Cell Physiology PDF

PHYSIOLOGY NOTES Topic 2: CELL PHYSIOLOGY  The Cell is the basic functional unit of a living organism Cell theory: It stated in 4 postulates which include;  All free living organisms are made up of cells and their products  All cells are bas...

PHYSIOLOGY NOTES Topic 2: CELL PHYSIOLOGY  The Cell is the basic functional unit of a living organism Cell theory: It stated in 4 postulates which include;  All free living organisms are made up of cells and their products  All cells are basically similar in their chemical composition and differ with regards to their need to specialize  New cells arise from existing cells by cell division  The activity of the organisms is the sum of activities and interactions of its entire cell The body is made up of fluids called protoplasm. The cell membrane divides the body mass into cells. The compartment of protoplasm enclosed by the nuclear membrane is called the nucleoplasm while that between nucleoplasm and plasma membrane is the cytoplasm. Assignment: Draw a well labelled basic cell and indicate the functions of the labeled parts Protoplasm composition 1. Water: Makes up 75 -85% and has the following functions;  It’s solvent for all biological substances (Universal solvent). Dissolves electrolytes, keeps suspended particles and their active forms  It has a high heat capacity therefore help to maintain a stable temperature  Acts as substrate in some biochemical reactions e.g. hydrolysis reactions   Has a high Latent heat of vaporization therefore its loss provides cooling mechanism of the body 2. Electrolytes: Both cations and anions are found in protoplasm. Cations include; Na, K+, Ca2+ and Mg2+ while anions include phosphates, sulphates, bicarbonates and chloride ions. The importance of these electrolytes include;  Contributes to osmotic potential of the body fluids therefore important in water retention  Substrates in metabolic body reaction ( reactants)  Participates in enzyme catalysed reaction as cofactors or co- enzymes  Acts as buffers  Some transmit electrical impulses in the nerve and muscles 3. Protein: Make up 20% and they are different type of proteins which include;  Globular proteins e.g. enzymes. These are proteins that have undergone secondary and tertially folding  Structural proteins: Composed of long filamentus polymers which make up the cytoskeletion of cilia and mitotic spindles. They provide muscles cells with contractile mechanism and form components of connective tissues like collagen and elastic fibres  Nucleoplasm e.g. histones form complexes with genetic materials like RNA and DNA. They are involved in genetic material transmission and also takes part in protein synthesis 4. Lipids: Make up 2% and include; phospholids, cholesterol and Triglycerides and neutral fats.  Helps in separating different protoplasmic compartments e.g. phospholipids.   Cholesterol is a raw material for steroid hormone synthesis  Neutral fats are depots of high energy compounds 5. Carbohydrates: They are sources of energy.  Glycogen is a storage form of carbohydrates.Its stored in liver and skeletal muscles  Nucleic acids e.g. DNA found in nucleus and its passes genetic information from one generation to another Cell membrane Physiology Cell membrane is a lipid bilayer with the hydrophobic groups focusing in the centre and hydrophilic groups projecting into the intra and extra cellular spaces. With this arrangement the membrane has two properties. i.e.  Flexibility and impermeability to water. Water passes via water soluble membrane protein pores  It’s made of proteins, lipids and Carbohydrates Functions of membrane proteins  Provide support to the lipid bilayer  Functions as carriers for transporting substances into or out of the cell  Others act as membrane receptors for hormones  Some act as pumps for specific ions, using ATP to transport ions against their concentration gradients  Some acts as enzymes in catalyzing membrane reaction   Acts as antigen in certain cell like on RBC. Trigger immune response  Some act as Channels pores for different ions to exit or enter the cell Functions of Carbohydrates  Act as receptors  Stimulates immunological properties of the cell  Interlace with glycocalyx of adjacent cells to bring them together in close attachment which is a basis for tissue function  Confer total negativity to cell surface which serves to repel other negative particles like pathogen Functions of Lipids  Regulate amount of water flowing in and out of the cells Functions of cell membrane  Separates intracellular fluids from extracellular fluids  Demarcates protoplasm in cells and provide shape and mechanical support to the protoplasm  Recognises hormones and co-ordinates their effect in the cell  Transports the required substances in and out of the cells  Selectively permeable to different ions which is a basis for generation and transmission of nerve impulse in excitable tissues (Nerve and muscle cells)  Transportation of material across cell membrane There are two mechanism involved in transportation i.e. passive and active mechanisms a). Passive mechanisms: Don’t require the use of metabolic energy and they include; simple diffusion, facilitated diffusion, Osmosis, filtration and Solvent drag 1. Simple diffusion: is movement of substances from a region of high concentration to a region of low concentration. It doesn’t involve the use of carrier systems. It occurs in two pathway that is through the lipid bilayer and watery channels. Lipid bilayer allows lipid soluble substances to dissolve in it. They include oxygen, carbondioxide, alcohol, steroid and fatty acids. Watery channels are areas through which water soluble substances can easily pass or diffuse. The net rate of diffusion will depend on the following.  