Cell Physiology PDF

General Physiology with Family Planning De La Salle Medical and Health Sciences Institute College of Dentistry David Pablo S. Fernandez Jr.,DMD  Cell Physiology To understand the functions of organs we need to understand the basic organization of cells  O...

General Physiology with Family Planning De La Salle Medical and Health Sciences Institute College of Dentistry David Pablo S. Fernandez Jr.,DMD  Cell Physiology To understand the functions of organs we need to understand the basic organization of cells  Organization of cells 2 major parts are the nucleus and cytoplasm The nucleus is separated from the cytoplasm by a nuclear membrane The cytoplasm is separated from the surrounding uids by a cell membrane or plasma membrane fl  Protoplasm The substances that make up the cytoplasm Protoplasm - the cytoplasm and the nucleus Five basic substances Water Protein Lipids Electrolytes Carbohydrates  Water Principal uid medium of the cell Present in most cells except fat cells in concentration of 70-85% Chemical reactions take place among dissolved chemicals or at the surface of suspended particles or membranes fl  Ions Include potassium, magnesium, phosphate, sulfate, bicarbonate Small quantities of sodium, calcium and chloride Provide inorganic chemicals for cellular reactions Ex: ions acting at the cell membrane are required for the transmission of electrochemical impulses in nerve and muscle bers fi  Lipids Several types of substances that are grouped together because of their common property of being soluble in fat solvents Phospholipids and cholesterol Constitute only about 2 percent of total cell mass Are mainly insoluble in water Used to form the plasma membrane and intracellular membranes Creates separation of cell compartments  Lipids Triglycerides (a type of lipid) “Neutral fat” In fat cells, triglycerides often account to 95% of cell mass Fat stored in these cells are energy giving nutrients which can be dissoluted to provide energy wherever in the body it is needed  Carbohydrates Have little structural function in the cell Averages 1 percent of total mass May increase to 3 percent in muscle cells and can reach 6 percent in the liver A small amount of carbohydrate is stored as glycogen which can be readily depolymerized rapidly to meet energy needs of cells Physical structure of cells Membranous structures of cells Cell membrane Cytoplasm Intracellular organelles  Membranous structures of cells Most organelles of the cells are covered by membranes made up by lipids and proteins Cell membrane Nuclear membrane Membrane of the Golgi apparatus Membrane of the endoplasmic reticulum Membranes of mitochondria and lysosomes  Membranous structures of cells Lipids of membranes impede the entrance of water to di erent cell compartments because water is not soluble in lipid ff  Cell membrane A thin, pliable elastic structure 7.5 to 10nm thick Approximate component Proteins - 55% Phospholipids - 25% Cholesterol - 13% Other lipids - 4% Carbohydrates - 3%  Lipid bilayer of the cell membrane Thin, double layer of lipids (each layer is one molecule thick) continuous over the entire cell surface Composed of phospholipid molecules One end of the phospholipid molecule is water soluble; hydrophilic One end of the phospholipid molecule is soluble only to fats; hydrophobic Phospholipid bilayer  Phospholipid bilayer The lipid layer in the middle is impermeable to water soluble substances such as ions, glucose, and urea Fat soluble substances such as oxygen, carbon dioxide and alcohol can pass with ease Cholesterol molecules are highly fat soluble and help determine the permeability or impermeability of the membrane  Membrane proteins Globular masses that oat in the lipid layer Most of them are glycoproteins There are two types of proteins in the cell membrane Integral proteins Peripheral proteins fl  Integral proteins Protrude all the way through the membrane May IP provide structural channels (pores) Through which water and ions can di use bet extracellular and intracellular uids Some IP act as carrier proteins Assist in the movement of substances that otherwise could not penetrate the lipid layer Sometimes transport substances in a direction opposite to their electrochemical gradient fl ff  Integral proteins Some act as enzymes Some act as receptors for water soluble substances (peptide hormones) that can not penetrate the lipid layer Interaction of the cell membrane receptors with ligands causes changes in the receptors Induce interaction between receptors and proteins in the cytoplasm Relay information from the extracellular part of the cell to the interior  Peripheral proteins Attached only to one surface of the membrane Often attached to integral proteins Function as enzymes or controllers of transport through cell membrane pores Membrane carbohydrates Occur variably in combination with glycoproteins or glycolipids Most integral proteins are glycoproteins About 1/10 of lipid molecule proteins are glycolipids “Glyco” component of these molecules protrude outside of the cell, dangling outward the cell surface Membrane carbohydrates Many other carbohydrate compounds exist as proteoglycans Which are carbohydrate substances attached to small core protein The outside surface of the cell often has a loose carbohydrate coat called the glycocalyx Cell membrane proteins The carbohydrate moieties attached to the outside surface of the cell has the functions Many have a negative charge; providing the cell an overall negative