The Endocrine System
Adipose cells release
, which serves to
tell your body how much stored energy (as fat) you have. Te
more fat you have, the more leptin there will be in your blood.
As we describe in Chapter 24, leptin binds to CNS neurons con-
cerned with appetite control, producing a sensation of satiety. It
also appears to stimulate increased energy expenditure.
±wo other hormones released by adipose cells both aﬀect the
sensitivity of cells to insulin.
is an insulin antagonist,
enhances sensitivity to insulin.
secreting cells sprinkled in the mucosa of the gastrointestinal (GI)
tract. Tese scattered cells release several peptide hormones that
help regulate a wide variety of digestive functions, some of which
are summarized in ±able 16.5. Enteroendocrine cells also release
amines such as serotonin, which act as paracrines, diﬀusing to and
inﬂuencing nearby target cells without ﬁrst entering the bloodstream.
Enteroendocrine cells have been referred to as
they are similar in certain ways to neurons and many of their hor-
mones and paracrines are chemically identical to neurotransmitters.
Te atria contain specialized cardiac muscle cells that
atrial natriuretic peptide (ANP).
As noted on p. 614,
ANP decreases the amount of sodium in the extracellular ﬂuid,
thereby reducing blood volume and blood pressure.
Interstitial cells in the kidneys secrete
ĕ-tin; “red-maker”), a glycoprotein hormone that
signals the bone marrow to increase production of red blood
cells. Te kidneys also release
, which acts as an enzyme to
is a temporary endocrine organ. Besides sus-
taining the fetus during pregnancy, it secretes several steroid
and protein hormones that inﬂuence the course of pregnancy.
Placental hormones include estrogens and progesterone (hor-
mones more oFen associated with the ovary), and human cho-
rionic gonadotropin (hCG).
We will discuss the roles of the gonadal, placental, and go-
nadotropic hormones in Chapters 27 and 28, where we consider
the reproductive system and pregnancy.
Check Your Understanding
Which of the two chemical classes of hormones introduced
at the beginning of this chapter do the gonadal hormones
belong to? Which major endocrine gland secretes hormones
of this same chemical class?
For answers, see Appendix H.
Hormone Secretion by Other Organs
Name a hormone produced by the heart.
State the location of enteroendocrine cells.
Brieﬂy explain the hormonal functions of the kidney, skin,
adipose tissue, bone, and thymus.
Other hormone-producing cells occur in various organs includ-
ing the heart, gastrointestinal tract, kidneys, skin, adipose tis-
sue, skeleton, and thymus
Symptoms of Insulin Deﬁcit (Diabetes Mellitus)
uptake and utilization
dehydration, soft eyeballs)
Polydipsia (and fatigue,
Loss of Na
Central nervous system