Usmle Step 1 - April 26 (Embryo)

Front 1

What are the regions of the GI, their ranges, and blood supplies?

Back 1

1) Foregut = pharynx -> duodenum (celiac a.)

2) Midgut = duodenum -> transverse colon / splenic flexure (SMA)

3) Hindgut = transverse colon / splenic flexure -> rectum (IMA)

Front 2

What are the defects caused by failure of anterior abdominal wall closure?

Back 2

Rostral fold --> Sternal defects

Lateral fold:
- gastroschisis
- omphalocele

Caudal fold --> bladder extrophy

Front 3

What is gastroschisis?

Back 3

Extruding abdominal contents d/t failure of the lateral folds to close.

- NOT covered by peritoneum
- liver never protrudes
- lateral to the midline (R>L)

Front 4

What is an omphalocele?

Back 4

Persistence of umbilical herniation of the abdominal contents.

- covered in peritoneum
- also liver usually protrudes
- 50% have other abnormalities (GI, GU, CV, CNS, MSK)

Tx = Sx (sometimes w/ a silo)

Front 5

What are the causes of different types of GI atresias?

Back 5

1) Down syndrome (21) = Duodenal

2) Vascular accident (apple pear atresia):
- jejunal
- ileal
- colonic

Front 6

What are the stages and timing of midgut development?

Back 6

6th Week = Herniation thru umbilical ring --> rapid growth

10th Week = Return & rotation around SMA

Front 7

What are the pathological consequences of failures in midgut development?

Back 7

- malrotation
- omphalocele (failure to return)
- volvulus (twisting around SMA)
- intestinal atresia & stenosis

Front 8

What is the most common type of tracheoesophageal sphincter and what are the signs?

Back 8

Type C:
- Blind upper esophagus
- Lower esophagus connected to trachea

Causes:
- choking & vomiting w/ food
- failure to pass NG tube
- pneumonitis (aspiration)
- cyanosis
- air bubble in stomach on CXR

Front 9

What is the most common condition requiring Sx int he first month of life? What are signs/symptoms?

Back 9

Congenital pyloric stenosis
(esp. first born males)

- Palpable "olive" epigastric mass
- NONbilious projectile vomiting (2 weeks old)

Metabolic findings:
- Hypochloremic
- Hypokalemic
- Metabolic ALKalosis

(d/t vomiting)

Front 10

What are origins of the parts of the pancreas?

Back 10

Liver diverticulum (from foregut) --> VENTRAL pancreatic bud (VPB)

VPB migrates around 2nd part of duodenum and fuses with DORSAL pancreatic bud (DPB)

VPB --> Uncinate process
DPB --> Body, Tail, Isthmus & accessory duct

BOTH = Head & Main duct

Front 11

What is the cause of an Annular pancreas?

Back 11

1) Abnormal encircling of 2nd part of duodenum by VENTRAL pancreatic bud

Front 12

What conditions are associated with annular pancreas in infants?

Back 12

1) Polyhydramnios
2) Down syndrome (21)
3) GI continuity problems
- atresias (esophagus & duodenum)
- meckel's diverticulum (ileum)
- imperforate anus (rectum)

Front 13

What is pancreas divisum and what causes it?

Back 13

Failure of the dorsal and ventral pancreatic buds to fuse by 8th week.

Front 14

What is the embryonic origin and blood supply of the spleen?

Back 14

- Mesoderm (dorsal mesentery)
- Celiac artery (foregut)

Front 15

What is the function / purpose of the mesonephros?

Back 15

1) 1st trimester acts as interim kindey

2) Ureteric bud --> gives rise to the drainage system:
- collecting ducts
- calyces
- pelvices
- ureters

3) Males: ducts --> internal structures

Front 16

What forms the permanent kidney?

Back 16

Metanephros

Begins @ 5 weeks --> through 32-36 weeks

Metanephric mesenchyme interacts w/ ureteric bud to create functional unit of kindey:
- glomerulus
- renal tubules (PT -> DCT)

Front 17

What condition results from malformation of the ureteric bud and what are its consequences?

Back 17

Potter's Syndrome = Bilateral renal agenesis

Results:
- oligohydramnios
- pulmonary hypoplasia
- limb & facial deformities

Front 18

What is the sequence of male genital embryology?