charge which in turn repel other negative objects The glycocalyx of some cells attaches to the glycocalyx of other cells; attaching cells to one another Act as receptor substances for binding hormones Immune reaction ff  Cytoplasm The cytoplasm is lled with both minute and large dispersed particles and organelles The clear uid portion of the cytoplasm is called cytosol - Dissolved proteins, glucose and electrolytes 5 important organelles fl fi  Organelles Endoplasmic reticulum Golgi apparatus Mitochondria Lysosomes Peroxisomes Endoplasmic reticulum A network of tubular and at vesicular structure that are interconnected to each other Walls are constructed of a lipid bilayer membranes Containing large amounts of proteins Total surface area can be as much as 20-30 times of the cell membrane area fl Endoplasmic reticulum The space inside the tubules and vesicles is lled with endoplasmic matrix A watery medium di erent from the uid in the cytosol outside the ER Vast surface are and attached enzyme systems provide machinery for metabolic processes of the cell fl fi ff  Granular endoplasmic reticulum Attached to the surface of granular ER are ribosomes Ribosomes are composed of a mixture of RNA and proteins They function to synthesize new proteins in the cell Some proteins extrude directly into the cytosol  Agranular endoplasmic reticulum No attached ribosomes Synthesis of lipid molecules Lipids and cholesterol  Agranular endoplasmic reticulum Lipids are rapidly incorporated onto the later of the endoplasmic reticulum itself SER is expanding  Agranular endoplasmic reticulum To prevent the SER from expanding beyond the needs of the cell Secretory vesicles pinch o from the SER Then migrate to the Golgi apparatus ff  Golgi apparatus Membranes similar to aER Composed of 4 or more stacked layers of thin, at enclosed vesicles lying near one side of the nucleus This apparatus is prominent in secretory cells where it is located on the side of the cell from which secretory substances are extruded fl  Golgi apparatus Functions in association with ER Small ER vesicles pinch o from the ER and fuse with the Golgi apparatus Substances are then processed in the GA to form lysosomes, secretory vesicles and other cytoplasmic components ff  Lysosomes Vesicular organelles that form by breaking o from the golgi apparatus Intracellular digestive system Allows the cell to digest Damaged cell structures Food particles Unwanted matter such as bacteria ff  Lysosomes Di erent in many cells 250 to 750nm in diameter Typical lipid bilayer membrane Filled with granules 5-8nm in diameter These granules are aggregates of as many as 40 hydrolazes ff  Lysosomes Hydrolytic enzymes are capable of splitting an organic compound into one or more parts Examples Protein is hydrolyzed into amino acids Glycogen is hydrolyzed to form glucose Lipids -> fatty acids and glycerol  Lysosomes The membrane of this organelle prevents the exit of hydrolytic enzymes and contact other substances in the cell Preventing digestive actions But there are conditions in the cell that break the membrane and release hydrolytic enzymes  Peroxisomes Similar to lysosomes Di erent in 2 ways They are believed to be a product of self replication rather than coming from the GA Contain oxidases rather than hydrolazes ff  Peroxisomes Several oxidases are capable of combining oxygen with hydrogen ions forming hydrogen peroxide Hydrogen peroxide is a highly oxidizing substance working closely with catalases Another oxidase present in peroxisomes Oxidizing substances that can be poisonous to the cell Ex: Alcohol oxidized by peroxisomes in liver cells  Mitochondria Powerhouses of the cell Present in all areas of the cell’s cytoplasm Varies from a several hundred to thousands Depending on the amount of energy requirement of the cell  Mitochondria The cell membrane has 2 parts The inner and outer membrane Infoldings of the inner membrane form compartments Compartments contain matrix that house enzymes necessary for extracting energy from nutrients  Mitochondria Liberation of energy is used to synthesize substance called ATP Mitochondria is self replicative One can replicate one, two or three more depending on the energy requirement Cell Cytoskeleton  Cytoskeleton Consists of proteins that support the cell Hold organelles in place Change the shape of the cell Proteins are known as microtubules, micro laments and intermediate laments fi fi  Microtubules Formed by protein subunits Assists the cell in cell division Support the cytoplasm Form components of organelles such as cili and agella fl  Micro laments Small brils that structurally support the cytoplasm Some micro laments are involved in cell movement Ex: The micro laments in muscle cell allow it to shorten or contract fi fi fi fi  Intermediate laments Smaller in diameter than microtubules but larger than micro laments Provide mechanical support to the cell fi fi  Centrosome Specialized zone of cytoplasm close to the nucleus This is where microtubule formation occurs Contains 2 centrioles oriented perpendicular to one another Each centriole is small, cylindrical organelle composed of nine triplets Each triplet contains three parallel microtubules joined together Centriole Centrosome Cilia, agella and microvilli Cilia - cylindrical structures that extend from the cell Flagella - longer than cilia, occur only one per cell Microvilli - specialized extensions of the cell membrane supported by micro laments Does not move the cell Involved in increasing