Repro-Embryo Flashcards
What are the important genes of embryogenesis?
Sonic hedgehog
Wnt-7 gene
FGF
Homeobox (Hox)
What is sonic hedgehog involved in during embryogenesis?
Involved in patterning along anterior-posterior axis, and CNS development.
Mutation in Hox would result in what?
Appendages in wrong locations
What occurs at Day 0 of gestation?
Fertilization occurs at the ampulla of the fallopian tubes
What hormones begin to elevate within one week of fertilization?
hCG secretion begins after implantation of the blastocyst in the uterine wall (stimulated by progesterone levels from the corpus luteum)
What embryogenic developments occur during week 2 of gestation? Week 3?
A bilaminar disc forms (epiblast and hypoblast)
2 weeks= 2 layers
During week 3 gastrulation causes the formation of a trilaminar embryonic disc. Cells from the epiblast invaginate to form the primitive streak and then the endo, meso, and ectoderm. The notochord form from the midline mesoderm and the overlying ectoderm becomes the neural plate (3 weeks= 3layers)
What embryogenic developments occur during weeks 3-8 of gestation?
neural tube formed by neuroectoderm and closes by week 4. Organ development begins during this time and fetus is extremely susceptible to teratogens during this time
Note that at week 6 fetal cardiac activity is visible by transvaginal ultrasound, and by week 8 fetal movements occur (gait at week 8)
The genital have male/female characteristics by week 10
When can a heart beat first be heard in a fetus?
typically around 4-5 weeks
What else is the fourth week of gestation marked by?
the heart begins to beat AND the limbs begin to form
4 weeks= 4 limbs
Describe the timeline between fertilization and implantation in the uterine wall
Fertilization occurs at day 0, followed by formation of a zygote at day 2, a morula by day 3, a blastocyst by day 5, and implantation by day 6
What is gastrulation?
The process that forms the trilaminar disc during week 3 of gestation. This process establishes the ectoderm, mesoderm, and endoderm.
What does the surface ectoderm develop into?
adenohypophysis (from Rathke’s pouch)
lens of the eyes
lining of the oral cavity
sensory organs of the ear and olfactory epithelium
Epidermis
anal canal below the pectinate line
parotid, sweat, and mammary glands
What does the neuroectoderm develop into?
Brain (neurohypophysis, CNS neurons, astrocytes, pineal gland)
retinal and optic nerve
spinal cord
What does the neural crest develop into?
PNS (dorsal root ganglia, cranial nerves, celiac ganglion, Schwann cells, and ANS)
melanocytes
chromaffin cells of adrenal medulla
parafollicular cells of the thyroid
pia and arachnoid
bones of the skull
What does the mesoderm develop into?
Muscle, bone, CT, serous linings of the body cavities (peritoneum)
spleen
CV structures
lymphatics and blood
wall of the gut tube and bladder
urethra, vagina, testes, and ovaries
dermis
kidneys
adrenal cortex
What are the effects of mutated mesodermal development?
VACTERL
Vertebral defects
Anal atresia
Cardiac defects
Tracheo-esophageal fistula
Renal defects
Limb defects (bone and muscle)
What does the endoderm develop into?
Gut tube epithelium (including anal canal above the pectinate line) and luminal epithelial derivatives (lungs, liver, gallbladder, pancreas, eustachian tube, thymus, parathyroid, and thyroid follicular cells)
Define agenesis and aplasia
Agenesis is the absence of an organ due to absent primordial tissue while aplasia is absent organ despite the presence of primordial tissue
Embryo are most susceptible to teratogens when?
During the 3rd’-8th weeks of development when organogenesis is occuring. If mutation occurs before then, either nothing will happen or the fetus will die.
What are the potential teratogenic effects of ACEIs?
renal damage
An ACE in the hole, kid
What are the potential teratogenic effects of Alkylating agents?
Absence of digits
Alk Charlie
What are the potential teratogenic effects of Aminoglycosides agents?
deafness
A mean guy hit the baby in the ear
What are the potential teratogenic effects of DES agents?
