Endocrine System Flashcards
Compare and contrast the general control of body functions by the nervous and
endocrine systems.
Nervous System - Regulates the activity of muscles and glands via electrochemical impulses delivered by neurons.
- initiates responses rapidly
- short duration responses in milliseconds
- acts vis AP’s and neurotransmitters
- acts on SPECIFIC LOCATIONS determined by axon pathways
- act over SHORT distances
Endocrine System- Influences metabolic activity by means of hormones released into the blood
- initiates responses slowly
- long duration responses (minutes, hours, days)
- Acts at DIFFUSE LOCATIONS (any location) targets can be anywhere blood reaches
- act over LONG distances
Distinguish between endocrine and exocrine glands.
Endocrine glands (ductless glands) - produce hormones and lack ducts. They released their hormones into the surrounding (interstitial) tissue fluid
Exocrine glands - secrete product into ducts that travel to the surface of the skin. ex: sweat and saliva
What is a hormone? a target cell?
Hormones- long distance chemical signals that were produces at one site and cause an effect on a different side of the body
Target cell - tissues/cells which have a receptor that is specifically able to recognize and bind to a particular hormone
Distinguish between classical endocrine signaling, paracrine signaling, and autocrine
signaling.
The classical endocrine signaling glands - anterior pituitary, thyroid, parathyroid, adrenal & pineal glands
classical endocrine signaling - circulating hormones are extreted into the blood and travel to DISTANT target cells
paracrine signaling - short-distance chemical signals that act within the same tissue, but affect different cell types other than those releasing the chemicals
autocrine signaling - short distance chemical signals that exert their effects on the same cells that secrete them.
In terms of their general chemistry, hormones can be broadly classified as amino acid-
based (this category includes biogenic amines, peptides, and protein hormones) and
steroid hormones. Explain the basic difference between each of these classes and list
several examples of each class of hormone.
amino acid base - water soluble
-cant travel through the plasma membrane
- have to bind to target cells embedded in the plasma membrane
steroid- lipid soluble
- can diffuse through the plasma membrane
- binds to intracellular receptors (within the cell)
Which class of chemical messenger is derived from cholesterol? from amino acids?
(most hormones are based on) amino acids: biogenic amines (ex: epinephrine and thyroxine) , peptides, proteins
cholesterol : steroid hormones . of the major endocrine organs, only gonadal and adrenocortical hormones are steroids.
Hormones in the biogenic amine class are all derived from a single amino acid. From
what amino acid are the catecholamines (i.e., epinephrine and norepinephrine) and
thyroid hormones derived?
tyrosine
Name the individual steroid hormones presented in this chapter. Identify the site of
secretion for each of the steroid hormones.
gonadal hormone - pituitary gland , triggers the gonads to secrete sex hormones called gondatropins : LH & FSH
adrenocortical - pituitary gland , triggers adrenal gland
Where are the receptors for most amino acid derived hormones located?
on the surface of target cells because hormones cannot pass through plasma membranes of cells
Describe the 5-stepped process of G protein activation (in your explanation include the role of the
hormone, its receptor, GDP, GTP, the alpha subunit and the beta-gamma dimmer).
hormones are the first messengers : it binds to the receptor
THEN
G proteins: involved in hormone-receptor binding (signal transduction)
step 1) Inactive G protein = GDP + alpha subunit + beta + gamma
step 2) ligand-receptor binding – when the G protein binds to the receptor protein, GDP is released for GTP instead
step 3) GTP binds and activates the G protein, which causes the alpha to dissociate. now the GTP is bound to the alpha subunit and beta+ gamma dimmer is there.
Describe the specific steps in the activation of the cAMP second messenger system.
step 1) the hormone-receptor binding activates the G-protein
step 2) G-stimulatory alpha subunit binds to and activates adenylate cyclase
step 3) adenylate cyclase generates cAMP from ATP
- cAMP phosphorylates (adds a phosphate) to protein kinase A, which activates it
- protein kinase A phosphorylates proteins that produce a physiologic effect (triggers the responses of target cells: activates enzymes, stimulates cellular secretion, opens ion channels etc)
step 4) cAMP is degraded by phosphodiesterase (PDE)
Why is cAMP called a “second messenger”?
because it translates the presence of the first messenger-the water soluble hormone into a response inside the cell
What is the function of phosphodiesterase (PDE)? How is PDE activated?
