Adrenal Hormones (Lecture 22)

Question 1

• What hormone is secreted by the adrenal medulla?
• What is this structure functionally related to?

Answer 1

• Medulla secretes:
  
  • Epinephrine and norepinephrine
  • Functionally related to sympathetic nervous system

Question 2

• What hormones are secreted by the adrenal cortex?
• Specify which part of the adrenal cortex is associated with each type of secretion.

Answer 2

• The Adrenal Cortex secretes
  
  • Coticosteroids
    
    • Mineralocorticoids
    • Glucocorticoids
    • Androgenic hormones

Question 3

Describe the synthesis of corticosteroids

Answer 3

• Provided mostly by LDLs in the plasma
• Most attach to coated pits
• ACTH increases number of LDL receptors
• Cholesterol converted to pregnenolone in mitochondria
• Enzyme for conversion
  
  • Cholesterol desmolase (rate-limiting step)
• Both ACTH and Angiotensin II increase the conversion of cholesterol to pregnenolone

Question 4

Describe the functions and control of secretion of mineralocorticoids

Answer 4

• Aldosterone is the major mineralocorticoid:
• Especially affects the electrolytes (sodium and potassium)
  
  • increases sodium reabsorption by kidney tubules:
    
    • Acts on principal cells in late distal tubule
  • Hyperkalemia increases aldosterone secretion
  • Aldosterone increases potassium secretion by kidneys:
    
    • Acts on principal cells in late distal tubule
  • Aldosterone increases hydrogen ion secretion by kidneys:
    
    • Acts on intercalated cells in late distal tubule
• Secretion is controlled mainly by angiotensin II and potassium
• Secreted by zona glomerulosa

Question 5

Describe the funcitons and control of secretion of glucocorticoids

Answer 5

• Cortisol is the major glucocorticoid
• Essential in stress response
• Secretion is controlled mainly by ACTH (from anterior pituitary):
  
  • ACTH up-regulates it own receptor
  • under the influence of CRH (corticotropin-releasing hormone from neurosecretory cells located in the paraventricular nuclei.)
• Secreted by zona fasciculata
• Cortisol has negative feedback response to both CRH and ACTH
• Cortisol oscillates with circadian rhythm:
  
  • Normally highest before waking
  • Normally lowest in evening

Question 6

What is the secretory product of the zona reticularis

Answer 6

• Androgeneic Hormones

Question 7

Describe the effects of insufficient secretion of aldosterone

Answer 7

• Total loss causes death in matter of days unless extensive salt therapy and mineralocorticoid injections are available
• Without mineralocorticoids potassium levels in ECF rise markedly and sodium and chloride are lost rapidly form the urine
• Total ECF and blood volume become greatly reduced
• Person develops diminished cardiac output and progresses to a shock-like state
• Hyperkalemia and serous cardiac toxicity

Question 8

Describe the effects of excess secretion of aldosterone

Answer 8

• Increase in ECF and arterial pressure
• Small effect on plasma sodium concentration because sodium reabsorption in renal tubules is acompanied by equivalent amount of water reabsorption
• Hypokalemia and muscle weakness
• Stimulates transport of potassium from ECF into most cells of the body
• Causes alkalosis (hydrogen ions are secreted in exchange fro sodium)

Question 9

Describe the relationship between aldosterone and sodium reabsorption

Answer 9

As aldosterone increases renal tubular reabsorption of sodium and increases potassium excretion in urine

Question 10

Explain how aldosterone secretion is regulated

Answer 10

• Almost entirely independent of the regulation of cortisol secretion
• increased potassium ion concentration greatly increases aldosterone secretion
• Increased angiotensin II concentration greatly increases aldosterone secretion
• ACTH is necessary for aldosterone secretion but has little effect in controlling rate of secretion

Question 11

List functions of cortisol

Answer 11

• Functions:
  
  • Resists stress
  • resists inflammaiton:
    
    • induces synthesis of lipocortin which inhibits phospholipase
    • inhibits production of interleukin-2
    • Inhibits release of histamine and serotonin
    • Blocks inlammatory response to allergic reactions
    • Decreases number of eosinophils and lymphocytes in blood
  • Causes resolution of inflammation
  • Inhibits immune response
  • Maintains vascular response to catecholamines

Question 12

Explain how glucocorticoid secretion is regulated

Answer 12

Highest in the morning after waking up

Question 13

Describe causes and specific disturbances of Addisons’s disease

Answer 13

• Primary Addison’s
  
  • Due to injury to adrenal cortex
• Secondary
  
  • Due to impaired funciton of pituitary gland
• Disturbances
  
  • Due to mineralocorticoid deficiency
    
    • decreased extracellular fluid volume
    • hyponatremia
    • hyperkalemia
    • mild acidosis
    • rise in RBC concentration
    • decrease in cardiac ouput
    • decrease in blood pressure
    • Metabolic acidosis
    • death from shock
  • Due to Glucocorticoid deficiency
    
    • Loss of ability to maintain normal blood glucose concentrations between meals —> hypoglycemia
    • Reduction in both proteins and fats leading to depression of other bodily functions
    • Weight loss, nausea, vomiting
    • Muscle weakness
    • Highly susceptible to stress
  • Due to Melanin pigmentation
    
    • may be causedd by loss of negative feedback to pituitary, allowing increased amounts of MSH
    • Results in uneven distribultion of pigmentation, especially in thin skin areas

Question 14

Describe causes and characteristics of Cushing’s disease

Answer 14

• Casues:
  
  • Administration of glucocorticoids
  • Adenomas of anterior pituitary
  • Abnormal function of hypothalamus
  • ectopic secretion of ACTH by tumor
  • adenomas of adrenal cortex
  • Excess ACTH secretion is cause of Cushings
• Characteristics:
  
  • Increase in corisol and androgen levels
  • “Buffalo torso”
  • Moon face
  • Acne and hirsutism
  • Hypertension
  • Increased blood glucose
  • Increase in protein catabolism and muscle wasting