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The Endocrine System
Dr. Tamie Lieto
Endocrine
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Endo=within
Krino= separate
The word implies that intercellular chemical
signals are produced within and secreted from
endocrine glands, but that the chemical signal
have effects at locations that are away from or
or separate from the endocrine glands that
secrete them. The chemical signals are
transported by way of the blood
Hormones
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Hormones – the intercellular chemical signals
that are secreted by the endocrine glands
Hormone means “set in motion” because
hormones set things in motion
Hormones are distributed in the blood to all
parts of the body BUT only certain tissues
called Target tissues respond
Regulation of Hormone Secretion
Negative Feed Mechanism based on the following:
blood levels of chemicals
eg glucose and insulin
hormones
eg some hormones control other hormones
Nervous System
eg epinephrine is released from adrenal
medulla because of nervous stimulation
Endocrine Glands and Their
Hormones
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Look at Table 10.3 Endocrine Glands,
Hormones and their Target Tissues
Classification of Hormones
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Proteins/ Amino Acids
thyroid
posterior pituitary
Lipids
Steroids
Eicosanoids
Pituitary Gland
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The pituitary gland is located posterior to the
optic chiasm and beneath the hypothalamus.
It is connected to the hypothalamus by a stalk
called the infundibulum
It is divided into anterior and posterior parts
It is part of the Hypothalamus Pituitary Axis
Pituitary Gland
Pituitary
The Pituitary Gland is divided into
Anterior and Posterior Parts
Hormones from the pituitary control control the
function of many other endocrine glands
such as the ovaries , testes, thyroid gland and adrenal
coortex
Also secretes hormones that affect growth, kidney
function, birth and milk production by the breast
Release of Hormones from the Pituitary is under the
control of the Hypothalamus
Hormones secreted by the Pituitary
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Growth Hormone- stimulates growth of bone
and organs by increasing protein synthesis
It resists protein breakdown during food
deprivation and promotes fat breakdown
instead
Growth hormone is under the control of
Growth hormone releasing factor (GHRF) and
Growth Hormone Inhibiting Factor)
Hormones secreted from the
pituitary gland
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AnteriorPituitary
Growth Hormone
Thyroid stimulating hormone
(TSH)
Adrenocorticotrophic hormone
( ACTH)
Melanocyte Stimulating hormone
Luteinizing Hormone
Follicle Stimulating Hormone
Prolactin
Posterior Pituitary
Antidiuretic Hormone
Oxytocin
Growth Hormone (GH)
Growth Hormone- increases protein synthesis
and growth of tissue and organs, breakdown of
lipids, and release of fatty acids, increase
blood glucose levels
Target Tissue : Most Tissue
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Deficient of
Growth
Hormone
Pituitary
Dwarfism
Excess Growth Hormone
Gigantism
Exces growth hormone can
result from hormones secreting
tumors of the pituitary gland
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Acromegaly
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IF growth hormone continues to be in excess
after the growth plates are closed bones will
grow wider . This condition is called
acromegaly
Thyroid Stimulating Hormone
(TSH)
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Thyroid Stimulating Hormone (TSH)
Target tissue: binds to the receptors on the thyroid
gland and causes the thyroid gland to secrete thyroid
hormone
Too much TSH over stimulates the Thyroid
gland ( enlarges)
Too little TSH under stimulates the Thyroid
gland (Shrinks)
TSH is under the control of the Thyroid Releasing
Hormone released form the hypothalmus
Adrenocorticotropic Hormone
ACTH
Adrenocorticotropic Hormone
Target Tissue: Binds to receptors on the adrenal
cortex gland and stimulates release of the
Glucocorticoid hormones such as cortisol
Target Tissue: Binds to melanocytes in the skin
and increase skin pigmentaion
ACTH is under the control of the ACTH releasing
hormone secreted by the hypothalmus
Gonadotropins
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Target Tissue: Bind to the receptors on the
gonads(ovaries and testes)
Luteinizing Hormone
Follicle Stimulating Hormone
Under control by the GNRH or gonadotropin
releasing hormones of the hypothalamus
Luteinizing Hormone (LH)
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Females- target tissue ovary, promotes
ovulation and progesterone in the ovary
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Males- target tissue testis, causes
testosterone synthesis and supports sperm cell
production in testis
t
Follicle Stimulating Hormone
(FSH)
-Female
Target tissue :Follicles in ovary. Promotes
follicle maturation and estrogen secretion in
ovary.
- Male
Target tissue- Seminiferous tubules in male
causing Sperm production
Prolactin
FemaleTarget Tissue: receptors in the breast and ovary
Helps promote breast development during
pregnancy and stimulates the production of
milk. Prolongs progesterone secretion
following ovulation and during pregnancy.
Male - Target tissue-testis increses sensitivity
to LH
Under control of the releasing hormones from
the hypothalamus
Site of Prolactin Action is the
Mammary Gland
Melanocyte Stimulating
Hormone (MSH)
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Target Tissue: MSH binds to receptors on the
skin and increase the production of
melanocytes causing them to synthesize
melanin
Causes the skin to darken
Under the control of releasing hormones that
increase or decrease its production
Antidiuretic Hormone
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ADH
Target Tissue: binds to receptors in the kidney
that increase water reabsorption by kidney
tubules. This results in less water loss as urine.
