Endocrine System Flashcards
The endocrine system influences metabolic activity by means of _________.
hormones
Steroidal or amino acid-based molecules released to the blood that act as chemical messengers to regulate specific body functions. Long-distance chemical signals that travel in blood or lymph throughout the body.
Hormones
- Initiates responses rapidly
- Short-duration responses
- Acts via action potentials and neurotransmitters
- Acts at specific locations determined by axon pathways
- Neurotransmitters act over very short distances
Nervous System
- Initiates responses slowly
- Long-duration responses
- Acts via hormones released into the blood
- Acts at diffuse locations-targets can be anywhere blood reaches
- Hormones act over long distances
Endocrine System
The scientific study of hormones and the endocrine organs is called
Endocrinology
Two kinds of glands are:
Endocrine Glands
Exocrine Glands
Produce nonhormonal substances, such as sweat and saliva, and have ducts that carry these substances to a membrane surface.
Exocrine glands
Also called ductless glands, produce hormones and lack ducts. They release their hormones into the surrounding tissue fluid, and typically have a rich vascular and lymphatic drainage that receives their hormones.
Endocrine glands
Most of the hormone-producing cells in ________ _______ are arranged in cords and branching networks, which maximizes contact between them and the surrounding capillaries.
endocrine glands
The hypothalamus, along with its neural functions, also produces and releases hormones, so we consider the hypothalamus a ________ _________
neuroendocrine organ
The endocrine glands include:
- Pituitary
- Thyroid
- Parathyroid
- Adrenal
- Pineal Glands
Organs that contain endocrine tissue include:
- Pancreas
- Gonads (ovaries/testes)
- Placenta
The major processes that hormones control and integrate include:
- Reproduction
- Growth and development
- Maintenance of electrolyte, water, and nutrient balance of the blood
- Regulation of cellular metabolism and energy
- Mobilization of body defenses
Short-distance chemical signals that exert their effects on the same cells that secrete them. For example, certain prostaglandins released by smooth muscle cells cause those smooth muscle cells to contract.
Autocrines
Short-distance chemical signals. They act locally (within the same tissue) but affect cell types other than those releasing the paracrine chemicals. For example, somatostatin released by one population of pancreatic cells inhibits the release of insulin by a different population of pancreatic cells.
Paracrines
A hormone’s chemical structure determines one of its critical properties: its ________ in water
solubility
A hormones ______ _______ affects how that hormone is transported in the blood, how long it lasts before it is degraded, and what receptors it can act upon.
water solubility
Most hormones are based on _____ ______. Molecular size varies widely in this group—from simple amino acid derivatives, to peptides, to proteins. These hormones are usually water soluble and cannot cross the plasma membrane.
amino acids
Include biogenetic amines (e.g. epinephrine) and thyroxine.
amino acid derivatives
Short chains of amino acids
peptides
Long polymers of amino acids
proteins
A class of lipids derived from (and including) cholesterol; act as hormones and as constituents of phospholipid bilayer membranes.
Steroids
Of the hormones produced by the major endocrine organs, only ______ and __________ hormones are steroids. These hormones are all lipid soluble and can cross the plasma membrane.
gonadal; adrenocortical
Signaling chemicals that mediate inflammation and some allergic reactions
Leukotrienes
Have multiple targets and effects, ranging from raising blood pressure and increasing the expulsive uterine contractions of birth to enhancing blood clotting, pain, and inflammation.
Prostaglandins
Include leukotrienes and prostaglandins. Nearly all cell membranes release these biologically active lipids (made from arachidonic acid).
Eicosanoids
Because the effects of eicosanoids are typically highly localized, affecting only nearby cells, they generally act as _______ and ________ and do not fit the definition of true hormones.
paracrines; autocrines
Influence distant targets.
