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Endocrine system
YaoYang, Physiology department of SMC
Introduction
Endocrine and nervous systems
coordinate complex body functions.
Classic distinction of these two is that
endocrine system communicates to distant
tissues through blood-borne chemicals
while the nervous system communicates
to adjacent tissues by local chemical
release.
Introduction
ⅠEndocrine and Endocrine system
⒈ Endocrine
Endocrine glands
vs Exocrine glands :
Endocrine glands do
not have ducts.
Exocrine glands
have ducts that carry
their secretions to
specific locations .
Hormone: Hormones are defined as
bioactive chemical messengers which are
secreted by the endocrine glands and the
endocrine cells ,and exert regulating effects
by the transmission of the blood stream and
the extracellular fluid.
Hormones are carried to receptors
in four manners
③ Autocrine
① Telecrine
④ Neuroendocrine
② Paracrine
Endocrine, or telecrine: glands or
specialized cells release hormones into the
circulating blood that influence the function
of cells at another location in the body.
Neuroendocrine: neurons secrete
substances (neurohormones) that reach the
circulating blood and influence the function of
cells at another location of the body.
Paracrine, in which cells secret substances that
diffuse into the extracellular fluid and affect
neighboring cells.
Autocrine: a cell secretes substances that
affect the function of the same cell.
⒉ Endocrine system
The endocrine system consists of endocrine
glands and cells that secrete hormones in
various tissues.
Functions:
 Maintain the homeostasis of internal environment to
play a role in regulation of BP, temperature and stress,
etc.
 Regulate metabolism
 Regulate growth and development
 Regulate water and electrolyte balance
 Control the reproduction process
Hypothalamus
and pituitary
Non-Classical
Organs
Thyroid and
parathyroid
Heart
Adrenal gland
(Medulla and cortex)
Pancreas
(islet)
Classical
Glands
Digestive tract
Ovary
Kidney
Testis
Ⅱ Classification of Hormones
Amine hormones
Protein and polypeptide
hormones
Lipid hormones
Amine hormones: secreted by the thyroid (thyroxine
and triiodothyronine) and the adrenal medullae
(epinephrine and norepinephrine) and pineal gland
(melatonin)
 Synthesized from a single amino acid
 Melatonin from tryptophan
 Thyroid hormone from tyrosine
 Catecholamines (EPI, DA) from tyrosine
Protein and polypeptide hormones: including
hormones secreted by the anterior and posterior
pituitary gland, the pancreas (insulin and glucagon),
the parathyroid gland (parathyroid hormone), and
many others.




Hydrophilic
Large
Can't fit through membrane
Second messenger mechanism
of action
 Most hormones
Lipid hormones: Steroids secreted by the adrenal
cortex (cortisol and aldosterone), the ovaries
(estrogen and progesterone), the testes
(testosterone), and the placenta (estrogen and
progesterone), and VD3
 Small
 Hydrophobic/Lipophilic
 Travel in blood with
carrier
 Cytoplasmic or nuclear
receptors
Ⅲ Mechanisms of Hormonal Action
The first step of a hormone’s action is to bind
to specific receptors at the target cell.
1. Hormone receptor of target cell:
Group Ⅰ: in the cell cytoplasm or nucleus.
For the Steroids and thyroid hormones.
Group Ⅱ: in or on the surface of cell
membrane.
For the protein, peptide, catecholamine
hormones
Hormone + Receptor
4. termination of hormone action
1. Regulation system stops the secretion of
hormone.
2. Hormone isolate from the receptor to stop the
signal transducer process.
3. Hormone are degraded by endocytosis at their
target cells.
4. Hormone are degraded in liver and blood
circulation.
5. Hormone are degraded by oxidation-reduction
or deaminization.
Ⅳ Properties of the hormone effect
Signal transmission
Enlargement
Relatively specific binding
with receptors
Interaction between the hormones
Signal Transmission
The role of the hormones is to transit the
regulatory signals from the control
(endocrine) system to the target cells
(organs or glands).
It could enhance or inhibit some function of
the target.
Enlargement
Low plasma concentration (nmol – pmol/L)
Great regulatory function
Stronger biological amplification of hormones in
hypothalamus pituitary target glands axis
regulation system
0.1 μg CRH→ 1.0μg ACTH release → 40μg
Cortisol →6000μg glycogen
Signal
amplification
during the
transmembrane
and intracellular
transmission
Specificity
The special feature of the the target cells is the
presence of receptors which can “attract” and
interact with the hormone.
Interaction Between the Hormones
Synergistic effect
When two or more hormones working together produces an effect
greater than the sum of their individual effects.
Permissive effect
A hormone is said to have a permissive effect on the action of a second
hormone when it enhances the responsiveness of a target organ to the
second hormone or when it increases the activity of the second
hormone.
Antagonist Effects
In some situations the actions of one hormone
antagonize the effects of another.
