Homeostasis Flashcards
Things that make up the ECM
- water
- proteins
- proteoglycan
Define homeostasis
Maintenance of relatively constant internal conditions despite changes in either internal or external environment
- a condition that may vary, but which is relatively constant.
How much of total body water is in ICF
2/3
How much of total body water is in ECF
⅓
How much of ECF is as plasma
1/5
How much of ECF is as Interstitial fluid
4/5
Normal conc of Na+
135-145mmol/L in ECF
Normal TOTAL PLASMA CONC of Ca2+
2.2-2.6mmol/L
Normal fasting glucose conc
3.5-6mmol/L
Normal non-fasting glucose conc
3.5-8mmol/L
Normal K+ conc in ECF
3.5-5mmol/L
Intracellular concentration of Na+, K+, Cl- and organic anions
Na+ = 12mmol/L
K+ = 150mmol/L
Cl- = 4mmol/L
Organic anions = 130mmol/L
Extracellular concentration of Cl-
104mmol/L
Extracellular concentration of organic anions
5mmol/L
Function and importance of Na+
- main extracellular cation
- largely determines extracellular fluid volume (and thus influences blood pressure)
- important in action potential generation in nerve and muscle tissue
Function and importance of Ca2+
- important for structural component of bone and teeth
- involved in neurotransmission and muscle contraction
- essential for blood clotting
- regulates enzyme function
Which cation is important for blood clotting?
Ca2+
Which cation largely determines extracellular fluid volume and therefore blood pressure?
Na+
Function and importance of glucose
- used by cells (esp neurons) to produce ATP
- neurons particularly affected by low glucose levels
- high blood glucose causes other problems (both acute and chronic)
Function and importance of
- most abundant extracellular cation
- maintains determinant of the resting membrane potential (RMP) - particularly important in excitable tissue i.e. nerve and muscle
Normal range for pH of ECM
7.35 - 7.45
Symptoms of acidosis
- dec neuronal function
- dec consciousness
Symptoms of alkalosis
- over-excitability of nerve and muscle, resulting in:
- pins and needles
- muscle spasm
- convulsions
Normal range for body temperature
36 to 37.5°C
Why is body temperature ta 36-37.5°C
Allows for optimal metabolic and physiological functioning
How do oral and axillary temperatures compare to rectal
Oral and axillary temperatures are usually about 0.5°C less than rectal, which is core
- peripheral temperature is more variable.
Why is core body temperature important?
- at higher temperatures proteins start to denature
- at lower temperatures, chemical reactions slow down, preventing normal cell functions
- as the cells of the nervous system become compromised, the ability to thermoregulate is lost
- rapid worsening of the initial condition and accelerated movement of temperature away from normal leading toward death -> vicious cycle, detrimental feedback loop
Describe the body temperature vicious cycle
- as the cells of the nervous system become compromised, the ability to thermoregulate is lost.
- > rapid worsening of the initial condition and accelerated movement of temperature away from normal leading toward.
- vicious cycle
- detrimental positive feedback loop
Relationship between distance travelled and time for diffusion
Distance travelled is proportional to the square root of time
- it takes 4 times as long to diffuse twice as far
- takes quarter of the time to diffuse half the distance
Is diffusion rapid over short distances
Yes. Due to the square root relationship
- rapid within cells and between cells and capillaries
Which substances diffuse directly through the lipid bilayer?
- O2, CO2
- steroid hormones
- anaesthetic agents
What is the channel for the diffusion of water
Aquaporins
Leak channels
Channels that open/close spontaneously
Channels that open/close in response to various stimuli
Ligand gated
Channels that open/close due to change in membrane potential
Voltage gated
Are channels usually specific
Yes
Describe carrier mediated passive transport
AKA facilitated diffusion
- substance binds to carrier on one side of the membrane which induces the carrier to change shape and release of substance to the other side (down conc grad)
eg for substances too large to pass thru pore/channel.
Describe Primary Active Transport
Energy from the hydrolysis of ATP used to move substances against their conc grad
Example of primary active transport
The sodium-potassium pump which moves 3Na+ out of the cell in exchange for 2K+.
- maintains ionic gradients
- helps regulate cell volume
Function of Na+-K+ pump
- maintains ion gradients
- helps regulate cell volume
Example of exocytosis
Secretion in insulin by Beta cells of pancreas
Example of endocytosis
Phagocytosis of microbes by neutrophils
Exocytosis and Endocyosis
Substances transported out of (or into) the cell in membranous (bilayer) vesicles
How is glucose transported across cell membranes
Glucose entry into cells when insulin present is by carrier mediated passive transport
- bonding causes change in shape in transmembrane protein
Osmotic pressure
The pressure required to stop osmosis
What can differences in solute concentration across cell membranes cause
- fluid shifts
- create pressure that can damage cells
Define osmolarity
A measure of the total number of solute particles per litre of solution, in osmol/L or mosmol/L
Units of osmolarity
osmol/L or mosmol/L
Osmolarity of ECF and ICF
275-300mosmol/L
- in ICF, interstitial fluid, plasma
What is tonicity
The effect that a solution has on cell volume
- hypertonic solutions will cause cells to shrink
- hypotonic solutions will cause cells to swell
- isotonic solutions cause no change in cell volume
Difference between osmolarity and tonicity
Osmolarity is a property of a particular solution (independent of any membrane).
- Tonicity is a property of a solution with reference to a specific membrane.
