General Physiology (Cell) PDF

 What is Physiology ? Overview of the history of Physiology  Dates back to ancient civilizations  Contributions from various cultures and scientists over the centuries. Ancient Civilizations (3000 BCE - 500 CE) 1. Egyptian Medicine: The Ebers Papyrus (circa 1550 BCE) contains the oldest known...

 What is Physiology ? Overview of the history of Physiology  Dates back to ancient civilizations  Contributions from various cultures and scientists over the centuries. Ancient Civilizations (3000 BCE - 500 CE) 1. Egyptian Medicine: The Ebers Papyrus (circa 1550 BCE) contains the oldest known physiological observations, including descriptions of the heart, blood vessels, and nervous system. 2. Greek Philosophers: Aristotle (384-322 BCE) and Galen (129-216 CE) made significant contributions to the understanding of human physiology, including the concept of homeostasis. Middle Ages to Renaissance (500-1600 CE) Examples of contributors and what they contribute: 1. Ibn Sina (Avicenna): A Persian physician who wrote "The Canon of Medicine" (1020 CE), which included detailed descriptions of human physiology and disease. 2. Andreas Vesalius: A Flemish anatomist who published "De Humani Corporis Fabrica" (1543 CE), a foundational text on human anatomy and physiology. 17th to 19th Centuries (1600-1900 CE) 1. William Harvey: An English physician who described the circulatory system and the concept of blood circulation (1628 CE). 2. Antoine Lavoisier: A French chemist who discovered oxygen and its role in respiration (1778 CE). 3. Claude Bernard: A French physiologist who introduced the concept of homeostasis and the regulation of the internal environment (1865 CE). 20th Century (1900-2000 CE) 1. Walter Cannon: An American physiologist who developed the concept of homeostasis and the "fight or flight" response (1915 CE). 2. Otto Loewi: A German-American physiologist who discovered neurotransmitters and their role in neural transmission (1921 CE). 3. Alan Hodgkin and Andrew Huxley: British physiologists who described the ionic mechanisms underlying nerve conduction (1952 CE). Modern Physiology (2000 CE - present) 1. Advances in molecular biology: The discovery of genes, proteins, and signaling pathways has greatly expanded our understanding of physiological processes. 2. Imaging techniques: Advances in imaging technologies, such as functional magnetic resonance imaging (fMRI), have enabled researchers to study physiological processes in real- time. 3. Systems physiology: The integration of physiological data from multiple systems has led to a more comprehensive understanding of how the body functions as a whole. Cell Physiology Definition: Cell is the smallest structural and functional unit capable of carrying out life processes. Principle of the Cell theory 1. The functional activities of each cell depend on the specific structural properties of the cell. 2. Cells are the living building blocks of all plant and animal organisms 3. All new cells and new life arise from pre-existing cells. 4. Organism’s structure and function ultimately depend on the individual and collective structural characteristics and functional capabilities of its cells. 5. Cells of all organisms are fundamentally similar in structure and function. Overview of Cell Structure - most cells have three major subdivisions namely the plasma membrane, nucleus and the cytoplasm. - the plasma membrane encloses the cell and separates the intracellular and extracellular fluid medium. - the nucleus contains the deoxyribonucleic acid (DNA), the cell’s genetic component - three types of RNA play a role in the protein synthesis coded by DNA; - mRNA = messenger RNA (carries the code for protein synthesis), - ribosomal RNA(catalytic process of protein synthesis and binding of transfer RNA for accurate translation - transfer RNA: translate genetic code and help in aa transport in the ribosomes - cytoplasm consist of cytosol, which is a complex gel-like mass laced with a cytoskeleton, and organelles which are highly organized membrane enclosed structures dispersed within the cytosol. These organelles are endoplasmic reticulum, golgi complex, lysosomes, peroxisomes, mitochondria and vaults. - Inclusions which vary in numbers are not membrane bound includes glycogen granules, fat droplets and are temporary cell contents. Plasma membrane: structure and composition - cells are bounded by plasma membrane forming a thin lipid bilayer about 7.5 -10nanometers in which proteins are interspersed, and to which carbohydrates are attached on the outer surface - Under the electron microscope plasma membrane appears as a tri laminar structure (2 dark lines separated by a light space). This is as a result of arrangement of the molecules in the plasma membrane. - lipids of the cell membrane make up about 90- 99% of the molecules in the cell membrane. 