USMLE - Endo Part 1
The thyroid diverticulum originates from the floor of the primitive pharynx and descends into the neck. It remains temporarily connected to the tongue via the thyroglossal duct, which usually involutes but may persist as a pyramidal lobe of the thyroid.
Thyroid development
Where does it arise from?
Where does it descend to?
Connected to what by what?
Thyroid diverticulum arises from floor of primitive pharynx. Descends into neck. Connected to tongue by thyroglossal duct, which normally disappears but may persist as pyramidal lobe of thyroid
Key Terms
Thyroid development
Where does it arise from?
Where does it descend to?
Connected to what by what?
Thyroid diverticulum arises from floor of primitive pharynx. Descends into neck. Connected to tongue by thyroglossal duct, which normally disappear...
Foramen Cecum
Normal remnant of thyroglossal duct in tongue
Most common ectopic thyroid tissue site
Tongue
Presentation of thyroglossal duct cyst
Anterior midline neck mass that moves with swallowing
Presentation of persistent cervical sinus leading to branchial cleft cyst in lateral neck
Small mobile mass on side of neck that does not move with swallowing
What does the Fetal Adrenal Gland consist of?
Outer adult zone and inner active fetal zone
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| Term | Definition |
|---|---|
Thyroid development | Thyroid diverticulum arises from floor of primitive pharynx. Descends into neck. Connected to tongue by thyroglossal duct, which normally disappears but may persist as pyramidal lobe of thyroid |
Foramen Cecum | Normal remnant of thyroglossal duct in tongue |
Most common ectopic thyroid tissue site | Tongue |
Presentation of thyroglossal duct cyst | Anterior midline neck mass that moves with swallowing |
Presentation of persistent cervical sinus leading to branchial cleft cyst in lateral neck | Small mobile mass on side of neck that does not move with swallowing |
What does the Fetal Adrenal Gland consist of? | Outer adult zone and inner active fetal zone |
Adult zone of fetal adrenal gland | Dormant during early fetal life but begins to secrete cortisol late in gestation |
What is fetal cortisol responsible for? | Fetal lung maturation and surfactant production |
Embryological origin of adrenal cortex? | Mesoderm |
Embryological origin of adrenal medulla? | Neural Crest Cells |
Layers of Adrenal Gland w/ Secretory Products | “GFR –> Salt, Sugar, Sex |
Zona Glomerulosa | Renin-Angiotensin –> Aldosterone |
Zona Fasciculata | ACTH, Hypothalamic CRH –> Cortisol, Sex Hormones |
Zona Reticularis | ACTH, Hypothalamic CRH –> Sex Hormones (androgens) |
Adrenal Medulla | Preganglionic sympathetic fibers –> ACh –> Catecholamines (NE, Epi) |
Most common tumor of adrenal medulla in adults? | Pheochromocytoma |
Most common tumor of adrenal medulla in children? | Neuroblastoma |
Pheochromocytoma vs Neuroblastoma in terms of clinical presentation | P –> episodic HTN |
Adrenal gland venous drainage | L Adrenal –> L Adrenal Vein –> L Renal Vein –> IVC |
Posterior Pituitary Gland AKA Products Source of products? How are they transported? Embryological origin | Neurohypophysis |
Anterior Pituitary Gland | Adenohypophysis |
Acidophils in the Anterior Pituitary gland secrete | GH and Prolactin |
Basophils in the Anterior Pituitary gland secrete | “B FLAT” Basophils –> FSH, LH, ACTH, TSH |
Which hormones share the same α subunit? | FSH, LH, TSH, and hCG |
Endocrine Pancreas | Islets of Langerhans "INsulin is on the INside" α: Glucagon, Peripheral β: Insulin, Central δ: Somatostatin, Interspersed Pancreatic Buds |
