Life Begins at Fertilization with the Embryo's Conception Life Begins at Fertilization The following references illustrate the fact that a new human embryo, the starting point for a human life, comes into existence with the formation of the one-celled zygote: "Development of the embryo begins at Stage 1 when a sperm fertilizes an oocyte and together they form a zygote." [England, Marjorie A. Life Before Birth. 2nd ed. England: Mosby-Wolfe, 1996, p.31] "Human development begins after the union of male and female gametes or germ cells during a process known as fertilization (conception). "Fertilization is a sequence of events that begins with the contact of a sperm (spermatozoon) with a secondary oocyte (ovum) and ends with the fusion of their pronuclei (the haploid nuclei of the sperm and ovum) and the mingling of their chromosomes to form a new cell. This fertilized ovum, known as a zygote, is a large diploid cell that is the beginning, or primordium, of a human being." [Moore, Keith L.

Essentials of Human Embryology. Toronto: B.C. Decker Inc, 1988, p.2] "Embryo: the developing organism from the time of fertilization until significant differentiation has occurred, when the organism becomes known as a fetus." [Cloning Human Beings. Report and Recommendations of the National Bioethics Advisory Commission. Rockville, MD: GPO, 1997, Appendix-2.] "Embryo: An organism in the earliest stage of development; in a man, from the time of conception to the end of the second month in the uterus." [Dox, Ida G. et al. The Harper Collins Illustrated Medical Dictionary. New York: Harper Perennial, 1993, p. 146] "Embryo: The early developing fertilized egg that is growing into another individual of the species. In man the term 'embryo' is usually restricted to the period of development from fertilization until the end of the eighth week of pregnancy." [Walters, William and Singer, Peter (eds.). Test-Tube Babies. Melbourne: Oxford University Press, 1982, p.

160] "The development of a human being begins with fertilization, a process by which two highly specialized cells, the spermatozoon from the male and the oocyte from the female, unite to give rise to a new organism, the zygote." [Langman, Jan. Medical Embryology. 3rd edition. Baltimore: Williams and Wilkins, 1975, p. 3] "Embryo: The developing individual between the union of the germ cells and the completion of the organs which characterize its body when it becomes a separate organism.... At the moment the sperm cell of the human male meets the ovum of the female and the union results in a fertilized ovum (zygote), a new life has begun.... The term embryo covers the several stages of early development from conception to the ninth or tenth week of life." [Considine, Douglas (ed.). Van Nostrand's Scientific Encyclopedia. 5th edition. New York: Van Nostrand Reinhold Company, 1976, p. 943] "I would say that among most scientists, the word 'embryo' includes the time from after fertilization..." [Dr.

John Eppig, Senior Staff Scientist, Jackson Laboratory (Bar Harbor, Maine) and Member of the NIH Human Embryo Research Panel -- Panel Transcript, February 2, 1994, p. 31] "The development of a human begins with fertilization, a process by which the spermatozoon from the male and the oocyte from the female unite to give rise to a new organism, the zygote." [Sadler, T.W. Langman's Medical Embryology. 7th edition. Baltimore: Williams & Wilkins 1995, p. 3] "The question came up of what is an embryo, when does an embryo exist, when does it occur. I think, as you know, that in development, life is a continuum.... But I think one of the useful definitions that has come out, especially from Germany, has been the stage at which these two nuclei [from sperm and egg] come together and the membranes between the two break down." [Jonathan Van Blerkom of University of Colorado, expert witness on human embryology before the NIH Human Embryo Research Panel -- Panel Transcript, February 2, 1994, p. 63] "Zygote.

This cell, formed by the union of an ovum and a sperm (Gr. zyg tos, yoked together), represents the beginning of a human being. The common expression 'fertilized ovum' refers to the zygote." [Moore, Keith L. and Persaud, T.V.N. Before We Are Born: Essentials of Embryology and Birth Defects. 4th edition. Philadelphia: W.B. Saunders Company, 1993, p. 1] "The chromosomes of the oocyte and sperm are...respectively enclosed within female and male pronuclei. These pronuclei fuse with each other to produce the single, diploid, 2N nucleus of the fertilized zygote. This moment of zygote formation may be taken as the beginning or zero time point of embryonic development." [Larsen, William J. Human Embryology. 2nd edition. New York: Churchill Livingstone, 1997, p. 17] "Although life is a continuous process, fertilization is a critical landmark because, under ordinary circumstances, a new, genetically distinct human organism is thereby formed....

The combination of 23 chromosomes present in each pronucleus results in 46 chromosomes in the zygote. Thus the diploid number is restored and the embryonic genome is formed. The embryo now exists as a genetic unity." [O'Rahilly, Ronan and Mï¿½ller, Fabiola. Human Embryology & Teratology. 2nd edition. New York: Wiley-Liss, 1996, pp. 8, 29. This textbook lists "pre-embryo" among "discarded and replaced terms" in modern embryology, describing it as "ill-defined and inaccurate" (p. 12}] "Almost all higher animals start their lives from a single cell, the fertilized ovum (zygote)... The time of fertilization represents the starting point in the life history, or ontogeny, of the individual." [Carlson, Bruce M. Patten's Foundations of Embryology. 6th edition. New York: McGraw-Hill, 1996, p.

3] "[A]nimal biologists use the term embryo to describe the single cell stage, the two-cell stage, and all subsequent stages up until a time when recognizable humanlike limbs and facial features begin to appear between six to eight weeks after fertilization.... "[A] number of specialists working in the field of human reproduction have suggested that we stop using the word embryo to describe the developing entity that exists for the first two weeks after fertilization. In its place, they proposed the term pre-embryo.... "I'll let you in on a secret. The term pre-embryo has been embraced wholeheartedly by IVF practitioners for reasons that are political, not scientific. The new term is used to provide the illusion that there is something profoundly different between what we nonmedical biologists still call a six-day-old embryo and what we and everyone else call a sixteen-day-old embryo. "The term pre-embryo is useful in the political arena -- where decisions are made about whether to allow early embryo (now called pre-embryo) experimentation -- as well as in the confines of a doctor's office, where it can be used to allay moral concerns that might be expressed by IVF patients.

