functional product is produced. The direct products of transcription are RNA molecules: messenger RNA (mRNA), regulatory RNA ( such as miRNA), or structural RNA ( such as rRNA). Regulatory and structural RNA is already a functional product, while mRNA needs to be translated into protein. In the case of protein-coding genes, the abundance of mRNA reveals the level of gene expression. Various techniques can be used to measure gene expression levels, such as next-generation sequencing or quantitative PCR.
Gene regulation is vital in all organisms. Both prokaryotic and eukaryotic organisms continually turn their genes on and off in response to internal and external environmental conditions. Initial gene regulation saves more energy than later regulation. For example, selectively blocking transcription is much more energy efficient than waiting for transcription and translation to complete before finally degrading or inhibiting proteins. In prokaryotic organisms, gene expression is usually regulated during the transcriptional step using operons. An operon is a group of genes with a single promoter that can be regulated by positive and negative controls. Most eukaryotic organisms are multicellular and consist of different cells with different functions despite having the same genome. To make different types of cells, eukaryotic organisms rely on gene regulation. Gene regulation is important for retaining the proper specialized function of each cell. In eukaryotic organisms, gene regulation can occur at various stages.
Embryology provides proof of interrelationships between very diverse groups of organisms today. Mutational changes in embryos can have serious outcomes in adults so embryonic development tends to be preserved. As a result, structures absent in some groups often appear in the embryonic form and disappear when the adult or juvenile form is attained. For example, all vertebrate embryos, including man, exhibit gill and tail slits at some point in their early development. They vanish in adults from terrestrial groups but persist in adults from aquatic groups such as fish and some amphibians and humans have a tail structure during development that is missing at birth.
Model organisms are species used to study certain aspects of biology and are non-human species that can be studied notably to understand certain biological phenomena in the hope that discoveries in model organisms will offer insight into how other organisms, especially the human body function. The following is a list of common model organisms:
Prokaryotes: E. coli
Eukaryotes: Yeast, C. elegant, fruit fly, Arabidopsis thaliana, chicken, mouse
Each has specific advantages. The type of experiment will determine the choice of animal to use. The following advantages of model organisms apply to different degrees for each model organism.
Easy to grow and care for under laboratory conditions
Short generation time
A large number of descendants
Well studied genome
Healthy embryos, such as chicken embryos, can be easily manipulated
Reduced complexity compared to humans
Efficient genome manipulation
Fewer ethical issues compared to human studies
Base position in evolution tree
Now that you have a good foundation let's go over five ways you can make embryology lessons more interesting, easier, and fun for you and your students.
Proposed by Marcello Malpighi, early embryology is known as preformationism, the theory that organisms evolved from pre-existing miniature versions of themselves. Aristotle proposed the now-accepted theory of epigenesis. Epigenesis is the idea that organisms develop from seeds or eggs in a series of steps. Modern embryology evolved from the work of Karl Ernst von Baer, although close observations were made in Italy by anatomists such as Aldrovandi and Leonardo da Vinci during the reawakening era.
Gallus gallus domesticus (chicken) is an important model organism for developmental biology. Chicken domestication is an activity that has been going on for more than 8,000 years. The earliest reference to the chicken as a model organism is attributed to Aristotle, who described the chicken embryo in his Historia Animulum. Chickens are great model organisms because eggs are readily available and can be used to observe and manipulate live embryos. The relatively large size of the embryo makes it easy to observe the embryo.
By the time the chicken egg is laid, the embryo has divided and has begun gastrulation, forming a bilayered blastoderm of nearly 60,000 cells. If the eggs are not incubated, development practically stops at this stage but continues as the temperature rises. Chicks hatch 21 days after oviposition. The stages of development of the chicken embryo are defined in the Hamburger-Hamilton series.
Place the egg sideways in the incubator and mark the top surface of the egg with an X. The yolk rotates so that its brightest point, the embryonic blastoderm, rotates from below the air chamber to its highest point. Therefore X indicates the position of the embryo. Incubate eggs at high relative humidity (>50%) and in the range of 37. 5 to 39°C.
