Adrenal gland

Adrenal (Suprarenal) Glands

Adrenal glands – paired, pyramid-shaped organs atop the kidneysStructurally and functionally, they are two glands in oneAdrenal medulla – neural tissue that acts as part of the SNSAdrenal cortex – glandular tissue derived from embryonic mesoderm

Adrenal Cortex

Synthesizes and releases steroid hormones called corticosteroidsDifferent corticosteroids are produced in each of the three layersZona glomerulosa – mineralocorticoids (chiefly aldosterone)Zona fasciculata – glucocorticoids (chiefly cortisol)Zona reticularis – gonadocorticoids (chiefly androgens)

Adrenal Cortex

Mineralocorticoids
Regulate electrolytes in extracellular fluidsAldosterone – most important mineralocorticoid Maintains Na+ balance by reducing excretion of sodium from the bodyStimulates reabsorption of Na+ and secretion of K+ by the kidneys

Mineralocorticoids

Aldosterone secretion is stimulated by: Rising blood levels of K+ Low blood Na+ Decreasing blood volume or pressure

The Four Mechanisms of Aldosterone Secretion

Renin-angiotensin mechanism – kidneys release renin, which is converted into angiotensin II that in turn stimulates aldosterone release Plasma concentration of sodium and potassium – directly influences the zona glomerulosa cellsACTH – causes small increases of aldosterone during stressAtrial natriuretic peptide (ANP) – inhibits activity of the zona glomerulosa


Major Mechanisms of Aldosterone Secretion

Glucocorticoids (Cortisol)

Help the body resist stress by: Keeping blood sugar levels relatively constant Maintaining blood volume and preventing water shift into tissue Cortisol provokes: Gluconeogenesis (formation of glucose from noncarbohydrates) Rises in blood glucose, fatty acids, and amino acids

Excessive Levels of Glucocorticoids

Excessive levels of glucocorticoids: Depress cartilage and bone formation Inhibit inflammation Depress the immune system Promote changes in cardiovascular, neural, and gastrointestinal function

Gonadocorticoids (Sex Hormones)

Zona Reticularis produces mainly androgens that are converted to testosterone in the testes Androgens contribute to: The onset of puberty The appearance of secondary sex characteristics Sex drive in females Androgens can be converted into estrogens after menopause

Adrenal Medulla

Made up of cells that secrete epinephrine and norepinephrine Secretion of these hormones causes: Blood glucose levels to rise Blood vessels to constrict The heart to beat faster Blood to be diverted to the brain, heart, and skeletal muscle

Adrenal Medulla

Epinephrine is the more potent stimulator of the heart and metabolic activities Norepinephrine is more influential on peripheral vasoconstriction and blood pressure

Stress and the Adrenal Gland