Introduction to Physiology and Cell Physiology PDF

Introduction to Physiology and cell physiology Dr. Hiwa Shafiq Namiq MSc, PhD, Clinical Neurophysiologist Lecturer/Physiology 28-Oct-2024 1 31 October 2024  Physiology is the science t...

Introduction to Physiology and cell physiology Dr. Hiwa Shafiq Namiq MSc, PhD, Clinical Neurophysiologist Lecturer/Physiology 28-Oct-2024 1 31 October 2024  Physiology is the science that seeks to explain the physical and chemical mechanisms that are responsible for the origin, development, and progression of life. The science of human physiology attempts to explain the specific characteristics and mechanisms of the human body that make it a living being Hunger, fear, cold… 2 31 October 2024  The Cell The basic living unit of the body is the cell. Each organ is an aggregate of many cells held together by intercellular structures. The cells of the body often differ markedly from one another but all have certain basic characteristics that are alike. Extracellular Fluid—The “Internal Environment” About 50% to 70% of the adult human body is fluid, mainly a water solution of ions and other substances (about 42 litters). Two third is inside the cells (intracellular fluid) and about one third is in the spaces outside the cells and is called extracellular fluid. All cells live in essentially the same environment—the extracellular fluid. 3 31 October 2024 For this reason, the extracellular fluid is also called the internal environment of the body, or the milieu intérieur, a term introduced more than 150 years ago by the great 19th- century French physiologist Claude Bernard (1813-1878) 4 31 October 2024  Diffusion of fluid and dissolved constituents through the capillary walls and through the interstitial spaces. 5 31 October 2024 6 31 October 2024 7 Constituents of ECF and ICF 31 October 2024  Body systems and Homeostasis 8 31 October 2024  Homeostasis Maintenance of nearly constant conditions in the internal environment (the term coined by Walter Cannon in 1929) Essentially all organs and tissues of the body perform functions that help maintain these constant conditions. For instance: -lungs provide oxygen -kidneys maintain constant ion concentrations -gastrointestinal system provides nutrients while eliminating waste from the body. 9 31 October 2024  Origin of nutrients in the extracellular fluid Respiratory system. Gastrointestinal tract. Liver and other organs (perform primarily metabolic functions). Musculoskeletal System and its contribution to homeostasis Removal of Metabolic End Products Removal of carbon dioxide by the lungs. Removal of waste products as urea, creatinine, uric acid by the kidneys. Liver : detoxification or removal of many drugs and chemicals that are ingested. 10 31 October 2024  REGULATION OF BODY FUNCTIONS Nervous System Hormone Systems. Protections of the body Immune system Integumentary system (skin, hair and nail) Reproduction 11 31 October 2024  Homeostatic Control systems of the body Regulation of arterial blood pressure Regulation of Oxygen and Carbon Dioxide concentrations in the extracellular Fluid. Regulation of concentration of nutrient molecules, waste products, water, salt, and other electrolytes. Regulation of temperature. Regulation of pH. 12 31 October 2024  Negative feedback control of arterial pressure by the arterial baroreceptors. 13 31 October 2024  Characteristics of Homeostatic Control Systems 1- Negative Feedback mechanism. If some factors become excessive or deficient a control system initiates a series of changes that return the factor toward a certain mean value, thus maintaining homeostasis. Most control systems of the body act by negative feed back. Negative feed back regulation of body temperature 14 31 October 2024 2- Positive Feedback (vicious cycle) Positive feedback is a self-amplifying cycle in which a physiological change leads to even greater change in the same direction (producing more of the same), rather than producing the corrective effects of negative feedback. E.g. positive feedback in fever. Frequently, positive feedback is a harmful or even life-threatening process. E.g when the body temp. raises to 42 C. 15 31 October 2024 16 Positive FB in fever 31 October 2024  Cell Physiology 17 The two major parts of a typical cell are the nucleus and the cytoplasm. The nucleus is separated from the cytoplasm by a nuclear membrane, and the cytoplasm is separated from the surrounding fluids by a cell membrane, also called the plasma membrane. The different substances that make up the cell are collectively called protoplasm. Protoplasm is composed mainly of five basic substances: water, electrolytes, proteins, lipids, and carbohydrates. 18  Internal organelles in the cytoplasm and nucleus. 19 Water About 70-85% of the cell mass. Contains dissolved chemicals and suspended solid particles Ion Most imp. : potassium, magnesium, phosphate, sulfate, bicarbonate Small quantities of sodium, chloride, and calcium Provide inorganic chemicals for cellular reactions. Necessary for operation of some of the cellular control mechanisms. Protein Most abundant substances after water (about 10-20%) Structural proteins and functional proteins. Structural PTNs : ▪ Cytoskeletons of cellular organelles as cilia, nerve axon and mitotic spindles of mitosing cells. ▪ Out side the cell, they provide collagen and elastin fibers of connective tissue, vessel walls, tendons and ligaments. Functional PTNs ✓ Catalyze intracellular chemical reactions ✓ Mobile in the cell fluid. 20 Lipids Have a common property of being soluble in fat solvents. Phospholipids and cholesterol (two main lipids (2%) of cell mass). Provide the cell membrane and other intracellular barrier that separate different cell compartment. Triglycerides, a form of lipid, accounts for as much as 95% of fat cells. They represent the body's main storehouse of energy-giving nutrients. They have little structural function, but playing a major Carbohydrates role in cell nutrition. Carbohydrate in the form of dissolved glucose is always present in the surrounding extracellular fluid so that it is readily available to the cell. Glycogen (stored carbohydrates) is an insoluble polymer of glucose that can be depolymerized and used rapidly to supply the cells’ energy needs. 