Page 777 - Atlas of Histology with Functional Correlations

the renal corpuscles.

Aldosterone has a major influence on fluid and electrolyte balance in the

body, with the main target being the distal convoluted tubules in the kidneys.
Aldosterone increases sodium reabsorption from the glomerular filtrate in
the distal convoluted tubules of the kidney and increases potassium excretion
into urine. As water follows sodium, fluid volume in the circulation

increases. Restoration of the blood pressure, blood volume, and electrolyte
balance decreases the release of renin from the juxtaglomerular apparatus.

The cells of the zona fasciculata secrete glucocorticoids, of which
cortisol and cortisone are the most important, and some small amounts of

weak androgens. Glucocorticoids are released response to stress, which then
stimulate protein, fat, and carbohydrate metabolism, especially by
gluconeogenesis to increase the concentration of blood glucose.
Glucocorticoids (cortisol) also suppress the immune system and have an anti-
inflammatory effect by reducing the number of circulating lymphocytes,

thereby decreasing antibody production and suppressing the tissue response
to injury.

The cells of the zona reticularis produce sex steroids, mainly weak
androgens that can be converted to testosterone and estrogen to influence the

development of secondary sex characteristics in both sexes. Glucocorticoid
secretions and the secretory functions of zona fasciculata and zona reticularis
are regulated by feedback control from the pituitary gland and ACTH.

ADRENAL GLAND MEDULLA

The functions of the adrenal medulla are controlled by the hypothalamus

through the sympathetic division of the autonomic nervous system. Cells in
the adrenal medulla are called the chromaffin cells because they stain with
chromium salts. These cells arise from neural crest, just like the
postganglionic neurons of sympathetic and parasympathetic ganglia, and can,

therefore, be considered as postganglionic neurons that lack dendrites and
axons. They are innervated and activated by preganglionic sympathetic axons
in response to fear or acute emotional stress, causing them to release the
catecholamines epinephrine and norepinephrine. The release of these

chemicals prepares the individual for a “fight-or-flight” response, resulting in
increased heart rate and respiratory rate, increased cardiac output and blood
flow, and a surge of glucose into the bloodstream from the liver for added
energy. Catecholamines produce the maximal use of energy and physical

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