physiology: cellular structure

• The body fluid compartments include the intracellular fluid, interstitial fluid, and extracellular fluid.
• The basic cellular structure includes the cell membrane, nucleus, and cytoplasm.
• The plasma membrane is important for various functions such as cell signaling, cellular transport, and cellular homeostasis.
• Peroxisomes are moderately dense oval bodies enclosed by a single membrane found primarily in the liver and kidney cells, which consume molecular oxygen and undergo reactions that remove hydrogen from organic molecules including lipids, alcohol, and potentially toxic ingested substances.
• Lysosomes are spherical or oval organelles surrounded by a single membrane that digest damaged cellular structures, food particles ingested by the cell, unwanted matter (bacteria and debris), and contain acidic fluid and digestive enzymes.
• Vaults are recently discovered cytoplasmic structures composed of protein and a type of RNA called vault RNA (vRNA), which function not certain but studies using electron microscopy and other methods have revealed that vaults tend to be associated with nuclear pores and are important for transport of molecules between the cytosol and the nucleus.
• Microtubules also radiate from a region of the cell known as the centrosome, which surrounds two small, cylindrical bodies called centrioles, composed of nine sets of fused microtubules.
• The polypeptide chain is a long, unbranched protein chain that serves as the template for the synthesis of proteins.
• The centrosome is a cloud of amorphous material.
• Mitochondria are spherical or elongated, rodlike structures with two membranes, an outer membrane that is smooth and an inner membrane that is folded into sheets or tubules known as cristae, which extend into the inner mitochondrial compartment, the matrix, and contain enzymes for citric acid cycle and fatty acid oxidation.
• Ribosomes are protein factories of a cell, where protein molecules are synthesized from amino acids, using genetic information carried by RNA messenger molecules from DNA in the nucleus.
• Vesicles containing proteins to be secreted from the cell are known as secretory vesicles.
• The Golgi apparatus sorts the modified proteins into discrete classes of transport vesicles that will travel to various cell organelles or to the plasma membrane, where the protein contents of the vesicle are released to the outside of the cell.
• The cytoskeleton is a filamentous network that is associated with processes that maintain and change cell shape and produce cell movements.
• Actin filaments make up a major portion of the cytoskeleton in all cells and are important for determining cell shape, enabling cells to move by ameboid-like movements, cell division, and muscle cell contraction.
• There are three classes of cytoskeletal filaments based on diameter and types of protein they contain.
• Intermediate filaments contribute to cell shape, help anchor the nucleus, provide considerable strength to cells, and are most extensively developed in the regions of cells subject to mechanical stress.
• Certain types of vesicles that pinch off the plasma membrane travel to and fuse with endosomes.
• Microtubules are hollow tubes about 25 nm in diameter, whose subunits are composed of the protein tubulin.
• Microtubules are the most rigid of the cytoskeletal filaments and provide the framework that maintains the neuronal processes’ cylindrical shape.
• Organelles are propelled along these tracks by contractile proteins attached to the surface of the organelles.
• During cell division, the centrosome generates the microtubular spindle fibers used in chromosome separation.
• Microtubules are implicated in the movements of organelles within the cytoplasm together with actin filaments by forming tracks.
• Centrosomes or Centrioles are non-membranous organelles that regulate the formation and elongation of microtubules.
• Intermediate filaments, once assembled, are less readily disassembled.
• Endosomes are involved in sorting, modifying, and directing vesicular traffic in cells.
• Vesicles are membrane-bound vesicular and tubular structures that lie between the plasma membrane and the Golgi apparatus.
• Actin filaments and microtubules can be assembled and disassembled rapidly, allowing a cell to alter these components of its cytoskeletal framework according to changing requirements.
• Actin filaments are composed of monomers of the protein G-actin (or “globular actin”) which assembles into a polymer of two twisting chains known as F-actin (for “filamentous”).
• Intermediate filaments are composed of twisted strands of several different proteins: Keratin, Desmin, Lamin.
• The nucleus forms a fine network of threads known as chromatin in association with proteins, which condenses into rodlike bodies known as chromosomes during cell division.
• The nucleus is a large organelle usually located near the center of the cell, storing and transmitting genetic information to the next generation of cells.
• The nucleolus is the most prominent structure in the nucleus, a densely staining filamentous region without a membrane associated with specific regions of DNA that contain the genes for forming the particular type of RNA found in cytoplasmic organelles called ribosomes, where the RNA and the protein components of ribosomes are assembled, then transferred through the nuclear pores to the cytoplasm, where they form functional ribosomes.
• The endoplasmic reticulum can be nonmembranous or membranous, with the membranous endoplasmic reticulum having ribosomes bound to its cytosolic surface, and a flattened-sac appearance, well developed in cells that produce and secrete proteins, involved in packaging proteins that, after processing in the Golgi apparatus, are secreted by the cell or distributed to other cell organelles, and the site of translation and posttranslational modification of proteins.
• The endoplasmic reticulum can also be smooth, with no ribosomal particles on its surface and a branched, tubular structure, functioning as the site at which certain lipid molecules are synthesized, playing a role in modification and detoxification of certain hydrophobic molecules, and storing and releasing calcium ions involved in controlling various cell activities.
• The Golgi complex or apparatus is a membranous organelle, the site of post-translational modification, for example, carbohydrates are linked to proteins to form glycoproteins, and the length of the protein is often shortened by removing a terminal portion of.
• The nuclear envelope surrounds the nucleus as a barrier composed of two membranes at regular intervals along the surface of the nuclear envelope, allowing RNA molecules that determine the structure of proteins synthesized in the cytoplasm to move between the nucleus and cytoplasm through these nuclear pores, and proteins that modulate the expression of various genes in DNA to move into the nucleus through these pores.
• The endoplasmic reticulum is the most extensive cytoplasmic organelle with a network of tubular and flat vesicular structures that have a lipid bilayer membrane continuous with the nuclear membrane, with multiple enzyme systems attached to its membrane, and a Ca 2+ pump that transports Ca 2+ from cytoplasm to ER lumen.