Back to PHI305 Home Page

Rachel Scott, Joni Payne, Kelly Hagan, Mickey Sutti, and Kelly Kincer

Fetal Development
 
  1. Fertilization and the Prenatal Period
  Fertilization: The union of an egg cell and sperm cell to form the zygote, which contains twenty-three pairs of chromosomes.

 

Prenatal Period: The period of development that occurs after fertilization and before birth and usually lasts for 40 weeks (10 lunar months); the prenatal period can be divided into three stages: a period of cleavage, an embryonic stage, and a fetal stage.

 

    1. Period of Cleavage—1st week
    2. Zygote>1st Cleavage>Morula>Blastocyst>Implantation

       

    3. Embryonic Stage—2nd week through 8th week
 
    1. Primary Germ Layers—responsible for forming all body organs
 
    1. Ectoderm: Cells of the ectoderm will give rise to the skin, the nervous system, and the lining of the mouth and anal canal.
    2. Mesoderm: Cells of the mesoderm will eventually form muscles, bones, the cardiovascular system, and the reproductive system.
    3. Endoderm: Cells of the endoderm will be important in forming the digestive tract, respiratory tract, and the urinary tract.
 

In the 3rd week of development, a slight depression, the primitive groove, forms on the ectodermal surface of the embryonic disk. With time this groove will evolve into the neural tube of the spinal cord and brain. In the 4th week, the flat embryonic disk becomes cylindrical in structure.

 

 

 

 

    1. Important Structures
 
    1. Placenta: The cells forming the wall of the blastocyst make
    2. up the trophoblast. One region of the trophoblast layer develops most rapidly and becomes the chorion, or the fetal placenta. The endometrium in which the chorion is embedded—the decidua basalis—is the maternal portion of the placenta.

       

      CHORION (embryonic portion of the placenta)

      + DECIDUA BASALIS (maternal portion of placenta)

      = PLACENTA

       

      This vascular relationship is established by the 3rd week of development. The embryo receives nutrients, hormones, maternal antibodies against disease, and DRUGS and ALCOHOL through the placenta. Also, CO2 and O2 are exchanged via the placenta.

       

    3. Amnion—develops around the edge of the embryonic disc in the 2nd week. Amniotic fluid fills the space between the amnion and the embryo. As the embryo is transformed into a cylindrical structure, the margins of the amnion close around the embryo so that the embryo is cushioned by the amnion and its fluid.
    4.  

    5. Umbilical cord—As the amnion encircles the embryo, the umbilical cord is formed by the gathering of the tissues that attach the embryo to the placenta. The cord consists of three blood vessels—two umbilical arteries and one umbilical vein.
    6.  

    7. Yolk sac—appears in 2nd week, and is attached to the underside of the embryonic disk. It forms blood cells and early sex cells, and becomes partially incorporated in the umbilical cord.
    8.  

    9. Heart—begins as a tube during the 3rd week. It beats and circulates blood during the 4th week. The tubular heart folds on itself and subdivides into the four chambers characteristic of the adult heart. By the 6th week, the chambers and valves are formed.
  3. Additional Physical Characteristics (Handout)

 

a. First 4 weeks

 

Spinal Cord¾ During the second week, a dark mark appears on the back of the embryo, denoting the position of the spinal cord.

Heart¾ By the end of the third week there is now a heart beginning to beat.

Sensitivity¾ In the third week, the embryo enters a sensitive phase of development when all major organs are forming. Drugs, alcohol, smoking and infections can harm the embryo.

Size¾ 1/8 inch in length and weigh less than .03 ounce

 

b. Up to 8 weeks

 

Heart rate¾ beats at 140-150 per minute approximately twice the rate of yours.

Body shape¾ the embryo’s head is still very large in comparison to the body and is bent forward on the chest. The body begins to straighten and elongate.

Internal organs¾ All organs will now be present and most major structures will have been formed.

