Membrane Dynamics Lecture 4 PDF

Illustration by Smart-Servier Medical Art Illustration by Smart-Servier Medical Art Membrane Dynamics PHYL311 | Lecture 4 Amanda S. De Los Santos, MS  Table of contents 01 Osmosis & 02 Transpor...

Illustration by Smart-Servier Medical Art Illustration by Smart-Servier Medical Art Membrane Dynamics PHYL311 | Lecture 4 Amanda S. De Los Santos, MS  Table of contents 01 Osmosis & 02 Transport Tonicity Processes 03 The Resting Membrane Potential  Illustration by Smart-Servier Medical Art Illustration by Smart-Servier Medical Art 01 Osmosis & Tonicity  Illustration by Smart-Servier Medical Art Illustration by Smart-Servier Medical Art A man walks into an ER having… What will you do and why? Homeostasis Does Not Mean Equilibrium Homeostasis and Osmotic Equilibrium What is the most important molecule in the human body? Homeostasis and Osmotic Equilibrium What is the most important molecule in the human body? Osmotic equilibrium – [fluid] are equal on both sides of the cell membrane ○ Does this mean that [solutes] are the same? Chemical disequilibrium → electrical disequilibrium  OSMOSIS The movement of water across a membrane in response to a solute concentration gradient ○ Movement through aquaporins, special protein channels How can we measure osmosis? ○ Osmotic pressure (atm/mm Hg) ○ Osmolarity (osmol/L) (#particles/L) ○ Osmolality (osmoles/kg H2O) How do we measure dehydration?  OSMOSIS vs TONICITY Comparing osmolarities b/w 2 fluids ○ Isosmotic = # of solute particles/unit volume are equal ○ Hyperosmotic = solution conc is greater than the other ○ Hypoosmotic = solution conc is lower than the other  OSMOSIS vs TONICITY Tonicity – describes a solution by how it would affect cell volume  OSMOSIS vs TONICITY OSMOLARITY TONICITY Number of solute particles dissolved in a volume of solution Comparative term; no units (osmoles/Liter) [osmometer] always compares a solution and can be used to compare any two a cell and by convention – solutions describes only the solution tells you what happens to does not tell you what happens cell volume at equilibrium when to a cell placed in a solution the cell is placed in the solution  OSMOSIS vs TONICITY Can osmolarity be used to predict tonicity? Are all solutes equal in terms of… ○ For osmolarity? For tonicity? Tonicity depends on the concentration of non-penetrating solutes  OSMOSIS vs TONICITY How are IV decisions based on these concepts? A man walks into an ER having… What will you do and why?  Intravenous Solutions supplemental fluids used in intravenous therapy to restore or maintain normal fluid volume and electrolyte balance when the oral route is not possible. Case Study 1: Brain Swelling (Cerebral Edema) A patient has been admitted to the emergency room with severe head trauma, leading to swelling in the brain (cerebral edema). The doctor is considering administering an intravenous saline solution to reduce the swelling. Your task is to recommend the appropriate solution to administer and explain why. Case Study 1: Brain Swelling (Cerebral Edema) 1. In this scenario, why would a hypertonic solution be recommended to reduce brain swelling? A hypertonic solution would draw excess water from the brain cells, reducing swelling (edema). The movement of water from the cells into the bloodstream reduces intracranial pressure.  Case Study 1: Brain Swelling (Cerebral Edema) 2. What risks might occur if a hypotonic or isotonic solution is administered instead? (Consider the impact on brain cells and overall patient health.) A hypotonic solution would worsen the swelling by causing more water to enter the swollen brain cells, potentially increasing pressure and leading to further damage. An isotonic solution would neither increase nor decrease the swelling but would not help resolve the edema. Case Study 1: Brain Swelling (Cerebral Edema) 3. What concentration of saline (e.g., 3% NaCl) would be ideal in this situation, and why? A hypertonic saline solution (e.g., 3% NaCl) would be ideal because it is more concentrated than the body’s cells and effectively pulls water out of the swollen brain cells to reduce pressure. Case Study 2: Fluid Loss Due to Vomiting A 7-year-old child arrives at the hospital after several days of severe vomiting and diarrhea, leading to dehydration and electrolyte imbalances. The medical team needs to administer an IV solution to rehydrate the child and restore electrolyte balance.  