Transport Flashcards
What is a solute?
Substance dissolved in water e.g. ions, glucose, vitamins, drugs
Why doe solutes need to be transported across the membrane?
Oxygen for respiration, food through gut, maintaining & changing membrane potential
What is circulation?
Movement in blood
What is transport?
Substance crossing a membrane
What are the factors affecting the ability of substances to cross the membrane?
Permeability & electro-chemical gradient
In what way does electrical gradient influence the movement of molecules crossing the membrane?
Inside of cell is negative relative to outside (similar conc. of +ve ions, more -ve ions) - resting membrane potential= -70mV
Forces -ve ions out & +ve ions in
In what way does chemical gradient influence the movement of molecules crossing the membrane?
Substances move from to low conc.
What is passive diffusion?
Hydrophobic substance & gases - move in direction of electro-chemical gradient - no energy or carrier proteins
What is facilitated diffusion?
Ions & hydrophobic substances can’t cross membrane even with electro-chemical gradient - require carrier proteins
What law dictates the rate of diffusion?
Fick’s Law of Diffusion
dn/Dt = PΔc
P=permeability
Δc =electro-chemical gradient
What is the limitation of diffusion
Can only occur at a small distance e.g. cell =10μm = 0.05 seconds - 1m = 15 years
What are the different types of carrier proteins
Channels (regulated & non-regulated)
Transporters (uniporter, symporter, antiporter)
Pumps (ATP-pump)
Which channel proteins are passive & which are active?
Channels & uniporters are passive
Symporters, antiporters, ATP-pumps are active
Explain channel proteins?
Pores in membrane - specificity for a single substance e.g. Na2+ & H2O - passive - follow electro-chemical gradient - regulated=gated & non-regulated=constitutive (always open)
Explain uniporters?
Passive - bind to & move large molecules e.g. glucose - follow electro-chemical gradient - regulated by insertion & removal of uniporters from cell membrane - e.g. insertion of GluT1 for glucose in the kidneys - more selective than channel & prevent similar shapes molecules from entering
What type of active transport are symporters & antiporters?
2° Active Transport
What is 2° active transport?
Use energy stored in conc. gradient established by 1° active transport
What is a symporter?
Moves 2 molecules across membrane in the same direction - Na+ & glucose transporter
What is an antiporter?
Moves 2 molecules across membrane in opposite directions
What is active transport?
Uses energy to move against conc. gradient
What is an ATP pump?
E.g. Na+ extruded against gradient - ATP used - maintain cell volume, nerve impulses, & muscle contraction
What type of transport is an ATP pump?
1° active transport
What is resting membrane potential?
-70mV - imbalance of ions (cation conc. equal - K+ inside & Na+ outside - trapped anions inside)
What are trapped anions?
Negatively charged ions - proteins (17-), organic phosphate (-), ATP (4-) - can’t pass through membrane explained by Fick’s Law (P=0, ∆c is high - rate of diffusion still 0)
What maintains resting membrane potential?
Na+/K+ pump - use ATP to pump 3 Na+ out of cell & 2 K+ into cell
What is osmosis?
Water moves across aquaporins from regions of low osmolarity to high osmolarity
What is the concentration of water?
55.5M
What is osmolarity?
Amount of solute dissolved in 1kg of water (1L) - 1 mole solute in 1L = 1 Osmolar (Osm)
*1 mole NaCL in 1L water = 2 Osm (dissociates in water)
How is osmolarity measured?
Depression of freezing point - 1 Osm will depress freezing point by 1.86°
E.g. plasma freezes @ -0.52° = 280 mOsm
How does osmolarity affect RBCs?
RBCs contain aquaporins & cytoplasm has osmolarity of 280 mOsm - solution of 280 mOsm isosmotic/isotonic no osmosis occurs - Osmolarity ECF < ICF (hypotonic, hypoosmotic) water rushes in & cell swells, lysis - Osmolarity ECF > ICF (hypertonic, hyperosmotic) water rushes our & crenation
How does glucose have to travel from intestine to muscle cells?
Leave intestine (pass 4 lipid membranes & interstitial space) circulate via blood system, & leave blood & enter muscle cells (cross 3 lipid membranes & interstitial space)
How are epithelial cells polarised?
Apical domain (facing lumen), tight junction (impermeable to water - tight & leaky), basolaterlal domain (face basal lamina)
What are the conditions of the cell & ECF and in terms of glucose & sodium?
ICF - High glucose & low sodium
ECF - low glucose & high sodium
Glucose cant enter cell from intestine via diffusion (∆c<0) but can exit via diffusion through basolaterlal layer (∆c>0) however p=0 (need carrier proteins)
Na+ can enter cell from lumen via diffusion(∆c>0), can only exit via active transport (∆c<0) - needs carrier proteins as P=0
Explain the Glu/Na+ transporter?
1) 1° Active Transport - ICF [Na+] kept low by Na+ pump in basolaterlal layer
2) 2° Active Transport - low Na+ creates a conc gradient - Na+ enters via Na+/glucose symporter on apical membrane - energy released is captured by symporter & allows glucose to enter against the conc. gradient
3) Facilitated diffusion - Glucose uniporter allows glucose to leave via basolaterlal membrane down a conc. gradient & enter interstitial space
Other examples of co-transporters?
Amino acids via Na+/Amino Acid transporter
Folate via H+/Folate transporter
Explain bulk absorption of water
Large amounts of water from lumen of intestine to interstitial space via leaky tight junctions - proximal tubule & small intestine - needs on osmotic gradient - constitutive process - Na+ move into cell via Na+/Glu symporter, Cl- follows due to electrical imbalance - water follows
Explain regulated absorption of water
Small volumes via transcellular pathways - collecting ducts - tight junctions impermeable - moves via aquaporins (channel proteins) - AQP-1 located in basolateral membrane
What happens to the aquaporins when ADH is absent?
AQP-1 in basolateral membrane - AQP-2 retained in secretory vessels in cytoplasm - water can’t be reabsorbed & urine is dilute
What happens to the aquaporins when ADH is present?
AQP-2 is inserted into apical membrane - water reabsorbed (AQP-2 provide permeability follows osmotic gradient) - urine concentrated & water retained
Explain healthy water secretion & loss vs. diarrhoea?
Healthy - 20L secreted - 19.9L reabsorbed, 0.1L lost as feaces
Diarrhoea - secretion increased & reabsorption decreased
Explain Oral Rehydration Therapy?
H2O only - interstitial fluid [Na+] too low
H2O & Na+ - no Na+ channels in lumen
Glucose, Na+. & H2O - Na/Glu symporter - water will follow via leaky tight junctions
Explain Sweating?
H2O secretion - 1)Cl- exported 2)Na+ follows 3) Water follows
Explain exocytosis?
Secretion of proteins (insulin), insertion of membrane proteins (Na+ pump), & release of neurotransmitters - mRNA from nucleus moves to ribosome & translation occurs - Polypeptide move to lumen of sER - transport vesicle breaks off sER & brought to cis face of Golgi apparatus - Exits via vesicles from trans face of Golgi - insertion or secretion
Explain endocytosis?
Uptake of bacteria/virus in macrophage & uptake of LDL cholesterol in liver - vesicles merge with cell membrane & release substances (protein) - travel to lysosome to be broken down & recycled or removed