Reflexes¾ the embryo can respond to touch. External features¾ the embryo’s eyes become pigmented and the first visible signs of nostrils, lips and ears also appear. The embryo’s muscles start to build and by the seventh week of life the first embryonic movement can be detected using ultrasound. Fingers and toes also appear. Size¾ 1inch in length and weighs .1 ounce

 

 

C. Fetal Stage¾ 9th week through birth

1. Month 3

 

2. Month 4

 

3. Month 5

 

4. Month 6

 

5. Month 7

 

6. Month 8

 

7. Month 9

 

 

 

 

II. Pain

 

Definition of Pain

 

Evaluation

 

A. Anatomical and Functional Requirements

 

1. Development of sensory receptors

2. Development of synaptic contacts

3. Corticogenesis

 

B. Fetal Movements

 

1. Simple Reflex Responses

2. Signal Processor

 

 

 

 

III. When does life begin?

 

A. Different Theories

 

1. Point of Viability

2. "Quickening"- 18 weeks

3. Brain wave detected- 6 weeks

4. Heart starts beating- 3 weeks

5. Conception--- this is a biological and medical answer

 

B. Other "opinionated" Theories

 

1. Creation of soul

2. Consciousness of self

3. Give and receive love

4. Recognizable sex organs

5. First breath--- Supreme Court decision

 

C. Age of Viability

 

1. Definition of Viability

2. Changes in age of viability

a. 40 years ago

b. 20 years ago

c. today

3. Why has age of viability changed?

a. medical know-how

b. sophistication of life support equipment

c. viability actually measures---

4. Why can a child survive after age of viability?

 

D. Decision for life’s beginning

 

1. Process

2. Biological fact, not religious belief

3. What is your opinion?

  



 

Fetal Development Write-up

The presentation explaining the development of a fetus biologically and psychologically was delivered by Rachel Scott, Joni Payne, Kelly Hagan, Mickey Sutti, and Kelly Kincer. The objectives of the presenters were to (1) give a factual, unbiased description of human prenatal development and (2) offer some of the existing theories on when human life begins.

Before human development can begin, fertilization, which involves the fusing of an egg and sperm cell to become a zygote, must occur. The period of development that occurs after fertilization and before birth and usually lasts forty weeks is called the prenatal period. It can be divided into three stages: a period of cleavage, an embryonic phase, and a fetal phase (Hole et al., 1994).

The first week of development after fertilization is called the period of cleavage. Shortly after fertilization, the zygote cleaves into two cells, which gradually yield four cells, eight cells, and so on. Around the third day of development, the pre-embryo exists as a solid ball of about sixteen cells called a morula. By day four, the morula has hollowed out into a fluid-filled ball called the blastocyst. The cells surrounding the blastocyst are called trophoblast cells, and a group of cells in the center, dubbed the inner cell mass, will eventually form the embryo. On or about the sixth day of development, the blastocyst implants into the endometrial lining of the mother's uterus (Hole, 1994;Traurig, 1997).

The second through the eighth weeks of development mark the embryonic phase. Early in the embryonic phase, the cells of the embryo begin to differentiate into three layers of cells; the endoderm and the ectoderm form first, and the mesoderm forms in between shortly thereafter. These layers will eventually give rise to all of the body organs (Hole, 1994). The ectoderm will form the nervous system, the skin, and the lining of the mouth and anal canal; the mesoderm will form the muscles, bones, the cardiovascular system, and the reproductive system; and the endoderm will form the digestive tract, respiratory tract, and the urinary tract (Traurig, 1997).

In the third week of embryonic development, a slight depression, the primitive groove, forms on the ectodermal surface of the embryonic disk. This groove is the beginning of the neural tube of the brain and spinal cord. At this point of development, the embryo exists as a flat disk of the three distinct layers of cells. In the fourth week of development, the flat disk becomes cylindrical in structure-as the human body is cylindrical, with the skin on the outside, skeletal muscles in the middle, and the gastrointestinal tract in the center (Hole, 1994).

