Endocrine

Question 1

when does embryologic devp of thyroid gland begin?

From which layer?

When does TRH start?

When does TSH production start and thyroid hormone production?

Answer 1

3 weeks

thyroid gland from endodermal thickening in primitive pharyngeal floor 5 - 7 weeks

TRH by 6 - 8 weeks

Fetal thyroid accumulate I by 8-10 weeks

TSH and thyroid hormone secretion by 12 weeks

Question 2

Transitions of T4 and T3 - how amounts change in utero and then post natally

Answer 2

T4 - low until 18 - 20 wks (as hypothalamus and pituitary mature) -> increases with GA -> surge at birth 2/2 TSH surge -> peak 24 - 36 hours -> levels down over 1 - 2 weeks

T3 - low until 30 weeks when fetus can convert T4 to active T3 (mature type 1 deiodinase) -> surge at birth -> peak 24 - 36 hrs -> T3 levels increase post natally b/c of neonate’s ability to convert T4 to active T3

NOTE: fetal brain and pit T3 levels higher than serum

Question 3

TSH and thyroid hormones in premature infant

Also… compare AGA term to SGA term re. TSH, fT4, T4, etc.

Answer 3

Question 4

thyroid hormones post-natal

Answer 4

Question 5

presentation of 3 beta hydroxysteroid dehydrogenase

Answer 5

EARLY in the steroidogenesis pathway – cannot convert pregnenolone to progesterone; 17 oH pregnenalone to 17 OH progesterone; DHEA to androstenedione –> small phallus, abnormal external male genitalia (underdeveloped)

Question 6

Evaluation of under-virilized male

Answer 6

Electrolytes, LH, testosterone, DHT, FSH in 1st 24 hours, MIS (for testicular function)

Question 7

what gene facilitates differentiation of gonads to testes?

Answer 7

SRY on Y gene

Question 8

Sexual differentiation - when does it embryologically start?

When does virilization start in ebryo?

Answer 8

Sexual differentiation week 6 - 7

Virilization week 6 - 12

Question 9

Match the following:

Embryologic origin - mosonephric duct, coelemic epithelium, genital tubercle, labiascrotal folds

with…

Wolffian duct
Mullerian duc
Corpus cavernosa or clitoris
Scrotum or labia majora

Answer 9

wolffian duct - from excretory mesonephric duct

mullerian duct - from coelemic epthelium

corpus cavernosum or clitoris - from genital tubercle

scrotum or labia majora - from labiascrotal folds

Question 10

Review path of sexual differentiation and devp

Answer 10

Question 11

Pre to post natal TSH, thyroid hormone

Answer 11

Question 12

Osteopenia vs osteomalacia

Answer 12

Question 14

Hormonal adjustments to Ca and Ph - in intestines, bone

Answer 14

Question 15

Hormonal adjustments of PTH, calcitonin, vit D

Answer 15

Question 16

Review adrenal steroidogenesis pathways

Answer 16

Question 17

NB presents with ambiguous external genitalia, HTN, normal electrolytes, increased deoxycorticosterone and deoxycortisol concentrations.

Presumed diagnosis

Most appropriate management (eg rx)

Answer 17

11 beta hydroxylase deficiency (#2 common cause)

Low cortisol - cannot convert 11 deoxycortisol to cortisol
Low aldosterone - cannot covert deoxycorticosterone to corticosterone
Increased testosterone (alternate pathways)

NO salt wasting b/c deoxycorticosterone functions as a mineralcorticoid. SO manage by giving glucocorticoid replacement and eventual reconstructive surgery of abnormal female genitalia if desired

Question 18

Expected male baby XY genotype. On exam, micropenis, urethral meatus at base. Testes palpable in inguinal canal bilaterally. FOB with a mutation in the DNA binding domain of the androgen receptor.

Answer 18

Mutation of the androgen receptor (AR) which is encoded on the X chromosome – lack of androgen signaling results in decreased virilization. Testosterone upregulated due to lack of gonadotropin releasing hormone inhibition by testosterone so HIGH levels.

Question 19

Steroid profile of 21 alpha hydroxylase deficiency

Answer 19

Elevated

• Progesterone
• 17 OH progesterone, 17 OH pregnenolone
• Dehydroepiandrosterone -> androstenedione -> testosterone
• Renin

Decreased
- 11 deoxycorticosterone
- Deoxycorticosterone
- Aldosterone

Question 20

Review other abnormal lab values of enzymes deficiencies in adrenal steroidogenesis pathway

Answer 20