Mechanism of Insulin Release | ↑ Glucose metabolism --> ↑ ATP --> closing of K channels --> depolarization --> V gated Ca channels open --> insulin secretion |
Does insulin cross the placenta? | No |
What organs take up glucose independently of insulin? | "BRICK L" | Brain, RBCs, Intestines, Cornea, Kidney, Liver |
GLUT1 | Insulin independent in Brain and RBCs |
GLUT2 | Bidirectional in β cells, liver, kidney, and small intestine |
GLUT4 | Insulin dependent in adipose tissue and skeletal muscle |
Effects of Insulin | Anabolic ↑ G transport into skeletal muscles and adipose tissue ↑ Glycogen synthesis and storage ↑ Triglyceride synthesis and storage ↑ Na retention by kidneys ↑ Protein synthesis in muscles ↑ K uptake by cells ↑ AA uptake by cells ↓ Glucagon release |
What triggers an ↑ in insulin release | Hyperglycemia |
What triggers a ↓ in insulin release | Hypoglycemia, Somatostatin, α2 agonists |
Insulin Receptor Cellular Pathway | Insulin --> Tyrosine Phosphorylation --> IP3 and RAS/MAP |
What does the brain use for energy during starvation? | Ketone bodies |
What do RBCs use for energy during starvation | RBCs can only use glucose b/c they cannot preform aerobic respiration |
Functions of Glucagon | Catabolic | ↑ Gluconeogenesis, Glycogenolysis, Lipolysis, Ketone production |
What is glucagon secreted in response to? | Hypoglycemia |
What inhibits glucagon production? | Insulin, Hyperglycemia, Somatostatin |
What does TRH do? | TRH --> TSH and Prolactin |
What does DA do in the Pituitary gland? | DA --/ prolactin |
What does CRH do? | CRH --> ACTH, Melanocyte Stimulating Hormone (MSH), β-endorphin |
What does GHRH do? | GHRH --> GH |
What does somatostatin do in the Pituitary? | Somatostatin --/ GH and TSH |
What does GnRH do? | GnRH --> FSH and LH |
What does Prolactin do in the pituitary? | Prolactin --/ GnRH |
Prolactin | Anterior Pituitary Gland |
Regulation of Prolactin Secretion | DA from Hypothalamus --/ Prolactin secretion from Anterior Pituitary |
Affects of DA agonists on prolactin? | DA agonists (bromocriptine) inhibit prolactin and can be used to treat prolactinoma |
What stimulates prolactin secretion? | TRH, DA antagonists (antipsychotics) and Estrogens (OCP, pregnancy) |
| Somatotropin |
Excess GH in adults vs children | Acromegaly in adults | Gigantism in children |
Desmolase | ACTH --> Desmolase |
Path of Aldosterone Synthesis | Pregnenolone --> [3β Hydroxysteroid dehydrogenase] --> Progesterone --> [21 hydroxylase] --> 11 deoxycorticosterone --> [11β hydroxylase] --> corticosterone --> [aldosterone synthase] --> Aldosterone |
Path of Cortisol Synthesis | Pregnenolone --> [17α hydroxylase] --> 17 hydroxypregnenolone --> [3β Hydroxysteroid dehydrogenase] --> 17 hydroxyprogesterone --> [21 hydroxylase] --> 11 deoxycortisol --> [11β hydroxylase] --> Cortisol |
Path of Testosterone and DHT production | Pregnenolone --> [17α hydroxylase] --> 17 hydroxypregnenolone --> Dehydroepiandrosterone (DHEA) --> [3β Hydroxysteroid dehydrogenase] --> Androstenedione --> Testosterone --> [5α reductase] --> DHT |
Synthesis of Peripheral Estrogens | Aromatase turns Androstenedione into Estrone |
Deficiencies in Bilateral Adrenal Hyperplasias | 17α hydroxylase, 21 hydroxylase, 11β hydroxylase |
Why do adrenal enzyme deficiencies lead to hyperplasia | ↑ ACTH stimulation because of ↓ cortisol |
17α hydroxylase deficiency Mineralcorticoids Cortisol Sex Hormones Presentation Male vs Female | Mineralcorticoids ↑ |
21 hydroxylase deficiency Mineralcorticoids Cortisol Sex Hormones Presentation | Mineralcorticoids ↓ |
11β hydroxylase deficiency Mineralcorticoids Cortisol Sex Hormones Presentation | Mineralcorticoids: ↓ Aldosterone, ↑ 11-deoxycorticosterone Cortisol ↓ Sex Hormones ↑ HTN, Masculinization |
