뒤로Anatomy & Physiology: Cells and Membrane Transport
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Cell theory states that the cell is the smallest unit of life, all organisms are made of one or more cells, and cells arise only from other cells.
The three basic parts are: plasma membrane (flexible outer boundary), cytoplasm (intracellular fluid with organelles), and nucleus (DNA-containing control center).
The plasma membrane is a phospholipid bilayer with embedded proteins, cholesterol, and surface sugars forming the glycocalyx.
Phospholipids have polar hydrophilic heads facing water inside and outside the cell, and nonpolar hydrophobic tails that hide from water inside the membrane.
Integral proteins span the membrane and function as transporters, enzymes, or receptors. Peripheral proteins are loosely attached and function as enzymes, motor proteins, or in cell-to-cell connections.
The glycocalyx is a sugar coating on the cell surface made of glycolipids and glycoproteins. It acts as a biological marker for cell recognition and immune system identification of self versus nonself.
The three types are tight junctions (impermeable seals), desmosomes (anchoring junctions), and gap junctions (channels for communication).
Passive transport requires no energy and includes simple diffusion, facilitated diffusion, and osmosis, all moving substances down their concentration gradients.
Speed of diffusion is influenced by concentration gradient, molecular size, and temperature.
Facilitated diffusion is passive transport assisted by carrier or channel proteins for hydrophobic molecules like glucose and ions.
Osmosis is the movement of water across a selectively permeable membrane from an area of low solute concentration to high solute concentration, often through aquaporins.
Tonicity is the ability of a solution to change cell shape by altering water volume. Isotonic solutions cause no change, hypertonic cause cell shrinkage, and hypotonic cause cell swelling or lysis.
Active transport uses energy (ATP) to move solutes against their concentration gradient, including primary active transport and secondary active transport.
The sodium-potassium pump uses ATP to pump 3 sodium ions out and 2 potassium ions into the cell, maintaining electrochemical gradients essential for nerve and muscle function.
Secondary active transport uses energy stored in ion gradients created by primary active transport to move other substances via symporters or antiporters.
Vesicular transport moves large substances across membranes inside vesicles and includes endocytosis, exocytosis, transcytosis, and vesicular trafficking.
Endocytosis types are phagocytosis (cell eating), pinocytosis (cell drinking), and receptor-mediated endocytosis (selective uptake via receptors).
RMP is the voltage across the plasma membrane at rest, typically negative inside the cell, due to ion separation and membrane permeability, especially to potassium ions.
CAMs anchor cells to the extracellular matrix or other cells, assist cell movement, attract white blood cells to injury, and transmit signals for cell migration and specialization.
Plasma membrane receptors mediate contact signaling, chemical signaling via ligands, and activate intracellular responses including enzyme activity and ion channel regulation.