#1 Notes 1Human Physiology – TandyHomeostasis, Cell Membrane, and Cell CommunicationTotal Body Water – 2/3 intracellular, 1/3 extracellular Intracellular Fluid (2/3)– inside of the cells Extracellular Fluid (1/3)o Outside Cells (80%) [interstitial fluid] – between the cells o In Blood Vessels (20%) [plasma]o Creates the internal environment within which our cells existHomeostasis All physiological process that work together to maintain a relatively steady state in an organism Variables Body Temperature pH K+ ConcentrationCell Membrane Made of phospholipidmolecules that form a phospholipid bilayer Heads face outside of thebilayer and tails face inside ofthe bilayer when in water –organized based on nature of the particles In the Cell Membraneo The bilayero Proteins Integral Membrane Proteins – integrated or embedded within the membrane- Trans-membrane protein – all across the phospholipid bilayer Peripheral Membrane Protein – on inside or outside of cell membrane, not integratedJunctions between Cells (3 types) 1. Desmosomeso Hold cells firmly together and provides mechanical strengtho Resist forces that act to pull cells apart o Where body needs them to be (ex: skin)o If damaged, tissue that is not anchored (i.e. tissue without desmosomes) will slough off because nothing holding the cells tightly together and resisting the force trying to pull them aparto Localized, and water cannot get around the desmosomes Phospholipid Head Phospholipid Tail Charged phosphate Carbon tails Hydrophilic – water loving Lipophilic – lipid loving Polar Non-polar/Minimally charged#1 Notes 2 2. Gap Junctionso Provides direct pathway for communications between cellso Important in rapid transmission of electrical signals 3. Tight Junctionso Restrict movement of large, hydrophilic molecules between cells, and regulating movement of molecules Need integral membrane protein (trans-membrane protein), which is specific to that molecule, so that only molecules with channels can get into cells o Extends around the entire cell o Polarize the epithelium (cells adjacent to each other creating a boundary of cells) Give the epithelium an apical surface (surface facing the lumen – top;hollow portion) and a basolateral surface (surface facing the rest of the cells – bottom and side; the stuff) o Present on absorptive surfaces because the molecules need to get into the cells and you want to only make sure you get what you need, so you have specific channels, etc. Movement of (Uncharged) Molecules Passive Transporto No external energy necessary o Always occurs down a chemical gradient (area of high area of low concentration) o Via Fick’s Law, the Rate of Flux (movement across a membrane) is related to Membrane permeability- Affected by lipid solubility, size and shape of molecules, temperature, membrane thickness- Increased net flux with small, lipophilic molecules because membrane more permeable to those molecules- Decreased net flux with large, hydrophilic molecules because membrane less permeable to those molecules Surface Area of the membrane- Increased net flux if membrane thin or has greater surface area- Decreased net flux if membrane thick or has smaller surface area Concentration Gradient across the membrane- Net flux is directly related to concentration gradiento Increase concentration gradient, increase net flux (morewill come into/out of a cell if the concentration gradientis steeper)o Seeks to establish no net flux – movement across the membrane, but the movement is equal and opposite o 2 types of Passive Movement#1 Notes 3 1. Simple Diffusion- Lipophilic molecules can diffuse directly across the cell membrane, needs no help - Small hydrophilic ions can move through channels and into the cell, without interaction between channels and ions 2. Mediated (Facilitated) Transport (Diffusion)- Hydrophilic molecules that are too large to go through a channel may be transported using a carrier molecule (mediator/carrier)- Transporter will change conformation spontaneously and the molecule binds to the facilitator and is transported - Still move based on concentration gradient - Use of a mediator based on:o Specificity Binding sites have specificity for which molecules they can bind to Ligand – molecule that will bind to a binding site Can be affected by minor alteration in the structure of the ligand or binding site o Saturation Ligands can only bind as long as there are binding sites available The availability levels off without regard to concentration. Based on the binding sites, not the concentrationof the ligando Affinity Ability of binding site to hold onto the molecules High if opposite charges and tight fit More able to transport because higher affinity and stronger bond If there is a high affinity outside cell and low affinity inside cell and binding site releases molecule?? Increasing the affinity of a carrier’s binding site will increase the rate of transfer- If it is an enzyme, a more rapid reaction will resulto Competition Ligands with similar chemical structures could compete for the same binding site and the one with the greater concentration and higher affinitywill likely win Active Transporto Sibstances moved against their concentration gradient#1 Notes 4o Primary Active Transport Directly uses ATP as energy source- Ex) Na+/K+ Pump - Na+ and K+ moved against their concentration gradient with hydrolysis of ATP o 3 Na+ out, 2 K+ in Always moves against concentration gradiento Secondary Active Transport Utilizes energy released from one ion (typically Na+) moving down itsconcentration gradient to power the movement of a second substance across the cell membrane against its gradient Na+ always moves passively into the cell, releases energy, which gives the secondary transporter the energy to actively transfer the other molecule against its concentration gradient Cotransport – if other substance is transported in same direction Countertransport – if other substance is transported in opposite direction Movement of Water Moves passively down its concentration gradient Osmosis – movement of water against a selectably permeable membrane caused by differences in solute concentration If pure water, no net movement of water because no concentration gradient, but if you add solute, you make
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