True hormones
All major hormones circulate to virtually all tissues, but a hormone influences the activity of only those tissue cells that have receptors for it. These cells are its _______ ______.
target cells
Hormones bring about their characteristic effects by _______ target cell activity, increasing or decreasing the rates of normal cellular processes.
altering
A hormone typically produces one or more of the following changes:
- Alters _______ _______ permeability or ________ potential, or both, by opening or closing ion channels
- Stimulates synthesis of ______ and other _______ within the cell
- Activates or deactivates _______
- Induces _______ activity
- Stimulates _______
- Plasma membrane; membrane
- enzymes; proteins
- enzymes
- secretory
- mitosis
Hormones act at receptors in one of two ways:
Water-soluble hormones and Lipid-soluble hormones
(all amino acid–based hormones except thyroid hormone) act on receptors in the plasma membrane. These receptors are usually coupled via regulatory molecules called G proteins to one or more intracellular second messengers, which mediate the target cell’s response.
Water-soluble hormones
(steroid and thyroid hormones) act on receptors inside the cell, which directly activate genes.
Lipid-soluble hormones
Receptors for water-soluble hormones must be in the plasma membrane since these hormones ______ diffuse across the plasma membrane
cannot
Receptors for lipid-soluble steroid and thyroid hormones are inside the cell because these hormones ____ diffuse across the plasma membrane into the cell.
can
Intracellular molecule generated by the binding of a chemical (e.g. hormone or neurotransmitter) to a receptor protein; mediates intracellular responses to the chemical messenger
Second messengers
With the exception of thyroid hormone, ______ ____–______ hormones exert their signaling effects through intracellular second messengers generated when a hormone binds to a receptor in the plasma membrane.
amino acid-based
Involves the interaction of three plasma membrane components—a hormone receptor, a G protein, and an effector enzyme (adenylate cyclase)—to determine intracellular levels of cyclic AMP.
Cyclic AMP Signaling Mechanism
Steps in cycling AMP signaling mechanism:
- ________ binds receptors
- Receptor activates ____ _______
- G protein activates _______ _______
- Adenylate cyclase converts ______ to ______ _____
- Cyclin AMP activates ______ _______
- Hormone
- G protein
- adenylate cyclase
- ATP; cyclic AMP
- protein kinases
Protein that relays signals between extracellular first messengers (such as hormones or neurotransmitters) and intracellular second messengers (such as cyclic AMP) via an effector enzyme
G protein
G protein is “off” when _____ is bound to it, and “on” when _____ is bound to it
GDP; GTP
Hormone binding causes the receptor to change ______, allowing it to bind a nearby inactive G protein
shape
Enzyme that makes the second messenger cyclic AMP (cAMP) from ATP
Adenylate cyclase
For as long as activated Gs is bound to it, adenylate cyclase generates the _______ ________ cAMP from ATP.
second messenger
Enzyme that phosphorylates a protein (transfers an inorganic phosphate from ATP to the protein), resulting in activation or inactivation of the protein
Protein kinases
Add a phosphate group to
Phosphorylate
The action of cAMP persists only briefly because the molecule is rapidly degraded by the intracellular enzyme _________
phosphodiesterase
In the PIP2-calcium signaling mechanism, intracellular _______ ____ act as a second messenger.
calcium ions
The PIP2-calcium signaling mechanism involves a G protein (Gq) and a membrane-bound effector, in this case an enzyme called ________ ___
phospholipase C
Phospholipase C splits a plasma membrane phospholipid called PIP2 (phosphatidyl inositol bisphosphate) into two second messengers:
diacylglycerol (DAG) and inositol trisphosphate (IP3)
Activates a protein kinase enzyme, which triggers responses within the target cell
Diacylglycerol (DAG)
Releases Ca2+ from intracellular storage sites.
Inositol trisphosphate (IP3)
The liberated Ca2+ also takes on a second-messenger role, either by directly altering the activity of specific enzymes and channels or by binding to the intracellular regulatory protein ________. Once bound, it activates enzymes that amplify the cellular response.
calmodulin
Thyroid hormone receptors are always bound to ____ even in the absence of thyroid hormone
DNA
When the receptor-hormone complex binds to DNA, it “turns on” a gene; that is, it prompts transcription of DNA to produce a ______
mRNA
The synthesis and release of most hormones are regulated by some type of _______ ________ _______
negative feedback mechanism
In such a mechanism, some internal or external stimulus triggers hormone secretion. As levels of a hormone rise, it causes target organ effects, which then feed back to inhibit further hormone release.
