BIOLOGY 4160
Part of a neuron
(soma) cell body, dendrites, axon -Dendrites receive incoming signals from upstream cells; cell body (i.e., soma) integrate these responses; axon carry outgoing signals from cell body to axon terminal
The nernst equation
(to calculate equilibrium potential for ions) calculates the equilibrium potential (Eion), which is the membrane potential required for a specific concentration gradient to be maintained in equilibrium by the opposing electrical gradient Z= ion valency , CL- = -1, K+ = +1 , Na+ = +1 , Ca2+ = +2
Which one of these has the greater negative membrane potential? A B C
* inside of cell yellow, outside of cell green ------------------------------------------------ C
ATPase transporters ( a type of Primary active transporters)
-ATPase or pumps are a class of transporters that have enzymatic activity -The enzymatic portion of the transporter catalyzes the decomposition of ATP into ADP and a free phosphate ion -This dephosphorylation reaction releases free energy to drive the active transport of one or more molecules -Examples include the: Na+/K+ ATPase or Na+/K+ pump (NKA) Ca2+ ATPase on the cell membrane (PMCA) Ca2+ ATPase on the sarcoplasmic reticulum or the endoplasmic reticulum (SERCA) -ATP binds to carrier protein, and the carrier protein's inherent ATPase activity cleaves a terminal phosphate - this energy release fuels transport
The three major types of receptors/sensors include:
-Chemoreceptors: monitor the concentration of the substance or of a suite of substances -Mechanoreceptors: respond to mechanical stimuli, such as pressure or stretch -Thermoreceptors: detect sensations of cold or warmth (i.e., amount of heat) •Receptors "transduce sensory information into an electrical (neural) or chemical signal (usually hormone)
The Goldman Equation can be used to answer questions on the influence of membrane permeability and ion concentration gradients on membrane potential
-Factors that increase the ratio of the numerator to the denominator will depolarize the membrane Either by increasing the numerator or by decreasing the denominator -Factors that decrease the ratio of the numerator to the denominator will hyperpolarize the membrane Either by decreasing the numerator or by increasing the denominator
Fick's Law
-Fick's Law can be used to calculate the net rate of diffusion of solutes by "simple" diffusion flux rate = (P x A x delta C)/ MW x X P is a permeability coefficient due to lipophilicity of a molecule and membrane A is the surface area of the membrane Δ C is the concentration gradient across the membrane MW is the molecular weight of the molecule X is the thickness of the membrane
Neurons are found:
-Found primarily in brain, spinal cord, and nerves -Somatic nervous system (N.S.) -Sympathetic & parasympathetic N.S.
What is the extracellular fluid made up of?
-Interstitial fluid (i.e., ECF outside blood vessels) -Vascular fluid (blood plasma or lymphatic fluid) (first two are most important) -Transcellular (e.g., cerebrospinal; pericardial; pleural; peritoneal; digestive secretions; synovial fluids)
Examples of physiological processes that are under homeostatic control
-Oxygen is required for ATP production -Nutrients including water, energy-building and anabolic nutrients, micronutrients (e.g., vitamins and minerals) -Temperature to maintain appropriate protein (e.g., enzyme) functions -pH to maintain appropriate protein function
secondary active transport
-Secondary active transport uses the kinetic energy of one molecule moving down its concentration gradient to fuel other molecules against their concentration gradient. -Does NOT require the direct input of ATP (although energy would have been required to establish the favorable electrochemical/chemical gradient -The most common secondary active transport systems are driven by the sodium electrochemical gradient. -As one or more Na+ move into the cell, it either brings one or more molecules with it or trades places with molecules exiting the cell. Ex: Sodium-glucose cotransport
The calcium ATPase (or pump)
-The calcium ATPase binds two or more calcium ions and ATP -Upon cleavage of terminal phosphate group of ATP, the carrier translocates calcium against its electrochemical gradient -Maintains low cytosolic calcium levels by pumping calcium out of cytosol, either across the cell membrane or into certain organelles -This low intracellular calcium concentration is essential for the role of this ion in intracellular signaling) -Examples include the: PMCA (Plasma membrane Calcium ATPase) and the SERCA (Sarcoplasmic and endoplasmic reticulum calcium ATPases)
Characteristics of graded potentials
