Body Fluid compartments and transport across cell membranes Flashcards
How do you calculate total body water?
weight in kg x .6= total body water
what percent of BW is total body water?
60%
what is the relationship between water and fat?
inversely related (i.e. more fat an animal has, less water)
what are the 2 major fluid compartments?
intracellular fluid (ICF) and extracellular fluid (ECF)
what makes up the extracellular fluid?
plasma and interstitial fluid
what % of BW is intracellular fluid?
40% BW
what % of BW is extracellular fluid?
20% BW
what % of BW is interstitial fluid?
16%
what % of BW is plasma?
4%
what is the average blood volume?
6-8% of BW or 60-80 mL/kg BW
how do you measure AMOUNTS?
in moles, equivalents, or osmoles
equivalent=
amount of charged solute (CaCl2= 2 Eq of Ca and 2 Eq of Cl)
- moles of solute multiplied by its valence
- Ca=valence 2+
- 1 mole of Ca= 2 Eq Ca + 2 Eq Cl
osmole=
of particles into which a solute dissociates in solution (NaCl= 2 osmoles in solution)
- contribute to osmotic pressure
- 2 osmol/L for osmolarity (concentration)
how do you measure CONCENTRATIONS?
in mol/L or mmol/L, mEq/L, Osm/L or mOsm/L
osmolarity=
osmoles/L
pH expresses…
H ion concentration
H ion concentration in body fluid are….
relatively low, so expresses as a logarithmic term (pH)
what is electroneutrality?
each body fluid compartment must have the same concentration of cations as of anions
what are the major ions in ECF?
- major cation= Na+
- major anions= Cl- and HCO3-
what are the major ions in ICF?
- major cations= K+
- major anions= proteins (negatively charged) and organic phosphates
what is specific to the ICF?
- low ionized Ca2+ and more acidic
- ionized Ca= free Ca -> biologically active
- total Ca= ionized and bound Ca
what is the osmolarity in the ECF and ICF?
THE SAME!- electroneutrality maintained
what is normal osmolarity?
290-300 mOsm/L
selectively permeable
cell membranes ARE NOT freely soluble to all solutes
what are transport mechanisms in the cell membrane?
- Na+/K+ ATPase pump
- Ca2+/ATPase pump
what does the Na+/K+ ATPase pump do?
pump Na out of cell and K into cell; creates high [Na] outside the cell
- DIRECTLY USES ATP
what does the Ca2+/ATPase pump do?
pumps Ca out of the cell
why are ion concentration differences important?
- allows nerve and muscle cells to have resting membrane potentials (DUE TO K+ DIFFERENCE)
- upstroke of action potentials in nerve and muscle cells, and absorption of nutrients DUE TO NA+ DIFFERENCE
- excitation-contraction coupling in muscle cells DEPENDS ON CA2+ DIFFERENCE
what are cell membranes composed of?
lipids and proteins
what are examples of lipids?
- phospholipids, cholesterol, glycolipids
what is important about lipids?
- allow membrane to be permeable to lipid soluble substances
- CO2, O2, fatty acids, steroid hormones receptors, antigens, ion and water channels
what is the phospholipid component of the cell membrane?
- glycerol backbone (water-soluble) + FA tails (lipid-soluble)= amphipathic
- helps to form a lipid bilayer
what are the protein components of the cell membrane?
- integral proteins: can be transmembrane proteins (hormone or neurotransmitter receptors, pores, ion channels)
- peripheral proteins: NOT bound to membrane, loosely attached
how can transport occur DOWN an electrochemical gradient?
- simple or facilitated diffusion
- no input of energy
how can transport occur AGAINST an electrochemical gradient?
- primary transport (direct input of energy)
- secondary transport (indirect input of energy)- i.e. using a Na gradient established using primary transport
is simple diffusion carrier-mediated?
NO! only one that doesn’t need carrier!
what happens when 2 solutions are separated by a membrane permeable to the solute?
the solute will equilibrate across the membrane
what factors does the movement of solute depend on?
- concentration gradient- driving force (larger [ ] diff., greater driving force)
- partition coefficient- based on lipid solubility of solute (greater the lipid solubility of solute, easier it can diffuse)
- diffusion coefficient- based on size of solute and viscosity of solution (very small solutes moving through a non-viscous solution diffuse easily)
- thickness of membrane
- surface area- greater surface area= higher diffusion rate
what are 2 additional consequences of CHARGE on an ion that is diffusing?
- a potential difference across a membrane will alter the rate of diffusion of a charged solute
- diffusion of a positively-charged ion will slow down if diffusing into an area of positive charge
- a diffusion potential can be created when a charged solute diffuses down its concentration gradient
what is facilitated diffusion?
- uses a carrier protein, NO INPUT OF ENERGY
- because of limited # of carriers, it will proceed faster at relatively low solute concentrations
what is an example of facilitated diffusion?
GLUT4 transporter in skeletal and adipose tissue
- transports glucose into cells
- D-galactose also competes for binding
- this affects rate of transport
- facilitated diffusion level off at saturation, while simple keeps going as long as there is conc. gradient
what are features of carrier-mediated transport?
- SATURATION
- carrier proteins have limited # of binding sites for solute; therefore: RATE of transport increases at a higher rate at lower solute concentrations
- STEREOSPECIFICITY
- binding sites for solute on carrier proteins are specific
- COMPETITION
- although binding sites are specific, carriers may recognize and bind chemically-related solutes
what is primary active transport?
one or more solutes MOVED AGAINST a concentration gradient directly using ATP
what is the Na+/K+ ATPase pump?
- present in membranes of ALL cells
- 3 Na+ pumped to ECF and 2 K+ pumped to ICF- creates a charge separation and POTENTIAL DIFFERENCE
- cardiac glycosides inhibit this protein transporter
what is the Ca2+ ATPase pump?
- plasma-membrane Ca2+ ATPase (PMCA)
- sarcoplasmic and endoplasmic reticulum Ca2+ ATPase (SERCA)- 2 Ca from ICF into SR or ER for every ATP
what is the H+/K+ ATPase pump?
parietal cells of gastric mucosa- pumps H+ into lumen of stomach
What is secondary active transport?
indirectly uses energy by utilizing the Na+ gradient to transport solutes against their concentration gradient
describe co-transport (symport)
- all solutes transported in same direction
- Na+/glucose co-transporter (SGLT1)
- Na+/amino acid co-transporter
- Na+/K+/2Cl- co-transporter in renal tubule
describe counter-transport (antiport)
- solutes move in opposite directions- Na+ moves INTO cell and other solute moves OUT of cell
- Ca2+/Na+ exchange
- Na+/H+ exchange
