conception and fetal development (unit 1) Flashcards
conception
•union of sperm and egg •sequential process 1. gamete formation 2. ovulation 3. fertilization 4. implantation
gametogenesis
- gamete formation
* each has 22 autosome and ONE sex chromosome
female gametes
- born w/ eggs
- estrogen in uterine cilia assists the ovum movement to uterine cavity
- ovulation 14 days prior to next menstrual period
- ovum viable for 24 hrs
male gametes
- continuously produce sperm from puberty
- few hundred of the millions ejaculated reach ovum
- only ONE sperm fertilizes
- flagellum propel sperm toward ovum (4-6 hrs)
- sperm viable for 2-3 days
ovulation
- pituitary releases FHS to get egg ready
- FSH stimulates more estrogen
- estrogen stiumlates pit to release LH
- LH triggers release of egg (ovulation)
- progesterone released in response to ovulation and prepares uterine lining for implantation
- if no fertilization, less progesterone release -> menstrual cycle begins
fertilization
- takes place in ampulla (outer 3rd of fallopian tube
* journey thru tube to uterus takes 3-4 days
sex determination
•based on male gamete
- XX+XX = female
- XX+XY = male
unifactorial (single) gene transmission
•dominant vs. recessive
- autosomal dominant
- autosomal recessive
- X-linked
multifactoral gene transmission
•2 or more genes on different chromosomes affected
X-linked dominant transmission
- affected males transmit abnormal gene to daughters ONLY
- can also be transmitted by heterozygous females
- Ex: FXS; vit D-resistant rickets
fragile X syndrome (FXS)
•most common inherited form of mental retardation
X-linked recessive transmission
- affected male receives defective gene from carrier mother and transmits abnormal gene ONLY to daughters on X chromosome
- daughters are usually carries and are affected ONLY if they receive an abnormal gene on the X chromosome from BOTH parents
- Ex: hemophilia, color blindness, Duchenne muscular dystrophy
Turner’s syndrome
- only have one X chromosome
- affects females only
- short statue
- no ovary development
Kleinfelter’s syndrom
•XXY •affects males only •tall/thin •small testicles -infertile -sparse body hair -slight body build
autosomal dominant inheritance
- only one copy of abnormal gene to be affected
- males and females equally affected
- no skipping generations
- Ex: Huntington’s Marfan, Dwarfism
autosomal recessive inheritance
- expressed only if there are 2 abnormal genes (homozygotic)
- parents are carriers and unaffected by faulty gene
- Ex: PKU, sickle cell, cystic fibrosis
autosomal abnormalities
•abnormalities of chromosome # or structure
abnormalities in chromosome #
- polyploidy- 69 or 92 chromosomes
* aneuploidy- Down syndrome (trisomy 21)- extra chrom. on 21st pair
abnormalities in chromosome structure
- translocation- exchange
- deletion- loss
- inversion- rearrange
implantation
- occurs 6-10 days after conception in upper uterus
- possible to have spotting
- implant into endometrium (outer layer)
pre-embryonic stage of pregnancy
- conception thru day 14
- zygote undergoes mitotic cellular division
- 50% of pregnancies end here and we never know preggo
morula/blastocyst
•dividing embryonic cellular mass
layers of embryo
- ectoderm- upper layer
- mesoderm- middle layer
- endoderm- lower layer
ectoderm
•epidermis, glands, nails & hair, central and peripheral nervous system, lens of the eye, tooth enamel, floor of the amniotic cavity
mesoderm
•Bones, teeth, muscles (skeletal, smooth, cardiac), dermis, connective tissue, cardiovascular system, spleen, urogenital system
endoderm
•Lining of the respiratory and digestive tracts, and the glandular cells of associated organs (oropharynx, liver, pancreas, urethra, bladder, and vagina), and the roof of the yolk sac
membranes around embryo
- begin to form once implanted
- amnion
- chorion
chorion
- contains chorionic villi
* becomes covering of fetal side of placenta
amnion
- inner cell membrane
- developing embryo draws amnion around itself forming fluid sac
- covers umbilical cord
amniotic fluid functions (4)
•cushions •maintains temperature •provides nutrients/waste disposal •keeps membrane away from developing fetus -provides freedom of growth movement
embryonic stage of development
- beginning of week 3 thru end of week 7
- major body organs formed
- differentiation begins
- cephalocaudal (head to toe)
- central to peripheral (inside to outside)
teratogens during embryonic stage
•embryo extremely vulnerable
•all or nothing effect
*this is before mom misses period, so may not realize exposing an embryo
week 3 pregnancy
- 1st missed period
- fetal CNS development (neural groove)
- early heart development
- primitive blood cells
week 4 pregnancy
•embryo C-shape •neural tube forming •face, upper resp. tract forming •upper extremity buds •partitioning of heart begins •HB at 17-18 days *earliest functioning system
week 5
- large head