'Don't worry,' a doctor might say, 'it's only pre-embryos that we're manipulating or freezing. They won't turn into real human embryos until after we've put them back into your body.'" [Silver, Lee M. Remaking Eden: Cloning and Beyond in a Brave New World. New York: Avon Books, 1997, p. 39] Embryo development stages described in Bhagavata Purana, Mahabharata, Aitareya Upanishad | Ulta Din Embryo development stages described in Bhagavata Purana, Mahabharata, Aitareya Upanishad 02 Aug, 2016 Print this article Font size - 16 + Embryo development stages described in Bhagavata Purana, Mahabharata, Aitareya Upanishad Embryology is the science of development of an embryo from the fertilization of the ovum to the fetus stage. The earliest scientific approach is credited to Aristotle (384 – 322 BC), but indians have done a lot of scientific work, long before Aristotle.

Kapil Muni was probably the first man who studied embryo. Ancient Indian rishis had discovered the body secretions, which reproduce and called them Raja (ovum) and Reta (sperm). The Mahabharata, Shanti Parva, 301, 320, 331, 356, and the Bhagawata 3/31 state that one fine particle of Shukra conjugates with that of Shonit during copulation. The fine particles are sperm and ovum. They termed the conjugate product as ‘Kalala’, whereas modern science terms it as ‘Zygote’ or fertilized ovum. Bhagawata states that only in one night, which means 12 hours’ time, from the coitus, Kalala forms. Science admits that an ovum remains fertilizable for a short time, measured in hours, after its release from ovary.

“dasahena tu karkandhuh” |”kalalam tv eka-ratrena” |”panca-ratrena budbudam” |”pesy andam va tatah param” – 3-31-2 says Bhagavata Purana Translation : On the first night, the sperm and ovum mix, and on the fifth night the mixture ferments into a bubble. On the tenth night it develops into a form like a plum, and after that, it gradually turns into a lump of flesh or an egg. Bhagavata Purana describes all the microscopic changes taking place up to 15 days of the embryonic life, in a womb of a living woman. Science has 2 used microscopes, uterine wash-outs, post-mortem examinations, etc and arrived at same conclusion.

“bahv-anghry-ady-anga-vigrahah” |”linga-cchidrodbhavas tribhih” |”masena tu siro dvabhyam” |”nakha-lomasthi-carmani” – 3-31-3 In the course of a month, a head is formed, and at the end of two months the hands, feet and other limbs take shape. By the end of three months, the nails, fingers, toes, body hair, bones and skin appear, as do the organ of generation and the other apertures in the body, namely the eyes, nostrils, ears, mouth and anus. Bhagavata Purana states that the Linga i.e. external genitalia are formed in the third month. Science has revealed that external genitalia are present in 8 weeks’ old embryo. According to science male genitalia take their final form at the end of the 3rd month and Utero-vaginal canal also forms by the third month. Anus is formed some time after the genitals.

“aturbhir dhatavah sapta | pancabhih ksut-trd-udbhavah | sadbhir jarayuna vitah | kuksau bhramyati daksine” < Within four months from the date of conception, the seven essential ingredients of the body, namely chyle, blood, flesh, fat, bone, marrow and semen, come into existence. At the end of five months, hunger and thirst make themselves felt, and at the end of six months, the fetus, enclosed by the amnion, begins to move on the right side of the abdomen. In the 7th month the soul of embryo remembers everything about its past lives and also gets knowledge about the present life. Science cannot demonstrate this fact, but it can be inferred indirectly. The foetus of 7th month is viable, so its brain must be functioning in the 7th month. Electro-encephalographic tracings of the foetus may prove this in future. Kapil Muni describes that the foetus lies with complete flexion of its back and head. It is a fact and is scientifically proved. He also said that the foetus is unable to do respiration.

This is also true, because the foetus lies in the amniotic fluid and requires no breathing. The foetus gets oxygen and nourishment from the mother’s blood. Kapil Muni also says that in the 10th month the foetus is forced down by Prasooti Vayu, through the maternal passage. During this process of delivery, the foetus gets lot of troubles and loses its past memory. Science cannot give any proof for the loss of memory, but we can assess it by the fact that during delivery foetal head is compressed to a great extent. It may compress the brain, which in turn, may cause loss of memory. It is a proved fact that compression and concussion of human brain causes loss of memory. In 1972, Dr. H.P.Robinson of Glasgow University, showed using ultrasonic Doppler technique, that the heart begins at about 12-14 weeks. Bhagavata Purana states that two ears develop and gets knowledge of sound and directions. Two separate functions are attributed to the ears, clearly.

It is proved true during 1936 when Ross and Tait published their paper showing that the directions are recognized by the Labyrinth, situated in the Internal ears. Aitereya Upanishad (1/1/4 and 1/2/4, written in 6000 BC) mentions the same fact. The Bhagavata Purana gives microscopic details about the origin of a person (Purusha). It is narrated in a form of a story of He and She. (3/6/1-5) He noticed that unless He and She unite, reproduction is not possible. Therefore He conjugated with She. He entered into her 23 principles and brought together all the 23 principles. He stimulated her creative energy. Her 23 principles got activated, they conjugated with his 23 principles and the combined energy of those 23 principles reproduced the person. Modern science discovery has shown that 23 chromosomes of a sperm join with those of an ovum and then an embryo forms. Chromosomes are called as Gunawidhi in bhagavata purana and mahabharata because they control Guna (characters) and Widhi (functions).