PDE degrades cAMP, lowering its cellular activity and thus reducing the enzyme activity
Activation process:
step 1) hormones bind to receptors associated with inhibitory G proteins (ligand-receptor binding)
- this activates an inhibitory alpha-subunit, which activates PDE
Explain why second messenger systems are said to have an “amplifying effect” on the
initial hormone signal.
because hormones can act through second messengers even in low concentrations since they cause a ripple effect that just amplify
Describe the specific steps in the activation of the PIP2-calcium signal mechanism.
step 1) hormone-receptor binding leads to activation of the G protein
step 2) activated G protein dissociates an alpha-subunit which activates phospholipase C (PLC)
step 3) phospholipase C catalyzes hydrolysis of a membrane phospholipid named PIPI2. and splits it into DAG and IP3 (second messengers)
DAG: Activates protein kinase C
IP3: Causes a release of calcium from the ER and the mitochondria
*Calcium acts kind of like a third messenger and binds to intracellular proteins (like calmodulin) to activate enzymes that amplify the cellular responses.
Name and identify the location of the second messengers of the PIP2-calcium signal
mechanism.
DAG and IP3 ?
dag - stays in plasma membrane
ip3- moves into cytoplasm to er and mitochondria
Identify several chemical messengers that induce signal transduction via
autophosphorylation of their receptor.
Insulin, growth factors and cytokines
Describe the structure of receptor tyrosine kinase (RTK).
two identical subunits
the ligand binding site is extracellular (outside the cell)
the intracellular portion of the molecule has a region with tyrosine kinase activity (meaning it is able to add a phosphate group to tyrosine residues in inside the cell)
Describe the process of signal transduction by the RTK (I suggest you use insulin as the
ligand).
1.) ligand-binding initiates dimerization (when two subunits become one) of the RTK (the tyrosine kinase receptor)
- when insulin binds to the tyrosine kinase enzyme, it adds phosphates to several of its own tyrosines.
2.) the dimerization activates tyrosine kinase activity in both monomers
3.) autophosphorylation (the addition of a phosphate to the receptor) occurs
4.) effector proteins are activated by attaching to the phosphotyrosines residues
- the activated insulin receptor provides docking sites for intracellular relay proteins
that, in turn, initiate a series of protein phosphorylation that trigger specific cell responses
Which hormones affect their target cells by binding to an intracellular receptor?
thyroid and steroid hormones
What is the general mechanism through which the thyroid and steroid hormones
induce changes in their target cell’s metabolism.
direct gene activation
Describe the specific steps in direct gene activation by a lipid-soluble hormone (note
that thyroid hormone also exerts its effect via direct gene activation).
They diffuse through he plasma membrane into their target cells.
There, they bind and activate intracellular receptors.
The activated receptor-hormone complex makes its way to the nuclear chromatin and binds to a specific region of DNA.
*(However, thyroid hormone receptors are always bound to DNA, even in the absence of thyroid hormones)
This alters the rate of transcription or specific genres which leads to the altered rate of translation
- helps modify the structure and or function of the cell
Identify the three types of stimuli that regulate endocrine gland secretion.
humoral stimuli- changes in blood levels (critical ions and nutrients) causes secretion
ex: rise in glucose triggers release of insulin
hormonal stimuli- the release of a hormone in response to another hormone
neural stimuli- a neural stimulus triggers the release of a hormone
ex: Here, neuronal signaling from the sympathetic nervous system directly stimulates the adrenal medulla to release the hormones epinephrine and norepinephrine in response to stress.
Give an example of negative feedback control of hormone secretion.
