Homeostasis A- Membrane Transport Mechanism .pdf

Homeostasis-A Cell Membrane Transport Mechanisms Unit I- Problem 2  Week 2 - Homeostasis A Problem 1: A 9-month-old boy is brought to the emergency department 1. Guyton, Textbook of Medical with a chief complaint of diarrhea and vomiting for 2 days. Physiology 14t...

Homeostasis-A Cell Membrane Transport Mechanisms Unit I- Problem 2  Week 2 - Homeostasis A Problem 1: A 9-month-old boy is brought to the emergency department 1. Guyton, Textbook of Medical with a chief complaint of diarrhea and vomiting for 2 days. Physiology 14th Ed., (2021). He has a fever, tachycardia, and an increased respiratory rate. The anterior fontanel is sunken, and his skin turgor is slightly diminished. He is given intravenous glucose saline in the Transport of substances through cell emergency department and is then hospitalized for further membrane, Chap. 4 Pp. 51 – 62. management. Body fluids compartments, Chap. 25 Pp. 305 – 316. Problem 2: An 86-year-old man was admitted to the hospital because he 2. Lab 2 in Physiology Manual (Practical) had become lethargic, confused, and was refusing to drink fluids. On admission, his skin felt hot and doughy, his eyes 3. Lab 3 in Physiology Manual were sunken, and his mouth was dry. Serum electrolytes (Cases/Calculations) revealed hypernatremia, hyperchloremia, and increased plasma osmolarity. 5% glucose in saline solution was given intravenously as prescribed. Learning Objectives List the primary functions of the cell membrane Describe the selective membrane permeability and how substances move across cell membranes Loading… List the transport mechanism of macromolecules: Endocytosis ( phagocytosis / pinocytosis) and exocytosis. 9/12/2024 3 General Functions of Plasma Membranes Important for maintaining homeostasis, for example, ion distribution Separates intracellular fluids from extracellular fluids Signal transduction Cell recognition by glycoproteins on the outside of the cell Transport of substances across 9/12/2024 4  Types of Membrane Transport Passive Transport Active Transport Occurs down electrochemical Occurs against a gradients from concentration gradient Loading… up to down Either no mediator is needed Involves a “carrier” (Simple diffusion) or Requires additional energy involves a “channel” or a Primary or secondary “carrier” (facilitated active transport diffusion). No additional energy (ATP) required (just kinetic energy) 9/12/2024 5 Simple Diffusion Extracellular fluid Membrane Lipid Molecula Concentratio surface solubilit r n area y size outside cell Fick’s law of diffusion Membran Concentratio e n thickness gradient Compositio n of lipid layer Intracellular Concentratio fluid n inside cell Fick's Law of Diffusion says: surface area concentration gradient membrane Rate of permeability membrane diffusion thickness Membrane permeability lipid Membrane solubility permeability molecular size Changing the composition of the lipid layer can increase or decrease membrane  Facilitated Diffusion: Passive Transport Aided by Proteins In facilitated diffusion, transport proteins speed the movement of molecules across the plasma membrane Type of transport proteins: A. Channel proteins provide corridors that allow a specific molecule or ion to cross the membrane. B. Carrier proteins undergo a subtle change in shape that translocates the solute-binding site across the membrane. - Involves the transport of hydrophilic molecules such as ions, glucose, and amino acids. 9/12/2024 7  transport transport usually open transport two directions In opposite only one substances · pen then closes Substance Gating of Channel Proteins Facilitated Diffusion: Carrier Mediated Diffusion Substances move down their chemical and electrical gradient. Not linked to metabolic energy Saturation kinetics: rate of diffusion approaches Vmax or Tmax. Chemical specificity: glucose, amino acids. 