reproductive: EMBRYOLOGY Flashcards
key roles of Sonic Hedgehog Gene (SHH gene) (2)
NOTE: embryonic SIGNALING protein
1- CNS development
2- Limb development
^^sonic like human with limbs and cns :)
Sonic Hedgehog Gene (SHH gene)
FUNCTION + MUTATION (+symptoms)
1- normal development of the hemispheres of brain
-abnormal: Holoprosencephaly
-remb: prosencephaly at wk3-4, at wk5 (telencephaly and diencephaly)
-symptoms:
a- single lobed brain
b- facial abnormalities (cleft lip/palate or cyclopia)
2- limb AP axis development: SHH is active in the zone of polarizing activity so influences the AER
limb development: 3 planes
1- Proximal to distal (humerus->radium->wrist) 2- dorsal- ventral axis (dorsal-extensor, ventral-flexors) ^^old famous drawing 3-Anterior-posterior axis Anterior towards head (radius and thumb) posterior (ulna fingers)
4 imp embryonic genes
1- Sonic Hedgehog
2- FGF
3- Wnt-7a
4- Homeobox (Hox) genes
proximal to distal development genes and description
structure called: Apical Ectodermal Ridge (AER); area of limb bud formation above “progress zone” in the mesoderm.
-key transcriptional factor: Fibroblast growth factor (FGF gene)
what happens if the AER is removed in proximal to distal development? is it replaceable?
LIMB stops growing
-replaced with FGF: normal growth
Wnt-7a gene
- function?
- gene deletion?
in the dorsal-ventral development
- KEY for DORSAL
- activates LMX-1 gene in mesoderm
- thus, DORSALIZES mesoderm
deletion: TWO VENTRAL sides
NOTE: ventral (Engrailed 1) represses Wnt-7 !!!
Wnt genes fxn
early embryo?
late embryogenisis?
early: DORSAL-VENTRAL axis
late: ANTERO- POSTERIOR axis
HOX genes fxn and mutation
- regulators of AP axis development
- mutation: abnormal limb (digits/toes) formations
e. g: fruit flies, polydactyly, syndactyly
(?N, ?C) in haploid spermatozoon ? haploid ovum ? zygote ? AFTER DNA SYNTHESIS IN ZYGOTE ? AFTER DIVISION ?
(1N, 1C) (1N, 1C) (2N, 2C) (2N, 4C) (2N, 2C)+(2N, 2C)
When does the two cell stage occur in fetus ?
first 1-2 days after ferilization
what forms after 2 cell stage? (2 steps)
MORULA (ball of cells) then BLASTULA (humans;blastocyst)
whats the difference b/w morula and blastula?
blastula contains fluid cavity (called BLASTOCOEL)
2 layers of blastocyst:
and their fxn
1- OUTER cells: Trophoblast -polarized (2 diff sides) -secrete watery fluid of blastocoel 2- INNER cell mass -apolar -give rise to ALL TISSUES of body (i.e embryonic stem cells)
what is implanted in implantation and when ?
- blastocyst in uterus
- day 6-10
when does B-hCG secretion begins?
what structure secretes it?
when pregnancy is detected?
- after implantation
- placenta
- day 6-10
what happens to the blastula?
GRANULATION 3 layered (gastrula) Ecto meso endo
describe the process of gastrulation. from what structures the 3 layers arise ?
-inner cell mass form bilaminar disc (2 layers separated by BM) 1- Epiblast GIVE RISE TO 3 germ layers 2- Hypoblast yolk sac (in womb) + other structures i.e not embryonic structures
what indicates the start of gastrulation ?
invagination of epiblast cells creates a VISIBLE LINE (primitive STREAK) in blastocyst
Ectoderm gives rise to (2)
1- epidermis
(outer surface skin, nailbed, hair)
2- NERVOUS system
what is the adult remnant of the notochord?
Nucleus pulposus of spine
NS development
notochord (from mesoderm) induces ectoderm to become neural plate that folds to give neural tube
Neural tube gives rise to
CNS structures
- CNS neurons, oligodendroctes, astrocytes
- retina
- spinal cord
Neural crest gives rise to
PNS structures
- cranial nerves
- dorsal root ganglia
- autonomic ganglia
- shwann cells
what CNS structures arise from the mesoderm ??
Microglia
Meninges
Endoderm gives rise to
- GI epithelium (and liver, gall bladder, pancreas)
- inner lung (alveoli, epithelium of trachea/bronchi)
airway cartilage
from what embryonic layer?
mesoderm
note alveoli, epithelium of trachea/bronchi from endoderm
mesoderm gives rise to
- muscle, bone, CT
- CV structures
- kidneys
- lymphatics
- blood
- airway cartilage
congenital defects from mesoderm derivatives (3)
1- congenital heart disease
2- limb deformities
3- renal defects
what is mesenchyme?
derived from what layer?
its tumors known as?