75% of this is phospholipids, 20% cholesterol and 5% glycolipids. - phospholipids are said to be amphiphilic because they orient themselves to form a bilayer with a hydrophilic (soluble in water) outer and inner surface to the ECF and cytoplasm respectively. - middle layer of the membrane is hydrophobic and therefore impermeable to water soluble substances like O2, CO2 and alcohol. - cholesterol molecules are tucked in between phospholipid contributing to the fluidity and stability of the membrane. -glycolipids are PL having short oligosaccharides with covalent bonds are found on the extracellular surface only. - membrane proteins (carry out major and specific functions of the cells) vary in type and distribution among cell. They make up 1-10% of cell membrane. Characteristics of Integral Protein - pass through the membrane - hydrophilic region in contact with the cytoplasm and ECF. - are mostly conjugated with oligosaccharides on the extracellular side anchored at times to the cytoskeleton Characteristics of Peripheral Proteins -don’t protrude into the phospholipid layer -adhere to the cytoplasmic surface of the membrane -are usually associated with integral pr- -mostly anchored by the cytoskeleton. Functions of membrane proteins 1. -serve as channels for passage of small ions across membrane 2. -serve as carriers for transport of specific substances in and out of cells 3. -serve as docking-marker acceptors for fusion with and subsequent exocytosis of secretory vesicles. 4. -serve as membrane bound enzymes that govern specific chemical reactions 5.serve as receptors for detecting and responding to chemical messengers that alter cell function. 6. serve as cell adhesion molecules that help hold cells together and structural link between the extracellular surroundings and intracellular cytoskeleton. 7. Serve as self-identity markers. Membrane carbohydrate which are short sugar chains (glycoprotein) projecting from the outer surface only serve as self-identity markers and important in recognition of “self” in cell to cell interactions such as tissues formation and tissue growth. Nucleus - largest organelle - membrane bound - spherical in shape, especially at interphase - mostly one per cell but could be more like in liver, skeletal and muscle cells - has diameter of 5µm - nuclear envelope has pore of about 30- 100 nm in diameter that allows for passage of molecules into and out of nucleus - contains DNA - the nucleoplasm is fine grained in appearance and usually contain one or more nucleoli (which is a mass of RNA) - Nucleoli are site of ribosome production and becomes enlarged when cell is actively synthesizing proteins. Functions: - Control centre of the cell - Replication of DNA - Synthesis of ribosome and RNA - Gene in DNA determine characteristics of cell”s proteins enzyme, - Gene control reproduction by undergoing meiosis and then mitosis Mitochondria: “power house” and houses the engine of the citric acid cycle (in the mitochondria matrix) and electron transport chain (on the cristae of the mitochondria inner membrane). Together, these two biochemical steps efficiently convert energy in food molecules to the usable energy stored in ATP molecules. The process is known as oxidative phosphorylation. It involves the use of molecular O2 to produce CO2 and H2O as by products. - Rod shaped -surrounded by double unit membrane -Inner membrane thrown into fold called CRISTAE -Mitochondria can self replicate whenever there is need -Mitochondria matrix contains mitochondria DNA which is genetically different from nuclear DNA. -Mutation in some mitochondria DNA responsible for some muscle, heart and eye diseases ageing etc Endoplasmic reticulum - is a single, complex membranous network that encloses a fluid-filled lumen - Primary function of ER is to serve as factory for protein and lipid synthesis to be used for: i. secretion of special products like enzymes and hormones ii. Production of new cellular components, particularly, cell membrane. - There are two types of ER namely; rough ER which are studded with ribosomes and smooth ER which lack ribosomes. - Rough ER synthesizes proteins, which are released into the ER lumen so that they are