Chapter 3 - Prenatal Development Flashcards Preview

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Prenatal Development

Prenatal development begins with conception The ovum is 1/175 inch, the largest cell in the human body Sperm cells are much smaller, 1/500 inch


Advantages and Disadvantages of parenthood mentioned by American Couples

Advantages • Giving and receiving affection • Experiencing the stimulation and fun that children add • Being accepted as a responsible and mature member of the community • Experiencing new growth and learning opportunities • Having someone to carry on to after ones death • Gaining a sense of accomplishment and creativity from helping children grow • Having someone to provide care in old age • Learning to be less selfish and to sacrifice • Help with work or add to income to family resources Disadvantages • Loss of freedom • Financial strain • Family work conflict • Interference with moms employment or career progress • Worries over children’s health, safety, wellbeing • Risks of the world • Reduced time with partner • Loss of privacy • Fear of children turning out badly, through no fault of their own


Ovulation and Menstruation

About once every 28 days, an ovum is released from one of the ovaries, and begins to travel down a fallopian tube The corpus luteum secretes hormones that will prepare the uterine lining for implantation If pregnancy doesn’t occur, the corpus luteum shrinks, and the uterine lining is discarded



On average, males produce about 300 million sperm per day During intercourse, sperm cells are released, and swim through the cervix and into the fallopian tube Only 300 to 500 sperm cells will reach the ovum, if one is present at the time of intercourse Or soon afterwards; sperm cells live for about 6 days Usually, fertilization occurs either the day of ovulation or in the 2 days afterwards


Prenatal development three phases

The period of the zygote The period of the embryo The period of the fetus


The Period of the Zygote

Lasts from conception until implantation is complete, approximately 2 weeks The zygote duplicates while travelling down the fallopian tube The first duplication takes about 30 hours, after which cell duplication speeds up considerably A yolk sac forms; this will produce blood cells until the liver, spleen, and bone marrow are mature enough to produce their own Note that perhaps as many as 30% of zygotes do not survive these first 2 weeks



the zygote 4 days after fertilization, when the tiny mass of cells forms a hollow, fluid-filled ball


Embryonic disk

a small cluster of cells on the inside of the blastocyst, from which the new organism will develop



the thin outer ring of cells of the blastocyst, which will become the structures that provide protective covering and nourishment to the new organism



attachment of the blastocyst to the uterine lining, which occurs 7 to 9 days after fertilization The trophoblast multiplies quickly after implantation begins, forming the amnion and chorion



the inner membrane that encloses the prenatal organism develops from the Trophoblast


Amniotic fluid

the fluid that fills the amnion, helping to keep temperature constant and to provide a cushion against jolts caused by the mother’s movement



develops from the Trophoblast it is the outer membrane that surrounds the amnion and sends out tiny, fingerlike villi, from which the placenta begins to develop These are the villi that are sampled in chorionic villus sampling



the organ that permits exchange of nutrients and waste products between the bloodstreams of the mother and the embryo, while also preventing the mother’s and embryo’s blood from mixing directly


Umbilical cord

Umbilical cord - the long cord that connects the prenatal organism to the placenta, delivering nutrients and removing waste products This cord grows to a length of 1-3 feet One large vein delivers nutrient-rich blood to Baby Two arteries remove Baby’s waste products The constant flow of blood keeps the cord firm, so it rarely tangles with Baby’s movements


The Period of the Embryo

Embryo - the developing organism from the third week, when implantation is complete, through the eighth week after conception Initially only about the size of an apple seed, but all major internal and external structures form during this period


The Period of the Embryo Week 3

Week 3, the inner cell mass differentiates into three layers 1. Endodermal: internal organs and glands 2. Ectodermal: the parts of the body that maintain contact with the outside world—the nervous system; the sensory parts of the eyes, nose, and ears; skin; hair 3. Mesodermal: muscles, cartilage, bone, sex organs, and heart The ectoderm folds over to form the neural tube. At 3 ½ weeks the brain starts to develop from the neural tube


The Period of the Embryo week 4

Beginning of week 4, the embryo looks like a tiny tube By the end of week 4, it assumes a curved form, with a bump below the head (a primitive heart) and tiny buds that will become the limbs


The Period of the Embryo 5th week

In the 5th week, the head and brain develop rapidly The upper limbs form The lower limbs appear and look like small paddles


The Period of the Embryo 6th week

In the 6th week, the head continues to grow rapidly Differentiation of the limbs occurs as elbows, fingers, and wrists become recognizable The ears and eyes are discernable


The Period of the Embryo week 7

the limbs develop rapidly Stumps appear that will form fingers and toes


The Period of the Embryo week 8,

By the end of week 8, the embryo has distinctly human features Almost half of the embryo consists of the head The eyes, ears, toes, and fingers are easily distinguishable All internal and external structures have formed


The Period of the Fetus

Fetus - the developing organism from the 9th week to the 38th week after conception During this period, we see mostly Further development of the already formed organ structures Increases in size and weight At the beginning of this period, the fetus weighs less than an ounce and measures about 5 cm in length By birth, about 266 days after conception, most weight 3 to 3.5 kg and measure about 51 cm in length Fetal growth begins to slow around the eighth month Appearance changes drastically during the fetal period The head grows less than the other parts of the body The head’s ratio decreases from 50% of the body mass at 12 weeks to 25% at birth By 6 to 7 months of age, the fetus has a chance of survival outside of Mom’s body This process isn’t complete until 9 months


First trimester 9 weeks to 3 months

The organs, muscles and nervous system start to become organized and developed Facial features become more human looking as the eyes move from the sides of the head to the front Fetal activity begins in the 3rd month, when the fetus is capable of forming a fist and wiggling toes Mom can’t feel this yet The fetus appears to become sensitive to environmental stimulation by this point—it moves its whole body in response to a touch stimulus The skin is transparent until the 3rd month, when it begins to thicken By 3 months, the brain is organized into functional subdivisions—seeing, hearing, thinking, etc Sexual development becomes apparent by the end of the 3rd month The eyelids seal shut near the beginning of the 3rd month, and stay that way for 3 months


Second trimester 4 months

By the 4th month, the eyes are sensitive to light through the lids Finger and toe nails appear by the 4th month, as do pads that will have the fingerprints Head hair begins to grow


Second trimester 5 months

By the 5th month, a loud noise may activate the fetus During this month, the fetus swims effortlessly The fetus is now capable of kicking and turning It may also begin to display rhythms of sleep and activity By about 17-20 weeks, the fetus has developed vernix and lanugo


Second trimester 6 months

By 6 months, a bone structure begins to support a more erect posture


third trimester 7 months

By the 7th month, brain connections are sufficient for the fetus to exhibit a sucking reflex when the lips are touched A baby born after only 7 months will need to be provided with extra oxygen, will have to take food in very small amounts, and will have to live for several weeks in an incubator for temperature control


third trimester 8 months

In the 8th month, fat appears under the skin to help regulate body temperature A baby born at 8 months is susceptible to infection Beginning in the 8th month, Mom’s body contributes disease-fighting antibodies to the fetus, developed through her own exposure to foreign bodies


vernix and lanugo

Vernix – white cheese like substance that protects the skin from chapping in the amniotic fluid Lanugo – also appears around the body helping the vernix