Cells, Tissues and Skin

• Cells


  Smallest structural and functional unit of life
• Cells


  • Human body made up of 50-100 trillion cells
  • Over 250 types of cells
• Features common to all cells

  • Plasma membrane
  • Cytoplasm
  • Nucleus

  
• Organelles


  "Little organs" found within a cell, each with a specific function
• Cytoplasm


  The watery space between plasma membrane and the nucleus, composed of cytosol or intracellular fluid (ICF)

  
• Nucleus


  Largest organelle, houses DNA which contains the instructions for the cell
• Ribosomes


  Site of protein synthesis, free ribosomes produce proteins for use inside cell, membrane bound ribosomes produce proteins for export
• Endoplasmic Reticulum (ER)


  Interconnected tubes continuous with the nucleus, functions: synthesis, storage, transport & detoxification
• Rough Endoplasmic Reticulum (RER)

  Studded with ribosomes, proteins produced by ribosomes on RER are packaged and exported out of cell
• Smooth Endoplasmic Reticulum (SER)

  No ribosomes attached, synthesis of lipids, cholesterol and steroid based hormones, involved in detoxification, storage of calcium ions

  
• Golgi Apparatus


  Consists of stacks of flattened sacs, modifies, concentrates and packages proteins and lipids, forms vesicles and distributes them
• Mitochondria


  "The power house", site of cellular respiration which releases energy in the form of ATP
• Lysosomes


  Membrane enclosed spheres containing lysosomal enzymes, digest biological material including proteins and cell debris, recycle molecules, dispose of invading bacteria, viruses and toxins

  
• Cilia


  Motile cellular extensions on the top of cells that sweep in a wave like manner to move materials across the surface
• Microvilli


  Minute finger like extensions of the plasma membrane that project from the cell surface, increase the surface area of the cell
• Plasma Membrane


  Thin and flexible boundary between the ICF & ECF, selectively permeable, allows for different chemical compositions between ICF and ECF to maintain homeostasis and create optimal working conditions for the cell

  
• Phospholipid Molecule


  Phosphate heads are hydrophilic ("love water"), lipid tails are hydrophobic ("hate water")

  
• Plasma Membrane: Phospholipid Bilayer

  Double layer of phospholipids, phosphate heads face towards ECF & ICF, lipid tails face towards each other creating a lipid core

  
• Lipid Soluble Substance


  Water insoluble substance, not repelled by the lipid core of plasma membrane

  
• Water Soluble Substance


  Lipid insoluble substance, repelled by the lipid core of plasma membrane

  
• Peripheral Proteins


  Attach loosely to integral proteins or float free, provide plasma membrane support, act as enzymes or motor functions

  
• Integral Proteins


  Embedded within the membrane and span entire membrane, classified as channels or carriers for transport of substances

  
• Channel Proteins


  Open at one end and can open and close at the other end, allow the passage of small lipid insoluble substances like ions and water

  
• Gated Channels


  Can open and close, substances that use: ions Na+, K+ & Ca2+
• Leakage Channels


  Always open at both ends, substances that use: water, ions like sodium (Na+) and potassium (K+)
• Carrier Proteins


  Transform shape to allow lipid insoluble substances or substances too large to use channel proteins to pass across the membrane

  
• Concentration


  Measure of the amount of a substance in an area
• Concentration Gradient


  The difference in concentration of a particular substance between 2 different areas
• Equilibrium


  Equal space between substances, state of stable conditions
• Diffusion


  Movement of a substance from an area of high concentration to an area of low concentration (down/along/with concentration gradient) to achieve equilibrium
• Factors affecting rate of diffusion

  • Concentration gradient
  • Size of the substance
  • Temperature
• Passive Transport


  Substances move down concentration gradient, requires no energy, includes simple diffusion, facilitated diffusion and osmosis
• Active Transport


  Substances move up concentration gradient, requires ATP, includes primary active transport with Na+/K+ ATPase pump
• Simple Diffusion


  Unassisted transport of lipid soluble or very small substances across a plasma membrane, down its concentration gradient, until equilibrium is reached

  
• Facilitated Diffusion


  Assisted transport of lipid insoluble substances across a plasma membrane, down its concentration gradient, using channel or carrier proteins

  
• Cells need substances such as nutrients, gases and waste to be transported across the plasma membrane to maintain homeostasis
• Simple Diffusion


  1. Unassisted transport of lipid soluble or very small substances, across a plasma membrane, down its concentration gradient

  2. Continues until equilibrium is reached then no net movement

  
• Substances that move by simple diffusion

  • O2, CO2, fats, steroid hormones, alcohol
• Facilitated Diffusion


  Assisted transport of large or lipid insoluble substances, from an area of high concentration to low concentration, across a plasma membrane, using an integral protein

  
• Substances that move by facilitated diffusion

  • Glucose, Sodium (Na+), Potassium (K+)