Endocrine Flashcards
What step in the citric acid cycle is essential to gluconeogenesis and why?
Gluconeogenesis requires the hydrolysis of GTP for the phosphorylation and decarboxylation of oxaloacetate to PEP (phosphoenopyruvate) by PEP carboxykinase.
GTP is formed during the conversion of succinyl CoA to succinate.
When is metformin contraindicated?
Major side effects are gastrointestinal upset and lactic acidosis
Metformin is contraindicated in any situation that might precipitate lactic acidosis:
- Renal failure
- Liver dysfunction
- Congestive heart failure
- Alcoholism
- Sepsis
How does prolactin affect the GnRH-LH/FSH axis?
Inhbits/decreases levels of all of them
Which congenital adrenal hyperplasia results in a virilized baby girl?
21-hydroxylase deficiency
What two reactions does 21-hydroxylase normally catalyze?
- Conversion of 17-hydroxyprogesterone –> 11-deoxycortisol
2. Conversion of progesterone –> 11-deoxycorticosterone
What can cause increased insulin, c-peptide, and pro-insulin levels?
- Sulfonylurea or meglitinide abuse
2. Insulinoma
What does an increased urinary VMA excretion and an adrenal mass raise your suspicion of?
Pheochromocytoma - VMA is a catecholamine metabolite
What is the genetic defect associated with MEN 2A and 2B?
Germ-line mutation of the RET proto-oncogene which affects neural crest cell migration
Both chromaffin cells of the adrenal medulla and parafollicular cells (C-cells) of the thyroid originate from neural crest; this is why we see tumors in both the adrenal medulla and the thyroid
What are the amino acids with 3 titratable protons?
- Arginine
- Aspartic acid
- Cysteine
- Glutamic acid
- Histidine
- Lysine
- Tyrosine
What enzyme does IP3 activate?
Protein kinase C
What can you give to prevent thyroid absorption of radioactive iodine isotopes?
Potassium iodide - competitive inhibition
Presentation: Vomiting, abdominal pain, hypotensive, tachycardic, hypoglycemic, generalized hyperpigmentation
Diagnosis?
Adrenal crisis
What is the treatment for adrenal crisis?
Corticosteroids
What is the mechanism of flutamide?
Competes with testosterone and DHT for testosterone receptors
Flutamide is a non-steroid anti-androgen used for treatment of prostate cancer in combination with GnRH agonists
What enzyme mutation can result in mild hyperglycemia?
Glucokinase - glucose sensor within pancreatic beta cells
How does septic shock lead to lactic acid formation?
Impaired tissue oxygenation decreases oxidative phosphorylation, leading to shunting of pyruvate to lactate after glycolysis
What is often the cause of pneumonia in elderly patients with dementia or hemiparesis?
Dysphagia leading to aspiration
Which tissues contain well-developed smooth endoplasmic reticulum?
All steroid-producing cells (e.g. cells in the adrenals, gonads, liver)
What is the medication of choice for gestational diabetes?
Insulin
What is biotin?
CO2 carrier on the surface of the carboxylase enzyme that is necessary for numerous conversions, including pyruvate to oxaloacetate
What volume condition does diabetes insipidus lead to?
Hyperosmotic volume contraction - loss of free water water with retention of electrolytes
In overweight individuals, what is believed to increase insulin resistance?
FFA and serum triglycerides
How do you differentiate diabetes insipidus from polydipsia?
Water deprivation test - with polydipsia, you will see a steady, reliable, and prompt increase in urine osmolality and a paltry response to vasopressin (< 10%)
With polydipsia, you will also see serum Na < 142 because of intake of so much water vs. DI where you are excreting water and retaining the electrolytes
How does estrogen affect thyroid hormone levels?
Estrogen leads to increase in TBG (thyroid binding globulin) which leads to increase in circulating total T4 and total T3. However, the level of free thyroid hormone is normal.
What is the only glucose transporter that is responsive to insulin and what tissues is it found in?
Glut 4 - found in muscle cells and adipocytes
What should be monitored in patients taking amiodarone (for side effects)?
Thyroid function tests
Is pancreatic islet amyloid deposition associated with type I or type II diabetes?
Type II
How do we treat congenital adrenal hyperplasia?
Low dose corticosteroids to suppress excess ACTH secretion
What is the characteristic histologic finding of Hashimoto’s thyroiditis?
Mononuclear, parenchymal infiltration with well-developed germinal centers
Why do antipsychotics (e.g. risperidone) cause amenorrhea?
They have antidopaminergic action which leads to hyperprolactinemia which inhibits the release of GnRH.
What are serum levels of LH, FSH, testosterone, and sperm count in Klinefelters?
Decreased testosterone, sperm count
Increased LH/FSH
In Klinefelter’s - serum inhibin levels are decreased as a result of damage to the semniferous tubules
What happens to testosterone and DHT levels when you give leuprolide?
Transient increase that gives way to decrease in both testosterone and DHT
Leuprolide is a GnRH analog
Thyroid histology: Extracellular deposits of amyloid formed by calcitonin secreted from neoplastic parafollicular cells
Diagnosis?
Medullary thyroid carcinoma
What is MEN 1?
Para-Pan-PIt: Parathyroid, Pancreas, Pituitary tumors
What is MEN 2A?
MPH: Medullary thyroid, Pheochromocytoma, Hyperplasia of the parathyroid
What is MEN 2B?
MMMP: Medullary thyroid, Marfanoid habitus, Mucosal neuromas, Pheochromocytoma
Where is ADH synthesized?
Hypothalamus - paraventricular and supraoptic nuclei
What causes a neonate to be hypoglycemic if the mother has gestational diabetes?
Diffuse hyperplasia of the islets
The baby responds to high sugars from mom by increasing its insulin production via hyperplasia of the insulin producing cells. This results in hypoglycemia once the baby is delivered.
Why does hyperaldosteronism lead to paresthesia and muscle weakness?
Excess K secretion to maintain electroneutrality from increased Na retention (increased ENaC is a result of aldosterone)
Hypokalemic states can give rise to paresthesia and muscle weakness
What is glyburide?
Sulfonylurea
What is the mechanism of action of sulfonylureas?
Insulin secretion in type II diabetics
What is neurophysin?
Carrier protein for oxytocin and vasopressin
Why might inhibin production impaired in patients with 1 testicle?
Inhibin is produced by sertoli cells which are found in the semniferous tubules of the testes
What is the mechanism of action of beta blockers in treating thyrotoxicosis?
- Decrease in the effect of sympathetic response of the target organs
- Decrease in the rate of peripheral conversion of T4 to T3