Download Thyroid Gland

There are 8 major endocrine glands
1. Pituitary gland
2. Thyroid gland
3. Thymus
4. Pancreas
5. Gonads (testis/ovaries)
6. Adrenal gland
7. Parathyroid gland
8. Pineal gland
Critical Thinking
The nervous and
endocrine systems are
responsible for
maintaining what?
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Comparison of the
Endocrine and Nervous Systems
a.
Nervous system:
acts through
electrical impulses
and
neurotransmitters


To cause muscle
contraction and
glandular secretion
Effect: short
duration, measured
in seconds, localized
b.
Endocrine system:
acts through chemical
messengers
(hormones)


Hormones influence
growth, development,
and metabolic
activities
Action is measured in
minutes, hours, or
weeks and is more
generalized
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Critical Thinking
What is the
difference in an
exocrine gland
and an endocrine
gland?
4
Comparison of Exocrine and
Endocrine Glands
1.
Exocrine glands: have ducts that carry their
secretory product to a surface

Examples: sweat, sebaceous, and mammary glands
and glands that secrete digestive enzymes
2. Endocrine glands: secrete hormones directly into
the into blood which carries them throughout body,
they have no ducts
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Critical Thinking
What are
hormones
made up of?
6
Characteristics of Hormones

Chemical classification
a. Proteins: make up most of the
hormones in the body

Difficult to administer orally


Inactivated by acid and pepsin in
stomach
Must be given by injection

(example: insulin)
b. Steroids: make up sex hormones and
hormones secreted by the adrenal
cortex

May be given orally
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Characteristics of Hormones

The specific cells that respond
to a given hormone have
receptor sites for that
hormone



“Lock and key” mechanism
If a hormone fits the
receptor site: there will be
an effect
If a hormone and a receptor
site do not match: there is
no reaction
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Characteristics of Hormones

Target tissue: a tissue
(cells) that responds to a
particular hormone
because it has receptor sites
for that hormone


May be localized in a
single gland or organ
May be diffuse and
scattered throughout
body

Many areas are affected
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Endocrine Glands
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The Pituitary Gland




The “Master Gland”
Small-size of a pea
Connected to
hypothalamus by a
slender stalk:
infundibulum
Two regions
a. Adenohypophysis:
anterior portion
b. Neurohypophysis:
posterior portion
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Hormones of the Anterior Lobe
(Adenohypophysis)
 Growth hormone (GH)
 Thyroid stimulating hormone (TSH)
 Adrenocorticotrophic hormone (ATCH)
 Gonatrophic hormone
 Follicle stimulating hormone (FSH)
 Leutinizing hormone (LH)
 Prolactin hormone (PRH)
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Hormones of the Anterior Lobe
(Adenohypophysis)
1.
Growth hormone (GH)

Stimulates growth of bones, muscles, and other organs

Influences height

Too little GH in a child: pituitary dwarf of normal proportions but small
stature

Excess of GH in a child: individual becomes exceptionally tall

After ossification is complete (bone length no longer possible)

Excess GH in adult causes enlargement in the diameter of the bones:
acromegaly bones of the hands and face become abnormally large
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Hormones of the Anterior Lobe
(Adenohypophysis)
2.
Thyroid-stimulating
hormone (TSH)




Causes glandular cells of
thyroid to secrete thyroid
hormone
Hypersecretion of TSH:
thyroid gland enlarges and
secretes too much thyroid
hormone
Hyposecretion of TSH: results
in atrophy of thyroid gland
and too little thyroid
hormone
HINT: this is not the same hormone that is
produced by the thyroid gland!
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Thyroid Gland
Thyroid Gland

Vascular organ: located in neck
 Consists of two lobes: one on each side of
trachea
Thyroxine and Triiodothyronine
 Thyroid hormone consists of:



Thyroxine: 95%
Triiodothyronine: 5%
Requires iodine for synthesis
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Iodine and the Thyroid Gland



Iodine is required for synthesis of
thyroid hormone
Iodine deficiency: thyroid cannot
make sufficient hormone and the
thyroid gland increases in size in an
attempt to produce more thyroid
hormone.
Known as simple goiter or iodine
deficiency goiter
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Thyroid Gland

Help to regulate the metabolism of carbohydrates,
proteins, and lipids





Increases rate at which cells release energy from
carbohydrates
Enhances protein synthesis
Necessary for normal growth and development
Stimulates nervous system
Do not have a single target organ

Affect most of the cells in the body
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Hypothyroidism

Deficiency of thyroid
hormone
a. Cretinism: in a child


Mentally retarded dwarf
with abnormal skeletal
features
Tx: thyroid hormone
therapy
b. Myxedema: in an adult


Lethargy, weight gain, loss
of hair, low metabolic rate
Thyroid hormone therapy:
usually alleviates
symptoms
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Hyperthyroidism

Enlarged thyroid gland that
produces too much hormone
 Symptoms: High metabolic
rate, hyperactivity, insomnia,
nervousness, irritability,
chronic fatigue
Exophthalmos: protruding
eyes due to swelling in tissues
behind the eyes
 Treatment: removal or
destruction of a portion of
the thyroid gland
Grave’s
Disease
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Thyroid Gland
Calcitonin
 Secreted by thyroid gland
 Reduces the calcium level in the blood by:



Reducing rate at which calcium is released from
bone
Increasing rate of calcium excretion by kidneys
Reducing calcium absorption in intestines
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Parathyroid Glands
1. Four small masses of
epithelial tissue located on
the posterior surface of the
thyroid glands
2. Secrete parathyroid
hormone (PTH)
3. When blood calcium levels
become low the PTH is
released to increase levels
4. Vitamin D is necessary for
dietary calcium to be
absorbed in intestines
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Parathyroid