separated from the cytosol. Lipids produced within the membranous walls of ER also enter the lumen. - synthesized products from rough ER moves to smooth ER where they are packaged and discharged as transport vesicles - Transport vesicles are formed as a portion of the smooth ER “bud off”, containing a collection newly synthesized proteins and lipids wrapped in smooth ER. SER: function -(detoxification) i.e. converts alcohol, Phenobarbital and other drugs to less toxic water soluble forms that could be excreted by kidney -synthesizes lipids like triglycerides, cholesterol and steroid -in skeletal muscle, they act as storage reservoir for Ca2+ Ribosomes - don’t have membrane - Small granules of protein and RNA found in the cytocol and on rough ER outer surfaces. Function: Ribosomes “read” the coded genetic messages from the nucleus and assemble amino acids into proteins specified by the code (shortly protein synthesis). Golgi complex - It is closely related to the ER and has membrane similar to rough ER. - They resemble stack or packs and under electron microscope appear as parallel sacs or cisternae with swollen edges. - They are located close to the nucleus and appear prominently in secretory cells. Function i. act as “refining” plant for modifying into a finished product newly synthesized molecules delivered to it in crude form. ii. Sort, package and direct molecular traffic to appropriate intracellular and extracellular destinations. Note: - Before budding off of the GC, vesicles take up a specific product that has been processed within the Golgi sacs. The membrane that wraps the vesicle contains docking markers that ensure that vesicle docks and unload its cargo only at appropriate destinations within the cell. - GC of secretory cells packages proteins to be exported out of the cell in secretory vesicles that are released by exocytosis on appropriate stimulation. Lysosomes - They are called suicide bag because they contain enzymes that are capable of killing cell if they escape into the cell. - Membrane –enclosed sacs that contain powerful hydrolytic (digestive) enzymes - They are formed by breaking off from golgi apparatus before dispersing into the cytoplasm - They are variable in shape but usually round or oval and about 250-750nm diameter Function: serve as intracellular digestive system, destroys foreign materials like bacteria that has been internalized by cell, demolish worn out cells part to make way for new ones. Peroxisomes -Are small membrane –enclosed sacs containing oxidative enzymes. -Similar physically to lysosomes but differ in their enzyme content - They are produced by self- replication or budding off from SER Function - specialized for carrying out particular oxidative reactions including detoxification of various wastes and toxic foreign compounds like alcohol and drugs. Note: during detoxification reactions, peroxisomes generate potent hydrogen peroxide, which decompose into harmless water and O2 by means of the action of a potent antioxidant catalase found in peroxisomes. H2O2 – H2O + O2 Vaults - are recently discovered structures shaped like hollow octagonal barrels - They are of same shape and size as nuclear pores - Research speculate vaults are cellular trucks that docks at nuclear pores and pick cargo for transport from the nucleus - Some suggest vaults may transport messenger RNA from the nucleus to the cytoplasmic site for protein synthesis Cytosol - contains the enzymes involved in intermediary metabolism and the ribosomal machinery essential for synthesis of these enzymes as well as other cytosolic proteins - Many cells store unusual nutrients within the cytosol in the form of glycogen granules or fat droplets. - Also present in cytosols are secretory, transport and endocytoic vesicles. Cytoskeletons Extending throughout cytosols are cytoskeletons which serve as “bone and muscle” of the cell. There are 3 types of cytoskeletal elements; microtubules, microfilament and intermediate filaments. Each are made up of different protein subunit. Collectively cytoskeletal elements give the cell shape and support, enable it to organize and move its internal structures as needed, and in some cells allow movement between the cell and its environment. Cell part No per cell Structure Function microtubules many Long, slender hollow 1. Maintain asymmetric cell shapes and tubes composed of coordinate complex cell movement, 2. tubulin molecules. Specifically facilitating secretory vesicle 25nm diameter. transport, 3. Serving as main structural and functional component of cilia and flagella and 4. Forming mitotic spindle during cell division. Microfilament many Interwined helical 1. Play vital role in various cellular chains of actin contractile systems, including muscle molecules, MF contraction and amoeboid movement 2. composed of myosin Serve as a mechanical stiffener for molecules also present microvilli. in muscle cells. 