Term
| Name 7 mechanical roles that water has in the body |
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Definition
moistening tissues
protecting organs/tissues (acts as cushion)
regulation of body temperature (sweating)
lubrication of joints
elimination of feces
vehicle to deliver nutrients and oxygen
flushing out waste/toxins (kidneys/liver) |
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Term
| approximately ___% of total body mass is water |
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Definition
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Term
| name 2 problems that continuous dehydration can lead to |
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Definition
neurological problems
renal problems |
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Term
| Explain the modern understanding of thirst in broad terms: what systems are involved in thirst? |
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Definition
| both periheral cues and CNS processing are involved in thirst |
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Term
Intracellular fluid makes up ___% of all body fluid. The main intracellular fluid is ______.
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Definition
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Term
Extracellular fluid makes up ___% of all body fluid.
Name three extracellular fluids. |
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Definition
33%
Interstitial Fluid
Intravascular Fluid
Cerebrospinal fluid
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Term
| what controls intracellular fluid exchange? |
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Definition
| interstitial fluid osmolality |
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Term
| Explain the difference between hypotonic isotonic and hyertonic environments in interstital fluid |
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Definition
hypotonic- fewer particles than blood
isotonic- same number of particles as blood
hypertonic- more particles than blood |
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Term
| Name the 2 forces that govern fluid exchange |
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Definition
osmotic pressure
starling equilibrium |
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Term
| name the 2 forces at work that alow for the starling equilibrium. |
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Definition
oncotic pressure
hydrostatci pressure |
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Term
| explain the difference in water movement from/to a cell in interstitial fluid is hypertonic vs hypotonic |
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Definition
hypertonic interstitial fluid- causes water to leave the cell (cellular dehydration)
hypotonic interstitial fluid- causes water to enter cell (too much water can cause cell rupture) |
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Term
| what is oncotic pressure? |
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Definition
| oncotic pressure is a specialized form of osmotic pressure that only accounts for mosmotic pressure determined by intravascular plasma protein concentrations (i.e. proteins in intravascular fluid attracts fluids away from interstitial space) |
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Term
| what is hydrostatic pressure? |
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Definition
| hydrostatic pressure is due to a difference in pressure between arteries and veins (i.e. higher pressure of intravascular fluid in ateries drives fluid from intravascula space to intersititial space.) |
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Term
Name the two components of thirst.
How does each occur? |
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Definition
Osmotic thirst- intracellular depletion of water
Hypovolemic thirst- extracellular depletion of water |
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Term
| Explain how water deprivation leads to osmometric thirst and volumetric thirst. |
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Definition
| There is a loss of water from inerstitial fluid as it moves to intracellular and intravascular spaces via osmotic processes (leaving interstital fluid hypertonic). Without replacement of water, hypertonic interstitial fluid will draw water from the intracellular and intravascular spaces causing hypertonic intracellular spaces (osmometric thirst) and decrease in blood volume (volumetric thirst). |
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Term
Explain the differences in intracellular fluid, blood and extracellular fluid volume and amount of water consumed by rats injected with regular water vs. salie after a night of water deprivation.
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Definition
Regular water injection: water moves mainly to dehydrated cells, little effect on blood volume, drank 70% less water than water-deprived rates not injected.
Saline injected: saline not taken into dehydrated cells, only effects volume of extracellular body fluid, drank 25% less water than water-deprived rates not injected.
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Term
| Name two things that can trigger osmotic thirst. |
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Definition
Simple dehydration
High Salt Meal |
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Term
| Explain how a high salt meal can trigger osmotic thirst. |
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Definition
A high salt meal will make vascular, interstitial, and intracellular fluids hypertonic.
