A human it consists of about 200 trillion cells and this multicellular organism that is made up of that much cells it arises, it originates from only a single cell and this single cell from this, from which the complete organism originates it is formed by fusion of male and female gametes, the male gamete sperm and female gamete ovum. Right, and when they fuse, when they undergo the process of fertilisation and they conjugates the cell that is formed is called Zygote. Zygote literally mean to conjugate so from zygote complete organism is formed.
Zygote, so what is the definition of zygote? Zygote is a cell that is formed by fusion of male and female gamete it is a cell that is formed by process of fertilisation and it has potential to form all the cells of an organism, it has potential to form complete organism, it is totipotent, it has potential to form total cells of an organism. Right, so this is zygote and what is an embryo? As the zygote grows and differentiates it forms first a ball of cell and then we will discuss later that then there is cavity is formed and then this it, it starts implanting into the uterine wall of female, of the mother. Right, after the process of implantation it is now called embryo.
According to literature before the process of implantation it is also called embryo but that is pre-implantation embryo. After the process of implantation is the actual embryo. So, zygote is an embryo or not?
Zygote is an embryo, zygote is single-celled embryo, single-celled pre-implantation embryo. Zygote is single-celled pre-implantation embryo. Right, then embryo in, what happens during developmental stages of embryo is that the primordial structures are formed from which different organ system originates and then primordia of different organs are formed from it.
Right, now at this stage you can see it does not quite resembles the actual human, the actual human baby but at about ninth week of gestation I mean ninth week after fertilisation, at about ninth week after fertilisation it actually start to resemble the baby of organism, organism to which it belong. In this case it starts to resemble human baby but it is not just resembling the human but most of the organ systems have been developed up till now. Right, above this point they start to differentiate and grow further, they have developed but they differentiate and grow further.
So, at this ninth week of gestation the embryo is given a new name and this new name is called foetus. Why it is given new name? Because it starts to resemble the actual organism, it start to resemble the baby. Now you know what is zygote, what is an embryo and what is a foetus.
Now let's discuss that what is an embryology? What do you think what is an embryology?
It's the study of an embryo. Most people think that it is study of embryo as its name indicate that it's the scientific study of an embryo but this is incomplete definition. Actually, embryology is not that simple. Embryology is study of developmental stages of an organism starting from development of gametes, male and female gametes till the birth of the new-born. So, in embryology what we discuss it includes the scientific study of development of gametes, I mean development of sperm and ovum, fertilisation, study of embryo, study of foetus and the birth process that is parturition.
So, study of embryo is just one aspect of embryology, it is one aspect of embryology but we have to study all these things in embryology. Foetus, study of foetus is also called fetology and it is considered to be a sub-branch of, it is considered to be a branch of embryology. We can study embryology at two levels general embryology and systemic embryology.
In general embryology courses in Bangalore, we study the synth, the synthesis or creation of primordia of different organ systems, the, the bilaminar and trilaminar germ disc, we will discuss these things later and in general embryology we do not focus on development of a particular system, we don't study it system wise but we study it in a chronological order that what happens on week zero, what happens on week one, week two, week three, month one, month two and so on. In this way we study embryology in general embryology but in systemic embryology we study system wise, we study the development of different systems, the development of cardiovascular system, the development of GIT, respiratory system and so on, system wise we study them. Right, now you cannot study systemic embryology directly without understanding the basics, the general embryology, the basic understanding of formation of different primordial structures.
So, first we will discuss general embryology and then we will discuss systemic embryology. Right, then embryology can be given a name according to the organism whose embryology we are studying. Right, for example we, we are right now studying human embryology but interestingly the embryology of human it resembles quite a lot with that of any other mammal.
Right, then there is medical embryology or clinical embryology. In medical or clinical embryology, we don't study just these things but we try to apply the basic concept of, the basic concepts of this, these things with clinical, with the clinical stuff, their clinical applications are also studied along with these basic things. Right, so also, we will discuss in clinical and medical embryology we will also discuss the, that how different drugs or different chemicals lead to different male formations in the baby and this branch of clinical embryology is called Teratology.
Right, so we are discussing human embryology but we are also discussing medical human embryology or clinical human embryology. Right, then there is a term called developmental biology. Is it same as embryology? No, it is not same.
