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Reading assignment:
Chapter 16
(Thibodeau & Patton
Anatomy
& Physiology) |
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ACT
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Interactive
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GA |
Gray's Anatomy |
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Animation |
pp |
PowerPoint
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FIG
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Figure |
term |
Define,
pronounce |
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Online preview:
Endocrine System
(Parts 1 & 2)
(Previews are found at
WebCT)
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Note: you must know the names and sources of all
hormones listed in tables of Chapter 16 (except the hypothalamic releasing
hormones).
In class, we will focus
mainly on the theories of how this system works. The details of
individual glands and their hormones will be learned mostly on your
own.
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Hormones
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Chemical
messengers released into the blood and having an effect outside the tissue
that made it |
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Source: endocrine (ductless)
glands
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"Regular"
endocrine tissue - glandular epithelium |
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Neurosecretory tissue -
modified neurons |
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Target concept
pp 
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Target cells, target
tissues, target organs |
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Receptors (specific to a
particular hormone) |
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Signal transduction |
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Pathway
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Gland --> Blood -->
Target tissue (receptor) |
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Two categories
pp
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Steroid - lipids derived
from cholesterol |
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Nonsteroid
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Protein |
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Glycoprotein |
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Peptide |
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Amine (derived from
amino acids) |
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Prostaglandins
(PG)
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Lipids (fatty acids) |
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Have LOCAL effects, but are
regulatory chemicals carried in the blood, so they are sometimes called
"tissue hormones"
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Paracrine agents or "hormones"
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Substances that regulate other
cells in the same tissue |
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Autocrine agents or "hormones"
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Substances that regulate the
same cell that produced it |
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Endocrine hormone
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Substances that regulate cells
outside the tissue that produced it |
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Classical definition of hormone
(one that we'll use in our course) |
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Mechanisms of
hormone actions
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Steroid hormones
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Lipid hormones derived from
cholesterol
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Examples: testosterone,
estrogens (e.g., estradiol), progesterone, aldosterone, cortisone |
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Mobile receptor model
(nuclear receptor model)
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Steroid hormone travels
in blood plasma (hormone is temporarily bound to a plasma protein) |
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Hormone dissolves
through phospholipid bilayer of plasma membrane of target cell |
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Hormone binds to
receptor inside cell (probably in nucleus), forming hormone-receptor
complex |
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Hormone-receptor complex
triggers the activation of a particular gene (on nuclear DNA) |
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mRNA is transcribed at
the activated gene |
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protein is made using
the gene encoded in the new mRNA |
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protein causes the
hormonal effect |
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Nonsteroid hormones (peptides,
proteins)
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Membrane-bound receptors
(face out of the target cell)
pp
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May move into
cell if small enough |
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Second messenger systems
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cyclic AMP
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hormone travels
in blood plasma |
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Hormone binds to
its receptor in the plasma membrane |
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Hormone-receptor
binding activates a G protein (in plasma membrane) |
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Activated G
protein in turn activates the enzyme adenyl cyclase |
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Adenyl cyclase
causes ATP to lose two P, becoming cAMP (cyclic AMP
[adenosine monophosphate]) |
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cAMP activates
protein kinases (enzymes that activate other
proteins/enzymes), producing the hormonal effect |
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Ca++-calmodulin
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hormone travels
in blood plasma |
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hormone binds to
its specific receptor in the plasma membrane |
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hormone-receptor
binding activates G protein, then adenyl cyclase, then
protein kinases |
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activated
protein kinase opens Ca++ channels in plasma
membrane |
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Ca++
diffuses into target cells (remember, cells HATE calcium, so
all the Ca++ was outside the cell to begin with) |
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Ca++
binds to calmodulin inside cell |
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Ca++-calmodulin
complex activates (or inactivates) an enzyme, producing the
hormonal effects |
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Many drugs are
targeted at G-protein-coupled receptors (GPCRs)—about
25% of the top-selling drugs and more than half of
all currently used drugs. |
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Amino
acid derivative hormones, such as thyroid
hormone,
may have intracellular receptors as do steroid
hormones |
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Hormones may work together to
regulate target cells
pp
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Synergistic effects:
combined effect is greater than sum of individual effects |
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Permissive effects: one hormone allows another hormone to have its full effect
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Agonistic effects: two hormones have similar effects
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Antagonistic effects: two hormones have opposing effects
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Trop(h)ic effects: hormones stimulate development of another gland
and secretion of that gland's hormones |
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Hormones have diverse functions
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Even though our course focuses on one or two main
actions for each hormone, each hormone may have hundreds of
secondary effects |
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Important for understanding the complexity of
endocrine function |
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| Not all hormones find their
targets
pp
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Metabolized or excreted |
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Clinically useful:
blood or urine analysis shows hormone levels |
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Regulation of
receptors
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Up regulation
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Target cells
increase their number of a particular hormone receptor, becoming more
sensitive to that hormone |
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Down regulation
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Target cells
decrease their number of a particular hormone receptor, becoming less
sensitive to that hormone |
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Receptor turnover
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Ongoing process of a cell moving receptors to its
plasma membrane or nucleus and removing other receptors, all
occurring at rates that can be increased or decreased under
different conditions |
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Regulation of
secretion
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Basal secretion (may be
periodic)
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Increase or decrease
via feedback controlling mechanisms |
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Feedback
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Negative; positive |
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Long loop; short loop |
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Responsive |
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Endocrine disorders
pp
Many endocrine disorders have historically been
classified as:
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hypersecretion
disorders: where there is too much of one or more hormones being
secreted |
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hyposecretion
disorders: where there is not enough of one or more hormones being
secreted |
However, we now know that such classifications can be
misleading because some disorders that appear to result from
hypersecretion may instead be caused by increased sensitivity due to
abnormal up regulation or changes in the signal transduction
mechanism.
