1- Homeostasis & Cell physiology.pdf

Introduction To Cell Physiology and Homeostasis Lecture-1 Instructor: Dr. Abbas Al-Momany, Ph.D (Human Physiology) Anatomy and Physiology Defined Two branches of science that deal with body’s parts and function ❑ Anatomy a field in the bi...

Introduction To Cell Physiology and Homeostasis Lecture-1 Instructor: Dr. Abbas Al-Momany, Ph.D (Human Physiology) Anatomy and Physiology Defined Two branches of science that deal with body’s parts and function ❑ Anatomy a field in the biological sciences concerned with the identification and description of the body structures of living things. First studies by dissection (cutting apart) Imaging techniques ❑ Physiology The science that is concerned with the function of the living organism and its parts, and of the physical and chemical processes involved. The science of body functions   SYSTEM LEVEL  A system consists of related organs with a Levels of structural common function organization  Organ-system level  Digestive system breaks down and absorbs food  It includes organs such as the mouth, small and large intestines, liver, gallbladder, and pancreas  Eleven systems of the human body  HOMEOSTASIS AND FEEDBACK CONTROL Homeostasis is constancy of the internal environment. Example (Arterial pH 7.35–7.45, Glucose 75–110 mg/100 ml) The main purpose of our physiological mechanisms is to maintain homeostasis. Deviation from homeostasis indicates disease. Homeostasis is accomplished most often by negative feedback loops.  Negative Feedback Loops Pathway 1. Sensors in the body to detect change and send information to the: 2. Integrating center, which assesses change around a set point. The integrating center (CNS, endocrine glands) then sends instructions to an: 3. Effector, (muscle or gland) which can make the appropriate adjustments (increase or decrease) to counter the change from the set-point  Mechanism of Negative Feedback Loops A. Moves in the opposite direction from the change B. Makes the change from the set-point smaller C. Reverses the change in the set-point D. This is a continuous process, always making fine adjustments to stay in homeostasis  Negative Feedback Loops Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 1 X Sensor Integrating center X Sensor Integrating center – – X Effector X Effector 2 2 Sensor activated Effector activated X Time Normal Normal 1 2 1 2 range range X Time Sensor activated Effector activated  3. Body temperature: example of negative feedback loops A. Sensors in the brain detect deviation from 37ºC. Another part of the brain assesses this as actionable, and effectors (sweat glands) are stimulated to cool the body. B. Once the body is cool, sensors alert the integrating center, and sweat glands are inhibited. C. The end result regulates the entire process. Production of the end product shuts off or down-regulates the process. This is why it is called a negative feedback loop. 3. Body temperature: example of negative feedback loops 3. Blood Glucose: example of negative feedback loops  Negative Feedback: Regulation of Blood Pressure External or internal stimulus increase BP ❑ Baroreceptors (pressure sensitive receptors) Detect higher BP Send nerve impulses to brain for interpretation Response sent via nerve impulse sent to heart and blood vessels BP drops and homeostasis is restored Drop in BP negates the original stimulus  Positive Feedback  The end product in a process stimulates the process.  The action amplifies the changes that stimulated the effectors  Positive feedback could not work alone, but it does contribute to many negative feedback loops. A. For example, if a blood vessel is damaged, a process is begun to form a clot. Once the damage is fixed, clotting ends (negative feedback). However, the process of forming the clot involves positive feedback. B. The strength of uterine contractions during childbirth is also regulated by a positive feedback loop.  Positive Feedback: Blood Loss Normal conditions, heart pumps blood under pressure to body cells (oxygen and nutrients) Severe blood loss ❑ Blood pressure drops ❑ Cells receive less oxygen and function less efficiently ❑ If blood loss continues Heart cells become weaker Heart doesn’t pump BP continues to fall  Positive Feedback BLOOD CLOTTING CHILD BIRTH  Negative Vs Positive Feedback systems Negative Feedback systems ❑ Reverses a change in a controlled condition Regulation of blood pressure (force exerted by blood as it presses again the walls of the blood vessels) Positive Feedback systems ❑ Strengthen or reinforce a change in one of the body’s controlled conditions Normal child birth Fast Na+ channels  Homeostatic Imbalances Normal equilibrium of body processes are disrupted ❑ Moderate imbalance Disorder or abnormality of structure and function Disease with recognizable signs and symptoms ❑ Severe imbalance Death  Homeostasis and Body Fluids Maintaining the volume and composition of body fluids are important ❑ Body fluids are defined as dilute, watery solutions containing dissolved chemicals inside or outside of the cell ❑ Intracellular Fluid (ICF) Fluid within cells ❑ Extracellular Fluid (ECF) Fluid outside cells Interstitial fluid is ECF between cells and tissues  Body Fluids  67% of our water is within cells in the intracellular compartment.  33% is in the extracellular compartment. Of this: A. 20% is in blood plasma. B. 80% makes up what is called tissue fluid, or interstitial fluid; connects the intracellular compartment with the blood plasma.  