602
UNIT 3
Regulation and Integration of the Body
16
Table 16.1
Pituitary Hormones: Summary of Regulation and Effects
HORMONE (CHEMICAL
STRUCTURE AND CELL TYPE)
REGULATION OF RELEASE
TARGET ORGAN AND EFFECTS
EFFECTS OF HYPOSECRETION
g
AND HYPERSECRETION
h
Posterior Pituitary Hormones (Made by Hypothalamic Neurons and Stored in Posterior Pituitary
Oxytocin
(Peptide, mostly from
neurons in paraventricular
nucleus of hypothalamus)
Stimulated
by impulses from
hypothalamic neurons in response
to cervical/uterine stretching and
suckling of infant at breast
Inhibited
by lack of appropriate
neural stimuli
Uterus: stimulates uterine
contractions; initiates labor
Breast: initiates milk ejection
Unknown
Antidiuretic hormone (ADH)
or vasopressin (Peptide, mostly
from neurons in supraoptic
nucleus of hypothalamus)
Stimulated
by impulses from
hypothalamic neurons in response
to increased blood solute
concentration or decreased blood
volume; also stimulated by pain,
some drugs, low blood pressure
Inhibited
by adequate hydration of
the body and by alcohol
Kidneys: stimulate kidney tubule
cells to reabsorb water
g
Diabetes insipidus
h
Syndrome of inappropriate
ADH secretion (SIADH)
Anterior Pituitary Hormones
Growth hormone
(GH)
(Protein,
somatotropic cells)
Stimulated
by GHRH* release,
which is triggered by low blood
levels of GH as well as by a number
of secondary triggers including
hypoglycemia, increases in blood
levels of amino acids, low levels
of fatty acids, exercise, and other
types of stressors
Inhibited
by feedback inhibition
exerted by GH and IGFs, and by
hyperglycemia, hyperlipidemia,
obesity, and emotional deprivation
via either increased GHIH*
(somatostatin) or decreased GHRH*
release
Liver, muscle, bone, cartilage, and
other tissues: anabolic hormone;
stimulates somatic growth;
mobilizes fats; spares glucose
Growth-promoting effects
mediated indirectly by IGFs
g
Pituitary dwarfism in
children
h
Gigantism in children;
acromegaly in adults
hypothalamus to the anterior lobe, each target cell distinguishes
the messages directed to it and responds in kind—secreting the
proper hormone in response to specific releasing hormones,
and shutting off hormone release in response to specific inhibit-
ing hormones.
Four of the six anterior pituitary hormones—thyroid-
stimulating hormone, adrenocorticotropic hormone, follicle-
stimulating hormone, and luteinizing hormone—are
tropic
hormones
or
tropins
that regulate the secretory action of other
endocrine glands (
tropi
5
turn on, change). All anterior pitui-
tary hormones except growth hormone affect their target cells
via a cyclic AMP second-messenger system.
Growth Hormone (GH)
Somatotropic cells
of the anterior lobe produce
growth hor-
mone
(
GH
, also called
somatotropin
). GH is essentially an ana-
bolic (tissue building) hormone that has both metabolic and
growth-promoting actions
(Figure 16.6)
.
Direct Actions on Metabolism
Acting directly, GH exerts
metabolic effects. It mobilizes fats from fat depots for transport
to cells, increasing blood levels of fatty acids and encouraging
their use for fuel. It also decreases the rate of glucose uptake
and metabolism, conserving glucose. In the liver, it encour-
ages glycogen breakdown and release of glucose to the blood.
previous page 636 Human Anatomy and Physiology (9th ed ) 2012 read online next page 638 Human Anatomy and Physiology (9th ed ) 2012 read online Home Toggle text on/off