-The graded potentials are caused by various stimuli that open/close different types of ligand-gated ion channels -Opening of Na+ channels leads to the net entry of Na+ into the dendrites and soma producing a localized depolarization (i.e., always excitatory) -Opening of K+ channels leads to the net exit of K+ from the dendrites and soma producing a localized hyperpolarization (i.e., always inhibitory) -Opening of Cl- channels can depolarize, hyperpolarize, or not change the membrane potential depending on the prevailing direction of the electrochemical gradient The amplitude of a graded potential is proportional to the strength of a stimulus producing it Strength of the stimulus is proportion to the amount of extracellular or intracellular ligand binding to the ion channel
General Properties of Carrier proteins (transporters)
-Transporters can be characterized on how many types of molecules they transport -•Uniporters always transport by facilitated diffusion (passive) •Secondary active transporters are either symporters or antiporters •Primary active transporters (ATPases or pumps) can behave like uniporters, symporters, or antiporters but require ATPase activity to transport --------------------------------------------- •Transporters have chemical specificity for their ligand •Transporters undergo conformational changes that bring shuttle solutes into and out of cells; this movement is called mediated-transport •Transporters move fewer solutes per unit time than do ion channels •Transporters can become saturated (i.e., maximum flux of molecules across the membrane that can be reached) •Many molecules, including amino acids and glucose, that are too polar to diffuse through lipid bilayers use transporters to pass through cell membranes
Features of action potential
-needs to be -55 mv (threshold) depolarization to start -its a rapid depolarization Vm
What do integrating centers do?
-receives the chemical or electrical signal from receptors(s) via afferent pathways -stores the set point for the regulated variable -calculates the difference between the set point value and the actual value of the regulated (sensed) variable- referred to as error detection -generates an error signal proportional to the amount of error detected in error detection -sends output signals (instructions or commands) to increase or decrease the activity of effectors- net effect of output signal is decrease error in the system
primary active transport
-the hydrolysis of ATP by the transporter fuels the movement of ions down their electrochemical gradient •ATPases (or pumps) can be uniporters, symporters, or antiporters •In our course, we will only discuss ATPase that transport ions
At electrical equilibrium
-the unidirectional flux due to the concentration gradient is equal but in the opposite direction to the unidirectional flux due to the electrical gradient Therefore, concentration gradient = - electrical gradient -At electrical equilibrium for an ion, there is no net movement of the ions, there is no net movement of the ion across the membrane -For each ion, the equilibrium (or reversal) potential is the membrane potential where the net flow through any open channels is 0
Uniporters
-transport a single type of molecule using the prevailing energy gradient -fueled by facilitated diffusion (passive) -Uniporters can transport large hydrophilic substances (e.g., amino acids; glucose; ADP) -Molecule transport is driven by concentration gradients (i.e., net flux is in direction from high energy to low energy)
What is the parenchyma of the: 1. kidney 2. heart 3. lungs 4.nervous system
1. epithelial tissue (b/c of role in absorption and secretion) 2. muscle tissue (b/c of role in contracting) 3. epithelial tissue (b/c of role in absorbing O2) 4.neurons
A molecule diffuses across a membrane by simple diffusion at a rate of 10 mmol/minute. What would happen to the rate of simple diffusion if the membrane area was doubled, the thickness of the membrane was doubled, and the concentration gradient was doubled. The new flux diffusion rate would be --------------. (1 point) 5 mmol/minute 10 mmol/minute 20 mmol/minute 40 mmol/minute
20 mmol/minute
Electrical gradient
= tendency for charged ions to diffuse down an electrical gradient (cations are attracted towards a −ve Vm; and anions are attracted towards a +ve Vm; ions are repelled from Vm of similar polarity
Despite the presence of a membrane potential, the Law of Electroneutrality still applies
A membrane potential (Vm) is due to the uneven distribution of cations and anions only at the cell membrane surface •The remainder of the fluids in the cytosol and in the extracellular fluid are electrically neutral - "principle of macroscopic electroneutrality" -The typical membrane potential of ~-70 mV is created by a very small amount of ionic charge (10-17 mols/L) compared to the total concentrations of these ions in the extracellular and intracellular fluids (10-3 mols/L)
If a cell has a membrane potential of -90 mV and sodium is allowed to permeate across the cell membrane due to the opening of sodium channels, which gradient(s) would drive sodium down its prevailing electrochemical gradient? (1 point) Just a chemical gradient. Just an electrical gradient. Both a concentration gradient and an electrical gradient. Neither since it sits at its electrochemical equilibrium.
