Introduction to Human Physiology PDF

PAGE 1 https://www.umfst.ro Lecture no1. https://edu.umch.de INTRODUCTION TO HUMAN PHYSIOLOGY April 2024 Lecturer Florina Gliga  PAGE 2...

PAGE 1 https://www.umfst.ro Lecture no1. https://edu.umch.de INTRODUCTION TO HUMAN PHYSIOLOGY April 2024 Lecturer Florina Gliga  PAGE 2 Summary 1.Physiology – Human Physiology 2.Cells - the Living Units of the Body 3.Homeostasis – internal environment 4.Control systems Introduction PAGE 3 Physiology studies the physical and chemical mechanisms that are responsible for the origin, development and progression of life. describes the “vital” functions of living organisms and their organs, tissues, cells, and molecules. each type of life - own functional characteristics (plant → the simplest virus→ the complicated human being). Introduction PAGE 4 Physiology Vast field of physiology can be divided into: – cellular physiology, – plant physiology, – viral physiology, – bacterial physiology, – invertebrate physiology, – vertebrate physiology, – mammalian physiology, – human physiology, and many more subdivisions. Introduction PAGE 5 General physiology Study of living organisms: structural – anatomy, histology functional – physiology structure and function are inseparably exercise physiology linked: cellular and molecular physiology structure determines function comparative physiology function influences structure medical physiology → biochemistry → biophysics → neuroscience Introduction PAGE 6 Human Physiology Properties of human body: organized into complex structures based on organic molecules able to acquire matter and energy from the external environment and converts it into different forms breathing digestion and absorption excretion and so on. Introduction PAGE 7 Human Physiology Properties of human body: responds to stimuli from the environment excitability motion – adaptation under widely varying conditions is the basis of survival, otherwise would make life impossible. – hunger makes us seek food, – fear makes us seek refuge growth and development reproduction The functions of the body are based on the laws of physics and chemistry Introduction PAGE 8 Human Physiology Human physiology links the basic sciences with medicine: Integrates multiple functions of the cells, tissues, and organs into the complex functions of the living human being. This integration requires communication and coordination by a vast array of control systems that operate at every level: – the genes that program synthesis of molecules – to the complex nervous and hormonal systems that coordinate functions of cells, tissues and organs throughout the body. Thus, the coordinated functions of the human body are much more than the sum of its parts, and life in health, as well as in disease states, relies on the organism global function. PAGE 9 Introduction PAGE 10 Cells - the Living Units of the Body The basic living unit of the body is the cell. Each tissue or organ - an aggregate of many different cells connected by intercellular supporting structures. Each type of cell need a constant environment for proper functioning – multicellular organisms - internal environment of the body = extracellular fluid = interstitial fluid is specially adapted to perform one or a few particular functions has certain basic characteristics that are alike with other types of cells Introduction PAGE 11 Cells - the Living Units of the Body Common characteristic of all living human cells: – oxygen needs - O2 reacts with carbohydrate, fat, and protein to release the energy required for all cells to function. – the general chemical mechanisms for changing nutrients into energy are basically the same in all cells, – all cells deliver products of their chemical reactions into the surrounding fluids, – when cells of a particular type are destroyed, the remaining cells of this type usually generate new cells until the supply is replenished.  Introduction PAGE 12 Cells - the Living Units of the Body Particular characteristics – the specific function - each type of cell is specially adapted to perform one or a few particular functions: – the red blood cells, numbering about 25 trillion in each person, transport oxygen from the lungs to the tissues. Redhouse White, Crash Course Haematology and Immunology, 2 Copyright © 2019 © 2019, Elsevier Limited. All rights reserved.  PAGE 13 Homeostasis Internal environment Homeostasis: A property of cells, tissues, and organisms that allows the maintenance and regulation of the stability and constancy needed to function properly. Homeostasis is a healthy state that is maintained by the constant adjustment of biochemical and physiological pathways. It requires: normal function of individual organ/system interconnection of organ systems work “hand in hand” with each other. The cells within an organ or a tissue often share information, The individual cells must act in concert to perform the proper function of the organ or tissue  PAGE 14 Homeostasis Internal environment Claude Bernard concept - animals have two environments: the “milieu extérieur” that physically surrounds the whole organism; the “milieu intérieur” internal environment - “the organic liquid that circulates and bathes all the anatomic elements of the tissues, the lymph or the plasma.” – isolates the organs and tissues of the body from the vagaries of the physical conditions of the environment – “fixité du milieu intérieur” (the constancy of the extracellular fluid) is the condition of “free, independent life.”- in certain conditions each organ contributes to “compensate and equilibrate” against changes in the external environment.  