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Endocrine system
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Endocrine glands are ductless
therefore their products are
secreted into the blood stream for
transport.
Exocrine
Endocrine
Exocrine glands secrete their products
into a duct.
Types of Regulatory Molecules
• Hormone—regulatory chemical that is
secreted into the blood by an endocrine
gland or an organ of the body exhibiting
endocrine function
• The blood carries the hormone to EVERY
cell in the body, but only the TARGET cell
can respond since it is the only one with
the proper RECEPTORS.
The difference between a
neurotransmitter and a hormone
• Norepinephrine [a.k.a. noradrenaline] is
released as a neurotransmitter by the
sympathetic nerve endings AND is secreted by
the adrenal gland as a hormone
• As a neurotransmitter it travels a very short
distance across the synaptic cleft and binds to a
receptor protein to stimulate the postsynaptic
cell—either another neuron, a muscle cell or a
gland cell
• As a hormone it travels throughout the
bloodstream and can thus act across a great
distance
A
neurotransmitter
jumps the
synaptic cleft and
is received by a
receptor protein
on an adjacent
muscle cell.
Wouldn’t you know? There’s a
neurohormone!
• Neurohormone—a chemical messenger
secreted into the blood stream by
specialized neurons
• The distinction between the nervous
system and endocrine system blurs when
it comes to such molecules
• The brain can be considered an endocrine
gland since some neurons in the brain
secrete hormones
Norepinephrine is a hormone when
secreted by the adrenal gland into
the blood stream
ENDOCRINE GLANDS &
HORMONES
• There are organs that secrete hormones in
addition to other functions
• There are organs that function exclusively
as endocrine glands
• There’s a huge table to follow—good to
know for multiple choice points
• PICK A COUPLE OF THESE AND KNOW
THEM WELL—IN DETAIL—FOR
ESSAYS!
Figure 45.5 Human endocrine glands surveyed in this chapter
Two big classes of hormones:
WATER SOLUBLE & WATER
INSOLUBLE
• LIPOPHILIC—fat soluble [thus NOT water
soluble!] hormones
– All steroids
– thyroxin
• HYDROPHILIC—water soluble [thus NOT
fat soluble!] hormones
– All other hormones
• THIS DISTINCTION IS CRITICAL since it
relates structure to function
ENDOCRINE GLANDS LACK DUCTS:
Products secreted into capillaries
FOUR different chemical categories of
products
• Polypeptides—insulin and antidiuretic hormone
(ADH)
• Glycoproteins—follicle-stimulating hormone
(FSH) and luteinizing hormone (LH)
• Amines—derived from the aa’s tyrosine and
tryptophan; include hormones secreted by the
adrenal medulla, thyroid and pineal glands
• Steroids—lipids derived from cholesterol;
include testosterone, estradiol, progesterone
and cortisol
Steroids further divided
• Sex steroids--secreted by testes, ovaries,
placenta and adrenal cortex [outer region
of the gland]
• Corticosteroids--secreted ONLY by the
adrenal cortex
– Cortisol—regulates glucose balance
– Aldosterone—regulates salt balance
Figure 45.13 Steroid hormones from the adrenal cortex and gonads
Ammine Hormones
• Cholamines—secreted by the adrenal medulla
[inner portion of the adrenal gland]
– Epinephrine [adrenaline] & Norepinephrine
[noradrenaline] the fight or flight hormone & its
“antidote”; derived from tyrosine
• Thyroxine—secreted by the thyroid gland;
derived from tyrosine
• Melatonin—secreted by the pineal gland;
derived from tryptophan
Neural and Endocrine Interactions
• The endocrine system cooperates with the
nervous system to regulate the activities of
the other organ systems of the body
Major site of neural regulation is
the brain’s regulation of the anterior
pituitary gland
• The hypothalamus controls the hormonal
secretions of the anterior pituitary which
regulates other endocrine glands
Table 45.1 Major Vertebrate Endocrine Glands and Some of Their Hormones
(Hypothalamus–
Parathyroid glands)
Table 45.1 Major Vertebrate Endocrine Glands and Some of Their Hormones
(Pancreas–Thymus)
Negative Feedback Inhibition
The adrenal glands
• Located just above each kidney
• Consist of 2 parts
– Outer cortex
– Inner medulla
Figure 45.10 Glucose homeostasis maintained by insulin and glucagon
Figure 45.9 Hormonal control of calcium homeostasis in mammals