Week 5 Flashcards
Osmolarity
Amount dissolved in moles/litre
Osmolality
Amount dissolved in grams/litre
What happens when [solutes]inside > [solutes]outside?
- Water moves in which lowers [solutes]inside
- [solutes]inside move out which lowers [solutes]inside
Sodium’s and Potassium ions are ….
Ubiquitous solutes of the cytosol and extracellular fluid
Na+/ K+ ATPase pump
Forms concentration gradients which facilitate a range of cellular functions
- transport of other solutes across the membrane
- propagation of action potential (cell signaling)
Also maintains osmolarity and resting potential
Passive Transport
- No energy required
- Movement down concentration gradient (channels, symporters, antiporters)
Primary Active Transport
Use chemical energy to move substrates against concentration gradient (pumps)
Secondary Active Transport
Use the energy contained in a concentration gradient to move solutes uphill (against concentration gradient)
Action Potential
The potential difference across the membrane allows for signal transduction via Action Potentials
General idea: change in charge across the membrane opens voltage-gated channels
- Stimulus causes depolarization of membrane. This opens voltage gated Na+ channel, allowing Na+ influx. Na+ influx depolarizes membrane.
- Voltage-gated K+ channels are slower to open than voltage-gated Na+.K+ exits down concentration gradient, causing repolarization of the cell
3.Depolarisation leads to opening of Voltage gated Ca2+ channels
- [Ca2+]i increase triggers release of Ach
- ACh binds its receptor (travels across synaptic cleft)
6.Ligand gated channel opens. Na+ and Ca2+ enter through this channel, starting depolarization
Oversupply of Sodium
Sodium is oversupplied in the Australian diet
- The SDT (adults) for sodium is 2 000 mg/day
- This is lower than the average intake for Australian adults (~4 000 mg/day)
- Excessive sodium intake can lead to increased risk of:
• Hypertension
• Heart attack
• Stroke
How does Na+ relate to hypertension?
- extracellular (ECF) volume maintains blood pressure
- blood pressure is important for adequate tissue perfusion
- changes in salt content of the ECF affect ECF volume
Na+
- The total-body content of Na+ is the main osmotic constituent of ECF
- Main determinant of ECF volume
- The total-body content of Na+ is changed through excretion (kidney)
- Initially, decrease in Na+ will change osmolality
- To maintain osmolality, H2O will also be lost.
- If the amount of H2O in the ECF is decreased, the volume of the ECF will decrease, leading to a decrease in blood pressure.
Hyponatremia
Low Na+
Caused by:
• excessive sweating
• vomiting
• diarrhoea
Roles of Potassium
- maintaining cellular polarization
- transport of other solutes
- maintaining cell volume
- regulation of intracellular pH
- regulation of vascular tone
- control of enzyme function: DNA and protein synthesis, cell growth
Supplied through leafy vegetables, onions, and some spices
There is a limit to how much Na+ the kidney can remove. If the amount of Na+ in the ECF increases, what will happen to blood pressure?
- increase in amount of water in ECF
- increase in ECF volume
- increase in blood pressure