21  Cell membrane Thin, elastic structure enveloping the cell. Double-layered film of lipids (lipid bilayer) which is composed of three main types of lipids: phospholipids, sphingolipids, and cholesterol. Phospholipids are the most abundant of the cell membrane lipids One end of each phospholipid molecule is soluble in water (hydrophilic). The other end is soluble only in fats (hydrophobic). The phosphate end forms both cell surfaces intracellularly and extracellularly. The middle layer is formed by the fatty acid end. Interspersed in this lipid film are large globular protein molecules. 22 The lipid layer in the middle of the membrane is impermeable to the usual water- soluble substances, such as ions, glucose, and urea. Conversely, fat-soluble substances, such as oxygen, carbon dioxide, and alcohol, can penetrate this portion of the 23 membrane with ease.  Cell Membrane Proteins Two types of proteins occur: integral proteins that protrude all the way through the membrane and peripheral proteins that are attached only to one surface of the membrane and do not penetrate all the way through 24  Integral proteins: Provide structural channels (pores) through which water molecules and water-soluble substances, especially ions, can pass. Act as carrier proteins for transporting substances (as in active transport). Enzymatic functions Receptor function for water-soluble chemicals, such as peptide hormones, that do not easily penetrate the cell membrane Cell to cell adhesion Antigens which help the organism to recognize self from non-self 25  Peripheral protein These molecules are often attached to the integral proteins. They function almost entirely as enzymes or as controllers of transport of substances through the cell membrane “pores.” Membrane Carbohydrates Carbohydrates are found as glycoproteins or glycolipids. The “glyco” portion almost invariably protrude to the outside of the cell 26  Functions of carbohydrates Many of them have a negative electrical charge that repel other negative objects. The Glycocalyx of some cells attaches to the glycocalyx of other cells, thus attaching cells to one another. Many of the carbohydrates act as receptor substances for binding hormones, such as insulin; when bound, this combination activates attached internal proteins that, in turn, activate a cascade of intracellular enzymes Some carbohydrate moieties enter into immune reactions. 27  Cytoplasmic organelles: 28  Endoplasmic Reticulum It consists of a network of flat vesicular structures attached to one another. Like the cell membrane, it is bounded by a lipid bilayer membrane. Attached to the outer surfaces of many parts of the endoplasmic reticulum are large numbers of minute granular particles called Ribosomes. 29 30  Functions of ER include: Rough ER: Synthesis of new protein molecules in the cell by the ribosomes (a mixture of RNA and proteins). Smooth ER: Synthesis of lipid substances (mainly phospholipids and cholesterol). Provides the enzymes that control glycogen breakdown (glycogenolysis) when glycogen is to be used for energy. Provides a vast number of enzymes that are capable of detoxifying substances, such as drugs, that might damage the cell. 31  Golgi apparatus: Four or more stacked layers of flat, enclosed vesicles lying near one side of the nucleus. Prominent in secretory cells, from which the secretory substances are extruded. Functions: Processing of vesicles transported from the endoplasmic reticulum to form lysosomes and secretory vesicles. Synthesizing certain carbohydrates that cannot be formed in the endoplasmic reticulum like hyaluronic acid and chondroitin sulfate. 32 33  Mitochondria Powerhouses of the cell. Without them, cells would be unable to extract enough energy from the nutrients. Total number per cell varies. Two lipid bilayer–protein membranes: an outer membrane and an inner membrane Filled with matrix that contains large quantities of dissolved enzymes necessary for extracting energy from nutrients, thereby forming carbon dioxide and water and at the same time releasing energy Mitochondria contain DNA and therefore they are self- replicative. 34 35 The Mitochondria Extract Energy From Nutrients The principal substances from which cells extract energy are foodstuffs that react chemically with oxygen— carbohydrates, fats, and proteins (oxidative reaction). All oxidative reactions occur inside the mitochondria, and the energy that is released is used to form the high-energy compound ATP 36 37 Uses of adenosine triphosphate  Nucleus It is surrounded by the nuclear membrane (nuclear envelope) which consists of two separate bilayer membranes, one inside the other. The outer membrane and the space between the two nuclear membranes is continuous with the endoplasmic reticulum. The nucleus is the control center of the cell and distinguishes a well developed cell from all lower forms of life It contains large quantities of DNA, which are the genes. The genes determine the characteristics of the cell’s proteins, including the structural proteins, as well as the intracellular enzymes that control cytoplasmic and nuclear activities 38 39  Functional Systems of the Cell Ingestion by the Cell Endocytosis (Pinocytosis and Phagocytosis) 40 Pinocytosis ✓ Ingestion of minute particles in the form of vesicles that contain extracellular fluid and particulate constituents inside the cell cytoplasm. ✓ Only means by which most large macromolecules (protein molecules) can enter cells. ✓ It occurs in most cells and in some cell (macrophage) it is so rapid that about 3% of the cell membrane is engulfed in form of vesicles each minute. ✓ There is inward invagination of the membrane. 41 42  Phagocytosis Ingestion of large particles, such as bacteria, whole cells, or portions of degenerating tissue. Only certain cells have the capability of phagocytosis (white blood cells). Is initiated when a particle (bacterium, dead cell, tissue debris) binds with receptors on the surface of the phagocyte. In the case of bacteria, each bacterium usually is already attached to a specific antibody, and it is the antibody that attaches to the phagocyte receptors, dragging the bacterium along with it, a process called opzonization. Outward evagination of cell membrane to surround the entire particle. 43