Case Study 2: Fluid Loss Due to Vomiting 1. What is the likely osmolarity of the child’s cells after days of fluid loss? The child’s cells are likely in a state of hyperosmolarity due to fluid loss. This means the concentration of solutes inside the cells is relatively high because the extracellular fluid (ECF) volume has decreased, leading to dehydration.  Case Study 2: Fluid Loss Due to Vomiting 2. Should the medical team use a hypertonic, hypotonic, or isotonic solution? Explain your answer. An isotonic solution should be used. The child needs both fluid and electrolyte replacement. An isotonic solution, like 0.9% saline, will restore fluid volume without causing dramatic shifts in water movement in or out of the cells.  Case Study 2: Fluid Loss Due to Vomiting 3. What potential complications might arise if the wrong type of solution is used in this case? A hypertonic solution could cause water to move out of the cells, exacerbating dehydration and cellular shrinkage. A hypotonic solution could cause water to rush into the cells, potentially leading to cellular swelling or lysis, which is particularly dangerous for brain cells. Case Study 3: Cellular Dehydration in the Elderly An 85-year-old patient was admitted to the hospital after becoming severely dehydrated due to not drinking fluids for several days. The patient's cells are dehydrated, and the medical team is considering an IV solution to rehydrate the cells. Case Study 3: Cellular Dehydration in the Elderly 1. In the context of cellular dehydration, what is the tonicity of the cells compared to the extracellular fluid? The cells are likely hypertonic compared to the extracellular fluid because they have lost water, making their internal solute concentration higher than the surrounding fluid’s. Case Study 3: Cellular Dehydration in the Elderly 2. Should the medical team treat this patient with a hypertonic, hypotonic, or isotonic solution? Justify your choice. The medical team should administer a hypotonic solution (e.g., 0.45% saline). This will allow water to return to the dehydrated cells, helping rehydrate and restore normal function.  Illustration by Smart-Servier Medical Art Illustration by Smart-Servier Medical Art 02 Transport Processes  DIFFUSION Movement of General Properties of Diffusion molecules from areas 1. Diffusion uses the kinetic energy of molecular movement and does not require an outside energy source. of high concentration 2. Molecules diffuse from an area of higher concentration to an area of to low lower concentration. ○ chemical gradient 3. Diffusion continues until concentrations come to equilibrium. The molecular movement continues, however, after equilibrium has been reached. 4. Diffusion is faster - along higher concentration gradients - over short distances - at higher temperatures (increased kinetic energy) - for smaller molecules 5. Diffusion can take place in an open system or across a partition that separates two systems.  DIFFUSION Movement of Simple Diffusion across a Membrane molecules from areas 6. The rate of diffusion through a membrane is faster of high concentration if - the membrane’s surface area is larger to low - the membrane is thinner ○ chemical gradient - the concentration gradient is larger What kind of - the membrane is more permeable to the molecule molecules can pass 7. Membrane permeability to a molecule depends on through a cell - the molecule’s lipid solubility membrane via - the molecule’s size - the lipid composition of the membrane diffusion?  