Usmle Step 1 - April 23

Front 1

Where is Sonic Hedgehog Gene produced and what is its function?

Back 1

SHH:
- produced @ BASE of limbs
(in the ZPA)
- Involves A-P Axis patterning
(anterior-posterior)
- Mediated ECTOdermal fx

Front 2

A mutation of what gene leads to holoprosencephaly?

Back 2

Defect in sonic hedgehog (SHH).

Holoprosenchephaly = Failure to develop 2 hemispheres in brain

Front 3

What is the function of WNT-7 gene?

Back 3

- Produced at the DISTAL end of developing limbs
(Apical Ectodermal Ridge)
- Necessary for D-V Axis organization
(dorsal-ventral)

Front 4

What is the FGF Gene and what is its function?

Back 4

FGF = Fibroblast Growth Factor
- produced at Apical Ectodermal Ridge
- Stimulates mitosis of MESODERM
- Results in lengthening of limbs

Front 5

What embryological gene is associated with Achondroplasia?

Back 5

Mutation in the FGF Gene
(fibroblast growth factor)

Front 6

What is the Hox gene & what is its function? What teratogen can interfere with it?

Back 6

Hox = Homeobox Gene
- involved in SEGMENTAL organization
(cranio-caudal direction)
- is the blueprint for skeletal morphology
(mutations = appendages in wrong location)

Teratogen = Retinoic acid (Vit A)

Front 7

What gene mutation results in Synpolydactyly?

Back 7

Mutation of HOX-D13

Synpolydactyly = extra fused digit b/w the 3rd and 4th digits

Front 8

Stages and timing from fertilization --> implantation of a pregnancy?

Back 8

Day 2 = Zygote (in tube)
Day 3 = Morula
Day 5 = Blastocyst
Day 6 = Implantation

Implantation --> release of ßhCG

Front 9

What is the primitive streak?

Back 9

First asymmetry in embryogenesis:
- Formed in the 3rd week
- Epiblast invaginates to form.
- Creates antero-posterior axis

This marks beginning of gastrulation.

Cells of primitive streak give rise to:
- Mesoderm
- Endoderm

Front 10

What embryological developments have taken place by week 2?

Back 10

Rule of 2's:

- 2 Germ cell layers
1) epiblast
2) hypoblast
- 2 Cavities:
1) amniotic cavity
2) yolk sac
- 2 Placental components
1) cytotrophoblast
2) syncytiotrophoblast

Front 11

What embryological developments have taken place by week 3?

Back 11

Rule of 3's:
- 3 Germ layers:
1) ectoderm
2) mesoderm
3) endoderm
(these are the Tri-Laminar Disc)
This is now the Gastrula.

Also:
- primitive streak has formed
- notochord & neural plate

Front 12

What is the bilaminar disc?

Back 12

This is the 2 germ layers that are present by week 2 of embryogenesis.

Includes:
- Epiblast
- Hypoblast

Front 13

What is the trilaminar disc?

Back 13

This is the 3 germ layers that make up the Gastrula in week 3 of development:
- Ectoderm
- Mesoderm
- Endoderm

Front 14

What are the early stages of neural development?

Back 14

1) Notochord induces ectoderm --> neuroectoderm --> neural plate

2) Neural plate --> invaginates forming Neural crest

3) Neural Crest --> Neural tube & Neural crest cells

Front 15

What happens to the notochord?

Back 15

After stimulating ecotderm --> neuroectoderm, it becomes the nucleus pulposus of the intervertebral disk in adults

Front 16

What are the landmarks of week 4 of embryological development?

Back 16

Rule of 4:
- 4 heart chambers (begins to beat)
- 4 limb buds formed

Also, the neural tube has closed by week 4 (problems e.g. spina bifida has occured by this point)

Front 17

Why is folic acid important to pregnant women immediately when they conceive?

Back 17

Folic acid is necessary for neural tube development, most of which is completed by week 4 of development.

Front 18

What is the embryonic period?