Negative Feedback Mechanism
Three types of stimuli trigger endocrine glands to manufacture and release their hormones:
humoral, neural, and hormonal stimuli
Secrete their hormones in direct response to changing blood levels of certain critical ions and nutrients. The simplest endocrine controls
Humoral Stimuli
Refers to moisture or bodily fluids
Humor
Hormones released in response to humoral stimuli include insulin (released in response to increased _______ _______) and aldosterone (released in response to low ____ or high _____ blood levels).
blood glucose; Na+ or K+
Nerve fibers stimulate hormone release. A response to stress in which the sympathetic nervous system stimulates the adrenal medulla to release norepinephrine and epinephrine.
Neural stimuli
Release their hormones in response to hormones produced by other endocrine organs. Promote rhythmic hormone release, with hormone blood levels rising and falling in a specific pattern.
Hormonal stimuli
It is the _______ _______ that makes certain adjustments to maintain homeostasis by overriding normal endocrine controls.
nervous system
The action of insulin and several other hormones normally keeps blood glucose levels in the range of ___–____ mg/100 ml of blood.
90-110mg
Hormone release is caused by another hormone
Tropic hormone
Reinforce sympathetic responses that help us deal with stress
Epinephrine and norepinephrine
Action potentials require ________ channels, whereas graded potentials require ________ channels.
voltage-gated; chemically gated
In order for a target cell to respond to a hormone, the cell must have specific _______ proteins on its plasma membrane or in its interior to which that hormone can bind
receptor
Although binding of a hormone to a receptor is required, the degree of target cell activation depends equally on three other factors:
- Blood levels of the hormone
- Relative numbers of receptors for that hormone on or in target cells
- Affinity (strength) of the binding between the hormone and the receptor
For a given level of hormone in the blood, having a large number of _____-______ receptors produces a pronounced hormonal effect, and having a smaller number of ____-______ receptors reduces the target cell response or causes outright endocrine dysfunction.
high-affinity; low-affinity
Persistently low levels of a hormone can cause its target cells to form additional receptors for that hormone.
Up-regulation
Prolonged exposure to high hormone concentrations can decrease the number of receptors for that hormone. This ______- ______ desensitizes the target cells, so they respond less vigorously to hormonal stimulation, preventing them from overreacting to persistently high hormone levels.
Down-regulation
Hormones circulate in the blood in two forms—_____, or bound to a _______ carrier
free; protein
Lipid-soluble hormones (steroids and thyroid hormone) are not ______ _______. As a result, they must travel in blood attached to proteins of the blood plasma (plasma proteins).
water soluble
The concentration of a circulating hormone in blood at any time reflects (1) its rate of ________ and (2) the speed at which it is _________ and removed from the body.
release; inactivated
Most hormones are removed from the blood by the _______ or ______, and the body excretes their breakdown products in urine or, to a lesser extent, in feces