Cortisol | Adrenal Zona Fasciculata "BBIIG" Maintains BP ↓ Bone formation ↑ Insulin Resistance AntiInflammatory/Immunosuppressive ↑ Gluconeogenesis, lipolysis, proteolysis Inhibits Fibroblasts --> striae CRH (hypothalamus) --> Anterior Pituitary --> ACTH --> Cortisol production in Zona Fasciculata |
How is cortisol transported in the blood? | Corticosteroid binding globulin (CBG) |
How does cortisol maintain BP? | Upregulates α1 receptors on arterioles --> ↑ sensitivity to NE and Epi |
How is cortisol an anti-inflammatory/immunosuppressive? | --/ production of leukotrienes and prostaglandins |
How does excess cortisol alter CRH, ACTH and Cortisol secretion | Decreases all of them |
How does chronic stress affect cortisol secretion? | Stress induces prolonged secretion |
PTH | Chief Cells of Parathyroid ↑ Bone resorption of Ca and PO4 ↑ Kidney reabsorption of Ca in DCT ↑ Calcitriol production by stimulating kidney 1α Hydroxylase ↓ Reabsorption of PO4 in PCT |
Regulation of PTH | ↓ Serum Ca --> ↑ PTH |
Common causes of ↓ Mg | Diarrhea, Aminoglycosides, Diuretics, EtOH abuse |
Number of Parathyroid glands | 4 glands |
How does PTH affect bone | Stimulate Ca release from bone mineral compartment |
Actions of Vit D | ↑ Intestinal absorption of Ca and PO4 |
Clinical manifestation of high PTH | ↑ serum Ca, ↓ serum PO4, ↑ urine PO4 |
How does PTH affect osteoblasts and osteoclasts | PTH --> ↑ production of M-CSF and RANK-L in osteoblasts which stimulates osteoclasts |
Source of Vit D | D3 from sun exposure in skin |
Regulation of Vit D | ↑ PTH, ↓ [Ca], ↓ PO4 --> ↑ VitD | ↑ Vit D inhibits its own production |
24,25-(OH)2 D3 | Inactive form of VitD |
VitD deficiency in adults vs children | Children --> rickets | Adults --> osteomalacia |
Calcitonin | Parafollicular cells (C cells) of thyroid |
Normal role of Calcitonin | "CalciTONin TONes down Ca levels" | Not important in normal Ca homeostasis but when active, opposes PTH |
Which hormones use cAMP | "Go Go FLAT ChAMP" | GHRH, Glucagon, FSH, LH, ACTH, TSH, CRH, Calcitonin, ADH (V2 receptor), MSH, PTH |
Which hormones use cGMP | "Vasodilators" | ANP, NO, EDRF (Endothelial Derived Relaxing Factor) |
Which hormones use IP3 | "HAG GGOAT" | Histamine (H1), Angiotensin II, Gastrin, GnRH, Oxytocin, ADH (V1 receptor), TRH |
Hormones that use steroid receptors | "VETTT CAP" | VitD, Estrogen, Testosterone, T3/T4, Cortisol, Aldosterone, Progesterone |
Hormones that use Intrinsic Tyrosine Kinases | "MAP kinase pathway - Think growth factors" | Insulin, IGF1, FGF, PDGF, EGF |
Hormones that use Receptor-Associated (Non-Receptor) Tyrosine Kinase | JAK/STAT pathway |
In men, what are the effects of ↑ sex hormone binding globulin | Lowers free testosterone --> gynecomastia |
In women, what are the effects of ↓ sex hormone binding globulin | Raises free testosterone --> hirsutism |
In a women, what happens to SHBG during pregnancy? | ↑ SHBG |
Thyroid Hormone | T3 and T4 | Follicles of thyroid. Most T3 is formed in target tissues |
Function of Thyroid Hormone | T3 --> 4 Bs |
How is TH transported in the blood | When is it active? | Thyroxine binding globulin binds most T3/T4 in blood | Only free hormone is active |
When does TBG levels change? | ↓ TBG in hepatic failure | ↑ TBG in pregnancy or OCP (estrogen ↑ TBG) |
What is the major thyroid product? | T4 | Converted to T3 in peripheral tissues by 5'-deiodinase |
Which thyroid product binds with greater affinity? | T3 |
Peroxidase in Thyroid | Oxidation and organification of Iodide as well as coupling of MIT and DIT |
Propylthiourcil | Inhibits Peroxidase and 5'-deiodinase |