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76 Cards in this Set

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endocrine system
includes all endocrine cells and tissues that produce hormones or paracrine factors
What are endocrine cells?
release secretions into extracellular fluid (no ducts)
What are exocrine cells?
release secretions onto epithelial surfaces via ducts
e.g. pancreas has both endocrine & exocrine structures
What is a hormone?
chemical messenger secreted into circulatory system to affect cell activity in another portion of the body (ENDOCRINE SYSTEM COMMUNICATION)
What is a neurotransmitter?
compound secreted by a neuron to affect transmembrane potential of another cell at a synapse (NERVOUS SYSTEM COMMUNICATION)
Norepinephrine and epinephrine act as _____ when released into the bloodstream, but _____ when released across a synapse.
hormones; neurotransmitter
What is the common goal for the endocrine and nervous systems?
maintain homeostasis
What are some characteristics of the Nervous System?
• Neurotransmitters
• Short response
• Specific, local effects
• Rapid acting (seconds to minutes)
What are some characteristics of the Endocrine System?
• Hormones
• Prolonged response
• General, widespread effects
• Slow acting (minutes to years)
If the Endocrine System's is to preserve homeostasis...
cellular activities must be coordinated
To coordinate cell activity, cells "communicate" information in various ways such as...
gap junctions, extracellular fluid, circulatory system, and synaptic cleft
What are the chemical mediators and distribution of effects of Gap junctions?
Chemical Mediators
ions, small solutes, lipid-soluble materials
Distribution of Effects
adjacent cells of same type
What are the chemical mediators and distribution of effects of Extracellular fluid?
Chemical Mediators
paracrine factors ("local hormones")
Distribution of Effects
Local; within same tissue
What are the chemical mediators and distribution of effects of Circulatory system?
Chemical Mediators
Hormones
Distribution of Effects
Distant tissues or organs
What are the chemical mediators and distribution of effects of Synaptic cleft?
Chemical Mediators
Neurotransmitters
Distribution of Effects
Limited to very specific area
Blood plasma levels of hormones are controlled primarily by ______.
negative feedback system
• vary only within a narrow desirable range
Hormones are synthesized and released in response to:
1. Humoral stimuli
2. Neural stimuli
3. Hormonal stimuli
What is Humoral Stimuli?
secretion of hormones in direct response to changing blood levels of ions and nutrients

Example: Ca²+ concentration in blood

• ↓ [Ca²+] stimulates parathyroid glands to secrete PTH (parathyroid hormone)
• PTH causes [Ca²+] to ↑
• ... then stimulus is removed
What is Neural Stimuli?
nerve fibers stimulate hormone release

Example:
sympathetic nervous system (SNS) fibers stimulate adrenal medulla to secrete catecholamines
What are catecholamines?
class of amino acid derivative hormones (e.g. epinephrine, norepinephrine)
What is Hormonal Stimuli?
release of hormones in response to stimulation from other hormones

Examples:
• Hypothalamus hormones stimulate the anterior pituitary to release hormones
• In turn, pituitary hormones stimulate target tissues to secrete still more hormones
tropic hormones
hormones that regulate activity of other endocrine glands ("trope" - turn on, change → look for "trope" in hormone names)
How are hormones classified?
• based on their chemical structure
• their most important chemical characteristic: water-soluble or lipid-soluble hormones
What are characteristics of water-soluble hormones?
• hydrophobic; polar/charged
• do not cross plasma membrane
• bind to receptors on plasma membrane

e.g. epinephrine, insulin, antidiuretic hormone (ADH), peptide & amino acid hormones (except thyroid hormones)
What are characteristics of lipid-soluble hormones?
• lipophilic; non-polar
• can cross plasma membrane
• bind to receptors inside cells (intracellular receptors)

