Cell Transport and Homeostasis PDF

Cell and transport mechanism, Homeostasis Dr.Rasha Eldeeb Associate Professor of Physiology www.gmu.ac.ae COLLEGE OF HEALTH SCIENCES  Cell and transport mechanism,...

Cell and transport mechanism, Homeostasis Dr.Rasha Eldeeb Associate Professor of Physiology www.gmu.ac.ae COLLEGE OF HEALTH SCIENCES  Cell and transport mechanism, Homeostasis Learning Objectives: Describe the general characteristics of cells Describe the structure of the plasma membrane (Fluid Mosaic Model) Describe the structure and function of the different cell organelles. Enlist the different types of transport mechanisms existing across the cell membrane and explain the mechanism of each Define Homeostasis and explain its mechanism  What Is Physiology? It is the branch of biology that studies the functions and vital processes of living organisms. It explains the physical and chemical factors responsible for life's origin, development, and progression.  Why Do We Study Physiology? To understand the physiologic principle that underlies normal function to cure impairments Distinguish between Process & Function Physiology Integrate both to complete the picture!  What You Should Know is… The Human body is organized from cells to organs The organ systems operate as integrated units The human body needs a constant internal environment to perform its function properly Physiology deals with the mechanisms that maintain a stable internal environment despite the changes in the external environment (Homeostasis) What is the structural and Functional Unit of life? The Cell The Cell  The Cell Membrane The cell membrane (plasma membrane) is a thin, elastic, and semipermeable barrier between the cell and its surroundings. Its Lipid bilayer consists of phospholipids and cholesterol, only 2 molecules thick, and continuous over the entire cell surface. Each molecule has : – Head: is the phosphate portion of phospholipids that are charged ( polarized) and soluble in water (hydrophilic). – Tail: is the lipid portion of phospholipids, that is uncharged (non-polarized) and relatively insoluble in water (hydrophobic) The hydrophilic ends are exposed to H2O present outside [extracellular fluid (ECF)] and inside [intracellular fluid (ICF)] the cell, while the hydrophobic ends meet in the water-poor interior of the membrane.  The Cell Membrane Proteins: 55% They do not form a continuous layer as lipids but, they exist as globular units that may be either : – Integral proteins: that extend through the whole thickness of the membrane. – Peripheral proteins: They are attached to the surface of the cell membrane either from inside or from outside i.e. they do not penetrate the whole thickness of the membrane. The functions of cell membrane proteins ▪ Structural proteins (lipoproteins and glycoproteins) ▪ Pumps (Na+/K+ pump) ▪ Receptors (for hormones, chemical transmitters,….) ▪ Carriers (glucose transporters) ▪ Enzymes (adenyl cyclase enzyme) ▪ Ion channels (Na +, K+, and Ca2+ channels) ▪ Tissue typing, and antibody processing (immunity) Carbohydrates: 3%: They are either combined with proteins (glycoproteins) or with lipids (glycolipids). When they cover the whole membrane, they are called glycocalyx.  The Cell Membrane The functions of the Cell Membrane Regulate the passage of substance into and out of cells Detect chemical messengers arriving at the cell surface Link adjacent cells together by membrane junctions Anchor a variety of proteins, including intracellular and extracellular protein filaments involved in the generation and transmission of force, to the cell surface  The Nucleus Usually, it is the largest organelles It is bounded by a nuclear membrane (envelope) with pores It controls the normal cell function Contains the DNA in chromosomes Each cell has a fixed number of chromosomes that carry genes The genes control cell characteristics What is inside the nucleus? It is the largest structure present inside the boundaries of the nucleus It is the dark staining zone in the center of the nucleus It is the place where intensive synthesis of ribosomal RNA takes place Its main components are ribonucleic acid (RNA), deoxyribonucleic acid (DNA) and proteins What is inside the nucleus? The genetic material (DNA) is found which is the hereditary material of the cell DNA is spread out and appears as Chromatin in non-dividing cells DNA is condensed and wrapped around proteins forming as Chromosomes in dividing cells  Cell Organelles Mitochondria Endoplasmic reticulum Ribosomes It contains its DNA; It is Two types: It contains two sub-units mDNA, RNA, and ribosomes. 1. Smooth- ribosome free It is the site of protein synthesis; therefore, it is It produces high- - detoxify drugs and pesticides. considered ad the Protein energy compound -absorb, synthesize, and transport fat factory of the cell ATP -break down glycogen to form glucose. It is either free-floating or It is the Powerhouse attached to the of the cell. 2. Rough - contains ribosomes: it manufactures proteins. Endoplasmic Reticulum.  