Endocrinology Flashcards
Dominant neonatal thyroid hormone
T3
Thyroid hormone that is increased during times of critical illness among preterm infants
Reverse T3
Which hormone helps with male external genital development during the first trimester of pregnancy?
Placental hCG
Which hormone helps with male external general development after the 1st trimester of pregnancy?
LH
Osteomalacia
Normal osteoid production
Decreased mineralization
Which enzyme deficiencies cause ambiguous male genitalia?
17 a-hydroxylase deficiency
3 b-hydroxysteroid dehydrogenase deficiency
5 a-reductase deficiency
Which enzyme deficiencies cause ambiguous genitalia in females?
21 Hydroxylase deficiency
11 b-hydroxylase deficiency
3 b-hydroxysteroid dehydrogenase deficiency
Aromatase deficiency
When is the pituitary gland formed?
14 weeks gestation
What is the thyroid gland formed from?
Primitive pharyngeal floor and 4th pharyngobronchial pouch
When does the thyroid gland develop?
3-4 weeks gestation
When does iodide trapping begin?
8-10 Weeks gestation
When does T4 and T3 synthesis and secretion begin?
12 weeks gestation
Adequate quantities of ___ are essential for fetal thyroid hormone synthesis
Iodide
Fetus relies on transplacental transfer of iodine for supply
When does TSH secretion begin?
12 weeks gestation
Where is TRH produced during pregnancy?
Pancreas and hypothalamus until closer to term
When does TSH surge occur after birth?
Peaks at 30 minutes of life
Lasts 3 to 5 days
Due to being cold at birth
When do fetal T3 levels increase during pregnancy?
30 weeks
Thyroid gland able to convert T4 to T3 more effectively
Most common cause of congenital hypothyroidism?
Thyroid dysgenesis
No thyroid or it’s in the wrong place
1:4000
Causes of congenital hypothyroidism
Thyroid dysgenesis
Thyroid dyshormonogenesis 1:40000
Central hypothyroidism 1:100000
Transient hypothyroidism 1:40000
Causes of thyroid dyshormonogenesis
TSH unresponsiveness
Iodide trapping defect
Organization defect
Iodotyrosine deiodinase deficiency
Symptoms of congenital hypothyroidism
Enlarged posterior fontanelle Macroglossia Prolonged jaundice Delayed passage of meconium Brittle hair/skin Edema Bradycardia Decreased reflexes
What causes decreased thyroid function in premature neonates?
Low TBG
Limited TSH surge
Premature withdrawal from maternal contribution
Can resolve after six weeks of age
What hormones in sick preemies can inhibit and reduce TSH secretion?
Dopamine
Glucocorticoids
What can methimazole cause in infants?
Cutis aplasia
Are infants of mothers with maternal Graves’ disease hypo or hyperthyroid?
Can be either
Thyroid receptor blocking antibodies and thyroid stimulating antibodies both cross the placenta
Treatment for hyperthyroidism
The order matters
- Methimazole
- Iodide (stuns thyroid, saturates receptors)
- Beta blocker (Controls HR)
What forms the anterior pituitary?
Evagination of oropharynx
Rathkes pouch
What forms the posterior pituitary?
Evagination of the floor of the third ventricle
When does the hypothalamic-pituitary axis mature?
20 weeks of gestation
Importance of testosterone from testes
Needed to allow for penile length
What is increased in 3beta HSD?
Pregnenolone
17-OH pregnenolone
DHEA
Symptoms of 3beta HSD
Salt wasting (no aldosterone) Cortisol deficiency Undervirilized male, virilized female
Newborn screen won’t catch this
Symptoms of 17beta HSD
Undervirilized male
Sufficient aldosterone and cortisol
Increased androstenedione
Symptoms of 5alpha reductase deficiency
Undervirilized male
Testes at 12 - enough testosterone with puberty to -> external genitalia development
Micropenis with decreased GnRH
GnRH receptor mutation
Micropenis with increased GnRH
LH receptor mutation
Symptoms of 21 hydroxylase deficiency
Salt wasting
Cortisol deficiency
Virilized female
Elevated 17 OHP
21 hydroxylase deficiency
Genetics of 21 hydroxylase deficiency
Autosomal recessive
CYP21A2 gene
Symptoms of 11 hydroxylase deficiency
Elevated deoxycorticosterone -> hypertension
Overvirilized female
How does maternal calcium adapt during pregnancy?
Increase calcium from gut and skeleton
Decreased calcium in urine
How much of total calcium is accumulated during the third trimester?
80%
When do phosphorus and magnesium accretion peak during pregnancy?
Third trimester
Ca > Phos > Mag
Mineral accretion is directly correlated to ___
Fetal weight gain
What are the actions of parathyroid hormone?
Increase Ca gut resorption
Decreased calcium in the urine
Increased calcium in the bone
What hormone does vitamin D need?
PTH
What role does PTH play in vitamin D metabolism?
25-OH -> 1,25-OH vitamin D
When does the fetal kidney have full capacity for vitamin D hydroxylation?
