membranes Flashcards
function of membranes
control exchange between body compartments (entry/exit of substances into cell)
What does the membrane consist of
Phospholipid bilayer, phospholipid head which is hydrophilic = on outside and fatty tail =hydrophobic= on inside
proteins embedded
What molecules can move through the membrane easily
small lipid soluble molecules
What do membrane proteins do
allow control of movement of molecules in/out of cell, by controlling protein synthesis you control access
What does the cell membrane of capillaries do
control exchange between the plasma and interstitial fluid
Is there more sodium inside or outside the cell
outside
Is there more calcium inside or outside of cell
outside ( and relatively low amount of both in/out compared to sodium)
More potassium inside or out of cell
inside (makes cell negative)
more chloride in/out of cell
outside (nacl)
define diffusion
substance move randomly down a concentration gradient until even (gas and liquids) due to energy in particles
define osmosis
movement of water through a semi-permeable membrane down a concentration gradient (water itself moves)
osmosis vs diffusion
both down a concentration gradient
both passive
diffusion is substance moving, osmosis is about solvent
osmosis is through a partially permeable membrane
define osmolarity
number of particles in a solution Osm/l (per litre) = solute osmotic concentration per volume solvent
define osmostic pressure
pressure needed to oppose osmosis = number of particles per unit volume of fluid
what is an aquaporin
membrane channel that transports water and controls water intake, only water not solutes
define osmolality
expression of solute osmotic concentration per mass solvent = Osm/kg
What is the rate of diffusion dependent on (4)
-membrane permeability to solute (lipid solubility or proteins present, size of molecule)
- diffusion distance (thickness of membrane)
-transmembrane gradients (ions= voltage gradient)
- membrane surface area (bigger=better)
iso/hyper/hypo osmotic
isosmotic = solutions both have same concentration of dissolved solutes (same osmotic pressure)
hyperosmotic= one solution has higher concentration of solutes , so has an increased osmotic pressure
hypoosmotic = one solution has lower concentration of dissolved solutes so has decreased osmotic pressure
what does tonicity depend on
osmolarity of solution and osmolality of cell, biological term relating to solution relative to living cells. tonicity has no units
osmolarity vs tonicity
osmolarity compares 2 solutions whereas tonicity compares solution and a cell , so has no units ( usually in reference to blood )
what happens if a red blood cell is in a hypertonic solution
water will leave the cell and cause it to shrivel up
how does transport of respiratory gases occur
simple diffusion as they are lipophilic
how does pneumonia affect gas exchange
pneumonia causes swelling of alveoli walls so membrane thickens so diffusion is harder = hypoxia
what can passive diffusion be divided into
simple and facilitated
simple diffusion + examples
substance is lipid soluble so can diffuse directly through lipid bilayer e.g. steroid hormones, fatty acids, O2 and co2
facilitated diffusion + examples
molecules need specific protein transporters to form a diffusion pathway, limited by number of proteins and can be affected by competitive inhibition
channel vs carriers vs pumps (proteins)
channel = won’t saturate, all/nothing (is either open or closed) no ATP needed
carrier = will saturate, can be used in active transport
pumps = require energy, against conc. gradient, graded
pumps and carriers are same thing
types of carriers
uniporter = transports one type of ion
symporter = more than one type of molecule transported simultaneously in same direction
antiporter = more than one type of ion/molecule transported simultaneously in opposite directions
types of ion channels
ungated (leak)- always open, small but continuous movement of an ion , maintains resting membrane potential
voltage-gated = selective, narrow pore , 4 sub-units, changes in membrane potential causes gate structure to change, muscle contraction and nerve
ligand-gated channels = larger, less selective, 5 subunits, controlled by signal molecules from ECF or IC signals
mechano-gated = affected by deformation of membrane (stretch/pressure) may cause pain
active transport + two types
active transport = requires carrier protiens and uses ATP to move molecules against gradient
primary = protein use ARP to flip substance through membrane against con. gradient
secondary = energy required to establish conc. gradient which cause transport of species
example of primary active transport
proton pump in stomach transports H ions from blood into stomach against electrochemical gradient
example of secondary active transport
movement of glucose and amino acids into intestine