Synergistic effect
Permissive effect
Cortisol enhances the responsiveness of
vessel to E and NE
cortisol E
NE
cortisol+E/NE
Ⅴ Control
1.Biorhythm regulation
Suprachiasmatic nucleus of hypothalamus
cortisol secretion rhythm
2.Humoral regulation
(1)Hypothalamus
pituitary target glands
axis
(2)Feed back control
Glucose
Ca 2+
(3) Interaction Between
the Hormones
3.Nervous regulation
Section II
Hypothalamus-Pituitary System
and Their Hormones
Location and Structure of Pituitary
Blood Connection to Anterior Pituitary
Secreting tropic hormones
 secrete into
the hypothalamuspituitary portal system
Portal vessels:
▪ link 2 capillary beds
▪ In capillaries is
where exchange
occurs between
blood and tissue
Figure 6.4
Neural Connection between hypothalamus and
Posterior Pituitary
 Antidiuretic Hormone (ADH or
vasopressin)
 Oxytocin
▪ Synthesized in the
supraoptic nucleus and
paraventricular nucleus
Hormone Secreted from
Hypothalamus and Pituitary
TRH
CRH
GnRH
GHRH//GHRIH
PRF//PIF
MRF//MIF
TSH
ACTH
LH/FSH
GH
PRL
MSH
ADH
OXT
Hypothalamus pituitary target glands axis
Neural input
Hormonal - negative
feedback loops
Long loop negative
feedback
Short loop negative
feedback
What the letters stand for…
TSH: thyroid-stimulating hormone
ACTH: adrenocorticotropic hormone
FSH: follicle-stimulating hormone
LH: luteinizing hormone
GH: growth hormone
PRL: prolactin
MSH: melanocyte-stimulating hormone
ADH: antidiuretic hormone
Oxytocin
Hypothalamus controls anterior pituitary
hormone release
hypothalamic regulatory peptide
Corticotropin-releasing hormone (CRH)
Stimulates secretion of ACTH
Gonadotropin-releasing hormone (GnRH)
Stimulates secretion of FSH and LH)
Thyrotropin-releasing hormone (TRH)
stimulates secretion of TSH
Melanocyte-stimulating hormone release
inhibiting factor (MIF)
inhibits secretion of MSH
Melanocyte-stimulating hormone releasing factor
(MRF)-stimulate secretion of MSH
Growth hormone inhibiting hormone (GHIH) or
Somatostatin (SS) – inhibits secretion of growth
hormone
Growth hormone-releasing hormone (GHRH)–
stimulates growth hormone secretion
Prolactin-inhibiting factor (PIF)- inhibits prolactin
secretion
Prolactin-releasing factor (PRF)-stimulates
prolactin section
Tropic Hormones of Hypothalamus & Anterior
Pituitary
So what do the pituitary hormones do?
The four tropic ones regulate the function of target gland
TSH stimulates the thyroid to produce thyroid
hormone
ACTH stimulates the adrenal cortex to produce
corticosteroids: aldosterone and cortisol
FSH stimulates follicle growth and ovarian
estrogen production; stimulates sperm
production and androgen-binding protein
LH has a role in ovulation and the growth of the
corpus luteum; stimulates androgen secretion by
interstitial cells in testes
The three ones regulate the function of target cell
GH (aka somatrotropic hormone)
stimulates growth of skeletal epiphyseal
plates and body to synthesize protein
PRL stimulates mammary glands in breast
to make milk
MSH stimulates melanocytes; may
increase mental alertness
OXT
ADH
Introduction of GH (Somatotropin)
Having 191 amino acids.
Variant species are present
Normal human, bovine and
porcine growth hormones.
secreted in pulse.
bound to a protein in plasma
metabolized rapidly, in the liver.
The basal plasma growth
hormone level in adult humans
is normally less than 3 ng/mL.
mechanism of the growth hormone effect
1.GH receptor
2.somatomedins
(SM) （also
called insulin-like
growth factor, IGF)
in the liver
growth of bone
and other
peripheral tissues.
Physiological functions of growth
hormone
1) Growth effect
Growth hormone stimulates cell
division, especially in muscle and
epiphyseal cartilage of long bones.
The result is muscular growth as
well as linear growth.
(Most
importantly, GH
stimulates cartilage and bone
growth in length and thickness)
Epiphyses
Cartilage
Diaphysis (shaft)

Promotes growth of many body tissues
skeletal muscle, heart, skin, connective tissue,
liver, kidney, pancreas, intestines, adrenals and
parathyroids.
Increase in cell size
and number;
Hypersecretion of GH leads to cause
gigantism in children and acromegaly in
adult.
Hyposecretion of GH results in
dwarfism during childhood.
Dwarfism
Jyoti Amge
68.2cm
The tallest male
271cm
gigantism
Gigantism
9Y
33 Y
16 Y
52 Y
Acromegaly
acromegaly
after the epiphysis of the long
bones have fused with shafts
– the person cannot grow
taller,
but the soft tissue can
continue to grow and the
bones can grow in thickness.