Ancient Indian sages revealed that Jeevatma(soul) is not perishable. At the time of death, it leaves the physical body and goes to Bhuvarloka. Then it comes down with rainwater, enters a food grain, goes in to a male and occupies a sperm. With that sperm it enters the female and joins with an ovum to create an offspring. The sperm on which rides Atman gets success to win an ovum. During one coitus 200 to 300 millions of sperms are deposited in a female passage. Out of them only one enters an ovum. Why that one only? Science says it is a chance. And why not a woman gets pregnant everytime she mates a man during her fruitful days ? Embryo is the first descent of a fraction of Aatma. That part of Aatma is named as Praana. Praana enters in and guides the sperm to enter an ovum. So, only that single sperm which is driven by the child’s soul will enter woman’s womb. by Proud to be born in India face book Facebook Comments Embryology - Interactive Biology, with Leslie Samuel Embryology +1 Noun, pl., embryologies 1.

Branch of biology that deals with the study of the development of embryo (from fecundation to birth). (dictionary.com) 2. The scientific study of embryos. (wiktionary.com) 3. The study of the embryo and its development from a single-celled zygote (fertilized ovum) to the establishment of form and shape (at which point, if it is an animal, it becomes a foetus). a subfield of developmental biology. The branch of biology that studies the formation and early development of living organisms. The study of embryos and related factors. (biology-online.org) 4. The science of the development of an embryo from the fertilization of the ovum to the fetus stage.

(wikipedia.com) Word origin: From Greek ἔμβρυον, embryon, the unborn, embryo + -λογία, –logia, study of Search the Site Embryo and Embryonic Development - humans, body, used, water, process, life, plants, type Embryo and Embryonic Development Embryo and embryonic development Photo by: Noel Powell The term embryo applies to the earliest form of life, produced when an egg (female reproductive cell) is fertilized by a sperm (male reproductive cell; semen). The fertilized egg is called a zygote. Shortly after fertilization, the zygote begins to grow and develop. It divides to form two cells, then four, then eight, and so on. As the zygote and its daughter cells divide, they start to become specialized, meaning they begin to take on characteristic structures and functions that will be needed in the adult plant or animal. An embryo is a living organism, like a full-grown rose bush, frog, or human. It has the same needs—food, oxygen, warmth, and protection—that the adult organism has. These needs are provided for in a variety of ways by different kinds of organisms.

Embryology The study of changes that take place in the embryo is known as embryology. As one might imagine, the subject of embryology has fascinated humans since the dawn of time. Every culture has had its own theories and beliefs as to how the young of any species are created and born. The earliest formal writings on embryology can be traced to about 1416 B.C. in India. A document in Sanskrit (an ancient Indian language) describes the origin of the embryo being the union of the blood from the mother and semen from the father. Although this is not completly accurate, the document goes on to describe various stages of embryo development. Words to Know Differentiation: The process by which cells mature into specialized cell types, such as blood cells, muscle cells, brain cells, and sex cells. Ectoderm: The outer layer or cells in the multilayered embryo. Endoderm: The innermost wall of a multilayered embryo. Fetus: In the higher vertebrates, the complex stage of development that follows the completion of the embryonic stage until hatching or birth. Mesoderm: The central layer of cells in an embryo covered by three walls.

Ultrasonography: A process used to obtain "pictures" of the developing embryo using ultrasound. Zygote: A fertilized egg. Our modern understanding of changes that take place within the embryo can be traced to the rise of the cell theory in about 1838. Scientists finally discovered the process by which sperm cells from a male and egg cells from a female combine to form a zygote. Studies by the Austrian monk Gregor Mendel (1822–1884) opened a way to explain how genetic characteristics were transmitted from one generation to the next. Finally, in 1953, the discovery of the molecular structure of DNA (deoxyribonucleic acid) by the American biologist James Watson (1928– ) and the English chemist Francis Crick (1916– ) provided a chemical explanation of changes that take place during fertilization and development. Embryonic development The term embryonic development refers to changes that take place as an embryo matures. Those changes differ from plants to animals and from species to species. The discussion that follows focuses on embryonic development in humans.

The zygote forms in one of the mother's fallopian tubes, the tubes that connect the ovaries with the uterus. It then travels to the uterus, where it becomes affixed to the uterine lining. Along the way, the zygote divides a number of times. By the time it reaches the uterus, it consists of about 100 cells and is called an embryoblast. The exact day on which the embryoblast implants on the uterine wall varies, but is usually about the sixth day after fertilization. By the end of the first week, a protective sac, the amniotic cavity, begins to form around the embryoblast. Changes now begin to take place at a rapid rate. During week two of embryonic development, embryonic cells have begun the process of differentiation. The identical cells formed by the early divisions of the zygote are beginning to take on the different characteristic of muscle, blood, nerve, bone, and other kinds of cells. The embryo has burrowed deep into the uterine wall and is visible as a bump on the inner uterine surface.

This position permits the embryo to receive oxygen and nutrients from the mother's blood and to excrete waste products into her bloodstream. Miscarriages are not uncommon at this stage of pregnancy. The mother's immune system may react to cells from the embryo that it classifies as "foreign" and will begin to attack those cells. The embryo may die and be expelled. During week three the embryo grows to a length of about 0.08 inches (2 millimeters) long and has become pear-shaped with a rounded head and a tapered tail end. Three distinct types of cells can be distinguished. Ectoderm cells will form the embryo's skin; mesoderm cells its bones, muscles, and organs; and endoderm cells its digestive tract. Blood vessels have begun to form and, by day 20, the embryo has developed its own arteries and veins. Cells begin to collect along the embryo's back in a formation known as the neural tube, a structure that will eventually develop into the brain and spinal cord. During the fourth week, the embryo becomes C-shaped with an enlarged forebrain and a visible tail. Eye stalks and ear pits appear. Upper and lower limb buds are observable.

