Forces Acting Across Membranes 1 Flashcards
What does the cell membrane do?
Separates ECF and ICF and is responsible for maintaining the difference in composition
What is a major difference between the ECF and the ICF?
The chemical composition
What is the ECF sub-divided into?
Plasma and interstitial fluid
What is ratio of Total body water in the ECF compared to the ICF?
-ECF= 1/3 TBW (combined 14L)-ICF=2/3 TBW (combined 28L)
How does gas pass across the capillary wall and cell membrane?
Freely
How do nutrients and waste pass across the capillary wall and cell membrane?
Pass easily but sometimes with help from membrane proteins
How does water pass across the capillary wall and cell membrane?
There is no barrier to water
How do ions pass across the capillary wall and cell membrane?
-Pass freely across the capillary wall so exchange readily between plasma and ISF-They do not penetrate the cell membrane
Describe the concentrations of K and Na ion in the ICF and ECF.
-K is high in the ICF, low in the ECF-Na is low in the ICF, high in the ECF
In what way does the distribution of solutes differ in the plasma and the ISF?
In their protein concentration
What is meant by the cell membrane being a selective barrier?
It is freely permeable to some substances such as O2 and CO2 but the difference I composition between ECF and ICF shows that permeability is selective and not universal
What is the cell membranes ability to vary permeability important for?
Various cell functions including transmission of nerve impulses
How do membranes provide binding sites for chemical recognition?
Embedded in cell membranes are receptors for chemical signals such as hormones and neurotransmitter which regulate cellular activity.
What tissues can respond to a hormone/ neurotransmitter signal?
Only tissues that express receptor for the specific hormone/neurotransmitter
What is meant by membranes being dynamic?
They are continually being formed and maintained or dismantled and metabolised according to the needs of the cell.
What is the structure of the cell membrane?
- Very thin bi-layer of phospholipids
Describe the structure of a phospholipid.
Hydrophilic phosphate heads and hydrophobic fatty acid tails.
How do phospholipids arrange themselves in an aqueous environment?
Their polar part is on the outside of the membrane and the fatty acid chains are on the inside
Lipophobic
Lipid repellent and hydrophlic
Lipophyllic
Lipid loving and hydrophobic
What is embedded in the phospholipid bilayer?
Proteins
Why are membranes flexible?
Fatty acids in vivo behave like an oil and therefore can stretch , although may rupture if over stretched
What is meant by membranes being insulators against movement of electrical charges?
They prevent the passage of electrons which is important in maintaining electrical stability of a cell
What are the 4 general classes of membrane proteins?
ReceptorsTransportersEnzymesPeripheral proteins
What are receptors, enzymes and transporters otherwise known as?
The integral membrane proteins
What are integral membrane proteins?
Proteins that are integrated into the structure of the membrane, typically spanning the hydrophobic core and cannot be extracted without disturbing the membrane
What are peripheral proteins?
They are proteins associated with the membrane but not incorporated into it. They do not span the hydrophobic core
What do receptors do?
Allow communication of an extracellular signal to the intracellular space to create response
What are transporters?
Proteins which allow movement of ions or molecules across the membrane.
What are the 2 forms of transporter
- Channels: create a port through the membrane through which molecules, usually ions flow, Can be gated or open
- Carrier proteins: do not create a continuous pore from ECF to ICF. Open to ECF the ICF but never at the same time. Can move larger molecules than channels e.g. glucose
What do membrane enzymes do?
Catalyse chemical reaction on the cell membrane
Give an example of internal and external enzymes
-External: those found in the small intestine which break down nutrients into smaller subunits,-Internal: those associated with converting signals carried from receptors into an intracellular response
What are the 3 main roles of peripheral membrane proteins?
-Maintain structure of cells by anchoring membrane to intracellular cytoskeleton.-Attach cells to the extracellular matrix e.g collagen-Perform signalling functions within cells e.g G proteins
What is myelin?
A membrane that serves as an insulator around myelinated nerve fibres and has a low protein content. A major component is lipid
What is the typical protein content of plasma membranes of cells other than that of myelinated nerve fibres?
50%
What membranes has protein contents of around 75%?
Membranes involved in energy transduction such as the inner membranes of the mitochondria
What are membrane carbohydrates linked to proteins and lipids as?
Glycoproteins and glycolipids
What role do membrane carbohydrates play?
Self-versus non-self recognition and in the immune system