14 GLUT for glucose; Insulin increases rate of glucose facilitated diffusion by activation of GLUT4. facilitated diffusion increases then reaches steady State a 9/12/2024 10 Primary Active Transport The proteins (carriers) involved in primary active transport require energy in the form of ATP to transport substances against their concentration gradients. Direct use of energy ATP used Na+- K+ ATPase Loading… pump Carrier transporting ions against electrochemical gradient (uphill). Carrier is an enzyme that hydrolyzes ATP. Inhibited by metabolic inhibitors. Coupling ratio (3 Na+:2K+), thus electrogenic pump Creates an electrical potential across cell membrane and contributes less than 10% to the membrane potential. Plays an important role in the osmotic balance of cells and controls cell volume. 9/12/2024 11 Na+/K+-ATPase Pump and Cardiac Glycosides Cardiac glycosides are medicines for treating heart failure, hypotension, and certain irregular heartbeats. The molecular target of cardiac glycosides is the Na+/K+-ATPase. Example: Ouabain binds to this enzyme, ceasing its function, and leading to an increase of intracellular sodium as well as calcium ions. Prevents the conformational changes necessary for the pump’s proper function. Ovabin binds to enzyme W Digoxin Increase Intracellular sodium W increase in calcium ions 9/12/2024 12 Other ATPases: Ca++ Pump and H+ Pump Pumps calcium from in Stomach (HCL CYtOSOl to ER secretion) Ca2+ ATPase Kidney (control blood PH) In Present on the cell membrane and H+ ATPase the sarcoplasmic reticulum Found in parietal cells of gastric glands Maintains a low cytosolic Ca2+ (HCl secretion) and intercalated cells of concentration renal tubules (controls blood pH). 9/12/2024 13 Secondary Active Transport: Na+ Co-Transport ~ sodium out - maintaining low sodium inside - so sodium can carry with it another molecule Moves substances against electrochemical gradients This is secondary active transport because it is dependent upon the diffusion gradient for Na+ created by the Na+/K+ pump (Transport is driven by the energy stored in the concentration gradient of another molecule (Na+)). Energy for transport is indirectly provided by the Na+- K+ ATPase pump (Indirect use of energy) Thus, indirectly, all secondary active transport processes are diminished by inhibitors of the Na+- K+ ATPase because their energy source, the Na+ gradient, is diminished. 9/12/2024 14  Types of Secondary Active Transport 1. Co-transport (symport): Solute moves against concentration gradient (up hill) in the same direction as Na+ ions. Example : Glucose-Na+ cotransport in the intestinal epithelium 2. Co-transport (antiport): Solute moves in the opposite direction of Na+. Examples: Uphill extrusion of Ca2+ from a cell by a type of pump that is coupled to the passive diffusion of Na+ into the cell. Hydrogen Sodium exchange in the kidney tubule. 15 9/12/2024 Other Mechanisms of Membrane Transport Paracellular transport: Movements of ions and water through the junctions between cells (epithelial cells in the kidney tubules, or in the GI tract). Solvent drag: Water is reabsorbed by osmosis and carries all other solutes along. Endocytosis: is the process of capturing a substance or particle from outside the cell by engulfing it with the cell membrane and bringing it into the cell. Exocytosis: describes the process of vesicles fusing with the plasma membrane and releasing their contents to the outside of the cell. Both endocytosis and exocytosis are active transport processes. 9/12/2024 16  Endocytosis – Pinocytosis and Phagocytosis Pinocytosis: “Cell-drinking” Phagocytosis: Endocytosis of fluid and small Endocytosis of large molecules (generally larger than particles associated with the engulfed 0.5 µm in diameter), such as bacteria, dead cells, and tissue fluid. debris. Invagination of membrane and Monocytes or macrophages formation of pinosome. 9/12/2024 17  Receptor Mediated Endocytosis 1. Receptors cluster in regions termed coated pits, as they are coated with proteins such as clathrin. Clathrin causes the coated pit to invaginate and become a vesicle, bringing the desired ligand into the cell. This process can be hijacked to allow for toxins and viruses (Opportunistic ligands) to enter the cell. 2. Requires energy (active process) and Ca++ in ECF. Exocytosis Ejection of substance from the cell. Requires energy and Ca++. Secretary products of endoplasmic reticulum to Golgi apparatus. Release of neurotransmitters Release of hormones 9/12/2024 19