Physiology PDF - Homeostasis & Cell Membranes

1: Homeostasis Overview Intended Learning Outcomes ​ Explain that physiology is based on understanding the mechanisms of living things; ​ Describe and explain homeostasis; ​ Explain negative feedback as the mechanism for the regulation of homeostasis; ​ Name the essential compon...

1: Homeostasis Overview Intended Learning Outcomes ​ Explain that physiology is based on understanding the mechanisms of living things; ​ Describe and explain homeostasis; ​ Explain negative feedback as the mechanism for the regulation of homeostasis; ​ Name the essential components of a negative feedback loop; ​ Explain the difference between a controlled variable and an effector mechanism and give examples; ​ Apply the principles of negative feedback control when encountering regulated/controlled variables. ​ Physiology: Science of the normal function and phenomenon of living things ○​ Mechanism that determines how the body respond to different stimuli Homeostasis Maintain constant internal environment of body ​ Homeo- Same ​ Stasis- Staying ​ Dynamic equilibrium- Variable change, but continually corrected, within narrow limits ​ Maintained via negative feedback Require rapid & efficient transfer of information between cell & around the body ​ Nervous system (automatic)- electrical communication, quick ​ Normal system (endocrine)- Chemical communication, slow Positive feedback ​ Diverge from equilibrium Negative feedback ​ Maintenance of equilibrium/ homeostasis ​ Controlled variable ​ Receptor (sensor) ​ Processor (integrating center) ​ Set point ​ Effector mechanism  Controlled variable Effector mechanism ​ Core body temperature ​ Heart rate ​ Blood pressure ​ Urine concentration ​ Blood glucose ​ Respiratory rate ​ Osmolarity of plasma ​ Blood oxygen levels Disturbance in homeostasis ​ May lead to illness and/or death Heat stroke ​ Disturbance/ increase in core temperature, beyond negative feedback mechanism can correct Diabete ​ Disturbance/ compromise in mechanism that control blood glucose Homeostatic mechanism maintain composition of extracellular fluid ​ All cells bathed in extracellular fluid (ECF) ​ Intracellular fluid affected by changes in intracellular fluid (ECF) composition Eg. ion concentration affect function of excitable cell (nerve cell, muscle) 2: The intra and extracellular environment Intended Learning Outcomes ​ Describe the intra- and extracellular environment as separated by the cell membrane; ​ Explain the movement of solutes across the cell membrane by diffusion; ​ Explain the different between transporters and channel proteins; ​ Explain the balances of fluids and solutes across the cell membrane; ​ Relate electrochemical gradient to cell function. Intra- and Extracellular environment Intra (ICF) and Extra (ECF) cellular fluid ​ Separated by the cell membrane Cell membrane ​ Allow separate of body fluid compartment/ difference in competition (solute concentration) ○​ Electrical activity in nervous system, ion concentration ○​ Muscle contraction ○​ Formation of urine in the kidney tubule Properties of cell membrane Lipid bilayer permeable to different molecules To ​ Diffusion in liquid Across ​ Diffusion through lipid bilayer ​ Diffusion through pore/ channel in membrane ​ Transport through membrane via carrier ​ Transport across membrane by endo or exocytosis Movement of solute to and across membrane Diffusion in liquid (Brownian motion) ​ Due to random thermal motion of particle ​ Speed of particle is inversely related to size ​ Molecule continuously collide with other molecule and change direction Movement of solute across cell membrane ​ Diffusion ​ Pore ​ Channel ​ Carrier (transports) ​ Pump Phospholipid bilayer, Diffusion ​ Simple diffusion ​ Small uncharged solute Pore (specialised pathway) ​ Simple diffusion, passive ​ Always open, non-selective ​ Porin (mitochondria) ​ Perforin (lymphocyte) Channel (specialised pathway) ​ Simple diffusion, passive Non gated ​ Always open ​ Eg. K+ leak channels Gated ​ Alternately open or close ​ Ion to cross membrane when open ​ Gate control by- Voltage, ligand (chemical), secondary messenger receptor) ​ Channel specific for different ions ​ Eg. Na+, K+, Ca2+, Anion Cl- Carrier/ transporters (specialised pathway) ​ Facilitate diffusion, passive ​ Secondary active transport (rely on gradient set up by active transport) ​ Small molecule ​ Specific binding of solute ​ Conformational change ​ Release of solute Types of carrier/ transporter 1.​ One solute (glucose, urea) 2.​ More than one solute, Same direction (Na+/glucose, Na+/HCO3, Na+/amino acid) 3.