Body Fluids And Membrane Transport Flashcards
How many litres of water do we have in our bodies?
42
What is the water content in our bodies split up into (give numbers)
25 litres intracellular fluid (ICF) 17 litres extracellular fluid (ECF): - 13 litres interstitial fluid (ISF) - 3 litres plasma - 1 litre transcellular fluid
What is interstitial fluid?
Fluid that is bathing the cells. Outside of blood vessels but not inside cells
What is the total blood volume?
6 litres
What is transcellular fluid?
Fluid that has crossed an epithelial cell barrier and has been modified in some way
Give some examples of Transcellular fluids and where they are located
- Cerebrospinal fluid - brain
- Urine - kidney and bladder
- Gastrointestinal secretions - saliva, gastric juice, pancreatic juice, bile
- Sweat
- aqueous and vitreous humors - eyes
- synovial fluid - joints
Why is there a higher composition of proteins in the intracellular fluid?
Because proteins are created within cells
Why is there no net force driving the movement of water at resting?
Because there’s the same osmolality in the intracellular and extracellular fluid
What happens to fluid entering your body?
It is absorbed in the gut and would then enter the plasma. It would then cross the endothelium barrier to enter the ISF. Once it is in the ISF it can be transported across a layer of epithelial cells to become transcellular fluid, or it can cross the plasma membrane to become the ICF
Give features of the plasma membrane
- It is highly selective in its permeability
- it has lots of transport proteins tor uptake and removal of specific solutes
- vital for regulation of the intracellular environment
- has a lipid bilayer: contains a hydrophilic outer head (attracted to water) and a hydrophobic outer tail (repulsed by water)
- provides structural support
What is the phospholipid bilayer impermeable to?
Ions and polar molecules
What is permeability it the membrane provided by?
Membrans proteins (transporters)
Give examples of membrane proteins
- Channels
- Carriers
- Pumps (require energy to move an ion against the concentration gradient)
How can lipid soluble membranes cross the plasma membrane?
Through simple diffusion
How can water soluble molecules cross the plasma membrane?
Through a channel, carrier or pump
What uses passive transport?
Diffusion, channel-mediated and carrier mediated transport
How are ion pumps powered?
By the hydrolysis of ATP (active transport)
What are the different types of carrier?
- Facilitator (uniport)
- Cotrans-porter (symport)
- exchanger (antiport)
They all work by passive transport
What is the function of a facilitator (uniport)?
It will only transport one ion species
What are the functions of cotrans-porters (symport)
It tranports two different ion species in the same direction. They are electroneutral. The net movement of charge across the membrane would balance out as it would carry one positive and one negative ion.
What’s the function of an exchanger? (Antiport)
It swaps ions of the same charge (to maintain electroneutrality)
What are the functions of transport proteins?
- help to maintain the internal environment of the cell
- uptake of nutrients, substrates and cofactors (needed for metabolic reactions)
- exports waste products
How do cells regualte pH?
Using a sodium potassium. This is an energy requiring process as the ions are being moved against their concentration gradient. In expending the energy to make the pump work the cell sets up gradients to let other substances in and out:
- if there is too much acid in the cell a gradient has been set up where H+ ions can move out of the cell while Na+ ions move in
- if there is too much base in the cell a gradient had been set up in which HCO3- ions can move out of the cell and Cl- ions can move in
How can cells regulate their volume?
- if they need to increase their volume they can move Na+, K+ and Cl- into the cell and that will create a gradient which will also transport water into the cell expanding the volume
- if the volume needs to be decreased Cl- and K+ can be moved out of the cell ceeating an osmotic gradient allowing water to be moved out of the cell
Why is Ca2+ kept at a very low concentration in the cell?
Because it is a signalling molecule and can trigger cellular action
Why do we have lots of organic negatively charged ions inside the cell?
Because they have no mechanism to move outside the cell
How do cells maintain an electrical gradient across the membrane?
The cell inside is negatively charged compared to the outside of the cell. This is because of the negatively charged organic ions trapped inside the cell
How does water move across the cell membrane?
Passively through osmosis
What cells are all blood vessels lined by?
A layer of endothelial cells
What do capillaries have an important role in?
The regulation of interstitial fluid - they act as a batrier against the movement of water and ions out of the plasma into the interstitial fluid
What is the approximate distribution of solutes across the capillary and endothelium?
- approximately equal concentration of small ions and organic solutes in ISF and plasma
- low concentration of protein in ISF and high concentration in plasma
What happens at the beginning of the capillary network?
At the beginning of the capillary network fluid is moving out of the blood into the interstitial compartment taking with it nutrients and ions the cell requires
What happens at the end of the capillary network?
The fluid moves from the interstitial compartment into the plasma taking with it the waste products the cell has produced
How do the hydrostatic and osmotic forces in the capillary network work?
