Lecture 2 2024 Functions of Body Functions and Biophysics PDF

Foundations of Body Functions and Biophysics Functional Organization of the Cell Membrane and Transport thorough the Cell Membrane Prof Dr. Abdelaziz M. Hussein Prof and Chairman of Medical Physiology Department Lecture Objectives At the end of this l...

Foundations of Body Functions and Biophysics Functional Organization of the Cell Membrane and Transport thorough the Cell Membrane Prof Dr. Abdelaziz M. Hussein Prof and Chairman of Medical Physiology Department Lecture Objectives At the end of this lecture you will be able to: 1. Define the cell membrane 2. List the functions of cell membrane 3. Recognize the components of the cell membrane 4. Define diffusion, active transport and vesicular transport 5. List the characters of the three types of transport and give example for each type Contents 01 Functions and organization of the cell membrane 02 Types and significance of ion channels in the cell membrane 03 Types and characteristics of Diffusion 04 Types and characteristics of active transport 05 Types and characteristics of vesicular transport  Cell Membrane 1 Def., It is a very thin elastic semi-permeable membrane (allowing some substances to pass through it and prevent others) that surrounds the cell. Thickness: About 7-9.0 nm (70 - 90 Ao = Angstrom = 10-10 of meter).  Functions of the Cell Membrane 1. Separates the cytoplasm from ECF. 2. Maintains cell's internal environment. 3. Transports of macromolecules into and out of the cell. 4. Controls distribution of ions e.g. Na, K extracellular ICF and ECF. 5. Contains receptors for hormones and transmitter substances. 6. Generates transmembrane membrane potentials.  It is formed of 3 components; Lipids 42% Proteins 55% Carbohydrates 3% 7  They form the basic structure or backbone of cell membran e Are 3 types: 1. Phospholipids 2. Cholesterol 3. Glycolipids 9 a) Integral proteins b) Peripheral proteins 10  Integral or Intrinsic Proteins Peripheral or Extrinsic Proteins Site: Bind to hydrophobic center of lipids Bind to the hydrophilic polar heads of the lipids or to the integral proteins Types i) Transmembrane proteins → span the i) Peripheral proteins: bind to the ICF and entire bilayer which act as: surface of the membrane and contribute to the cytoskeleton. functions: a. Channels → for diffusion of small ions b. Carriers: transport substances e.g. gluco ii) Peripheral proteins: bind to the ECF se surface of the membrane and contribute to the glycocalyx or cell coat c. Pumps: actively transport ions d. Receptors initiate intracellular reactions when activated. ii)Present only on one side of the membr ane: act as enzymes e.g. adenyl cyclase which form cyclic AMP from ATP Channels Pumps Carriers Receptors 12 Def. Are protein channels that allow passage of ions e.g. Na+ ion through the cell membrane Types: 3 types  Leak ion channels Chemical-gated ion channels Voltage-gated ion channels Channels that are always Channels open when chemical Channels open by changes in open substance bind to its receptor cell membrane potential e.g. K channels in cell K and Na channels of cholinergic Na and K channels in cell membrane of neurons receptors at neuromuscular membrane of neurons junction Important in resting me Important in graded membrane Important in action potential mbrane potential in potential e.g. motor end plate in neurons neurons potential Transport Mechanisms through Cell Membrane  Low concentration High concentration 17 Def. It is movement of substances across the cell membrane down its electrochemical gradient. 18  Low ATP concentration High concentration 19 Def. It is movement of substances across the cell membrane against its electrochemical gradient 20 Def It is the process by which large sized substances are engulfed by the cell membrane to be either pushed inside the cell (endocytosis) or pushed outside the cell (exocytosis) It is an active process 21 Def., It is movement of substances across the cell membrane down its electrochemical gradient due to the continuous random motion of its particles. Types: It is divided into 3 subtypes: 1.Simple diffusion. 2.Facilitated diffusion. 