Physiology PRAC Notes Flashcards
Definitions for mechanisms of red blood cells
Hyperosmotic (NaCl)
- solution that has an overall higher concentration of solutes compared to another solution
Hypertonic
- high concentration
- water moves OUT of cell (causing shrinkage)
Hypo-osmotic (water)
- solution that has a lower solute concentration
Hypotonic
- low concentration
- water moves INTO cell (causing bloating)
Isotonic
- solutions that have the same concentrations of water and solutes in cell
Iso-osmotic
- same concentration
- NO net movement of water
- iso-osmotic solutions of permeant solutes are typically hypotonic
What is the direction of the osmotic gradient and water flow in hypotonic cells?
- water is hypo-osmotic, so water flows into cells
- diffuses down its concentration gradient (low to high osmolarity)
Appearance:
- swollen appearance – water has moved into cells
- makes cells swell and even burst, to become faint as the contents are lost and membrane is ruptured
Why don’t all the red blood cells lyse (rupture their membrane)?
- osmotic strength of water increases as some cells lyse
- bursting cells release salts and other constituents into water so that osmotic gradient for remaining cells is reduced
- water can go pink-ish (haemoglobin from cells that were lysed)
How would you describe the cell in hypertonic conditions (1.8% saline) as compared to the control?
- shrunken
- crenated (scalloped or notched) appearance
- cytoplasmic volume has decreased, causing cell shrinkage and the development or notches/wrinkles in the membrane
What was the direction of the osmotic gradient and flow in hypertonic solutions?
- concentrated salt solution is hyperosmotic, so water flows out of the cells
- causes shrunken appearance
- water diffuses down concentration gradient (low to high osmolarity)
- external solution has high osmolarity, water flows out
When cells are added to iso-osmotic glucose – how would you describe the typical cell appearance as compared to the control?
- although not as severe as when in water, appear swollen
- no crenated cells, some cells appear faint and ghostly
This suggests that water has entered the cells, causing them to swell. So, the isomotic glucose is actually hypotonic. Why is this so?
- glucose can enter the cell, raising the osmolarity of the cytoplasmic solution
- it is permeable across many cells because of glucose facilitated diffusion transporters
- high concentration gradient driving diffusion of glucose into cell
- glucose enters, raising the intracellular osmolarity and creating an osmotic gradient for water to enter the red blood cell
Blood typing! - Reverse typing
Refer to table!
Just refer to table in notes!!
Antibody A - agglutination with A antigens
Antibody B - agglutination with B antigens
Type A
- A antigens, B antibodies
Type B
- B antigens, produces A antibodies
Type AB
- A and B antigens
- no antibodies
Type O
- has no A or B antigens
- produces A and B antibodies
When reverse typing:
- it will agglutinate with the opposite blood type
How is a membrane potential generated?
Key concept 1:
With a concentration gradient and ion selective membrane
How was the negative membrane potential generated?
The permeant ions moving from ICF to ECF creates the negative membrane potential
Key concept 2:
- only a small amount of ions move across the membrane to generate membrane potentials
- the concentrations of ions don’t significantly change under most physiological conditions
- K+ moved across membrane to cause ICF to have less K+ and ECF to have excess K+
- surplus of Cl- in ICF caused more negative charge (negative membrane potential)
Which direction does the chemical force on K+, and Cl- act?
- both want to move from ICF to ECF
- ions move from high to low concentrations
What way do electrical forces act on ions (use K+ as example)?
- electrical force acts according to the law that opposite charges attract while like charges repel
- therefore negative Vm attracts K+ to ICF
If the membrane is only selective for one ion, what happens to membrane potential?
- it reaches equilibrium at Nernst potential (no net movement), where chemical and electrical forces are equal
If in a graph, membrane potential goes down for Cl-, what happens?
- it means the membrane is Cl- selective
- ions move down conc. gradient from ICF to ECF to set up an excess of K+ in ICF and surplus Cl- in ECF resulting positive membrane potential
What happens to permeant ions before equilibrium?
What does changing membrane selectivity do?
This is key concept 3!
- permeant ions will continue to flow across the membrane until electrochemical equilibrium is reached
Membrane selectivity:
This is key concept 4!