Oxytocin
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Target Tissue: Binds to membrane bound
receptors in uterus and mammary glands.
Causes contraction of the smooth muscle in the
uterus and milk let down in breast
The Thyroid
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made up of two lobes connected by a
narow band called the ithmus
lobes are on either side of the trachea
highly vascular
contains follicles filled with the protein
hormone
Secretes Thyroid Hormone
Thyroid Hormone
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Target Tissue : most cells of the body
regulates your rate of metabolism
also important for growth and development
The thyroid gland requires iodine to synthesize thyroid
hormone
deficiency of iodine in the diet can lead to thyroid
hormone deficiency
regulation is through feed back mechanism
Fig10.14
Hypothalamus-PituitaryThyroid Axis
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Lack of thyroid hormone is called
Hypothyroidism
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Excess amout of thyroid hormone can lead to
GRAVES DISEASE
Parathyroid Gland
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Four glands that are embedded in the posterior
wall of the thyroid
Secretes
Parathyroid hormone
Calcitonin
hormones which regulates calcium metabolism
Parathyroid Hormone
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Target tissue : bone and kidney
PTH binds to membrane bound receptors of cells and
increases the absorption of calcium from the intestines which
increases active Vitamin D
PTH also causes the resorption by incresing the rate of bone
breakdown by osteoclasts of bone tissue to release Ca
(calcium) into the circulation and decreases the rate at which
Ca is lost in the urine
PTH acts on tissue to raise blood Calcium Levels to normal
Calcitonin
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Target Tissue – Bone
Decreases the rate of bone breakdown,
prevents large increase in blood calcium levels
following a meal
Adrenal Gland
Divided into
Adrenal Cortex (outer)
Glucocorticoids (cortisol)
Aldosterone
Adrenal Androgens
Adrenal Medulla
Epinephrine and Norepinephrine
Layers of the Adrenal Gland
Arenal Cortex Hormones
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Mineralocorticoids- Aldosterone – regulation
of NA and K and water balance.
Glucorticoids- Cortisol – decreases
inflammation, increases glucose
Adrenal Androgens DHEA- axillary and
pubic hair in females
Excess Adrenal Androgens
(DHEA) in females
Cushing Syndrome
( excess cortisol)
The Pancreas
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Both Endocrine and Exocrine Gland
The Endocrine part
pancreatic Islets which secrete
insulin (beta cells)
glucagon( alpha cells)
Pancreatic Islet cells
Blood Glucose control
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Under the control of insulin and glucagon
It is very important to maintain blood glucose
levels within a normal range of values.
A decline in blood glucose level below its
normal range causes the nervous system to
malfunction because glucose is the nervous
system’s main source of energy
Insulin
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Insulin is released from the beta cells primarily in
response to the elevated blood glucose levels and
increased parasympathetic stimulation that is
associated with the digestion of a meal.
Increased blood levels of certain amino acids also
stimulate insulin secretion.
Decreased insulin secretion results from decreasing
blood glucose and from stimulation by the
sympathetic division of the nervous system This
allows blood glucose to be conserved to provide the
brain with glucose.
Glucagon
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Binds to receptors on liver cells and causes the
release of glucose from glycogen
The glucose is then released in the blood to
increase blood glucose levels
Glucagon secretion is reduced after a mealb
Diabetes Mellitus
Two Types
Type I - secretion of too little insulin from the
pancreas
- onset childhood, very thin , require insulin
Type 2 - insufficient numbers of insulin
receptors on target cells or defective
recepetors
- adult onset, usually overweight, can take
medications that help increase endogenous
insulin activity.
Diabetes Mellitus Type I
The signs and symptoms
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As a result, tissues can not take up glucose
and the blood becomes Hyperglycemic
Satiety center responds as if there is no
glucose and patients feeel hungry
Excess glucose is secreted in urine and they
become dehydrated
Fats and protein become energy source and
body wasting occurs
Table 10.4
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Effects of Insulin and Glucagon on Target
Tissue
Testes and Ovaires
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Testes secrete testosterone- growth of male and
development of male reproductive structures, muscle
enlargement, hair, voice change and male sexual
drive
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Ovaries secrete estrogen and progesterone- female
characteristics
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Both are under control of FSH and LH form the
pituitary
Pineal Gland
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Small gland superior and posterior to the
thalamus
Secretes a hormone called melatonin which
decreases LH and FSH by decreasing GNRH
which may help regulate the onset of puberty
by acting on the hypothalmus
Thymus
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Secretes thymosin which enhances the ability
of the immune system
Thymosin helps in the production of the white
cells ( called T cells)
Other Hormones
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Prostaglandins- role in inflammation
Erythropoietin-comes from kidney and
stimulates red blood cell production
HCG ( human chorionic gonadotropin) –
secreted by the placenta during pregnancy to
maintain the pregnacy.
Age Related Changed in the
Endocrine System
Age related changes include a gradual decrease
GH inpeople who do not exercise
Melatonin
Thyroid Hormone
Reproductive Hormones
Thymus Hormones
Increase in Diabetes