Patho Exam 2 Review Updated version 2025/2026 Correctly
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Membrane Transport:
• Essential for homeostasis: nutrients in, wastes out
• Plasma membrane is selectively permeable:
o Allows only certain substances to pass through enabling cell to maintain structure
o Lipid solubility and particle size affect membrane permeability
▪ High lipid solubility: cross easy (some water solubility is important)
• Blood is aqueous and intestines is water environment
▪ Low lipid solubility:
• <0.8nm diameter – utilize protein channels (ion channels)
• >0.8nm diameter – assisted transport (glucose)
• Forces are required:
o Passive Force: no energy expenditure by cells for
transport
▪ Ex – concentration gradient and electrical gradient
o Active Force: energy (ATP) expenditure by cells for transport
3 Types of Membrane Transport:
1. Unassisted: molecules can traverse on their own
a. Diffusion: spreading out down a concentration gradient
b. Movement along an electrical gradient
, c. Osmosis
2. Assisted: molecules that cannot traverse on own
a. Carrier mediated transport
i. Facilitated Diffusion
ii. Active Transport
1. Na-K ATPase pump
2. Secondary Active Transport
b. Vesicular Transport
i. Endocytosis: out things get into cell
ii. Exocytosis
1. Caveolae: membrane transport and signal transduction
a. Cave-like structures
b. Endocytosis: how substances get into cell
Unassisted Membrane Transport:
1. Diffusion: movement of molecules from high concentration to area of low concentration
• Concentration gradient – passive mechanism
• If membrane separating 2 areas there will still be movement – as long as can cross
• Steady State: not net diffusion although movement can still be occuring
• Ex – Co2 is higher in body and lower in lungs – can move into lungs without using
energy
• Ficks Law of Diffusion: factors influencing rate
o Magnitude of conc. Gradient directly proportional - ∆C
o Permeability of membrane directly proportional – P
o Surface area of membrane directly proportional –A
, ▪ Lumen: has microvillus which increases surface area
o Molecular weight of substance inversely proportional – MW
o Thickness of membrane inversely proportional – X
o Net Rate of Diffusion:
▪
C.P.A
MW .X
2. Electrical Gradient: charge (driving force) difference between adjacent areas
• Promotes movement towards opposite charge
• Electrochemical Gradient: electrical and concentration gradient
o Difference in charge and concentration
• RMP: resting membrane potential
3. Osmosis: net diffusion of water down its own concentration gradient when
separated by a semi-permeable membrane
• Important for water movement in and out of cells
• Water passes but solute does not:
o Water and solute concentration not equal
o Osmosis ceases when osmotic pressure is exactly balance by opposing
hydrostatic pressure
• Tonicity: concentration of non-penetrating solutes
o Determines whether water moves in or out
o Isotonic: same tonicity
▪ 0.9% solution of NaCl
▪ Important for intravenous administration and eye drops
o Hypotonic: less/below
▪ Water enters and cell swells and lyses
, o Hypertonic: more/above
▪ Water would come out of cell and it would shrink
Assisted Membrane Transport
1. Carrier-Mediated Transport
• Specificity and selectivity:
o One carrier one substance (or closely related substances
o Different cells may have different carriers
▪ Thyroid: only gland in body that can uptake Iodine due to having the
carriers
• Saturation:
o Finite number of carrier molecules, rate-limiting factor, affinity/number
regulated
▪ Insulin: when present more can be carried
o : transport maximum
Tm
▪ Transport proportional to concentration below maximum when all
carriers saturated
• Competition:
o Occurs when carrier transfers closely related substances
o Diminishes the rate but not the amount of transfer
▪ Ex: alanine and glycine: each will both decrease but same total number
is transported
• Facilitated Diffusion:
o Carrier-mediated transport down a concentration gradient
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Membrane Transport:
• Essential for homeostasis: nutrients in, wastes out
• Plasma membrane is selectively permeable:
o Allows only certain substances to pass through enabling cell to maintain structure
o Lipid solubility and particle size affect membrane permeability
▪ High lipid solubility: cross easy (some water solubility is important)
• Blood is aqueous and intestines is water environment
▪ Low lipid solubility:
• <0.8nm diameter – utilize protein channels (ion channels)
• >0.8nm diameter – assisted transport (glucose)
• Forces are required:
o Passive Force: no energy expenditure by cells for
transport
▪ Ex – concentration gradient and electrical gradient
o Active Force: energy (ATP) expenditure by cells for transport
3 Types of Membrane Transport:
1. Unassisted: molecules can traverse on their own
a. Diffusion: spreading out down a concentration gradient
b. Movement along an electrical gradient
, c. Osmosis
2. Assisted: molecules that cannot traverse on own
a. Carrier mediated transport
i. Facilitated Diffusion
ii. Active Transport
1. Na-K ATPase pump
2. Secondary Active Transport
b. Vesicular Transport
i. Endocytosis: out things get into cell
ii. Exocytosis
1. Caveolae: membrane transport and signal transduction
a. Cave-like structures
b. Endocytosis: how substances get into cell
Unassisted Membrane Transport:
1. Diffusion: movement of molecules from high concentration to area of low concentration
• Concentration gradient – passive mechanism
• If membrane separating 2 areas there will still be movement – as long as can cross
• Steady State: not net diffusion although movement can still be occuring
• Ex – Co2 is higher in body and lower in lungs – can move into lungs without using
energy
• Ficks Law of Diffusion: factors influencing rate
o Magnitude of conc. Gradient directly proportional - ∆C
o Permeability of membrane directly proportional – P
o Surface area of membrane directly proportional –A
, ▪ Lumen: has microvillus which increases surface area
o Molecular weight of substance inversely proportional – MW
o Thickness of membrane inversely proportional – X
o Net Rate of Diffusion:
▪
C.P.A
MW .X
2. Electrical Gradient: charge (driving force) difference between adjacent areas
• Promotes movement towards opposite charge
• Electrochemical Gradient: electrical and concentration gradient
o Difference in charge and concentration
• RMP: resting membrane potential
3. Osmosis: net diffusion of water down its own concentration gradient when
separated by a semi-permeable membrane
• Important for water movement in and out of cells
• Water passes but solute does not:
o Water and solute concentration not equal
o Osmosis ceases when osmotic pressure is exactly balance by opposing
hydrostatic pressure
• Tonicity: concentration of non-penetrating solutes
o Determines whether water moves in or out
o Isotonic: same tonicity
▪ 0.9% solution of NaCl
▪ Important for intravenous administration and eye drops
o Hypotonic: less/below
▪ Water enters and cell swells and lyses
, o Hypertonic: more/above
▪ Water would come out of cell and it would shrink
Assisted Membrane Transport
1. Carrier-Mediated Transport
• Specificity and selectivity:
o One carrier one substance (or closely related substances
o Different cells may have different carriers
▪ Thyroid: only gland in body that can uptake Iodine due to having the
carriers
• Saturation:
o Finite number of carrier molecules, rate-limiting factor, affinity/number
regulated
▪ Insulin: when present more can be carried
o : transport maximum
Tm
▪ Transport proportional to concentration below maximum when all
carriers saturated
• Competition:
o Occurs when carrier transfers closely related substances
o Diminishes the rate but not the amount of transfer
▪ Ex: alanine and glycine: each will both decrease but same total number
is transported
• Facilitated Diffusion:
o Carrier-mediated transport down a concentration gradient
