Transcript Endocrine System

Comparison of Nervous and Endocrine
System
Nervous system
• communicates with
electrical impulses and
neurotransmitters
• reacts quickly to stimuli,
usually within 1 to 10
msec
• stops quickly when
stimulus stops
• adapts relatively quickly to
continual stimulation
• has relatively local,
specific effects on target
organs
Endocrine system
• communicates with
hormones carried in blood
• reacts more slowly to
stimuli, often taking
seconds to days
• may continue responding
long after stimulus stops
• adapts relatively slowly;
may continue responding
for days or weeks
• sometimes has very
general, widespread
effects on many organs in
the body
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One way to transmit messages through the
body is through nerve impulses
Another way is to secrete chemical
messengers (hormones) into the
bloodstream
The endocrine system comprises of all
hormone secreting cells and glands in the
body
The endocrine system is typically slower
and has longer acting effects than the
nervous system
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Hypothalamus, pineal gland, pituitary gland,
thyroid gland, thymus, adrenal gland,
pancreas, ovary, testis
Summarize the key hormones & effects of
these glands using the provided handout &
chart
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Lipid (Steroid) Hormones: can diffuse directly into
cells through lipid bilayer. Once in the cell, lipid
hormones bind to receptor proteins which activates
specific genes. Examples include estrogen,
progesterone, testosterone
Peptide (Water soluble) Hormones: cannot diffuse
through lipid bilayer. Attach to receptor protein on
cell membrane and signals a cascade of events to
activate certain enzymes or effector molecules
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World’s tallest man
(2.36m) and his wife
(1.68m)
Excessive hGH
secreted by pituitary
during childhood
Contrast: dwarfism
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Thyroid gland secretes thyroxine which helps the body
metabolize fats, proteins, and carbohydrates
Thyroxine is controlled by negative feedback.
The anterior pituitary released TSH (thyroid stimulating
hormone) which causes the thyroid gland to release
thyroxine. As thyroxine levels in the blood increase, the
hypothalamus & anterior pituitary notice this and they stop
the production of TSH.
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Hypothalamus (in brain) releases GnRH (gonadotropin
releasing hormone)
This signals the pituitary gland (in brain to release LH
(leutenizing hormone) and FSH (follicle stimulating hormone)
LH stimulates the production of testosterone (in testes) and
testosterone stimulates the production of sperm
FSH stimulates production of molecules needed in
spermatogenesis
Notice the positive feedback mechanisms at play in this
pathway
This pathway is also regulated by a negative feedback loop.
When testosterone levels are too high, GnRH, LH, and FSH are
inhibited.
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Key Terms:
Menstrual Cycle: monthly cycle of events in a sexually
mature female which prepares the uterus for
implantation of a fertilized egg.
Endometrium: tissue lining the uterus
Follicle: structure in ovary which contains an oocyte
(immature egg/ovum)
Corpus Luteum: a temporary endocrine structure found
in the ovary which secretes progesterone and estrogen
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http://www.womenshealth.gov/publications/
our-publications/factsheet/menstruation.cfm
Timeframe of
Reproductive Cycle
Major Events
Day 1 – 6
The drop of hormone levels (FSH & LH) indicate
that the body is not pregnant. This triggers
shedding of the endometrium, blood and tissue.
Day 7 – 14
FSH levels rise and starts to develop the follicle.
As the follicle develops, estrogen levels
increase, which also causes an increase in LH.
The endometrium begins to thicken, and blood
supply increases, in preparation for fertilization.
Day 14 – 15
The follicle has produced a mature egg which bursts
from the ovary (ovulation).
Day 16 – 28
The egg now travels down the fallopian tube where
it may be fertilized by sperm. A structure called the
corpus lutem (in the ovary) develops and secretes
progesterone, which thickens the endometrium. If
fertilization does not occur, the cycle begins again
at day 1.
The pineal gland
produces melatonin which weakly
modulates wake/sleep patterns.
In some mammals it regulates
reproductive activity in response to
photoperiod.
It may play a role in seasonal affective
disorder, a condition in which
depression develops during the winter.
This condition responds well to
treatment with light