e.g. steroid hormones; thyroid hormones
Mechanisms of Hormone Action
• Hormones circulate in blood to all tissues but only affect cells referred to as target cells
• Target cells have specific receptors that bind to a specific hormone
• These receptors may be located:
∙ inside target cell (cytosol/nucleus)
∙ on the plasma membrane
Lipophobic hormones
bind to receptors located in the plasma membrane
• cannot cross lipid bilayer plasma membrane
∙ amino acid derivatives (except thyroid hormone) & peptide hormones
Lipophilic hormones
typically bind to receptors located in the target cell
• can cross lipid bilayer plasma membrane
∙ lipid derivatives & thyroid hormone
Lipophobic hormones cannot have direct effect inside the cell, therefore, they can indirectly affect the cell by using a _______.
second messenger
What are two common second messengers for lipophobic hormones?
cAMP (cyclic AMP) and Ca²+
Explain what occurs during the cAMP second messenger system
1. 1st messenger (lipophobic hormone) binds to receptor → activates G protein
2. G protein releases alpha subunit, which binds to & activates adenylate cyclase
3. Adenylate cyclase (enzyme) catalyzes conversion of ATP to cAMP
4. cAMP activates protein kinase
5. Protein kinase catalyzes transfer of a phosphate group from ATP to a protein (therefore altering protein's activity)
6. Altered protein activity → causes response in the cell
Explain what occurs during the Calcium second messenger system
1. 1st messenger (lipophobic hormone) binds to a receptor → G protein
2. G protein releases alpha subunit, which binds to & activates phospholipase C
3-6. second messenger Ca²+ is released from the ER, binds to calmodulin, activating protein kinase (phosphorylates a protein) → response in cell
_____ hormones can have direct effect inside the cell and can diffuse into the cell
Lipophilic
Explain the mechanisms of Hormone Action
1a. bind to receptor in nucleus → forming hormone-response complex
1b. bind to receptor in cytosol → forming hormone-response complex that enters the nucleus
2. Inside nucleus, hormone receptor complex binds to region of DNA (hormone response element (HRE)); is beginning of a specific gene
3. Binding of complex to HRE activates or deactivates genes; if activated → causes transcription (mRNA synthesis)
4. mRNA moves into cytosol
5. mRNA is translated by ribosomes into proteins
Signal Amplification in Second Messenger Systems
2nd messenger system acts as cascade (series of sequential steps that progressively ↑ magnitude)
Transport of Hormones in blood occur in two ways, what are they?
Hydrophilic messengers & Hydrophobic messengers
Hydrophilic messengers
secreted by exocytosis → enter bloodstream
• dissolved in plasma
Hydrophobic messengers
secreted by diffusion → enter bloodstream
• majority bind to carrier proteins
• only free hormones are available for use
What are the major endocrine glands in other organs?
Pancreas and ovaries
What hormone(s) does the pancreas secrete?
insulin and glucagon
What hormone(s) does the ovaries/testes secrete?
females: estrogens & progesterone
males: androgens (testosterone)
What are the minor endocrine glands in other organs?
heart, kidneys, GI tract (etc)
Hypothalamus
• part of the brain
• secretes several hormones, many that control the pituitary gland
• synthesizes AND secretes 9 hormones
Pituitary Gland
• major endocrine gland
• infundibulum attaches it to hypothalamus
∙ 2 lobes: anterior and posterior
Neuroendocrine organ
nervous + endocrine tissue
The anterior lobe (adenohypophysis) arises from the _____.
pharynx
The posterior lobe arises as a ____________.
down growth of the brain
2 hormones travel via the _____ to the _____ pituitary.
hypothalamic-hypophyseal tract; posterior pituitary
7 hormones travel via the _____ to the _____ pituitary
hypophyseal portal system; anterior
Supraoptic & paraventricular nuclei
synthesize 2 hormones that travel along axons in infundibulum to posterior pituitary (axoplasmic transport)
**hormones are stored & later released by posterior pituitary)
ADH (Antidiuretic Hormone)
What is the stimuli & effect?
Stimuli: ↑ blood osmolarity, ↓ in blood volume or pressure, dehydration