Both a concentration gradient and an electrical gradient.
What initiates an action potential?
Depolarization of sufficient magnitude (i.e., threshold potential) Voltage-gated sodium channels and voltage-gated potassium channels on the axon are responsible for the action potential
Receptors are just active when a regulated variable is outside of its 'normal' range. True or False
False, they are constantly active •The activity of the receptors is affected by the concentration or level of the regulated variable - it serves as a stimulus •The activity of receptors is proportional to the magnitude of the stimulus
Example of a uniporter
GLUT-1
This is a follow-up to question HW1_Q13. In the original question, I asked, "Imagine a scenario in which a cell has a membrane potential of -70 mV. This cell has an intracellular chloride concentration of 8 mM and the extracellular fluid surrounding the cell has a chloride concentration of 110 mM. Furthermore, initially, the cell membrane has no chloride permeability. A scientist applies a drug that increases the chloride permeability 1000 fold. What would happen to membrane potential?" For this question, I wonder what would happen, if before adding the drug that increases chloride permeability 1000-fold, the experimenter were to increase potassium concentration in the extracellular fluid causing the membrane to depolarize to -60 mV. What would happen to membrane potential upon the application of the drug? It would become more depolarized than -60 mV It would hyperpolarize to between -70 to -60 mV. The membrane potential would stay at -70 mV.
It would hyperpolarize to between -70 to -60 mV.
If a cell has a membrane potential of 0 mV and sodium is allowed to permeate across the cell membrane due to the opening of sodium channels, which gradient(s) would drive sodium down its prevailing electrochemical gradient? (1 point) Just a chemical gradient. Just an electrical gradient. Both a concentration gradient and an electrical gradient. Neither since it sits at its electrochemical equilibrium.
Just a chemical gradient.
Neurons have similar ion concentration gradients across their cell membranes
K+: high concentration inside cell (relative to outside) Na+: high concentration outside cell (relative to inside) Cl- : high concentration outside cell (relative to inside) Negatively-charged proteins and other anions: high concentration inside cell
The dendrites and soma of neurons have ligand-gated channels for K+, Na+, and Cl- that produce graded potentials
Ligands released by other cells, which include neurotransmitters and neurohormones, can stimulate the gates on these channels directly or indirectly, open or close Depending on ion channel type, the membrane can hyperpolarize or depolarize (or no change at all)
Compartmentalization
Membrane-bound organelles allow different parts of the cell to perform different functions at the same time
If a cell has a membrane potential of approximately 66 mV and sodium is allowed to permeate across the cell membrane due to the opening of sodium channels, which gradient(s) would drive sodium down its prevailing electrochemical gradient? (1 point) Just a chemical gradient. Just an electrical gradient. Both a concentration gradient and an electrical gradient. Neither since it sits at or near its electrochemical equilibrium.
Neither since it sits at or near its electrochemical equilibrium. equilibrium is around 60?
Two types of integral proteins involved in membrane transport:
Protein ion channels and Protein carriers (transporters)
A membrane that is permeable to Na+ but it is not permeable to Cl− separates a container into side A and side B. Side A is filled with 1000 mM of NaCl and side B is filled with 10 mM of NaCl. Electrodes from a voltmeter are placed in each compartment and side A is set as the ground (0 mV) (i.e., reference). The membrane potentials below are side B relative to side A, which is arbitrarily set at 0 mV. Side B would develop a membrane potential of +61.5 mV. Side B would develop a membrane potential of +123 mV. Correct Side B would develop a membrane potential of - 61.5 mV. Side B would develop a membrane potential of - 123 mV.