A great deal of development takes place in the embryonic phase. In the class presentation, a few of the most important structures were chosen to explain in detail. These were the placenta, amnion, yolk sac, umbilical cord, and the heart.

One region of the trophoblast layer (defined above), develops most rapidly and becomes the chorion, the embryonic portion of the placenta. The endometrium in which the chorion is embedded-the decidua basalis-is the maternal portion of the placenta. The placenta is an important vascular relationship between the mother and the embryo, and is established by the third week of development. The embryo receives nutrients, hormones, maternal antibodies against disease, and drugs and alcohol through the placenta. Also, carbon dioxide and oxygen are exchanged via the placenta (Traurig, 1997).

Early in the embryonic phase, the amnion, which contains amniotic fluid, forms on the upper margin of the disk, while the yolk sac, which produces blood cells, forms on its underside. As the embryo becomes cylindrical in shape, the amnion encloses it, thereby cushioning it in amniotic fluid. The yolk sac and other tissues on the embryo's underside are gathered in this process and become the umbilical cord, which extends from the umbilicus of the embryo into the placenta and is important in the vascular relationship between mother and embryo. It consists of two umbilical arteries and one umbilical vein (Hole, 1994).

The last structure discussed in the presentation was the heart. It begins as a tube in the third week, and by the fourth week it beats and circulates blood. Gradually, the tubular structure folds on itself to form the four chambers of the adult heart. By the sixth week, all chambers and valves are formed (Traurig, 1997).

At the end of the fourth week, the embryo is 1/8th of an inch in length and it weighs less than three hundredths of an ounce. The embryo has grown 10,000 times bigger than the original egg on the day of fertilization.

The second four weeks of development is a time of extremely rapid and crucial development as the embryo quadruples in size. Its cells are constantly differentiating to form new structures. The brain begins controlling the movement of muscles and organs. The brain waves can be detected and recorded. The head is growing rapidly to accommodate the enlarging brain. The embryo's head is still very large in comparison to the body and is bent forward on the chest. The body begins to straighten and elongate. All major organs develop- the stomach, liver, spleen and intestines. The heart takes on its final form and beats strongly. It beats at 140 to 150 beats per minute, which is twice the rate of ours.

Some pigment can already be detected in the eyes, which are covered and very far apart. The internal and external parts of the ears begin to form, and the taste buds start developing. The tooth buds of all non-permanent teeth are now in place. Under the skin of the face, primitive facial bones emerge and begin to fuse together. The first visible signs of the nostrils, lips and ears appear.

The embryo's arm and hands develop faster than its legs and feet. This trend will continue after birth-that the baby will be able to grasp objects long before it can walk. The embryo's muscles start to build and by the seventh week, the first movement can be detected using ultrasound. The embryo can also respond to touch. The embryo sucks its thumb; it can grasp an object placed in its hand and can also swim with a natural swimmer's stroke. At the eighth week the embryo is one inch in length and weigh a tenth of an ounce. Even at such a small size the fetus now has everything present that will be found in a fully developed adult (Stoppard, 1993).

The fetal stage begins at the end of the eighth week of development and lasts until the time of birth. Although existing body structures continue to grow and mature, only a few new parts appear. The rate of growth is great, and body proportions change considerably.

At three months, growth in length of the body is accelerated while the growth of the head slows. Lung and brain growth is largely complete. Unique fingerprints are evident and never change. The arms achieve the relative length they will maintain throughout development, and ossification centers appear in most of the bones. By twelve weeks all the organs and systems of the body are functioning. External reproductive organs are distinguishable as male or female. The only major activity from now until birth is growth-the increase in size. At this point the fetus is three inches long.

The fetus now sleeps, awakens, and exercises its muscles by turning its head, curling its toes, and opening and closing its mouth-often sucking its thumb. The palm, when stroked, will make a tight fist. It breathes amniotic fluid to help develop its respiratory system, and sometimes hiccups in the process. Its eyelids close if touched.

