Download Direct stimulation from the nervous system

Endocrine System
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Endocrine System
Works together with nervous system to maintain homeostasis
► Primary function: produces hormones
► Hormones act on specific target cells
to produce specific effects
► No ducts
►
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Exocrine/Endocrine Glands
Gland
Pancreas
Ovary
Testes
Kidney
Exocrine
Endocrine
digestive enzymes
insulin, glucagon
egg
estrogen, progesterone
sperm
testosterone
urine
erythropoietin
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Endocrine System vs. Nervous System
Characteristic
General Function
Reaction to stimuli
Duration of effect
Target tissue
Chemical messenger
Endocrine System
Nervous System
Maintain homeostasis
Maintain homeostasis
slow
rapid
long
short
entire body
muscles and glands
hormone
neurotransmitter
Messenger producing cell
endocrine gland
neurons
Distance to target cells
long (via bloodstream) short (across synaptic space)
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►
Chemical messengers
produced by endocrine glands
►
Secreted into interstitial fluid
and absorbed into blood
vessels
Hormones
 Contact all cells in body
►
Produce effects only on cells
containing specific receptors
 Target cell
 ‘Lock and key’ arrangement
causes a change in activity of
target cell
► Growth hormone—all cells
► Prolactin—mammary tissue
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Control of
Hormone Secretion
Negative feedback systems (like a
thermostat)
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If hormone level is low:
 Appropriate endocrine gland is
stimulated to produce more hormone
Once adequate hormone concentration is
attained in the bloodstream:
 Stimulation of endocrine gland is
reduced and production of the hormone
is stopped/reduced
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Control of Hormone Secretion
►
Direct stimulation from the nervous system
 Secretion of some hormones is stimulated by sympathetic nerve
impulses when an animal feels threatened.
► “Fight or flight" response
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Hypothalamus
(controls pituitary gland)
►
Part of diencephalon section of brain
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Controls activities of pituitary gland
 Portal system of blood vessels links
hypothalamus with anterior portion of
pituitary gland
►
Modified neurons in hypothalamus secrete
releasing and inhibiting hormones into
portal blood vessels
 Specific for a particular anterior pituitary
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hormone
Hypophyseal Portal System
GHRH, GHIH (Don’t memorize)
Thyrotropin releasing hormone (TRH)
Gonadaotropin releasing hormone (GnRH)
PRH, PIH
Corticotropin releasing hormone (CRH)
Growth hormone
Thyroid stim hormone (TSH)
Follicle stim hormone (FSH)
Luteinizing hormone (LH)
Prolactin
Adrenocorticotropic hormone (ACTH)
Melanocyte stim hormone (MSH)
Posterior
pituitary
Oxytocin
Antidiuretic hormone (ADH)
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Hypothalamus
►
Modified neurons in hypothalamus also
secrete antidiuretic hormone (ADH) and
oxytocin
►
Transported to posterior pituitary (along
neurons) for storage
►
Released into the bloodstream by nerve
impulses from hypothalamus
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►
Two separate glands with different
structures, functions, and
embryological origins
 Anterior pituitary adenohypophysis; rostral
portion
 Stimulated by hypothalamus
(portal system) and direct (neg)
feedback from target tissues to
produce hormones
 Posterior pituitary neurohypophysis; caudal portion
 Stores and releases hormones
produced in hypothalamus
(oxytocin, ADH)
Pituitary
Gland
(Hypophysis)
Rostral
Caudal
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Growth Hormone (GH)
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a.k.a. somatotropin and somatotropic hormone
Promotes body growth in young animals
Helps regulate metabolism of proteins, carbohydrates, and
lipids in all body cells
The effect of GH on protein metabolism is to encourage
anabolism (synthesis of proteins by body cells)
The effects of GH on carb and lipid metabolism are linked.
 While lipids are broken down via catabolism for energy production, the
use of carbs (especially glucose) as energy sources is discouraged.
 Less glucose is removed from the blood and hyperglycemia occurs
(hyperglycemic effect).