What happens if the osmolarity of one compartment changes
Water will diffuse by osmosis until equilibrium has been restored
eg intravenous distilled water would dilute the plasma and cause water to move
- firstly to the interstitial compartment
- then the ICF
- until eq reached
Concentration of normal saline solution
0.9%
Iso-osmotic and iso-tonic
If the concentration of solutes on either side of the cell is similar
AND
if those solutes cannot easily cross the cell membrane
THEN
there is no osmotic gradient for water to diffuse and cell volume will remain unchanged.
Can Na+ and Cl- move across the membrane readily
No. Need specific channels
Are substances that are able to diffuse across the membrane osmotic
eg 300mmol/L urea
- isosmotic because urea does not dissipate in water and remains a single molecule so concentration = osmolarity but different units
- Urea is not isotonic because it is able to diffuse across the cell membrane via urea transporters
- there is not much urea inside the cell
Thus, the solution is hypotonic because its effect on cells is to cause them to swell.
How does the RMP arise
The RMP results from the separation of a SMALL NUMBER of oppositely charged ions across the lipid bilayer
- membrane acts as capacitor
- overall concentrations of ions in the ICF and ECF are not significantly affected
What does RMP refer to
inside of the cell membrane is negatively charged compared to its external surface
- an electrical potential that exists across the cell membrane and is due to different concentrations of ions on each side of the membrane and their respective permeabilities to it
What is the magnitude of RMP
Typically -70mV
if the outside of the membrane is taken as zero mV
Which ion is the major determinant of RMP
K+
Why is K+ the major determinant of RMP
The cell membrane is NORMALLY much more permeable to K+ than other ions
How is the RMP established?
When the amount of K+ leaving the cell down its conc grad is balanced by that moving back in due to the electrical gradient.
For which tissues must the membrane potential change in order for them to function?
Excitable tissues (i.e. nerve and muscle)
Why must the membrane potential change in order for excitable (nerve and muscle) tissues?
For them to function.
How does the membrane potential change for excitable tissues?
via opening or closing of specific channels
Why is it very important to control ECF [K+]?
Because K+ is the major determinant of RMP
- otherwise excitable tissues won’t function normally
- cardiac arrhythmia
- muscle weakness
Define regulate variable
The variable that the system SENSES and tries to keep stable
What is the set point
the target value for that variable
What is the reference (normal) range
- values of regulated variable within acceptable limits
Intra and inter individual variation
Variation in regulated variable values within and between normal people
How are normal ranges for physiological variables established?
- measurements obtained from healthy group of people
- values within 2 SD of the mean are considered “normal”
- middle 95%
By chance, 5% of tests outside the reference range might be from people who are actually healthy.
How does variation in set points between individuals arise
Genetic factors
How does variation in set point within an individual arise
- in response to normal activity (within the acceptable range)
- eg core body temp
- in response to biological rhythms
eg cortisol
eg monthly rhythm of hormones and body temp
Define feedback
Oppose the change in the regulated variable and move it back toward the set-point
4 components of negative feedback systems
- Sensor
- Integrator
- Effector(s)
- Communication Pathways
Role of sensor
Monitors actual value of the regulated variable
Role of integrator
- compares actual and set point values
- generates an error signal if any discrepancy between these
- determines and controls the response
- sensor and integrator can be the same cell
Role of effector
Produce the response that restore the regulated variable to its “set point”
Role of communication pathways
Carry signals between components
2 types of physiological communication pathways
- Neuronal
2. hormonal
Describe neuronal communication pathways
- involves action potentials in axons and neurotransmitter release at synapses
- fast
- specific
- good for when conditions are changing rapidly and where an immediate response is required to prevent tissue damage or loss of homeostatic control
- good for brief responses
What type of response is neuronal communication pathways good for
When conditions are changing rapidly and where an immediate response is required to prevent tissue damage or loss of homeostatic control.
Describe hormonal communication pathways
- hormones released into the blood (or ECF)
- target any cells that have receptors specific for the particular hormone
- so one hormone can potentially affect several tissues or organs
- good for widespread, sustained responses eg fluid volume regulation
What type of response is hormonal communication pathways good for
- widespread, sustained responses
- targets any cells that have receptors specific for the particular hormone.
4 ways of heat loss
Radiation
Conduction
Convection
Evaporation
Responses of decrease in body temp
- muscles shiver
- vasoconstriction in skin + piloerection
Where is a decrease in core temp deteced
By the hypothalamus in the brain.
What’s a feedforward system
Involves detection or anticipation of external (or internal conditions) or situations that COULD alter a regulated variable (or disrupt homeostasis) if some sort of PREEMPTIVE action was not taken
- the integration centre establishes a future predicted value for the regulated variable, compares this with the “set-point” and makes anticipatory correction
- eg getting goosebumps and shivering as you enter a cold environment (physiological feedforward)
- putting on more clothes if skin feels cold (behavioural feedforward)
- putting on more clothes if it looks cold outside (behavioural feedforward)
When environmental temp is greater than body temp, what’s the best way to lose heat
Evaporation.
Describe positive feedback
a response to a stimulus that moves the controlled variable even further away from the “set point”
- i.e. reinforces the initial changes
- vicious cycles
an example of detrimental positive feedback
Lose blood -> heart fail as a pump = dec BP even further. Move further and further away from set point
Useful positive feedback
When there is a specific end-point or purpose eg childbirth or bloodclotting
- both situations must be carefully controlled to prevent inappropriate activation and to limit outcome
Childbirth as positive feedback
Baby moves into birth canal.
Stretch inc
detected by stretch receptors
feeds info via nerve fibres back to integrator (hypothalamus and pituitary)
oxytocin stimulates muscle
stronger, more frequent labor contractions (uterine muscle)
Describe the anatomical position
- upright
- face forwards
- feet together
- palm faces forwards
- same regardless of motion
