Chapter 7b
Introduction to the
Endocrine System
Simple Endocrine Reflex: Parathyroid Hormone
Low plasma
[Ca2+]
Negative feedback
Parathyroid
cell
Parathyroid
hormone
Bone
and
kidney
Bone
resorption
Kidney
reabsorption of
calcium
Production of calcitriol
leads to intestinal
absorption of Ca2+
Plasma
[Ca2+]
Figure 7-10
Neurohormones: Major Groups
• Adrenal medulla
• Catecholamines
• Hypothalamus
• Anterior pituitary
• Posterior pituitary
Endocrine Control
• Three levels
• Hypothalamic stimulation—from CNS
• Pituitary stimulation—from hypothalamic
trophic hormones
• Releasing factors or Neurohormones
• Endocrine gland stimulation—from pituitary
trophic hormones
• Stimulate other hormones
Negative Feedback Controls
Figure 7-14
Control Pathway for Cortisol Secretion
Figure 7-15
A Complex Endocrine Pathway
HYPOTHALAMUS
• Growth hormone is an
example of a complex
endocrine pathway
Hypothalamus
GHRH
ANTERIOR
PITUITARY
GH cells
in anterior
pituitary
GH
Liver
IGFs
Bone and
soft tissue
Growth
Figure 7-17
The Pituitary Gland Anatomy
Figure 7-11
The Pituitary Gland: Anterior
HYPOTHALAMIC
HORMONES
Neurons in hypothalamus
secreting trophic hormones
Dopamine*
PRFs
TRH
CRH
GHRH*
GnRH
Somatostatin
Portal system
Anterior pituitary
ANTERIOR
PITUITARY
HORMONES
Prolactin
TSH
ACTH
GH
FSH
LH
Endocrine
cells
(Gonadotropins)
ENDOCRINE TARGETS
AND THE HORMONES
THEY SECRETE
To target
tissues
Thyroid
gland
Thyroid
hormones
Adrenal
cortex
Liver
Cortisol
IGFs
GTFLAP
Endocrine cells
of the gonads
Androgens
Estrogens,
progesterone
NONENDOCRINE
TARGETS
Breast
Many
tissues
Germ cells
of the gonads
Figure 7-13
The Hypothalamic-Hypophyseal Portal System
HYPOTHALAMUS
1 Neurons synthesizing
trophic hormones release
them into capillaries of
the portal system.
Capillary bed
Artery
2 Portal vessels carry the
trophic hormones directly
to the anterior pituitary.
POSTERIOR PITUITARY
3 Endocrine cells release
their hormones into the
second set of capillaries
for distribution to the
rest of the body.
Capillary bed
ANTERIOR PITUITARY
Veins
TO TARGET ORGANS
Prolactin
Gonadotropins (LH & FSH)
GH
TSH
ACTH
Ovary
Mammary glands
Musculoskeletal system
Thyroid gland
Adrenal cortex
Testis
Gonads
Figure 7-16
The Pituitary Gland: Posterior
• Posterior pituitary
• Vasopressin (ADH)
• Oxytocin
HYPOTHALAMUS
1 Hormone is made and
packaged in cell body
of neuron.
2 Vesicles are transported
down the cell.
3 Vesicles containing
hormone are stored in
posterior pituitary.
POSTERIOR PITUITARY
Vein
4 Hormones are released
into blood.
Figure 7-12
The Pituitary Gland: Posterior
HYPOTHALAMUS
1 Hormone is made and
packaged in cell body
of neuron.
POSTERIOR PITUITARY
Figure 7-12, step 1
The Pituitary Gland: Posterior
HYPOTHALAMUS
1 Hormone is made and
packaged in cell body
of neuron.
2 Vesicles are transported
down the cell.
POSTERIOR PITUITARY
Figure 7-12, steps 1–2
The Pituitary Gland: Posterior
HYPOTHALAMUS
1 Hormone is made and
packaged in cell body
of neuron.
2 Vesicles are transported
down the cell.
3 Vesicles containing
hormone are stored in
posterior pituitary.
POSTERIOR PITUITARY
Figure 7-12, steps 1–3
The Pituitary Gland: Posterior
HYPOTHALAMUS
1 Hormone is made and
packaged in cell body
of neuron.
2 Vesicles are transported
down the cell.
3 Vesicles containing
hormone are stored in
posterior pituitary.
POSTERIOR PITUITARY
Vein
4 Hormones are released
into blood.
Figure 7-12, steps 1–4
The Pituitary Gland: Posterior
HYPOTHALAMUS
1 Hormone is made and
packaged in cell body
of neuron.
2 Vesicles are transported
down the cell.
3 Vesicles containing
hormone are stored in
posterior pituitary.
POSTERIOR PITUITARY
Vein
4 Hormones are released
into blood.
Figure 7-12
Hormone Interactions
• Synergism
• Multiple stimuli—more than additive
• 1+1=3
• Permissiveness
• Need second hormone to get full expression
• Antagonism
• Glucagons oppose insulin
Example of Synergism
Glucagon + Epinephrine + Cortisol
Glucagon + Epinephrine
Epinephrine
Glucagon
Cortisol
Figure 7-18
Endocrine Pathologies
Figure 7-19
Endocrine Pathologies
• Hypersecretion: excess
hormone
• Tumors or cancer
• Autoimmune
• Grave’s disease—thyroxin
• Hyposecretion: deficient
hormone
• Goiter—thyroxin
• Low Iodine
• Diabetes melitus type I—insulin
Goiter
Pathologies: Abnormal Receptors
• Downregulation
• Hyperinsulinemia
• Transduction abnormalities
• Testicular feminization syndrome
• Pseudohypothyroidism
• Abnormalities of control mechanisms
Primary and Secondary Pathologies
Figure 7-20
Stress Pathologies: Hypocortisolism
(a) Hyposecretion from
damage to the pituitary
(b) Hyposecretion from atrophy
of the adrenal cortex
Hypothalamus
CRH
Hypothalamus
CRH
Anterior pituitary
ACTH
Anterior pituitary
ACTH
Adrenal cortex
Cortisol
Symptoms
of
deficiency
Adrenal cortex
Cortisol
Symptoms
of
deficiency
Figure 7-21
Pineal Gland and Melatonin
• Influences body clock and antioxidant activity
• Other roles need research
• SAAD and sexual behavior
Pineal Gland and Melatonin
Corpus
callosum
Thalamus
The pineal gland
Figure 7-22 (1 of 3)
Pineal Gland and Melatonin
Figure 7-22 (2 of 3)
Pineal Gland and Melatonin
Figure 7-22 (3 of 3)
Summary
• Introduction to hormones
• Classifications and features of hormones
• Regulation controlled by the endocrine and
nervous systems
• Interactions of hormones with other
hormones
• Endocrine pathologies