Chapter 10 Fetal Development And Genetics Flashcards
Fetal development stages
Pre-embryonic stage: fertilization through the second week
Embryonic stage: end of the second week through the eighth week
Fetal stage: end of the eighth week until birth
Fertilization
The union of ovum and sperm which is the starting point of pregnancy. Usually around two weeks after menstrual period. Takes place in outer third of ampulla of the fallopian tube
Zona pellucid a
Clear protein layer to block extra sperm. Disappears in five days
Zygote
The new life that is formed from the 23 chromosomes each joining making 46. XX is female XY is male. Implants in the endometrium about 7 to 10 days after conception
Morula
4 sets of mitosis/cleavages, 16 Cells appear as a ball of cells. Reaches the uterine cavity in 72 hours
Blastocyst
Within the morula, a hollow ball of fluid filled space or cells (inner cell mass). The inner surface will form the embryo and amnion.
Trophoblast
The outer layer of cells surrounding the blastocyst. Will develop the embryonic membranes, the chorion, and helps form placenta.
Implantation
Usually occurs in the upper uterus or fundus. Usually with in 7 to 10 days after conception
Amniotic fluid
Surrounds the embryo and increases in volume up to 1 L at term. It comes from fluid transported from the maternal blood and fetal urine. It helps maintain constant body temperature, symmetric growth and development, and cushions the fetus, Allows the umbilical cord to be free of compression, promotes fetal movement and muscular development.
Oligohydramnios
Too little amniotic fluid, less than 500 mL at term. Associated with utero placental Insufficiency and fetal renal abnormalities
Hydramnios
Too much amniotic fluid, greater than 2000 mL at term. Associated with maternal diabetes, neural tube defects, chromosomal deviations, and malformations of the central nervous system and/or GI tract That prevents normal swallowing of amniotic fluid by the fetus.
Umbilical cord
From amnion, Contains one large vein and two small arteries. Whartons jelly is a connective tissue that surrounds them to prevent compression. Average is 22 inches long and 1 inch wide. The vein supplies the oxygen, the arteries bring waste back to the mom
Placenta
It is a gland that produces hormones. Made from trophoblasts which make hCG that ensures the endometrium will be receptive to the implanting embryo. It makes hormones to control physiology of the mother so the fetus is supplied with nutrients and oxygen. It protects from an immune attack, removes waste products from the fetus, induces the mother to bring more food, produces hormones that ready fetal organs. It’s function depends on maternal blood pressure. Completely formed within 12 weeks
HCG
Preserves the corpus luteum and it’s progesterone production so tha endometrial lining of the uterus is maintained
hPL Human placental lactogen
Controls fetal and maternal metabolism, develops maternal breast for lactation, decreases maternal insulin sensitivity to increase availability for fetus
Estrogen estriol
Enlarges women’s breasts, uterus, and external genitalia, stimulates myometrial contractility
Progesterone progestin
Maintains endometrium, decreases contractility of the uterus, stimulates maternal metabolism and breast development, provides nourishment for the early conceptus
Relaxin
Synergistic with progesterone to maintain pregnancy, causes relaxation of pelvic ligaments, softens cervix in preparation for birth
Fetal stage
Pregnancy is 280 days. fetal stage is the end of the eighth week until birth. Longest period of prenatal development. Conceptus is now a fetus. All major systems are present.
Dramatic growth and maturation of organ systems
Fetal circulation
Carries oxygenated blood to vital areas the heart and brain while first shunting it away from the lungs and liver. The placenta takes over the functions of the lungs and liver during fetal life. As a result large volumes of oxygenated blood are not needed.
Three shunts of fetus
Ductus venosus-Umbilical vein to interior vena cava
Ductus arteriosus-Main pulmonary artery to the aorta
Foramen ovale-Anatomic opening between right and left atrium
Allele
Two or more alternative versions of the gene at a given position or Locus on the chromosome that imparts the same characteristic of that gene. Example an allele might be able to produce blue eyes or one for brown eyes.