surface area of cells for absorption fl fi  Locomotion of cells 1. Ameboid movement 2. Cilia and Ciliary movements  Ameboid movement Movement of the entire cell in relation to its surroundings Name is derived from the fact that amebae move in this manner Locomotion begins with protrusion of a pseudopodium from one end of the cell  Ameboid movement Pseudopodium projects far out, partially securing itself Then remainder of the cell is pulled toward the pseudopodium  Ameboid movement The most common cells to exhibit this type of movement are white blood cells and tissue macrophages Fibroblasts Embryonic cells  Ciliary movement Whip like movement of the cilia on the surfaces of cells Occurs in only 2 places of the human body Surface of respiratory airways Inside surfaces of the uterine tubes (fallopian tubes)  Ciliary movement In the nasal cavity, cilia causes a layer of mucus to move at a rate of 1 cm/min toward the pharynx Clearing the passageway of mucus and particles In the uterine tubes, cilia causes slow movement of uid from the ostium of the uterine tube toward the uterus This movement of uid causes transport of ovum to the uterus fl fl  Ciliary movement Sharp pointed or curved hair Projects 2-4 mm from the surface of the cell Covered by an outcropping of cell membrane  Ciliary movement Each cilium is an outgrowth of a structure beneath the cell membrane basal body Supported by 11 microtubules 9 double 2 single tubules at the center  Movement through the cell membrane Selectively permeable Allows other some molecules but not all Passive transport Does not require the cell to expend energy Di usion, osmosis, facilitated di usion Active membrane transport Requires the use of energy usually in the form of ATP Active transport, secondary active transport, endocytosis, exocystosis ff ff  Diffusion Movement of solute from an area of higher concentration of solute to an area of lower concentration of the same solute  Osmosis The di usion of water(solvent) across a selectively permeable membrane From a region of higher water concentration to a lower water concentration The ability to predict the direction of water movement across the cell membrane depends on knowing which solution on either side of the membrane has the higher water concentration ff  Osmosis Osmotic pressure The force required to prevent the movement of water across a selectively permeable membrane is a measure of the tendency of water to move by osmosis across a selectively permeable membrane  Osmosis The greater the concentration of a solution, the greater osmotic pressure, the greater tendency for the water to move into the solution Hypotonic - water concentration is higher, lower solute concentration than the cell Isotonic - concentration of water and solutes is the same Hypertonic - water concentration is lower, higher solute concentration than the cell Osmosis Carrier mediated transport Movement of large water soluble molecules or electrically charged molecules across the cell membrane Amino acids, glucose, and proteins can not enter the cell through di usion A molecule binds with a carrier molecule on one side of the membrane Transported molecule moves to the opposite side of the membrane ff Carrier mediated transport Carrier mediated transport Carrier mediated transport exhibit speci city Only speci c molecules are transported by the carriers Three types of CMT Facilitated di usion Active transport Secondary active transport fi ff fi  Facilitated diffusion A carrier mediated transport that moves substances from an area of higher concentration to an area of lower concentration Metabolic energy in the form of ATP is not necessary  Active transport A type of CMT that moves substances from an area of lower concentration to an area of higher concentration against a gradient Requires ATP, without it active transport stops Secondary active transport Involves the active transport of one substance across a membrane The di usion of that transported substance provides energy to transport a secondary substance ff Secondary active transport Cotransport - di using substance move in the same direction as the transported substance Countertransport - the di using substance move in the opposite direction as the transported substance ff ff Endocytosis & Exocytosis Large water soluble molecules, matter and even cells can be transported across cell membranes in membrane bound sacs called vesicles Endocytosis is the uptake of material Exocytosis is the process of elimination from the cell  Endocytosis The uptake of a material through a cell membrane by the formation of a vesicle Cell membrane invaginates to form a vesicle containing the material to be taken Movement into the cytoplasm  Receptor mediated endocytosis Endocytosis exhibits speci city The cell membrane contains speci c receptors to which speci c molecules bind Binding to receptors would trigger endocytosis fi fi fi Receptor mediated endocytosis  Phagocytosis Type of endocytosis that involves the uptake of solid particles  Pinocytosis Di erent that phagocytosis Formed vesicles are much smaller Contain liquid rather solid particles ff  Exocystosis Membrane bound sacs accumulate materials for release from the cell Secretory vesicles move and fuse with the cell membrane Materials in the vesicle are excreted from the cell Requires energy in the form of ATP (Endo and Exo) Exocytosis  Laboratory Accomplish worksheet # 2 and # 3 Deadline of submission: 5pm today Review for 30 minutes 1st quiz for laboratory (20 items)