For example, the hypothalamus produces hormones that stimulate the anterior portion of the pituitary gland. The anterior pituitary
1164 Chapter 37 | The Endocrine System
in turn releases hormones that regulate hormone production by other endocrine glands. The anterior pituitary releases the thyroid-stimulating hormone, which then stimulates the thyroid gland to produce the hormones T3 and T4. As blood concentrations of T3 and T4 rise, they inhibit both the pituitary and the hypothalamus in a negative feedback loop.
How are hormones transported in the blood? Explain the importance of transport
proteins in circulating lipid-soluble hormones.
Water soluble hormones travel through the blood freely because blood is water-based, while lipid-soluble hormones have to be bound to plasma proteins in order to travel faster through the blood (lipids are not attracted to water and move slower)
List the ways in which the hypothalamus contributes to homeostasis of body systems.
-control the ANS
- regulates temperature, hunger, body fluids etc
Name the two active lobes of the adult pituitary gland. Describe the general histology
and identify the embryologic origins of each.
anterior pituitary or adenophypohysis -
- the larger lobe
- develops from an out pocketing of ectodermal cells from roof of mouth
- forms glandular part of the pituitary
posterior pituitary or neurohypophysis -
- forms from an out pocketing of ectodermal cells in embryonic hypothalamus
- consists primarily of neurological cells called pituicytes
- contains axons and axon terminals of neurons whose cell bodies are located in the supraoptic& paraventricular nuclei of the hypothalamus
Describe the hypophyseal portal system, noting the general location of each of the three
main components of the system –i.e., the primary capillary, the hypophyseal portal
veins, and the secondary capillary plexus.
How the hypothalamus communicates with the anterior pituitary
- hypothalamic neurons synthesize and release inhibiting and releasing hormones into the primary capillary plexus
- blood flows from the the primary capillary plexus to the hypophyseal portal veins to the secondary capillary plexus into the anterior pituitary
What is the functional significance of each of the structures noted above (#28)?
primary capillary-
the hypophyseal portal veins-
the secondary capillary plexus-
What cells create the structural and functional relationship between the hypothalamus
and the posterior lobe of the pituitary?
Bundle of axons called hypothalamic - hypophyseal tract running through infundibulum
Neurosecretory cells - when they fire, the release stored hormones into a capillary bed for distribution
What are the hormones associated with the posterior pituitary?
ADH and OT
Where are the posterior pituitary hormones synthesized? where are they stored?
in large neurons of supraoptic and paraventricular nuclei (which synthesize ADH and OT)
They’re stored into the capillary beds of the posterior pituitary
Describe the process through which posterior pituitary hormones are secreted.
1) tract arises in large neurons of supraoptic & paraventricular nuclei - which synthesize/ release ADH & OT
2) hormones pass down the axons of the large neurosensory cells into the posterior pituitary
- the hormones released from axon terminals ( as an NT) fo into the capillary beds of the posterior pituitary
Describe the effects of antidiuretic hormone (ADH) on its target cells and tell how its
secretion is regulated.
when plasma osmolarity increases (meaning its hypertonic, more solutes in the blood) or BP is low, it triggers the osmoreceptors on the hypothalamus to release ADH.
ADH is what brings more water from the kidney collecting ducts that secrete urine, into the blood (which eventually causes the capillaries to expand, increase BP), which decreases the amount of water in your pee
so this explain why when youre dehydrated (and have a lot of solutes in your blood), your pee is concentrated because it is signaling to bring the water out of the urine into the blood
and when youre over hydrated, your osmolarity (amount of solutes) can fall as low as 50-100mOsm because theres not enough of a gradient to signal the release of ADH to bring more water into the blood so it goes out with your urine
Describe the effects of oxytocin (OT) on its target cells and tell how its secretion is
regulated.
Stretching of cervix of the uterus as birth nears dispatches afferent impulses to the hypothalamus which synthesizes oxytocin and releases from posterior pituitary. Also triggered by suckling of babies on nursing women
Causes uterine contraction and ejection of breast milk
Acts via PIP2-CA2+ second messenger system to mobilize Ca 2+ allowing stronger contractions
Positive feedback mechanism
Also promotes nurturing, sexual, affectionate behavior in brain
What is a tropic hormone?
a hormone that regulates the release of hormones by other endocrine glands
