(1) Physiology

• Moderately permeable to Na+.
• Freely permeable to Cl- and K+.
• Cell Membrane limits the boundary of the cell.
• Intercellular Bridges
fasten the cells to one another and to the surrounding tissues and permit transfer of ions and other molecules from one cell to another.
• Mitochondria
power-generating unit of the cell.
• Lysosomes contain enzymes which would cause destruction of cellular components once released.
• Microfilaments cause contraction.
• Microtubules make up the skeletal framework of the cell; provide the pathway along which secretory granules move to the cell membrane; play a key role in nerve fiber outgrowth.
• Centrioles are concerned with the movement of the chromosomes during cell division.
• Golgi complex packages cellular products.
• Endoplasmic reticulum contains ribosomes which are the sites of protein synthesis.
• Nucleolus
contains RNA which regulates protein synthesis.
• Nucleus
contains chromosomes which are the carriers of hereditary traits of the individual.
• Body weight is approximately 60% water and 40% protein, fats, and minerals.
• 60% of the body weight is water, 40% is intracellular, and 20% is extracellular, with 25% in the vascular system and 75% outside the vascular system.
• Forces producing movements of water and other molecules across membranes or barriers include diffusion, solvent drag, filtration, osmosis, active transport, exocytosis/endocytosis.
• Diffusion is the process by which a gas or a substance, in solution, expands because of the motion of its particles to fill all of the available volume.
• The movement of the particles of a substance dissolved in a solvent are in continuous random movement.
• In regions where they are abundant, particles frequently collide and, therefore, tend to spread from regions of high concentration to regions of low concentration until the concentration is uniform throughout the solution.
• Diffusion is also affected by electrical charge and the permeability of the barrier.
• Solvent Drag occurs when solvent is moving in one direction, the solvent tends to drag along some molecules of the solute.
• Those with greater pressure are hypertonic.
• Facilitated diffusion is a process where transport is from an area of greater concentration of the transported molecules to an area of lesser concentration, and no energy is required.
• Active transport is a process that requires energy and is carried out by "pumps" and energy is supplied by ATP.
• Those with lesser pressure are hypotonic.
• Hormones and large polypeptides enter the cell by endocytosis and are secreted by exocytosis.
• The invagination is pinched off, leaving the engulfed material in the membrane enclosed vacuole and the cell membrane intact.
• The unique properties of the cell membranes are responsible for the differences in the composition of the intracellular and interstitial fluid compartments.
• V is the movement of solvent molecules across a membrane into a region in which there is a higher concentration of a solute to which the membrane is impermeable.
• Active transport involves the transport of ions and larger non-ionized molecules by carrier molecules in the membrane.
• There is a potential difference across the membranes called the resting membrane potential, the intracellular area is negatively charged and the extracellular area (interstitial area) is positively charged.
• In exocytosis, proteins that are secreted by cells move from the endoplasmic reticulum to the Golgi complex where they are packaged into secretory granules which in turn move along tracks of microtubules to the cell membrane, the granule membrane and the cell membrane then fuse and the area of fusion breaks down, leaving the contents of the granule outside the cell and the cell membrane intact.
• Cell membranes are impermeable to intracellular proteins and other organic anions (A-).
• Solutions that have the same EOP as plasma are said to be isotonic (NSS - normal salt solution or 0.9% NaCl).
• The vacuole inside the cell will be mixed with the digestive enzymes of the lysosome.
• The pressure necessary to prevent solvent migration is called effective osmotic pressure of the solution.
• Endocytosis is the reverse of exocytosis, where the cell engulfs bacteria, dead tissue and other bits of material which then makes contact with the cell membrane which in turn will invaginate.
• Filtration is the process by which fluid is forced through a membrane or other barriers due to a difference in hydrostatic pressure on the two sides; molecules that are smaller in diameter than the pores of the membrane pass through with the fluid and larger molecules are retained.
• Osmosis is the process by which water moves across a membrane from a region of high water concentration to a region of low water concentration.
• Active transport is the process by which molecules move across a membrane against a concentration gradient.