Download Endocrine System Notes 1

Endocrine System
Chemical Control
Endocrine System
- the system that secretes
hormones in the body
- hormones can last for
minutes or for hours
- a major gland, once called the master gland, is the
pituitary
- things under this system include regulation of blood
sugar levels and your metabolism
Endocrine Functions: Hormones

Hormones:
 Come from endocrine glands
 Circulate in the blood stream
 Act on specific cells in the body
• Hormones can be classified as fast acting or
•
slow acting. It is also interesting to note that
some hormones travel bound to plasma proteins
Alterations in plasma protein concentrations (as
can result from say liver failure) can lead to
abnormal endocrine function. A malfunctioning
liver may fail to break down hormones which will
also manifest itself as an endocrine disorder.
• Notice that glandular tissue receives 'input' from
a number of sources including signals (via
hormones) from other glands, nervous input,
and importantly by monitoring the extracellular
environment in which it sits. Those tissues which
are stimulated by hormones often require a low
level of that hormone just to remain healthy;
larger concentrations causing the tissue to
secrete. The influence of the low levels of
hormone is known as the trophic effect of a
hormone.
Next to the nervous system the endocrine system is the
system that controls the body. However, the endocrine
system uses hormones to stimulate the metabolic activities
of the cells. These hormones are released into the blood
stream. Tissue response to hormones usually occur after a
lag time of seconds or days. Once started the responses
tend to be much more prolonged than those that are
induced by the nervous system.
Control in The Endocrine
System
• The endocrine system comprises (like the
•
nervous system) of relatively simple
components, which interact and work together
in a complex fashion.
With respect to the endocrine system, there are
two roles for negative feedback. The first is the
control of the internal environment - regulating
some internal 'variable'; the second is control of
the release of hormones.
Example of a
Negative
Feedback
Loop:
Homeostasis
Location of Major Endrocrine Organs
Figure 9.3
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 9.14
Endocrine System Characteristics
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Access to every cell
Each hormone acts only on specific cells
(target cells)
Only specific cells have receptors for specific
hormones
Endocrine control slower than nervous
system
Endocrine and nervous systems interact
Classification of Hormones:
Steroid

Steroid Hormones:

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
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Lipid soluble, chemically derived from
cholesterol
Enter target cells
Activate specific genes to produce specific
proteins
Slower acting than nonsteroid hormones,
minutes to hours
Steroid Hormone Action on a
Target Cell
Figure 13.2
Steroid Hormone Action
• Video
Classification of Hormones:
Nonsteroid
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Nonsteroid hormones:
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Water soluble
Bind to receptors on target cell membranes
Work through intermediate mechanisms to
activate existing enzymes
Faster action than steroid hormones, seconds
to minutes
Nonsteroid Hormone Action on a
Target Cell
Figure 13.3
Non Steroid Hormone Action
• Video
The Pituitary Gland
The pituitary gland is a
small oval-shaped gland
found at the base of the
brain below the optic
nerve. It secretes
hormones which control
and regulate the other
glands in the body. These
glands release hormones
which are responsible for
the body's growth and
metabolism.
Hormones of the Pituitary Gland
Table 13.1
Hypothalamus and the Anterior Pituitary Gland
Figure 13.7
Hypothalamus and the Anterior
Pituitary Gland

Anterior pituitary
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Connection to hypothalamus: releasing and
inhibiting hormones from hypothalamus
travel to pituitary through pituitary portal
system
Hormones

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ACTH: stimulates adrenal cortex
TSH: acts on thyroid gland
FSH, LH, Prolactin: related to control of
reproductive cycles and lactation
Growth Hormone: widespread effects on body
Hypothalamus and the Posterior
Pituitary Gland

Posterior pituitary
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Connection to hypothalamus: hormones made
in hypothalamus, stored in posterior pituitary
Hormones: nonsteroidal
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Antidiuretic hormone (ADH): conserves water in
kidneys, regulates water balance in body
Oxytocin: causes uterine contractions during labor
and milk ejection through neuroendocrine reflex
Pituitary Disorders