 Important for the body to maintain a balance between GH and insulin to
control blood glucose levels.
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Prolactin
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Helps trigger and maintain lactation
in females
 Secretion of milk by mammary
glands
Prolactin production continues as
long as teat/nipples are stimulated
by nursing or milking
When prolactin stimulation stops:
 Milk production stops
 Mammary gland shrinks to
original/nonlactating size
1. Baby sucks/stimulates
2. ↓PIH, ↑PRH
3-4. Stimulates milk glands
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ThyroidStimulating
Hormone (TSH)
►
a.k.a. Thyrotropin/Thyropropic
►
Stimulates growth/development of
thyroid gland and Causes thyroid to
produce its hormones.
►
Secretion regulated by:
Feedback (neg) from thyroid gland
hormone
Hormone
► Thyroid
hormone levels too low- TSH
production increases
► Thyroid hormone levels too highTSH production diminishes
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Adrenocorticotropic Hormone (ACTH)
►
Stimulates growth/development of
adrenal cortex and the release of some
of its hormones
►
Regulated by:
 Release of CRF from hypothalamus
to anterior pituitary through portal
system
 Neg feedback from adrenal
hormones and administered
cortisones
 During sudden stress, ACTH can
quickly be released after the
hypothalamus is stimulated to send
out ACTH- releasing factor to the
anterior pituitary via the portal
system
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►Females—stimulates
growth/development of ovarian
follicles – where oogenesis occurs
►Also stimulates the cells lining
the follicles to produce/secrete
estrogens
►Used to superovulate
Males- stimulates
spermatogenesis in the
testes
FollicleStimulating
Hormone
(FSH)
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►
Completes follicle development in
ovary
►
Increasing amounts of estrogens
feedback to the anterior pituitary and
cause reduced production of FSH and
increased production of LH
►
LH levels reach a peak when follicle is
fully mature
Luteinizing
Hormone (LH)
 Usually causes ovulation
►
After ovulation, LH stimulates cells in
empty follicle to multiply and develop
into corpus luteum (CL)
 CL produces progesterone necessary for
maintenance of pregnancy
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Luteinizing Hormone (LH)
►
In males, LH stimulates interstitial cells to produce testosterone
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Melanocyte-Stimulating Hormone (MSH)
► Controls
color changes in
pigment cells (melanocytes)
of reptiles, fish, and
amphibians
► Administration of artificially
large amounts of MSH to
higher mammals can cause
darkening of skin from
melanocyte stimulation (↑
melanin)
 Effect at normal levels in
mammals unknown
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► Stores
(does NOT produce)
two hormones produced in
hypothalamus
Posterior
Pituitary
 Antidiuretic hormone (ADH) and
oxytocin
► Transported
from
hypothalmus to post pituitary
along axons and stored in
nerve endings
► Periodically
released into
bloodstream in response to
nerve impulses from
hypothalamus
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Posterior
pituitary
Oxytocin
ADH
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Helps prevent diuresis
Receptors in hypothalamus detect changes in osmotic pressure
(concentration) of blood (due to dehydration - hemoconcentration)
 Generates nerve impulses from hypothalamus- causes release of ADH
► ADH causes kidneys to reabsorb more water
from urine and return it to bloodstream
► Urine then more concentrated
ADH deficiency causes Diabetes Insipidus (PU/PD occurs)
Antidiuretic
Hormone
(ADH)
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Oxytocin
►
Effects on uterus - causes contraction of myometrium at breeding and at
parturition
 Induces uterine contractions that aid transport of spermatozoa to
oviducts
 Stimulates uterine contractions that aid in delivery of fetus and placenta
►
Effect on active mammary glands - causes milk let down to lower parts of
gland
 Stimulation of teat/nipple by nursing or milking causes oxytocin release
into bloodstream
 Causes contraction of musclelike myoepithelial cells around mammary
gland alveoli and small ducts
 Forces milk into lower parts of gland, making it accessible for
nursing/milking (milk letdown)
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Oxytocinpositive
feedback
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