Human Anatomy, First EditionMcKinley & O'Loughlin Chapter 2 : The Cell: Basic Unit of Structure and Function
The Cell • Cells: • structural and functional units of all living organisms. • building blocks of the human body. • adult human body contains ~ 75 trillion cells. • Each cell type performs specific functions. • ~200 cell types in humans • subcategories of most
Common Characteristics of Cells • Perform the general functions necessary to sustain life: • Obtain nutrients and other materials from its surrounding fluids. • Fuel molecules, O2, building blocks, minerals,etc • Dispose of wastes products • Urea (from nitrogen), CO2, metabolic waste • Maintain shape and integrity • Size and shape are related to function • Cell division: • Mitosis: growth and repair • Meiosis: gamete formation
Study of Cells • Cytology: study of cells • Microscopic anatomy • Individual cells observable by light microscopy • Subcellular structures observable by electron microscopy. • TEM • SEM • Unit of measure: micrometer (um) • RBC: 7-8um
Cells • Parts of a cell • Cell Membrane (or plasma membrane) • Cytoplasm • Cytosol • Organelles • Membranous Organelles • Non-membranous Organelles • Inclusions • Nucleus
Plasma (Cell) Membrane • the outer, limiting barrier • separates the internal contents of the cell from external materials.
Cytoplasm • general term for all cellular contents located between the plasma membrane and the nucleus.
Nucleus • “control center” of the cell • controls protein synthesis • directs the functional and structural characteristics of the cell.
Plasma membrane: composition • Lipids • Phospholipids • Head: hydrophilic • Tail: hydrophobic • Form lipid bilayer • Cholesterol • Glycolipids • Carbohydrate component • Part of glycocalyx
Plasma membrane: composition • Protein • Integral membrane proteins • Peripheral membrane proteins • Some serve as enzymes, ion channels or receptors • Glycoproteins
Plasma membrane: functions • Selectively permeable barrier • Nutrient in • Waste out • Communication • Intercellular connections • Physical barrier
Transport Mechanisms • Passive Transport • Active Transport • Bulk Transport • Solution= solvent (H2O)+ solute
Passive Transport • Movement of substances along a concentration gradient • [Hi] to [Low] • ATP is not required • Types: • Simple Diffusion: solutes • Facilitated Diffusion: solutes • Bulk Filtration: solution • Osmosis: solvent
Facilitated Diffusion • Requires the participation of specific transport proteins that help specific substances or molecules move across the plasma membrane. • “Carrier-mediated”
Bulk Filtration • Involves the diffusion of both solvents and solutes together across the selectively permeable membrane. • Pressure gradients
Osmosis • Involves the diffusion of a solvent (H2O), across a selectively permeable membrane. • Can cause a volume change
Active Transport • Movement of a substance across a plasma membrane against a concentration gradient. • Materials must be moved from an area of low concentration to an area of high concentration. • requires cellular energy in the form of ATP (adenosine triphosphate) • uses transport proteins (carrier-mediated) • ATP is continually synthesized by mitochondria
Ion Pumps • Active transport processes that move ions across the membrane are called ion pumps. • ion pumps allow a cell to maintain its internal concentrations of small molecules or ions
Bulk Transport - Exocytosis • Used by cells that secrete • Usually movement of large molecules • Movement out of the cell.
Bulk Transport - Endocytosis • process by which the cell acquires materials from the extracellular fluid: (3 Forms) • Phagocytosis: • Cell forms pseudopodia • engulfs a particle • internalize it into a vacuole • Pinocytosis: • incorporation of droplets of extracellular fluid (solution) • Taken into the cell in small vesicles • Receptor-mediated endocytosis: • receptors in the cell membrane • Bind with specific molecules • Invagination forms around them to create a cytoplasmic vesicle
Cytoplasm: cytosol • Matrix; intracellular material • Different in different cell • Mostly water
Cytoplasm: Organelles • Complex, organized structures • Have unique, characteristic shapes. • Each type performs a different function for the cell. • Are essential for normal cellular structure and activities.
Membranous Organelles • Include: • Endoplasmic Reticulum • Rough Endoplasmic Reticulum (RER) • Ribosomes • Make protein for export • Peroxisomes made here • Smooth Endoplamic Reticulum (SER) • Lipids and carbohydrates • Detoxification
Membranous Organelles • Peroxisomes • Vesicles formed from RER • Use oxygen to detoxify • Mediated by specific enzymes • Most abundant in liver
Membranous Organelles • Golgi Apparatus • Modifies, stores and sorts material from RER • Receiving region (cis-face) • Shipping region (trans-face) • Produces Lysosomes • Autophagy: removal of old organelles • Autolysis: destruction of the cell
Mitochondria • Mitochondria are organelles with a double membrane. • Produce large amounts of ATP. • Are called the “powerhouses” of the cell.
Non-Membranous Organelles • Not made of a membrane. • Usually made of protein • Include: • Ribosomes: free and fixed • Cytoskeleton • Microfilaments • Intermediate fibers • microtubules • Centrosome • centrioles
Ribosomes • Small, dense granules • Protein • RNA • Site of protein synthesis. • Each ribosome has a small and a large subunit. • small subunit is about one-half the size of the large subunit.
The Cytoskeleton • Made of filamentous proteins • Helps give the cell its shape • Coordinates cellular movements. • Three categories: • microfilaments • intermediate filaments • microtubules
Non-membranous Organelles • Centrioles and the centrosome • Centrosome • Area close to the nucleus • Organization site for microtubules • Centrioles (exist as a pair) • In the centrosome • Perpendicular to each other • 9 sets of microtubule triplets • Important in cell division (spindle)
Microvilli, Cilia and Flagella • Appendages extending from the surface of some cells. • Microvilli: • short, cytoplasmic extensions • For absorption • Cilia: • usually occur in large numbers • work together to move materials or fluids along the surface of a cell. • Flagella: • longer than cilia, and usually occur as single appendages. • Move the cell
The Nucleus • Control center of cellular activities. • Usually, it is the largest structure within the cell • Appears as a single spherical or oval structure.
The Nucleus • Enclosed by a double membrane called the nuclear envelope. • The nuclear envelope: • controls the entry and exit of materials between the nucleus and the cytoplasm.