PTH has opposite effect of calcitonin from the
thyroid gland
Hypoparathyroidism: insufficient secretion of
PTH can cause increased nerve excitability due to
low blood calcium levels
Hyperparathyroidism: excessive secretion of PTH

Excess calcium in the blood:


May precipitate in abnormal locations
Causes kidney stones
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Hormones of the Anterior Lobe
(Adenohypophysis)
3. Adrenocorticotropic hormone
(ACTH)

Reacts with receptor sites in the
cortex of adrenal gland


To stimulate secretion of cortical
hormones (cortisol)
Affects melanocytes in the skin:
increases pigmentation
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Adrenal Glands (Suprarenal)
1. Paired glands: one
located near upper
portion of each
kidney
2. Divided into 2
regions:
a. Adrenal cortex:
outer region
b. Adrenal medulla:
inner region
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Hormones of the Adrenal Cortex
Mineralocorticoids: Regulate the concentration of
mineral electrolytes in the blood (Aldosterone)
2. Glucorticoids: Produce cortisol which helps to
maintain glucose levels and counteract
inflammation
3. Gonadocorticoids: Sex hormones
1.


Androgens: Males
Estorgens: Females
4. Addison’s disease: hyposecretion
5. Cushing’s syndrome: hypersecretion
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Hormones of the Adrenal Medulla
Epinephrine and Norepinephrine
2. Prepares body for strenuous activity
1.

Sometimes called fight-or-flight hormones
3. Effect on body: increased heart rate, increased
respiratory rate, increased blood supply to skeletal
muscles
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Hormones of the Anterior Lobe
(Adenohypophysis)
4. Gonadotropic hormones
 React with receptor sites in the gonads (ovaries and
testes)


To regulate development, growth, and function of these
organs
Follicle-stimulating hormone (FSH)


Stimulates development of eggs in the ovaries and
sperm in testes
Stimulates estrogen production in female
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Hormones of the Anterior Lobe
(Adenohypophysis)

Luteinizing hormone (LH)
Female: causes ovulation, production and secretion of
female sex hormones
1) Progesterone
2) Estrogen
 Male: sometimes called interstitial cell-stimulating
hormone (ICSH)

Stimulates interstitial cells of testes
1) To produce and secrete testosterone (male sex hormone)

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Hormones of the Anterior Lobe
(Adenohypophysis)


Without gonadotropins:

Ovaries and testes decrease in size

Ova and sperm are not produced

Sex hormones are not secreted
Prolactin (PRL)


Promotes development of glandular tissue in female
breast during pregnancy
Stimulates milk production after birth of infant
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Hormones of the Posterior Lobe
(Neurohypophysis)
1.
Antidiuretic hormone (ADH)

Promotes reabsorption of water by the kidney
tubules


Less water is lost as urine
Conserves water for the body
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Hormones of the Posterior Lobe
(Neurohypophysis)
b. When not enough ADH is produced there is
excessive water loss in urine

c.
Large amounts of dilute urine: known as diabetes
insipidus
Large amounts of ADH: cause blood vessels to
constrict


Increases blood pressure
ADH sometimes called vasopressin
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Hormones of the Posterior Lobe
(Neurohypophysis)
2. Oxytocin
 Causes contraction of smooth muscle in wall of
uterus
 Stimulates ejection of milk from lactating breast
 Pitocin: commercial preparation of this hormone

Used to induce labor
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Endocrine Glands and
Their Hormones
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Pancreas




Islets of Langerhans
Long, soft organ
Located posterior to
stomach
Exocrine portion:
secretes digestive
enzymes

Carried through a
duct to duodenum




Endocrine portion:
secretes hormones into
blood
Alpha cells: secrete
glucagon
Beta cells: secrete
insulin
Glucagon & insulin
regulate blood glucose
levels
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Glucose
 Glucose
 Primary energy source for nervous system
 If glucose levels too low nervous system does not
function properly
 If glucose levels too high kidneys produce large
volumes of urine that can lead to dehydration
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Pancreas
Glucagon
 Secreted by alpha cells in pancreatic islets


Action: raises blood glucose levels


In response to low concentration of glucose in blood
Stimulates liver to break down glycogen into glucose
Prevents hypoglycemia from occurring


Between meals
When glucose is being used rapidly
 Given in response to severe hypoglycemic episodes
in injection form
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Insulin
Insulin
 Secreted by beta cells in pancreatic islets


In response to a high concentration of glucose in
blood
Action of insulin: decreases blood glucose level
(opposite or antagonistic to glucagon)


Promotes cellular uptake and use of glucose for
energy
Stimulates liver and muscle to remove glucose from
blood

Stores it as glycogen
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Pancreas

When the liver has stored all the glycogen possible:

Glucose is converted to fat
 Hypoactivity of insulin
 Insufficient insulin secretion
 Insufficient receptor sites on target cell membranes
 Defective receptor sites that do not recognize insulin

Leads to diabetes mellitus (abnormally high blood
glucose)
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Gonads
Gonads (Testes and Ovaries)

Primary reproductive organs


Testes: male secrete androgens
Ovaries: female secrete estrogen and
progesterone
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Pineal Gland

Extends from third ventricle of brain
 Synthesize melatonin





Secrete it directly into cerebrospinal fluid: takes it into
blood
High levels: secreted at night
Low levels: secreted during day
Regulation of circadian rhythms
Example: sleepiness/wakefulness cycle

Increased plasma melatonin levels (night): associated
with sleepiness
 Plays a role in hunger/satiety cycles, mood changes,
and jet lag
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