Back 18

1) SRY gene (Y chrom) --> Testis determining factor:

2) Sertoli cells --> Müllerian inhibiting factor --> suppresses paramesonephric ducts

3) Leydig cells --> Testosterone --> stimulate mesonephric ducts (internal genitals)

4) Testosterone --> DHT --> stimulates:
- genital tubercle (glans & corpus cavernosum / spongiosum)
- urogenital sinus (glands: prostate & bulbourethral)

Front 19

What genital abnormalities would be seen with absent Sertoli cells?

Back 19

BOTH male and female INTERNAL genitalia

Male EXTERNAL genitalia

(same effect as missing anti-Müllerian hormone)

Front 20

What genital abnormalities would be seen in a 5α-reductase deficiency?

Back 20

For a genetic male (SRY active):
- Male INTERNAL genitalia
- Ambiguous EXTERNAL

Front 21

What are the derivatives of the Genital Tubercle in males and females?

Back 21

Males:
- glans penis
- corpus (cavern & spong)

Females:
- glans clitoris
- vesibular bulbs

Front 22

What are the derivatives of the Urogenital sinus in males and females?

Back 22

UGS = Glands

Males:
- Bulbourethral glands
- Prostate gland

Females:
- Vestibular glands
- Urethral / Paraurethral glands

Front 23

What are the derivatives of the Urogenital folds in males and females?

Back 23

Folds = the Middles

Males = Ventral SHAFT of penis

Females = Labia MINORA

Front 24

What are the derivatives of the Labioscrotal swelling in males and females?

Back 24

Labio-Scrotal?

Females = Labia MAJORA
Males = Scrotum

Front 25

What are the derivatives of the mesonephric ducts?

Back 25

aka wolffian ducts

Male internal structures = SEED:
- Seminal vesicles
- Epididymis
- Ejaculatory duct
- Ductus deferens

Front 26

What are the derivatives of the paramesonephric ducts?

Back 26

aka müllerian duct

Female internal structures:
- fallopian tube
- uterus
- UPPER 1/3 vagina

(the lower 2/3 = urogenital sinus)

Front 27

How can Paramesonephric / Müllerian duct abnormalities present?

Back 27

1) Primary amenorrhea in females w/ secondary sexual characteristics.

Anatomical defects but functional ovaries.
(NOTE: lower 2/3 vagina normal)

2) Bicornuate uterus d/t incomplete fusion (if severe can see "double-barreled vagina")

Front 28

What is hypospadia and what causes it?

Back 28

Abnormal opening of penile urethra on INFERIOR side

d/t failure of: Urethral fold closure
(folds = the middle / shaft)

Front 29

What is epispadia, what causes it, and what is associated with it?

Back 29

Abnormal opening of penile urethra on SUPERIOR side of penis.

d/t faulty position of: Genital tubercle
(tubercle = head / "meat" of penis)

Associated w/ Extrophy of bladder

Front 30

What are the remnants of the Gubernaculum?

Back 30

Gubernaculum GLUEs everything down
(band of fibrous tissue).

Male = Anchors testes
Female = Ligaments:
- ovarian ligament
- round ligament (of uterus)

Front 31

What are the remnants of the Processus vaginalis?

Back 31

It's an eVAGination of the periotoneum:

Males = tunica vaginalis
Females --> obliterated
(females already have 1 vagina)

Front 32

What is cryptorchism?

Back 32

Undescended testis
(usually unilateral; higher risk in premies)

Effects:
- Sertoli cells ~ impaired:
- spermatogenesis
- inhibin --> therefore increased FSH

- Leydig cells ~ not affected:
- normal Testosterone (therefore normal LH)

35x increased risk of germ cell tumors if not removed

Tx = Orchiopexy if young, orchiectomy if older

Front 33

What condition would you commonly workup for infertility in a man?

Back 33

Klinefelter's (XXY)
- Sertoli: ↓ inhibin --> ↑FSH
- Leydig: ↓ test --> ↑LH --> ↑E2

Also, look for Barr body

Front 34

What is the most common cause of 1º amenorrhea w/o 2º sexual characteristics?

