Physiology 31 Lecture
Chapter 7 - Introduction to the Endocrine System
I. Overview
A. Hormones
B. Classification of Hormones
C. Control of Hormone Release
D. Hormone Interactions
E. Endocrine Pathologies
II. Hormones
A. General hormone functions
1. _____________ are chemical messengers released by a cell or tissue into the
bloodstream, in which they travel to target cells
2. Processes under the __________ of hormones include
a. __________ and development
b. _____________
c. ______________ of the internal environment (temperature, water balance, ions)
d. _______________
B. Endocrine _________ produce hormones, and may be completely or partially endocrine
1. Completely endocrine glands include the ___________, thyroid, parathyroid, adrenal,
and pineal glands.
2. Partially endocrine glands are the _______________, thymus, pancreas, ovaries,
testes, kidneys, stomach, liver, small intestines, skin, heart, and placenta
C. What is a Hormone?
1. Hormone means to “excite” or “________”
2. Hormones are secreted into the blood by a cell or _________, including
a. _____________ tissue of endocrine glands
b. ___________, which release neurohormones
c. _____________ system cells, which secrete cytokines
3. Although most hormones are secreted into the blood, _________ are chemical signals
secreted into the external environment
4. Hormones travel in the bloodstream to ____________ cells
5. Hormones exert their effects at very _____ concentrations (nanomolar to picomolar
range)
D. Hormones act by binding to ___________
1. Hormones bind to target cell receptors and initiate biochemical ___________ (cellular
mechanisms of action)
2. One hormone may act on __________ tissues, and its effects may vary in the different
tissues. Example: _________
a. In ___________ and adipose tissues, insulin alters __________ transport proteins
and enzymes for glucose metabolism
b. In the _______, insulin modulates __________ activity but has no effect on glucose
transport proteins
c. In the _______, glucose metabolism does not require ________
3. A cell must have _________ for a particular hormone to respond to that hormone
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E. Hormone action is _____________ by ending secretion, removing the hormone from the
blood, or terminating activity at the target cell
1. Hormones in the blood are __________ into inactive metabolites by specific
__________ produced mainly in the liver and kidney
2. The rate of hormone breakdown is related to its _____-____ – the amount of time
required to reduce its concentration by one half
III. Classification of Hormones
A. Hormones are __________ according to their source, receptor type, or chemical structure
1. Their _______ is generally structures in the _________ or other endocrine glands in the
body
2. Some hormones bind to ___________ receptors, some to tyrosine _________-linked
receptors, others to intracellular receptors, etc.
3. Chemically, all hormones are ________ from either amino acids or cholesterol
a. _______________ based hormones include peptides, proteins, and amines; these
hormones are ________ soluble
b. _____________ derived hormones are steroids, which are _______ soluble
B. Most hormones are peptides or _________
1. __________ hormone synthesis, storage, and release involves ______, RNA, the rough
ER, and the golgi apparatus
a. These hormones are first formed on the ____ as inactive _________hormones (e.g.,
preproinsulin)
b. As the preprohormone moves through the ER and ________, it is cleaved into a
_____hormone (e.g., proinsulin)
c. In the Golgi, prohormones are packaged into secretory _______ with proteolytic
_________ that cleave the prohormone into the active ________ and other fragments
(e.g., insulin & C-peptide)
d. When the cell receives a _________ for secretion, the secretory vesicles
____________ the peptide hormones
2. Peptide hormones dissolve in blood plasma and have relatively ________ half-lives
3. Cellular _____________ of action of peptide hormones
a. Peptide hormones bind to ___________ receptors and cause rapid cellular responses
via signal ___________
b. Most of these hormones stimulate ____ 2nd messenger systems
c. A few peptides also initiate _________ of new proteins
C. _________ hormones are derived from two _______ acids
1. ____________ is converted to __________ in the pineal gland
2. __________ is used to form thyroid hormones and catecolamines
3. _______________ - dopamine, epinephrine, and norepinephrine, are neurohormones
that bind to cell ___________ receptors
4. ___________ hormones act more like steroids, binding to ______________ receptors
to activate genes
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D. Steroid hormones are derived from _____________
1. _________ are produced in the smooth ER of the adrenal cortex, _________, and
placenta
2. Steroids are synthesized as they are __________ (not stored in vesicles like peptide
hormones)
3. Because steroids are not _____ soluble, they must bind to ______ carrier molecules in
the blood (e.g., globulins and albumin)
4. Steroid binding to _________ extends their half-lives (e.g., ______ compared to
seconds or minutes for amines and peptides)
5. Since steroids are _______ soluble, they usually diffuse through cell membranes, bind
to __________ receptors, and turn _______ on or off, thus affecting protein synthesis
6. Protein synthesis takes time, so steroid pathways are generally ___________ than those
of peptide hormones
7. Some steroids can also bind to __________ receptors and initiate rapid responses
IV. Control of Hormone Release
A. Hormones can be ___________ by their reflex pathways
1. All _________ pathways have a stimulus, a sensor, an input signal, integration, an
output signal, and a response
a. In the endocrine system, the response is a __________
b. The response is a ________hormone or an electrical signal in the nervous system
c. In simple reflex pathways, the response usually serves as a ___________ feedback
that turns off the reflex
d. Example: a rise in blood glucose levels triggers _________ release from pancreatic
cells; insulin stimulates uptake of ________ by target cells, which terminates insulin
secretion
B. The endocrine cell is the __________ and integration center in the simplest endocrine
reflexes. Example: parathyroid hormone (____)
1. Parathyroid cells monitor blood _____ concentration via G protein-coupled Ca2+
receptors in their cell membranes
