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Chapter 20
Endocrine System
• Endocrine glands transmit signals
through blood stream to cells far
away
• Different from nervous system; Neuron
Neuron can affect only cells it
contacts
Nerve
signal
Neurotransmitter
Fig. 20.1
Endocrine gland
Hormone
Blood
Target cells
Target cells
(a) Nervous system (b) Endocrine system
Fig. 20.2
Major endocrine glands
Pituitary gland
Pineal gland
Thyroid gland
Organs containing endocrine cells
Hypothalamus
Thymus
Heart
Kidney
Gastrointestinal
(GI) tract
Pancreatic
islets
Parathyroid
glands
Adrenal
glands
Fig. 20.4
Hypothalamus
The hypothalamus produces
regulatory hormones that
either stimulate or inhibit
anterior pituitary hormone
secretion.
Anterior
pituitary
The hypothalamus produces
two hormones (antidiuretic
hormone and oxytocin) that are
stored in and released from
the posterior pituitary.
Posterior
pituitary
Adrenal cortex
Adrenal glucocorticoids
• Adrenal cortex secretes three types of
steroid hormones
• Aldosterone (aka mineralocorticoid)
• Glucocorticoids, including cortisol
• Increase plasma glucose concentrations
• Sex hormones, including estrogens,
progesterone, and androgens
• DHEA (dietary supplement) converted to
testosterone
Kidney
Growth hormone
Hypothalamus
• Released by anterior pituitary throughout life
• Anabolic
• Required for growth in childhood
• Combined with thyroid, insulin, sex hormones in
some cases
• In adults, GH stimulates release of insulin-like
growth factors (IGF)
• Stimulate bone and soft tissue growth
Anterior
pituitary
Posterior
pituitary
Growth hormone pathologies
• In childhood, lack of GH leads to dwarfism
with proportional body
• (one of many possible causes of dwarfism)
Growth hormone pathologies
• Excessive GH leads to acromegaly
• Long jaw, coarse facial features, excessive height
Thyroid
• In adults:
• Increase oxygen
consumption in tissues
• Modulate metabolism of
proteins,
carbohydrates, and fat
Larynx
• In children
Thyroid gland
• Necessary for expression of
growth hormone
• Necessary for development of nervous system
Trachea
Fig. 20.11
Hypothalamus
1 Hypothalamus secretes
thyrotropin-releasing
hormone (TRH), which acts
on the anterior pituitary.
stimulatory
inhibitory
Negative feedback
inhibition
TRH
5 Secretion of TRH by the
hypothalamus is inhibited. TH
prevents the formation
of TSH in anterior pituitary
2 Anterior pituitary
releases thyroidstimulating
hormone (TSH).
TSH
Anterior
pituitary
Target organs in body
TH
4 Target cells increase metabolic
activities.
3 Thyroid gland releases thyroid hormone (TH).
Hyperthyroidism
• Elevated TSH causes enlargement of thyroid gland
= goiter
• Increases oxygen consumption and metabolic
heat production
• Causes warm, sweaty skin; intolerance to heat
• Protein catabolism causes weak muscles
• Weight loss
• Hyperexcitable reflexes
• Insomnia, irritability, psychosis
• Rapid heartbeat
Hyperthyroidism
• Graves’ disease
• Body produces antibodies that mimic TSH
• Thyroid overstimulated
• May cause exophthalmos (bulging eyes)
• Caused by enlargement of tissues around eyes
Marty Feldman
Parathyroid gland
• Regulates calcium levels in the blood
• vital for muscle contractions
Fig. 20.15
Body of
pancreas
Pancreas
• Located
behind
stomach
Pancreatic
ducts
Tail of
pancreas
Major
duodenal
papilla
Duodenum
of small
intestine
Spleen
Head of
pancreas
Fig. 20.15
Fig. 20.15
Pancreas
• Acinar cells produce
digestive juices (not
endocrine)
• Pancreatic islets are
clusters of endocrine cells
Pancreatic
acinus
Alpha cell
Blood
capillary
Pancreatic islet cells
Alpha cell
Beta cell
Beta cell
Delta cell
Delta cell
F cell
F cell
Pancreatic islet
Fig. 20.15
Fig. 20.15
Pancreas
• Alpha cells secrete
glucagon when blood
glucose is low
• Beta cells secrete insulin
when blood glucose is
high
• Delta cells and F cells
affect digestion and
release of insulin and
glucagon
Pancreatic
acinus
Alpha cell
Blood
capillary
Pancreatic islet cells
Alpha cell
Beta cell
Beta cell
Delta cell
Delta cell
F cell
F cell
Pancreatic islet