kidneys; liver
The length of time for a hormone’s blood level to decrease by half
half-life
_________ hormones have the shortest half-lives because they are rapidly removed from the blood by the kidneys.
Water-soluble
_______ hormones require hours to days before their effects are seen
Steroids
Many characteristics of a hormone (such as its half-life and the time it takes to have an effect) depend on its solubility in ______ or ______
water; lipids
Lipid-soluble hormones consist of all _______ hormones and ______ hormones
steroid; thyroid
Water-soluble hormones consist of all ______ _____-_______ hormones except thyroid hormones
amino acid-based
Sources of lipid-soluble hormones are:
- Adrenal cortex
- Gonads
- Thyroid gland
Sources of water-soluble hormones are:
All other endocrine glands
Lipid-soluble hormones are _____ stored in secretory vesicles
not
Water-soluble hormones _____ stored in secretory vesicles
are
Lipid-soluble hormones are bound to ______ _______
plasma proteins
Water-soluble hormones are usually _______ in plasma
free
Lipid-soluble hormones have a _____ half-life in blood
long
Water-soluble hormones have a ______ half-life in blood
short
Lipid-soluble hormone receptors are usually located _______ the cell
inside
Water-soluble hormone receptors are located on _______ __________
plasma membranes
Lipid-soluble hormones activate ______, causing synthesis of new proteins
genes
Water-soluble hormones usually act through _______-________ systems
second-messenger
Three types of hormone interaction:
permissiveness, synergism, and antagonism.
The situation in which one hormone cannot exert its full effects without another hormone being present.
Ex. Thyroid hormone is also necessary for normal timely development of reproductive structures
Permissiveness
Occurs when more than one hormone produces the same effects at the target cell and their combined effects are amplified.
Ex. Both glucagon and epinephrine cause the liver to release glucose to the blood
Synergism
Occurs when one hormone opposes the action of another.
Ex. Insulin, which lowers blood glucose levels, is antagonized by glucagon, which raises blood glucose levels.
Antagonism
Neuroendocrine gland located beneath the brain that serves a variety of functions including regulation of gonads, thyroid, adrenal cortex, lactation, and water balance. Securely seated in the sella turcica of the sphenoid bone, it secretes at least eight hormones.
Pituitary gland
To grow under
Hypophysis
- A stalk of tissue that connects the pituitary gland to the hypothalamus; 2. The distal end of the uterine (fallopian) tube
Infundibulum
In humans, the pituitary gland has two major lobes:
Posterior pituitary lobe and anterior pituitary lobe
Neural part of pituitary gland; part of the neurohypophysis. Composed largely of neural tissue such as pituicytes and nerve fibers. It releases neurohormones (hormones secreted by neurons) received ready-made from the hypothalamus. A hormone-storage area and not a true endocrine gland.
Posterior pituitary
Posterior pituitary plus plus infundibulum; portion of the pituitary gland derived from the brain.
Neurohypophysis
The glandular part of the pituitary gland. Also called adenohypophysis. It manufactures and releases a number of hormones.
Anterior pituitary
__________ branches of the internal carotid arteries deliver arterial blood to the pituitary.
Hypophyseal
Bundle of axons that runs through the infundibulum and connects the posterior pituitary to the hypothalamus. Arises from neurons in the paraventricular and supraoptic nuclei of the hypothalamus.
Hypothalamic-hypophyseal tract
The _______ _______ _______ originates from epithelial tissue as a superior outpocketing of the oral mucosa
glandular anterior lobe
There is no direct neural connection between the anterior lobe and hypothalamus, but there is a ________ connection
vascular
The _______ ______ _______ in the infundibulum communicates inferiorly via the small hypophyseal portal veins with a secondary capillary plexus in the anterior lobe.
primary capillary plexus
The primary and secondary capillary plexuses and the intervening hypophyseal portal veins make up the ________ _______ _______
hypophyseal portal system
An unusual arrangement of blood vessels in which a capillary bed feeds into veins, which in turn feed into a second capillary bed.
portal system
Via the hypophyseal portal system, ________ and ________ hormones secreted by neurons in the ventral hypothalamus circulate to the anterior pituitary, where they regulate secretion of its hormones.
releasing; inhibiting hormones
The _______ _______ ensures that the minute quantities of hormones released by the hypothalamus arrive rapidly at the anterior pituitary without being diluted by the systemic circulation.
portal system
All these hypothalamic regulatory hormones are ______ ______ based, but they vary in size from a single amine to peptides to proteins.
amino acid
The paraventricular neurons primarily make _______
oxytocin
The supraoptic neurons mainly produce ________ _________
antidiuretic hormone (ADH)
Oxytocin and ADH, each composed of ____ amino acids, are almost identical. They differ in only two amino acids.
nine
Hormone synthesized in the hypothalamus and secreted by the posterior pituitary; stimulates contraction of the uterus during childbirth and the ejection of milk during nursing.
