Chapter 5: Fetal Development

Fetal circulatory shunts

Foramen ovale- shunts highly oxygenated blood from the right atrium to left atrium ( right to left shunting) Ductus arteriosus- protects lungs against circulatory overload; strengthens right ventricle ductus venosus- connects fetal blood vessels from umbilical vein to inferior vena cava; by pass-liver

What are the implications of a two-vessel cord?

If there is only one of each, it could mean that they might have lung issues or GI issues.

Placental hormones

Progesterone, estrogen, human chorionic gonadotropin (hCG), and human placental lactogen - Some women take progesterone shots in order to maintain pregnancy

Fetal period (13-20)

- all nourishment is from placenta -you may hear the heartbeat at your next appt. -fluttering movements=quickening -liver functions: sex glands to correct position; brain fully developed -skeleton is transforming from cartilage to bone -immunities are being transferred from mom, weight=~10.58 ounces -passive immunity- antibodies are being passed from mom to baby to protect baby.

Human placental lactogen functions in the placenta

- also known as human chorionic somatomammotropin (hCS) -hPL causes decreased insulin sensitivity and utilization of glucose by mother --helps to make more glucose available to fetus to meet growth needs -hCS- have more sugar in her system so she can pass on to her fetus.

Fetal development ( 20- 30 weeks)

-WBC's production -skin is no longer translucent -infant can hear -the brain in rapid-growth stage -liver begins to breakdown bilirubin -20 weeks is age of viability. survival at week 20 ~ 25-35% -surfactant being produced (21-24). Levels increase during 26-28 weeks increasing survival odds. Best surfactant levels at week 38-40 -SURFACTANT IS USED TO TAKE FIRST BREATHE -Testes are moving down; testosterone is being produced -1.5 pints of amniotic fluid surround fetus -bone marrow produces RBC's -eyes reopen at 26 weeks -usually head down 1. inverted egg drop 2. head heavy and gravity pulls down

Fetal development (31-40 weeks)

-accumulation of fat is constant -LUNGS are ONLY major organ left to mature -fetus turns towards light outside uterus -all 5 senses are working -periods of dream sleep (REM) begin -Amniotic fluid is at its highest level -antibodies are being transferred

endometrium

-also called the decidua from implantation through end of pregnancy

circulation before birth

-blood enters fetal body through UMBILICAL VEIN -about half goes to the liver, remainder enters inferior vena cava through the ductus venosus, then goes through foramen ovale, then ductus arteriosus -blood containing waste products is returned to placenta through UMBILICAL ARTERIES -sends a limited amount of blood through the lungs

Intrauterine growth restriction may reduce number of cells in organs

-can predispose to the development of diseases later in life -fetal growth best assessed when weight, length or gestation, placental size and newborn head and abdominal circumference are considered -fetal growth limited by nutrients and oxygen received from mother

human chorionic gonadotropin (hCG) functions in the placenta

-causes the corpus luteum to persist and continue production of estrogen and progesterone to sustain pregnancy -hCG is detectable in maternal blood as soon as implantation occurs (usually 7 to 9 days after fertilization) -hCG- seen in pregnancy tests. You an have it in a urine test or blood test. blood test is more accurate.

yolk sac

-cleans things out before it goes into placenta -a cavity develops on the ninth day after fertilization -functions only during embryonic life -initiates production of red blood cells -continues until fetal liver takes over around 6 weeks. -umbilical cord encompasses yolk sac which then degenerates

diamniotic- dichorionic twins

-each develop in their own amniotic sac -placentas do not share any vessels

inheritance

-each gene is coded for inheritance -genes carry instruction for dominant and recessive traits -passed on to offspring

diamniotic- monochorionic twins

-each have their own amniotic sac but share a common chorionic sac - each have a separate placenta but the placentas share some vessels

Circulation after birth

-foramen ovale closes within 2 hours after birth (permanently by age 3 months) -ductus arteriosus closes within 15 hours (permanently in about 3 weeks) -ductus venosus closes functionally when cord is cut (permanently in about 1 week) -after permanent closure, the ductus arteriosus and ductus venosus become ligaments

