18. Prenatal Development

zona pellucida
thin layer of acellular material surrounding the ovum
granulosa cells
cells lining the ovarian follicles
the fertilized ovum
-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
-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
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.
-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
-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
-all organ systems are formed
-critical period of development
-embryo development can be disturbed and cause congenital abnormalities
the developing human organism from the 3rd-7th weeks of gestation
Fetal Period
-8th week - time of delivery
-no longer called an embyro
-becomes larger and heavier
-no major changes in basic structure
-about 38 weeks
-total duration of pregnancy from fertilization to delivery
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
-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
-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
congenital malformation; absence of brain
-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
-an elevated blood glucose concentration
-harmful to fetus
-congenital malformations
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
-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
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
identical twins
fraternal twins
fraternal twins
-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
-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)
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
-pregnancy-associated elevated blood pressure exceeding 140/90
-accompanied by protein in the urine
-severe cases of elevated blood pressure exceeding 160/110
-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
-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
-fluid filled vesicle
-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
-severe form of erythroblastosis
-extremely anemic & edematous
-severe edema in the affected infant (from heart failure and impaired hepatic plasma-protein synthesis
-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
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
-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
-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