Cell physiology - Random Flashcards
Name 3 lipid soluble substances (hydrophobic)
CO2
O2
Steroid hormones
Name 3 water soluble substances (hydrophilic)
Na+
Cl-
Glucose
K+
H20
Cell membranes are composed of… (2)
Phospholipids and proteins
How are cell proteins anchored to the cell membrane?
Through hydrophobic interactions
Examples of cell membrane proteins
Ion channels
Transport proteins
Receptors
GTP binding proteins
Name and describe 2 types of intercellular junctions
Tight junctions
- Attachment between epithelial cells
- Impermeable (ex: renal distal tubule) or permeable (ex: renal proximal tubule, gallbladder)
Gap junctions
- Attachments that permit intercellular communications
- Ex: myocardial cells
Name 5 types of transport across cell membranes
- Simple diffusion
- Facilitated diffusion
- Primary active transport
- Cotransport
- Countertransport
What factors impact permeability of a solute?
- Oil/water partition coefficient
- Radius (size)
- Membrane thickness
Which solutes need transporters or pores or channels to cross membranes?
Hydrophilic solutes
Name the 3 characteristics of carrier mediated transport.
Stereospecificity
Saturation (transport maximum)
Competition
In diabetes mellitus, glucose uptake with insulin is done through which transport mechanism?
Carrier mediated - Facilitated diffusion
The Na+-K+-ATPase pump works through which transport mechanism?
Primary active transport
- Na+ is transported from intra- to extra-cellular
- K+ is transported from extra- to intra-cellular
How does the proton pump work?
H+, K+-ATPase
- Primary active transport
- Present in gastric parietal cells and renal α-intercalated cells
- Transports H+ into the lumen against its electrochemical gradient
Describe secondary active transport
- The transport of two or more solutes is coupled
- Metabolic energy is provided indirectly from the Na+ gradient that is maintained across cell membranes
- Solutes move in the same direction across the cell membrane = cotransport (ex: Na+-glucose cotransport in the small intestine and renal early proximal tubule and Na+–K+–2Cl– cotransport in the renal thick ascending limb)
- Solutes move in opposite directions across the cell membranes = countertransport or exchange (ex: Na+-Ca2+ and Na+–H+)
What is osmolarity?
The concentration of osmotically active particles in a solution
How do you calculate osmotic pressure (van’t Hoff’s law)?
π = g × C × RT
π = osmotic pressure (mm Hg or atm)
g = number of particles in solution (osm/mol)
C = concentration (mol/L)
R = gas constant (0.082 L—atm/mol—K) T = absolute temperature (K)
What do you call osmotic pressure created by proteins?
Oncotic pressure or colloid osmotic pressure
What does a reflection coefficient of 1 mean?
Reflection coeficient = ease with which a solute permeates a membrane
Reflection coefficient of 1 = impermeable solute
Reflection coefficient of 0 = completely permeable solute
Name a solute with a reflection coefficient of almost 0.
Urea = ineffective osmole
What is effective osmotic pressure?
Osmotic pressure X reflection coefficient
If the reflection coefficient is one, the solute will exert maximal effective osmotic pressure. If the reflection coefficient is zero, the solute will exert no osmotic pressure.
Voltage-gated channels
Opened or closed by changes in membrane potential.
- The activation gate of the Na+ channel in nerve is opened by depolarization.
- The inactivation gate of the Na+ channel in nerve is closed by depolarization.
When both the activation and inactivation gates on Na+ channels are open, the channels are open and permeable to Na+
Ligand-gated channels
Opened or closed by hormones, second messengers, or neurotransmitters.
Resting membrane potential
- Expressed as the intracellular potential relative to the extracellular potential
- Established by diffusion potentials that result from concentration differences of permeant ions
- Each permeable ion attempts to drive the membrane potential toward its equilibrium potential.
What is the contribution of the Na+-K+ pump to the resting membrane potential?
Contributes only indirectly to the resting membrane potential by maintaining, across the cell membrane, the Na+ and K+ concentration gradients that then produce diffusion potentials.
The direct electrogenic contribution of the pump (3 Na+ pumped out of the cell for every 2 K+ pumped into the cell) is small.
Define depolarization
Makes the membrane potential less negative (the cell interior becomes less negative)
- Inward current (flow of positive charge into the cell) depolarizes the membrane potential.
Define action potential
Property of excitable cells (i.e., nerve, muscle) that consists of a rapid depolarization, or upstroke, followed by repolarization of the membrane potential.
Define hyperpolorization
Makes the membrane potential more negative (the cell interior becomes more negative)
- Outward current (flow of positive charge out of the cell) hyperpolarizes the membrane potential.
Define threshold
Membrane potential at which the action potential is inevitable.
What happens during the action potential?
Rapid depolarization caused by inward Na+ current.
What is the resting membrane potential?
Approximately -70mV
Action potential diagram
What is the impact of lidocaine on action potentials?
Blocks voltage-sensitive Na+ channels, abolishing action potentials
What happens during repolarization?
Outward K+ current.
The velocity of conduction of action potentials along a nerve will be increased by
Increased fibre size
Myelination
How does hyperkalemia cause muscle weakness?
Elevated serum K+ concentration causes depolarization of the K+ equilibrium potential and therefore depolarization of the resting membrane potential in skeletal muscle. Sustained depolarization closes the inactivation gates on Na+ channels and prevents the occurrence of action potentials in the muscle.
Describe the PIP2-IP3 signal pathway
- G-coupled receptors lead to activation of phospholipase C after hydrolysis of GTP (under the action of various ligands, eg. vasopressin on V1 receptor)
- Phospholipase C hydrolyzes PIP2 (phosphatidylinositol biphosphate) into IP3 (inositol triphosphate)
- IP3 has various functions (eg. opening of Ca2+ channels on endoplasmic reticulum)