Homeostasis PAGE 15 Internal environment Concept of Steady-State Balance The human body is an “open system,” - substances are added to the body each day and, similarly, substances are lost from the body each day. The amounts added to or lost from the body can vary widely, depending on the environment, access to food and water, disease processes, and even cultural norms. In such an open system, homeostasis occurs through the process of steady-state balance.  Homeostasis PAGE 16 Internal environment Concept of Steady-State Balance Key concepts are important for understanding the concept: 1.There must be a “set point” so that deviations from this baseline can be monitored. 2.The sensors that monitor deviations from the set point must generate “effector signals” that can lead to changes in either input or output, or both, to maintain the desired set point. 3.“Effector organs” must respond in an appropriate way to the effector signals generated by the set point monitor. 4.The sensitivity of the system (i.e., how much of a deviation from the set point is tolerated) depends on several factors: the nature of the sensor, the time necessary for generation of the effector signals, and how rapidly the effector organs respond to the effector signals. Homeostasis PAGE 17 Steady-State Balance Berne and Levy Physiology, 2, 17-34 Copyright © 2018 Copyright © 2018 by Elsevier, Inc. All rights reserved.  Homeostasis PAGE 18 Steady-State Balance Deviations Water balance determines the osmolality of the body fluids. Cells within the hypothalamus of the brain monitor body fluid osmolality for deviations from the set point (normal range: 280- 295 mOsm/kg H2O). When deviations are sensed, two effector signals are generated. – One is neural and relates to the individual's sensation of thirst. – The other is hormonal (antidiuretic hormone, also called arginine vasopressin ), which regulates the amount of water excreted by the kidneys. With appropriate responses to these two signals, water input, water output, or both are adjusted to maintain balance and thereby keep body fluid osmolality at the set point. Homeostasis PAGE 19 Steady-State Balance Deviations Deviations from steady-state balance do occur. When input is greater than output - a state of positive balance. When input is less than output - a state of negative balance. Transient periods of imbalance can be tolerated. Prolonged states of positive or negative balance are generally incompatible with life.  PAGE 20 Volume and Composition of Body Fluids Internal environment Water constitutes a high proportion of body weight. The total amount of fluid (a water solution of ions and other substances ) or water is called total body water, which accounts for 50% to 70% of body weight. In general, total body water correlates inversely with body fat. – Total body water is a higher percentage of body weight when body fat is low / a lower percentage when body fat is high. – Females have a higher percentage of adipose tissue than males → tend to have less body water.  PAGE 21 Volume and Composition of Body Fluids Internal environment Total body water - two major body fluid compartments: – intracellular fluid (ICF) - within the cells and is 2/3 of total body water; – extracellular fluid (ECF) - outside the cells and is 1/3 of total body water. ICF and ECF are separated by the cell membranes. Cellular Physiology,Costanzo, Linda 1-45 Copyright © 2018 by Elsevier, Inc. All rights reserved. Volume and Composition of Body Fluids PAGE 22 Netter's Essential Physiology, Chapter 1, 2-11 Copyright © 2016 by Elsevier, Inc. All rights reserved. Composition of Body Fluid Compartments PAGE 23 Internal environment The composition of the body fluids is not uniform. ICF and ECF have vastly different concentrations of various solutes. There are also certain differences between plasma and interstitial fluid that occur as a result of the exclusion of protein from interstitial fluid.  PAGE 24 Volume and Composition of Body Fluids ECF is further divided into two compartments: plasma and interstitial fluid. Plasma is the fluid circulating in the blood vessels; is smaller of the two ECF subcompartments. Interstitial fluid is the fluid that actually bathes the cells - an ultrafiltrate of plasma, formed by filtration processes across the capillary wall, containing little, if any, protein ( the capillary wall is virtually impermeable to large molecules such as plasma proteins). Plasma and interstitial fluid are separated by the capillary wall.  PAGE 25 Differences in Extracellular and Intracellular Fluids ECF is in constant motion throughout the body - is transported rapidly in the circulating blood and then mixed between the blood and tissue fluids by diffusion through the capillary walls. The ECF contains ions and nutrients needed by the cells to maintain life : – large amounts of sodium (Na + ), and the balancing anions are chloride (Cl − ) and bicarbonate (HCO 3 − ) ions – the Ca 2+ concentration in ECF is higher by approximately four orders of magnitude than in ICF – plus nutrients for the cells, such as oxygen, glucose, fatty acids, and amino acids – carbon dioxide that is being transported from the cells to the lungs to be excreted – cellular waste products that are being transported to the kidneys for excretion.  PAGE 26 Differences in Extracellular and Intracellular Fluids The ICF contains: – high potassium (K + ) and magnesium (Mg 2+ ), and the balancing anions are proteins and organic phosphates (instead of the sodium and chloride ions found in the ECF). – a very low concentration of ionized Ca 2+ – is more acidic (has a lower pH) Special mechanisms for transporting ions through the cell membranes maintain the ion concentration differences between the extracellular and intracellular fluids.  