Side B would develop a membrane potential of +123 mV.
Example of homeostasis by negative feedback
Temperature regulation in the body
Consider the forces pushing potassium across the membrane of a resting cell. (1 point) The electrical gradient and the chemical gradient both push potassium out of the cell. The electrical gradient draws potassium into the cell while the concentration gradient pushes it out. The electrical gradient and the chemical gradient both draw potassium into the cell. The chemical gradient draws potassium into the cell while the electrical gradient pushes it out.
The electrical gradient draws potassium into the cell while the concentration gradient pushes it out.
The sodium-potassium ATPase or pump, Na+-K+-ATPase
The free energy from each ATP dephosphorylation fuels the translocation of 3 Na+ out of a cell and 2 K+ into a cell •This transport is critical in all cells (maintenance of solute concentrations and cell volume regulation, etc.)
resting membrane potential (Vm)
The membrane potential for a resting cells -Vm is typically expressed as the charge inside the cell relative to the charge outside the cell (i.e., outside is the reference or set to 0 mV) •Most cells have a negative Vm (i.e., negative relative to the outside)
Imagine a scenario in which a cell has a membrane potential of -70 mV. This cell has an intracellular chloride concentration of 8 mM and the extracellular fluid surrounding the cell has a chloride concentration of 110 mM. Furthermore, initially, the cell membrane has no chloride permeability. A scientist applies a drug that increases the chloride permeability 1000 fold. What would happen to membrane potential? (1 point) It would become more depolarized than -70 mV. It would become more hyperpolarized than -70 mV. The membrane potential would stay at -70 mV. There is insufficient information to answer the question.
The membrane potential would stay at -70 mV.
threshold potential
The minimum membrane potential that must be reached in order for enough voltage gated channels to open to lead to sufficient depolarization of all voltage channels (so an action potential is generated)
set point
The value of a regulated variable is kept at a relatively constant value
VDF = Vm - Eion equation for electrochemical gradient
This equation states that an ion will diffuse down its electrochemical gradient until its net diffusion decreases the gradient until membrane potential is equal to the electrical gradient for any ion
driving force for ion diffusion?
When ion channels are open, ions will diffuse from until electrochemical equilibrium is reached (i.e., when there is no longer an electrochemical equilibrium)
Which of the following would have the greatest depolarizing effect of a resting cell such as a neuron? a 5 mM increase in the extracellular potassium concentration a 5 mM increase in the intracellular potassium concentration a 5 mM in the extracellular sodium concentration a 5 mM increase in intracellular sodium concentration
a 5 mM increase in the extracellular potassium concentration
If membrane potential depolarizes above threshold potential, then an
action potential is produced
action potentials are _____
all or nothing
Where do action potentials occur?
along the axon of the neuron
Electroneutrality
an equal number of positive and negative charges (i.e., no net charge)
What makes up the peripheral nervous system?
anything outside of the central nervous system
•Integral proteins
are amphipathic molecules closely integrated to the lipid bilayer
Carrier Proteins (transporters)
are complexes that move a wide variety of molecules- do not form open pores
Interneurons
are in the spinal cord and brain and connect the afferent neurons and efferent neurons in the peripheral nervous system
Gated channels
are protein channels that are closed most of the time but have gates that open with different stimuli responsible for excitability
Epithelial cells
are specialized for the selective secretion and absorption of ions and organic molecules
•Peripheral proteins
are water soluble molecules that do not associate with the nonpolar regions of the lipids •Some peripheral proteins bind to integral proteins
Skeletal muscle:
attached through other structures to bones and produce movements of the limbs or trunk
What makes up the central nervous system?
brain and spinal cord
What regulates the composition of the ECF?
cell membranes and transporting epithelia (lungs, GI tract, kidneys) -The GI tract, the lungs, and kidneys perform solute/water exchanges between the outside and the extracellular fluid -The ECF exchanges solutes and water with the intracellular fluid
organizational hierarchy of humans
cells -> tissues -> organs --> organ systems
Neurons
cells specialized to initiate, integrate, and conduct electrical signals to other cells, sometimes over long distance -"glued" together by connective tissue to form nerves
Where are integrating centers found?