- heart 4 chambers
- paddle shaped limbs w/ notches b/t fingers
- lower limbs less differentiated
week 6
- heart finishes formation
- more defined extremities
- facial, eye, ear development
neural tube
- structure that becomes brain and spinal cord
- requires folic acids
- development interference can result in defects (ex: spin bifida)
week 7
- continued growth/refinement of organs
- face more human
- intestines OUTSIDE abdominal cavity
- sex diff. begins
8 weeks
- eyes, ear, nose recognize
- s. intestine coils in um. cord
- ossification begins
- fetus begins moving
- heart/lung cavities forming
- external genitalia forming
- brain development begins
- spinal cord lengthens
fetal stage of pregnancy
- beginning of week 8 thru delivery
- all major organ systems present
- continued growth/refinement
teratogens during fetal stage
- can still cause CNS damage
* less likely to cause structural abnormalities
weeks 9-12
- fetal movement begins (undetectable)
- body grows faster than head
- intestines into abd. cavity
- blood formation in liver, then spleen
- produce urine
- fetal sex can be determined by autopsy
weeks 13-16
- rapid growth in length
* female has lifetime egg supply
16 weeks
- 5.5 inches tall; 6 oz
- brows, lashes, hair
- grasp, kick, somersault
- finger/footprints
- maybe determine sex w/ u/s
weeks 17-20
•quickening begins •vernix caseosa •lanugo •brows/head hair •swallow amniotic fld •produce own insulin *best time to do u/s
quickening
•start to feel fetal movement
vernix caseosa
•greasy deposit covering skin of baby at birth
lanugo
•fine soft hair
weeks 21-24
- 8”-9”; 1.5 lbs
- lungs produce surfactant
- capillary network around alveoli
24 weeks
- respond to sound
- distinguish taste
- react to temp
28 weeks
•3 lbs •storage of brown fat •eyelids un-fused (can see) •longer scalp hair •cerebral fissures •weak suck, cry *good chance of survival
brown fat
- unique source of heat for neonates
- around kidneys, neck, and b/t scapulae
- present for several weeks after birth
weeks 29-32
- 12”; 3.75 lbs
- finger/toenails extend
- subcutaneous fat deposited
- skin pigmented, pink, smooth
- surfactant increase
- may favor head-down position
lecithin (L)
- alveoloar surfactant required for post-natal lung expansion
- detectable @ 21 weeks
- increases after 24 weeks
sphingomvelin (S)
- pulmonary phospholipid
* remains constant in amnt
L/S ratio
- 2:1 indicates mature
* measured in amniotic fld
40 weeks
- 18-21”; 7.5 lbs
- good muscle tone
- myelination of brain
- sleep-wake cycle
- strong suck reflex
- testes/labia majora developed
placenta formation
- arises from Chorion
- implants into decidualized layer of uterus
- maternal spiral arteries adjust to accommodate blood flow
placenta gas exchange
- maternal and fetal circulation not directly attached to each other
- gas exchange occurs at lacunae areas b/t spiral arteries and fetal villi
fetal side of placenta
•placental arteries/veins converge into 2 placental arteries and 1 vein of umbilical cord
maternal side of placenta
- rough
* not covered with amnion
placental circulation supporting fetus
- completely by week 12
* placental malformations can result in miscarriage
post-conception
- ovary secretes progesterone from corpus luteum for 12 weeks prior to placenta taking over
- inadequate progesterone results in miscarriage
- ovulation also ceases
fetal gas exchange
- umbilical vein carries O2 blood and nutrients to fetus from placenta
- umbilical arteries carry CO2 wastes from fetus to placenta
fetal PO2
•~30 mmHg •fetus tolerates low PO2 b/c -higher Hgb and hct -high O2 carrying capacity of fetal Hgb -fetal HR 110-160 bpm
placental metabolic fxns
- gas exchange
- nutrient transfer (glucose major)
- waste removal
- antibody transfer
- maternal hormone transfer
good antibody transfer
•IgM
•protects infant 1st 2 months of life
•continued 3-6 months if breast fed
*baby immune to what immune to
bad antibody transfer
•Rh isoimmunization
estrogen fxn
•stimulates uterine growth
progesterone fxn
- maintains uterine lining to prevent miscarriage
- relaxes smooth muscle to prevent ctxn
- induces labor
human placental lactogen (hPL)
- growth hormone that stimulates mom’s metabolism to supply baby w/ glucose
- stimulates breast development
human chorionic gonadotropin (hCG) fxn
- produced by placenta following implantation
- detected 8-10 days post-conception
- preggo test positive
monozygotic twins
- identical
- 1 egg, 1 sperm
- same sex/genotype
dichorionic diamniotic
*division shortly after fertilization
•2 amnions
•2 chorions
•2 placentas
monochorionic diamniotic
*division 4-8 days after fertilization
•2 amnions
•1 chorion
•1 placenta
monochorionid monoamniotic
*division 8+ days after fertilization •1 amnion •1 chorion •1 placenta *conjoined twins
dizygotic twins
- fraternal
- 2 eggs, 2 sperm
- may be different sexes
- 2 amnions, 2 chorions, 2 placentas
- different genotype