Cell Organelles Golgi Apparatus Lysosomes Cytoskeleton It is a membrane-bound organelle It is the framework of the cell It is a series of flattened sacs containing a variety of enzymes. It contains small microfilaments and that modifies, packages, It contains digestive enzymes larger microtubules. stores, and transports They support the cell, giving it its materials out of the cell. It helps digest food particles inside or outside the cell. shape and helping with the Works with the ribosomes movement of its organelles. and Endoplasmic Reticulum. They are called suicide bags  The Cytoskeleton MICROTUBULES It is a hollow tube present in all cell types except RBCs It is responsible for the intracellular movement of cytoplasmic Organelles It forms Cilia and Flagella MICROFILAMENTS It is attached to the cytoplasmic side of the Plasma Membrane It strengthens the cell surface INTERMEDIATE FILAMENTS It is tough, insoluble protein fiber with strength It resists pulling forces on the cell  The Cellular Extensions Microvilli: Tubular extensions of the plasma membrane which contain actin filaments Stereocilia: Modified Microvilli seen on the cells in the Epididymis Cilia are shorter and more numerous in cells; they move in a single direction across the cell pair Flagella are longer and fewer (usually 1-3) on cells What is the difference between Cytosol and Cytoplasm? https://www.menti.com/alueetusxe5p  TRANSPORT MECHANISMS Solutes (e.g. ions, glucose, gases …… etc) can cross the cell membrane by: ▪ Diffusion: either simple or facilitated ▪ Active transport: either primary or secondary ▪ Endocytosis and exocytosis Solvents (e.g. H2O) can pass across the cell membrane by: ▪ Filtration ▪ Osmosis  Transport of Solutes Diffusion It is a passive process substance in a solution (or in a gas) that expands to occupy all the available volume. It is produced by the kinetic motion of the molecules, and it occurs in the direction of their concentration gradient. This occurs through either the lipid bilayer or the proteins embedded in it (transport proteins), depending on the: molecular size, lipid solubility, and charge of the substance. Generally, diffusion across cell membranes can be divided into 2 main types: Simple diffusion It occurs through the lipid bilayer. The following substances can diffuse through the lipid bilayer of cell membranes: Lipid-soluble substances (e.g. O2, N2, and alcohols), Water, Small uncharged water-soluble molecules (which cross the lipid bilayer along with water molecules) e.g. CO2 (which is also lipid soluble). Diffusion is directly related to Lipid solubility, Concentration gradient, Surface area, Temperature. Diffusion is inversely related to the thickness of the membrane and the Molecular weight. Facilitated diffusion This mechanism moves substances passively in the direction of their chemical (concentration) gradient, but it requires a type of transport protein The molecules of substances that diffuse by this mechanism (e.g. glucose and most amino acids) The facilitated diffusion is regulated by hormones  Different types of Carriers If the carrier transports only If the carrier transports two If the carrier transports two one molecule, it is called molecules (Cotransport) in the molecules (Cotransport) in uniport [e. g. glucose same direction it is called opposite directions, it is called transporters (GLUT1, symport e.g. Na-dependent antiport (Counter transport) GLUT2,….) glucose transport e.g. Cl-/HCO3- exchange. Transport of Solutes Active Transport Primary active transport It is the transport of substances against their electrical or concentration gradients (i.e. from a lower to a higher concentration. It requires: Specific carrier proteins and Energy (provided only by hydrolysis of ATP) Examples: Na+ - K+ pump (Na+/K+ ATPase),Ca2+ pump ,H+ pump (proton pump). Secondary active transport It is the cotransport of Na+ down its electrochemical gradient (created by the primary active transport) and another substance (e.g. glucose or amino acids) by a carrier protein (symport). Example: Sodium-dependent glucose transport (glucose absorption in the intestine and glucose reabsorption in the kidney).  Remember -Na+ - K+ pump In the cell membrane, there are carrier proteins that have: – Three receptor sites for Na+ from inside – Two receptor sites K+ from outside. – The inside part (near mitochondria) has ATPase activity. So, three Na+ ions will bind to the carrier from inside, while two K+ ions will bind from outside. This will activate the ATPase carrier leading to hydrolysis of ATP liberating the energy. This energy causes configuration change in the carriers pushing Na+ to outside and K+ to inside the cell [i.e. it has a coupling ratio of 3/2]. Function of Na+ - K+ pump: – Electrogenic pump; creates more positivity outside the cell (and more negativity inside). – Controls the cell volume.  Endocytosis and Exocytosis Both pinocytosis and phagocytosis are called Endocytosis. Pinocytosis (Cell Drinking): This is a transport mechanism by which large particles. The particle at first contacts the cell membrane, then, the latter is depressed, and, on each side, it rises and folds over the particle (which will thus become a vacuole inside the cytoplasm, the wall of which is made of a part of the cell membrane). Phagocytosis (Cell Eating) It is a process by which bacteria and dead tissue are engulfed by cells, and ingested. Exocytosis (Cell Vomiting): This is the reverse of endocytosis. The membrane of the granule or vesicle fuses with the cell membrane, then the area of fusion breaks down and its contents are expelled outside the cell while the cell membrane remains intact.  