Lung, liver, pancreatic, and gall bladder buds emerge. The umbilical cord and early facial areas also form. By the end of this week, the embryo is comprised of millions of cells and is about 0.12 to 0.16 inches (3 to 4 millimeters) long. To the naked eye, the embryo looks like a small oval. Extensive neural (nerve) and cardiac (heart) development takes place this week. Early bone formations, that will later be the vertebrae, appear along the neural tube. Nerves, muscle, and connective tissues emerge around the primitive bone formations. By the end of fifth week, the embryo is almost 0.5 inch (about 7 to 9 millimeters) long and has all of its internal organs. The external ears emerge, and upper limb buds extend to form paddlelike hands. The mouth, stomach, and urinary bladder are present. Nose pits and eye lenses are visible. A few days after upper limb bud extension, the lower limb buds evolve further. Much more brain development occurs at this time, and the head enlarges, causing it to bend forward and appear large compared to the body. The umbilical cord becomes more clearly defined.

During the sixth week, the trunk straightens and upper limb development continues. The neck, elbows, and wrists form. Mammary and pituitary gland buds appear. Bone, cartilage, and muscles become defined around the spinal cord and in the embryonic chest. Early in this week, tooth buds appear. These buds will become the "baby" teeth that are lost in childhood. Rib cells line up horizontally along the trunk sides, and skin A human embryo at five to six weeks of development. (Reproduced by permission of Photo Researchers, Inc. ) layers that will hold sweat glands develop. The regions of the brain that will become the cerebral hemispheres are very prominent at this time. The embryo appears more human by this point. It is about 0.44 to 0.56 inch (11 to 14 millimeters) long, and its heart is beating at the rate of 140 to 150 beats per minute. During the seventh week, future fingers and thumbs are clearly visible on the hands. The torso lengthens, the tail begins to disappear, and the primitive organs continue to evolve. The heart has become divided into chambers. The cornea of the eye is also present.

By the end of this week, the embryo is about 0.8 inch (20 millimeters) long and about the size of a quarter. During the eighth week, remarkable development occurs. Nerve cells in the brain form at a rate of about 100,000 a minute. The top of the head becomes more rounded and erect. Between day 52 and day 56, the fanshaped toes go from being webbed to separated. The fingers are entirely distinct. The eyelids close over the eyes and become fused shut until about the twenty-sixth week. External genital (sex organ) differences begin to develop. All appearances of the tail are gone. By day 56, the embryo is roughly 1 to 1.25 inches (27 to 31 millimeters) long. Continued development The first three months of embryonic development are known as the first trimester, that is, the first three-month period of growth. At the end of the first trimester, the embryo looks like an adult, with all major organs having been formed. It is about 3 inches (7.5 centimeters) long. Still, an embryo born during this period trimester will not survive.

Additional time in the mother's womb is needed to permit further development of the organs. At the beginning of the second trimester, the growing organism is no longer called an embryo, but a fetus. Fetal development continues through the second and third trimesters until it is ready for birth at the end of the ninth month. Embryo diagnosis A number of techniques have been developed to study the development of the embryo. These techniques can be used to determine the presence of problems in the growing embryo. An ultrasound diagnosis can be performed at any time during pregnancy. Ultrasound diagnosis is a type of technology that uses high-pitched sounds that cannot be heard by the human ear. The sound is bounced off of the embryo and the echoes received are used to identify embryonic size. The technique is similar to the one used by submarines to locate underwater structures. By 18 weeks of pregnancy, ultrasound technology can detect structural abnormalities such as spina bifida (various defects of the spine), hydrocephaly (water on the brain), anencephaly (no brain), heart and kidney defects, and harelip (in which the upper lip is divided into two or more parts). Embryonic Transfer Imagine a baby with two mothers!

At one time, that idea may have seemed absurd. Today, the practice is common. It is accomplished by a procedure known as embryonic transfer. Embryonic transfer is carried out by removing the eggs from one female and transferring them into the body of another female. The embryos have, in effect, two mothers: the one that provided the egg necessary for fertilization and the one that provided the uterus during pregnancy. Embryonic transfer has been widely used among animal breeders to increase the number of offspring from a valuable cow, sheep, or horse. Some endangered species have benefitted from zoo breeding programs that use embryonic transfer. In humans, embryonic transfer is sometimes used as part of a fertility program. Egg donation or the use of a surrogate uterus offers hope to infertile women who have healthy eggs but lack either normal ovaries or a normal uterus. The technique used in embryonic transfer is typified in the procedure used with domestic animals. A prize female is stimulated with hormones (organic chemicals) to produce many eggs. These eggs are then fertilized, either through normal breeding or artificial insemination, with the sperm of a champion male. Next the embryos are flushed from the uterus with a saline (salt-water) solution.

Scientists use a microscope to search for the tiny clump of cells that signify an embryo at this stage. Once found, the embryos are ready for transfer. They can also be frozen for future thawing and use, if desired. When the embryos are implanted, a syringelike device delivers them into the uterus of the foster mother. If multiple embryos exist, multiple foster mothers are needed. Breeders can typically produce six calves from one embryonic transfer. In this manner, a single prized cow can produce many calves each year. With proper training and equipment, embryonic transfer can be mastered by cattle farmers themselves. A similar procedure is used in humans when a woman who is not able to produce eggs wishes to have a baby. Another woman is found to serve as an egg donor. The egg donor may be a close relative or may be anonymous, just as the men who donate to sperm banks are anonymous. Several donor eggs are retrieved through a minor operation. The egg from the donor and the sperm from the male are combined in the lab in a procedure known as in vitro fertilization. The fertilized egg is then implanted in the infertile woman's uterus for a normal pregnancy and birth. Three months of hormone treatment are needed to establish the pregnancy.

