Endo Flashcards
When is fetal thyroid functional?
10-12 weeks Begins thyroglobulin at 8 wks Accumulates iodide at 10 wks TSH 12 wks Thyroid hormones 12 wks
What is the highest type of thyroid in fetal life?
rT3
T4 low until rises at 18-20 wks
T3 low until rises ~30 wks
Both T3 and T4 rise 2-6x after birth
What maternal thyroid hormone does not cross placenta?
TSH
All others do: T3, T4 (partial); TRH, TSH receptor antibodies
What are components of T3? T4?
T3: monoiodotyrosine and diiodotyrosine
T4: two diiodotyrosine
How are T3 and T4 different?
T3 more potent, intracellular, only 9% of secreted thyroid hormone
T4 90% of secreted thyroid hormone, extracellular, higher concentration in blood (50-100x), binds proteins more
What is best test for hypothyroidism after the TSH surge?
TSH
What is most common cause of congenital hypothyroidism?
Thyroid dysgenesis (75%): ectopic, aplasia, hypoplasia
What is Pendred syndrome?
Autosomal recessive
Organification defect with congenital 8th nerve abnormality. Deafness, goiter
What is incidence of neonatal hyperthyroidism if mom has Graves?
1-5%
Due to transplacental passage of TSH receptor stimulating antibodies and blocking antibodies
How to treat neonatal hyperthyroidism?
- Treat with propylthiouracil or methimazole
- Beta blocker
- Iodide (rapidly inhibit thyroid hormone release)
- Glucocorticoids
Ok to breastfeed
What are 3 main pathways of adrenal cortex and what are end products?
- Mineralcorticoids - aldosterone
- Glucocorticoids - cortisol
- Androgens/Estrogens - estrogen, testosterone
What is most common cause of congenital adrenal hyperplasia?
21- hydroxylase deficiency
Leads to elevated 17-OH, lack of mineralcorticoid and glucocorticoid. Too much androgens
What is second most common cause of congenital adrenal hyperplasia?
11- beta hydroxylase deficiency
Cant make cortisol or aldosterone (but can make aldosterone precursor so no salt wasting). Still too much androgens.
Dx: high deoxycorticosterone and 11-deoxycortisol
What is difference between 17 alpha hydroxylase deficiency and 3 beta hydroxysteroid dehydrogenase deficiency?
17 alpha: ambiguous male genitalia, normal female but no secondary sexual traits. Low 17-OH progesterone and 17-OH pregnenolone
3 beta: small penis, severe hypospadias; high 17-OH pregnenolone, high 17-OH pregnenolone, DHEA
How is cortisol made?
Corticotropin - releasing hormone (CRH, hypothalamus) -> ACTH (anterior pituitary) -> cortisol (adrenal cortex)
What is the typical genotype of a true hermaphrodite?
Over half are 46, XX but majority raised as males
Why is Kleinfelter syndrome infertile?
Atrophy of seminiferous tubules
Also have small genitals and gynecomastia (in 1/3, with inc risk of breast cancer)
How does aromatase deficiency present?
Inability to convert testosterone to estradiol and androstenedione to estrone.
Ambiguous female genitalia, multicystic ovaries, tall, virilization at puberty, delayed bone age
How does 5 alpha reductase deficiency present?
Males with ambiguous genitalia, small penis, blind vaginal pouch. Infertile. Testes descend at 12.
Females have normal phenotype.
How does androgen resistance or insensitivity present?
Present as females, but have have hernias/labial masses. No uterus, testes present
High LH, normal FSH, high testosterone
Which testicle is more likely to be undescended?
Right
Only 1/3 of cases are bilateral
When do majority of testes descend?
By 9 months (90% of preterm infants, 75% of full term infants)
Orchiopexy by 1 year
What hormone does anterior pituitary make? Posterior?
Anterior: 1. TSH 2. LH 3. FSH 4. Prolactin 5. GH 6. ACTH Posterior: 1. Vasopressin (ADH) - stored and secreted here 2. Oxytocin (also stored and secreted)
How do Ca, Mg, and Ph cross placenta?
Active transport