Effect: targets kidneys to preserve water & promotes thirst
Oxytocin
What is the stimuli & effect?
Stimuli: suckling, cervical & uterine stretching
Effect: ejection of milk from mammary glands, uterine contractions
7 hormones travel to the anterior pituitary: ___ are releasing hormones and ___ are inhibiting hormones
5; 2
Releasing Hormones
stimulate synthesis & secretion of hormone(s) in anterior pituitary
Inhibiting Hormones
prevent synthesis & secretion of hormone(s) in anterior pituitary
What are the 7 hormones traveling to the anterior pituitary?
1. Prolactin Releasing Hormone (PRH)
2. Prolactin Inhibiting Hormone (PIH)
3. Thyrotropin Releasing Hormone (TRH)
4. Corticotropin Releasing Hormone (CRH)
5. Growth Hormone Releasing Hormone (GHRH)
6. Growth Hormone Inhibiting Hormone (GHIH)
7. Gonadotropin Releasing Hormone (GnRH)
The anterior pituitary synthesizes and secretes ____ hormones in response to stimuli from the ___ hypothalamic hormones
7; 7
What are the 7 hormones that the anterior pituitary synthesizes and secretes?
1. Prolactin (PRL)
2. Thyroid-stimulating hormone (TSH)
3. Adrenocorticotropic hormone (ACTH)
4. Growth hormone (GH)
5. Follicle stimulating hormone (FSH)
6. Luteinizing hormone (LH)
7. Melanocyte-stimulating hormone (MSH)
Prolactin Releasing Hormone (PRH)
What is the target and effect(s)?
Target:
anterior pituitary
Effect:
stimulates anterior pituitary to release PRL
Prolactin Inhibiting Hormone (PIH)
What is the target and effect(s)?
Target:
anterior pituitary
Effect:
prevents anterior pituitary from releasing PRL
Prolactin (PRL)
What is the target, effect(s), and stimulus?
Target:
mammary glands
Effect:
stimulates milk production in females; male function not understood
Stimuli:
↓ PIH (late pregnancy); after birth - suckling stimulates PRH release (further stimulating PRL release)
Thyrotropin Releasing Hormone (TRH)
What is the target and effect(s)?
Target:
anterior pituitary
Effect:
stimulates anterior pituitary to release TSH
Thyroid Stimulating Hormone (TSH)
What is the target and effect(s)?
Target:
thyroid gland
Effect:
stimulates release of thyroid hormones (T₃ & T₄)
Corticotropin Releasing Hormone (CRH)
What is the target and effect(s)?
Target:
anterior pituitary
Effect:
stimulates anterior pituitary to release ACTH
Adrenocorticotropic Hormone (ACTH)
What is the target and effect(s)?
Target:
adrenal cortex
Effect:
stimulates release of adrenocortical hormones (esp. glucocorticoids)
Growth Hormone Releasing Hormones (GHRH)
What is the target and effect(s)?
Target:
anterior pituitary
Effect:
stimulates anterior pituitary to release GH
Growth Hormone Inhibiting Hormone (GHIH)
What is the target and effect(s)?
Target:
anterior pituitary
Effect:
prevents anterior pituitary from releasing GH
Growth Hormone (GH)
What is the target, effect(s), and stimulus?
Target:
most cells, primarily bone & skeletal muscle
Effect: stimulates cell growth & replication by increasing protein synthesis (causes lengthening of bone, increase in muscle mass, etc)
Stimulus:
GHRH, hypoglycemia*, exercise, stressors

*encourages use of fat for fuel (conserves glucose)
Gonadotropin Releasing Hormone (GnRH)
What is the target and effect(s)?
Target:
anterior pituitary
Effect:
stimulates release of LH and FSH
Gonadotropin Releasing Hormone (GnRH)
What is the target and effect(s)?
Target:
anterior pituitary
Effects:
stimulates release of LH and FSH
Follicle Stimulating Hormone (FSH)
What is the target and effect(s)?
Target:
gonads
Effects:
stimulate gamete production
Luteinizing Hormone (LH)
What is the target and effect(s)?
Target:
gonads
Effects:
stimulate production of sex hormones
Melanocyte Stimulating Hormone (MSH)
What is the target and effect(s)?
Target:
melanocytes of the skin
Effect:
increase melanin production; important in control of skin pigmentation in other vertebrates (in humans functional significance unknown)
Name the hormone in the unlabeled spaces below:
a
Negative feedback loops affecting hypothalamus and anterior pituitary
image here
Identify the structures
A: Pineal Gland
B: Hypothalamus
C: Pituitary Gland
D: Thyroid Gland
E: Parathyroid Gland
F: Thymus Gland
G: Adrenal Gland
H: Pancreas
I: Gonads (Ovaries)
J: Gonads (Testes)