Vaginal clear cell adenocarcinoma (from vaginal adenosis) and congenital mullerian abnormalities
What are the potential teratogenic effects of Folate antagonist agents?
Neural tube defects (includes methotrexate, trimethoprim, and antiepileptic drugs)
What are the potential teratogenic effects of Lithium agents?
Ebstein abnormality (apical displaceent of the tricuspid valve)
What are the potential teratogenic effects of tetracyclines agents?
discolored teeth
What are the potential teratogenic effects of Thalidomide agents?
Limb defects (flipper limbs)
Limb defects with tha-limb-domide
Which is teratogenic, warfarin or heparin?
Warfarin
Dont wage warfare on a baby, keep it heppy
What are the potential teratogenic effects of Warfarin agents?
bone deformities, fetal hemorrhage, eye problems, SAB
What substance use during pregnancy has been linked to ADHD?
smoking. Nicotine is also related to low birth rate, placental problems, SIDS, and preterm labor
How would an iodine deficiency present during childbirth?
congenital goiter or hypothyroidism (cretinism)
What teratogen has been linked to increased prevelance of spontaneous abortions and birth defects including cleft palates and neural tube defects?
Vitamin A excess
How might X-ray exposure affect a fetus?
microcephaly or mental retardation
How are dizygotic twins made?
These arise from two seperate eggs that are seperately fertilized by 2 different sperm (always 2 zygotes), and will have 2 seperate amniotic sacs and placentas.
How are monozygotic twins made?
These twins arise from a single fertilized egg (1 sperm and 1 egg) that splits into two zygotes in early pregnancy
Conjoined monozygotic twins can arise if cleavage of the zygotes occurs after what point in gestation?
Day 13
What are the fetal components of the placenta?
cytotrophoblasts, which comprise the inner layer of the chorionic villi, and syncytiotrophoblasts, which comprise the outer layer
What do cytotrophoblasts do?
Make cells
What do syncytiotrophoblasts do?
secretes hCG, which stimulates the corpus luteum to secrete progesterone during the first trimester (lacks MHC I expression so there is less of a chance of attack by the maternal immune system)
syncytiotrophoblasts synthesis hormones
What is the maternal portion of the placenta?
Decidua basalis, which is derived from the maternal endometrium
What are the contents of the umbilical cord?
The umbilical cord consists of 2 umbilical arteries that return deoxygenated blood from fetal internal iliac arteries to the placenta, and a single umbilical vein which supplies oxygenated blood from the placenta to the fetus (drains via the ductus venosus into IVC)
The umbilical arteries and veins are derived from what?
the allantois
When does the allantois form?
during the 3rd week from the yolk sac.
What happens to the allantois (which removes nitrogenous wastes in utero)?
It forms part of the umbilicus and becomes the urachus, a duct between the bladder and yolk sac
What happens if the urachus fails to regress (i.e a patent urachus)?
urine discharges from the umbilicus after birth
NOTE: A urachal cyst forms when there is partial failure of the urachus to obliterate, leaving a fluid-filled cavity lined with uroepithelium between the umbilicus and the bladder. This can lead to infection or adenocarcinoma
What connects the yolk sac to the midgut lumen during gestation?
vitelline duct
When does the vitelline duct regress?
7th week of gestation
What happens if the vitelline duct fails to close?
A vitelline fistula forms, marked by meconium leaking from the umbilicus after birth
What is a Meckel’s divericulum?
Partial closure of the vitelline duct before birth, with a patent portion attached to the ileum.
What are the derivatives of the first aortic arch?
part of the maxillary artery from the external carotid a. (1st arch is maximal)
What are the derivatives of the second aortic arch?
stapedial artery and hyoid artery
Second= stapedial
What are the derivatives of the third aortic arch?
Common carotid artery and proximal part of the internal carotid artery
3rd letter of the alphabet is C
What are the derivatives of the fourth aortic arch?
on the left, the aortic arch, and the proximal aprt of the right subclavian artery on the right
What are the derivatives of the sixth aortic arch (fifth=0)?
proximal part of the pulmonary aa. and ductus arteriosis
Why does the left recurrent laryngeal nerve get caught under the aortic arch?
ligamentum arteriosum
What is the branchial apparatus?
