Anatomy & Physiology I Unit Three

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Fluid Mosaic Model of the Plasma Membrane

Fluid Mosaic Model of the Plasma Membrane

Fluid Mosaic Model of the Plasma Membrane

Fluid Mosaic Model of the Plasma Membrane

Fluid Mosaic Model of the Plasma Membrane

Passive Transport Does not require energy from the cell Substances move from an area of high concentration to an area of low concentration Substances can move in both directions, depending on the concentration gradient

Examples of Passive Transport Diffusion – the movement of a substance from an area of high concentration to an area of low concentration Facilitated diffusion – same as above, but with the help of membrane proteins Osmosis – the diffusion of water

Active Transport Does require energy from the cell Substances move from an area of low concentration to an area of high concentration Substances can move in only one direction, against the concentration gradient

Active Transport Example Sodium/Potassium pump – a membrane protein that moves sodium out, while moving potassium in

Active Transport

Membrane Transport

Filtration

Bulk Transport Endocytosis * Phagocytosis * Pinocytosis

Bulk Transport Exocytosis

Osmosis Solute – substance that is dissolved in a medium (solvent) Solvent – substance (usually liquid) that dissolves a solute Solution – mixture of solutes dissolved in a solvent Osmotic pressure is created by the movement of water toward a higher solute concentration

Semipermeable membrane Osmosis Diffusion Semipermeable membrane Osmosis

Osmosis

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Plant Cell Osmosis Turgor

Osmosis Therefore, the higher the solute concentration, the higher the osmotic pressure Many body systems create high solute concentrations so as to produce higher osmotic pressure

Osmosis Edema – the excess collection of extracellular fluids due to high solute concentration Dehydration – the loss of extracellular fluids due to various causes

Electrolyte Functions The functions of electrolytes are varied and important: + chemically reactive and participate in metabolism + determine charge difference across cell membranes

Electrolyte Functions The functions of electrolytes are varied and important: + powerfully affect the osmolarity of body fluids and the body’s water content and distribution + form essential minerals + regulate acid/base balance

Electrolyte Concentrations Extracellular fluids (ECF) are fluids of the body found outside the cells Intracellular fluids (ICF) are fluids of the body found inside the cells (cytoplasm)

Electrolyte Concentrations HPO43- (Lo) Na+ (145mEq/L) Ca2+ (Hi) Mg2+ (Lo) K+ (4mEq/L) K+ (150mEq/L) Mg2+ (Hi) Ca2+ (Lo) Na+ (12mEq/L) HPO43- (Hi)

Electrolyte Concentrations Cl- (103mEq/L) OH- HCO3-(Hi) H+ HCO3- (Lo) Cl- (4mEq/L) H+ OH-

ICF vs. ECF ICF ECF 65% of body fluids Major electrolytes K+ Mg2+ HPO43- 35% of body fluids Major electrolytes Na+ Ca2+ Cl-

ICF vs. ECF 26L 40L total body fluid 10L 3.2L 0.8L Interstitial Fluids Blood Plasma Lymph How much fluid is found in the ICF and the ECF? Which one do you think has the most fluid? *ICF is the largest fluid compartment in the body. For the average person it will hold about 25 liters of fluid. *About 12 liters of the ECF are in the interstitial fluid. *The remaining ECF makes up the blood. It contains about 3 Liters. *The total amount of fluid in the body will be about 40 liters. 0.8L Other 40L total body fluid

Movement of Water Fluids are constantly exchanged between these compartments Osmosis occurs across capillary walls and plasma membranes

Movement of Water The movement of the water from one compartment to the other is determined by solute concentrations

Movement of Water

Introducing Fluids in the Body As has been established, body cells must maintained in isotonic conditions On an average the solute concentration of body cells is 300mosm

Introducing Fluids in the Body This means on an average, the ECF osmolarity would also be 300mosm There are exceptions to both ICF and ECF osmolarities

Introducing Fluids in the Body Since a loss of fluids also means a loss of electrolytes, fluid replacement therapy (IVs) may be necessary to restore homeostatic concentrations and volumes

Introducing Fluids in the Body Fluids introduced to the body must therefore have the same osmolarity > 0.9% normal saline (NS) or physiological saline (PSS) > D5W (dextrose 5% in water) (5% glucose) > Ringer’s lactate solution

Fluid Balance Balance of body fluids means that fluid intake should equal fluid output In addition, the fluid gained or lost must be added to or taken from the right compartment (ICF or ECF)

Fluid Balance

Fluid Balance As has been seen, electrolyte concentrations in the different compartments must also be stringently maintained Electrolytes attract water through osmosis, therefore a loss of fluids results in the loss of electrolytes

Fluid & Electrolyte Balance ICF 65% of body fluids ECF Major electrolytes K+ Mg2+ HPO43- 35% of body fluids Major electrolytes Na+ Ca2+ Cl-

Fluid Balance The three structures that play the major role in fluid and electrolyte balance are: * brain (hypothalamus) * kidneys * adrenal glands

Regulation of Fluid Intake Decreased volume of ECF or Increased osmolarity of ECF Hypothalamus Decrease saliva Creates thirst Increased volume of ECF which decreases osmolarity of ECF Drink fluids