- cells can change the membrane potential
- achieved by opening and closing of specific ion-selective channels in membrane
- how action potentials, synaptic potentials and sensory potentials are generated
Refer to graphs with selectivity points!!
Assuming a nerve cell membrane is only permeable to Na+ and K+ what are the PK/PN values and the membrane permeabilities?
- Resting membrane potential
- PK/PNa ratio: ~100
- membrane permeability: steady, mostly K+ - Depolarisation
- decreasing
- Na+ permeability increasing - Peak of depolarisation
- ~ 0.01
- mostly Na+ permeable - Repolarisation
- increasing
- Na+ permeability decreasing
- K+ permeability increasing - Afterhyperpolarisation
- ~ 1000
- K+ permeability at its maximum
What happens at rest?
- membrane potential does not equal K+ equilibrium potential
- K+ is not at equilibrium, small force moves K+ out of the cell, but membrane potential change (steady state)
- K+ efflux is exactly balanced by Na+ influx
- high membrane permeability for K+
- small electrochemical force for efflux
- low permeability for Na+ but high electrochemical driving force for Na+ influx
What type of muscle contractions were measured in experiment 1? What did they look like on graphs?
isometric
- kept the muscle at a fixed length (iso) length (metric) during the contractions and used a force transducer to measure the tension developed
Graphing:
- threshold level then steadily incline to a plateau (like an ‘S’ shape)
What happened in experiment 1?
How do you explain the stimulus-tension relationship? What happens with stimulation below and above the twitch threshold?
Experiment 1: recruitment
- sciatic nerve is draped over stimulated electrodes
- when stimulator is activated, an electric field is generated around the electrodes
- any axons within the field will be depolarized and fire action potentials (axons will be recruited)
Stimulation below the twitch threshold
- results in a small field, creating no muscle twitch
Stimulation above the twitch threshold
- larger field
- all axons in field activiated
- all muscle fibres innervated by axons will contract
Is twitch response graded because increasing stimulus intensities produce progressively bigger action potentials?
No
- it is graded because an increased stimulus intensity can recruit more axons and therefore generate a bigger twitch response
- remember all or none, so each axon’s potential doesn’t change as stimulus intensity is increased
What is the size principle?
- when smaller diameter motor neurons are recruited first, then larger motor neurons as more force is required
Does each motor neuron only innervate one muscle fibre?
- size correlates with number of muscle fibres it innervates (motor unit)
- small motor units involved in fine muscle control
- larger motor units involved in more coarse motor control
- by recruiting more motor units of increasing size, the force output can be graded according to how much tension is required
What does experiment 2’s graph look like? Why?
- a steep incline then sudden decline near the y-axis line
- because of summation!
How does summation work?
- level of tension produced is proportional to intracellular Ca2+ concentration at that time
- tension rises following Ca2+ release from sarcoplasmic reticulum
- tension falls as Ca2+ it pumped back into sarcoplasmic reticulum
- however! when a muscle fibre is excited to produce a single switch, not all Ca2+ from SR is released
- so, if a second action potential is fired before all the Ca2+ has been sequestered
- newly released Ca2+ will add to produce a higher overall Ca2+ concentration
- tension will then be greater
What about the data point that goes against the trend in the graph?
- the absolute refractory period! lasts 1-3 milliseconds
- time after action potential can’t be stimulated
- because voltage-gated Na+ channels are in their innactive state so they cannot be triggered to generated an action potential
For the muscle,
- only one stimulation!
- the second stimulus will not reach the fibre as the nerve is refractory
- the Na+ channels are refractory, so cannot generate an action potential that propagates along the nerve to the neuromuscular junction
What happened in experiment 3? Explain tetanus
- applied trains of stimulus pulses
- frequency of stimulation and number of pulses delivered increased
- peak tension was measured and expressed as a tetanus: twitch ratio
Explanation
- as frequency of stimulation increased, peak tension developed during the stimulus increased
- caused an even greater accumulation of intracellular Ca2+, allowing more cross-bridges to form, and so a greater total tension
Tetanus:
- when multiple action potentials result in a state of sustained muscle contraction
Types:
Fused
- when multiple action potentials result in a state of sustained muscle contraction
(what makes our movements occur smoothly!)
Unfused
- individual pulses can still be resolved
