Endocrine System
Chapter 25
Endocrine System
• Communication
• Integrates body functions in conjunction w/
nervous system
• Ductless glands that secrete hormones directly
into the extracellular space where hormones
diffuse into blood stream
• Some specific functions are:
–
–
–
–
Growth of body and reproductive structures
Mobilize body fat
Maintain proper blood chemistry
Maintenance of metabolic rate
Comparison of Nervous System and Endocrine System
Regulation of Homeostasis
Characteristic
Nervous System
Endocrine Systems
Mechanism of Control
Neurotransmitters
released in response to
nerve impulse.
Hormones delivered
throughout the body
through the blood stream.
Cells Effected
Muscle cells, gland cells,
other neurons.
Virtually all body cells.
Type of Action
Muscular contraction or
glandular secretion.
Changes in metabolic
activities and growth
patterns.
Time to onset of action
Within milliseconds.
Seconds to hours.
Duration
Briefer
Longer
Hormone Secretion Stimulation and Inhibition:
• Signals from the
nervous system
– e.g. adrenal medulla
release of epinephrine
Hormone Secretion Stimulation and Inhibition:
• Chemical changes in
the blood
– e.g. blood calcium
level regulates
parathyroid hormone
Hormone Secretion Stimulation and Inhibition:
• Other hormones
Feedback Systems
• A product of the target
organ causes the
hormone producing gland
to produce less hormone.
Endocrine vs. Exocrine
• Recall, endocrine glands are ductless and
release hormones which diffuse into blood
stream.
– e.g. pituitary, thyroid, etc.
• Exocrine glands are ducted and secrete
products into body cavities or surfaces.
– e.g. sweat glands, mammary glands, mucous
glands, liver (bile), pancreas (digestive
enzymes)
Hypothalamus
• Influences the pituitary by
– Direct nervous stimulus
– Hormonal influence
• Considered a neuroendocrine gland
• Pain, stress, emotions effect responses
Hypothalamus → pituitary → other endocrine glands
Pituitary
• Descends from
hypothalamus and
secretes 9 hormones
• Gland considered to
be part of the
nervous and
endocrine system.
Pituitary + Hypothalamus
• Important roles in regulation of:
– Growth
– Development
– Metabolism
– Homeostasis
Hypothalamus → pituitary → (thyroid, adrenal cortex, gonads)
Pineal
(epithalamus)
• Secretion of melatonin
which is important for
biological rhythms.
• Sunlight received through
retina ultimately inhibits
secretion of melatonin.
• Darkness stimulates
melatonin….sleepy.
Thyroid
• Mainly controlled by
pituitary (TSH) to
regulate basal
metabolic rates.
Parathyroid
• Located on posterior
surface of the thyroid.
• Regulates blood
calcium and
phosphate levels
through (PTH).
Thymus
• Located in the
mediastinum behind
sternum and between
lungs.
• Lymphocytes
differentiate into T-cells
under influence of
thymus….
immunological
responses.
• Thymus atrophies with
age.
Adrenals
• Each gland is located
on the superior and
medial aspects of each
kidney.
• Adrenals made up of
two encapsulated
glands.
Adrenals
• Outer adrenal cortex
– Cortex is involved in metabolic reactions and
secretes steroid hormones (corticosteroids)
necessary for life. Control fluid and
electrolyte balance.
• Inner adrenal medulla
– Secretes epinephrine (adrenaline) and
norepinephrine (noradrenaline) to elicit “fight
or flight” reaction. These are protein
hormones.
– Under ANS control
Pancreas
• Located poster to the
stomach and attached
to small intestine.
• Both an endocrine
(1%) and exocrine
(99%) organ.
• Endocrine portion
produces 4 peptide
hormones, 2 of which
help in controlling
blood sugar.
– Insulin & glucagon
The Gonads
• Ovary
– Promotes the
development and
maintenance of
female sex
characteristics,
reproductive
structures, etc.
– Regulates female
menstrual cycle,
maintains pregnancy,
and readys mammary
glands for lactation.
The Gonads
• Testes
– Produce gonadal homrone
testosterone.
– Stimulates descent of tests
during male development
– Regulates spermatogenesis
– Promotes development and
maintenance of male sexual
characteristics
• Facial hair, muscular
build, size of larynx, and
sex drive.