central nervous system or part of an endocrine gland
If membrane potential is -70, and equilibrium potential for Cl- is -60, when more Cl channels are opened, the membrane potential goes to ?
closer to -60 b/c membrane potential becomes most similar to the permeability of most permeable ion to the membrane
Electrochemical gradient
combined effects of concentration and electrical force on the passive diffusion of ions
Afferent nervous system
consist of afferent neurons packaged in nerves that convey information from the tissues in the periphery towards the central nervous system
Efferent nervous system
consist of efferent neurons are packaged in nerves that convey information from the central nervous system towards the effector cells in the periphery
Graded potentials __________ in strength as they spread from the point of origin
decrease
What is the other 50% of the membrane made up of?
different types of proteins are embedded in or attached to the phospholipid bilayer •Integral proteins are amphipathic molecules closely integrated to the lipid bilayer (Note: Transmembrane proteins are always integral proteins) •Peripheral proteins are water soluble molecules that do not associate with the nonpolar regions of the lipids •Some peripheral proteins bind to integral proteins
tissues
differentiated tissues with similar properties
integrating center
effector > response (negative feedback) > regulated variable > stimulus > receptor > integrating center > effector >>
Smooth muscle:
encloses and controls the movement of contents through hollow tubes and organs
The four general tissue types
epithelial, connective, muscular, nervous
Four basic cell types:
epithelial, connective, neuron, muscular
Goldman-Hodgkin-Katz (GHK)
equation is used to calculate mathematically the membrane potential (Vm)
The two broad classes of body fluid compartments consist of the
extracellular fluid (ECF) and the intracellular fluid (ICF)
Maintaining "constancy" in the ECF is not critical for normal function (i.e., function of cells). T or F
false
Protein channels ( ion channels)
form pore-like pathways for charged ions to move through a cell membrane
Cardiac muscle:
found only in the heart and generate blood pressure
Chemically (ligand)-gated channels:
gates open by different intracellular or extracellular molecules (i.e., ligands) (examples: intracellular phosphorylation or extracellular hormones or neurotransmitters)
Ligand-gated channels
gates open by different intracellular or extracellular molecules (i.e., ligands) (examples: intracellular phosphorylation or extracellular hormones or neurotransmitters)
The two types of membrane potential changes:
graded potentials and action potentials
Describe the gate(s) of Voltage-gated potassium channel
has one activation gate regulated by depolarization and closes once the membrane is repolarized
Mechanosensitive-gated channels
have gates that are controlled by physical state of cell
Mechanically-gated channels
have gates that are controlled by the physical state of cell
Voltage-gated channels
have gates that are opened by the membrane potential of the cell
Describe the gate(s) of Voltage gated sodium channels
have two gates (activation gate and an inactivation gate); each of these gates is differentially regulated by membrane potential
Epithelial Transport
involves the coordination of different types of protein channels and protein carriers
Membrane Potential is primarily controlled by ______ and ______
ion diffusion through ion channels the Contribution of Ion Concentration Differences and Ion Channel Permeability
Intracellular fluid
is any fluid inside cells
Extracellular fluid
is any fluid outside cells
Parenchyma
is the functional tissue of an organ as distinguished from the connective and supporting tissue (stroma)
Homeostasis
is the physiological process by which an organism maintains a constant internal environment (steady state) in a fluctuating external environment (outside the body
In blood pressure homeostasis, what is the function of the heart in blood pressure regulation? It serves as a receptor (sensor) It serves as the afferent pathway It serves as the integrating center It serves as an effector pathway It serves as an effector
it serves as an effector
what causes cells to be negative inside?