2. When Ca2+ is bound to the receptors, PTH secretion is _________
3. If blood Ca2+ levels __________, fewer receptors are bound, inhibition ceases, and the
cells release ____
4. PTH travels to _________ tissues (e.g., bone and small intestine), where it triggers
responses that increase Ca2+ levels
C. Many endocrine reflexes involve the ____________ system
1. Neurons can stimulate some __________ glands (e.g, the adrenal medulla) to release
hormones, or
2. Some neurons release _______hormones into the bloodstream
D. Three groups of ______hormones are secreted into the blood by neurons
1. _____________ made by modified neurons in the adrenal medulla
2. _____________ neurohormones secreted by the post. pituitary
3. Hypothalamic neurohormones (releasing factors) that control hormone release by the
____________ pituitary
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E. The pituitary gland (____________) is actually two fused glands suspended from the
hypothalamus of the brain
1. Anterior pituitary (______hypophysis) - a true endocrine gland composed of
___________ tissue
2. Posterior pituitary (______hypophysis) – an extension of the hypothalamus, composed
of __________ tissue
F. _____________ pituitary - stores and releases two peptide neurohormones produced by
neurons in the ______thalamus
1. Vasopressin (____) regulates water balance in the body
2. ___________ stimulates uterine contractions during childbirth and milk ejection during
breast-feeding
G. ___________ pituitary - secretes at least 6 hormones
1. Ant. Pituitary hormone secretion or the lack thereof is in response to _________ and
___________ hormones from the hypothalamus
2. Five ant. Pituitary hormones are ________ (“feeder”) hormones – they stimulate other
endocrine glands to release hormones
a. _____ is released in response to hypothalamic _____, and stimulates the thyroid to
secrete _________ hormones, which regulate metabolism in most body cells
b. ________ is released in response to hypothalamic ______, and stimulates the adrenal
cortex to secrete _________, which affect several organs
c. ____ release is inhibited by _____ (somatostatin) and stimulated by ______ from the
hypothalamus; GH affects ___________ in many tissues, and stimulates hormone
secretion by the liver
d. Gonadotropins (____ & ___) are releases in response to _____ from the
hypothalamus; FSH & LH stimulate the ________ (ovaries and testes) to release
steroidal ____ hormones
3. Prolactin (____) is a nontrophic hormone released in response to hypothalamic ____, and
stimulates breast tissue to produce _____; ____ inhibits PRL release
H. Feedback loops in the hypothalamic-pituitary pathway involve 3 ___________ centers –
the hypothalamus, pituitary gland, and their target tissues
1. Each hormone in the pathway ______ _____ to suppress hormone secretion by earlier
integrating centers
2. When __________ of one hormone increases or decreases, it can affect the secretion of
other related hormones
a. Example: corticoids feed back to inhibit CRH and _______; this is termed a ______loop negative feedback
b. In ______-loop negative feedback, ant. Pituitary hormones inhibit the release of
hypothalamic hormones
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I. The Hypothalamic-Hypophyseal ________ System directs trophic hormone delivery
1. Two ___________ beds connected by _________ comprise the portal system that
connects the hypothalamus and ant. Pituitary
2. Hypothalamic _________ secreted into the portal system travel to the ______ Pituitary
and stimulate cells therein to release hormones
V. Hormone ____________ include synergism, permissiveness, and antagonism
A. In ____________, the effect of interacting hormones is more than ___________. Example:
blood glucose levels are increased by glucagon, epinephrine, and cortisol
1. __________ from the pancreas might elevate BG levels 10 mg/dl
2. __________ from the adrenal medulla might elevate BG levels 5 mg/dl
3. ______ glucagon and epinephrine can elevate BG levels 22 mg/dl
B. A __________ hormone may be needed to allow another hormone to exert its full effect
1. Example: if ________ hormone is not present, gonadotrophic hormones alone aren’t
sufficient for reproductive system maturation
C. ______________ hormones have opposing effects
1. Antagonists may act through different pathways, or may ______-regulate the number of
the other hormone’s receptors
2. Example: ___________ and growth hormone are antagonistic to insulin because they
______ BG levels, whereas insulin ______ BG levels. GH decreases insulin
__________
VI. Endocrine _____________ include hypersecretion, hyposecretion, and abnormal
responsiveness of target tissues to a hormone
A. _______secretion exaggerates a hormone’s effects
1. Causes for ________ hormone secretion include tumors on endocrine glands
2. Example: excess GH in children can cause ___________
B. _______secretion diminishes or eliminates a hormone’s effects
1. Insufficient or ______ of a hormone’s production is often caused by the _________
(shrinkage) of a gland due to disease
2. Example: insufficient GH production in children leads to _________
C. ___________ or 2nd messenger problems cause abnormal tissue responsiveness
1. ______-regulation of a hormone’s receptors can occur if the hormone level is
abnormally ______ for an extended time (e.g., decreased number of insulin receptors
due to high insulin levels in type 2 diabetics)
2. Receptor and signal _____________ abnormalities
a. Genetic ____________ can occur that result in defective receptors (e.g., testicular
feminizing syndrome caused by defective androgen receptor in male fetus)
b. Genetic alterations in _______ pathways can lead to hormone excess or deficiency
(e.g., defect in a G protein leads to pseudohypoparathyroidism)
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D. ____________ of endocrine pathologies depends on the complexity of the reflex
1. If a pathology (deficiency or excess) arises in the _______ endocrine gland in a reflex, it
is called a ___________ pathology (e.g., if a damaged adrenal gland produces excess
cortisol, it’s called primary hypersecretion)
2. If dysfunction occurs in a tissue producing _________ hormones, the problem is a
__________ pathology (e.g., if pituitary ACTH secretion diminishes, it’s called
secondary hyposecretion)
3. The diagnosis of endocrine pathologies depends on understanding __________
feedback in the control pathways