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Cell Physiology Chapter 4 OBJECTIVES To become familiar with terminology used to describe the cell environment especially in regard to transport of ions and fluids To understand how the various membrane processes work and how they differ from each other To understand basics of the cell cycle & cel...

Cell Physiology Chapter 4 OBJECTIVES To become familiar with terminology used to describe the cell environment especially in regard to transport of ions and fluids To understand how the various membrane processes work and how they differ from each other To understand basics of the cell cycle & cell differentiation Cellular Environments Intracellular Extracellular CELLULAR ENVIRONMENTS & BODY FLUID Intracellular fluid = water inside the cell (ICF) = most of water in body Extracellular fluid (ECF) = outside the cell  Intravascular = inside lymphatic & blood vessels Interstitial Intravascular HYDRATION Normal hydration is necessary for cellular function and is maintained by taking in the same amount of water that is lost by eating moist foods and drinking Metabolic water = water of oxidation produced as a by-product of cellular metabolism Water loss occurs overtly from sweating, urinating, defecating & vocalizing DEHYDRATION Moderate to severe dehydration requires fluid therapy to prevent cellular dysfunction that can lead to organ failure and death See the clinical application box on page 78-80 for a discussion of fluid therapy Body fluids contain different kinds of charged particles called ions: Positive = cations Negative = anions  Potassium, magnesium, hydrogen phosphate & sulfate are highest inside cells  Sodium, chloride & bicarbonate have highest concentration in the extracellular compartment More than one ion together = ionic compound (ex.) salt = composed of oppositely charged ions that separate when mixed in water Because all ions are able to conduct an electrical current in solution, they are called electrolytes ACIDS AND BASES Electrolytes   Acids - release hydrogen ions (H+) Bases - release hydroxyl ions (OH) Body solutions have high concentrations of both these ions Their relative proportions to each other determine the acidity or alkalinity of the fluid pH The concentration of hydrogen ions in fluid is measured inversely by pH. Scale 0-14 Pure water has a neutral pH (7) Acidic (< 7) –> lots of H+, few OHAlkaline (> 7) –> lots of OH-, few H+ Ill / Debilitated Animals Electrolyte concentrations and the pH of intracellular and extracellular fluid can become abnormally high or low Organ function can become impaired Additives in IV fluids are used to adjust the ionic imbalances and aid in maintenance of homeostasis   Potassium Chloride (KCl) Sodium bicarbonate (NaCO3) MEMBRANE PROCESSES: ABSORPTION & EXCRETION Tissue fluids also contain:      Fatty acids Vitamins Amino acids Regulatory hormones Dissolved gases In order for cells to maintain homeostasis they must bring nutrients into the intracellular compartment and eliminate wastes and transport products out into the extracellular environment for use in other parts olf the body This flow of fluid and nutrients into & out of cells is regulated by the plasma (cell) membrane   Membrane transport processes can be complex and varied Selectively permeable – impermeable to some substances & freely permeable to others Passive processes (do not require energy) (Simple) diffusion  Facilitated diffusion  Osmosis  Filtration  Active processes (require energy) Active transport  Endocytosis  DIFFUSION Kinetic energy – increases w/ higher temp Movement from a higher to lower concentration -> concentration gradient Size - Small molecules like H2O pass easily Lipid solubility - dissolved gases, alcohols and steroids easily pass through cell’s lipid bilayer Charged ions – specialized protein pores FACILITATED DIFFUSION Movement of some larger and/or nonsoluble molecules with the assistance of a protein carrier located in the lipid bilayer Binding of the extracellular molecule to the membrane protein causes the protein to change shape and allow the molecule to pass into the cell Glucose is too large to rely on simple diffusion so it must enter cell via a carrier protein (or via active transport) This process is limited by the number of carrier proteins available for binding OSMOSIS Passive movement of water through a semipermeable membrane from a dilute to a more concentrated environment Occurs to achieve the same concentration of solution on both sides of the membrane = concentration equilibrium Force of moving water across the membrane = osmotic pressure Isotonic – ECF has same concentration of dissolved substances as ICF fluid Hypotonic – ECF less concentrated than ICF > water into cells -> cells swell Hypertonic – ECF more concentrated than cytoplasm -> water into ECF -> cells shrink ONCOTIC PRESSURE = difference between the osmotic pressure of blood and that of interstitial fluid or lymph = force, provided by plasma proteins (pp), keeping fluid in blood vessels Diseases causing decrease in pp -> decrease in oncotic pressure -> leakage of fluid out of vessels & into the interstitium or into body cavities FILTRATION Does not rely on concentration gradients to drive the activity of the molecules Based on pressure gradient – if the pressure is greater on one side of a membrane than on the other side, liquids may be pushed