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
Hypokalaemia
** Low K+**
- Causes: diuretics, excessive vomiting, diarrhoea
- Effects: Muscle weakness, heart arrhythmia
- Potassium wasting can occur where [Na+]ECF is high:
•Na+ loss achieved by increased glomerular flow rate
• Adversely affects K+ reabsorption in the kidney.
Na+/ K+ Balance
- Raised Na+ → decreased K+ reabsorption
- Need to consume adequate K+
- K+ has a direct effect on vascular tone:
Hypokalaemia → exacerbation of the primary hypertension - For this reason, the dietary guidelines recommend considering increasing K+ intake when reducing Na+ to treat sodium-sensitive hypertension.
3 primary macronutrients
- fat
- protein
- carbohydrate
Macronutrients provide what?
- energy
- essential biomolecular components
How do protein, fat and carbohydrate affect metabolic health
- quantity of the macronutrient
- quality of the macronutrient
Role of fat
- Some fats are essential
• linoleic acids
• α-linolenic acids - Fat soluble vitamins are absorbed and transported with fats
- Metabolism of fat provides energy
- Fats are necessary for the production of steroid hormones, bile salts, lipoproteins
What are some fats “good” and some “bad”?
Different types of fat promote the formation of different kinds of cholesterol.
Important: Cholesterol can either refer to
• the family of chemical compounds, or
• the lipoproteins which carry cholesterols and other fats
LDL – low density lipoprotein = “bad” cholesterol. Accumulates, causes atherosclerotic plaques in arteries. Saturated fat contributes to formation of these.
HDL – high density lipoprotein = “good” cholesterol. Can help remove these plaques.
Unsaturated fat contributes to formation of these.
Hydrogenated fats
- Unsaturated fats can become rancid – unpalatable
(chemically: spontaneous conversion to ketones) - Can be prevented by converting unsaturated fats to saturated fats
(hydrogenation – adding hydrogens across double bond)
Problem with hydrogenation
Some cis double bonds are converted to trans double bonds
Trans fats
• Increase risk of cardiovascular disease (CVD)
• Increase LDL (“bad”) cholesterol, decrease HDL (“good”) cholesterol
• Increase inflammatory response, further increasing risk of CVD
• Are rare in Australia, but no legal requirement to declare them in nutritional information
Essential PUFAs p Omega 3 and 6 fatty acids
- Polyunsaturated Fatty Acids - more than one double bond
- The double bond closer to the methyl end of the chain is of greater biological importance
- “Omega” indicates we are counting from the methyl end
- Omega 3 fatty acids have a double bond between carbons 3 and 4
Essential PUFAs - Omega fatty acids
- We cannot synthesise Omega 3 (α-linolenic) and Omega 6 (linoleic) fatty acids, and therefore they must be taken in through the diet.
- The ratio is important to health:
• 4:1 or 1:1 is optimal omega 6 FAs : omega 3 FAs
• The North American settler diet is closer to 30:1
• Imbalance in this ratio is associated with inflammation, and CVD, and increase in “bad” cholesterol. - Omega 3 fatty acids are high in leafy salads and fish oils.
Role of protein
- Provides essential amino acids
• 9 essential, 6 conditionally essential - Provides nitrogen for protein synthesis
• Growth, maintenance, repair - Source of energy
- Very important in growth and development
- Protein quality is dictated by
• Amino acid composition
• Digestibility - There is no storage of amino acids
Protein metabolism
- Carbon backbone is used to produce energy
- Glucogenic → pyruvate or TCA cycle intermediates
- Ketogenic → acetoacetate or acetyl CoA
- Some AA - both categories
Carbohydrates
- Primary source of energy for most people
- Types of carbohydrates
• Fibres
• Starches
• Sugars - Carbohydrate metabolism
• Glycolysis
• Pentose Phosphate Pathway
• Glycogenesis / Glycogenolysis (storage)
• FA synthesis (storage)
Assessing carbohydrate quality
- Glycaemic index
- High GI food causes rapid rise in blood glucose
- Low GI food causes gradual, lower rise in blood glucose
Whole and refined carbohydrates
Whole grains contain fibre
• Can be milled (remove endosperm, germ, bran), as long as product contains those elements
Refined
• Only the starch component
Dietary Fibre
- Non-digestible forms of carbohydrates, and lignin.
- Increases satiety
- Protects against cardiovascular disease, obesity, type 2 diabetes
- Essential for digestive health: colonic lubrication and transit
- Provided in the diet by whole grain foods, cooked dry beans and peas, vegetables, fruit and nuts
Added Sugars
- Dietary guidelines state to reduce intake of added sugar
- Added sugar has no additional nutrients, and overconsumption can eventually lead to type 2 diabetes
- Added sugar consumption occurs almost exclusively through consumption of sweetened beverages, and in snack foods
