18. Prenatal Development

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zona pellucida

thin layer of acellular material surrounding the ovum

granulosa cells

cells lining the ovarian follicles

zygote

the fertilized ovum

morula

-a mulberry-shaped solid cluster of cells formed by the division of the fertilized ovum
-reaches the endometrial cavity around the 3rd day
-fluid begins to accumulate in the center
-it is now referred as a blastocyst

blastocyst

-a stage of development of the fertilized ovum (zygote) in which a central cavity accumulates with a cluster of developing cells
-lies free within the endometrial cavity for several days
-begins to burrow into the endometrium by the end of the first week and soon completely embedded

inner cell mass

a group of cells that are derived from the fertilized ovum and are destined to form the embryo

trophoblast

cell derived from the fertilized ovum that gives rise to the fetal membranes and contributes to the formation of the placenta

germ disk

a 3-layered cluster of cells that will eventually give rise to an embryo
-3 layers include:
1. ectoderm
2. mesoderm
3. entoderm

amniotic sac

the fluid-filled sac surrounding the embryo
-one of the fetal membranes
-forms between the ectoderm of the germ disk and the surrounding trophoblast

yolk sac

-a sac that is formed adjacent to the germ disk and that will form the gastrointestinal tract and other important structures in the embryo.

mesoderm

-the middle germ layer of the embryo, which gives rise to specific organs and tissues
-covers the external surfaces of the amniotic sac and yolk sac

chorion

-the layer of the trophoblast and associated mesoderm that surrounds the developing embryo

chorionic vesicle

-the chorion with its villi and enclosed amnion, yolk sac, and developing embryo

chorionic villi

finger-like columns of cells extending from the chorion that anchor the chorionic vesicle in the endometrium

body stalk

-the structure connecting the embryo to the chorion
-eventually develops into the umbilical cord

What are the 3 stages of prenatal development?

1. Preembryonic period
2. Embryonic period
3. Fetal period

Preembryonic period

-first 3 weeks after fertilization
-blastocyst becomes implanted
-inner cell mass differentiates into 3 germ layers

Embryonic period

-3rd-7th week
-human shape forms
-embryo
-all organ systems are formed
-critical period of development
-embryo development can be disturbed and cause congenital abnormalities

embryo

the developing human organism from the 3rd-7th weeks of gestation

Fetal Period

-8th week - time of delivery
-no longer called an embyro
-fetus
-becomes larger and heavier
-no major changes in basic structure

gestation

-about 38 weeks
-total duration of pregnancy from fertilization to delivery

decidua

the endometrium of pregnancy

decidua basalis

part beneath the chorionic vesicle

decidua capsularis

part that is stretched over the vesicle

decidua partietalis

part that lines the rest of the endometrial cavity

chorion frondosum

the portion of the chorion that develops into the fetal portion of the placenta

amniotic sac

-enclosed within the chorion
-completely fills the chorionic cavity
-functions as a buoyant, temperature-controlled environment that protects the fetus throughout pregnancy
-Assists in opening the cervix during childbirth

Yolk sac

-Never contains yolk
-becomes part of the intestinal tract

Placenta

-flat-disk shaped structure
-weighs about 500 g.
-dual organ (fetal and maternal)
-contains 2 arteries and 1 vein
-synthesizes 2 steroid hormones (estrogen & progesterone)
-2 protein hormones (HCG & HCL)

fetoplacental circulation

-delivers arterial blood low in oxygen from the fetus to the chorionic villi through the 2 umbilical arteries
-returns oxygenated blood to the fetus in the single umbilical vein.

uterplacental circulation

-delivers oxygenated arterial blood from the mother into the large placental spaces located between the villi

human placental lactogen (HPL)

-stimulates maternal metabolic processes

Human Chorionic Gonadotrphin (HCG)

-similar to the gonadotrophic hormones produced by the pituitary gland
-pregnancy tests detect this hormone

amniotic fluid

-produced by filtration and excretion
-quantity varies on stage of pregnancy

polyhydramnios

-an excess of amniotic fluid
- 2 causes
1. congenital maldevelopment of the fetal brain where the fetus is unable to swallow amnionic fluid
2. congenital obstruction of the fetal upper intestinal tract that blocks the entry of swallowed fluid into the small intesting to be absorbs

anencephaly

congenital malformation; absence of brain

oligohydramnios

-insufficient quantity of amnionic fluid
-kidneys have failed to develop and no urine is formed
-congenital obstruction that blocks the urethra so that urine cannot be excreted

hyperemesis gravidarum

-excessive vomiting of pregnancy
-more prolonged and severe
-weight loss
-dehydration

hyperglycemia

-an elevated blood glucose concentration
-harmful to fetus
-congenital malformations
-death

gestational diabetes

-developing diabetes during pregnancy
-blood glucose returns back to normal after pregnancy
-occurs in 2% of pregnancies (higher in older or obese people)

spontaneous abortion

-miscarriage
-most occur in early pregnancy
-result of chromosomal abnormalities
-cause can not be determined

placental abruption

detachment of the placenta from the wall of the uterus

dissemiated intravascular coagulation syndrome

a disturbance of blood coagulation as a result of activation of the coagulation mechanism and simultaneous clot lysis
-caused by a retained dead fetus

ectopic pregnancy

-development of embryo outside uterine cavity
-most occur in the fallopian tubes
2 reasons:
1. A previous infection in the fallopian tubes
2. Failure of muscular contractions to propel ovum through tube

