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What proportion of lean body mass does water account for?
2/3 (higher in children)
Where is most of the water in the human body?
Intracellular (2/3) with interstitial water accounting for about 1/4, plasma 7% and remaining fraction transcellular water
What two components make up extracellular water content?
Plasma and interstitial water
What is meant by transcellular fluid?
Fluid contained within epithelial lined spaces including CSF, gastrointestinal tract fluids and joint fluids
What is a hydrophilic substance?
One that dissolves readily in water and are polar in nature
What is a hydrophobic substance?
Non-polar insoluble substances
What type of molecules have polar and non-polar refions?
Amphiphilic
Give examples of hydrophilic substances
Glucose, sodium ions, ethanol and many proteins
Give examples of hydrophobic substances
Fats, waxes and cholesterol
Define osmotic pressure
The hydrostatic pressure sufficient to stop the flow of water (osmosis)
Which equation can be used to calculate the amount of a substance moved in diffusion?
Fick’s law of diffusion
What symbol is used to represent osmotic pressure
Pi
In the equation osmotic pressure (pi) = MRT, what do the letters M, R and T represent
M is molarity
R is universal gas constant (8.31J/mol K)
T is the absolute temperature (310K at normal body temperature)
Why is the osmotic pressure exerted by salts twice the molar concentration of the salt?
Because salts separate into their constituent ions
Which (M,R, or T) is the only variable that changes when doing an experiment to calculate osmotic pressure (pi) at a fixed body temperature?
Amount of solute (M)
What is the difference between osmolarity and osmolality?
Osmolarity is moles of solute particles/litre solution, osmolality is moles solute particles/kg water
One gram of a non-dissociating substance in 1kg of water exerts an osmotic pressure of how much (give units)?
1 osmol/kg
What is the unit of osmotic concentration?
The osmole
What is tonicity?
The influence of osmotic concentration on the volume of cells
What is the word used to describe two solutions with the same osmotic concentration?
Iso-osmotic
What happens if a cell is placed into an iso-osmotic solution of urea?
The cell will swell (iso-osmotic does not mean isotonic!!)
What happens if a red blood cell is placed into hypertonic solution?
It will become shrivelled (pronated) and star-shaped
What happens if a red blood cell is placed into hypotonic solution?
It will swell and may burst (becoming a ‘ghost‘)
Plasma volume can be measured using which dye
Evans Blue
Extracellular volume be measured using which substance
Inulin (a type of plant polysaccharide)
Which substance can be used to measure total body water
Radioactively-labelled H20
Give three factors that determine a cell’s electrochemical gradient
Concentration gradient, charge of molecule/ion and membrane potential
Which type of channels are open all the time?
‘Leak‘ channels
How many ions per second can travel through a channel protein?
10^8
What is the difference between channel and carrier proteins?
Channel proteins transport material through passive diffusion down its concentration gradient, but carrier proteins transport chemicals both up and down concentration gradients
What does it mean that carrier proteins are stereoselective?
They can (for example) differentiate between D- and L-glucose
What is meant by uniport?
The movement of a particular type of molecule through a membrane through a carrier protein, independent of any other type of molecule
What is meant by symport?
When two different types of molecule are moved across a membrane in the same direction
What is meant by antiport?
A process in which two different types of molecules are moved across a membrane in opposite directions
Briefly describe the function of the sodium pump
It uses ATP to pump (three) sodium ions out of cells in exchange for (two) potassium ions
What is meant by secondary active transport?
The electrochemical gradients set up by primary active transport store energy, which can be released as the ions move back down their gradients. Secondary active transport uses the energy stored in these gradients to move other substances against their own gradients.
Give examples of products transported by secondary active transport
Amino acids and glucose (across epithelial linings of the kidneys and intestines)
What is the difference between transcellular and paracellular absorption?
Transcellular absorption is when substances pass through cells (as opposed to paracellular absorption where absorption occurs across tight junctions)
What is the typical membrane potential of a neuron?
-70mV
What are quiescent cells?
Non-excitable cells (typically those in the G0 phase)
Resting membrane potential is mainly determined by the gradient of which ion across the plasma membrane?
Potassium
Which equation can be used to predict the equilibrium potential of an ion?
Nernst equation
The potassium equilibrium potential is the point at which WHICH two tendencies exactly balance?
The tendency for potassium ions to move down their concentration gradient out of cells, the negative membrane potential that attracts potassium ions back into the cell
The activity of which protein leads to the accumulation of potassium ions inside cells?
The sodium-potassium pump
What is the resting membrane potential for mammalian skeletal muscle?
-90mV
Why is the resting membrane potential different from the potassium equilibrium potential?
Because there is (a very small amount of) movement of sodium ions and other ions as well as potassium
What does the Goldman equation determine?
The resting potential across a cell’s membrane, taking into account ALL ions that can permeate through that membrane
What is the difference in capacity for transport between channel proteins and carrier proteins?
Channel proteins have a high capacity for transport (10^8 ions per second) compared to carriers (10²-10^4 ions/second)
Give an example of a ligand-gated channel protein
Nicotinic acetylcholine receptor
What causes voltage-gated channels to open?
Changes in the membrane potential
What is the difference between endocrine, autocrine and paracrine signalling?
Endocrine signalling is for generalised signalling to sites remote from the site of secretion
Autocrine and paracrine signalling act more locally (autocrine signals affect the secreting cell itself, paracrine signals affect cells within a relatively small radius)
What is the different between endocrine and exocrine glands?
Exocrine glands have ducts (eg. salivary and mammary glands)
Endocrine glands are ductless and their products are secreted into blood
Give an example of a signalling pathway that involves direct control of an ion channel
Nicotinic ACh receptor
Give an example of a signalling pathway that involves direct control of an effector enzyme
Insulin receptor
Give an example of a signalling pathway that involves indirect (g protein) coupling via second messengers/ ion channels
Muscarinic ACh receptors
Give an example of a signalling pathway that involves control of DNA transcription
Oestrogen receptor
Which motor protein carries precursor synaptic vesicles to the nerve ending along microtubules?
Kinesin
Regulated exocytosis is triggered by an increase in which type of ion
Calcium ions
Why are chemical messengers such as nitric oxide and eicosanoids only synthesized when they are needed immediately?
Because they are too lipid soluble to be stored in vesicles
Which cells types perform phagocytosis (ingestion of large matter like cell debris or bacteria)
neutrophils of blood and macrophages, which together are the reticuloendothelial system
What is a syncytium?
A collection of cells fused together, as in the heart muscles
What are connexons?
Proteins assemblies that form the pore for a gap junction between the cytoplasm of two adjacent cells
What are gap junctions?
Membrane channels between adjacent cells that permit direct exchange of cytoplasmic substances
Which class of hormones are able to cross the plasma membrane freely and why?
Steroid hormones because they are lipids themselves
What is electrical coupling?
The passive spread of charge between cells
