Endocrine System I: Superior Glands
 Homeostatic Mechanisms
 Endocrine System vs Nervous System
 Endocrine vs Exocrine Glands
 Types and Actions of Hormones
 Interaction of Hormones with Target Cells
 Effects of Hormones on Target
 Control Mechanisms of Endocrine Glands
 Endocrine Signaling as Simple/Complex Reflexes
 Major Superior Endocrine Organs
• Pituitary
 Anterior: GH, Pl, FSH, LH, TSH, ACTH
 Posterior: Oxytocin, ADH
• Thyroid: TH synthesis and release; Calcitonin
• Parathyroids: PTH
Pituitary Gland
Flip and enlarge
Hypophyseal
blood portal
system
glandular tissue
Nervous
system that
hormones
can drip
down on
nervous tissue
Hypophyseal Portal System
Hypothalamus
Hypothalamic neuron
cell bodies
Superior
hypophyseal artery
Hypophyseal
portal system
(a venous connection
between two capillary
beds)
• Hypophyseal
portal veins
Anterior lobe
of pituitary
When appropriately
stimulated,
hypothalamic neurons
secrete releasing and
inhibiting hormones
into the primary
capillary plexus.
Hypothalamic hormones
travel through the portal
veins to the anterior pituitary
where they stimulate or
inhibit release of hormones
from the anterior pituitary.
Anterior pituitary
hormones are secreted
into the venus circulation.
Figure 16.5b
Hormones of the Anterior Pituitary
 Six anterior pituitary hormones
• Two affect non-endocrine targets
• Four stimulate other endocrine glands
(tropic hormones)- TSH, ACTH, FSH,
and LH
 Characteristics of all anterior
pituitary hormones
• They are proteins (or peptides)
• They act through secondmessenger systems (except GH)
• 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
Anterior Pituitary: Growth Hormone
Type: Protein/peptide hormone
Regulation: increased by hypothalmic GHRH and
decreased by GHIH (somatostatin)
Target: Most cells, but especially bone and skeletal muscle
Action: Promotes protein synthesis and encourages use of
fats for fuel; elevates blood glucose by decreasing glucose
uptake and encouraging glycogen breakdown (anti-insulin
effects of GH)
Hypersecretion: gigantism in children, acromegaly in
adults
Hyposecretion: pituitary dwarfism
Anterior Pituitary: Prolactin
Type: Protein/peptide hormone
Regulation: hypothalmic prolactin releasing
hormone (PRH) stimulated by suckling
Target: Mammary glands of the breast
Action: Causes milk production
Hypersecretion: overproduction of breast milk
Hyposecretion: underproduction of breast milk
Anterior Pituitary: Gonadotropins FSH & LH
Type: Protein/peptide hormones
Regulation: released in response to
gonadotropin-releasing hormone
(GnRH) during and after puberty.
GnRH supressed by feedback of
gonadal hormones.
Targets: Ovaries and testes for both
FSH and LH
Action: FSH stimulates gamete (egg
or sperm) production
LH promotes production of gonadal
hormones like testosterone and
estrogen. Both gonadotropins are
tropic hormones.
Hypersecretion: For LH & FSH:
infertility
Hyposecretion: For LH: polycystic
ovarian disease; for FSH: Infertility
Endocrine System I: Superior Glands
 Homeostatic Mechanisms
 Endocrine System vs Nervous System
 Endocrine vs Exocrine Glands
 Types and Actions of Hormones
 Interaction of Hormones with Target Cells
 Effects of Hormones on Target
 Control Mechanisms of Endocrine Glands
 Endocrine Signaling as Simple/Complex Reflexes
 Major Superior Endocrine Organs
• Pituitary
 Anterior: GH, Pl, FSH, LH, TSH, ACTH
 Posterior: Oxytocin, ADH
• Thyroid: TH synthesis and release; Calcitonin
• Parathyroids: PTH
Anterior Pituitary: Thyroid Stimulating Hormone
Type: Protein/peptide hormone
Regulation: produced in response to
hypothalmic thyroid releasing hormone
(TRH). Inhibited by rising blood levels
of thyroid hormones that act on the
pituitary and hypothalamus
Target: Certain cells of the thyroid.
Action: Causes certain cells of the
thyroid to produce thyroxin. TSH is a
tropic hormone.
Hypersecretion: hyperthyroidism
(Grave’s disease)
Hyposecretion: hypothyroidism
(Sometimes
called
thyrotropin)
Anterior Pituitary: Adrenocorticotropic Hormone (ACTH)
Type: Protein/peptide hormone
Regulation: Triggered by hypothalamic corticotropin-releasing
hormone (CRH) in a daily rhythm and also internal and external
factors such as fever, hypoglycemia, and stressors.