Follow these steps for windows:
Clean the eggs with 70% ethanol to avoid contamination.
Pierce the blunt end of the egg with the tip of a scalpel, to open the air chamber.
Insert the 19 g 5 ml syringe through the hole, point the needle tip down and take 2- 4 ml of liquid albumin.
Clear tape should be used to cover the top of the egg.
Make a hole in the center of the X with the tip of the scissors to let air in.
Set the egg aside for a few minutes while the embryo sinks just below the shell into the space created by the extraction of the egg white.
Use the scissors to make a circular incision in the shell about 15 mm in diameter just above the blastoderm. Don't make a full cut. Leave the casing and tape so you can turn the cut casing over.
Now observe the embryo under a dissecting microscope. Ensure to close the tape before incubating, otherwise, the eggs will dry out. Chicken embryos are ordered according to a series known as the Hamilton and Hamburger series. Each phase is labeled and timed and fully identifiable. Estimated time is:
Stage 6, at 24 hours: head folding level. somites not visible, primitive streaks posterior to the embryo, neural plate at the anterior end.
Stages 7-14 are based on the number of pairs of somites seen.
Stage 13, after 48 hours: nineteen pairs of somites. The head is partially or completely turned to the left. The cranial and cervical indentations create a wide curve. Telencephalon extension. The atrioventricular canal is indicated by contraction. The fold of the amniotic head covers the forebrain, midbrain, and anterior part of the hindbrain.
Stages 15 - 35: The appearance of certain structures in the limbs and the length of the toes are used to determine the stage.
Stages 36 - 46: These stages are determined by the development of the eyelids, feathers, and beak.
The rat (Mus musculus) is a classic mammalian model. The genetic and physiological similarities to humans, combined with short generation times and low maintenance costs, make them ideal model organisms. There is a complete catalog of mouse strains that have been genetically engineered to study certain diseases that would not occur naturally in mice. The data obtained from this study is an additional advantage of mice over other mammals.
Using next-generation sequencing (NGS), a massively parallel sequencing technology that offers ultra-high scalability, and speed. This technology is used to determine nucleotide sequences across the genome or target regions of DNA or RNA. NGS is revolutionizing the biological sciences, enabling laboratories to perform various applications and study biological systems at a level never before possible and permitted, sequence the whole genome on the fly, sequence depth of the target region, use RNA sequencing (RNA-Seq) to discover new RNA variants and splice sites or to quantify mRNA for gene expression analysis, analysis of epigenetic factors such as genome-wide DNA methylation and DNA-protein interactions, sort cancer samples to check for rare somatic variants, tumor subclones, explore human microbiome and Identification of new pathogens.
Figure 3: X-ray of Liebenberg patient (left) and normal hand (right)
Liebenberg syndrome is a condition that involves abnormal hand development, resulting in distinct hand deformities of varying severity. In people with this disease, the bones and other tissues in the elbows, forearms, wrists, and hands show specific similar structures to the lower extremities. Liebenberg syndrome is characterized by stiffness of the elbow joint and fusion of the wrist bones. The arms of the Liebenberg patient generally resemble the legs. This partial transformation is caused by faulty homeotic gene expression.
Liebenberg syndrome is inherited dominantly. There is currently no cure, but it is possible to surgically remove some of the wrist bones to create more correct wrist function.
A good mnemonic for the progressive stages of human embryonic development is FaCt By GlOVe excluding lowercase letters as shown:
F - fertilization
C - cleavage-stage
B - blastula stage
G - gastrulation
O - organogenesis (formation of organs)
V - vertebrate formation
A unique way to teach embryology is through a virtual laboratory simulation. At Labster, we’re dedicated to delivering fully interactive advanced laboratory simulations that utilize gamification elements like storytelling and scoring systems, inside an immersive and engaging 3D universe.
Check out the Labster embryology simulation that allows students to learn about embryology through active, inquiry-based learning.
Learn more about the embryology simulation here or get in touch to find out how you can start using virtual labs with your students.
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