Physiology: Lecture 2 Flashcards
CASE #2
Paramedics respond to a call at a local, authentic Japanese restaurant. A patron is unconscious and cyanotic on the floor. The EMTs rapidly incubate and mechanically ventilate the patient. He is no longer cyanotic, but is severely hypotensive and unresponsive. Patients family report they had just finished dinner when he complained of numbness and tingling of his face. This progressed to an inability to breathe (dyspnea) and finally unconsciousness. Waitstaff performed the Heimlich, nut no foreign body was ejected. Patient is taken to the ER. He is continued on ventilation and is given IV saline to boost his blood pressure. After 24 hours, the patient recovers and is released in perfect health the next day.
What is your diagnosis?
What physiological processes were altered?
- Diagnosis: Blowfish toxin
- Physiologic processes that were altered: membrane and action potential were inhibited by the blowfish toxin, affecting Na from crossing the membrane, stopping the action potentials
Permeability of cell membrane?
Selective permeable; some things (small, non-polar molecules, steroids, oxygen, etc.) can diffuse through membrane
Why can most solutes in the body not cross the membrane?
They are large and/or charged
How is conductance carried out for the solutes that are not able to cross the membrane?
By use of transport proteins and ion channels
The amount of solutes that are able to cross the membrane is based on what?
Number and activity of these proteins
What are ion channels?
Small holes that allow specific size/charge of ion to cross
What is conductance based on within ion channels?
The number of channels that aren’t ‘open’
What are the two characterizations of ion channels and ionic movement?
- SPECIFIC to ionic size and charge
- Flow depends on number open (channels)
What’s it called if a sodium channel can exclude a calcium/potassium ion due to different molecule size?
Size exclusion
What’s it called when the interior of the channel is lined with charged amino acids, preventing like ions from crossing it?
Charge exclusion
Characteristics of leak channels
- always open
- some K channels and Cl channels
*K is very important to remember
Characteristics of gated channels
- Closed until stimulus opens
- Ligand (drug or hormone or neurotransmitter that binds to receptor on cell surface), 2nd messenger, voltage, mechanical, light, etc.
Channels that remain closed until the proper ligand (drug, hormone, chemical) binds, but remains open as long as the ligand is around, and closes when it is removed.
Ligand gated channel
Nicotinic receptors in skeletal muscle’s neuromuscular junction are examples of what? Explain what they do.
Ligand gated channels
They bind ACh, allowing Na (mostly) and K (little) to flow down gradients [transmits signal from nerve to muscle]
Channels that remain open as long as the 2nd messenger is around, but close when it’s removed
2nd Messenger Gated channel
What is made in a 2nd messenger channel until the receptor is no longer stimulated?
2nd messenger
Ca2 channels in smooth muscle cells are examples of what type of channel? Explain what happens
2nd Messenger gated channel
Angiotensin II binds to its receptor, causing production of IP3, which binds to and opens Ca2 channels (InsP3R).
Channels that remain closed until the membrane potential reaches a specific value, but remains open depending on the membrane potential and channel properties
Voltage gated channel
The Sodium Channel (Nav) in muscles is an example of what kind of channel? What happens in it?
Voltage gated channel
Once the membrane potential gets above a certain point, they open. When it reaches a 2nd set point, they close.
QUESTION:
Which type of channel would have the most rapid effect on ionic flow?
Ligand gated because you are going to open up a channel
QUESTION:
Which type of channel could lead to a more varied cellular response?
2nd messenger gated
What do ions do when they move down a concentration gradient?
They generate a current
What is the diffusion potential?
Only moves until the charge changes, not big change in concentration; measured in mV
The potential difference (charge) required to stop ionic movement [ions moving down concentration gradient to create a diffusion potential continues until they reach this]
Equilibrium potential
What do ions move in response to in the equilibrium potential?
Concentration AND Charge
What generates an electrical potential? What’s it the basis for?
-Movement of charged particles (relatively few ions have to move to make a charge difference across a membrane)
-This is the basis for resting membrane potential and the nervous system.
(This does NOT create an isotonic or hypertonic solution)
What does the Nernst equation determine?
The Equilibrium potential per ion
(-2.3RT/zF)log(Ci/Co) = ? = -60/z log(Ci/Co)
Nernst equation Z = charge of ion Ci = concentration inside the cell Co = concentration outside the cell *Sign is with respect to the cell interior (can infer sign based on where ion usually is and its charge)