Likewise, the appearance of hyposecretion may instead
be caused by abnormal down regulation of receptors or by problems in
signal transduction in the target cells. |
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Hypothalamus-pituitary
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Neuroendocrine cells are neurons
that release their transmitters directly into the blood (rather than across
a gap to another neuron), so the transmitters then act as hormones |
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Hypothalamus
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Part of brain on inferior
side, just in front of (and above) the brain stem |
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Part of it is nervous
tissue, part is neuroendocrine tissue |
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Pituitary (hypophysis)
GA
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Divided into two parts:
Anterior Pituitary and Posterior Pituitary
GA
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Anterior pituitary (adenohypophysis)
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"regular"
endocrine tissue |
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Releasing
(release-inhibiting hormones) from the hypothalamus regulate
anterior pituitary secretion
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Hypophyseal
portal system |
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Major hormones
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Pr (prolactin) |
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GH (growth
hormone) |
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Tropic hormones
(trigger development of/secretion by other glands)
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ACTH (adrenocorticotropic
hormone) |
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TSH
(thyroid-stimulating hormone) |
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LH (luteinizing
hormone) |
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FSH
(follicle-stimulating hormone) |
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Posterior pituitary (neurohypophysis)
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Neuroendocrine cells
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Body of cell is
in hypothalamus |
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Fiber extends
from each neuron cell body down into posterior pituitary |
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Thus, posterior
pituitary hormones are made in the hypothalamus but released
from the posterior pituitary |
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Oxytocin and ADH (antidiuretic
hormone) |
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Thyroid
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Location - below larynx, wrapped
around trachea
GA
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Structure
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Two lateral masses and
isthmus |
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Follicles
GA
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Follicular cells -
release thyroid hormone |
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Thyroid colloid - store
thyroid hormone |
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Thyroid hormone
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T3 -
triiodothyronine |
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T4 -
tetraiodothyronine |
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Parafollicular cells
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Calcitonin |
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Parathyroid
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Location
GA
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Imbedded in posterior
surfaces of thyroid |
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Structure
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4-5 small round bodies made
of glandular epithelium |
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Hormone: parathyroid hormone (PTH) |
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Adrenal (suprarenal)
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Location
GA
GA
GA
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On top of each kidney (renal
= "kidney") |
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Structure
GA
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Cortex (endocrine)
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zona glomerulosa
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mineralocorticoids (aldosterone) |
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zona fasciculata
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glucocorticoids
(cortisone) |
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zona reticularis
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glucocorticoids
(cortisone) |
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gonadocorticoids
(testosterone, estrogens) |
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Medulla (neurosecretory)
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catecholamines (epinephrine[adrenaline]) |
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Pancreas
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Location
GA
GA
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Lies within the C
of the duodenum, inferior to the stomach |
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Structure
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Pancreatic islets (of Langerhans) (endocrine)
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Alpha cells (A) -
glucagon |
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Beta cells (B) - insulin |
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Delta cells (D) -
somatostatin |
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PP cells (F) -
pancreatic polypeptide |
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Acinar cells (exocrine) |
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Other endocrine glands
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Ovaries
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Estrogens and progesterone |
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Testis
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Testosterone |
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Placenta
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Human chorionic gonadotropin (HCG) |
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Estrogens |
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Progesterone |
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Placental lactogen |
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Thymus
GA
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Thymosin |
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GI (gastrointestinal) mucosa
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Several hormones regulate GI function |
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Heart
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Atrial natriuretic hormone (ANH) |
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Pineal
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Melatonin |
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Please refer to
Table 16-10 in Anatomy
and Physiology for a summary of
these and other additional hormones of the human body. |
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Example of
homeostatic endocrine regulation
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