through Hydrostatic pressure = force pushing a liquid = Blood pressure Best example of filtration = filtering of ACTIVE MEMBRANE PROCESSES Energy (ATP) is required to transport molecules and substances across the cell membrane Energy is required to transport molecules that are:    Not lipid soluble Too large On the wrong side of the pressure gradient Two processes:   Active transport Cytosis ACTIVE TRANSPORT Some amino acids and ions need this to enter cells Relies on a carrier protein with a specific binding site, but does not require a concentration gradient All cells participate in active transport of electrolytes Na+, K+, Ca2+, Mg2+ and specialized cells can transport Cl-, I- and Fe2+ Sodium-potassium pump (see text pg 86-88) Sodium-Potassium Pump ACTIVE TRANSPORT During transport, the ion binds to a specific carrier protein in the cell membrane -> triggers the release & use of cellular energy (ATP) The orientation of the carrier protein is altered, the ion becomes lipid soluble and the carrier protein now can move the ion through the cell membrane ATP is provided by cellular respiration and the enzyme ATPase For every 1 ATP molecule, 2 K+ ions are pumped into the cell and 3 Na+ ions are pumped out of the cell CYTOSIS Active processes (require energy) Endocytosis = going into cell  Phagocytosis  Pinocytosis CYTOSIS Exocytosis = going out of cell ENDOCYTOSIS Enables large particles, liquids and entire cells to be taken into the cell by engulfing    Phagocytosis - engulfs solid material forming a phagosome Pinocytosis - engulfs liquid forming pinocytic vesicle Receptor-mediated - very selective, occurs in cells w/ specific protein receptor sites in their cell membranes for binding of ligands like hormones, iron & cholesterol > taken into cell forming vesicle called a coated pit EXOCYTOSIS Substances to be exported out of cells are packaged in vesicles in the ER & Golgi body and moved through the cytoplasm -> vesicles fuse w/ the plasma membrane and release contents from the intracellular environment into the ECF Excretion - exocytosis of waste products Secretion - exocytosis of manufactured molecules (neurotransmitters, hormones, mucus, histamine, etc.) RESTING MEMBRANE POTENTIAL The difference in permeability of the plasma membrane leads to changes in the distribution of the charged particles on either side forming a voltage which = potential electrical energy created by the separation of opposite charges RESTING MEMBRANE POTENTIAL Outside of cell is slightly more positive than inside of cell, mostly due to Na+ and K+ ions Both passive and active processes work to place more + ions on the outside and keep the inside of the cell slightly negatively charged relative to the outside. There is more K+ inside the cell which diffuses out, while Na+ is more concentrated outside but cannot enter cell easily. So via diffusion the influx of Na+ is lower than the outflow of K+. For every cycle of active transport, 3 Na+ are pumped out for every 2 K+ retrieved Also cytoplasmic proteins tend to be negatively charged CELL CYCLE Two categories based on the way cells divide Reproductive cells - divide by meiosis Somatic cells - divide by mitosis Ability of the animal to grow and repair tissue is based on the division of somatic cells MITOSIS Interphase - period between cell divisions -“metabolic” phase when cell is growing, maturing and differentiating:    Growth 1 (G1) Phase – intense metabolic activity & cellular growth -> cell doubles in size Synthetic (S) Phase – DNA synthesis & replication Growth 2 (G2) Phase – synthesis of enzymes & proteins needed for cell division & continued growth Mitotic (M) Phase - cell is actively MITOTIC PHASE (Fig. 4-13, pg 95) Four stages:     Prophase – chromosomes & mitotic spindle formed; disintegration of nuclear envelope Metaphase – chromosomes line up in equator (exact center) of spindle; chromosomes form metaphase plate Anaphase – chromosomes split & take on V form; cell elongates & cytoplasm begins to constrict Telophase – chromosomes unravel, elongate & return to diffuse thread-like form (chromatin); nuclear envelope forms around each new set of chromosomes; spindle disassembles; cytoplasm divides (cytokinesis) marking the end of mitosis CONTROL OF CELL Cell divisionDIVISION is important during growth but once adult size is reached, cell division becomes a function of tissue repair and cellular replacement Normal cells stop dividing when they come in contact with other cells = contact inhibition Growth-inhibiting substances may be released from cells when numbers reach a certain point Checkpoints in G1 & G2 phases of cell cycle when cell reassesses the division process Neoplasms (tumors) develop when cells CELL DIFFERENTIATION Cells are able to form organs & tissues with diverse shapes and functions because genes controlling a characteristic are located in different positions on a chromosome Differentiation involves the temporary or permanent inhibition of genes that may be active in other cells BE ABLE TO: Explain what ions, cations, anions, and electrolytes are Define intracellular, extracellular, and interstitial environments Explain acids and bases, pH and the properties that make a fluid acidic or alkaline Define isotonic, hypertonic and hypotonic Explain passive & active membrane processes and how each works Explain the cell cycle, cell replication and the genetic basis of cell