24 weeks gestation
What happens if maternal vitamin D levels are low?
Congenital rickets
No vitamin D to cross the placenta
What are the effects of estrogen on bone metabolism?
Increased mineral accretion in bone
What is the effect of GH on bone metabolism?
Proliferation of chondrocytes
What is the effect of PTHrP on bone metabolism?
Differentiation and proliferation of resting chondrocytes
What is the effect of vitamin A on bone metabolism?
Deficiency inhibits longitudinal bone growth
What is the effect of elevated calcitonin on bone metabolism?
Inhibition of bone resorption
Worse for bones
Umbilical Cord versus maternal calcium levels
Cord calcium levels are 1-2 mg/dL higher than maternal concentration
Neonatal compensation after birth for calcium
Increase PTH
Increase efficiency of intestinal Ca absorption (without vitamin D) - 1 month only
Renal maintenance of Ca and Phos homeostasis
Why do IDM babies have hypocalcemia?
Decreased transplacental transfer of calcium
2/2 increased urinary excretion of Ca and Mg (maternal glycosuria)
Which mineral is needed for PTH release?
Magnesium
Why do blood transfusions lead to hypocalcemia?
Transfused blood contains citrate which sequesters calcium
Why do glucocorticoids lead to hypocalcemia?
Transient suppression of bone turnover - Decreased osteoblast proliferation/activity
What mineral in TPN reduces vitamin D conversion in the kidneys?
Aluminum
Leads to decreased PTH secretion
Which medications can decrease calcium levels?
Caffeine
Loop diuretics
Glucocorticoids
What is the primary nutritional cause of developing osteopenia of prematurity?
Phosphorus deficiency
All enzymatic processes using phosphorus as an energy source require ___ for activation
Magnesium
Familial hypocalciuric hypercalcemia
Inactivation of calcium sensing receptor in kidney
PTH is elevated
What is the principal metabolic fuel for the brain?
Glucose
Where does a fetus get its glucose from?
Maternal glucose thru placental transfer via GLUT1 receptor
There is no fetal endogenous production of glucose
What happens at birth once the neonates glucose transfusion is disrupted?
3-5X increase in glucagon
Increased epinephrine
Increased growth hormone
Decreased insulin
What are some adaptive mechanisms during a fast/hypoglycemia?
Glycogenolysis
Lipolysis
Gluconeogenesis
Ketogenesis
What are the four neonatal sources of glucose?
Dietary
Glycogen stores from liver
Cleavage of complex sugars from the gut
Gluconeogenesis
Definition of neonatal hypoglycemia
<50 first 48 hours
<60 After 48 hours
Causes of transient neonatal hypoglycemia
Immature adaptation
Hyperinsulinism
Causes of prolonged neonatal hypoglycemia
Hyperinsulinism due to:
IUGR, prematurity
Birth asphyxia
Maternal toxemia/preeclampsia
Causes of persistent neonatal hypoglycemia
Hormonal- Hyperinsulinism, deficiency of cortisol or GH
Glycogenolysis disorders
Gluconeogenesis disorders
Fatty acid oxidation disorders
During hyoglycemia what should the insulin level be?
Undetectable
Congenital hyperinsulinism
Due to a focal lesion or entire pancreas secreting insulin
CT and PET scan with 18 fluro L dopa scan can differentiate between the two
Congenital disorders of glycosylation
Carbohydrate deficient glycoprotein syndrome
Cannot make N-linked oligosaccharides
Symptoms of Congenital disorders of glycosylation
Hypoglycemia Developmental delay FTT Hypotonia Coagulopathy Acquired hypothyroidism Seizures
Most common cause of neonatal hyperglycemia
Iatrogenic
Transient Diabetes in neonates
First 4-6 weeks of life
Mutation on chromosome 6
Self resolves between 3-6 months of age
Large insulin requirements
Permanent causes of neonatal hyperglycemia
Pancreatic agenesis
Mutations in glucokinase
Mutations in sulfonylurea receptor
Wolcott-Rallison syndrome
Wolcott-Rallison syndrome
Cause of neonatal hyperglycemia
Cardiac/hepatic/renal anomalies
Multiple epiphyseal/spondyloepiphyseal dysplasia
Symptoms of Neonatal diabetes mellitus
First 6 months of life IUGR Dehydrated Poor weight gain Hyperglycemia
Genetic defect in neonatal diabetes mellitus
KCNJ11 or ABCC8
Activating mutations in K-ATP channels in pancreas
Genetics of DEND syndrome
KCNJ11 mutation
Chr 11p15.1
Only 20% of patients with this mutation develop DEND syndrome
All will have diabetes mellitus
Symptoms of DEND syndrome
Developmental delay
Epilepsy
Neonatal diabetes

Thyroid surge in SGA versus AGA neonates
TSH higher and T4 lower in SGA neonates compared to AGA
Thyroglobulin is ___ in preterm infants compared to term infants
Elevated