Back 34

Turner Syndrome (XO)

Front 35

What is the likely diagnosis for:
↑ LH
↑ Testosterone?

Back 35

Defective androgen receptor (e.g. Androgen insensitivity syndrome)

W/o Andro-R on Anterior Pit, there is loss of negative feedback

Front 36

What is the likely diagnosis for:
↓ LH
↑ Testosterone?

Back 36

Exogenous Testosterone:
- tumor
- supplementation

Negatively feeds back to Anterior Pit, which stops secreting LH

Front 37

What is the likely diagnosis for:
↑ LH
↓ Testosterone?

Back 37

1º Hypogonadism

Lacking Leydig cells, so will not produce Testosterone even w/ increased LH secretion from Anterior Pit

Front 38

What is the likely diagnosis for:
↓ LH
↓ Testosterone?

Back 38

HYPOgonadotropic HYPOgonadism

(missing the Anterior Pit or just LH, but can't stimulate Leydig cells to secrete T)

Front 39

What are the components of the Triple Test and how/when is it used?

Back 39

1) AFP
2) (ß)hCG
3) E3

Performed @ 16-18 weeks; if abnormal, then U/S to determine if development is consistent w/ dates.

Front 40

What is the most common cause for elevated AFP?

Back 40

Dating error (underestimating date of gestation)

Front 41

In pregnancy, what produces AFP and what are conditions associated w/ abnormal levels?

Back 41

AFP produced by:
- Yolk sac (early)
- Fetal Liver
- Fetal GI

↑ AFP a/w:
- neural tube defects
- anterior abdominal wall defects:
- omphalocele
- gastroschisis
- multiples

↓ AFP a/w:
- Down syndrome

Front 42

In pregnancy, what produces hCG and what are conditions associated w/ abnormal levels?

Back 42

hCG produced by trophoblasts.

↑ hCG a/w:
- multiples
- moles
- choriocarcinoma

Front 43

In pregnancy, what produces Estriol and what are conditions associated w/ abnormal levels?

Back 43

E3 produced by both:
- fetus
- placenta

↓ E3 a/w
- placental insufficiency

Front 44

What is an "apple peel atresia"?

Back 44

It is a small bowel or colonic atresia d/t a vascular accident leading to SMA obstruction. The mesentery of that bowel is absent and its associated bowel segment forms a spiral around the vessel.

This is not congenital, as it is not d/t abnormal fetal development.

Front 45

What neoplasias are associated with MEN 1?

Back 45

3 P's (diamond):
- Pituitary
- Parathyroids
- Pancreas

Front 46

What neoplasias are associated with MEN 2A?

Back 46

2 P's (square)
- Parathyroids
- Pheochromocytoma (medulla)
- Thyroid (medulla)

RET proto-oncogene

Front 47

What neoplasias are associated with MEN 2B?

Back 47

1 P (triangle)
- Pheochromocytoma (medulla)
- Thyroid (medulla)
- Oral/Intestinal mucosa (anglioneuromatosis)

Front 48

What lab finding corresponds with a pheochromocytoma?

Back 48

Increased vanillymandelic acid (VMA) = catecholamine metabolite.

Measured in urine.

Front 49

Unilateral aplasia of the fibula is an example of a failure of what embryologic process?

Back 49

Proliferation

Front 50

Autoimmune disease d/t persistence of autoreactive T/B Cells is an example of a failure of what embryologic process?

Back 50

Apoptosis

Front 51

Branchial cleft cysts is an example of a failure of what embryologic process?

Back 51

Obliteration

Front 52

Hirschsprung disease is an example of a failure of what embryologic process?

Back 52

Migration

Front 53

Hypospadias is an example of a failure of what embryologic process?

Back 53

Fusion

Front 54

An ostium primum atrial septal defect is an example of a failure of what embryologic process?

Back 54

Fusion

(of the endocardial cushions)

Front 55

What are the phases of cellular replication that female germ cells are arrested in?

Back 55

1) 1º oocytes = Prophase 1
(all are in this stage after about 5 months gestation)

↑FSH stimulates to complete Meisosi 1....

2) 2º oocytes = Metaphase 2
(↑E2 & ↑LH cause release from follicle and remain in Metaphase 2 until fertilization)