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THE ENDOCRINE SYSTEM
Endocrine System
• Consists of a variety of glandular organs which act with the nervous
system in controlling body activities and maintaining homeostasis.
• HORMONES-Are chemicals secreted by glands of the endocrine
system and are transmitted in the blood to the tissue they affect.
– The physiological effect of a particular hormone is restricted to a
certain tissue called TARGET TISSUE.
– Cells of target tissue possess specific receptor sites for the
hormone molecules.
– Endocrine- “ductless gland” They secrete their hormones directly
into the blood.
– The endocrine glands include the: pituitary gland, thyroid,
parathyroid, adrenal, pancreas, pineal, thymus, and gonads,
(testes) for males and (ovaries) for females.
Types of Hormones
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•
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Proteins
Steroids
Amines
Prostoglandins
Types of hormones
• Amines
• prostaglandins
Functions of the Endocrine System
1. Regulate metabolic processes
2. Control the rate of certain chemical reactions within the
body
3. Aid in the transport of substances through the cell
membranes
4. Play vital roles in cell growth, water and electrolyte balance
5. Control reproduction
Control of Hormone Secretions
Negative Feedback System
• Gland A secretes Hormone A.
• Hormone A stimulates Gland B to secrete Hormone B
• Hormone B inhibits Gland A from secreting more Hormone A
• Gland A will not secrete more Hormone A until the levels of
Hormone B drop to a certain level.
• The Hypothalamus controls the secretion of endocrine gland
hormones 2 ways:
• 1. by secreting releasing or inhibitory factors
• 2. by nerve control
Endocrine Glands
Pituitary Gland (hypophysis) “MASTER GLAND”
• Located on the inferior center of the brain below the hypothalamus
• Suspended beneath the brain on a stalk called the infundibulum
• Divided into 2 main parts:
Anterior pituitary (adenohypophysis)
Posterior pituitary (neurohypophysis)
Pituitary gland
• Ant. Pituitary is controlled by releasing factors from the
hypothalamus
• Post. Pituitary is controlled by nerves from the hypothalamus.
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6.
Anterior Pituitary secretes 6 different hormones:
Growth Hormone (GH)
Thyroid Stimulating Hormone (TSH)
Adrenocorticotrophic Hormone (ACTH)
Follicle Stimulating Hormone (FSH)
Lutenizing Hormone (LH)
Prolactin
Posterior Lobe Hormones
• The post. Pituitary does not
synthesize hormones.
• They are synthesized in the
hypothalamus.
Post. Pituitary Hormones
1. Antidiuretic hormone
2. Oxytocin
Anterior Lobe Hormones
1. Growth Hormone (GH)
(Somatotropin)
• Stimulates body cells to
increase in size and undergo
rapid cell division
Conditions concerning GH
• Dwarfism-hypopituitary dwarf
all body parts are proportional
most are normal intellectually .
• Some need hormone therapy
so they can develop sexually
GH conditions
Giantism- hyperpituitary due to
oversecretion of GH, usually
due to a tumor.
Acromegaly- Secretion of GH after
growth plate closure of the long
bones.
• These people are characterized
by large hands and feet,
protruding jaw, large tongue
and nose
Ant. Lobe Hormones
2. Prolactin- milk production in the
pregnant female breast.
3. Thyroid Stimulating Hormone
(TSH) (thyrotropin)
• Controls the secretions of thyroid
hormones.
• Some external features influence
the release, extreme cold and
emotional stress
4. Adrenocorticotrophic hormone
(ACTH)
• Controls the manufacture and
secretion of hormones by the
adrenal cortex
Ant. Pit. Hormones cont.
Follicle Stimulating Hormone
(FSH)- responsible for the growth
and development of the egg
containing follicle in the female
ovary, also stimulates the
follicle cells to secrete extrogen
• In males, stimulates the
production of sperm cells in the
testes
Lutenizing Hormone (LH)
• Promotes the secretion of sex
hormones in both male and
female
• Essential for the release of the
egg cells from the ovary
Posterior Lobe Hormones
• Posterior pituitary composed
primarily of neuroglial cells
(pituicytes).
• These cells seem to function as
supporting cells for nerve fibers
that run from the
hypothalamus and synthesize
the hormones.
1. ADH Antidiuretic Hormone –
inhibits urine formation. It
acts on the kidneys and
reduces the amount of water
they excrete.
• ADH is important in regulating
the water concentration of the
body.
ADH
•Diabetes insipiduscondition in which there
is not enough ADH being
secreted of total absence
of ADH being secreted.
• Causes massive
amounts of urine to be
produced and intense
thirst.
•As much as 45 liters of
urine produced in a day.
•Treated with synthetic
ADH.
Post. Pit. Hormones
Oxytocin- causes contraction of the
smooth muscle in the walls of the
pregnant uterus.
• Released at the end of pregnancy
and plays an important role in
childbirth.
• Also causes milk to be ejected
from the lactating breast after
childbirth.
The Thyroid
Vascular organ that consists of 2
large lobes connected by a
broad isthmus.
• Located just inferior to the
larynx on either side of the
trachea.
• It has the ability to remove
iodine from the blood.
• Composed of groups of
secretory cells called follicles.
