Facts on File Encyclopedia of Health and Medicine

adrenal glands can flood cortisol, epinephrine, and
norepinephrine into the BLOODcirculation. On a
mundane basis the adrenal glands also broadly
regulate myriad functions of survival, such as
BLOOD PRESSURE and HEART RATE, continuously
adjusting the levels of these hormones in the
bloodstream to meet the body’s daily needs.

ADRENAL HORMONES

Adrenal cortex

ALDOSTERONE
CORTISOL
ESTROGENS
PROGESTERONE
TESTOSTERONE
Adrenal medulla

DOPAMINE

EPINEPHRINE

NOREPINEPHRINE

The Adrenal Cortex

The primary hormones of the adrenal cortex—
aldosterone and cortisol—regulate many functions
necessary for survival. Cortisol directs numerous
chemical interactions that facilitate GLUCOSEbal-
ance and are integral for carbohydrate and fat
METABOLISM. Aldosterone regulates the sodium–
potassium balance, maintaining appropriate blood
volume and blood pressure. The adrenal cortex
arises from the same tissue in the EMBRYOas the
sex glands (OVARIESand TESTES) and retains a func-
tional connection to them in that it also synthe-
sizes and secretes estrogen, progesterone, and
testosterone in males and females alike. These
hormones have numerous roles in functions other
than those of reproduction. Testosterone helps
maintain MUSCLEmass and BONE DENSITY; estrogen
is essential for cholesterol metabolism; and the
adrenal cortex needs progesterone to synthesize
aldosterone.
The adrenal gland has three distinct layers, or
zones, each of which exclusively produces specific
hormones. These zones are

• The zona glomerulosa, the outermost zone,
  synthesizes and secretes aldosterone under the
  regulation of ADRENOCORTICOTROPIC HORMONE
  (ACTH) and the enzyme angiotensin II (synthe-
  sized when the kidneys release RENIN).
  
  
  • The zona fasciculata, the middle zone, synthe-
    sizes and secretes cortisol under the regulation
    of ACTH.
  
  
  • The zona reticularis, the innermost zone, synthe-
    sizes and secretes sex hormones (estrogen,
    progesterone, and testosterone) under the pri-
    mary regulation of ACTH with secondary influ-
    ence from FOLLICLE-STIMULATING HORMONE (FSH)
    and LEUTEINIZING HORMONE(LH).
  
  
  
  

The Adrenal Medulla

The adrenal medulla develops from the same tis-

sue as the NERVOUS SYSTEMand remains under neu-

rologic control. The adrenal medulla produces the

hormones dopamine, epinephrine (also called

adrenaline), and norepinephrine (also called nora-

drenaline). These function in the body as hor-

mones, facilitating chemical interactions among

cells, and as neurotransmitters, facilitating the

passage of nerve signals. The interactions occur

within the adrenal gland as well; the adrenal

medulla needs cortisol to synthesize epinephrine.

BODY AND BRAIN: SAME CHEMICALS,

DIFFERENT CONCENTRATIONS

The adrenal medullary hormones DOPAMINE, EPI-

NEPHRINE, and NOREPINEPHRINEare the same chem-

ical composition as their NEUROTRANSMITTER

counterparts in the BRAIN. However, the brain

requires much higher concentrations of these

substances than the body can tolerate. A protec-

tive mechanism called the BLOOD–BRAIN BARRIER, a

membranous layer of cells in the BLOODvessels

of the brain, regulates the size of molecules that

can enter and leave the brain’s circulation. The

molecules of these hormones are too large to

pass through, keeping the body (central) and

brain supplies of them separate.

Kidney Disease and Adrenal Function

RENAL FAILURE, RENAL CANCER, and KIDNEY TRANS-

PLANTATIONmay affect various aspects of adrenal

function. When the kidneys fail, they stop produc-

ing the hormone renin, which is essential for

blood pressure regulation within the renin–

angiotensin–aldosterone (RAA) system. The kid-

neys release renin when blood volume drops as a

hormonal signal to the adrenal cortex to release

108 The Endocrine System