This condition is known as
acromegaly.
Effect of
hypophysectomy
on growth of the
immature rhesus
monkey.
Both monkeys
were the same
size and weight
2 years
previously, when
the one on the
left was
hypophysectomi
zed.
2) Metabolic effects of GH
A, On Protein metabolism
Enhance amino acid transport to the interior of
the cells and increase RNA translation and
nuclear transcription of DNA to form mRNA, and
so increase rate of protein synthesis.
GH also reduces the breakdown of cell proteins
by decreasing catabolism of protein.
B, On fat metabolism
Cause release of fatty acids from adipose tissue
and then increasing the concentration of fatty acids.
Therefore, utilization of fat is used for providing
energy in preference to both carbohydrates and
proteins.
C. On glucose metabolism
Decreases cellular uptake of glucose and glucose
utilization, leads to increase of the blood glucose
concentration.
(2) Regulation of GH secretion
The plasma concentration of GH changes with age. 5 –
20 years old, 6ng/ml; 20 – 40 years old, 3ng/ml; 40 –70
years old, 1.6ng/ml.
The change of GH concentration within one day.
1) Role of hypothalamus and feedback
mechanism
- Hypothalamus
-
- GHIH
GHRH +
-
Pituitary
GH
Liver
SM
Target tissues
+ increase the secretion; - inhibit the secretion
2) Other factors influencing GH secretion
Stimulatory factors
Inhibitory factors
Low blood glucose, free fatty
acids
High blood glucose, free fatty
acids
Protein deficiency
Aging, Obesity etc
Excitement, excise, stress,
slowwave sleep etc
GH & IGF
GHRH
GHIH
PROLACTIN (PRL)
The hormone prolactin is a protein.
Having 198 amino acids.
In human beings it has been shown to process
some activity of the growth hormone as well; this
because its structure resembles that of GH.
1. Physiological function of PRL
1) On breast: stimulate the development and milk secretion
puberty
E, P, GH, cortisol,
insulin, thyroid
hormones and
prolactin
pregnancy
After baby
born
estrogen, Click to add Text
prolactin
progesterone
prolactin
2) Effect on sexual organs
In women, PRL combined with PRL receptors in
granulosa cells stimulates production of LH
receptors. Through LH receptors, LH promotes
ovulation and then formation of corpus luteum.
(permissive effect)
But high PRL→GnRH↓→FSH、LH↓
In male, PRL promotes growth of prostate glands
and seminal vesicle, enhancing the effect of LH on
the interstitial cells producing testosterone.
Prolactin Excess
The most common secretory neoplasm of
the interior pituitary gland is prolactin
secreting adenoma (prolactinoma).
Increase plasma level of prolactine
decreases plasma testosterone leading to
decrease in both libido and potency.
Symptoms:
Galactorrhea
Males: Decrease Libido
Menstrual irregularity
Sexual Impotence
Amenorrhea
Infertility
Infertility
(2) Regulation of PRL secretion
1) Hypothalamic hormones and feedback
mechanism
Hypothalamus: PIF
+
Anterior pituitary:
PRF
+
Prolactin
+ increase the secretion; - inhibit the secretion
2) Milk ejection reflex
Sucking, tactile stimulation
Afferent nerve (somatic nerve)
Centers including spinal cord and hypothalamus
PRF secretion
PRL secretion
Milk production increase
Oxytocin secretion
Myoepithelial cells contraction of
mammary glands
Milk flows
PROLACTIN
SECRETION
ADH
(1)Roles of ADH
1) Antidiuretic effect (refer to chapter 8)
2) Pressure effect. High concentration of ADH
have a potent effect of constricting the
arterioles everywhere in the body, raise the
resistance blood flow and blood pressure
ADH
Antidiuretic effect
Antidiuretic hormone V2-receptor:
collecting duct
 Pressure effect
Vasopressor hormone V1-receptor:
vascular smooth muscle

Role of Oxytocin (OXT)
1) Effect on mammary glands.
Cause the contraction of the myoepithelial
cells that surround the outer walls of the alveoli
of the mammary glands, press the milk from
the alveoli to the duct and make it flow out --milk ejection
OXYTOCIN
OXT & PRL
2) Effect on uterus
OXT powerful stimulate the smooth muscle
contraction, especially that towards the end of
gestation.
It is believed that OXT is at least partially
responsible for causing birth of the baby
Pineal Gland
 Glandular tissue in brain
 Secretes melatonin
 Function unknown
 May be involved in circadian rhythms
▪ Melatonin secretion rises at
night & falls during the day
▪ Melatonin is a potent sleepinducing agent
▪ Melatonin also enhances
immune function and exerts a
suppressive effect on
reproduction function by
interfering with the activity of
certain hormones.
Key point
Hormone
Paracrine
neuroendocrine
Permissive effect
Properties of the hormone effect
Physiological functions of growth hormone
Role of Prolactin (PRL)
Role of Oxytocin (OXT)