Gigantism: hypersecretion of growth
hormone
Pituitary Dwarfism: hyposecretion of growth
hormone
Pituitary
Gigantism
Various Hormones
Growth hormone - controls growth
Prolactin - stimulates production of milk after childbirth
ACTH (adrenocorticotrophic hormone) - stimulates
production of hormones from the adrenal glands
TSH (thyroid stimulating hormone) - stimulates production
of hormones from thyroid gland
FSH (follicle stimulating hormone) and LSH (luteinizing
stimulating hormone) - stimulate activity in the ovaries of
women and the testes in men.
ADH (anti-diuretic hormone) - controls the concentration of
urine
Oxytocin - stimulates the contraction of the womb during
childbirth and the secretion of milk for breast feeding.
• The organs of the endocrine system are small and
•
unimpressive. The endocrine glands of the body include
the pituitary, thyroid, parathyroid, adrenal, pineal, and
thymus.
Hormones are chemical compounds that regulate
metabolic function of cells in the body. There are two
types of hormones: amino acid-based hormones and
steroids. Most hormones are amino acid-based. Steroid
hormones are synthesized from cholesterol. Only the
gonadal hormones and adrenocortical hormones are
steroids.
• A hormone is a chemical that is synthesized and
secreted by a group of specialized cells that are
called glands. Glands are classified in two ways:
exocrine or endocrine. Exocrine glands use
ducts to transport their secretions. Endocrine
glands, on the other hand, don’t use ducts to
transport their hormones. Instead they secrete
into the blood stream for distribution.
• Another key component of the endocrine system is the
•
•
receptors for the hormones on the surface of the cell
membrane. Receptors are composed of proteins and
imbedded in the cell membrane just like other proteins.
There are over 50 hormones in the human body, and
they can be grouped together by their chemical
structure. Steroids are produced from
cholesterol. Peptides are chains of amino acids. Other
hormones are derived from amino acids.
Several glands comprise the endocrine system. The
hypothalamus integrates the endocrine system and the
nervous system. It receives signals from the brain and
the peripheral nerves. It then initiates the endocrine
system. The cells that comprise the hypothalamus are
called nuerosecretory cells. The cells are able to receive
a nerve impulse just like a nerve cell would, but instead
of passing it on to another cell they trigger the release of
hormones in the blood stream.
• The pituitary is sometimes referred to as the
master gland. However, most of the time the
pituitary receives orders from the
hypothalamus. There are two lobes on the
pituitary. The posterior lobe, called the
neurhypophysis, stores hormones manufactured
by the hypothalamus and secretes them on
command. The anterior lobe, called the
adenohypophysis, is able to produce it’s own
hormones which act on other glands.
Endocrine Glands
• The thyroid gland is located on the front surface
of the trachea. It has two lobes, and it
produces two hormones: Triiodothyronine (T3)
and Thyroxine (T4). Both T3 and T4 have the
same effect on the target cell, but T3 is usually
most active. The thyroid also regulates
metabolism. The thyroidal secretions are
controlled by both the hypothalamus and the
pituitary.
• The pancreas secretes insulin, a hormone that regulates
•
glucose in take of the cells. A deficiency in this hormone
results in diabetes mellitus. Insulin regulates the blood
sugar levels by stimulating cells to take in glucose. It
also stimulates the synthesis of protein and fat storage.
The adrenal medulla is the gland behind the fight-orflight reaction. It secretes two hormones: epinephrine
and norepinephrine. (Epinephrine is also known as
adrenaline.) Epinephrine secretion is triggered by stress,
both positive and negative stress. It increases the rate
and the stroke volume of the heart.
Pancreas: Endocrine Functions
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Structures: islets of Langerhans
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Hormones: nonsteroidal
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Glucagon: made by alpha cells, raises blood
sugar
Insulin: made by beta cells, lowers blood sugar
Roles of Insulin and Glucagon in
Regulating Blood Glucose
Figure 13.9
Adrenal Glands: Cortex
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Adrenal cortex
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Secretion: mediated through hypothalamuspituitary secretions
Hormones: steroidal
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Glucocorticoids: cortisol – blood glucose regulation
Mineralocorticoids: aldosterone – sodium/fluid/urine
Secretion of Cortisol
Figure 13.10
Adrenal Glands: Medulla
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Adrenal medulla: neuroendocrine organ
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Secretion: sympathetic nervous system
Hormones: nonsteroidal
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Epinephrine and Norepinephrine: enhance
function of sympathetic nervous system
(Fight or flight)
Roles of the Hypothalamus and Adrenal Glands in the Stress Response
Figure 9.12
Slide 9.31
Thyroid Gland
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Secretion: mediated through hypothalamuspituitary secretions
Steroidal hormones:
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Thyroxine (T4) and Triiodothyronine (T3):
both regulate production of ATP from
glucose, affects metabolic rate
Calcitonin: lowers blood calcium levels
Negative Feedback Control of Thyroxine Secretion
Figure 13.13
Homeostatic Regulation of Blood
Calcium Concentration
Homeostatic Regulation of Blood Calcium concentration (cont.)
Parathyroid Glands
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Secretion: response to lowered blood
calcium levels
Hormone: Parathyroid hormone (PTH),
nonsteroidal
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Removes calcium and phosphate from bone
Increases absorption of calcium by the
digestive tract
Increases renal retention of calcium and
excretion of phosphate
• The testis and ovaries secrete hormones that are
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grouped into three major categories: androgens,
estrogens, and progestins. All three are found in both
males and females, but each in varying amounts.
Androgens are primarily produces by the
testis. Testosterone is the primary hormone in this
group. Androgens stimulate the maintenance and
development of the male reproductive system.
Estrogens are the female equivalent of Androgens. They
maintain the female reproductive system and trigger the
development of female second sex
characteristics. Progestins maintain and prepare the
uterus for growth and development of an embryo.
Testes
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Hormone: testosterone (steroidal)
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Functions:
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Regulates development and normal functioning of
sperm, male reproductive organs, male sex drive
Development of male secondary sex characteristics
Ovaries
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Hormones (steroidal) and functions:
Estrogen: initiates development of secondary
sex characteristics, regulates menstrual cycle
 Progesterone: regulates menstrual cycle
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Ovarian Cycle
Figure 16.6
Disorders of the Endocrine
System
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Thyroid
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Hypothyroidism:
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Children: cretinism
Adults: myxedema
Hyperthyroidism: Graves Disease
Adrenal glands
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Addison’s Disease: failure of adrenal cortex,
cortisol deficiency
Cushing’s Syndrome: excessive cortisol
Grave’s Disease – overactive thyroid