​ More than one solute, Different directions Pumps (specialised pathway) ​ Active transport (from hydrolysis of ATP), net transport against electrochemical gradient ​ Eg. Na+/K+ pump (ubiquitous), H+/K+ pump (stomach) Exocytosis ​ Active transport ​ Intracellular → Extracellular fluid ​ Release substance outside cell Endocytosis ​ Active transport ​ Extracellular → Intracellular fluid ​ Take in substance into cell ​ Eg. Pinocytosis (fluid filled vesicles), Receptor mediated endocytosis (fluid filled vesicle), Phagocytosis (particulate/ bigger matter) Composition of fluid (relative) and solute across cell membrane For electroneutrality in each fluid compartment: ​ Σ Cation = Σ Anion Intercellular fluid Extracellular fluid Blood plasma (ECF) Na+ Low ↓ High ↑ High ↑ K+ High ↑ Low ↓ Low ↓ Cl- Low ↓ High ↑ Low ↓ Protein High ↑ est Low ↓ High ↑ er Electro Gradient gradient Electrochemical gradient to cell function. Driving force for passive transport ​ Equilibrium potential- When the electrical gradient and concentration gradient are equal for a particular ion Clinical importance ​ Eg. changes in extracellular potassium concentration can have profound effects on excitable cells ○​ Hypokalemia– Muscle weakness, cardiac arrhythmias ○​ Hyperkalemia– cardiac arrhythmias Summary ​ Membrane permeability to solutes varies according to size charge and lipid solubility ​ Transport of solutes across the membrane occurs via integral membrane proteins ​ These may be; Pores, channels, carriers or pumps ​ There is an electro-chemical gradient across cell membranes ​ Low intracellular sodium ‘drives’ aspects of cell function 3: Water Transport and Distribution in the Body Intended Learning Outcomes ​ Define mole, osmole, osmolarity, osmosis and osmotic pressure; ​ Explain the difference between osmolarity and tonicity; ​ Explain the movement of water between body compartments by osmosis; ​ Explain Gibbs-Donnan effect ​ Extracellular fluid (ECF)- Homeostatic mechanism maintain a constant osmotic pressure of ECF ​ Intracellular fluid (ICF)- Changes in ICF osmolarity secondary to change in ECF osmolarity Properties of water ​ Physicochemical (or colligative) properties of a solvent are altered by adding a solute ​ Depends on the number of solute particles (rather than the nature of the particles) Definitions Mole (mol) ​ Unit of quantity ​ Same number of particle as atoms in 12g of carbon-12 isotope ​ Avagadro’s number 6.02 x 1023 Molarity ​ Unit of concentration ​ Number of moles of solute, per unit volume of solution ​ 1 molar solution = Molecular mass of the substance in grams dissolved in distilled water (enough) to make volume of 1 litre Osmole ​ Unit of quantity ​ Number of particles (rather than molecules) (relates to level of dissociation) ​ Avagadro’s number 6.02 x 1023 of osmolyte particles ​ Each particle will alter the activity (colligative properties) of the solvent ​ Independent of molecular weight and/or charge of solute particle Osmosis ​ Process which water moves between body compartments ​ Movement (or flow) of water, from an area of higher solvent activity to an area of lower solvent acidity, across a semipermeable membrane Or ​ Movement of water, from an area of lower osmolarity to higher osmolarity ​ Characteristic of water as a solvent ​ Solute content affect water movement across cell membrane Osmolarity ​ Measure of activity of the solvent ​ Number of osmole per unit volume of solution (ionic compound dissociate in solution) ​ Increase in osmolarity, decrease in solvent activity ​ Need to include all osmolyte particle (ionic molecule may dissociate in solution) ​ Ionic compound may not completely dissociate in solution ​ G- Degree of dissociation, osmotic coefficient Osmotic pressure ​ Increase hydrostatic pressure- Increase acidity of a solvent ​ Osmotic pressure- Pressure required to stop osmosis ​ Reverse osmosis- Application of hydrostatic pressure greater than osmotic pressure In biological system, the actual or effective osmotic pressure depends on ​ Properties of the membrane separating membrane compartments ○​ Reflection coefficient/ how permeable membrane is to solute ○​ Permeability the membrane is to the solute Difference between osmolarity and tonicity ​ Tonicity: Effect of a bathing solution on cell volume ​ Volume of a cell changes if water enters or leaves by osmosis ​ Determined by- Osmolarity of the solution, permeability of the cell membrane to solute Effect of different extracellular solution Isotonic Hypotonic Hypertonic ​ No net movement of ​ Net inward movement ​ Net outward water of water movement of water ​ No change in cell ​ Cell volume increase- ​ Cell volume reduce- volume Lysis Crenation ​ Effective osmotic ​ Effective osmosis ​ Effective osmotic pressure same in ECF pressure (tonicity) pressure (tonicity) & ICF ECF < ICF ECF > ICF ​ Normal saline (0.9% Sea water, fluid in renal NaCl) medulla Movement of water between body compartments by osmosis Gibbs-Donnan effect ​ Positive charge + attracted to the Negative charge – Intracellular protein ​ Counteracted by NaKATPase- 2 K+ in, 3 Na+ out Clinical importance ​ ECF is normally isotonic to ICF ​ If there is an imbalance, lead to oedema (swelling) or cell shrinkage Summary ​ Osmosis is the movement of water across the cell membrane. ​ The osmotic pressure of a solution is determined by the number of dissolved particles ​ Tonicity describes the effect of a solution on cell volume. ​ The movement of water into and out of capillaries is determined not only by osmosis (oncotic pressure) but also by the hydrostatic pressures in capillaries ​ The Gibbs-Donnan effect leads to a build up of ions inside the cell leading to movement of water into the cell– this is counteracted by action of the Na/K pump ​ Movement of water is clinically important because disturbances in osmotic and/or osmotic forces can lead to problems such as oedema