Target: The outer layer of the adrenal glands (adrenal cortex)
Action: Causes release of cortiocosteroids; a tropic hormone.
Hypersecretion: Pituitary Cushing’s disease, usually from
pitutitary tumor - “moon face”, obesity, excessive sweating
(hyperhidrosis), baldness, loss of muscle mass, hypertension
Hyposecretion: Addison’s disease (hypocortisolism) - fatigue,
weight loss, skin darkening, hypotension
Endocrine System I: Superior Glands
 Homeostatic Mechanisms
 Endocrine System vs Nervous System
 Endocrine vs Exocrine Glands
 Types and Actions of Hormones
 Interaction of Hormones with Target Cells
 Effects of Hormones on Target
 Control Mechanisms of Endocrine Glands
 Endocrine Signaling as Simple/Complex Reflexes
 Major Superior Endocrine Organs
• Pituitary
 Anterior: GH, Pl, FSH, LH, TSH, ACTH
 Posterior: Oxytocin, ADH
• Thyroid: TH synthesis and release; Calcitonin
• Parathyroids: PTH
Posterior Pituitary - Hypothalamus Relationship
 The posterior pituitary is not strictly an
endocrine gland because it does not produce
any hormones.
 Instead, it is a storage depot for hormones
produced in the hypothalamus.
 Release of posterior pitutitary hormones is
controlled by neural stimulation from the
hypothalamus
 Hypothalamus produces two hormones that
are transported to neurosecretory cells of the
posterior pituitary
Posterior Pituitary: Antidiuretic Hormone
Type: Protein/peptide hormone
Regulation: Released when hypothalamic
osmoreceptors sense high blood solute
concentrations and send neural stimulus.
Not released when solute concentration
low, causing water loss in urine. Alcohol
inhibits ADH release.
Target: Kidneys
Action: Inhibits diuresis (urine production)
and increases blood pressure
(Also called
vasopressin)
Hypersecretion: Syndrome of
Inappropriate ADH secretion (SIADH),
common in CNS injury patients in hospitals,
trauma, come cancers; causes
hyponatremia (headache, nausea, vomiting)
Hyposecretion: Diabetes insipidus;
dehydration from excessive urine output;
intense thirst.
Posterior Pituitary: Oxytocin
Type: Protein/peptide hormone
Regulation: Stretching of uterus, sexual
arousal, hearing baby’s cry and suckling;
enhanced release by positive feedback;
stimulus removal inhibits release
Target: Uterine smooth muscle; breast,
amygdala of the brain diencephalon
Action: Stimulates uterine contractions during
childbirth; triggers milk ejection (“letdown”
reflex) in women producing milk; plays a role in
sexual arousal and orgasm in males and
females; increases level of trust between
males and females, mate bonding, & mothernewborn bonding.
Hypersecretion: Stronger labor contractions
(possibly leading to fetal distress), hyperactive
milk “letdown”; more trust and bonding
Hyposecretion: Labor that is slow to progress,
insuffcient milk “letdown”; less trust & bonding
Endocrine System I: Superior Glands
 Homeostatic Mechanisms
 Endocrine System vs Nervous System
 Endocrine vs Exocrine Glands
 Types and Actions of Hormones
 Interaction of Hormones with Target Cells
 Effects of Hormones on Target
 Control Mechanisms of Endocrine Glands
 Endocrine Signaling as Simple/Complex Reflexes
 Major Superior Endocrine Organs
• Pituitary
 Anterior: GH, Pl, FSH, LH, TSH, ACTH
 Posterior: Oxytocin, ADH
• Thyroid: TH synthesis and release; Calcitonin
• Parathyroids: PTH
Thyroid Gland
Consists of two lobes and a connecting isthmus
(thyroglobulin)
Lumen
of
follicle
Figure 9.6
Thyroid Hormone is Really Two Hormones
Required for
synthesis:
tyrosine
(amino acid)
and iodine
Thyroxine or T4, most active of the two hormones
T3, least active of the two hormones
The Production and Secretion of Thyroid Hormone/Thyroxine (T3 and T4) in
a Thyroid Follicle
Thyroid follicle cells
Colloid
1 Thyroglobulin is synthesized and
discharged into the follicle lumen.
Tyrosines (part of thyroglobulin
molecule)
Capillary
4 Iodine is attached to tyrosine
in colloid, forming DIT and MIT.
Golgi
apparatus
Rough
ER
Iodine
3 Iodide
is oxidized
to iodine.
2 Iodide (I–) is trapped
(actively transported in).
Iodide (I–)
Lysosome
T4
T3
T3
T3
5 Iodinated tyrosines are
linked together to form T 3
and T4.
Lumen of follicle
T4
T4
DIT (T2) MIT (T1)
Thyroglobulin
colloid
6 Thyroglobulin colloid is
endocytosed and combined
with a lysosome.