Liposolubility  Membrane thickness  Temperature  Molecular weight 2. Facilitated diffusion: It requires carrier systems which are membrane bound. It’s used to transport hydrophilic substances like glucose, amino acid and urea against a concentration gradient and doesn’t require energy. They bind to lipophilic protein carrier and this carrier can easily penetrate the cell membrane carrying with them the hydrophilic substances. It may be coupled or exchange facilitated diffusion.  Coupled facilitated diffusion: two substances are moved by the same lipophilic carrier e.g. Na+ with D- glucose or L- aminoacids.   Exchange facilitated diffusion: E.g. in RBC Introduction of galactose molecules is accompanied by extrusion of one glucose molecule. 3. Osmosis  It’s net diffusion of solvents across semi permeable membrane separating two solutions of un equal concentration but of equal volume. The membrane must be permeable to water and not solutes.  Its diffusion of water down its concentration gradient i.e. from dilute to more concentrated solution until equilibrium is reached.  The pressure required to prevent net flow of water in more concentrated side is called Osmotic pressure of the solution. Osmotic pressure depends on number of osmotically active particles. 4. Filtration  Process by which fluids are forced through a membrane or barrier by hydrostatic pressure difference across the membrane  The amount filtered depends on Pressure difference across the membrane, the Surface area through which filtration occurs and Permeability of the membrane (size of pore through which fluids pass) 5. Solvent drag Has little physiological application. It involves solvents flowing in one direction and dragging along with them some solute molecules. b). Active mechanisms: Substances can’t diffuse against their concentration or electrical gradient with out a force. Transportation of substances uphill (from low conc. to high conc.) is important and its through these active processes. Characteristics of active transport  It requires use of metabolic energy /ATP.  Substances are moved uphill (against their conc. gradient).  There are two mechanisms; a). Active transport Utilise energy to overcome the movement of substances against their natural direction flow. Also carrier proteins may be involved. Therefore it exhibits the following characteristics; Saturability, specificity, competitive inhibition, sensitivity to temperature changes. The substances transported include; Sugar, aminoacid, Na, K, Fe. There are two types of active transport.  Primary active transport. Energy used is from break down of ATP or other high energy compound like GTP. Substrate include Na+ Ca+, H+ and Cl-. It involves mechanisms like;  Na – K+ pump: It’s present in all body cells where it pumps Na+ out side and K+ inside the cell through the membrane which creates the conc. difference of these ions across the cell membrane. The pump is responsible for the resting membrane potential (RMP) of the  body cells and RMP is the basis of transmission of impulses in nerve and muscle. The protein carrier complex has 3 major properties which include; 1. It has a receptor site for binding Na+ located at protrusion to cell interior. 2. Has a receptor site for binding K+ at the extra cytoplasmic surface. 3. ATPase activity adjacent to Na+ binding site which splits the energy. -Ca2+ pump: there are two pumps. One pumps to outside of the cell while the second one pumps in intracellular organelles like the sarcoplasmic reticulum. The carrier has binding sites for Ca2+ as well as ATPase activity.  Secondary active transport When sodium is extracted out of the cell by primary active transport, high concentration gradient developes in extra cellular fluids.The energy reservoir is capable of pulling other substances with Na+ to either side depending on the charge on the particles. Negatively charged would move to the outside to neutralize the electrical imbalance and positively charged to the interior. Pulling action is also mediated by carrier proteins which attach both Na+ and substances to be transported. When substances are transported in same direction is called secondary Co - transport and if it’s in opposite direction then its counter transport. Na+ bind to exterior and second substance binds to the interior of the carrier protein e.g. Na and Ca2+. Cytosis/ Bulk transport It’s characterized by formation of enclosed vesicles which are constricted off from plasma membrane or membranous organelles. Breakage of membrane and reconstitution requires ATP expenditure but doesn’t require membrane specific receptors. It includes endocytosis and exocytosis. -Endocytosis: It’s where Particles are transported into the cell. It’s divided in to two a). Pinocytosis (cell drinking): Its uptake of micro volumes of liquid from Extracellular fluids. Its visible under an electron microscope. Pinocytic vesicles are formed through invagination and proliferation of membrane to enclose and engulf the material. b). Phagocytosis (Cell eating): Visible in light microscope and Large particles like bacteria can be phagocytosed. ATP and Ca2+ are required.An e.g. phagocytes are macrophages. Exocytosis: It’s the transport of substances to outside of the cell.