Endocrine System
 Role of the Endocrine System
 Hormones: Types
 Transport of Hormones
 Interaction of Hormones with Target Cells
 Effects of Hormones on Target
 Control Mechanisms of Endocrine Glands
 Endocrine Organs
• Pituitary (Anterior and Posterior)
• Thyroid
• Parathyroids
• Adrenals (Cortex, Medulla)
• Pancreas
• Gonads
 Ovaries
 Testes
The Endocrine System
 A more broad-based and long-lasting
communication system than the nervous system
 Uses chemical messages (hormones) that are
released into the blood
 Hormones control several major processes
• Reproduction
• Growth and development
• Mobilization of body defenses
• Maintenance of much of homeostasis
• Regulation of metabolism
Types of Hormones
 Protein-based hormones
Insulin
 Steroid hormones
 Prostaglandins and catecholamines
Growth hormone
Hormones as Chemical Messengers
Endocrine gland (source)
Target organs or glands
Hormones move through the bloodstream to target organs
Hormone Interaction with Target Cells
 Hormones bind to receptors sticking out from the plasma membrane of
target cells or within target cells
growth factor
insulin
epinephrine
Hormones
Receptors
Examples of receptors found in the plasma membrane of cells
Effects Caused by Hormones
 Changes in electrical state of the cell,
stimulating change
 Causes enzymes to be made, changing
metabolic abilities of target cell
 Turn on or off enzymes that alter metabolism
inside cell
 Stimulate cell division and multiplication
 Turn on certain genes
Control Mechanisms of Endocrine Glands
Hormonal: Chemical
stimulus (i.e. endocrine
glands are activated by other
hormones)
Humoral/Blood-Based:
Changing blood levels of
certain ions stimulate
hormone release
Neural: Nerve impulses
stimulate hormone release; most
are under control of the
sympathetic nervous system
Location of Major Endrocrine Organs
Figure 9.3
Pituitary Gland
Flip and enlarge
blood
portal
system
glandular tissue
Nervous
system that
hormones
can drip
down on
nervous tissue
Hormones of the Anterior Pituitary
 Six anterior pituitary hormones
• Two affect non-endocrine
targets
• Four stimulate other endocrine
glands (tropic hormones)
 Characteristics of all anterior
pituitary hormones
• They are proteins (or peptides)
• They act through secondmessenger systems
• They are regulated by hormonal
stimuli, mostly negative
feedback
Hormones of the Anterior Pituitary
Increases
bone and
skeletal mass
Causes
milk
secretion
in breasts
Causes follicle and
sperm maturation,
ovulation and
testosterone production
Stimulates
thyroid
hormone
secretion
Causes
aldosterone,
glucocorticoid,
or androgen
release
Hormones of the Posterior Pituitary
Inhibits diuresis (urine
production) and
increases blood pressure
Stimulates uterine
muscle contraction in
labor and intercourse;
causes milk ejection
Thyroid Gland
Consists of two lobes and a connecting isthmus
Thyroid hormone
Controls rate of cellular
respiration. All body cells are
targets.
Calcitonin
Decreases blood calcium levels
by causing bone calcium
deposition. Made by
parafollicular cells.
Figure 9.6
Thyroid Hormone
 Lack of Dietary Iodine: Goiter
 Hyposecretion of thyroxine
( hypothyroidism in adults)
 Hyperthyroidism (Grave's disease)
Calcitonin (Calcium deposition)
 Decreases blood
calcium levels by
causing its
deposition on bone
 Antagonistic to
parathyroid hormone
 Produced by C
(parafollicular) cells
Figure 9.9
Parathyroid Glands (Calcium removal)
Found on posterior surface of thyroid
Parathyroid hormone
1.
Stimulates osteoclasts to
remove calcium from
bone
2.
Stimulates the kidneys
and intestine to absorb
more calcium
3.
Raises calcium levels in
the blood
Adrenal Glands
 Two parts that act as if
separate glands
• Cortex – outer
glandular region in
three layers
• Medulla – inner
neural tissue region
 Sits on top of the
kidneys
Ad-renal
both mean “upon or
Epi-nephros
next to the kidney”
&
Adrenal Hormones and Their Locations
Adrenal Cortex
Outer portion produces
mineralocorticoids like
aldosterone
Middle layer produces
glucocorticoids like cortisone
and cortisol
Innermost layer produces
androgens like estrogens and
testosterone
Medulla produces catecholoamines
like epinephrine and norepineprhine
Adrenal Cortex (Outer Portion)
Aldosterone release causes salt and water retention, increasing blood pressure
Hormones of the Innermost Cortex Layer
 Sex hormones (steroids)
• Produced in the inner layer of the adrenal
cortex
• Androgens (male) and some estrogen
(female) -- both produced regardless of
gender
• Hypersecretion causes masculinization
(regardless of gender) - most obvious
effects in females
• Hyposecretion causes Addison's disease
Hormones of the Adrenal Medulla
 Produces two similar hormones
(catecholamines)
• Epinephrine
• Norepinephrine
 These hormones prepare the body to deal
with short-term stress
 Sympathetic system stimulates catecholamine
release in fight or flight: increased heart rate,
blood pressure, blood gluocose, respiratory
rate
Pancreatic Islets
 The pancreas is a mixed gland
 The islets of the pancreas produce hormones
• These hormones are antagonists that
maintain blood sugar homeostasis
Pancreatic Islets
Insulin
Allows glucose to
cross plasma
membranes into cells
from beta cells
(hypoglycemic
hormone)
Glucagon
Allows glucose to
enter the blood from
alpha cells
(hyperglycemic
hormone)
Figure 9.13
Pancreatic Hormones and Blood Sugar
Figure 9.14
Pineal Gland
 Found on the third
ventricle of the brain
 Secretes melatonin
• Helps establish the
body’s wake and
sleep cycles
• May have other asyetunsubstantiated
functions
Hormones of the Ovaries
 Estrogens
• Produced by Graafian follicles
or the placenta
• Stimulates the development of
secondary female characteristics
• Matures female reproductive
organs
• Helps prepare the uterus to
receive a fertilized egg
• Helps maintain pregnancy
• Prepares the breasts to produce
milk
Hormones of the Ovaries
 Progesterone
• Produced by the corpus luteum
• Acts with estrogen to bring about the
menstrual cycle
• Helps in the implantation of an embryo in
the uterus
Hormones of the Testes
 Interstitial cells of testes are hormoneproducing
 Produce several androgens
 Testosterone is the most important
androgen
• Responsible for adult male
secondary sex characteristics
• Promotes growth and maturation of
male reproductive system
• Required for sperm cell production
Other Hormone-Producing Tissues and
Organs
 Parts of the small intestine
 Parts of the stomach
 Thymus
 Kidneys
 Heart
 Many other areas have scattered endocrine
cells
Developmental Aspects of the Endocrine
System
 Most endocrine organs operate smoothly until old age
 Menopause is brought about by lack of efficiency of the
ovaries
 Problems associated with reduced estrogen are common
 Growth hormone production declines with age
 Many endocrine glands decrease output with age