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Endocrine System
SBI4U
Regulation of
Serum Glucose
Levels
Regulation Ca++
Metabolism
catecholamines
Regulation of
Body Temperature
Endocrine System
Hormones
Regulation of
Body’s H2O
Content
Regulation of
Rate of Metabolism
steroids
prostaglandins
peptides
(proteins)
“little ones”
“really big ones”
“big ones”
Hormone Interactions in the Human Body
catecholamines
peptides
anterior
pituitary
protein
thyroid
glycoproteins
hypothalamus
steroids
TSH
ovaries
posterior
pituitary
FSH &
LH
ACTH
adrenal
cortex
somatostatin
&L
H
tin
lac
pro
testes
FSH
estro
gen &
tes
tos
ter
on
e
proge
s
oxytocin
uterus
teron
e
oxytocin
estro
gen
HG
bones
PTH
glu
coc
T3 & T4
calcitonin
n)
opi
totr
a
som
H(
aldos
teron
e
orti
c
breast
oid
s
ADH
epin
e
nore phrine &
pine
phrin
e
kidney
parathyroid
insulin
epinephrine &
norepinephrine
adrenal
medulla
glucacon
liver
gut
body cells
& muscles
alpha cells
in pancreas
blood
beta cells
in pancreas
Negative feedback regulates the secretion
of the thyroid hormones T3 & T4.
• The hypothalamus secretes
TRH which stimulates the
anterior pituitary to secrete
TSH.
• TSH stimulates the thyroid
to synthesize and release
T3 and T4.
• Elevated levels of T3 and T4
inhibit TRH secretion
Serum Ca2+ levels are regulated by negative feedback of
two antagonistic hormones calcitonin and parathyroid
hormone
Serum glucose levels are regulated by negative feedback of
two antagonistic hormones glucagon and insulin.
Hormones are chemical messengers that…
are secreted directly into the blood stream
are produced by a specialized gland or a group of cells
in minute quantities
effect body parts removed from the source
effect a response in specific target cells
Hormones signal cells at a distance
Hormones are secreted into
the blood stream and reach
virtually every cell in the body.
blood stream
endocrine cell
Only cells sensitive
to the presence of
the hormone
respond.
target cell
Hormones belong to one of 4 groups
1. Catecholamines are modifications of the amino acid
tyrosine.
2. Peptide hormones are polypeptide chains of various size
ranging from
little ones,
big ones, &
really big ones.
3. Steroid hormones are either produced by the sex organs
(the sex hormones) or the adrenal cortex
(corticosteroids).
4. Prostaglandins are a diverse group of modified fatty
acids that are secreted by almost all tissues.
1) The four common catecholamines are
derived from the amino acid tyrosine.
I
HO
I
H
H2N
C
C
H
H
HO
CH 2 C
O
N
HO
OH
C
O
H
CH3
H
I
I
OH
OH
CH 2
epinephrine
thyroxine (T4)
C
CH
O
NH2
HO
HO
I
H
tyrosine
C
C
H
H
H2N
HO
CH 2 C
O
H
N
HO
H
H
I
I
OH
norepinephrine
tri-iodothyronine (T3)
OH
C
O
2) The peptide hormones are amino acid
chains of various lengths
Three Examples of “little ones”:
• Enkephalins are pentapeptides consisting of the 5
amino acids.
• Enkephalins are the body’s natural pain killers:
met enkephalin: tyr-gly-gly-phe-met
leu enkaphalin: tyr-gly-gly-phe-leu
The primary structures of oxytocin and
vasopressin: two nonapeptides.
Oxytocin
cysteine
tyrosine
isoleucine
glutamine
asparganine
cysteine
proline
leucine
glycine
Vasopressin (ADH)
cysteine
tyrosine
phenylalanine
glutamine
asparagine
cysteine
proline
arginine
glycine
Four Examples of Peptide Hormones that
are “Big Ones”
• Endorphins are natural pain killers having 30
amino acids.
• Glucagon is a hyperglycemic having 29 amino
acids.
• Insulin is a hypoglycemic with 51 amino acids in
two polypeptide chains.