Interstitial Fluid and Body Function Body’s internal environment Cellular function depends on the regulation of composition of interstitial fluid Movement back and forth across capillary walls provide nutrients (glucose, oxygen, ions) to tissue cells and removes waste (carbon dioxide)  Concentration of ions across cell membrane Cations = + ions Anions = - ions  A Generalized Cell 1. Plasma membrane  forms the cell’s outer boundary  separates the cell’s internal environment from the outside environment  is a selective barrier  plays a role in cellular communication  Plasma Membrane Structure Flexible yet sturdy barrier The fluid mosaic model - the arrangement of molecules within the membrane resembles a sea of lipids containing many types of proteins The lipids act as a barrier to certain substances The proteins act as “gatekeepers” to certain molecules and ions Plasma Membrane Structure….Cont’d  Structure of a Membrane  Consists of a lipid bilayer - made up of phospholipids, cholesterol and glycolipids  Integral proteins - extend into or through the lipid bilayer  Transmembrane proteins – most integral proteins, span the entire lipid bilayer  Peripheral proteins - attached to the inner or outer surface of the membrane, do not extend through it  Structure of a Membrane Glycoproteins - membrane proteins with a carbohydrate group attached that protrudes into the extracellular fluid Glycocalyx – aka (pericellular matrix) the “sugary coating” surrounding the membrane made up of the carbohydrate portions of the glycolipids and glycoproteins  Functions of Membrane Proteins Some integral proteins are ion channels Transporters - selectively move substances through the membrane Receptors - for cellular recognition; a ligand is a molecule that binds with a receptor Enzymes - catalyze chemical reactions Others act as cell-identity markers Functions of Membrane Proteins  Membrane Permeability The cell is either permeable or impermeable to certain substances The lipid bilayer is permeable to oxygen, carbon dioxide, water and steroids, but impermeable to glucose Transmembrane proteins act as channels and transporters to assist the entrance of certain substances, for example, glucose and ions Introduction to Cell Physiology and Transport Lecture-2 Instructor: Dr. Abbas Al-Momany, Ph.D (Human Physiology) Active Transport 1- Primary Active Transport Molecules are “pumped” against a concentration gradient at the expense of energy (ATP)- Direct Energy 2– Secondary Transport is driven by the energy stored in the concentration gradient of another molecule (Na+) – indirect use of energy Saturation Similar to facilitated diffusion Rate limited by Vmax of the transporters Energetics Up to 90% of cell energy expended for active transport Diffusion Simple diffusion occurs when the solute (a substance dissolved in a liquid solvent) moves from a higher concentration to a lower concentration (down their concentration gradient). ❑ Steepness of :  concentration gradient  Temperature  Mass of diffusing substance  Surface area  Diffusion distance  Simple Diffusion, Channel-mediated Facilitated Diffusion, and Carrier mediated Facilitated Diffusion  Ions and polar molecules cross membranes by facilitated diffusion.  Facilitated diffusion is also passive transport. Membrane proteins (carriers and channels) assist the movement of the molecule across the membrane.  Channel-mediated Facilitated Diffusion of Potassium ions through a Gated K + Channel Carrier-mediated Facilitated Diffusion of Glucose across a Plasma Membrane Extracellular Plasma membrane Cytosol fluid Glucose Glucose transporter Glucos Figure 7.16 Passive transport Active transport Diffusion Facilitated diffusion ATP Bulk Transport Macromolecules are too large to move with membrane proteins and must be transported across membranes in vesicles. The transport of macromolecules out of a cell in a vesicle is called exocytosis. The transport of macromolecules into a cell in a vesicle is called endocytosis. Bulk Transport (cont.) Three types of endocytosis: 1.If the material taken up by endocytosis is a large particle it is called phagocytosis. This type is important in amoeba and in white blood cells in humans. 2.If the material taken up by endocytosis is a liquid or small particle it is called pinocytosis. 3.Receptor-mediated endocytosis is a selective, highly efficient form of endocytosis, that requires a protein on the plasma membrane. Transcytosis - a combination of endocytosis and exocytosis Bulk Transport (cont.) Bulk Transport (cont.) Bulk Transport (cont.) Transcytosis: is a type of transcellular transport in which various macromolecules are transported across the interior of a cell. Macromolecules are captured in vesicles on one side of the cell, drawn across the cell, and ejected on the other side.  Simple Diffusion, Channel-mediated, Facilitated Diffusion, and Carrier mediated Facilitated Diffusion Osmosis Net movement of water through a selectively permeable membrane from an area of high concentration of water (lower concentration of solutes) to one of lower concentration of water Water can pass through plasma membrane in 2 ways: 1 -through lipid bilayer by simple diffusion 2 -through aquaporins, integral membrane proteins  Relation between osmolarity and molarity Molarity is defined as the moles of a solute per liters of a solution Molality is defined as the total moles of a solute contained in a kilogram of a solvent. Osmolality is a measure of the number of dissolved particles in a fluid 300 mM glucose = 300 mOsm 150 mM NaCl = 300 mOsm  The Effect of Osmosis on Cells Osmosis can affect the size and shape of cells, depending on differences in water concentration across the membrane. Three types of solutions: 1. Isotonic solution: Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane. 2. Hypertonic solution: Solute concentration is greater than that inside the cell; cell loses water 3. Hypotonic solution: Solute concentration is less than that inside the cell; cell gains water  Tonicity and its effect on RBCS Normal RBC RBC undergoes RBC undergoes Shape hemolysis Crenation