After that, the hormones produced normally by the woman are enough to maintain the pregnancy. Nine months later, the infertile woman gives birth to a baby to whom she bears no genetic relationship. Although much less common than in vitro fertilization, embryonic transfer offers couples a higher success rate. Chorionic villus sampling (CVS) is the most sophisticated modern technique used to assess possible inherited, genetic defects. This test is usually performed between the sixth and eighth week of embryonic development. During the test, a narrow tube is passed through the vagina or the abdomen, and a sample of the chorionic villi is removed while the physician views the baby via an ultrasound. Chorionic villi are small hairlike projections on the covering of the embryonic sac. They are rich in both embryonic and maternal blood cells. By studying these embryonic cells, genetic counselors can determine whether the baby will have any of several defects, including Down syndrome (characterized by mental retardation, short stature, and a broadened face), cystic fibrosis (which affects the digestive and respiratory systems), and the blood diseases hemophilia, sickle-cell anemia, and thalassemia. It can also show the baby's gender.

Human development of the unborn child - SPUC Human development of the unborn child The face and hands of an unborn child at five months (when abortion is still legal) Every human being starts developing well before birth, at the moment of conception. Unborn children develop and grow at a remarkable speed. Advances in technology over the last 50 years mean that we now know radically more about life before birth than any previous generation. With modern imaging technology - such as ultrasound scans - becoming increasingly widely used, now we all have the opportunity to gain an insight into the humanity of our younger selves. Here you will find descriptions of the stages of development of the new human being in his/her mother's womb. This extraordinary process is given visual form in the SPUC schools presentation through a remarkable video which takes students through each stage. We also sell life-size foetal models which are commonly used in educational displays and presentations. What do human embryologists have to say about the beginning of human life? "The scientific answer is that the embryo is a human being from the time of fertilization because of its human chromosomal constitution. The zygote is the beginning of a developing human." Keith L. Moore, T.V.N. Persaud, Mark G.

Torchia, Before We Are Born: Essentials of Embryology, 8th edition. Philadelphia, PA: Saunders, 2013. p.327 If there's any scientific terminology ahead that you don't understand, you can look it up in the Glossary , or go to our References and Medical advisers pages for more background. The first month Fertilisation Every human being begins life as a single cell, formed when father's sperm fertilises mother's egg. Fertilisation normally takes place in the mother's Fallopian tube, which connects the uterus (womb) with the ovary. The uterus is the size and shape of a large pear: it is made of muscle and it stretches to allow the baby's growth throughout the months of pregnancy. A woman ordinarily has two tubes and two ovaries, one at each side of her uterus. Every month one of the ovaries in turn releases an egg (ovum) which passes slowly along the tube towards the womb cavity If the egg is not fertilised within 12 hours or so of being released, it dies; it cannot develop further.

But if the woman has sexual intercourse during the days of her monthly cycle just before or at the time when an egg has been released from the ovary, then many sperm cells released by her partner may travel up to the Fallopian tube and one may fertilise the egg. When fertilisation is completed and the nuclei of egg and sperm have combined, a new being comes into existence and is capable of further development. Because the parents are human - belonging to the species Homo sapiens - the new being is also human. Fertilisation (by which we mean conception) marks the beginning of the human lifespan. A consultant specialising in the care of pregnant women writes: "Life does not begin with birth. When born, we are already nine months old... we have a responsibility to learn how to study the life in utero, and how to care for it"1 Heredity The cells of living beings contain DNA (deoxyribonucleic acid), the substance in the nucleus that enable cells to reproduce and transmit characteristics from generation to generation. When cells divide, the DNA takes the form of chromosomes - the units carrying the genes that pass hereditary features from parents to offspring.

Different species have varying numbers of chromosomes per cell: for example, a mouse has 40 while a cat has 38. Human body cells normally contain 46 distinctively human chromosomes. But an egg and a sperm cell contain only 23 chromosomes each, to allow for their adding together at fertilisation: sperm and ovum are termed gametes (from a Greek word for "marriage partners"). When they "marry" they make one completely new cell - the human embryo, zygote or conceptus - with 46 chromosomes carrying a fresh, unique combination of genes. At fertilisation this human embryo is about 0.1mm in diameter. Since characteristics come from both parents the zygote is never the same as, or part of, the mother, but is a genetically distinct individual. The colouring of hair, skin and eyes, the sex of the new human being, and factors influencing height and build, are determined at fertilisation by information on the DNA. Gender A baby's sex is determined at fertilisation. A chromosome from the father's sperm determines whether the child is male or female.

If an X chromosome is present the baby is a girl; if a Y chromosome is carried by the sperm instead, the baby is a boy. Twins Occasionally two eggs are released by the ovary and fertilised. This results in fraternal twins who are different in appearance and may be of different sexes because their genes form from two eggs and two sperm cells. Rarely, one embryo splits into two and both cells develop separately, as identical twins, similar in appearance. "They have the same genetic make-up and apparently the whole genetic message is the same in both of them. Nevertheless, they are obviously different human beings."2 Blueprint, builder and house The embryo is not simply a set of instructions for making a new human being, like a blueprint for building a house. A blueprint is inert and cannot carry out instructions, but the embryo is active and begins work at once. A house needs builders, carpenters, electricians and plumbers to complete it; but the embryo has the ability to grow spontaneously, moving on to other phases of development and constructing the skeleton, flesh, nerve connections and a waste disposal system of the human body.

