Lecture 16- Homeostasis Flashcards
Does blood pressure change over a long period of time?
-no remains very similar despite stress and eating, exercise etc.
Does blood pressure change very much in response to intake of salt?
-no -still remains constant (reasonably) -homeostasis
How is heart beat and blood pressure affected in a rat with sinoartic denervation?
- heart rate is stable as it is not receiving the signal to change -the blood pressure is all over the place, every time it moves etc causes dramatic change in bp -due to loss of reflex circuitory
What is the relationship of heart beat and blood pressure?
-heart beat changes to keep blood pressure within normal range
Why is blood pressure dangerous?
-life expectancy is short= the variation in bp causes hypertrophy of the muscle, becomes floppy and can cause a dislodgement of clot with high spike in blood pressure
What is the role of insulin?
-brings levels of glucose down after a meal
What are the two types of homeostasis we can consider?
-whole body -cellular
Why do you not want change in neuronal excitability?
-control breathing etc.
What determines the excitability of neurons?
-the ion channels they express
How often are the ionic channels in neurons recycled?
-every few weeks
What are the two types of maintaining the excitability in neurons?
-activity dependent expression -activity independent coupled expression
Does the excitability of a neuron remain stable over a lifetime?
-yes
What is the activity dependent neuronal homeostasis mechanism?
-if new channel is expressed on the membrane that alters the excitability of the cell then within a very short period of time (minutes) will lead to expression of ion channels that will bring the cell’s activity back to normal -happens too quickly to be genetic expression, there must be channels ready to respond to change!
What is the activity independent neuronal homeostasis mechanism?
- activity independent coupled expression
- certain channels responsible for cellular excitability that if expression of one goes up, this one goes up, so at genetic level cell is looking to decrease the changes
- so have positive go up in expression, negative will also go up in expression so that you come down to zero sum
What will happen here?
- two chambers, semi-permeable membrane only to H2O not NaCl, higher concentration of NaCl in one half and H2O will move there so end up with equal ionic concentration
- but if this happens in a closed chamber then also increase pressure= volume!
What happens to a cell when more solute enters?
-with solute comes more water= larger volume thus the cell swells
What happens to a cell when solute leaves?
-with solute leaves water= thus smaller volume and the cell will shrink
What is regulatory volume decrease and increase?
-
What is the short term solution for cells to maintain normal volume?
- when too much solute (thus volume) have transporters that take out the solute out of the cell and decrease volume of the cell
- when too little solute the opposite happens, and solute brought in, with it comes water and the volume increases
- ionic transporters -electrolytes
What is the problem with cells solving adjusting their volume with adjusting ionic concentrations?
-long term becomes a problem= as the solute concentration is important for membrane potential, determining the excitability of the cell, if you change the ion concentration too much then changing the excitability of the cell as well
What is the longterm solution of cells to maintain their volume?
-if require more or less fluid make proteins that have osmotic potential but don’t influence the membrane potential
What are the proteins involved in maintaing cell volume? -the osmolytes
-amino acids -polyols -methylamines
What happens to a person who has very low Sodium?
-high blood pressure (aldosterone blocker pill= causes loss of Sodium) -most people respond ok, some lose sodium at a remarkable rate -delirious, vouldn’t tell where she was etc. -then the neuronal cells couldn’t maintain homeostasis so brain function from normal to rubbish -got a drip and fine in an hour
Do all mammals maintain the osmolarity as strictly as humans do?
-yes irrespective of being aquatic
How does exercise affect osmolarity?
- when have fluids during= osmolarity before and after remains very similar
- if don’t have fluids then osmolarity after is much higher
- if have mouthwash, then feel less thirsty but osmolarity just as high as with no fluid
What does change of 10mOsm per kilo do to a person?
-too much salt= can lead to reduced learning, headaches, -changes in the other direction can lead to delirium (too little salt)
What is the body’s response when you’re hypertonic (too much salt)?
- increase in thirst (more water intake)
- increase in vasopressin secretion(water retention)
- decrease Na+ appetite (this not very strong in people)
- increase in natriuresis (excretion of Na+ in urine)
What is the body’s response when you’re hypotonic?(too little salt)
- decrease in thirst(less water intake)
- increase in Na+ appetite(salt intake)
- decrease in Vasopressin secretion (leads to more water excretion)
- decrease in Natriuresis (Na+ retention instead of going with urine)
What is the set point if osmolarity in a human?
290 mOsm per kilo
What are the two types of sensors that detect changes in osmolarity?
-sensors in digestion -sensors in blood -send information to the brain
Where are the sensors in the body detecting changes in osmolarity?
-splanchnic mesentry -gastrointestinal tract - (pharynx-esophagus) -and hepatic portal vein
What are the circumventricular organs?
-OVLT part of this (also AP, PP) -have no blood brain barrier, so changes in plasma concentrations of peptides or so,that wouldn’t normally get to the brain are able to this way! -specialised in order to sense plasma concentration
What is OVLT?
- major sensor of plasma osmolarity, contains cells that are responding to very small changes in plasma osmolarity = and they don’t accommodate to the changes, faithful representers to the change= signal the brain that behaviour needs to change to change osmolarity
What areas of the brain are involved in thirst?
- OVLT in lamina terminalis= involved in the sensation of thirst
- angular cingulate cortex (ACC)=saying I am thirsty (our perception of thirst)
How does angular cingulate cortex ACC behave when take in water?
- as soon as drink some water it decrease in activity as the pharyngeal sensors send info to it saying water coming in
- this is despite that the osmolarity has not changed! (tricked)
How does lamina terminalas behave when take in water?
- doesn’t respond very much
- depends on the osmolarity of plasma not if you drink water or not
How does the activity of OVLT neurons change when osmolarity changes?
- recording of an OVLT neuron, change the osmolarity= can see the cells faithfully represent the changes in osmolarity, the bigger the change the bigger the response
- also a linear representation of the osmolarity and firing of the OVLT cells
What do the osmoreceptors respond to? (exact)
-it is the volume of the cell that is important -the osmoreceptors do not have the transporters that allow them to respond to changes in solute concentration so their volume changes -change size in response to change in osmolarity= that is the signal conductance= cation action (so decrease means excited = activity) -something within the cell is changing the conductance, opening a cation channel in response to swelling or shrinking -link of size of cell to excitability of cell
What is happening here?
- G = conductance, decreases=something excitatory happens in the cell
- then suck out the interior of the cell (so just changing the volume, then conductance back to normal
What is the role of TRPV1 in osmoreception?
-the channel responsible for the link between volume and excitability -if expressed then can detect the osmolarity -if doesn’t have it no response to volume change
Where is vasopressin produced and secreted?
-in the brain, in the hypothalamus in the magnocellular cells
Where are the magnocellular neuronal cells of the thalamus?
-along the midline of the thalamus
What is hypothalamus important for?
-maintaining homeostasis
What is the relationship of alcohol and vasopressin?
-alcohol inhibits secretion of vasopressin= must pee
How does the vasopressin get from the brain to the kidney?
-via posterior pituitary
Where are the neurons of vasopressin?
-in the paraventricular and supraoptic nucleus of the hypothalamus
