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The Endocrine System
Chapter 11
-Endocrine System
I. Function
A. Body’s source of hormones
B. Hormonally controls body function
II. Structure
A. Glands or gland cells
1. secretory cell or structure derived
from epithelium, sources of hormones
2. 2 types
a. endocrine – ductless, secrete
into bloodstream
b. exocrine – have ducts or tubes
that secrete into epithelial tissue
Endocrine System
Main Sources
• Pituitary gland
• Adrenal glands
• Thyroid gland
• Parathyroid
glands
• Pineal gland
• Thymus gland
Figure 36.2
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3. 9 main “glands”
a. hypothalamus – brain, controls pituitary
b. pituitary – brain, “master gland”
-posterior (stores and secretes hormones made in
hypothalamus)
-anterior (makes and secretes its own hormones)
c. adrenals -medulla – inner portion
-cortex –outer portion
d. thyroid - throat
e. parathyroids - throat
f. gonads – lower abdomen, primary reproductive organs,
secretes gametes and sex hormones
-testes (male)
-ovaries (female)
g. pancreatic islets – endocrine clusters in the pancreas,
abdomen
-alpha cells
-beta cells
-delta cells
h. thymus - chest
i. pineal - brain
The Hypothalamus
• Region in the
forebrain
hypothalamus
• Contains hormonesecreting cells
• Interacts with
pituitary
pituitary gland
Pituitary Gland
• Pea-sized gland at base of hypothalamus
• Two lobes
– Posterior lobe stores and secretes hormones
synthesized in the hypothalamus
– Anterior lobe produces and secretes its own
hormones
4. others
a. stomach and small intestine
b. liver
c. kidneys
d. heart
B. Hormones
1. secretory products of endocrine glands, endocrine
cells and some neurons that the delivers to nonadjacent
target cells
a. one type of signaling molecule (molecules that
help integrate activities within and between cells)
-some other signaling molecules are:
-neurotransmitters – that we talked
about in nervous system
-local signaling molecules – released
by many cells in localized tissue
-phermones – secretions of exocrine
glands that diffuse outside of the body
and act on other individuals
2. over 50 known hormones
3. we will study mainly vertebrate (human
hormones), but invertebrates have hormones
as well
4. each “gland” or endocrine organ secretes
specific hormones (see chart below)
5. target cells – any cell with receptors for a
signaling molecule that may chamge its
activities in response to it
6. antagonistic
a. many hormones work in pairs to
“counteract” each other
b. classic examples
-glucagon and insulin
-calcitonin and parathyroid hormone
-epinephrine and norepinephrine
7. 2 main types
a. steroid hormones
-lipid soluble so they can diffuse through the
membranes
-can enter the cell and even the nucleus
-can affect gene expression by initiating or
Inhibiting transcription
-ex. estrogens, androgens, progesterone,
cortisol, aldosterone
b. peptide hormones
-water soluble, cannot diffuse through
membrane
-bind to membrane receptor, don’t get inside cell
-second messenger is activated inside the cell, the
second messenger affects gene expression
-cAMP is common second messenger
-ex. glucagon, ADH, OCT, TRH, insulin, STH,
PRL, FSH, LH, TSH
Two Main Hormone Types
• Steroid hormones
– Derived from
cholesterol
– Estrogens,
progestins,
androgens, cortisol,
aldosterone
• Peptide hormones
– Peptides, proteins,
or glycoproteins
– Glucagon, ADH,
oxytocin, TRH,
insulin,
somatotropin,
prolactin, FSH, LH,
TSH
Steroid
Hormones
hormone
• Most diffuse across the
plasma membrane and
bind to a receptor
• Hormone-receptor
complex acts in nucleus
to inhibit or enhance
transcription
receptor
hormone-receptor
complex
Figure 36.3
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gene product
Protein
Hormone
glucagon
glucagon receptor
• Hormone binds to a
receptor at cell surface
cyclic AMP + Pi
• Binding triggers a
change in activity of
enzymes inside the cell
Figure 36.4
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ATP
cAMP activates
protein kinase A
Protein kinase A converts phosphorylase
kinase to active form and inhibits an
enzyme required for glucagon synthesis.
C. Mechanisms
1. feedback
a. positive feedback – rising levels
stimulates further secretion
b. negative feedback – rising levels
inhibits further secretion
2. environmental factors can affect
hormone secretion
a. ex. pineal gland secretes
melatonin in the absence of light
and is therefore affected by time of
day and seasons
Feedback Mechanisms
• Negative feedback
– Increase in hormone triggers activities that
inhibit further secretion
• Positive feedback
– Increase in hormone triggers activities that
stimulate further secretion
3. direct responses to internal environment
a. the pancreatic islets respond to blood
sugar levels
- if blood sugar drops the pancreas
secretes glucagon to raise blood sugar
- if blood sugar is high the pancreas
secretes insulin to lower blood sugar
4. therefore, some endocrine glands react to
chemical changes and are not controlled by
hypothalamus and pituitary
5. hormones interact with protein receptors on
target cells
a. different hormones act on different
mechanisms in target cell
b. not all types of cells respond to a given
signal
Responses to Hormones Vary
• Different hormones activate different
responses in the same target cell
• Not all types of cells respond to a
particular hormone
Local Signaling Molecules
• Prostaglandins
– Produced and secreted in response to local
changes
– Sixteen types with a variety of effects
• Growth factors
– Affect cell division rates in tissues