After a house is built, a blueprint remains separate; but the embryo - already an essential human by virtue of the genes - is blueprint, builder and "house" together. Implantation After fertilisation the single cell splits into two, then the two cells double to four, four to eight, eight to sixteen and so on. Because the cell cluster looks superficially like a berry it is called the morula (Latin for "mulberry"), but the new life is always biologically human (species Homo sapiens). The journey along the Fallopian tube continues slowly for about four days. Growth increases. By the time the womb cavity is reached, the cell cluster becomes hollow and fluid-filled, and is referred to as the blastocyst. However, this is not an inert clump of cells but a busily developing human individual: differentiation (organisation into different parts and functions) is already taking place. Meanwhile the uterus is forming a spongy lining within which the embryo will implant. To achieve this the embryo burrows into the wall of the womb and is covered over by the lining of the womb. This begins 6 days after fertilisation and is completed within the next 7 days.

If fertilisation has not taken place, the lining of the uterus comes away at the end of the monthly cycle as the woman's menstrual period. But once implantation occurs, the embryo sends out a hormonal signal which prevents the mother's period. This is usually her first indication of pregnancy. Estimating length of pregnancy Generally a woman does not know the exact date of her baby's conception. When she misses a period she may take a pregnancy test; she should see a doctor promptly to obtain professional care for herself and her child. The doctor takes the date of the first day of the mother's last menstrual period as the starting-point for a 40-week pregnancy. This gives the baby's gestational age. However since fertilisation only occurs when the ovum is released from the ovary, some two weeks from the beginning of the last period, the baby's actual (conceptional) age is also two weeks less. Full-time delivery occurs 38 weeks after fertilisation, but 40 weeks after the mother's last menstrual period.

(In this booklet all developments of the embryo and foetus are dated from the time of conception, or fertilisation unless stated otherwise.) Protection and life support During and after implantation the embryo develops a protective, fluid-filled capsule which surrounds and cushions the developing body to prevent injury. Embryo and fluid are enclosed in two membranes, an inner amnion and an outer chorion. The chorion is covered in rootlike tufts, some of which form the early placenta - an organ made by the baby and the mother which transfers nutrients from the mother's bloodstream and removes waste products from the child's, though mother's and baby's circulatory systems remain separate. The placenta also produces hormones to maintain the pregnancy. In the ninth month it will alter the mother's hormonal balance and triggers off the birth process - although we are still unsure what causes labour to begin. The baby is connected to the placenta by the umbilical cord, the lifeline channelling nourishment in and taking wastes out, which will be cut close to the baby's abdomen at birth and will leave the mark of the navel. During pregnancy the baby obtains oxygen from the mother's blood via cord and placenta, so does not drown in the surrounding fluid.

Body development By 25 days from fertilisation the body is developing. Head and trunk appear and tiny arm buds begin to form, followed by leg buds. The early embryo seems to have a "tail", but this is really a protective covering for the spinal cord. Because the central nervous system (brain. spine and spinal cord) is so important, governing sensory and motor functions, the embryo's body is designed for rapid growth of head and back. By 21 to 25 days the baby's heart is beating. Other internal organs are present in simple form and functioning as they grow. Early facial features appear. The doctor who performed the first-ever blood transfusion to an unborn baby has described the embryo at the end of the first month from fertilisation: "By 30 days, just two weeks past mother's first missed period, the baby - one quarter of an inch long - has a brain of unmistakable human proportions, eyes, ears, mouth, kidneys, liver, an umbilical cord and a heart pumping blood he has made himself."3 The second month Growing The embryo increases in size from 5mm at four weeks to 4Omm by the end of the eighth week.

The baby in the womb is usually measured from the top of the head to the bottom of the spine (crown-rump lengths). Hands and feet By the sixth week from fertilisation tiny fingers appear, followed within days by the toes. By the seventh week the baby has individual fingerprints; no two sets of fingerprints are ever the same. Even in utero the baby has unique characteristics. Eyes and ears By six weeks the eyes which appeared in simple form in the first month develop lens and retina; the eyelids start to take shape. The ears continue to develop: by seven weeks the outer ear is present, and the inner ear, with its hearing and balancing mechanisms, is well established (see 'Hearing') Movements Spontaneous movements begin at seven weeks: "By 45 days, about the time of the mother's second missed period, the baby's skeleton is complete in cartilage, not bone, at first; ...

he makes the first movements of his body and new-grown limbs, although it will be another 12 weeks before his movements are strong enough to be transmitted through the insensitive uterus to be detected by the mother's sensitive abdominal wall."4 Brain function Brain waves have been recorded by EEG (electro- encephalograph) in the human embryo 40 days after fertilisation.5 Response to touch Human embryos of five weeks gestational age have been seen to move away from an object touching the mouth area. The sensitive area extends to include the rest of the face in the sixth and seventh weeks and the palms of the hands and soles of the feet in the eighth and ninth weeks respectively.6 A British study shows that the baby's movements begin at the same time as sensory nerves begin to grow into the spinal cord in the second month of pregnancy; the nerve fibres respond to touches to the skin and movement of the limbs: at this stage the baby's sensory nerves "appear to be more sensitive than those of the adult or newborn baby."7 From embryo to foetus Around eight weeks the baby's cartilage skeleton begins to turn into bone. The body is essentially complete.