By the end of month four, the fetus is eight to ten inches in length and weighs a half a pound or more. It may reach a length of 13 to 17 centimeters by the end of this month and quadruple its weight. Its ears are functioning. The umbilical cord has become an engineering marvel, transporting 300 quarts of fluids per day and completing a round-trip of fluids every 30 seconds. The fetal heart pumps six gallons of blood each day at this point. Downy hair covers the entire body. The legs lengthen considerably and the skeleton continues to ossify.

There is evidence that the baby hears her mother's voice and heartbeat, as well as external noises. Because the fetus is now larger, the mother usually begins to feel her baby's movements during this month.

In month five, half the pregnancy has now passed. The fetus weighs in at about one pound and is around 12 inches long. The rate of growth decreases somewhat. The legs achieve their final relative proportions, and the skeletal muscles become active. Some hair appears on the head, and the skin becomes covered with a protective covering called the vernix.

Because the skeletal muscles become active in this month, the mother may feel fetal movements (quickening). If a sound is especially loud or startling, the fetus may jump in reaction to it.

By month six, oil and sweat glands are functioning. Fingernails and toenails are now present. Eyebrows and eyelashes appear. The skin is wrinkled and translucent. It is also reddish, due to the presence of dermal blood vessels. The lungs continue to mature. The fetus is now one foot long.

At this point, the mother can feel the fetus make small movements such as hiccup. Babies born at this stage of development have a significant chance at survival, thanks to advances in medical technology.

The fetal brain has as many cells as it will have at birth by month seven. It now weighs three pounds. The fetus uses the four senses of vision, hearing, taste, and touch. The skin becomes smoother as fat is deposited in the subcutaneous tissues. The eyelids, which fused together during the third month, reopen. At the end of this month, a fetus is about 37 centimeters in length. Research has documented that it can now recognize its mother's voice.

In month eight, the skin, still reddish and somewhat wrinkled, continues to thicken. Antibodies increasingly build up. It has been urinating for several months. The testes of males descend from regions near the developing kidneys through the inguinal canals and into the scrotum. The fetus is able to swallow at this point, and swallows a gallon of amniotic fluid per day, more if it is sweetened.

During month nine, the fetus reaches a length of about 47 centimeters. The reddishness of the skin fades to pinkish or bluish pink, even in fetuses of dark-skinned parents, because melanin is not produced until the skin is exposed to light. Toward the end of this month, the baby is ready for birth. The skin has lost its downy hair, but is still coated with the vernix. The scalp is usually covered with hair, the fingers and toes have well-developed nails, and the skull bones are largely ossified. By this time the infant's heart is pumping 300 gallons of blood per day. At the end of the ninth month, the fetus weighs 7 ¼ pounds and is near to 20 inches long.

The average duration of pregnancy is 280 days from the first day of the mother's last menstrual period, but this varies. In response to signals from the brain the child triggers labor, and birth occurs. After birth new brain cells are being formed for nine months. Likewise, other organ systems are still maturing. Of the 45 generations of cell divisions before adulthood, 41 have taken place in the womb. Only four more will come-during the rest of infancy and childhood, but before adolescence. In developmental terms we spend 90% of our lives in the womb.

Evaluating whether a fetus can feel pain is very difficult. James DeCamp, author of the Fetal Pain website, defines pain as "an unpleasant sensory and emotional experience associated with actual and potential tissue damage or described in terms of such damage."

Evaluating pain in the fetus and infant is difficult because pain is generally defined as a subjective phenomenon. Probably the reason most often given for why fetuses do not experience pain is because pain, as experienced by human adults, is not just a physical parameter but includes the psychological response of the individual to the physical circumstance that is considered painful. However, a number of more recent medical publications have raised questions as to the accuracy of traditional perceived wisdom with regard to fetal pain. This includes investigations into the hormonal response to painful stimuli, studies of the anatomical and functional requirements for pain perception in infants and fetuses and ultrasound observation of fetal movement (Ranalli, 1997).

