Endocrine System
Chapter 26
Endocrine System
 A bodily system that uses hormones for communication and
chemical regulation
 Hormones are chemical signals carried by the circulatory
system, made and secreted by endocrine glands
 Long-distance regulators
 Not quick acting system because hormones must be made,
circulated to all body cells, and sensed
 Control whole body activities like responses to stress and long-
term developmental processes such as growth
Chemical Signaling
 Endocrine cells are secretory vesicles that transport
hormones for release directly into the circulatory system
 Hormones travel throughout the body, but only act on target
cells that are equipped to respond
 Can turn on or off enzymes = may alter cellular metabolism
 Local regulators secrete signals into interstitial fluid and
affects nearby cells
 Pheromones carry messages between individuals of a species
 Neurosecretory cells conduct nerve signals AND secrete
hormones into blood
 E.g. epinephrine (adrenaline) as a ‘fight-or-flight’ hormone and
a s a neurotransmitter
Hormonal Signaling
 2 major types of hormone molecules
 Amino acid derived
 Proteins, peptides, and amines
 hydrophilic
 Steroids
 Sex hormones made from cholesterol (lipids)
 Hydrophobic
 All hormonal signaling has 3 events
 Reception: hormone binding to a receptor protein or target cell
 Signal transduction: coverts the signal from 1 form to another
 Response: result or change in cell’s behavior
 Target range is vast so 1 hormone may effect many or few targets
 E.g. sex hormones most body tissues while glucagon liver and fat cells
only
Water-soluble Hormones
 Receptors is PM of target
cells
 Hormone binds to receptor
protein to activate it
 Initiates a series of changes
in cellular proteins
 Converts extracellular signal
to an intracellular one
 Final relay molecule
activates a protein to evoke
the response
Lipid-soluble Hormones
 Bind receptors inside the cell
 Are small and nonpolar so can
diffuse through the PM
 Binds a receptor protein in the
cytoplasm or nucleus
 No signal pathway, self sufficient
 Attaches to enhancer site on
DNA
 Stimulates transcription and
translation
 Steroid hormones turn genes on
or off
 Focus on
hypothalamus and
pituitary gland
secretions
 Also adrenal gland
and gonads
Connection of Brain Structures
 The pituitary gland hangs on a stalk-like structure that
projects inferiorly from the hypothalamus
 The hypothalamus monitors internal conditions and emotional
states
 Controls anterior pituitary by secreting releasing and inhibiting hormones
 The pituitary gland has 2 distinct parts with different roles
 Anterior pituitary
 Endocrine cells that synthesize and secretes numerous hormones into
the blood
 Control activity of other endocrine glands
 Posterior pituitary
 Bundle of nervous tissue that stores and secretes 2 hormones made in
the hypothalamus
 Review positive and negative feedback
Posterior Pituitary
 Hypothalmus to posterior
pituitary connection is direct
 Oxytocin: uterine
contractions during childbirth
and milk letdown during
nursing
 Antidiuretic hormone:
acts on walls of kidney
tubules to control body’s
water and solute levels
Anterior Pituitary
 Hypothalmus to anterior
pituitary connection is
through blood vessels
 Feedback controls the
secretion of these
hormones
Growth Hormone (GH)
 Promotes protein synthesis and the use of body fat for
metabolism in a variety of target cells
 In young mammals encourages development and
enlargement of the body
 Too much or too little causes developmental problems
depending on stage on development of occurrence
 Can be made artificially now by bacteria that carry the gene
 Used to counter deficiencies in youth
 Abused by athletes to bulk up
 Can lead to heart failure, cancers, or disfigurement
Thyroid Regulation
 Thyroid affects almost every tissue in the body by producing
2 amine hormones, both containing iodine (I)
 Throxine (T4)
 Triiodothyronine (T3)
 Same effects on different target cells
 Crucial for development and maturation
 Maintain normal blood pressure, heart rate, and digestion
 Increase rate of O2 consumption = what effect on metabolism?
 Excess or insufficient amounts can have adverse health effects
 E.g. hypothyroidism: weight gain, intolerance to cold, lethargy
Pancreatic Hormones
 The pancreas produces insulin and glucagon to help
manage the body’s energy supply
 Islets of Langerhans with beta (insulin) and alpha (glucagon)
cells
 Antagonisitc hormones that regulate glucose levels
circulating in the blood
Glucose Homeostasis
o Glucose up =
insulin up = cells
store/take up
more glucose
until return to
normal
o Glucose down
= glucagon up =
liver break
glucagon into
glucose until
return to normal
Diabetes Mellitus
 When cells can’t absorb glucose from blood
 Develops when not enough insulin or cells don’t respond to
insulin
 Cells starved for fuel so begin burning fats and proteins
 Glucose absorbed by digestive system so concentration in urine is
high
 Treatments but no cure
 Blindness, dehydration, kidney and cardiovascular disease occur
 Type 1 (insulin dependent)
 Autoimmune disease: WBC’s attack beta cells
 Type 2 (non-insulin dependent)
 Onset is older and often associated with obesity
 Gestational diabetes
 Can effect any pregnant woman
Adrenal Glands
 Paired structures atop the kidneys consisting of 2 parts
 Each contains different cells and produce different hormones
 Both respond to stress
 Adrenal medulla produces ‘fight-or-flight’ response
 Short term response
 Produces epinephrine (epi) and norepinephrine (nor) to cause
 Responds to nerve signals from the hypothalamus
 Adrenal cortex
 Slower, longer lasting responses
 Produces corticosteroids (2 types)
 Responds to endocrine signals
Adrenal Medulla
 Nerve cells in
hypothalamus respond to
(+)or (–) stress stimuli
 Signals via spinal cord to
adrenal medulla to release
epi or nor into blood
 Prompts multiple rxns
 Liver releases glucose
 Raise blood pressure,
breathing and metabolic
rates
 Change blood flow
patterns
Adrenal Cortex
 Hypothalamus secretes
releasing hormone to
anterior pituitary to release
adrenocorticotropic
hormone (ACTH)
 Adrenal cortex releases
corticoids
 Mineralocorticoids
 Reabsorb salt and H20 to
increase blood volume and
pressure
 Glucocorticoids
 Increase glucose production
from fats and proteins
 Suppresses immune system
(inflammatory response)
 Cortisone injections
Sex Hormones
 Steroid hormones that affect growth and development as well
as regulate reproductive cycles and sexual behavior
 Gonads or sex glands secrete sex hormones and produce
gametes
 3 main types found in both males and females, but ratio differs
 Estrogens
 Maintain female repro. system and development of female features
 Progestins (progesterone)
 Prepare and maintain uterus to support an embryo
 Androgens (testosterone)
 Maintain and stimulate development of male repro. System
 Synthesized by gonads in response to releasing factor from
hypothalmus to anterior pituitary to secrete FSH and LH
Hormones Vary Between Species
 Prolactin is secreted by the anterior pituitary
 Humans
 Stimulates mammary glands to grow and produce milk during
pregnancy
 Prevents ovaries from releasing eggs, decreasing the chances of a
pregnancy while breast feeding
 Evolutionary adaptation to ensure adequate care to newborns possibly
 Birds
 Stimulates nestbuilding, regulates fat metabolism, and reproduction
 Amphibians
 Stimulates movement toward water in preparation for breeding and
affects metamorphosis
 Fish
 Regulate salt and water balance in fish that move between fresh and
salt water