Back 18

Weeks 3-8 of development
- Organogenesis takes place.
- Extemely susceptible to teratogens

Front 19

When does the fetal period begin?

Back 19

Week 8 of development.

There is fetal movement and fetus looks like a baby

Front 20

By what time does the fetus have male/female genital characteristics?

Back 20

Week 10 of development
(12 Weeks since LMP)

Front 21

What are the embryologic derivatives of the Surface ectoderm?

Back 21

1) Adenohypophysis (anterior pituitary)
2) Lens (anterior of eye)
3) Epithelia:
- oral cavity
- olfactory
- anal canal (below pectinate)
- epidermis
4) Sensory organs of ear
5) Glands:
- sweat
- salivary
- mammary

Front 22

What is a craniopharyngioma and from what does it develop?

Back 22

A benign tumor from Rathke's pouch (surface ectoderm).

Seen with:
- cholesterol crystals
- calcifications

Front 23

What are the embryological derivatives of Neuroectoderm?

Back 23

Think CNS and Brain:
1) Brain
- CNS neurons
- neurohypophysis (posterior pituitary)
- pineal gland
- ependymal cells (line ventricles)
- glia (astrocytes, oligodendrocytes)
2) Retina (posterior eye)
3) Spinal Cord

Front 24

What are the embyrological derivatives of the Neural Crest?

Back 24

CACA MOTEL PASS:

C = Cranial Nerves
A = ANS - chain ganglia
C = Craniofacial structures (skull)
A = Arachnoid, pia

M = Melanocytes
O = Odontoblasts
T = Tracheal cartilage
E = Enterochromaffin cells - Adrenal medulla
L = Laryngeal cartilage

P - Parafollicular cells (C cells) - of thyroid
A = All ganglia - Dorsal root, Celiac, CN, ANS Chain
S = Schwann cells
S = Spiral septum - Aorticopulmonary septum

(think the PNS and non-neural surrounding structures)

Front 25

What are the embryological derivatives of Endoderm?

Back 25

1) Gut tube epithelium (above pectinate line)
2) Derivatives (2L, 2P, 2T):
- Lung
- Liver
- Pancreas
- Para-Thyroid
- Thymus
- Thyroid (follicular cells)

Front 26

What are the embryological derivatives of Mesoderm?

Back 26

1) Muscle, bone, CT
2) Linings (e.g. peritoneum)
3) Spleen
4) Circulation (CV, Blood, Lymphatics)
5) Uro-Genital & Gonads
6) Dermis (skin)
7) Notochord --> nucleus pulposus of intervertebral disk

Front 27

Birth defects related to Mesoderm?

Back 27

VACTERL Defects:

V = Vertebral defects
A = Anal atresia
C = Cardiac defects
T-E = Tracheo-Esophageal Fistula
R = Renal defects
L = Limb defects (muscle/bone)

Front 28

Classic characteristics of Fetal Alcohol Syndrome?

Back 28

1) Facial Abnormalities:
- nose = flat
- philtrum = smooth
- ears = low set ("railroad track")
- eyes = epicanthal folds
2) Retardation
3) Limb dislocation
4) Fistulas (heart and lung)
5) Cranial development (microcephaly, holoprosencephaly)

Front 29

When is developing baby most susceptible to teratogens?

Back 29

Embryonic period (3-8 weeks)

Time of organogenesis.
- before week 3 = all or nothing
- after week 8 = growth & fx

Front 30

What is the teratogenic effect of ACE Inhibitors?

Back 30

Renal damage

Front 31

What is the teratogenic effect of alkylating agents?

Back 31

Absent digits.
Multiple anomalies.

Are used in chemo to stop cell growth.

Front 32

What is the teratogenic effect of Aminoglycosides?

Back 32

CN VIII toxicity (hearing defects)

Front 33

What is the teratogenic effect of Carbamezepine?

Back 33

Neural tube defects (inhibit maternal folate absorption ~ like valproate)
Also:
- Craniofacial defects
- Fingernail hypoplasia
- Developmental delay
- IUGR

Front 34

What is the teratogenic effect of Diethylstilbestrol (DES)?