- at the start of the capillary network there is a higher hydrostatic pressure (pressure from the heart contracting) in the capillaries compared to the ISF which forces fluid out along with nutrients and ions
- At the end of the capillary network the pressure decreases and we see the net movement of water from the ISF into the plasma. This is caused by a change in colloid osmotic pressure (due to the protein concentration differences between the ISF and plasma). As fluid is moving out of the capillary network protein remains behind because it can’t cross the endothelial barrier. So the conc. of protein is goung up at the same time as the hydrostatic pressure is decreasing because of resistance of flow. So towards the end of the capillary network the colloud osmotic pressurenis sufficient to move water and waste products back to the capillary
What are the layers of cells called that cover internal and external surfaces of organs and tissues?
Epithelial cells
What is the importance of epithelial cells?
- protective/ barrier function
* important role in absorption and secretion (e.g. secretion into the kidney tubules)
What in the intestine is lined by epithelial cells?
- The villi (inner layer of intestine)
* The outer layer of the intestine
What is the inner intestinal epithelial cell membrane called?
The apical membrane
What is the outer intestinal epithelial cell membrane called?
The basolateral membrane
Why can nothing pass between inner epithelial cells in the intestine?
Because the cells are joined by a tight junction. Anything that wants to pass must go through
What is the result of the intestinal inner epithelial cells Na+/K+ pump
It means that the sodium you have eaten can passively move through the apical membrane then glucose can follow. This creates a gradient which allows the absorption of water
How is water able to move from the ISF into the gut?
Some cells in the villi have a Na+, K+ and Cl- gradient where the ions move from the basolateral membrane into the cell and then the chloride moves into the gut. This creates a gradient allowing water to move from the ISF into the gut
What happens if you have cholera or food poisoning?
The bacteria priduce toxins which blocks the transporter from absorbing water into the ISF and only allow water to move into the gut which can lead to diarrhoea
What does the plasma membrane contain?
Lipids, proteins, carbohydrates and cholesterol which stiffens it
What are integral proteins?
Part of the plasma membrane structure and cannot be easily seperated from it without damaging or destroying the membrane. Most intergal proteins span the width of the membrane and are known as trans-membrane proteins
Describe a peripheral protein
It is bound to the inner or outer surface of the membrane and are easily seperated from it. There are many more peripheral proteins than integral proteins
What do anchoring proteins do?
Atrach the plasma membrane to other structures and stabilise it’s position
How do the cells of the immune systems recognise other cells as normal or abnormal?
Based on the presence of absence of characterisitc recognition proteins (glycoproteins)
What can the cytoplasm be divided into?
Cytosol (a fluid) and organelles
What are receptor proteins in the plasma membrane sensitive to?
The presence of specific extracellular molecules or ions called ligands. When a ligand bindsnto the appropriate receptor the binding may trigger changes in the activity of the cell
How do carrier proteins get solutes across the membrane?
They bind to them
What does a channel do?
Forms a passageway completely through the plasma membrane. Often found in integral proteins. Theg permit small solutes and water to move across the plasma membrane
What are gated channels?
Channels that can open or close to regilate the passage of substances
What is the glycocalyx?
The carbohydrate portions of glycoproteins that extend beyond the outer surfave of the membrane
What are the functions of the glycocalyx?
- lubrication and protection
- anchoring and locomotion
- specifity if binding
- recognition
What are important factors that influence diffusion rate?
- Distance
- Ion and molecule size (the smaller it is the faster the rate of diffusion)
- temperature (the higher the temperature the faster the rate of diffusion)
- concentration gradient
- electrical forces (opposite electrical charges attract eachother and like charges repel eachother)
What is the electrochemical gradient?
The net result of the chemical and electrical forces acting on an ion
What does an ion crossing a particluar membrane channel depend on?
- size of the ion
- charge of the ion
- size of the hydration sphere
- interaction between the ion and channel walls
What generates hydrostatic pressure?
Pushing against a fluid
What can water also cross a membrane through?
Abundant water channels callef aquaporins
Whhat is the osmolatity/osmotic concentration?
The total solute concentration in an aqueous solution
What is tonicity?
The nature of the solute and how the solution affects the shape of the cell
What does carrier mediated transport require?
Specialised intergal membrane proteins. It can be active or passive
What does vesicular transport involve?
Moving materials within vesicles, it’s always an active process
What happens in carrier mediated transport?
Integral proteins bind to specific ions of organic substrates and carry them across the plasma membranes
What are the characteristics of all carrier-mediated transport which they share with enzymes?
- specifity
- saturation limits
- the binding of other molecules such as hormones can affect the activity of carrier protiens
What is faciliated diffusion?
It passively transports large substances such as glucose through the membrane. The molecule to be transported must first bind to a receptor site on the carrier protein. The shape of the protein then changes, moving the molecule across the plasma membrane and releasing it into the cytoplasm
What mechanism does an exchange pump carry out?
A counter-transporter or antiporter mechanism
What is primary active transport?
The process of pumpung solutes agaunst a concentration gradient using the energy from ATP
What is transcytosis?
When endocytosis produced vesicles on one side of the cell that are discharged through exocytosis on the opposite side
How is a potential difference set up across the plasma membrane and what is this referred to as?
A potential difference is set up because the plasma membrane keeps the positive and negative charges on either side apart. This is called the membrane potential
What is a difference between intracellular and extracellular fluid?
They have different electrolyte compositions