7 Lysosomal enzymes cleave
T4 and T3 from thyroglobulin
colloid and hormones diffuse
into bloodstream.
Colloid in
lumen of
follicle
To peripheral tissues
Figure 16.9
Thyroid Hormone (TH): T3 and T4 (most active)
Type: Protein/peptide hormone
Regulation: Released in response to TRH from the
anterior pituitary. Rising TH levels provide negative
feedback inhibition on release of TSH from thyroid.
Hypothalamic TRH can overcome the negative feedback
during pregnancy or exposure to cold.
Target: Skeletal and muscle tissue
Action: Increases metabolic rate and heat production
(calorigenic effect); indirectly involved in BP, tissue
growth, skeletal and nervous development, reproduction
Hypersecretion: Grave’s disease; fatigue, goiter, weight
loss, hypertension, exopthalmos, breasts in men,
nervousness, restlessness.
Hyposecretion: In adults, hypothyroidism (myxedema)
and endemic goiter if iodine deficient; in children,
cretinism. Hypothyroidism caused by
autoimmune/Hashimoto’s hypothyrodism, surgical
removal, cancer. Causes fatigue, cold sensitivity,
depression, puffy face, weight gain.
Marty Feldman
with exopthalmos
Thyroid Gland: Calcitonin
Type: Protein/peptide hormones
Regulation: Released by thyroid
parafollicular/C cells when blood Ca+2
high; inhibited when blood Ca+2 is
low. Regulated by humoral feedback
negative feedback mechanism.
Works as an antagonist to parathyroid
hormone.
Targets: Bone tissue
Action: Decreases blood calcium
levels by causing bone calcium
deposition; inhibits osteoclasts,
stimulates osteoblasts.
Hypersecretion: Possible
hypocalcemia
(“C” Cell)
Hyposecretion: Possible
hypercaclemia but thyroid removal
doesn’t effect Ca+2 homeostasis.
Blood Calcium Regulation
Figure 9.9
Endocrine System I: Superior Glands
 Homeostatic Mechanisms
 Endocrine System vs Nervous System
 Endocrine vs Exocrine Glands
 Types and Actions of Hormones
 Interaction of Hormones with Target Cells
 Effects of Hormones on Target
 Control Mechanisms of Endocrine Glands
 Endocrine Signaling as Simple/Complex Reflexes
 Major Superior Endocrine Organs
• Pituitary
 Anterior: GH, Pl, FSH, LH, TSH, ACTH
 Posterior: Oxytocin, ADH
• Thyroid: TH synthesis and release; Calcitonin
• Parathyroids: PTH
Parathyroid Glands: Parathyroid Hormone (PTH)
Type:
Protein/peptide
hormone
Found
on posterior surface
of thyroid
Regulation: Humoral sensing of blood
calcium levels; PTH released if low;
rising calcium levels inhibit release
Target: Bone osteoclasts, kidneys,
intestines
Action: Stimulates osteoclasts to
remove calcium from bone. Stimulates
the kidneys and intestine to absorb more
calcium. Increases Ca+2 absorption by
intestines. Hypercalcemic.
Lateral
view with
posterior
pulled
forward
chief cells
that
secrete
parathyroid
hormone
(PTH) or
parathorm
one
Hypersecretion: hyperparathryroidism
caused by parathyroid cancers or if
Vitamin D low; causes softening of
bones, depressed nervous system,
blurred vision
Hyposecretion: Hypoparathyroidsim
leads to muscle spasms, respiratory
paralysis, death
Regulation of Blood Ca+2 By PTH
Hypocalcemia (low blood Ca2+) stimulates
parathyroid glands to release PTH.
Rising Ca2+ in
blood inhibits
PTH release.
Bone
1
PTH activates
osteoclasts: Ca2+
and PO4-2 released
into blood.
2 PTH increases
Kidney
Ca2+ reabsorption
in kidney
tubules.
3 PTH promotes
kidney’s activation of vitamin D,
which increases Ca2+ absorption
from food.
Intestine
Ca2+ ions
PTH Molecules
Bloodstream
Figure 16.12
Endocrine System I: Superior Glands
 Homeostatic Mechanisms
 Endocrine System vs Nervous System
 Endocrine vs Exocrine Glands
 Types and Actions of Hormones
 Interaction of Hormones with Target Cells
 Effects of Hormones on Target
 Control Mechanisms of Endocrine Glands
 Endocrine Signaling as Simple/Complex Reflexes
 Major Superior Endocrine Organs
• Pituitary
 Anterior: GH, Pl, FSH, LH, TSH, ACTH
 Posterior: Oxytocin, ADH
• Thyroid: TH synthesis and release; Calcitonin
• Parathyroids: PTH