Fundamentals: Physiology - Cellular physiology Flashcards
Define moles
Gram-molecular weight of a substance (i.e. MW of substance in grams)
1 mole = 6x10^23 molecules
Define osmole
Concentration of osmotically active particles in a solution
1 osmole = gram-molecular weight/number of freely moving particles each molecule liberates in solution (1.g. each mole of NaCl supplies 2Osm: Na+ and Cl-)
Define equivalents
1 mole of an ionised substance / its valence
E.g. 1 Eq of Ca2+ = 40g / 2 = 20g
Define oxidation
Combination of substance with O2, or loss of hydrogen, or loss of electrons
Define reduction
Inverse process to oxidation (loss of O2, or gain of hydrogen/electrons)
Define transcellular fluid
Proportion of body water contained in epithelium-lined spaces (constitutes a very small percentage of total body fluids)
Define osmolarity
Number of osmoles per litre of solution (R = ragbag)
What is normal plasma osmolarity?
290mOsm/L
Define osmolality
Number of osmoles per kg of solvent (L = liquid only)
What is normal plasma osmolality?
290mOsm/kg
What is the difference between osmolarity and osmolality?
Osmolality is not affected by various solutes in solution, or effects of temperature
Define osmolal concentration
Measured by degree to which a substance in a fluid depresses the freezing point
How much does 1 mole of an ideal solution depress the freezing point?
By 1.86 degrees Celsius
Define tonicity
Osmolality of a solution relative to plasma
Define pH
-log([H+])
What is the pH of water at 25 degrees Celsius? What does this mean in terms of the relative concentration of H+ and OH-?
7
[H+] = [OH-]
Define buffer
Substance that can bind or release H+ in order to maintain a stable pH
Give 3 examples of buffer systems
H2CO3
Phosphate
Protein
Define diffusion
Process whereby a gas or substance in a solution expands to fill the total available volume via movement of its particles
During diffusion there is a net flux of particles moving from areas of high to low concentration
What is the relationship between time to equilibrium and diffusion distance?
Time to equilibrium is proportional to square of diffusion distance
What is the relationship between magnitude of diffusing tendency, cross-sectional area, and concentration gradient?
Magnitude of diffusing density is proportional to cross-sectional area across which diffusion is taking place, and the concentration gradient
Define concentration gradient and provide a formula
Aka chemical gradient
Difference in concentration of the diffusing substance divided by thickness of the boundary
Δc/Δx
What is Fick’s law?
J = -DA(Δc/Δx)
Where J = rate of diffusion
D = diffusion co-efficient
A = area
Δc/Δx = concentration gradient
Define osmosis
Diffusion of solvent molecules into a region in which there is a higher concentration of a solute to which the membrane is impermeable
Define osmotic pressure. What is it proportional to?
Pressure necessary to prevent solvent migration via osmosis
Proportional to number of particles in solution per unit volume of solution
Define solvent drag
Influence exerted by flow of solvent through a membrane on simultaneous movement of solute through the membrane
Explain the Donnan effect
Describes the unequal distribution of permeant charged ions on either side of a semipermeable membrane which occurs in the presence of impermeant charged ions
Product of diffusible ions on one side of membrane = product of diffuse ions on other side
Define oncotic pressure
Colloid osmotic pressure due to plasma colloids
Form of osmotic pressure exerted by proteins in blood vessels that tend to pull water into the circulatory system
What % of body weight is total body water?
60%
Describe the distribution and composition of total body water
Total body water = 60% of total body weight
ICF = 60% of total body water, 40% of total body water
ECF = 40% of total body water, 20% of total body weight
Describe the composition of ECF
Blood plasma = 25% (~5% of total body weight)
Interstitial fluid = 75% (~15% of total body weight)
What is blood volume as a % of total body weight?
Blood volume = plasma + cell components of blood = ~8%
Explain the general difference in contents between ICF and ECF
ICF: high in K+, Mg2+, phosphates, protein
ECF: high in Na+, Cl- (no proteins in interstitial fluid, some in plasma)
What is the Na+ concentration in ICF vs ECF?
ICF: 15mmol/L
ECF: 150mmol/L
What is the K+ concentration in ICF vs ECF?
ICF: 150mmol/L
ECF: 5.5mmol/L
What is the Cl+ concentration in ICF vs ECF?
ICF: 9mmol/L
ECF: 125mmol/L
What is the Mg2+ concentration in ICF vs ECF?
ICF: 13mmol/L
ECF: 1mmol/L
What is the PO4(3-) concentration in ICF vs ECF?
ICF: 100mmol/L
ECF: 1mmol/L
What are 4 methods of transport across cell membranes?