Eventually excess water and sodium is drawn into vasculature and excreted by the kidneys. |
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Term
| what senses osmometric thirst? |
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Definition
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Term
| explain how osmoreceptors can sense osmometirc thirst |
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Definition
| osmoreceptors are specialized neurons whose firing rate will increase when water loss causes decrease in volume of cell. water loss occurs as a result of hypertonic interstitial fluid that draw water out of osmoreceptors. |
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Term
| _________ _________ are regions in the brain that lack a blood brain barrier in the forebrain |
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Definition
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Term
| name two places that osmoreceptors can be found |
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Definition
OVLT and SON
OVLT- organum vacsulosum of the lamina terminalis
SON- supraoptic nucleus
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Term
| explain how the osmoreceptors of the OVLT and SON can vary their signaling dependent on tonicity |
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Definition
Stretch-inhibited (SI) ion channels are expressed on OVLT and SON neurons.
Under hypertonic conditions: cause shrinkage of osmosenstive cells increases opening of SI channels causing depolarization (and increased firing)
Under hypotonic conditions: cause swelling of osmosensitive cells, decreasing opening of SI channels inhibiting depolarization
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Term
| briefly describe the direct and indirect methods by which osmoreceptors induce thirst |
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Definition
direct: activation of neural circuits which mediate the experience of thirst
indirect: increased release of vasopressin from posterior pituitary (regulate kidneys) |
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Term
| What is one proposed possibility for the 'thirst center' in the CNS? |
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Definition
| The medial preoptic nucleus (MPN) |
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Term
| explain the proposed neural circuitry that is involved in the 'direct' method of osmoreceptor activation |
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Definition
| activation of osmoreceptors in the OVLT or SON will directly innervate the MPN which modulate drinking behavior. |
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Term
| name two places that the synthesis of Vasopressin precursors occur |
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Definition
magnocellular neurons within the hypothalamic nuclei (SON and PVN)
SON- supraoptic nucleus
PVN- Paraventricular nucleus |
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Term
| Where is Vasopressin stored and released from? |
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Definition
| Stored in vesicles of in the posterior pituitary and released from te posterior pituitary directly into the bloodstream |
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Term
| does Vasopressin circulate bound to plasma proteins? |
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Definition
| no- circulates unbound to plasma proteins |
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Term
| what is the approximate half life of vasopressin in the bloodstream? |
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Definition
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Term
| name two things that degrade vasopressin |
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Definition
endo-peptidase
amino-peptidase |
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Term
| Name the three vasopressin receptor subtypes and how their activation is mediated |
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Definition
V1-R: Gq mediated activation of phospholipase C
V2-R: Gαs mediated activation of adenylyl cyclase
V3-R: Gq mediated activation of phospholipase C |
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Term
| ______ are water channel proteins that are expressed in the nephron. |
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Definition
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Term
| what are the 2 main functions of aquaporins? |
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Definition
allow for reabsorption of water
resonsible for excretion of concentrated urine |
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Term
| where does blood enter the kidneys from? |
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Definition
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Term
| how does vasopressin effect the concentration of urine? |
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Definition
| vasopressin causes concentration of urine by promoting reuptake of water from distal tubule, by increasing expression of aquaporins on cell surface of distal tubule, allowing water to exit distal tubule. |
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Term
| how does vasopressin effect vasodilation? |
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Definition
| vasopressin stimulates constriction of blood vessels |
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Term
| what is the projection circuitry involved for vasopressin release? |
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Definition
| OVLT detects ECF osmolality and projects to the PVN and SON. The PVN and SON then project to the posterior pituitary which releases vasopressin into the bloodstream |
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Term
| under normal conditions how does plasma osmolality and plasma vasopressin relate? |
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Definition
| They are directly related: increases in plasma osmolalty increase vasopressin concentrations in a linear manner |
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Term
| Name three instances that are considered exceptions to the 'normal' VP response |
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Definition
Rapid changes in plama osmolality- result in exaggerated VP release
During the act of drinking-rapidly suppresses VP release through afferent pathways originating in the oropharynx
Pregnancy-the osmotic threshold for VP release is lowered in pregnancy
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Term
| how does a decrease in blood pressure effect vasopressin release |
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Definition
| decrease in blood pressure casuses and exponential increase in vasopressin release |
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Term
