Excitable Tissue 1 Flashcards
What is homeostasis?
Maintaining the internal environment within physiological limits or steady state (thermostat analogy).
Such as blood. Glucose being kept within 70-110 mg/100ml
Why homeostasis ?
Single cell organisms live within the environment and their physiology/biochemistry is controlled by that environment
Multi-cellular organisms generate their own environment in which the cells live and that environment must be controlled and maintained by the organism
Describe the relation between external and internal environment
- Some organisms regulate their internal environment by controlling the external environment
- Homeostatic mechanisms evolved to maintain a steady state within our internal environment, despite variations in the external environment
What is the composition of Na+ (mM)?
ECF- (140 or 136-145)
ICF- 14
What is the composition of K+(mM)?
ECF- 4 (or 3.5-5)
ICF- 120
What is the composition of Ca+2(mM) ?
ECF - 2. (or 1.9-2.6)
ICF- 0.0002
What is the composition of Cl-?
ECF- 100( or 95-105)
ICF- 10
What is the composition of HCO3-?
ECF- 24 (or 22-28)
ICF- 10
What is the composition of pH?
ECF- 7.4 (7.35-7.45)
ICF- 7.1
What is the composition of osmolarity?
ECF- 290 (or 275-295)
ICF- 290
What is the composition of glucose?
ICF: 70-110 mg/dL
What is the composition of BUN (blood urea nitrogen)?
ICF:7-18 mg/dL
What ‘s the composition of creatinine?
ICF: 0.6-1.2 mg/dL
Define steady state
Maintenance of a state that doesn’t change with time. Energy expenditure may be necessary ( e.g., ECF [Na+]> ICF[Na+] and concentrations are maintained at sea level balanced over time —> required energy)
What is equilibrium?
When two components have the same amount of energy
Give examples of steady state and equilibrium
Steady state: ECF and ICF solutes are in steady state. Body expends energy to maintain uneven solute concentrations to allow optimal function
Equilibrium: water is in equilibrium between the compartments (due to solute concentration differences)
DESCRIBE homeostasis
- maintenance of steady states in the body by coordinated physiological mechanisms
- ability of the body to maintain a relatively stable internal environment despite external environment variations
- regulation of the internal environment around a given set point
- requires energy
Describe each of the homeostatic mechanisms
Controlled variable: physiological parameter be8bg controlled
Sensor: receptor type (sense organ) that detects changes in the controlled variable
Integrator/comparator: integration center that analyzes data from the sensor and compares to set point
Set point: “Normal” values predetermined but influenced by environmental adaptations
Effectors: nerve pathways, hormones, cells, tissues that carry out the response needed to restore homeostasis
Explain blood pressure regulation: hemorrhage
Blood loss —> decreased Blood pressure —> baroceptors in carotid sinus/aorta send info to CNS —> CNS determines if BP is above/below set-point —> restores BP back to normal via autonomic nervous system —> acts on various effector organs (heart and vasculature) to change HR, contractility and vascular diameter
What are the types of homeostatic feedback?
Negative and positive
What is negative feedback?
Response reverses the original the initial disturbance restoring controlled variable back towards “normal” value- action taken to prevent further change (slow or stop process)- majority of systems
What is the positive feedback system?
Response amplifies the original disturbance deviating the controlled variable even further. Positive feedback must eventually be interrupted - minority of systems (e.g., ovulation, birth, ejaculation, blood clot formation)
How is an increase in blood glucose a negative feedback?
Increase in blood glucose concentration—> pancreas secretes more insulin, causing glucose uptake into cells and reducing plasma glucose concentration. Pancreas cells are the sensor, comparator and effector- no CNS involvement
How is a decrease in blood glucose a negative feedback?
Decrease in blood glucose concentration—> increased glucagon secretion from pancreatic a-cell, resulting in normalization of glucose levels. Pancreatic cells are the sensor, comparator and effector- no CNS involvement
Describe the positive feedback of childbirth
- Head of baby pushes against cervix, increasing uterine muscle tension
- Nerve impulses from cervix transmitted to brain
- Brain stimulated pituitary gland to secrete oxytocin
- oxytocin carried one bloodstream to uterus and increases uterine muscle contraction and more tension develops
- These contractions pushes baby towards cervix, ultimately leading to birth
What is feed forward control?