Pre-embryonic period

-from fertilization to end of the 2nd week -BETTER FOR THE EGG TO IMPLANT WHERE IT'S HIGHER VS IT BEING LOWER DUE TO GETTING VAGINAL BLEEDING -fertilization occurs at distal end of fallopian tubes (ampulla and cell division begins) -traveling zygote -implantation in the decidua=Nidation -maintaining the decidua= hormonal influence -location of implantation=upper uterus -mechanism of implantation

multifetal pregnancy

-helps releasing more eggs -contributing factor for multifetal pregnancy -history of twins -recent stoppage or oral contraceptive -tall or large stature of mother -African American heritage -fertility medication use ---- when hormones are used to assist with ovulation, twinning and other multifetal pregnancies occur

Umbilical cord

-lifeline between mother and fetus -normal placenta has three vessels. "AVA" stands for "artery-vein-artery" -two arteries carry blood away from fetus -one vein returns blood to the fetus -Wharton's jelly cover and cushions cord vessels -normal length is 55 cm (22 inches) -usually protrudes near the center of the placenta

functions of amniotic fluid

-maintains an even temperature -prevents the amniotic sac from adhering to the fetal skin -allow symmetrical growth of fetus -allows buoyancy and fetal movement -acts as a cushion to protect the fetus and umbilical cord from injury

C-shaped

-maintains this in spinal curve of neonate

sex determination

-male determines the gender of the fetus -sperm can carry either an X or Y chromosome -pH of female reproductive tract influences survival rate of the x and y-bearing sperm, including speed of motility

cell differentiation

-occurs after implantation -during embryonic period - at the time of implantation, the cells are identical. -2 layers - chorion and amnion

Accessory structures of pregnancy

-placenta -umbilical cord -fetal circulation

Meiosis

-same process when taking place in sex cells -4 different sperm or ovary -reproductive cells undergo two sequential divisions -# of chromosomes is 23 per cell with only one sex cell -at fertilization, the new cell contains 23 chromosomes from the sperm and 23 from the ova.

development- amnion

-second membrane -thin structure that envelops and protects embryo -together, chorion and amnion form an amniotic sac filled with fluid (bag of waters) -amniotic fluid is clear, mild odor, may contain bits of vernix of lanugo -volume of fluid steadily increases from -30 mL at 10 weeks to 350 mL at 20 week; at 37 weeks, fluids is 1000 mL

Mitosis

-the division and multiplication of body cells. -making a new sex cell -continuous process -body grows, develops, and dead cells are replaces -each daughter cell contains the same number of chromosomes as parent cell

What is the function of the placenta?

-transfers nutrients, such as oxygen and glucose, to the fetus while removing waste products, such as carbon dioxide and urea. -HAS TWO ARTERIES AND ONE VEIN. ARTERIES CARRY DEOXYGENATED BLOOD AND THE VEIN CARRIES THE OXYGENATED BLOOD. -The maternal blood is rich in oxygen and nutrients reaches the placenta at the level of the intervillous spaces that are surrounded by the chorionic villi. -the chorionic villi contain the fetal blood vessels -exchange of nutrients for wastes occurs by simple diffusion or active transport across a thin membrane that separates the fetal and maternal bloodstreams

Tubal transport of the zygote

-transported through fallopian tube into uterus -during transport, zygote undergoes rapid mitotic division (cleavage) -size of zygote does not increase, individual cell becomes smaller as they divide, then form a solid ball known as a morula

The placenta

-two sides: Shiny Shultzy (fetal side) and Dirty Duncan (maternal side)- shiny side means that baby and placenta separated okay! -umbilical cord usually attaches on fetal side -Fetal Hgb carries 20-50% more O2 than adults=ability to thrive in low O2 environment

Implantation of the zygote

-usually in upper section of posterior uterine wall -cells burrow into prepared lining- endometrium -by 10th day after fertilization blastocyst is buried in uterine lining. -begins to produce human chorionic gonadotropin. (hCG) - on the 7th day it implants in the uterus. 1 side is placenta and the other is embryo

Types of teratogenic agens

1. ingested-prescription and over-the-counter medications, illicit drugs, and alcohol 2. Infectious- Varicella, cytomegalovirus(CMV), and rubella 3. Environmental substance- ionizing x-rays, radioactive substances and certain chemicals