leak potassium channels
Graded potentials are due to the opening and closing of _____
ligand-gated and mechanically-gated ion channels
The permeability of a molecule by simple diffusion is correlated with its __________
lipid solubility -Permeability is the rate (i.e., how easily) a molecules moves across a membrane
Action of the activation gate and inactivation gate of the voltage-gated sodium channel
memorize chart
Action of the activation gate of the voltage-gated potassium channel
memorize chart
Potassium diffusion creates an inside _____ membrane potential
negative
Homeostatic processes work to keep the regulated variables at values near their set points by a reflex arcs that function by
negative feedback -The goal of negative feedback is to return a regulated variable back to its set point when perturbed by internal and external disturbances (i.e., compensatory responses)
leak channel gates are always________
open
In a resting nerve cell, potassium ions diffuse through membrane channels: (1 point) equally well in both directions; there is no net movement because there is no concentration gradient. out of the cell down its chemical gradient. equally well in both directions; there is no net movement because potassium ions are at equilibrium. into the cell, is down its chemical gradient.
out of the cell down its chemical gradient.
The most ____________ ions will influence membrane potential the most; as ions pass through a membrane, they "drive" the membrane potential towards its own equilibrium potential
permeant
Approximately 50% of a cell membrane is composed of a _____ bilayer
phospholipid -Each phospholipid has a polar head (hydrophilic) and two nonpolar tails (hydrophobic)- molecules with this mixed chemical nature are amphipathic molecules -The phospholipids self-assemble themselves into a lipid bilayer with hydrophilic heads oriented outwards
Sodium diffusion creates an inside ______ membrane potential
positive
All regulated variables must be monitored by
receptors (i.e., sensors) ( the body can't regulate something unless it can measure its concentration/level in the exchangeable pool)
Cooperation between the voltage-gated sodium and voltage-gated potassium channels
refer here for the 2 charts
every cell in the body has a unique membrane potential that is determined by the _______________
relative permeability of ions through ion channels on its cell membrane
The pool
represents that portion of a substance that is freely exchangeable with the environment
CHANGES IN membrane permeability to Na+, K+, Cl-, and Ca2+ occur due to the _______
reversible open and closing of gated channels (i.e., ligand-gated and voltage-gated)
Cell membranes are _________ barriers
semipermeable
Three types of muscle tissue
skeletal, cardiac, smooth
Once a membrane depolarizes or hyperpolarizes, the electrical charge will ______________
spread along the membrane from that area Charge spreads across the membrane from the site of ion channel movement through channels
Physiology
study of normal functions of and activities of living organisms
Chemical gradient
tendency for molecules (including ions) to diffuse down their concentration gradient (from a high to low concentration) − Nernst equation expresses this concentration gradient into mV units
Simple diffusion
the diffusion of lipid soluble and small uncharged polar molecules directly through the phospholipid bilayer •Simple diffusion DOES NOT require any transport proteins •Molecules diffusing through cell membranes by simple diffusion include: -lipid soluble molecules (i.e., carbon dioxide, oxygen, fat soluble vitamins and steroids) to permeate easily -small polar molecules like water, urea, ethanol, glycerol and alcohol to permeate slightly to moderately -------------------------------- •Large uncharged and polar molecules or charged molecules (i.e., ions) are unable to move across membranes by simple diffusion •These impermeable molecules require specific types of transmembrane proteins to move across a cell membrane
Cells are:
the smallest biological unit that can carry out all functions necessary for life
Pathophysiology
the study of how disease processes affect the function of the body
Describe inactivation gates of potassium
they do not exist, voltage gated potassium channels only have one activation gate
What connects epithelial cells to each other?
