Forces Acting Across Membranes Flashcards
Why does difference in chemical composition of ECF and ICF exist?
Presence of cell membrane
Which membranes divide the different water compartments and what are they permeable to?
Capillary wall (separates Plasma and ISF within the ECF)- most things apart from plasma proteins and blood cells
Plasma (cell) membrane - selective barrier which only allows for passive diffusion of gases and water by osmosis
What is the cell membrane studded with and what are they always?
Aquaporin channels - permanently open to water, allowing its movement between ECF and ICF
What else can freely pass between compartments
Gases
Explain ions in relation to movement between compartments?
Pass freely across capillary wall so exchange readily between plasma and ISF, but don’t penetrate cell membrane
What are the concentrations of K and Na either side of the membrane?
K+ high in ICF but low in ECF
Na+ high in ECF but low in ICF
What is the distribution of solutes like between compartments in terms of concentration?
Identical (apart from plasma proteins) between Plasma and ISF, however these vary greatly from ICF
What are the differences in composition of fluid essential for and how are they possible
Life (biochemical and physiological processes relying on conc gradients)
Presence and properties of cell membrane
What are the 7 important things about membranes?
- Selctive barrier
- Permeability can vary
- Membranes are dynamic
- Thin double layer of sheets of lipids (lipid bi-layer)
- very flexible
- Exellent insulators
- Embedded with proteins (and associated with carbs)
- Cell membrane is a selective barrier
Freely permeable to some substances (O2/CO2) but difference in composition of ICF and ECF shows that permeability is selective
- permeability can vary
May inc/dec at different times which is important for various cell functions (e.g. transmission of nerve impulses)
- membranes are dynamic
Continually being formed and maintained or dismantled and metabolized according to the needs of the cell
- Very thin double layer of sheets of lipids (lipid bi-layer)
Phospholipids: hydrophilic (lipophobic) head and hydrophobic (lipophilic) fatty acid tail. In aqueous environment they arrange themselves so the head is pointing outwards and tail inwards, with the FA chains on the inside of the membrane away from the H20
- Membranes are flexible
FA behave like oil in vivo, so can stretch (although may rupture if overstretched)
- Membranes are insulators
AGAINST MOVEMENT OF ELECTRICAL CHARGE. This prevents the passage of electrons which maintains the electrical stability of the cell
- Membranes are insulators
AGAINST MOVEMENT OF ELECTRICAL CHARGE. This prevents the passage of electrons which maintains the electrical stability of the cell
- embedded with proteins (and associated carbs)
Can have integral (all way through) or peripheral proteins embedded in the membrane carrying out tasks as enzymes, channels, transporters…
Explain membrane carbohydrates
Carbs may attach to phospholipids or proteins embedded in the lipid bilayer - known as glycolipids or glycoproteins - ALL are extracellular
Important in CELL COMMUNICATION (e.g. self vs non-self recognition by immune system). Flag on surface of cell with tell the immune system something about the identity of that cell
Integral membrane protein
Span hydrophobic core of lipid bi-layer
Peripheral protein
Associated only with phosphate head of lipid bi-layer; doesn’t penetrate hydrophobic core
Give 5 common functions of membrane proteins
- Receptors
- Transport (transporter or channel proteins)
- Enzymes
- Maintenance of cell structure (anchorage)
- Communication
What can membrane protein functions often be?
Linked
- Receptors
Penetrate cell membrane from ECF to ICF which allows for communciation of an extracellular signal (neurotransmitter/hormone) to the intracellular space, creating a cellular response. Only tissues that express receptors for that particular ligand can respond to it.
- Explain receptor action in more detail
The cell responds to this extracellular chemical signal because the ligand binds to a receptor protein which then causes a confirmation of change in that protein that is transmitted to the intracellular side. Once that signal reaches the intracellular side, it can then change events in the cell and it changes the cell behaviour.
Effectively, extracellular signal brings about change in intracellular activity of cell through the presence of receptor proteins which act to translate that extracellular signal to an intracellular response