Understanding the development of the higher brain is very crucial in understanding if a fetus can feel pain. The human brain develops very early after conception, exactly 18 days after conception. Over the next period of time the brainstem continues to develop, as do sensory receptors in various locations in the body. At about seven weeks, sensory receptors are apparent in the perioral area. These sensory receptors spread to the rest of the face, the palms of the hands and the soles of the feet by the 11th week of gestation, and to all skin and mucosal surfaces by week 20. The spread of these sensory receptors is preceded by the development of synaptic contacts in the perspective cortex. These synaptic contacts, which are essential for the transmission of nerve impulses, can first be detected at about the seventh week of gestation (Ranalli, 1997).

After the development of the higher brain, corticogenesis begins. Corticogenesis, the development of the prospective cortex, begins at about the eighth week and continues for much of the rest of gestation and is probably influenced by the brainstem. The developing cortex remains unconnected to the brainstem and the rest of the developing nervous system until about mid-gestation when the connection is made through a structure called the thalamus, which transmits sensory input from the rest of the nervous system to the cortex (DeCamp, 1997).

It has been argued that given the timing of the cortical connection through the thalamus that fetuses are unable to consciously experience pain until at least mid-gestation. However, fetal awareness is clearly exhibited before the cortical connection is made and maybe as early as the 8th week of gestation or even earlier since an eight-week fetus is certainly capable of a limited response to stimulation.

It can be determined that fetuses can feel pain. Fetuses at an early stage of development with a functional brainstem but without the cortical connection in place would therefore almost definitely also be aware of painful stimuli in some way. One study has suggested that the sensory neurons of the fetus are more sensitive than those of adults or newborns. Although ideally suited to the low levels of stimulation in the uterus, they may elicit more intense responses to higher levels of stimulation than those in the uterus. Far from being less sensitive to pain than adults or children, the fetus may actually experience greater pain (DeCamp, 1997).

Analyzing the fetal movements can help determine if a fetus can feel pain. The first spontaneous movements by the fetus are made at seven-week post-menstrual age and are simple reflex responses to stimuli, which involve the whole body. By 12-13 weeks of gestation these whole body reflexes have given place to local reflexes where only a particular part of the body is moved. The whole body reflex responses of fetuses require a neutral system that is sufficiently developed to pass information from the stimulated nerve to some sort of "signal processor" which in turn generates and sends an impulse to the other parts of the body that move. This "processor" is the very beginnings of the brainstem. This neutral network system also permits the spontaneously generated movement that can be seen in fetuses as early as seven weeks old. The localized reflex action, which is seen later in older fetuses, is a result of various developmental changes that result in increasing sensory input into the brainstem and increased control by the brainstem (Ranalli, 1997).

The increased control by the brainstem is apparent in very premature neonates. It has been shown that premature neonates have been shown to respond to a pinprick in the leg by moving the limbs as well as grimacing and/or crying. Evidently these newborns, who, were they not premature, would still be considered fetuses, are very capable of responding to painful stimuli in such a way as to try and withdraw from it (Ranalli, 1997).

In concluding with the development of a fetus, one very important ethical decision should be considered. When does life actually begin? This question has given rise to various arguments concerning the ethical implications of life's beginning. There have been many different theories that have evolved from this ethical dilemma. Through religious, philosophical, political and medical/biological perspectives, the beginning of life has been defined. Some of the most notable theories are age of viability, quickening, detection of brain waves, beginning of heart beats, first breath and most importantly, at the point of conception. Other theories have originated; however, they are products of mere opinions that most people disapprove of (recognition of sex organs, can give and receive love, creation of the soul, etc).