-embryonic CT
(in adults only found as stem cells)
-mostly mesoderm
-sarcmas
what is the embryonic period/ fetal period?
embryonic:
- 1st 8 weeks
- organogenesis
fetal:
- adult structures established
- organ/ structures grow
most vulnerable period for teratogens
EMBRYONIC PERIOD
Heart development wks?
week 4
heart begins beating
week 6
Transvaginal US detects fetal heart movement
Limbs development wks?
week 4
limbs form
week 8
baby begins moving
genitalia development wks?
identification of sex
prior to week 10 (genitalia looks similar)
- SRY gene (Y chromosome) : penis development
- lack of SRY: clitoris development
Ultrasound identification: usually weeks 15-20
Pituitary gland (anterior vs posterior) arises from
Anterior:
ECTODERM (rathke’s pouch)
outpouching of upper mouth
Posterior:
NEURAL TUBE
Adrenal gland (cortex vs medulla) arises from
Cortex:
MESODERM
aldosterone, cortisol, androgen
Medulla:
NEURAL CREST
epinephrine, norepinephrine
2 types of errors of morphogenesis +define briefly
Intrinsic: failure of embryo to develop
Extrinsic: external force impacts normal development
types of Intrinsic errors of morphogenesis (4)
- Agenesis
- Aplasia
- Hypoplasia
- Malformation
types of extrinsic errors of morphogenesis (2)
- Disruption
2. Deformation
difference between Agenesis and Aplasia
with EXAMPLE !
- Agenesis: missing organ caused by MISSING EMBRYONIC TISSUE
e. g: Renal agenesis - Aplasia: missing organ caused by GROWTH FAILURE OF EMBRYONIC TISSUE (present!)
e. g: thymic aplasia (DiGeorge syndrome)
what is hypoplasia ? e.g?
incomplete organ development
-microcephaly
- neural tube defects
- cleft lip palate
- congenital heart defects
what error of morphogenisis (intrinsic/extrinsic) and what type?
INTRINSIC
MALFORMATION:
abnormal development of structure
difference between disruption and deformation with examples
- Disruption: normal tissue GROWTH ARRESTED due to external force
e. g: AMNIOTIC BAND SYNDROME - Deformation: external force leads to ABNORMAL GROWTH (NOT ARREST)
e. g: Potter’s syndrome
diagnose:
-fetal structure entrapped by fibrous bands in utero (often involves limbs or digits)
and what type of errors in morphogenisis
- EXTRINSIC
- DISRUPTION
- AMNIOTIC BAND SYNDROME
what is potter’s syndrome? cause?
fetus exposed to ABSENT or LOW amniotic fluid!!
so amniotic fluid is frim fetal urine :)
caused by SEVERE RENAL MALFUNCTION (i.e reduced amniotic fluid)
leads to loss of fetal cushioning to external forces (fxn of normal amniotic fluid)
what is potter’s SEQUENCE ?
sequence of fetal abnormalities, all resulting from single problem: RENAL DYSFUNCTION
leads to:
1- External compression of the fetus (abnormal face/limb formation)
2- alteration in lung liquid content (abnormal lung formation)
(SUMMARY:
-PULMONARY HYPOPLASIA, LIMB/SKELETAL DEFORMITIES)
what trimester has the highest risk of teratogens fetal exposure
1st (i.e embryonic period)
first 2 weeks teratogens leads to:
“ALL or NONE” period
- spontaneous abortion
- no effect
in wks 2-8, teratogens lead to
Structural defects (organogenesis)
after wk 8 teratogens lead to
- decreased growth
- CNS dysfunction
- usually NO BIRTH DEFECTS
CATEGORIES A-D,X
A: no risk to fetus in HUMAN studies B: no risk to fetus in OTHER studies C: risk CANNOT BE RULED OUT D: POSITIVE evidence of risk X: CONTRAINDICATED IN PREGNANCY
ACEIs and ARBs in pregnancy
- class?
- 1st, 2nd, 3rd trimester?
1st: numerous congenital malformations
2nd 3rd !!!!!: OLIGOHYDRAMNIOS
(thus can lead to potter’s syndrome - sequence) (RAAS interferes w/ kidney)
seizure drugs in pregnancy
- most common effect on fetus?
- high risk drugs?
- in case of EPILEPSY women needs to take it, what do you give with it?
- NEURAL TUBE DEFECTS
- VALPROIC ACID!!, phenytoin, phenobarbital, carbamazepine
- HIGH dose folic acid supplementation
use of PHENYTOIN in pregnancy leads to:
Fetal Hydantoin Syndrome A) growth deficiency B) abnormal facial features -MICROCEPHALY -CLASSICALLY CLEFT LIP/PALATE -nose: broad, short -eyes: wide-spaced -ears: malformed
what malignancy is common in pregnant women ?
HODGKIN LYMPHOMA
ideally chemotherapy deferred to: what periods?
- after birth
- 2nd/3rd trimester
(note 1st trimester: high risk of fetal malformation)
What are the chemotherapeutics with the highest risks? (2)
what is their classic symptom?
1-Alkylating agents
2- antimetabolites
classically: MISSING DIGITS
embryopathy:
-abnormal facial features (low ears, wide spread eyes)
-congenital heart disease
-hydrocephalus
or spontaneous abortion
what drug did the mom take? class?
-Isotretinoin (derivative of vit A)
used to treat acne
-class X
women of reproductive age taking isotretinoin, should take what with it?
birth control mandatory