Physiology of Ion Distribution

Question 1

What is an ion?

Answer 1

Atoms/molecules that carry a net electrical charge

Question 2

What is a cation?

Answer 2

Positive electrical charge

Question 3

What is an anion?

Answer 3

Negative electrical charge

Question 4

What is ionic charge relative to?

Answer 4

Valency

Question 5

Give examples of physiological ions and their functions

Answer 5

• Sodium= determines osmolarity
• Potassium= membrane potential
• Calcium = muscle contraction
• Phosphate = ATP
• Hydrogen = pH
• Chloride = Acid-base
• Bicarbonate= buffer in the blood

Question 6

What is the purpose of gradients?

Answer 6

Allow storage of potential energy

Question 7

Give examples of passive transport

Answer 7

Filtration and osmosis which require gradients

Question 8

Give examples of active transport

Answer 8

Primary and secondary which require energy

Question 9

Give examples of vesicular transport

Answer 9

Endo and exocytosis

Question 10

Describe filtration

Answer 10

• Passive movement from high to low hydrostatic pressure
• Filtration through glomerulus
• Osmotic pressure in capillary
• Net difference drives movement
• Not crossing membranes
• Occurs between cells without entering cells

Question 11

Describe passive diffusion

Answer 11

• Selectively permeable membrane
• Passive diffusion for lipid soluble molecules
• -> Gases and steroid hormones act as intracellular
• Down concentration gradinet

Question 12

Describe facilitated diffusion

Answer 12

• Polar hydrophilic substances as they cannot cross hydrophobic core
• Requires channel
• Cells regulate expressed channels, changes permeability
• This establishes gradients
• Ionic movement, calcium and sodium moves in potassium out

Question 13

Describe membrane channels

Answer 13

• Relatively specific, competition can occur for similar molecules (like glucose and galactose)
• Limited number of carriers available which makes saturation possible (finite movement)

Question 14

Describe uniports

Answer 14

One molecule in

Question 15

Describe symports

Answer 15

Co-transport

Question 16

Describe antiports

Answer 16

One in and one out

Question 17

Describe ligand-gated channels

Answer 17

Opened by change in ligand, regulated changes response to stimulus

Question 18

Describe voltage gated

Answer 18

Potential change, closed during rest, required threshold potential to open

Question 19

Describe active transport

Answer 19

• Against gradient, requires energy

Question 20

What is primary active transport?

Answer 20

Uses ATP (can create gradient)

Question 21

What is secondary active transport?

Answer 21

Uses gradients created by primary active transport

Question 22

Describe sodium/potassium ion ATPase

Answer 22

• Na+ binds to the inner membrane
• ATP is hydrolysed
• Protein expels sodium
• Shape of protein reverts and K+ moves in (3rd ATP usage)

Question 23

What is the importance of gradients?

Answer 23

• Gradients store energy
• Energy expended to create gradient
• Energy release when molecules diffuse

Question 24

Describe transport for larger molecules

Answer 24

Enter via vesicular transport, too big to diffuse or enter channels

Question 25

Describe endocytosis

Answer 25

- Active - Phagocytosis, pinocytosis and receptor mediated endocytosis - Invaginations form in the membrane as part of continual recycler - Vesicles formed traps same extracellular fluid internalising it - Vesicles digested and contents recycled - Pinocytosis is random/untargeted

Question 26

Describe receptor mediated endocytosis

Answer 26

- More specific forms of transport - Target binds to cell-surface receptor, stimulating internalisation of ligand-receptor complex - Created vesicle digested and contents used by cell - All require energy

Question 27

Describe exocytosis

Answer 27

- Molecules packaged into vesicles - Vesicles fuse with membrane - Contents released and vesicle recycled - Active - Membrane could get too big with all the fusion, so recycling occurs

Question 28

Describe relative distributions

Answer 28

- Overall osmolality balanced (extra/intracellularly) - Permeability depends on number of available channels - All cells have a resting membrane potential

Question 29

Describe membrane potentials and how they are established

Answer 29

- Excitable cells can rapidly change membrane potential- change membrane permeability - Electrical gradients - > fixed anions in the cell (overall negative in the cell)- proteins and phosphates - > Na+/K+ ATPase- one positive charge out- leaves cell relatively negative - Ion movement due to both conc. and electrical gradients; ions move down gradients

Question 30

Describe equilibrium potentials

Answer 30

- E.g. potassium - Pumped in through Na/K+ pumps at rest K+ leaves cell - Charge is not sufficient to hold in K+ - EP= -90mV (no longer diffusion) - EP for sodium- +60mV - Membrane more permeable to K+, resting potential determined mostly by K+

Question 31

Define equilibrium potential

Answer 31

Theoretical voltage difference across membrane when diffusion gradient = electrical gradient

Question 32

Describe action potential

Answer 32

- Changing membrane permeability allows for establishment of new equilibrium - Depolarisation causes influx of ions which makes potential positive - Change in permeability caused by opening of voltage-gated channels