Three stages of prenatal development

1. pre-embryonic stage as a zygote- cell formed by union of sperm and ovum 2. embryonic stage as an embryo-second to eighth week of development 3. fetal stage as a fetus-ninth week until birth

estrogen function in the placenta

1. stimulates uterine growth -- increases the blood flow to uterine vessels --stimulates development of the breast ducts to prepare for lactation 2. Effects of estrogen, not related to pregnancy --increased skin pigmentation --vascular changes in the skin and mucous membranes of nose and mouth --increased salivation

What is the age of Viability?

20 weeks of gestation-but requires NICU care to survive

age of embryo

3-8 weeks

When are the organs fully functional on an embryo?

8 weeks- organs are fully functional

fetal period (9-12 weeks)

9-12 weeks -the most critical part of the fetus is complete at the end of week 8. -only need growth for most structure/organs -weight=~ .25 ounces -alveoli are forming -eyes close at 9weeks; reopen at 26 weeks -kidneys are making urine -external genitalia develop

fetal period

9-38 weeks

Fetal period

9-40 weeks

Wharton jelly

a clear gelatinous substance that gives support to the cord and helps prevent compression of the cord, which could impair blood flow to the fetus

ectopic pregnancy

a pregnancy that occurs outside of the uterus -zygote implants in places other than the uterus -95% occur in the fallopian tube -usually causes by blockage or scarring of the fallopian tubes either from infection or trauma -occurrence is 1% to 2% of all pregnancies

chorion

a second layer of thick fibrous tissue that surrounds the amnion

amnion

a thick fibrous lining, made up of several layers, that helps to protect the fetus and forms the inner part of the sac in which the fetus grows

decidua basalis

area under blastocyst and becomes maternal part of the placenta

undernutrition

can result in permanent changes in fetal structure, physiology and metabolism -can influence development of conditions such as heart disease and stroke in adulthood -exposure to toxins in utero - can also influence health in later life.

Embryonic Period= weeks 3-8

development occurs simultaneously in all embryonic organ systems -cephalocaudal -central to peripheral -simple to complex -general to specific (limb bud to bone/joints/fingers, etc) -Intestines remain in umbilical cord -by the end of this period all major organs are in place and function -size of poppy seed at 4 weeks and kidney bean at 8 weeks -vulnerable to teratogens

development-chorion

develops from trophoblast -envelops amnion, embryo, and yolk sac -thick membrane has projections called villi -villi extend into decidua basalis on uterine wall -form the embryonic/fetal portion of placenta

XX

female

chorionic villi

finger-like projections that extend out from the chorion giving it a rough appearance

dizygotic

fraternal twins that develop from separate egg and sperm fertilizations

teratogen

from the greek terato-meaning monster, and genesis, meaning birth; an agent or influence that causes a defect or disruption in the prenatal growth process. The effect of a teratogen depends on when it enters the fetal system and the stage of differentiation of the organs or organ systems at that time. Generally, the fetus is most vulnerable to teratogens during the first trimester.

progesterone function in the placenta

functions during pregnancy 1. maintains uterine lining for implantation of the zygote 2. reduces uterine contractions to prevent spontaneous abortion 3.prepares the glands of the breasts for lactation 4. stimulates testes to produce testosterone, which aids the male fetus in developing the reproductive tract.

momoamniotic- monochorionic

have one amniotic cavity that they both share

monozygotic

identical twins that are derived from one zygote; one egg and one sperm divide into two zygotes shortly after fertilization -twins occur once in every 90 pregnancies

endoderm

lining of trachea, pharynx, and bronchi, lining of digestive tract, lining of bladder and urethra.

gametogenesis

making sex cells (gametes)

XY

male

fertilization

occurs when a sperm penetrates an ovum and they unite -takes place in the outer third of the fallopian tube, near the ovary -once it occurs, a chemical change in the membrane around the fertilized ovum prevents further sperm from penetrating the ovum.

foramen ovale

opening between the left and right atria of the fetal heart that closes with the first breath -shunts highly oxygenated blood from the right atrium to left atrium (right to left shunting)

zygote

or conceptus, results when an ovum and spermatozoon unite. The zygote has the full complement of 46 chromosomes, arranged in 23 pairs.

