Endocrine - Embryology and Anatomy Flashcards
Describe thyroid development
Thyroid diverticulum arises from floor of primitive pharynx, descends into the neck.
How is thyroid diverticulum connected to the tongue?
Thyroglossal duct
What is the pyramidal lobe of thyroid?
Persistent thyroglossal duct
What is the foramen cecum of thyroid?
Normal remnant of thyroglossal duct
Most common ectopic thyroid tissue site
Tongue
Describe thyroglossal duct cyst
Anterior midline neck mass that moves with swallowing or pertrusion of the tongue
How is thyroglossal duct cyst different from a brachial cleft cyst?
Brachial cleft cyst - persistent cervical sinus Lateral neck (vs midline for thyroglossal duct cyst)
Describe fetal adrenal gland
Consists of an outer adult zone and inner active fetal zone.
Adult zone is dormant during early fetal life but begins to secrete cortisol late in gestation.
What controls cortisol secretion in the fetus?
ACTH and CRH from fetal pituitary and placenta
Role of cortisol in the fetus
Fetal lung maturation and surfactant production
What are the embryologic derivatives of the adrenal cortex and medulla?
Cortex - mesoderm
Medulla - neural crest
What are the layers of adrenal gland?
Capsule Zona glomerulosa Zona fasciculata Zona reticularis Medulla (Chromaffin cells)
Primary regulatory control and secretory products of: Zona glomerulosa
Regulation: Renin-Angiotensin-Aldosterone System
Secretion: Aldosterone
Primary regulatory control and secretory products of: Zona fasciculata
Regulation: ACTH and CRH
Secretion: glucocorticoids (cortisol)
Primary regulatory control and secretory products of: Zona reticularis
Regulation: ACTH and CRH
Secretion: sex steroids (androgens)
Primary regulatory control and secretory products of: Adrenal medulla (Chromaffin cells)
Regulation: Pre-ganglionic sympathetic fibers (acetylcholine)
Secretion: Catecholamines (Epi, NE)
What is the most common tumor of adrenal medulla in adults? And in children?
How are they different?
Adult: pheochromocytoma
Children: neuroblastoma
Pheochromocytoma causes episodic hypertension; Neuroblastoma does not
Describe adrenal gland drainage
Left adrenal -> Left adrenal vein -> Left renal -> IVC
Right adrenal -> Right adrenal vein -> IVC
Same as left and right gonadal veins
What are the embryologic derivatives of anterior and posterior pituitary?
Anterior pituitary (Adenohypophysis): oral ectoderm (Rathke’s pouch)
Posterior pituitary (neurohypophysis): neuroectoderm
Function of posterior pituitary gland
Secretes vasopressin and oxytocin made in hypothalamus and shipped to posterior pituitary through neurophysins (carrier proteins)
Function of anterior pituitary gland
Secretes FSH, LH, ACTH TSH, prolactin, GH, melanotropin (MSH)
Describe structure of TSH, LH, FSH, hCG
Alpha and Beta subunit
Alpha: common to all
Beta: determines hormone specificity
How do pituitary acidophils appear on histology and what do they make?
Pink
Prolactin, GH
How do pituitary basophils appear on histology and what do they make?
Blue
FSH, LH, ACTH, TSH
Describe organization of islets of langerhans
Alpha cells in periphery
Beta cells central
Delta cells interspersed
What are the different cell types of islets of langerhans and what do they secrete?
Alpha: glucagon
Beta: insulin
Delta: somatostatin
What does the islets of langerhans arise from?
Pancreatic buds
Structure of insulin
Alpha and Beta chains connected by sulfur bonds
Describe insulin secretion in the pancreatic beta-cell
- Glucose enter cell
- Glycolysis increases ATP/ADP ratio
- ATP closes ATP-sensitive K+ channels
- Depolarization of cell
- Influx of Ca2+ through voltage-gated Ca2+ channels
- Exocytosis of insulin granules into blood vessel
Does insulin cross the placenta?
No
What organs have insulin-independent glucose uptake? (6)
Brain RBC Intestine Cornea Kidney Liver
What organs use: GLUT-1
RBCs, Brain
Insulin independent
What organs use: GLUT-2
Beta islet cells, liver, kidney, intestines
What organs use: GLUT-4
Adipose tissue, skeletal muscle
Insulin dependent
Major functions of insulin (7)
- Increase glucose transport into skeletal muscle/adipose
- increase glycogen synthesis/storage
- increase TG synthesis/storage
- increase Na+ retention in kidneys
- increase protein synthesis (muscles)
- increase cellular uptake of K+ and AA
- decrease glucagon release
What upregulates insulin secretion? (3)
hyperglycemia
GH
Beta-2 antagonists
What inhibits insulin secretion? (3)
hypoglycemia
somatostatin
alpha-2 agonists
What pathway does insulin acts in cells?
RAS/MAP kinase -> cell growth/DNA synthesis
Phosphoinositide-3 kinase -> glycogen, lipid, protein synthesis; GLUT4 vesicles
What does brain use in starvation?
Ketone bodies
What does RBC use in starvation?
Always depend on glucose - no mitochondria for aerobic metabolism
Major functions of glucagon
Catabolic effects
Glycogenolysis, gluconeogenesis
Lipolysis, ketone production
What promotes (1) or inhibits (3) glucagon production?
Promoted by hypoglycemia
Inhibited by insulin, hyperglycemia, somatostatin
What is a lingual thyroid?
Persistence of thyroid tissue at base of tongue
Base of tongue mass