Now the baby can be referred to as the foetus - a Latin term meaning "young, offspring." Latin- or Greek-derived names are given to human beings at successive phases of development, e.g. "zygote" for the newly-conceived, "neonate" for newborn baby, "adolescent" for growing-up teenager, "geriatric" for a pensioner. These terms simply identify different stages in the human lifespan which begins at fertilisation. The third month Development By the end of the twelfth week the baby measures almost 90mm and weighs 45g. The baby's face, at first broad, now becomes narrower; the eyes are closed for protection from about 10 weeks until the sixth month. Boyhood or girlhood is now obvious. Sensitivity Two British consultants, one caring for pregnant women and the other for children after birth, describe human development at this stage: "Nine weeks after conception the baby is well enough formed to bend his fingers round an object in the palm of his hand. In response to a touch on the sole of his foot he will curl his toes or bend his hips and knees to move away from the touching object.

At 12 weeks he can close his fingers and thumb and he will open his mouth in response to pressure applied at the base of his thumb."8 From a simple, generalised response to stimulation at 6 weeks gestational age, the foetus develops an almost complete range of responses to touches on the skin by 12 weeks.9 Feeling pain The brain and nerve fibres must be functioning for anyone to feel pain. Brain cells which are essential for consciousness in the adult are known to be present in the foetus by 10 weeks. Nerve fibres which transmit pain impulses are known to be present before fibres inhibiting pain are completed. According to a scholarly study of the available evidence, this "implies that the first trimester foetus may be more susceptible to pain than slightly older subjects."10 The first trimester of pregnancy is the first three months. In other words, if the baby can experience pain before the body's mechanisms to suppress pain have developed, this means that the baby may be able to feel pain at a much earlier stage than was previously thought, and perhaps even more keenly in the first three months of pregnancy than later.

The same study concludes that there is a likelihood that the "foetus has started to acquire a sentient capacity perhaps as early as six weeks, certainly by nine to ten weeks of gestation. Anatomical examination of such foetuses indicates the probability that differentiation sufficient for reception, transmission and perception of primitive pain sensation has already occurred."11 Practising for life outside the womb "At 11 weeks after conception the foetus starts to swallow the surrounding amniotic fluid and to pass it back in his urine. He can also produce complex facial expressions and even smile."12 Swallowing prepares the baby for taking in milk at birth. Thumb-sucking has also been recorded in the foetus.13 Foetal breathing movements have been detected as early as 11 weeks14. Although the baby does not breathe air inside the fluid-filled amnion, these movements help develop the respiratory organs. Four to five months Enlargement of baby and uterus By sixteen weeks the baby measures 140mm from crown to rump, just over one third of the size he or she will be at full term, and weighs around 200g. The heart now pumps 30 litres of blood a day.

The uterus expands and changes shape to accommodate the growing baby; pregnancy begins to show externally. The doctor can tell approximately how advanced the pregnancy is by locating the fundus (the top part of the uterus between the Fallopian tubes, which stretches upwards towards the mother's chest as the uterus expands). Hearing There is evidence that from four months the foetus responds to sound. Doctors testing unborn children for deafness, while monitoring their reactions to noise with ultrasound (a technique for visualising the children in utero), have observed eye movements and "blink-startle" responses in foetuses of 16 to 32 weeks gestation.15 The authors of a textbook on the unborn which is used in medical schools world-wide explain why the foetus can hear while immersed in fluid: "The ears of the foetus function as early as the fourth month, and there is evidence that it hears a good deal. One might object that if a person dives under water and someone else talks to him he hears only a muffled sound. This is true. The sound is muffled by the cushion of air remaining in the auditory canal outside the ear drum.

But the foetus living in the amniotic fluid has no muffling air cushions around its ear drum - and water conducts sound better than air does. The silent world of the foetus (or, below the surface of the ocean) is a fantasy, unfounded in reality."16 The baby hears sounds from the outside world as well as from the mothers heart and digestive system: "In fact the inner ear of the foetus is completely developed by mid-pregnancy, and the foetus responds to a wide variety of sounds. He is surrounded by a constant very loud noise in the uterus - the rhythmical sound of the uterine blood supply punctuated by the noises of air passing through the mother's intestine. Loud noises from outside the uterus such as the slamming of a door or loud music reach the foetus and he reacts to them."17 Tests using different types of music indicate that the baby even appears to have preferences: "A four- or five-month-old foetus definitely responds to sound and melody - and responds in very discriminating ways. Put Vivaldi on the record player and even the most agitated baby relaxes ...

In a film made at the City of London Maternity Hospital, Yehudi Menuhin demonstrated that it was possible to contact the unborn via music."18 Babies learn to recognise their mothers' voices whilst in the womb19 and even to recognise stories which are read to them in the womb20 Newborn babies whose mothers watched Neighbours during pregnancy have been seen to stop crying and become alert when they hear the theme tune after birth.21 Sensitivity to light From the sixteenth week the foetus responds to light. If a blinking light is shone on to the mother's abdomen, the foetal heartbeat fluctuates.22 "In late pregnancy, some light penetrates through the uterine wall and amniotic fluid, and foetal activity has been shown to increase in response to bright light."23 The womb is a more stimulating environment than some people think; its occupant is alert and responsive. The fifth month and beyond After 20 weeks the baby is 190mm from crown to rump and weighs 460g. Head hair, eyebrows. eyelashes and nails are growing.

To protect the baby's skin from prolonged contact with the amniotic fluid, a greasy substance called vernix covers the body. Between this stage and birth the baby will gain weight and will develop an insulating layer of fat beneath the skin. He or she will also receive maternal antibodies against some infections as a temporary protection until the infant's own immune system is better developed. Waking and sleeping Foetal activity is affected when the mother is tired or under stress.24 The baby is usually most notably active when the mother is lying down at night. The mother feels the baby's kicking and may notice sharp movements when the baby gets hiccups after drinking the amniotic fluid or practises its breathing movements. In later pregnancy the foetus has been observed to show "behavioural states" - waking, calm sleeping, and "rapid eye movement sleep" which is associated with dreaming in adults.25 The quest for comfort The baby still has some room to manoeuvre inside the womb and seeks the position which feels most comfortable: "It is very easy to demonstrate now with ultrasound that the babies make the most of all the space and room available to them ...