• They produce and secrete three
hormones that effect the
metabolic rate of most body
cells and blood calcium levels.
Thyroid hormones
Thyroxine & triiodothyrine
• They act to increase the rate of
energy release from CHO’s and
the rate of protein synthesis.
Calcitonin
• Helps regulate the calcium level
of the blood by inhibiting the
rate at which calcium leaves the
bones and enters the blood.
• Lowers the blood Ca++ level
• Decreases osteoclast activity of
the bones as well as allows
Ca++ to exit body thru the
kidneys and large intestine.
Disorders of the Thyroid
Hypothyroidism- not enough
thyroxine or I-3 produced.
Cretinism- infants and children,
stunted growth, abnormal bone
formation, retarded mental
development, low body
temperature.
• If not corrected within the first
month of birth permanent
mental retardation will occur.
Myxedema- adults and teens, low
metabolic rate, mentally slow,
gain in a considerable amount
of weight. Swollen tissues due
to edema.
Hyperthyroidism
Grave’s Disease –elevated
metabolic rate, abnormal weight loss,
excessive perspiration, muscle
weakness and emotional instability.
• Eyes are likely to protrude due to
edema behind the eyes.
• Thyroid is likely to enlarge (goiter)
Goiter
• Is an enlargement of the thyroid.
Toxic goiter- due to the oversecretion
of TSH from the ant. Pituitary
Simple Goiter- due to lack of iodides
in the diet.
Banjo Goiter
Parathyroid Gland
• Located on the posterior surface
of the thyroid
• There are usually 4, 2 each on
the lateral lobes of the thyroid.
• Yellowish brown structure
covered with a thin layer of
connective tissue
• Hormone secreted is called
parathormone (PTH).
• Causes an increase in blood Ca++
levels and a decrease in
phosphate levels.
• Does this by influencing the
bones, intestines, and kidneys.
Parathormone
Does this by:
• Activates bone reabsorbing
osteoclasts
• Enhances the absorption of Ca++
rich food by the small intestine.
• Kidneys conserve blood Ca++ and
increase the excretion of
phosphates in the urine.
• Seems to be free of control by
the hypothalamus.
Adrenal Glands
• Each sits atop the kidneys and are
embedded in a mass of fat that
encloses the kidneys.
• Pyramid shaped and very vascular
divided into 2 parts:
Adrenal medulla- inner portion
Adrenal cortex- outer portion makes
up the bulk of the gland.
Hormones of the A. medulla
Epinepherine & Norepinepherine
Increases the rate of heart, elevates
blood pressure, raises blood sugar,
raises breathing rate, dialation of
airways, lowers digestive activity.
(FIGHT OR FLIGHT RESPONSE)
Hormones of the Adrenal Cortex
• All steroids, all are vital to life.
• 3 types of hormones secreted
by different layers of the cortex.
1. Mineralocorticoids- regulate
the concentration of
extracellular electrolytes.
2. Glucocorticoids-influence the
metabolism of carbs, proteins,
and fats.
3. Sex hormones-effect sexual
characteristics of both male
and females.
Sex hormones
PANCREAS
• Flattened globular organ just
posterior to stomach and small
intestine.
• Islets of Langerhans are
secretory cells. 2 types:
1. Alpha cells- glucagon which
converts glycogen to glucose.
Raising blood sugar levels.
2. Beta cells- insulin facilitates
the transport of glucose into
the cells of the body.
lowering blood sugar levels.
Disorders of the Islets
Diabetes Mellitus- severe upset
of carbohydrate metabolism.
2 types:
1. Type I- childhood onset.
Complete lack or severe
shortage of insulin secretion
2. Type II – adult onset. Insulin
receptors do not recognize
insulin secreted
Both cause elevated blood glucose
levels. This can cause a great
deal of side effects to all
systems of the body.
Hypoglycemia-too much insulin
secreted. Resulting in low
blood sugar after a spike in
blood sugar levels.
Diabetes mellitus
Pineal Gland
• Located deep within the cerebral
hemispheres of the brain
• Functions not entirely clear
known to secrete at least 1
hormone.
• Melatonin-thought to stimulate
the secretion of releasing factors
from the hypothalamus.
• This affects the secretion of
gonadotropins and ATCH.
• Thought to control the menstrual
cycle in human females
• Controls the circadian rhythmsperiod of wakefulness and
sleeping.
Thymus gland
• Located in the mediastinum
between the lungs and heart.
• Relatively large in children but
diminishes in size with age.
• Secretes a hormone called
thymosin
• Thymosin- affects the
production of certain white
blood cells. (lymphocytes)
• Immune system function
The Gonads
Female- Ovaries
• Secretes the hormones estrogen
and progesterone.
• Estrogen-causes the maturation of
the sexual organs and the
development of secondary sexual
characteristics.
• Causes menarche at puberty
Male-Testes
• Secretes testosterone
• Causes maturation of the male
sexual organs and the
development of the secondary
sexual characteristic
• Causes maturation of sperm cells
The Placenta
• Is a fetal-maternal capillary bed
• Sustains the fetus during
pregnancy
• Secretes estrogen and
progesterone during the first
trimester of pregnancy
• Secretes HCG human chorionic
gonadotropin which sustains
the uterus during pregnancy.