Lecture 16- Homeostasis

Question 1

Does blood pressure change over a long period of time?

Answer 1

-no remains very similar despite stress and eating, exercise etc.

Question 2

Does blood pressure change very much in response to intake of salt?

Answer 2

-no -still remains constant (reasonably) -homeostasis

Question 3

How is heart beat and blood pressure affected in a rat with sinoartic denervation?

Answer 3

• 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

Question 4

What is the relationship of heart beat and blood pressure?

Answer 4

-heart beat changes to keep blood pressure within normal range

Question 5

Why is blood pressure dangerous?

Answer 5

-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

Question 6

What is the role of insulin?

Answer 6

-brings levels of glucose down after a meal

Question 7

What are the two types of homeostasis we can consider?

Answer 7

-whole body -cellular

Question 8

Why do you not want change in neuronal excitability?

Answer 8

-control breathing etc.

Question 9

What determines the excitability of neurons?

Answer 9

-the ion channels they express

Question 10

How often are the ionic channels in neurons recycled?

Answer 10

-every few weeks

Question 11

What are the two types of maintaining the excitability in neurons?

Answer 11

-activity dependent expression -activity independent coupled expression

Question 12

Does the excitability of a neuron remain stable over a lifetime?

Answer 12

-yes

Question 13

What is the activity dependent neuronal homeostasis mechanism?

Answer 13

-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!

Question 14

What is the activity independent neuronal homeostasis mechanism?

Answer 14

• 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

Question 15

What will happen here?

Answer 15

• 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!

Question 16

What happens to a cell when more solute enters?

Answer 16

-with solute comes more water= larger volume thus the cell swells

Question 17

What happens to a cell when solute leaves?

Answer 17

-with solute leaves water= thus smaller volume and the cell will shrink

Question 18

What is regulatory volume decrease and increase?

Answer 18

-

Question 19

What is the short term solution for cells to maintain normal volume?

Answer 19

• 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

Question 20

What is the problem with cells solving adjusting their volume with adjusting ionic concentrations?

Answer 20

-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

Question 21

What is the longterm solution of cells to maintain their volume?

Answer 21

-if require more or less fluid make proteins that have osmotic potential but don’t influence the membrane potential

Question 22

What are the proteins involved in maintaing cell volume? -the osmolytes

Answer 22

-amino acids -polyols -methylamines

Question 23

What happens to a person who has very low Sodium?

Answer 23

-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

Question 24

Do all mammals maintain the osmolarity as strictly as humans do?

Answer 24

-yes irrespective of being aquatic

Question 25

How does exercise affect osmolarity?

Answer 25

- 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

Question 26

What does change of 10mOsm per kilo do to a person?

Answer 26

-too much salt= can lead to reduced learning, headaches, -changes in the other direction can lead to delirium (too little salt)

Question 27

What is the body's response when you're hypertonic (too much salt)?

Answer 27

- 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)

Question 28

What is the body's response when you're hypotonic?(too little salt)

Answer 28

- 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)

Question 29

What is the set point if osmolarity in a human?

Answer 29

290 mOsm per kilo

Question 30

What are the two types of sensors that detect changes in osmolarity?

Answer 30

-sensors in digestion -sensors in blood -send information to the brain

Question 31

Where are the sensors in the body detecting changes in osmolarity?

Answer 31

-splanchnic mesentry -gastrointestinal tract - (pharynx-esophagus) -and hepatic portal vein

Question 32

What are the circumventricular organs?

Answer 32

-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

Question 33

What is OVLT?

Answer 33

- 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

Question 34

What areas of the brain are involved in thirst?

Answer 34

- OVLT in lamina terminalis= involved in the sensation of thirst - angular cingulate cortex (ACC)=saying I am thirsty (our perception of thirst)

Question 35

How does angular cingulate cortex ACC behave when take in water?

Answer 35

- 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)

Question 36

How does lamina terminalas behave when take in water?

Answer 36

- doesn't respond very much - depends on the osmolarity of plasma not if you drink water or not

Question 37

How does the activity of OVLT neurons change when osmolarity changes?

Answer 37

- 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

Question 38

What do the osmoreceptors respond to? (exact)

Answer 38

-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

Question 39

What is happening here?

Answer 39

- 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

Question 40

What is the role of TRPV1 in osmoreception?

Answer 40

-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

Question 41

Where is vasopressin produced and secreted?

Answer 41

-in the brain, in the hypothalamus in the magnocellular cells

Question 42

Where are the magnocellular neuronal cells of the thalamus?

Answer 42

-along the midline of the thalamus

Question 43

What is hypothalamus important for?

Answer 43

-maintaining homeostasis

Question 44

What is the relationship of alcohol and vasopressin?

Answer 44

-alcohol inhibits secretion of vasopressin= must pee

Question 45

How does the vasopressin get from the brain to the kidney?

Answer 45

-via posterior pituitary

Question 46

Where are the neurons of vasopressin?

Answer 46

-in the paraventricular and supraoptic nucleus of the hypothalamus