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Endocrine System
1. The endocrine system consists of several
glands throughout the body that produce
hormones.
2. Hormones are chemical messengers that are
transported through the blood to other parts of
the body where they produce a specific effect.
3. Most hormones are either peptides or lipids.
4. Each hormone fits into generally a single
receptor site on a target cell where it elicits
a quick response. The hormone is then degraded.
Example
Pathway
Low blood
glucose
Stimulus
Receptor
protein
Pancreas
secretes
glucagon ( )
Endocrine
cell
Blood
vessel
Target
effectors
Response
Liver
Glycogen
breakdown,
glucose release
into blood
Simple endocrine pathway
SECRETORY
CELL
NonSteroid
Hormone
SECRETORY
CELL
Hormone
molecule
VIA
BLOOD
Hormone
molecule
VIA
BLOOD
Signal receptor
TARGET
CELL
TARGET
CELL
Signal
transduction
pathway
OR
Signal
receptor
Cytoplasmic
response
DNA
Signal
transduction
and response
mRNA
DNA
NUCLEUS
Nuclear
response
NUCLEUS
Receptor in plasma membrane
Synthesis of
specific proteins
Receptor in cell nucleus
Steroid
Hormone
5. The hypothalamus and pituitary work jointly
as the neuroendocrine control center.
6. The hypothalamus stimulates the pituitary
which then secretes hormones including some
releasing and inhibiting hormones that target
the anterior pituitary.
7. In response, the anterior pituitary releases
hormones that stimulate other glands. These
hormones include follicle stimulating hormone
and growth hormone.
8. Posterior Pituitary – This is actually an extension of the
hypothalamus. It releases these two hormones that
are produced in the hypothalamus.
a. Oxytocin - induces uterine contractions
and milk ejection.
b. Antidiuretic hormone (ADH) enhances
water reabsorption in the kidneys.
Hypothalamus
Neurosecretory
cells of the
hypothalamus
Axon
Posterior
pituitary
Anterior
pituitary
HORMONE
TARGET
ADH
Kidney tubules
Oxytocin
Mammary glands,
uterine muscles
9. The thyroid produces 3 hormones. Two of the three
hormones, T3 and T4 are involved in metabolic rates and
require iodine. Without it, goiter can develop. The third
hormone is calcitonin. It reduces blood calcium levels.
10. The parathyroid glands are imbedded in the
thyroid gland. When calcium levels in the blood
drop, the glands release parathyroid hormone
that stimulates the release of more calcium
from the bones.
Dorsal view of the thyroid
gland (pink) and the
parathyroids (yellow). The
enlarged parathyroid is
cancerous in this illustration.
GOITER
11.Pancreas –most of its function is in the
production and secretion of enzymes. There is a
section of islet cells that secrete the hormone
glucagon. Glucagon is released when blood
sugar levels drop. It stimulates the liver to break
down stored glycogen into glucose. The
pancreas also has other islet cells that
produce insulin which has the opposite
affect on blood glucose levels. These two hormones
work together to create a negative feedback loop.
Negative Feedback Loop
Body cells
take up more
glucose.
Insulin
Beta cells of
pancreas
release insulin
into the blood.
Liver takes
up glucose
and stores it
as glycogen.
STIMULUS:
Rising blood glucose
level (for instance, after
eating a carbohydraterich meal)
Blood glucose level
declines to set point;
stimulus for insulin
release diminishes.
Homeostasis:
Blood glucose level
(about 90 mg/100 mL)
Blood glucose level
rises to set point;
stimulus for glucagon
release diminishes.
Liver breaks
down glycogen
and releases
glucose into the
blood.
STIMULUS:
Dropping blood glucose
level (for instance, after
skipping a meal)
Alpha cells of pancreas
release glucagon into
the blood.
Glucagon
12. Adrenal glands – the adrenal glands have two
functioning tissues: cortex = outside and
the medulla = the inside.
13. The adrenal cortex secretes hormones that
affect absorption in the kidneys, sex characteristics and anti-inflammatory response.
14. The adrenal medulla secretes epinephrine
and norepinephrine. These hormones bring
about the flight or fight response (superhuman
strength etc !)
Stress
Nerve
Spinal cord signals
(cross
section)
Hypothalamus
Releasing
hormone
Nerve
cell
Anterior pituitary
Blood vessel
Nerve cell
ACTH
ACTH
Adrenal
gland
Kidney
Short-term stress response
Effects of epinephrine and norepinephrine:
1. Glycogen broken down to glucose;
increased blood glucose
2. Increased blood pressure
3. Increased breathing rate
4. Increased metabolic rate
5. Change in blood flow patterns, leading to
increased alertness and decreased
digestive and kidney activity
Long-term stress response
Effects of
mineralocorticoids:
Effects of
glucocorticoids:
1. Retention of sodium 1. Proteins and fats
broken down and
ions and water by
converted to glucose,
kidneys
leading to increased
2. Increased blood
blood glucose
volume and blood
pressure
2. Immune system may
be suppressed
15. Gonads – the ovaries produce estrogen and
progesterone – these help control female
reproductive functions.The testes produce
testosterone which aids in male reproductive
functions.
16. The thymus gland – located behind the
sternum, its function is to aid in cell
development for the immune system
(T-lymphocytes).
17. The Pineal Gland – located deep in the brain
above the brain stem, it is responsible for
melatonin which may be involved in circadian
rhythms (daily cycles)