3.Osmosis (water only) 22 Def It is movement of substances across the cell membrane down its electrochemical gradient by simple movement without the necessity of binding with carrier proteins Mechanisms: a) Through lipid interstices e.g. transport of lipid soluble substances e.g. O2 and CO2 through cell membrane b) Through ion channels e.g. transport of ions such as Na and K+ 23 Characters: It is characterized by; a) Occurs down an electro-chemical gradient b) Passive i.e. no external energy is required c) It is not rate-limiting i.e. linear with concentration gradients d) It does not need protein carrier, so the diffusion process is not saturable 24 Def It is the diffusion of substances across the cell m embrane (down electrochemical gradient) which needs the presence of carrier proteins → carrier mediated diffusion. Example Transport of glucose by glucose transporter 25 Def the passive flow of water across a semi-permeable membrane down a concentration gradient of water i.e. from high concentration of water to low concentration of water or low concentration of solute to high concentr ation of solute 26 Factors affecting net rate of diffusion of a substance include; a) Concentration gradient for the solute (Cin - Cout in mmol/L) b) Diffusion Coefficient (D) or permeability coefficient of the membrane c) Membrane surface area (A in cm2). The rate of diffusion is directly proportional to these factors d) Membrane thickness (X in cm) or distance, the rate of diffusion is inversely pr oportional to the thickness of the membrane 27 Def. It is movement of substances across the cell membrane against its electrochemical gradient. 28 Characters: It is characterized by; a) Occurs against an electro-chemical gradient b) Active i.e. external energy is required c) Need protein carrier, so the transport process is saturable, rate limited and shows competitive inhibition and stereospecificity 29 Types: 1) Primary active transport → obtain its energy directly from the hydrolysis of ATP e.g. Na-K Pump, Ca ATPase, H-K ATPase 2) Secondary active transport → use the energy stored in the Na concentration gradient e.g. Na-glucose co-transport and Na-Ca exchange 30  It transports 3 Na+ ions from ICF to ECF and 2 K+ ions from ECF to ICF. This maintains low intracellular Na and high intracellular K. It utilizes about 40% - 50% of energy 31 Differences between Simple Diffusion, Facilitated Diffusion and Active Transport Simple diffusion Facilitated diffusion Active transport Downhill Downhill Uphill Does not need energy Does not need energy Needs energy Does not need carrier Needs carrier Needs carrier Not limited Limited Limited Not Saturable Saturable Saturable Does not show stereospecificity Show stereospecificity Show stereospecificity Does not show competition Show competition Show competition 32 Def Mechanism by which the large sized substances can cross the cell membranes Types: Vesicular Transport Endocytosis Exocytosis EC material engulfed and IC material is engulfed and pushed into cells pushed out the cell 33  Is 3 types; Endocytosis Phagocytosis Receptor Pinocytosis mediated Solid particles e.g. bacteria Substance in solution Iron and and dead tissues e.g. proteins cholesterol 34 Def In exocytosis the intracellular material is trapped within vesicles, then the vesicles fuse with the cell membrane and release their contents to the ECF Example: Release of hormones, digestive enzymes, and synaptic transmitters 35  The cell membrane consists of lipids, proteins and carbohydrates  Ion channels are 3 types leak, voltage and ligand gated ion channels Summary & Wrap up  Transport through the cell membrane include diffusion, active transport and vesicular transport  Diffusion is a passive process and include simple diffusion, facilitated diffusion and osmosis  Active transport needs carrier and energy and include 2 types primary and secondary types  Vesicular transport include endocytosis and exocytosis  Questions 2- Examples for primary active transport 1-Simple diffusion is characterized by: include a) Occurs against electrochemical gradients a) Ca+2 ATPase b) Needs energy b) Ca+2-Na+ exchanger c) Needs carriers c) Na+-Glucose cotransporter d) Is not rate limited d) Na+-amino acid cotransporter e) Is saturable e) Na+- H+ exchanger 3- Phagocytosis: a) Is the process of exit of proteins from the cells b) Is the process of entry of proteins inside the cells c) Is the process of diffusion of ions d) Is a passive process e) Is the process of engulfing of bacteria and dead cells by the cells  References 1. Costanzo, Linda S. "BRS Physiology (Board Review Series)." (2018).‫‏‬ 2. Ganong, William F. "Review of medical physiology." (2020).‫‏‬ Discussion and Feedback THANK YOU