| how does a high salt meal effect intravascular volume? |
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Definition
| increases volume of intravascular fluid becasuse makes iv fluid hypertonic, which pulls in water |
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Term
| ______ ______ is a rare disease in which the kidneys produce abnormally large volumes of dilute urine |
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Definition
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Term
| explain the difference between neurogenic and nephrogenic subtypes of diabetes insipidus |
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Definition
neurogenic- is caused by a deficiency of vasopressin
nephrogenic- is caused by insensitivity of the kidneys to vasopressin (defective receptors) |
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Term
| explain how osmoreceptors and their inhibitory interneurons can modulate levels of vasopressin that is released |
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Definition
| interneurons are tonically inhibit vasopressinergic neurons of SON and PVN. If osmoreceptor is swollen, the interneuron increases its firing rate, increasing its inhibition. If osmoreceptor is shrunken, the interneuron will not fire as much, decreasing inhibition |
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Term
| what is the reason for volumetric thirst? (what causes it?) |
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Definition
| occurs when volume of blood plasma decreases - i.e. after loss of blood, vomiting, diarrhea |
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Term
| name the two detectors which cause volumetric thirst and where they are each located |
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Definition
juxtaglomerular cells - kidneys
atrial baroreceptors- heart and large blood vessels |
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Term
| what cells release renin? where in the body are these cells found? |
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Definition
| Renin is released by juxtaglomerular cells in the kidneys |
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Term
| what is the precursor to renin? |
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Definition
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Term
| where is the highest concentration of angiotensin converting enzyme found in the body |
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Definition
| vascular endothelium of in the lungs |
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Term
| explain how juxtaglomerular cells receive input from the SNS |
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Definition
| hypotension and hypovolemia cause release of NE. JG cells express beta-adrenergic receptors, which when bound to NE causes release of renin |
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Term
| ___ receptors are in the target organs associated with body fluid homeostasis in response to AngII |
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Definition
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Term
| name two specific ligands for AT1 receptors |
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Definition
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Term
| why is losartan, an AngII receptor blocker, clinically useful for lowerin blood pressure? |
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Definition
decreases vasoconstriction
decreases release of vasopressin from posterior pituitary
decreases release of aldosterone |
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Term
| AngII is a ______, and agent that causes thirst |
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Definition
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Term
| on what part of the brain does AngII take its effect? |
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Definition
| AngII takes effect on the receptors of the SFO (subfornical organ) which then projects to the MPN, SON, and PVN |
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Term
| how are atrial baroreceptors firing rate modulated dependeing on blood volume? |
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Definition
| decreased firing with decrease in blood volume |
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Term
| where do atrial baroreceptors project to in the brain? |
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Definition
nucleus of the solitary tract (NTS) in the medulla
which then projects to the MPN to illicit thirst |
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Term
| explain the pathway of projections that allows response from atrial baroreceptors to affect vasopressin release |
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Definition
| baroreceptors project to NTS, NTS projects to parabrachial nucleus (PBN), which then projects to both SON and PVN to increase release of vasopressin |
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Term
| explain the difference in firing rate of baroreceptors during normal periods vs. during periods of low blood pressure, and how this affects vasopressin release. |
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Definition
under normal conditions, baroreceptors have high rate of firing to tonically inhibit release of vasopressin,
during periods of low blood pressure, there is a decrease in rate of firing of baroreceptors, causing loss of inhibition of VP release |
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Term
| how does hyponatremia affect VP release |
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Definition
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Term
| how does deceased blood volume affect VP release? |
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Definition
| normally stimulates VP release |
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Term
| if a patient has both hypoatremia and blood loss, will they experience an inhibition of VP release or increase of VP release? |
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Definition
| patient will experience inhibition of VP release, because osmotic control overrides volumetric mechanisms |
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Term
| explain the difference between baroreceptor and osmoreceptor connections to PVN and SON neurons, and how this determines what overrides what |
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Definition
baroreceptors synapse on most distal dendrites
osmoreceptors synapse near axon hillock, this allowed osmoreceptors to inhibit any baroreceptor activation of VP release |
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Term
| ingestion of a high salt meal would cause activationg of osmoreceptors in what brain area? |
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Definition
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