Aka the pharyngeal apparatus, composed of branchial clefts, arches, and pouches
CAP covers outside from inside
Clefts (aka grooves)= ectoderm
Arches= mesoderm (and some neural crest)
Pouches= endoderm
What does the first branchial cleft develop into?
the external auditory meatus
What does the 2nd-4th branchial cleft develop into?
temporary cervical sinuses, which are obliterated by proliferation of 2nd arch mesenchyme.
NOTE: A persistance cervical sinus results in a branchial cervical sinus within the lateral neck
What are the cartilage derivatives of the 1st branchial arch?
Meckel’s cartilage; mandible, malleus, incus,
mandibular ligament
What are the muscle derivatives of the 1st branchial arch?
Muscles of mastication (tmeporalis, massester, lateral and medial pterygoids)
Mylohyoid
anterior belly of the digastric
tensor tympani
tensor veli palatini
What are the nerve derivatives of the 1st branchial arch?
CN V2 and V3 chew
What would abnormality of the 1st branchial arch cause?
Treacher Collins syndrome: 1st arch neural crest fails to nigrate leading to mandibular hypoplasia, and facial abnormalities
What cartilage structures derive from the 2nd branchial arch?
Reichert’s cartilage; stapes, styloid process, less horn of the styloid, and stylohyoid ligament
What muscle structures derive from the 2nd branchial arch?
Muscles of facial expression including the:
stapedius
stylohyoid
posterior belly of the dagastric
What nerve structures derive from the 2nd branchial arch?
CN VII-smile
What cartilage structures derive from the 3rd branchial arch?
greater horn of the hyoid
What muscle structures derive from the 3rd branchial arch?
stylopharyngeus (remember, the sytlopharyngeus is innervated by the glossopharyngeal nerve)
What nerve structures derive from the 3rd branchial arch?
CN IX (swallow stylishly)
What cartilage structures derive from the 4th-6th branchial arch?
thyroid, cricoid, arytenoids, corniculate, and cuneiform
What muscle structures derive from the 4th-6th branchial arch?
4th arch: pharyngeal constrictors: cricothyroid, levator veli palatini
6th arch: all intrinsic muscles of the larynx except cricothyroid
What nerve structures derive from the 4th-6th branchial arch?
4th: CN X (superior laryngeal branch)-simply swallow
6th: CN X (recurrent laryngeal branch)-speak
Nmeomic for nerve derivation of the branchial arches:
When at the restaurant with the golden arches, children tend to first chew (1), then smile (2), then swallow stylishly (3), or simply swallow (4), and then speak (6)
What are the derivatives of the 1st branchial pouch?
middle ear cavity, eustachian tube, and mastoid air cells
the 1st pouch contributes to the endoderm-lined structures of the ear
What are the derivatives of the 2nd branchial pouch?
epithelial lining of the palatine tonsil
What are the derivatives of the 3rd branchial pouch?
dorsal wings- develops into inferior parathyroids
ventral wings- develops into thyrmus
The 3rd pouch develops into 3 structures (thymus, and right/left inferior parathyroids)
What are the derivatives of the 4th branchial pouch?
dorsal wings- develop into superior parathyroids
What is DiGeorge Syndrome?
Aberrant development of the 3rd and 4th branchial pouches that results in T-cell deficiency (thymis aplasi) and hypocalcemia
What is MEN2A?
Mutation in germline RET (neural crest cells) causing:
parathyroid tumor, medullary thyroid cancer, and a pheochormocytoma
What causes cleft lip?
Failure of fusion of the maxillary and medial nasal processes (formation of primary palate)
What causes cleft palate?
failure of fusion of the lateral palatine processes, the nasal septum, and/or the median palatine process (formation of the 2ndary palate)
NOTE: Cleft lip and celft palate have 2 distinct etiologies, but often occur together