One theory of life's first starting existence is the age of viability. It is defined as the age when the fetus can survive outside of the mother's womb on its own. This is not the medical theory of when life actually begins; however, it plays an important role in the developmental process of a fetus. Changes in the age of viability have occurred over the years invariably due to the progress of medical technology. Forty years ago, the age of viability was about 30 weeks. Twenty years ago, it was about 25-26 weeks. Today, medical professionals have determined that it is possible for a 20-21 week fetus to survive (developmental deficits can still occur). Viability today has changed due to the increased medical knowledge of physicians and the improvement of life support systems. The term viability "actually measures the state of medical science and technology in a particular place and particular time"(Johansen, 1997).

Why is there a survival difference between the age before viability and the age once viability has been reached? In other words, how can a fetus of 21 weeks survive, but one of 18 weeks would most likely not make it? The fetus' lung sacs, called alveoli, is the site where gas exchange takes place. The alveoli are lined by a substance called surfactant which keeps the lung sacs from collapsing; therefore, the baby can breathe and survive on its own. The age of viability denotes the completion of surfactant synthesis. If the infant is born too early, the surfactant synthesis is not complete and will result in the inability to maintain lung stability (Ladewig, London & Olds, 1992).

Some other theories that have played an important role in determining life's beginning is the point of quickening. Quickening is defined as "becoming alive" and is determined by the first movement the unborn fetus. This occurs around 18 weeks. Years ago, technology wasn't available to see into the mother's womb like ultrasounds do today; hence, this theory evolved. Life seemed to begin when the mother could first feel the unborn child move inside her. The first detection of brain waves by an EEG has also been a theory of when life actually begins. The argument for this theory is that if we are dead when an EEG can no longer detect brain waves, then we should ultimately become alive when brain waves are detected. Not only has the brain been an interesting view of life's start, but that of the heart has come into play as well. The heart begins beating around sixth week of fetal development. This argument seems reasonable because if we are dead when our heart stops, then we should be alive when our heart begins. Another important assumption is when the baby takes its first breath. This has been the Supreme Court decision; therefore, allowing abortion of a fetus up to a certain term. With all of these theories in mind, the highest regarded theory if life's beginning is the time of conception. The chromosomes from both the father and mother combine to form a unique individual that continues to grow and develop. This theory is the medical and biological answer to when life actually begins (Johansen, 1997).

Life begins at the moment of conception. This has indeed been proven by much scientific and medical research. As the Father of Modern Genetics, Dr. Jerome Lejeune has stated, "To accept the fact that after fertilization has taken place a new human has come into being is no longer a matter of taste or opinion…it is plain experimental evidence" (When does life begin?). From this point on, every developmental stage is just part of the whole life process. From zygote to fetus and eventually to who we are today, are all stages in human life. Not one part means not living. There will always be various theories about when life begins; however, this should not be misunderstood by the beginning of personhood. Personhood itself is another ethical topic that should be kept separate from an organism's biological beginning.


An evaluation of our performance by the class audience yielded mostly positive criticism. A good majority of the class wrote that the presentation given was both interesting and clear, clarified by the handouts, overheads, fetal models, and main points summary. Comments were made congratulating our ability to keep our opinions out of the presentation and ease in condensing a large amount of potentially technical information. The preparedness and knowledge of the presenters was praised and most stated they would have done nothing differently. Statements were made such as "One of the clearest presentations so far", "It gave me something to think about", "I really enjoyed the presentation by this group", and "You all covered the information in a very unbiased/unopinionated way."

Few negative criticisms were made. One person was concerned that the presentation was too technical; another said it was too quick. Class involvement should have been more emphasized, said one classmate. Finally, along these same lines, one person was concerned that a discussion should have been included comparing the beginning of biological life versus the beginning of the person.

Overall, judging both by the knowledge gained by the presenters and the feedback from the class, the presentation was a huge success. We enjoyed researching and learning about the topic of fetal development and appreciated the opportunity to convey this newfound knowledge to our peers.