Oxytocin
Oxytocin acts via the _____−_____ second-messenger system to mobilize Ca2+, allowing stronger contractions.
PIP2−Ca2+
_________ causes a reflex-initiated release of oxytocin, which targets specialized myoepithelial cells surrounding the milk-producing glands.
Suckling
Both childbirth and milk ejection result from _______ _______ ________
positive feedback mechanism
Acts as a neurotransmitter in the brain. Involved in sexual and affectionate behavior (as the “cuddle hormone”), and promotes nurturing, couple bonding, and trust.
Oxytocin
oxy-
rapid
-tocia
childbirth
Urine production
Diuresis
A substance that inhibits or prevents urine formation
Antidiuretic
Hormones produced by the hypothalamus and released by the posterior pituitary; stimulates the kidneys to reabsorb more water, reducing urine volume
Antidiuretic hormone (ADH)
Hypothalamic neurons called _________ continually monitor the solute concentration (and thus the water concentration) of the blood.
osmoreceptors
ADH targets the ______ tubule cells, which respond by reabsorbing more water from the forming urine and returning it to the bloodstream.
kidney
Under certain conditions, such as severe blood loss, exceptionally large amounts of ADH are released, causing vasoconstriction and raising blood pressure. This response targets different ADH receptors found on vascular smooth muscle. For this reason, ADH is also called _________.
vasopressin
Disease characterized by passage of a large quantity of dilute urine plus intense thirst and dehydration caused by inadequate release of antidiuretic hormone (ADH). Can be caused by a pituitary tumor or by a blow to the head that damages the hypothalamus or the posterior pituitary.
Diabetes insipidus
___________ of ADH, can occur in children with meningitis, or in adults who have neurosurgery, hypothalamic injury, or cancer (particularly lung cancer) in which cancer cells are additional sources of ADH
Hypersecretion
Marked by retention of fluid, headache and disorientation due to brain edema, weight gain, and decreased solute concentration in the blood
syndrome of inappropriate ADH secretion (SIADH)
The _________ is known to control the activity of the anterior pituitary.
hypothalamus
The anterior pituitary releases ____ hormones, all of them peptides or proteins—growth hormone, thyroid-stimulating hormone, adrenocorticotropic hormone, follicle-stimulating hormone, luteinizing hormone, and prolactin
six
diabetes =
overflow
insipidus =
tasteless
______ of the six anterior pituitary hormones—thyroid-stimulating hormone, adrenocorticotropic hormone, follicle-stimulating hormone, and luteinizing hormone—are tropic hormones or tropins that regulate the secretory action of other endocrine glands
Four
A hormone that regulates the secretory action of another endocrine organ
Tropic hormones
tropi =
turn on, change
__________ cells of the anterior lobe produce growth hormone
Somatotropic
Hormone that stimulates growth in general; produced in the anterior pituitary; also called somatotropin
Growth Hormone (GH)
Acting directly, GH exerts ________ effects
metabolic
GH mediates most of its growth-enhancing effects indirectly via a family of growth-promoting proteins called ______-______ _______ _______(IGFs)
insulin-like growth factors
Hypersecretion in children results in ________ because GH targets the still-active epiphyseal (growth) plates.
gigantism
Literally translated as “enlarged extremities,” this condition is characterized by overgrowth of bones of the hands, feet, and face
Acromegaly
Anterior pituitary hormone that regulates secretion of thyroid hormones
Thyroid Stimulation Hormone (TSH)
The hypothalamic peptide _______-______ _______ triggers the release of TSH from thyrotropic cells of the anterior pituitary.
thyrotropin-releasing hormone (TRH)
Anterior pituitary hormone that influences the activity of the adrenal cortex. Secreted by the corticotropic cells. Stimulates the adrenal cortex to release corticosteroid hormones, most importantly glucocorticoids that help the body resist stressors.
Adrenocorticotropic hormone (ACTH)
