190 ❯ STEP 4. Review the Knowledge You Need to Score HighEndocrine System
Endocrine signaling occurs when cells dump hormonesinto the bloodstream to affect cells
in other parts of the body. Hormones are chemicals produced by glands such as the pituitary
and distributed by the circulatory system to signal faraway target cells. Here we are at the
pituitary gland. As you can see, it is not very big at all—it is the size of a pea and is divided
into an anterior and a posterior division. The anterior pituitary gland is also called the adeno-
hypophysis, and it produces six hormones: TSH, STH, ACTH, LH, FSH,andprolactin;
the posterior pituitary gland, also known as the neurohypophysis,releases only two hormones:
ADHandoxytocin(see definitions of these acronyms in the Glossary at the end of the book).
The two lobes of the pituitary gland differ in the way they deliver their hormones. If you
look closely, you will see that there is a short stalk that connects the anterior portion of the
pituitary gland to the brain. This stalk, called the hypothalamus,controls the output of hor-
mones by the pituitary gland. The anterior pituitary is linked to the hypothalamus via the
bloodstream. When the concentration of a particular anterior pituitary hormone is too low
in the circulation, the hypothalamus will send releasing factors via the bloodstream that
stimulate the production of the needed hormone. The posterior lobe of the pituitary gland
is different—it is derived from neural tissue. Because of this, its connection to the hypothal-
amus is neural. ADH and oxytocin are produced by the nerve cell bodies that are located in
the hypothalamus, where they are packaged into secretory granules and sent down the axons
to be stored in the posterior pituitary. The posterior pituitary gland releases the hormones
when appropriately stimulated by a nervous impulse from the hypothalamus. The following
is a breakdown of the hormones you should be familiar with for the exam:Hormones of the anterior pituitaryare
FSH Follicle-stimulating hormone. A gonadotropin—stimulates activities of
the testes and ovaries. In females, it induces the development of the
ovarian follicle, which leads to the production and secretion of estrogen.
In males, it stimulates the production of sperm.
LH Luteinizing hormone. A gonadotropin—stimulates ovulation, formation
of corpus luteum, and synthesis of estrogens and progesterone in females.
In males, it stimulates the production of testosterone.
TSH Thyroid-stimulating hormone. Works to stimulate the synthesis and
secretion of thyroid hormones in the thyroid gland, which in turn
regulate the rate of metabolism in the body.
STH (or HGH) Somatotropic hormone (or human growth hormone). Stimulates
protein synthesis and general growth in the body.
ACTH Stimulates the secretion of adrenal cortical hormones, which work to
maintain electrolytic homeostasis and help to cope with chronic stress.
Prolactin Controls lactogenesis—production of milk by the breasts. Decreases
the synthesis and release of GnRH (gonadotropin-releasing hormone),
inhibiting ovulation.Hormones of the posterior pituitaryare
ADH Stimulates reabsorption of water by the collecting ducts of the kidney.
Oxytocin Stimulates uterine contraction and milk ejection for breastfeeding.CT teacher:
“Have a good
general under-
standing of these
hormones and
their functions.”BIG IDEA 3.B.2
A variety of inter-
cellular and intra-
cellular signals
mediate gene
expression.