• Parathormone elevates serum Ca+2 has 84
amino acids.
Examples of “Really Big” peptide
hormones
• Human growth hormone (HGH) is a
protein having 191 amino acids and a
molar mass of 22 124 g.
• Prolactin is a polypeptide with a molar
mass around 24 000 g.
3. The Steroid Hormones
Since the steroid hormones are derived from
cholesterol, they have structural formulas
similar to cholesterol.
H3C
CH3
CH3
HO
CH3
CH3
The three steroid sex hormones
CH3
H3C
CH3
O
CH3
HO
estrogen (estradiol)
O
CH3
progesterone
CH3
O
testosterone
OH
OH
Aldosterone is a mineralocorticoid.
• stimulates the active
transport of Na+
from the kidney into
the blood stream
OH
O
• reduces Na+ content
of the urine
CH3
• produced by the
adrenal cortex
O
• 400 μg secreted per
day
aldosterone
CH
OH
H2C
O
Cortisol & cortisone are glucocorticoids
• Glucocorticoids raise blood glucose levels by
stimulating the conversion of amino acids into glucose
in the liver.
• Elevated glucose levels speed cell recovery.
OH
OH
H2C
CH3
HO
H2C
CH3
O
O
OH
CH3
O
CH3
O
cortisol
cortisone
O
OH
4.
The Prostaglandins
• Prostaglandins are modified
fatty acids.
• Localized effect.
• Chemically each
prostaglandin has a 5 carbon
ring and a total of 20 carbon
atoms.
• Although prostaglandins act
as chemical messengers they
are rarely classified as
hormones.
4.
The Prostaglandins cont’d
Prostaglandins have a wide variety of actions because they
act on a wide range of cells.
•
•
•
•
•
•
Contraction of smooth muscle cells
Contraction and relaxation of smooth muscle cells in blood vessels
Clumping of platelets during clotting
Control cell growth
Regulate calcium movement
Sensitize spinal neurons to pain
Prostaglandins are potent but are short lived. They exert
only a local influence or act on the same cell from which it
is synthesized.
Hormones trigger responses three different
ways
1. Signal transduction pathway via a membrane
receptor
2. Ligand-gated ion channels
3. Intracellular receptors
1. Cells sensitive to the presence of a
hormone have hormone receptors in their
cell membranes.
hormone
(signal molecule)
Hormones fit into protein
receptors on the membrane
of the target cell.
extracellular
fluid
plasma
membrane
receptor protein
cytoplasm
Reception:
The First Step of the Signal Pathway
hormone
(signal molecule)
The hormone binds to the
receptor protein. Reception
of the hormone is the first
step of a signal pathway.
extracellular fluid
plasma
membrane
cytoplasm
receptor protein
Transduction:
The Second Step of the Signal Pathway
Reception of the hormone triggers the
formation of series of chemical compounds
in the cytoplasm of the cell. This series of
compounds comprise the signal
transduction pathway.
signal transduction
pathway
Response:
The third step of the signal pathway
glycogen
The relayed signal triggers a metabolic
response. For example, the hormone
epinephrine triggers the hydrolysis of glycogen
by way of a signal transduction pathway.
2. Ligand-Gated Ion Channel
ions (Na+ & Ca++)
extra cellular fluid
hormone
(ligand)
plasma membrane
ion channel protein
cytoplasm
2. Ligand-Gated Ion Channel
The hormone (ligand)
binds to the receptor
protein, the protein
changes shape, the
channel opens and ions
diffuse into the cytoplasm.
The change in ion
concentration in the cell
triggers metabolic
changes.
2. Ligand-Gated Ion Channel
The ligand dissociates and
the channel closes.
Neurotransmitters trigger the
nerve impulse in this manner.
Steroid hormones interact with
intracellular receptors.
•
The hormone testosterone diffuses through the cell
membrane.
•
Testosterone binds to a receptor protein in the
cytoplasm.
•
The receptor-hormone complex enters the nucleus
and binds to a specific gene or genes that control male
characteristics.
•
The receptor-hormone complex stimulates
transcription of the gene into mRNA.
•
The mRNA is translated into protein.