Embryology starts from development of gametes up till the birth of baby. So, this development, do you think development starts, development ends when a baby is born? No, otherwise we all would, would have been a baby up till now. So, we do not remain baby fortunately or unfortunately we develop into a complete adult human and then we become an old man or woman and we have to die one day as well.
Dr. Kamini Rao Hospitals takes pride in being one of the best IVF Centres for their work, and the good quality embryos serve as testimony to the quality service we give to our patients and goodly patients. It's expected of us to show every patient their embryos before transferring them to their uterus. And our Chief Embryologist and Infertility specialist in Bangalore them about their cycle, quality of embryos developed, and giving them all the important details from number of eggs retrieved to the husband's sperm information. We do embryo transfer procedure. This procedure involves the transfer or placement of day two or day three embryos for cleavage transfer, and day five embryos for blastocyst transfer to the patient's uterus. It's performed by guiding the catheter containing the embryo with a probe using transvaginal ultrasound to the transfer site with or without anaesthesia.
So, embryology is up till here but developmental biology it also includes the developmental stages that transforms a newborn into a child and then child into an adult and then adult into a old man or woman. Right, so developmental biology it includes all these stages as well but embryology is a subset, you can say embryology is a subset of developmental biology. You have a question? Then what is developmental anatomy? Yeah, there is a term that is called developmental anatomy, it is a field of study and developmental anatomy is a subset, it is a branch of developmental biology and in developmental biology we study not just anatomy we also study the genetics of this, this process of development, we study the molecular biology of these steps.
Right, that how different genes work together to transform an organism from let's say child to an adult and so on. Right, the for example the genetics of ageing process, the molecular biology of ageing process and all these things but in developmental anatomy we all, we only study the structural changes that occur when, when transformation occurs, when this transformation occurs. For example fontanelles are closed and what is the process of closure of fontanelles, all these things we discuss in developmental biology and developmental anatomy.
Similarly you know Zephysternum ossifies in old age, all these things are related with developmental anatomy, it is a branch of developmental biology but if we discuss that what genes are involved in let's say ageing process that is developmental genetics you can say or developmental molecular biology rather. Right, then there are a few terms that are related with this embryology. Right, let's suppose if we divide this embryo into front and back part.
Right, anything that we equally divide it into two parts so anything that lies towards the belly on the interior side is called ventral. Right, vent means belly and anything that lies behind this plane is called dorsal, dorsum mean back. Similarly we can divide it into two equal parts upper and lower parts.
Right, so cranium is skull is also called cranium so anything that is superior or above this part it is called cranial and anything that is below this part towards this tail end caudal mean tail towards the tail so caudal is inferior or below this plane. Why we have introduced these terms to make a subject confusing for you? No, it is not. You know in adult anatomy we call this ventral as interior and dorsal as posterior and superior and inferior but why this confusing terminology is used here? Actually, let's suppose this is a female legs and you know this is, she is pregnant right now and in her, in her womb you can say here a baby is lying.
No, my question is that this is the actual presentation of baby inside. Now here you can see the head of baby, the head of baby's cranial or caudal should be called cranial. Yeah, head of the baby's cranial but it is superior or inferior? It is inferior with reference to adult anatomy it is inferior it is lying downward so to avoid the confusion with adult anatomy to avoid the confusion with anatomy of female body we use these terms ventral cranial caudal.
Right, so that we avoid this confusion so it is not to confuse you but to avoid the confusion. Right, finally I would like to discuss that who this series is for? This lecture series is mainly for medical and dental students. Embryology Training is mostly taught as a beginner course as a primer course in usually first year of medical school so during this lecture series I will assume that you don't know anything about embryology so I will start it with very basic concept at a very basic level.
Anyone who is interested in studying the developmental stages of a human is he or she is most welcome to join Medline Academics. In Medline Academics’ Embryology Training, our learning objectives are to define infertility and the commonly used terms in the field, identify causes of male and female infertility, understand basic infertility evaluation, understand infertility treatment, we'll also discuss about what the term assisted reproductive technology (ART) means, and lastly, we'll discuss about the various expansions of IVF / ART that are becoming increasingly relevant.