4-7nm diameter. Intermediate Many Irregular, threadlike Play structural role in parts of cell subjected filament proteins 8-10nm to mechanical stress e.g. joints. diameter. Extension of cell surface a. microvilli i.e. brush border -are finger like extensions on cell surface -Functions primarily to increase cells surface area up to 40X -found mostly in cells specialized for absorption e.g. intestine, kidney Villi b. Cilia: hair-like process, about 7-10µm long, may be up to 50-200 cilia on the surface of a single cell. -Normally motile, and their 1o purpose is to move substance e.g. mucus in respiratory tract, ovum in uterine tubes. -Usually beat in same direction -may be non motile in some organs like retina where it has a sensory role (absorbing light) nose, inner ear (hearing and balance). c.Flagella: whip like and long, functional in the tail of the sperm cells. Found also in epithelia cells of the uterus, testis, kidney, pancreas e.t.c. Cell to Cell Adhesions -special cells are known to secrete complex extracellular matrix that acts as biological “glue” between cells of a tissue. -extracellular matrix consists of a watery, gel- like substance interspersed with 3 major types of protein fibers; collagen, elastin and fibronectin. -many cells are further joined by specialized cell junctions namely; desmosomes, tight junctions and gap junctions. Gap junctions: are communicating junctions between two adjacent but not touching cells. Cells are connected by small tunnels (connexon)permitting exchange of ions and small molecules. Such movement of ions play key role in the spread of electrical activity to synchronize heart and muscle contractions Tight junction: here cells are lured together sealing off passage between cells(occludins) and thereby permitting only regulated passage of materials through cells. They are common in the epithelial sheets separating compartment with differing chemical compositions. Desmosomes: they are adhering junctions holding cells together mechanically important in tissues subjected great stretching. Cellular communication Intercellular communication are achieved by 1. Gap junctions 2. Transient interactions between cells 3. Extracellular chemical messengers. - Communications by cells help ensure coordination of various cellular activities. This is achieved by dispatching extracellular chemical messengers, which then act on particular target cells to bring about desired response. - There are 4 types of extracellular chemical messengers, depending on source and the distance by which they get to their site of action. 1. paracrine (local chemical messengers) 2. Neurotransmitters (very short-range chemical messengers released by neurons. 3.Hormones(long–range chemical messengers secreted into the blood by endocrine glands 4. Neuro-hormone (long-range chemical messengers secreted into the blood by neuro-secretory neurons) Signal transduction: Definition: transfer of the signal carried by the extracellular messenger into the cell for execution. Processes of a typical transduction 1. Attachment of an extracellular chemical messenger that cannot gain entry to the cell e.g. protein hormone (1st messenger) to a membrane receptor/or to an intracellular receptor for a chemical messenger that can enter a cell e.g. steroid hormone 2. Several related intracellular pathway activities are initiated 3. Desired response augmented Responses can be augmented by either of 1. Opening or closing of specific channels 2. Activating an intracellular messenger i.e. second messenger - when intracellular second messengers are activated they then initiate a cascade of intracellular events that lead to change in the shape and function of particular proteins to cause appropriate cellular response. Example of second messengers 2+ Typical signal transduction of steroid molecule- an example of lipid soluble substance Mechanism of action testosterone: Testosterone diffuses through the lipid bilayer and combines with intracellular receptors the testosterone- receptor complex then binds to DNA  This promotes the formation of mRNAs that contain codes for the formation of new proteins which modify cell functions.