Week 8: Adrenal Hyperfunction Flashcards
Identify
Identify
Describe adrenal steroidogenesis
Cortex layers and secretions
Zona glomerulosa (aldosterone)
Zone Fasiculata (cortisol)
Cona reticularis (andreogens)
Medulla secretions
epinephrine and norepinephrine
Zona glomerulosa secretion
(aldosterone)
Zona Fasicularis secretions
Cortisol
Zona reticularis secretions
Androgens
Adrenal steroidogenesis things to know
ACTH is the stimulus for adrenal steroidogenesis and cholesterol is needed (from de novo from acetate or taken from LDL or HDL from the circulation)
Cholesterol -STAR protein-> brings cholesterol into the mitochondria to start steroidogenesis)
*1st step is the rate-limiting step* (shown below)
Cholesterol -cholesterol desmolase or CYP11A1-> Progenolone
Describe the Hypothalamic-pituitary-adrenal axis and regulatory mechanisms
What are the acute effects of ACTH?
increased conversion of cholesterol to Pregnenolone via activation of CYP11A1
What are the chronic effects of ACTH?
- Increased synthesis of the enzymes involved in steroidogenesis
- Increased RNA and DNA synthesis
- Increased Cell growth
- Increased synthesis of LDL and HDL receptors
Systems affected by cortisol
11 listed
- Increased production of glucose (gluconeogenesis)
- Carbohydrate metabolism
- Protein metabolism
- Lipid Metabolism
- Immune System
- Body Water
- Mineralocorticoid activity
- Arterioles
- Osteoblasts
- Hepatocytes
- Cardiomyocytes
Cortisol effects on metabolism
9 listed
- Antagonizes secretion and action of insulin
- Decreased peripheral uptake of glucose
- insulin resistance
- Increased gluconeogenesis
- Increased protein breakdown
- Increased nitrogen excretion
- Decreased protein synthesis
- Free fatty acid mobilization
- Activation of cellular lipase
Cortisol effects on the immune system
6 listed
- Maintains vascular responsiveness to circulating vasoconstrictors
- Opposes increase in capillary permeability during acute inflammation
- Leukocytosis (release from bone marrow and inhibition of movement through the capillary wall)
- Impairs cell-mediated immunity
- Inhibits production and action of mediators of inflammation (Leukotrienes, Prostaglandins, IL-2)
- Blocks histamine release from mast cells
Cortisol effects on body water
4 listed
- Promotes renal water excretion
- inhibition of vasopressin excretion
- Increase glomerular filtration rate
- Direct action of the renal tubule
Cortisol mineralocorticoid effects
Weak mineralocorticoid effects
- Promotes renal tubular Na+ reabsorption
- Increase urine potassium excretion
Cortisol effects on the vascular system
- Upregulates α1-receptors on arterioles → increased sensitivity to norepinephrine and epinephrine
- Opposes capillary permeability during acute inflammation
- Maintains vascular responsiveness to circulating vasoconstrictors
Cortisol effects on bone
Induces the destruction of osteoblasts → decreased bone formation
Cortisol effects on the liver
Promotes the survival of hepatocytes
Cortisol effects on the heart
Promotes the survival of cardiomyocytes
How much cortisol is secreted daily?
15-20 mg/day
How does cortisol circulate?
- <5% is free cortisol
- 95% is protein-bound to CBG (corticosteroid-binding globulin) & Albumin
Cortisone binding properties of CBG
3 listed
- High-affinity
- low capacity
- Reduced in areas of inflammation
Cortisone binding properties of albumin
- Low affinity
- High capacity
What is CBG?
Corticosteroid-binding globulin
Binds cortisone in the blood for transport
Where is the cortisol receptor expressed?
Nearly every cell in the body
What kind of receptor is the glucocorticoid (cortisol) receptor?
member of the nuclear receptor superfamily of ligand-dependent transcription factors
What genes are affected by the glucocorticoid receptor?
induces or represses the transcription of target genes that comprise 10-20% of the human genome
What is the defect in Cushing’s Syndrome?
Excess endogenous cortisol secretion
Etiologies of Cushing’s Syndrome
4 listed
Pituitary (Cushing’s Disease)
Ectopic (Small cell lung cancer or Bronchial carcinoid)
Exogenous steroids
Excess cortisol secretion from an adrenal tumor (hyperplasia, adenoma or carcinoma)
What is the most common cause of Cushing’s Syndrome
Pituitary (Cushing’s Disease) is the most common endogenous cause
Etiologies of ectopic Cushing’s Syndrome
- Small cell lung cancer
- Bronchial carcinoid
Epidemiology of Cushing’s Syndrome
- Female predominance
- Onset common in the first decade of life as well as 40-50 years old
Signs and symptoms of Cushing’s Syndrome
18 listed
Lab tests for Cushing’s Syndrome
3 listed
- 24 hour urine cortisol
- salivary cortisol
- Dexamethasone suppression test
Diagnostic criteria of Cushing’s Syndrome
2 tests are needed to confirm the cortisol excess
- ACTH to determine the source of cortisol excess
- 24-hour urine cortisol
- Salivary cortisol
- Dexamethasone suppression test
How to determine the source of cortisol excess in Cushing’s Syndrome
ACTH to determine the source of cortisol excess
- ACTH is undetectable if the source is adrenal
- Elevated ACTH indicates a pituitary or ectopic source
Diagnostic approach to Cushing’s Syndrome