Phenotype
Outward characteristics of an individual
Karyotype
Pictorial analysis of the number, form, and size of individuals chromosomes.
Mendels law
Inheritance of single gene disorders also referred to as monogenic or sometimes Mendelian disorders
Autosomal dominant inheritance disorder
When a single gene in the heterozygous state is capable of producing the phenotype. Examples include neurofibromatosis, Huntington’s disease, achondroplasia, polycystic kidney disease. Offspring have a 50% chance of being abnormal. Male can pass the disorder onto his son. Dn nn
Autosomal recessive inherited disorders
Two abnormal genes in the homozygous state are needed for the individual to demonstrate signs and symptoms of a disorder. Examples are cystic fibrosis, phenylketonuria, TaySachs disease, sickle cell disease. 25% chance of inheriting normal 50% chance of being a carrier, and a 25% of being abnormal. Male Can pass disorder onto son. Nd Nd
X-linked inheritance disorders
The altered gene is present on the X chromosome. If the male inherits the X-linked gene he will express the condition because he only has one X-chromosome. Females inherit 2 x chromosomes so they can be heterozygous or homozygous.
Three embryonic layers
Ectoderm, mesoderm, endoderm
Ectoderm
Forms the central nervous system, special senses, skin, and glands
Mesoderm
Forms the skeletal, urinary, circulatory, and reproductive organs
Endoderm
Forms the respiratory system, liver, pancreas, and digestive system
X-linked recessive inheritance
Males are more affected than females because all the genes on a man’s X chromosome will be expressed. There is no mail to mail transmission. Examples include hemophilia, colorblindness, and Duchenne muscular dystrophy
X linked dominant inheritance
Occurs when a male has abnormal X chromosome or female has one abnormal X-chromosome. All the daughters and none of the sons of an affected male will inherit the condition while both the male and female offspring of an affected woman would have a 50% chance of inheriting the condition. Males are more severely affected than females. Examples include hypophosphatemic rickets and fragile X syndrome
Multifactorial inheritance disorders
Caused by multiple gene and environmental factors. Examples include cleft lip, cleft palate, spina bifida, Pyloric stenosis(More often in males), clubfoot, congenital hip dysplasia(more often in female), and cardiac defects
Chromosomal abnormalities
Caused by too many or too few chromosomes or also due to an error in the structure of the chromosome. Some pieces of the chromosome maybe deleted, duplicated, inverted, misplaced, or exchanged with part of another chromosome. Mosaicism Is when chromosomal abnormalities do not show up in every cell.
Monosomies
Only one copy of a particular chromosome instead of two. All fetuses spontaneously abort in early pregnancy.
Trisomies
Three chromosomes instead of two. Down syndrome is chromosome 21, trisomy 18 and trisomy 13.
AutoSome
Nonsex chromosomes. We have 22 pairs
Mutation
Change in gene structure or location, may alter the type and amount of protein produced.
Amnion
Originates from the ectoderm germ layer during the early stages of embryonic development. Thin protective membrane that contains the amniotic fluid.
Chromosomes
Long, continuous strands of DNA that carry genetic information.
Polyploidy
Causes an increase in the number of haploid sets, 23, of chromosomes in a cell
Triploidy
Three whole sets of chromosomes in a single cell.
Mosaicism
Chromosomal abnormalities that do not show up in every cell.
Maternal serum Alpha/fetoprotein. MSAFP
Usually between 15 and 18 weeks gestation.
Increased levels indicate open neural tube defects, Turner syndrome, tetralogy of fallot, multiple gestation, hydrocephaly, omphalocele gastrochisis
16-18 weeks
Decreased level might indicate down syndrome or trisomy 18
Chorionic villus sampling
Removal of a small tissue specimen of the fetal portion of the placenta and shows genetic makeup. Complications include limb defects and pregnancy loss. Can detect sickle cell anemia, phenyl ketone urea, down syndrome, Duchenne muscular dystrophy, and other genetic disorders. Usually between 10 to 12 weeks just station