Ectoderm

outer layer of skin, oil glands and hair follicles of skin, nails and hair, external sense organs, mucous membrane of mouth and anus

Where is the best place for fertilization?

outer third of the fallopian tube is the best place for fertilization

diploid

parent cell

ductus arteriosus

prenatal blood vessel between the pulmonary artery and the aorta that closes functionally within the first 3 or 4 days of life. -protects the lungs against circulatory overload; strengthens right ventricle

ductus venosus

prenatal blood vessel between the umbilical vein and the inferior vena cava; does not achieve complete closure until the end of the second month of life. -connects fetal blood vessels from umbilical vein to inferior vena cava; by-pass liver

oogenesis

process of mitosis for ovum

spermatogenesis

process of mitosis for sperm

fetus

term for the organism after it has reached the eighth week of life and acquires a human likeness

embryo

the developing conceptus, from weeks 2 through 8

decidua

the endometrium that has changed to support a pregnancy

gametogenesis

the formation and development of gametes or germ cells by the process of meiosis

cleavage

the process of mitotic division performed by the zygote

morula

the solid cell cluster that forms about 3 days after fertilization, when the total cell count has reached 32. -blastocyte

amniotic fluid

the specialized fluid that fills the amniotic cavity ad serves to protect the fetus

blastocyst

the structure that forms about 5 days after fertilization when the dividing cell mass develops a hollow, fluid-filled core.

mesoderm

true skin, skeleton, bone and cartilage, connective tissue, Muscles, blood and blood vessels, kidneys and gonads

Impaired prenatal development

undernutrition and intrauterine growth restriction may reduce number of cells in organs

When do most women find out they are pregnant?

when they are pregnant 3-8 weeks

germs layers

zygote in blastocyst stage transforms into three primary germ layers -Ectoderm, Mesoderm, and Endoderm

A woman with epilepsy was on phenytoin (Dilantin) when she became pregnant. She is worried that her baby will have a birth defect. Which reply by the nurse is most therapeutic?

A. "All substances and medications increase the risk of birth defects when you are pregnant. It is important for you to discontinue any medications or over the counter medications immediately. This is the best way you can protect your baby" B. Please don't worry. Dilantin is a very safe medication and unlikely to cause a birth defect." C. Yes, Dilantin increases the risk of certain defects in the fetus; however, overall the risk is low that your baby will be affected. Your doctor weighs the risk of untreated epilepsy on the fetus with the risk of the medication when making decisions about your treatment plan." D. "Yes, there is a very high risk that you fetus will have major birth defects. Your doctor will most likely switch you to a safer medication. Are you on any other medications?" C

A new pt has had blood drawn to determine if she is pregnant. The hormone responsible for a positive test result is:

A. Human chorionic gonadotropin (hCG) B. Estrogen C. Human placental lactogen (hPL) D. follicle-stimulating hormone (FSH) A

In the development of a human being, a process occurs in which cells divide to produce a germ cell with 23 unpaired chromosomes. What is this process called?

A. Meiosis B. Mitosis C. Oogenesis D. Gametogenesis A

During which time frame does the embryonic stage last?

A. Ovulation to conception B. 1 to 14 days after conception C. 3 through 8 weeks after conception D. 9 through 38 weeks after conception

Which is a fetal shunt that aids in fetal circulation?

A. foramen primum B. foramen ovale C. ductus deferens D. septum secundum B

Amniotic fluid exceeding 1000 mL at term is known as

A. megahydramnios B. Oligohydramnios C. tetramnios D. polyhydramnios

what is the main purpose of the chorionic villi?

A. to adhere the blastocyst to the endometrial lining B. To form the tissues that will become the placenta C. To produce amniotic fluid D.To provide an exchange site for the exchange of nutrients and wastes D

What is the classification of twins who share the same chromosomal material?

A.monozygotic B. Dizygotic C. Fraternal D. Trizygotic B

cell differentiation special functions

chorion, amnion, yolk sac, primary germ layers

haploid

chromosome