We know that foetal comfort determines foetal position, that changes in maternal position provoke baby to seek a new position of comfort."26 Survival outside the womb If the baby is born too early, there is still a good chance that he or she will survive, given special medical care. A document from the Royal College of Obstetricians and Gynaecologists (the professional body of doctors who treat pregnant women) states: "In 1984, 72 per cent of liveborn infants of 22 to 27 weeks' gestation born at the Bristol Maternity Hospital survived, as did 64 per cent of infants of 500 to 999 grammes birthweight."27 These percentages had increased from previous years. With advances in technology and in understanding of human foetal development, premature babies' chances of survival are improving. These figures refer to the length of the pregnancy from the time of the mother's last menstrual period. and not to the age of the baby from fertilisation. which would usually be two weeks less.

(see 'Estimating length of pregnancy', section 1, above) Birth Labour and delivery In the last weeks of pregnancy the baby lies head downwards, as the head is normally the first part to emerge at birth. Occasionally, if a baby's position of personal comfort is not changed to fit in with the normal birth process, there may be a "breech" presentation - rear end first - which needs medical attention. The mother's labour begins as (following hormonal signals including that from the placenta) the muscular uterus contracts to expel the baby. The cervix (neck of the womb) gradually opens to allow the baby to pass into the vagina (birth canal). The amnion tears and releases its fluid (this is often referred to as "the waters breaking"). Contractions become more frequent as the baby is pushed through the cervix and vagina. If the mother has attended ante-natal classes she will have learned what to expect and how to control her breathing and pushing process. A midwife and/or a doctor supervises the mother and baby during labour. The baby's father may wish to be present to lend support and encouragement and to see his baby from the moment of birth.

After labour, which varies in length but usually lasts some hours, the baby is born. A gasp and a cry start the lungs working. The umbilical cord is cut and the baby is examined and weighed. Normal birthweight is approximately 3,400 grammes or about 7½ lb, but considerable variations sometimes occur because of genetic factors, health problems and outside influences such as the mother's smoking during pregnancy. Finally the membranes and placenta are expelled. The baby no longer needs a direct life support system as he or she can now breathe air and take milk. The same before and after birth After delivery babies who have been studied in utero show the same individual behaviour that was observed while they were in the womb: "After birth you see many babies sleeping in the odd positions that they chose to rest in within the uterus prior to birth ... The good drinkers in utero are the good drinkers in the nursery and the dainty, tedious swallowers in utero are the tedious ones out of the uterus as well ... The behaviour traits also bridge the birth."28 From the one-celled zygote to the multi-million-celled infant and adult, every human being is a distinct individual.

Mother and baby Ante-natal care A doctor caring for a pregnant woman has two patients, the mother and the baby. As soon as he is aware of the pregnancy, the doctor will take the needs of both into account. The doctor should know about a pregnancy as early as possible so that any medicines he prescribes are safe for both his patients. This is particularly important as the pregnancy may, of itself, cause symptoms such as headaches and fatigue for which the mother may seek medical treatment. If the mother has "morning sickness", caused by normal hormonal responses to pregnancy, a harmless antacid can be given. Tablets of iron and folic acid (a B vitamin) are routinely prescribed to prevent anaemia: it is safe and important to take these. Pregnancy can also lead to an increased sense of well-being and contentment. Many women find that their complexions improve and they feel more relaxed as a result of the hormonal changes in their bodies. During pregnancy the mother should attend her doctor's ante-natal clinic for regular checks on her weight and blood pressure, and on her baby's heartbeat, growth and position in the uterus. Arrangements will be made for the baby's birth at home or (more likely) in hospital.

Mother and perhaps father may also attend parentcraft classes: there they will learn how the baby develops, how to care for mother and child before and after birth, and how to cope with the process of birth itself. Nutrition & diet The mother does not need to "eat for two" in the sense of increasing her food intake. Adequate amounts of protein, vegetables, fruit and milk should be taken (particularly milk, since the mother needs to replace the calcium taken from her system to make the baby's bones). The doctor will advise on any special dietary needs. During pregnancy a mother can expect to gain around 12kg (allowing for baby. placenta, fluid and her own physical changes), but weight gain should not be excessive and too much carbohydrate should be avoided. Foetal breathing movements are substantially decreased if the mother smokes cigarettes during pregnancy. There is evidence that prematurity, stillbirth and slower development may be related to this practice.29 It is important not to smoke during pregnancy or when near a pregnant woman.

Even moderate amounts of alcohol taken in early pregnancy may affect the child's growth and development (including that of the brain); heavy drinking carries a still higher risk.30 During the first three months of pregnancy the developing baby may be harmed by certain infections and drugs. For example, rubella (German measles) may damage the baby's heart, eyes or ears if the mother contracts it in early pregnancy. Such harm can be prevented by receiving immunisation against rubella as a small child or as a schoolgirl, long before pregnancy occurs. However, by the end of the third month the baby is less likely to develop a disability because the body is well developed. Post-natal care Mother and baby will be visited by the midwife for some days after the birth to check that all is well with both of them. The mother should return to her doctor six weeks later for her post-natal examination to be sure that the uterus has regained its former shape and that she is otherwise in good health. Download our Pregnancy Guide Download our free Pregnancy Guide for more information on life before birth! Fill in the form below to download our guide now:

Question: What science is concerned with the development of an embryo from the fertilization of the ovum to the foetus stage?
Answer: Embryology