- Exocytosis
- Endocytosis
- Passive diffusion
- Transport proteins
- Filtration
- Transcytosis
Explain the process of exocytosis
Vesicles containing cell material for transport bind to the cell membrane, and the act of fusion then breaks down the membrane, leaving the vesicle contents outside the cell with the cell membrane intact
Explain the process of endocytosis
Reverse of exocytosis (substance to be endocytosed is enclosed in pocket formed by outer cell membrane, pocket buds off to become intracellular vesicle containing endocytosed substance, membrane is left intact)
What molecules undergo passive diffusion? Give examples
Small non-polar (e.g. O2, N2)
Small uncharged polar (e.g. CO2)
Membranes have limited permeability to other substances
List 5 cell membrane transport methods involving transport proteins
- Aquaporins
- Ion channels
- Facilitated diffusion
- Active transport
- Secondary active transport
Explain facilitated diffusion
Carriers bind ions and other molecules, resulting in configurational change of the transport protein and causing movement of bound molecule from one side of membrane to the other down their electrochemical gradient
What is active transport?
When substances are transported against their electrochemical gradient (e.g. Na+ K+ ATPase)
What is secondary active transport?
When active transport of one molecule is linked to transport of other substances (e.g. Na+ K+ ATPase indirectly affects Ca2+ transport in heart)
May be co- (same direction) or counter- (opposite direction) transport
What is a uniport?
Transport protein that transports only one substance
What is a symport?
Transport protein that transports >1 substance together
What is an antiport?
Transport protein that exchanges one substance for another
Define filtration. Where does it typically occur?
Pressure-driven movement of water and solute across a membrane
Typically occurs across capillary walls
What is transcytosis?
Transport of proteins out of capillaries across endothelial cells via endocytosis on the capillary side followed by exocytosis on the interstitial side
Describe the structure of Na K ATPase and draw a picture. What steps are involved in its function?
Heterodimer with alpha and beta subunits which both extend through cell membrane
B unit is a glycoprotein (has attached carbohydrate residues)
a unit has intracellular Na+ and ATP binding sites, and a phosphorylation site; extracellularly it has K+ and ouabain binding sites
Function:
1. Na+ and ATP bind a subunit concurrently
2. ATP undergoes hydrolysis to form ADP, with a phosphate being transferred to Asp 376 at the intracellular phosphorylation site of a subunit
3. Protein undergoes a conformational change and Na+ is released into ECG
4. K+ binds extracellularly, resulting in dephosphorylation of a subunit and reversal of conformational change: K+ is then released into cytoplasm
Describe the function of Na K ATPase
Catalyses the hydrolysis of ATP to ADP, using energy to extrude 3 Na+ and take in 2 K+ (i.e. is an electrogenic pump with a coupling ratio of 3:2)
What factors increase Na K ATPase activity? How?
Increased Na+ (receptors not saturated at normal levels of intracellular Na+)
Thyroid hormone (increased transcription)
Aldosterone increases number of pumps
Insulin increases activity via a variety of mechanisms
What factors reduce Na K ATPase activity? How?
Dopamine decreases Na K ATPase activity in the kidney by phosphorylating the pump, causing natriuresis
Outline 5 mechanisms of intercellular communication
- Gap junctions
- Synaptic
- Paracrine/autocrine
- Endocrine
- Juxtacrine
Compare and contrast mechanisms of intercellular communication
What is juxtacrine communication?
Some cells express multiple repeats of GFs, which anchor the cell and may then bind to GF receptor on another cell to link the two
Outline four possible types of cell responses to receptor binding
- Ion channel activation
- G-protein activation
- Activation of enzyme activity
- Direct activation of transcription
Give an example of ion channel activation as a response to receptor binding
Noradrenaline activates K+ channels
Give examples of mediators which activate G-proteins on receptor binding
Adrenaline, NA
Dopamine
Histamine
Angiotensin II
TSH
FSH/LH
Give an example of enzyme activity activation in response to receptor binding
Angiotensin II activates phospholipase C
Give examples of a mediators which directly activate transcription
Thyroid and steroid hormones
Vit D
Retinoids
What is a second messenger?
Molecules that undergo a rapid concentration change in the cell following primary receptor recognition, and which initiate changes in cell function
Give 6 examples of second messengers
Ca2+
cAMP
cGMP
IP3
NO
DAG
What is the concentration of Ca2+ in cytoplasm vs interstitial fluid? What is the significance of this?
Free Ca2+ in cytoplasm: 100nmol/L
Free Ca2+ in interstitial fluid: 12,000nmol/L
Strong inwardly directed electrochemical gradient
Where is intracellular Ca2+ mainly stored?
ER
Explain the process of G protein activation and deactivation
Activation: G-protein exchanges GDP for GTP (active form)
Deactivation: inherent GTPase activity converts GTP back to GDP (inactive form)
What are the two types of G-proteins?
- Small G-proteins
- Heterotrimeric G-proteins
Explain the structure and function of a heterotrimeric G-protein, drawing a picture
Structure: a, B and y subunits
Function:
1. a subunit is bound to GDP: when ligand binds receptor, GDP is exchanged from GTP and a subunit separates from B and y subunits
2. a subunit brings about many biologic effects; B and y subunits together form a signalling molecule that can also activate a variety of effectors
4. Intrinsic GTPase activity of a subunit converts GTP to GDP and a becomes reassociated with B and y