septicemia

fatal bloodstream infection

velamentous insertion of umbilical cord

-attachment of the umbilical cord to the fetal membranes rather than to the placenta
-hazardous to the fetus
-vessels can become compressed or ruptured
-fetus bleeds to death
-mother does not suffer any effects

placenta previa

-attachment of the placenta in the uterus such that it partially or completely covers the cervix
-blocks the exit from the uterus
-bleeding during last part of pregnancy

monozygotic

identical twins

dizygotic

fraternal twins

fraternal twins

-72%
-results from 2 separate ova by 2 different sperm
-enclosed with each of their own amnion and chorion
-fused placenta is called a diamnionic dichorionic placenta

identical twins

-30%
-result from splitting of a single fertilized ovum
-70% of monozygotic twins the inner cell mass diveds after blastocyst

siamese twins

occurs if the division of the inner cell mass is incomplete (conjoined)

polycythemic

overloaded with blood

blighted twin

degenerated embryo or fetus that is retained within the uterus until the surviving fetus is delivered

conjoined twins

-identical twins that are joined to one another and often share organs in common.
-Siamese twins
-failure to sepearate

preeclampsia

-pregnancy-associated elevated blood pressure exceeding 140/90
-accompanied by protein in the urine

eclampsia

-severe cases of elevated blood pressure exceeding 160/110
-convulsions

toxemia

-preelampsa & eclampsia
-caused by inadequate blood flow to the placenta
-bed rest

gestational trophoblast disease

-a general term for all diseases characterized by abnormal trophoblast proliferation.
-includes both hydatidiform mole & choriocarcinoma
-treatment consists of anticaner chemotherapy

What are the 3 types of gestational trophoblast disease?

1. Hydatidiform Mole
2. Invasive Mole mole
3. Choriocarcinoma

Hydatidiform Mole

-most common type of gestational trophoblast disease
-80% of affected patients
-benign trophoblat proliferation
-associated with formation of large cystic villi
-most occur from abnormal fertilization lacking chromosomes

Invasive Mole

-more aggressive and destructive type of gestational trophoblst disease
-occurs in 15% of patients
-invades the uterine wall
-resembles a complete hydatidiform mole
-does not metastasize

Choriocarcinoma

-malignant growth of trophoblastic tissue
-affects only a small percent of people
-aggressive neoplastic neoplasm that can metastasize and kill patient
-behaves like a malignant tumor

hydatid

-fluid filled vesicle

mole

-shapeless mass of tissue

hemolytic disease of the newborn

-hemolytic anemia
-results from sensitization o the mother
-Rh incompatibility
-mother reacts by forming antibodies

erythoblastosis fetalis

-damage of red blood cells leading to anemia in the affected fetus
-comes from large numbers of nucleated red blood cells in the blood of severely affected anemic infants

compensatory hematopoiesis

-increasing the rate of red cell production to keep up with the blood destruction

hydrops

-severe form of erythroblastosis
-extremely anemic & edematous
-severe edema in the affected infant (from heart failure and impaired hepatic plasma-protein synthesis

hyperbilirubinemia

-levels of unconjugated bilirubin in the infants blood rapidly rises
-hazardous to the infant
-toxic to the nervous system
-cerebral palsy, mental retardation, and hearing loss

kernicterus

an abnormal accumulation of bile pigment in the brain and other nerve tissue

bilirubin encephalopathy

high levels of bilirubin cross blood/brain barrier and attach to brain cells leading to neurological deficit.

Rh hemolytic disease

-rarely occurs
-can result from sensitization of the mother to another antigen
-maternal-fetal blood group incompatibility

Rh system

-consists of genes that determine multiple Rh antigens on red cells

exchange transfusion

-treatment of hemolytic disease
-provides the infant with a population of cells that will not be destroyed by the antibody
-provides infant with bilirubin-free plasma to replace the jaundice plasma
-has no effect on infants own blood type

phototherapy

-fluorescent light treatment of jaundiced babies to reduce the concentration of unconjugated bilirubin in their blood

Rh immune globin

-a gamma globin containing high concentration of Rh antibody

ABO hemolytic disease

-a mild hemolytic disease in group A or B infants or group O mothers
-as a result of maternal anti-A and anti-B antibodies
-less severe than Rh factor

fertilization

-union of sperm and ovum occurs in fallopian tube
-ovum is expelled from follicle after fertilization
-first cell division completed 30 hours after fertilization

chorion laeve

superficial smooth chorion

chorion frondosum

bushy chorion

fetoplacental ciirculation

from fetus to villi

uteroplacental circulation

maternal blood circulates around villi

velamentous insertion

-cord attached to fetal membranes than placenta
-may tear or is compressed during labor
-may be fatal to infant
=no adverse side effects on mother

placenta previa

placenta covers entire cervix

partial placenta previa

margin of placenta covers cervix

hydatidiform mole (complete)

both X chromosomes come from the father
no embryo develops

hydatidiform mole (partial)

-normal ovum fertilized by 2 sperm
-results in a fertilized ovum with 3 sets of chromosomes (69) chromosomes
-embryo forms but does not survive

erythoblastosis fetalis (pathogenesis)

-1. sensitization of mother to a blood group antigen in fetal RBCs
-2. Mother forms antibodies that cross placenta
3. Maternal antibodies damage fetal RBCs
4. Fetus increases blood production to compensate for increased RBC destruction

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