Adrenal Cortex: Aldosterone + Cortisol

Adrenal Glands

Pyramid-shaped glands located on the superior ends of the right and left kidneys

consist of an outer Adrenal Cortex, which is a typical endocrine gland, and an inner Adrenal Medulla, which is a neuroendocrine organ

Three Zones of the Adrenal Cortex

Outer Zona Glomerulosa produces Mineralocorticoids

middle Zona Fasciculata produces Glucocorticoids

inner Zona Reticularis produces some glucocorticoids and Androgenic Steroids

all are steroid hormones derived from cholesterol

Mineralocorticoids

Fluid and Electrolyte Homeostasis

Mineralocorticoids regulate concentrations of minerals in the body

the main mineralocorticoid is Aldosterone

Effects of Aldosterone

Maintaining the concentrations of extracellular sodium and potassium ions within their normal range

– Aldosterone stimulates transcription of sodium potassium ion pumps, sodium ion channels, and sodium/chloride/potassium ion cotransporters

– Sodium and chloride ions are returned to the blood

Potassium ions are removed in the urine

Regulating extracellular fluid volume

– Effects on sodium and chloride ions in the tubule cells create a more concentrated interstitial fluid

– Water moves by osmosis from the fluid in those tubules to the interstitial fluid and blood

– Note this is an indirect effect—aldosterone has no direct actions on water molecules or water channels

Maintaining blood pressure

– By promoting water reabsorption indirectly, maintains ECF and blood volume, which maintains blood pressure

– Part of the Renin-Angiotensin-Aldosterone System (RAAS)

– Increase blood pressure, and preserves blood flow to the heart, brain, and kidneys

Maintaining acid-base homeostasis

– Blood pH is about 7.35–7.45

– Aldosterone activates hydrogen ion pumps in cells of the kidney tubules which transport hydrogen ions from the ECF into the tubules, where they are excreted in the urine

– Preserves the slightly alkaline pH

Regulation of Aldosterone

Major factors that stimulate aldosterone release are elevated blood potassium concentration, decreased blood pH, and Angiotensin II

Hypothalamic-Pituitary-Adrenocortical (HPA) Axis

– Corticosteroid-Releasing Hormone (CRH) from the hypothalamus triggers release of ACTH from the anterior pituitary, which stimulates aldosterone production and release

Hyperaldosteronism

Hypersecretion of aldosterone

can cause Hypokalemia (low potassium), Hypernatremia (high sodium), high blood pressure, and overly alkaline blood from disruption of acid-base balance

generally idiopathic (unknown cause) but can result from an aldosterone-secreting tumor

Glucocorticoids

Metabolic Homeostasis

Glucocorticoids primarily mediate the body's response to stress

the most potent glucocorticoid is Cortisol (Hydrocortisone), produced mainly by the zona fasciculata

Effects of Cortisol

Gluconeogenesis in the liver

– Stimulates liver cells to synthesize enzymes that convert amino acids and fats into glucose

• Release of amino acids from muscle tissue

• Release of fatty acids from adipose tissue

– Amino acids and fatty acids enter the bloodstream and can be used by the liver for gluconeogenesis

Acts as a potent anti-inflammatory agent by decreasing certain leukocytes

• Led to development of synthetic Corticosteroids, used to treat conditions of inflammation

• Cortisol is also given to patients with autoimmune disorders to suppress the immune response and to organ transplant patients to help prevent rejection of the organ

Stress Response – Series of changes that maintains homeostasis when the body is faced with a Stressor;

Cortisol is called the “stress hormone”

• Consider how cortisol would be used if you were chased by an alligator and suffered an injury:

– Triggers breakdown of fats and proteins for gluconeogenesis

Fatty acids from adipose tissue provide additional fuels

Anti-inflammatory actions prevent inflammation if you are injured, which allows you to continue to run

Regulation of Cortisol Synthesis

primarily controlled by the HPA axis:

– CRH from the hypothalamus is secreted daily in a rhythmic fashion, but peaks usually in the morning

– CRH is influenced by parts of the cerebral cortex

– CRH stimulates ACTH release from the anterior pituitary

– ACTH stimulates cortisol production from cells of the zona fasciculata