Filtration Filtration is the passive movement of water through a porous membrane due to a difference in hydrostatic pressure on the two sides of the membrane [e.g. formation of interstitial (tissue) fluid through the capillary membrane and glomerular filtrate in nephrons]. The amount of fluid filtered per time unit is directly proportional to the: ▪ Pressure gradient ▪ Surface area of the membrane ▪ Membrane permeability ▪ Dissolved molecules (solutes) with smaller diameters than the pores pass with the filtered fluid.  Osmosis Osmosis is the passive movement of water through a semipermeable membrane from an area containing pure water or a diluted solution of a solute (NaCl or glucose) to an area in which there is a higher concentration of solute (the membrane is impermeable to the solute and permeable to the solvent). The pressure required to apply the concentrated solution to prevent water movement from the diluted solution is called the osmotic pressure. The amount of osmotic pressure is directly proportional to the number of particles per unit volume of solution. So, ionizing solutes (e.g. NaCl) are more osmotically active (because each ion is active by itself) than non-ionizable solutes (e.g. glucose). The osmotic pressure is expressed in osmoles or milliosmoles which can be converted to mmHg, since one milliosmole = about 19.3 mmHg.  The osmolarity of a certain solution is the number of osmoles per liter of this solution, while its osmolality is the number of osmoles per kilogram of solvent. In the body, the osmotically-active substances are dissolved in water (= solvent), and are usually measured and are expressed in milliosmoles per liter of water (since water density is 1). All body fluids have the same osmolality =290 milliosmoles/liter. Solutions that have an osmolality equal to that of the plasma are called isotonic solutions, while those having a higher osmolality are hypertonic, and those having a lower osmolality are hypotonic. A 0.9% NaCl solution is isotonic with the plasma and is known as the isotonic (or physiological) saline solution. Remember Transport aims to maintain homeostasis https://www.menti.com/als6szng19sg  What is Homeostasis? Is to maintain the physical and chemical composition of the internal environment (Extracellular Fluid) constant despite the changes in the external environment It is a vital concept in human physiology Normal Physiological ranges in fasting blood : ▪ Arterial pH 7.35-7.45 ▪ O2 content 17.2-22.0 ml/100 ml ▪ Glucose75-110 mg/100 ml  Regulation of the Body Functions Regulation- the ability of an organism to maintain a stable internal condition in a constantly changing environment, done by: ▪ Chemical (hormonal) Regulation: a regulatory process performed by hormone or active chemical substance in blood or tissue. It responds slowly, acts extensively, and lasts for a long time ▪ Nervous Regulation process in which body functions are controlled by the nervous system. It responds fast; acts exactly or locally, lasts for a short time ▪ Auto-regulation: a tissue or an organ can directly respond to environmental changes that are independent of nervous and hormonal control. The Amplitude of the regulation and the Extension of the effects are smaller than the other two types.  When the internal environment is disturbed by a stimulus either a successful compensation occurs, and homeostasis is reestablished, or homeostasis Fail to compensate, and the pathology appears (illness, death)  Feedback Homeostasis is maintained through the regulatory process called “feedback” A feedback loop is a cycle of events in which a body condition (such as temperature) is continually monitored and adjusted to be within specific limits The basic components of the feedback loop are: o Receptor : detects changes (stimuli) in the body o Control center : determines a set point for a normal range, receives input from the receptor, and sends output when changes are needed o Effectors': causes the response determined by the control center  There are two types of feedback loops: Positive loops where the response enhances the condition as it increases the action of the control system; examples: blood clotting, contraction of the uterus during childbirth (parturition) Negative loops where the response counteracts or antagonizes the condition Most feedback loops in the body are negative feedback loops Negative Feedback Positive Feedback Learning Resources: 1. Marieb EN. Human Anatomy and Physiology, 9th Edition, Pearson International Edition; 2014. ISBN-13: 978-1-2920-2649-7 2. Guyton, Arthur C. Textbook of medical physiology / Arthur C. Guyton, John E. Hall.—11th ed. 3. Ganong's Review of Medical Physiology/Kim E. Barrett, Susan M. Barman, Scott Boitano and Heddwen L.Brooks,23rd ed. 4. Instructional Web site 5. Lectures PDF on Moodle 6. https://www.clinicalkey.com/#!/content/book/3-s2.0-B9780702031144000026  DISCLAMER The contents of this presentation, can be used only for the purpose of a Lecture, Scientific meeting or Research presentation at Gulf Medical University, Ajman. www.gmu.ac.ae