tight junctions
Neurons have negative membrane potentials due to their high permeability ______
to K+ Leak channels are distributed on the cell membrane throughout the entire neuron
cell differentiation
transforms an unspecialized cell into a specialized cell type
Cell membranes are found on all cells including epithelial membranes. T or F
true
Action potentials are due to the opening and closing of ____
voltage-gated ion channels
action of baroreceptors in blood pressure regulation
•Baroreceptors monitor blood pressure in blood vessels such as systemic arteries location of baroreceptors: carotid sinus, aortic body medulla>> (integrating center) heart, kidneys, blood vessels >> effector blood pressure receptors represent what portion of the negative feedback loop? •The frequency of action potential transmission along nerves (from the receptors to the integrating center) depends on blood pressure •In other words, the frequency of action potentials is proportional to blood pressure
Forces that influence passive and active transport
•Concentration (chemical) potential gradient due to the non-equilibrium distribution of solutes, include: -High sodium and low potassium concentrations in the extracellular fluid -Low sodium and high potassium concentrations in the intracellular fluid -Low calcium concentration in the cytosol relative to subcellular and extracellular concentrations -These gradients affect the flow of all types of molecules by simple diffusion, facilitated diffusion, and charged molecules through ion channels •Electric potential (electrical gradient) due to the movement of charge in an electric field -Only affects the flow of charged molecules such as ions
Core concept of cell membrane
•Each cell type including epithelia has a distinct cell membrane that affects the mechanism by which substances enter or leave a cell •Some molecules are permeable to a cell membrane (i.e., can pass through a cell membrane) Some molecules are impermeable to a cell membrane (i.e., unable to pass through a cell membrane
mass balance of substance
•Each substance has different routes of entry (i.e., gain) and exit (i.e., loss) between the environment and the internal pool •Some substances can change in abundance within the pool due to synthesis (metabolism) or reversible incorporation into other molecules or storage
What are effectors?
•Effectors are the cells, tissues, or organs that determine the value of the regulated variable in the extracellular fluid •Effectors receive the output signals from the integrating center •The magnitude of the output signal from the integrating center affects the activity of the effector •The goal of the effectors is to maintain the stability of the regulated variable within a system.
How are epithelial tissues connected?
•Epithelial cells are connected to one another by tight junctions •Tight junctions separate the lumen side (i.e., outside environment) from the basolateral side (i.e., ECF side)
symporters and antiporters fueled by secondary active transport
•In secondary active transport, the movement of an ion down its (electro)chemical gradient is coupled to the transport of one or more molecules against its/their electrochemical gradient •As such, these transporters move two or more different types of molecules
General Properties of Protein Channels
•Ion channels are formed of several individual proteins (i.e., subunits) •Ion channel complexes are classified by the type of ion that moves through (specificity), the number of gates the channel has, and the manner gate opening and closing is regulated -Channels have gates that regulate the movement of molecules through the pore -Ions only move through an ion channel when the gate(s) is/are open
The open or closed state of a channel is set by regions of the protein channel called gates
•Open channels (i.e., leak channels and pores) are open most of the time (even though they do have gates) •Gated channels are protein channels that are closed most of the time but have gates that are opened by different stimuli -Chemically (ligand)-gated channels: gates open by different intracellular or extracellular molecules (i.e., ligands) (examples: intracellular phosphorylation or extracellular hormones or neurotransmitters) -Voltage-gated channels have gates that are opened by the membrane potential of the cell -Mechanically-gated channels have gates that are controlled by the physical state of cell
Thermodynamics of solute transport across cell membranes
•The flow (i.e., net flux) of solutes occurs because of the existence of an energy gradient between two points •The magnitude of the flow is a direct function of the magnitude of the energy gradient - the larger the gradient, the greater the flow (e.g., concentration gradient) •More than one type of gradient can determine the magnitude and direction of flow (sometimes they oppose one another and other times they combine together)
Factors that maintain the resting cell membrane potential
•The plasma membrane has leak channels that are always open in the cell •The two major types of leak channels include, K+ leak channels and Na+ leak channels •Ions move down prevailing electrochemical gradients -net flow of K+ through K + leak channels is directed outward -net flow of Na + through Na + leak channels is directed inward •In resting cells, the cell membrane is approximately 40-100 times more permeable to K+ than it is to Na+ •Membrane potential can change VERY quickly due to changes in a membrane's relative ion permeability - at times a cell membrane may be much more permeable to Na+ than it is to K+
The direct and indirect sources of the cell membrane potential
•The primary active transporter, Na+, K+- ATPase, creates disequilibrium in K+ and Na+ concentrations across the cell membrane -high Na+ concentration in the extracellular fluid and a low Na+ concentration in the intracellular fluid -high K+ concentration in the intracellular fluid and a low K+ concentration in the extracellular fluid -HOWEVER, this primary active transport and other carrier-mediated transporters have only a small direct effect on membrane potential •More importantly, membrane potential is determined by the diffusion of ions through protein ion channels (referred to as diffusion potentials)