Cell Membranes Divide ICF from ECF Lipid bilayer Selectively permeable Protein embedded ○ Peripheral proteins ○ Integral proteins Ion channels Membrane Proteins Four main functions – not always distinct ○ Structural ○ Enzymes ○ Receptors ○ Transporters Mediated transport Facilitated diffusion Active diffusion Transport Proteins Two main types 1. Channel proteins (water & ions) Water channels (aquaporins) Ion channels Open channels Gated channels Chemically gated Voltage-gated Mechanically gated Transport Proteins Two main types 2. Carrier proteins (solutes/ions) Uniport Symport Antiport  FACILITATED DIFFUSION Passive mediated transport “down” a chemical gradient Example: GLUT4 transport  ACTIVE TRANSPORT Energy requiring mediated transport of a solute against a chemical gradient 1. Primary active transport – if the energy comes directly from ATP → ADP 2. Secondary active transport – energy comes from potential energy stored in the concentration gradient of one molecule to “push” other molecules against their gradient Common Active Transporters Primary Active Transporters  Na+ -K+ Pump Primary Active Transport ○ 3 Na+ ICF → ECF ○ 2 K+ ECF → ICF ○ 1 ATP → 1 ADP + Pi Sodium potassium pump = single most important transport protein ○ Electrogenic – creates a charge separation and potential difference  Sodium- Potassium Pump  Na+ -K+ Pump Primary Active Transport ○ 3 Na+ ICF → ECF ○ 2 K+ ECF → ICF ○ 1 ATP → 1 ADP + Pi Sodium potassium pump = single most important transport protein ○ Electrogenic – creates a charge separation and potential difference  Common Active Transporters Secondary Active Transporters  Na+ -glucose secondary active transporter (SGLT) Uses the Na+ gradient to move glucose into the cell against its concentration gradient. Differences between GLUT and SGLT? Why do we need both?  Na+ -glucose secondary active transporter (SGLT) Uses the Na+ gradient to move glucose into the cell against its concentration gradient. Differences between GLUT and SGLT? Why do we need both?  Carrier-Mediated Transport Specificity, Competition, and Saturation Specificity ○ Move only one molecule or group of related molecules ○ ex. GLUT transporters → only 6-C sugars Competition ○ Substrates compete with one another for binding sites ○ Competitive inhibitor – ex. galactose  Carrier-Mediated Transport Specificity, Competition, and Saturation Specificity ○ Move only one molecule or group of related molecules ○ ex. GLUT transporters → only 6-C sugars Competition ○ Substrates compete with one another for binding sites ○ Competitive inhibitor – ex. galactose Saturation ○ Rate of substrate transport = [substrate] and # of carrier molecules ○ Transport maximum  VESICLE TRANSPORT Phagocytosis ○ Actin mediated ○ Engulfs  VESICLE TRANSPORT Phagocytosis ○ Actin mediated ○ Engulfs Endocytosis ○ Brings large molecules into the cell ○ Occurs at membrane – indents ○ Constitutive Exocytosis ○ Removes large molecules from the cell ○ Reverse of endocytosis EPITHELIAL TRANSPORT  EPITHELIAL TRANSPORT Transcellular ○ substances passing through epithelial cells (apical & basolateral) ○ involves active transport mechanisms ○ Ex. Glucose uptake in the intestines via SGLT and GLUT  EPITHELIAL TRANSPORT Paracellular ○ substances moving between epithelial cells through the tight junctions ○ passive and driven by concentration or electrochemical gradients ○ Ex. Movement of ions like sodium or chloride  Illustration by Smart-Servier Medical Art Illustration by Smart-Servier Medical Art 03 Resting Membrane Potential  Membrane Potential There is an electrical disequilibrium maintained by cell membranes ○ Cations = K+ (ICF) Na+ (ECF) ○ Anions = Cl- (ECF), P- (ICF) Resting membrane potential difference or membrane potential = electrical gradient between ICF and ECF Generally, ICF = negative (less K+) ; ECF = positive (more K+) Most cells in the human body ~ 40x more permeable to K+ than Na+ ○ Resting membrane potential ~ -70mV (ICF)  Illustration by Smart-Servier Medical Art Illustration by Smart-Servier Medical Art Thank you! Slidesgo CREDITS: This presentation template was created by Slidesgo, including icons Flaticon Freepik by Flaticon, infographics & images by Freepik