Mass Balance in the Body (through intestine, lungs, skin) (by kidneys, liver, lungs, skin) BODY LOAD Metabolic production Metabolism to a new substance Mass balance Existing body load Law of Mass Balance + Intake or metabolic production Excretion or metabolic removal = – IntakeExcretion

Homeostasis

Mass Balance and Homeostasis Clearance –Rate at which a molecule disappears from the body –Mass flow = concentration  volume flow Homeostasis  equilibrium –Osmotic equilibrium –Chemical disequilibrium –Electrical disequilibrium

Map of Membrane Transport

Diffusion is the net movement of particles from an area of higher particle concentration to an area of lower particle concentration. Net movement = flux Both the size and direction of movement is concentration- dependent. Diffusion

Simple Diffusion Fick’s law of diffusion Rate of diffusion surface area concentration gradient membrane permeability membrane thickness Extracellular fluid Membrane surface area Intracellular fluid Composition of lipid layer Lipid solubility Molecular size Concentration outside cell Concentration inside cell Membrane thickness Concentration gradient Fick's Law of Diffusion says: lipid solubility molecular size Membrane permeability Changing the composition of the lipid layer can increase or decrease membrane permeability.

Simple Diffusion

Two classes of compounds move by simple diffusion 1.Lipid soluble compounds 2.Small ions which move through protein channels a.channels are selective b.channels can be regulated

Membrane Transport Proteins

Channel Proteins: Gated Usually closed Often highly Selective (size, charge) Chemical (e.g. intracellular messengers) Temperature Mechanical/tension Electric (voltage) signals Consist of subunits Ion channels: e.g. K+, Na+, Ca 2+ Leak channels open all time e.g. allow water, ions movement

Gating of Channel Proteins

Active Transport Can transport against a concentration gradient Requires energy input (ATP to ADP, P) Two forms: primary active transport secondary active transport

Primary Active Transport ADP ATPase is phosphorylated with P i from ATP. ADP 2 ATP ICF ECF 3 Na + from ICF bind 1 1 Protein changes conformation. 3 Na + released into ECF 3 2 K + from ECF bind 4 2 K + released into ICF 5

Secondary Active Transport Mechanism of the SGLT Transporter [Na + ] low [glucose] high SGLT protein Lumen of intestine or kidney Intracellular fluid Glucose binding changes carrier conformation. Na + binds to carrier. [Na + ] high [glucose] low Na + binding creates a site for glucose. Na + released into cytosol. Glucose follows

Energy Transfer in Living Cells ATP Secondary active transport Primary active transport Metabolism The chemical bond energy is converted into high-energy bonds of ATP through the process of metabolism. The energy in the high-energy phosphate bond of ATP is used to move K + and Na + against their concentration gradients. This creates potential energy stored in the ion concentration gradients. The energy of the Na + gradient can be used to move other molecules across the cell membrane against their concentration gradients. Energy is imported into the cell as energy stored in chemical bonds of nutrients such as glucose. Glucose Pyruvate CA cycle Heat H2OH2O CO 2 ADP+P i O2O2 High [K + ] Low [Na + ] Na + Glycolysis ETS K+K+ K+K+ 2 Cl – Low [K + ] High [Na + ] Glucose ATP ETS = Electron transport system = Citric acid cycle CA cycle KEY

Membrane Transport Proteins

Carrier Proteins: Proteins are Required for Carrier-mediated Transport Specificity Saturation Competition

Carrier-Mediated Transport Competition

Carrier-Mediated Transport Saturation

Phagocytosis: important in immune cells

Vesicular Transport

Polarized cell transporting epithelia

Transepithelial Transport of Glucose

Transcytosis

46-61% body weight is water How is water distributed in body?

Osmosis and Tonicity Net diffusion of water from an area of low solute concentration to an area of higher solute concentration when movement of solute is prevented by a membrane.

Copyright © 2009 Pearson Education, Inc. Tonicity Tonicity depends on the relative concentrations of nonpenetrating solutes

Osmolarity Total number of osmotically active particles Osmolarity = molar conc x # particles of solute in solution (1 mM glucose) x 1 particle =1 mOs glucose (1 mM NaCl) x 2 particles = 2 mOs NaCl

Tonicity Describes only number of non-penetrating solutes 300 mOs 300 mM NaCl = 600 mOs NaCl Hypertonic solution Water moves out; cell shrinks Isotonic = same as cell; size stable Hypotonic = less than cell; cells lyse

NaCl, protein: non-penetrating Urea: penetrating

The cell membrane enables separation of electrical charge in the body Resting membrane potential is the electrical gradient between ECF and ICF

Resting Membrane Potential Extracellular fluid 0 mV Intracellular fluid -70 mV

Terminology associated with changes in membrane potential

Equilibrium Potential Nernst Equation E ion = 61 x log [ion] out z [ion] in Z is electrical charge on ion E for K+ = -90 mV E for Na+ = +60 mV

Tonicity Problems RBC in a solution, what will happen to the cell? 300 mOs NaCl ? 300 mOs NaCl mOs urea? 300 mOs NaCl mOs protein? 300 mOs NaCl mOs urea?

Kidney Dialysis urea NaCl, proteins urea

Movement across Membranes Movement across Membranes