Feed-forward control can be used very successfully to improve a (homeostatic) control loop’s response to disturbances - without having to wait for a deviation in process variable
Give examples of feed forward control
- Start line of a race: cardiac output and heart rate increase although no metabolic demand has been placed on body
- Salivation that occurs upon smelling food -helps lubricate and solvate food
Set point deviation are due to:
- Circadian rhythm- set points vary between active (day) and passive(night) times (hormones , etc)
- Environmental changes: change in external environment
Acclimation—> one adapts to high altitudes, set point for PO2 levels change - Protective response: fever- increase in body temperature is an adaptation of set point to minimize viral replication
- Aging or pathological changes: As disease progresses, set point changes (e,g. Lowered body temperature set point)
What are the effects of deficient homeostatic mechanisms?
- Normal negative feedback mechanisms may initially work to the benefit of the individual
- As the disease progresses —> normal compensatory responses fail
- Pathological positive feedback loops may take precedence
Why is knowledge of water volume important?
Important for water movement understanding
Especially during dysfunction/disease
What is osmosis?
Movement of water across a semi-permeable membrane
What is drives by osmolarity?
Concentration of ions and osmolytes (e.g., glucose, urea)
-water flow/osmosis from high to low water concentration
What is osmolarity?
The number of osmotically active particles per volume (liter) of water (e.g., 290 mOsmoles/liter)
What is osmolality?
The number of osmotically active particles per weight (kg) of water (e.g., 290 mOsmoles/kg) . It involves the total concentration of all particles in the solution
What is the normal range of plasma osmolarity?
275-295 mOsm/L
Water volumes in different compartments and ionic concentrations are important because….
Affect osmosis and electrical activity
What are penetrating solutes?
Can enter cell/freely move across cell membrane (glucose, urea, glycerol)
-solutes will distribute /diffuse to equilibrium across membrane
WHat are non-penetrating solutes?
Cannot freely move across cell membrane (sucrose, NaCl, KCl)
-water will move across membranes to dilute these solutes
What is tonicity?
Pressure caused by osmotic gradient across cell membrane
Which particles contribute to tonicity?
Only impermeant, non-penetrating particles contribute to tonicity and cause changes in cell volume (different concentrations on either side of membrane)
-permeant ions do not typically affect tonicity as they equilibrate across the membrane
How does tonicity (extracellular)dictate changes in the cellular volume ?
- isotonic( no change in volume)
- hypotonic (cells expand and may burst with water water gain
- hypertonic- cells shrink due to water loss)
Contrast tonicity and osmotic pressure
Osmotic pressure is the pressure required to prevent water movement across a semi-permeable membrane
What is dehydration ?
Removal of water- Intracellular/extracellular alters osmotic pressure
-cells can shrink/swell
What are the most common causes and treatment for dehydration ?
Insufficient water intake, excess water loss ( e.g. excess sweating, vomitting, diahrrea )
Water loss from plasma leads to water loss from interstitial compartment, which leads to water loss from cells and hence cellular shrinking
Treatment- replacement of lost fluids and electrolytes
What is diffusion?
Movement down concentration gradient due to kinetic energy. Brownian motion provides energy.
Distinguish the types of diffusion
Direct diffusion- directly through membrane (small solutes [e.g., gases, urea] )
Channel-mediated transport- pores (remain open, water )
Facilitated diffusion- saturable- involves conformational change (ion channels, carrier proteins)
What is active transport?
Energy source needed to move a solute AGAINST its concentration gradient
- primary -Na/K pump, carrier mediated
- secondary- glucose, carrier mediated
What are the characteristics of iron channels?
- selective
- gating
- conductance
- signals
How are ion channels selective?
Permit the passage of some ions, but not others
In what way are ion channels gating?
May be open nor closed. Ion flows through open channel. Opening and closing of channels are controlled by gates
In what ways do ion channels have conductance ?
Probability that the channel is open. The higher the probability that a channel is open, the higher the conductance or permeability
In what ways do ion channels use signals?
- voltage gated channels are opened for closed by transmembrane electrical potential (Na+ or K+ channels)
- Ligand gated channels are opened or closed by hormones, second messengers of neurotransmitters
What is primary active transport ?
Carrier protein requires an energy source (ATP) to move a solute AGAINST its concentration gradient
What is secondary active transport?
Doesn’t rely directly of ATP instead it uses concentration gradient of one ion used to drive movement of another against its concentration gradient
How is the sodium potassium pump used for primary active transport?
Na+ greater outside
K+ greater inside
Na+/K+ ATPase pump moves ions against concentration gradient
ATP used to pump 3 Na+ from inside to out and 2 Na+ from outside to in
Resulting in net negative charge inside cell
Ionic gradient across cell membrane