Back 34

Mullerian abnormalities (fallopian tubes, uterus, cervix, vagina)

Also increased vaginal clear cell adenocarcinoma risk.

Affects the "DES Daughters"

Front 35

What is the teratogenic effect of Tetracyclines?

Back 35

Discolored teeth

Front 36

What is the teratogenic effect of Thalidomide?

Back 36

Phocomelia = Limb defects
("flipper" limbs)

Front 37

What is the teratogenic effect of Warfarin?

Back 37

Bone deformities
Fetal hemorrhage
Ophthalmic abnormalities
Abortion

(use Heparin instead b/c it doesn't cross placenta)

Front 38

What is the teratogenic effect of DM?

Back 38

Caudal regression syndrome
Heart defects (transposition of great vessels)
Neural tube defects
Macrosomia

Front 39

What is the teratogenic effect of Retinoic Acid?

Back 39

Spontaneous abortions
Many birth defects d/t interference w/ HOX Gene

Front 40

What are the fetal components of the placenta and what do they do?

Back 40

1) Cytotrophoblast = INNER layer of chorionic villi that makes cells

2) Syncytiotrophoblast = OUTER layer of chorionic villi that makes hCG
(stimulates corpus luteum to continue to secrete PROG)

Front 41

What is the maternal component of the placenta and where does it develop from?

Back 41

The Decidua basalis.

It is derived from endometrium.

Front 42

What are the vessels in the umbilical cord?

Back 42

- 2 x Umbilical arteries = return DE-OXYGENATED blood from the fetal internal iliacs

- 1 x Umbilical Vein = brings OXYGENATED blood to fetus, draining into the fetal IVC

NOTE: umbilical vessels are derived from the allantois

Front 43

What is the most common congenital abnormality?

Back 43

Single umbilical artery.

Usually inconsequential, however commonly associated w/ renal problems; also associated w/ other congenital and chromosomal abnormalities.

Front 44

What problems occur if the urachal duct fails to close?

Back 44

Should obliterate in 3rd week.

1) Patent urachus = urine discharged from umbilicus

2) Vesicourachal diverticulum = outpouched bladder

Front 45

What problems occur if vitelline duct fails to close?

Back 45

Should obliterate in 7th week.

1) Vitelline fistula = meconium discharged from umbilicus

2) Meckel's diverticulum = partial closure

Front 46

What is Meckel's diverticulum, what is its cause, and what are some symptoms?

Back 46

Incomplete closure of vitelline duct leads to diverticulum @ the ileum.

Syx = periumbilical pain and melena
(can be d/t ectopic gastric mucosa)

Front 47

What are congenital anomalies associated with the Truncus arteriosus?

Back 47

Gives rise to ascending aorta & pulmonary trunk; neural crest cells --> aorticopulmonary septum

1) Transpotition of great vessels (failure to spiral)
2) Tetralogy of Fallot (skewed AP septum)
3) Persistant truncus arteriosus (partial AP septum)

Front 48

Where does fetal erythropoeisis occur?

Back 48

"Young Liver Synthesizes Blood"

Y = Yolk Sac (up to 8 weeks)
L = Liver (8-28 weeks)
S = Spleen (8-28 weeks)
B = Bone Marrow (28 weeks +)

Front 49

Difference b/w fetal and adult hemoglobin?

Back 49

Fetal has 2 gamma chains
Adult has 2 beta chains

Gamma has higher O2 affinity / lower 2,3-DPG affinity

Results in O2 shunt from mom --> infant

Front 50

Why does the foramen ovale close?

Back 50

Infant's first breaths cause:
1) decrease pulmonary pressure
2) increase (relative) LA pressure (vs RA pressure)

Foramen ovale --> Fossa ovalis

Front 51

What causes closure of the ductus arteriosus?

Back 51

Increase in O2 --> decrease in PG's

Rx = Indomethacin (helps close PDA)

PG's will keep PDA open

Front 52

What drug can help close a PDA?

Back 52

Indomethacin.

PG's will keep a PDA open.