PAGE 27 Differences in Extracellular and Intracellular Fluids Substances found in high concentration in ECF are found in low concentration in ICF, and vice versa. PhD, Guyton and Hall Textbook of Medical Physiology, Chapter 4, 47-59 Copyright © 2016 by Elsevier, Inc. All rights reserved. Electroneutrality of Body Fluid Compartments PAGE 28 Each body fluid compartment is governed by the principle of macroscopic electroneutrality - each compartment must have the same concentration, in mEq/L, of positive charges (cations) as of negative charges (anions). Even when there is a potential difference across the cell membrane, charge balance still is maintained in the bulk (macroscopic) solutions. – the separation of just a few charges adjacent to the membrane, this small separation of charges is not enough to change bulk concentrations in a measurably manner. Homeostasis PAGE 29 Maintenance of a Nearly Constant Internal Environment all organs and tissues of the body perform functions that help maintaining these relatively constant conditions: – the lungs - oxygen to the ECF , – the kidneys - constant ion concentrations, – the gastrointestinal system - nutrients. Homeostasis PAGE 30 Extracellular Fluid Transport - Blood Circulatory System Extracellular fluid is transported through the body in two stages. – movement of blood through the body in the blood vessels, – movement of fluid between the blood capillaries and the intercellular spaces between the tissue cells. Homeostasis -Blood Circulatory System PAGE 31 Extracellular Fluid Transport All the blood in the circulation traverses the entire circulatory circuit an average of once each minute when the body is at rest as many as six times each minute when a person is extremely active. Guyton and Hall Textbook of Medical Physiology, Chapter 1, 3-10 Copyright Copyright © 2016 by Elsevier, Inc. All rights reserved.  Homeostasis- Blood Circulatory System PAGE 32 Extracellular Fluid Transport As blood passes through the blood capillaries, continuous exchange of extracellular fluid occurs between the plasma in the blood and the interstitial fluid that fills the intercellular spaces. The walls of the capillaries are permeable to most molecules in the plasma of the blood (exception of plasma proteins - too large). Large amounts of fluid and its dissolved constituents diffuse back and forth between the blood and the tissue spaces. Guyton and Hall Textbook of Medical Physiology, Chapter 1, 3-11 Copyright © 2016 by Elsevier, Inc. All rights reserved. Homeostasis -Blood Circulatory System PAGE 33 Extracellular Fluid Transport This process of diffusion is caused by kinetic motion of the molecules. The fluid and dissolved molecules are continually moving and bouncing in all directions within the plasma and the fluid in the intercellular spaces, as well as through the capillary pores. Thus, the extracellular fluid everywhere in the body is continually being mixed – ECF homogeneity throughout the body. Berne and Levy Physiology, 17, 345-385 Copyright © 2018 by Elsevier, Inc. All rights reserved. Homeostasis - Origin of Nutrients PAGE 34 Extracellular Fluid Transport -Respiratory System The blood picks up oxygen in the alveoli, thus acquiring the oxygen needed by the cells. The membrane between the alveoli and the pulmonary capillaries, the alveolar membrane, is only 0.4 to 2.0 micrometers thick, and oxygen rapidly diffuses by molecular motion through this membrane into the blood. Guyton and Hall Textbook of Medical Physiology, Chapter 40, 511-520. Copyright © 2021 by Elsevier, Inc. All rights reserved. Homeostasis - Origin of Nutrients PAGE 35 Extracellular Fluid Transport - Gastrointestinal Tract A large portion of the blood pumped by the heart also passes through the walls of the gastrointestinal tract. Guyton and Hall Textbook of Medical Physiology, Chapter 66, 823-832. Copyright © 2021 by Elsevier, Inc. All rights reserved. Homeostasis - Origin of Nutrients PAGE 36 Extracellular Fluid Transport - Gastrointestinal Tract Here different dissolved nutrients, including carbohydrates, fatty acids, and amino acids, are absorbed from the ingested food into the extracellular fluid of the blood..Dominiczak, Marek H., Medical Biochemistry, Chapter 30, Copyright © 2019 by Elsevier, Inc. All rights reserved.  PAGE 37 Homeostasis – Metabolism and removal of end products Extracellular Fluid Transport – Liver – Metabolic Function Some of the absorbed substances from the from the gastrointestinal tract can’t be used in their primary form by the cells. The liver changes their chemical compositions to more usable forms. It also has the property of storing them. The liver also eliminates certain waste products produced in the body and toxic substances that are ingested. Berne and Levy Physiology, 32, 568-579 Copyright © 2018 by Elsevier, Inc. All rights reserved. Homeostasis - Removal of Metabolic End Products PAGE 38 Extracellular Fluid Transport - Carbon Dioxide Carbon dioxide is the most abundant of all the metabolism products. Is released from the blood into the lung alveoli; the respiratory movement of air into and out of the lungs carries the carbon dioxide to the atmosphere. Guyton and Hall Textbook of Medical Physiology, Chapter 40, 511-520. Copyright © 2021 by Elsevier, Inc. All rights reserved.  PAGE 39 Homeostasis - Removal of Metabolic End Products Kidney Waste excretion first filtering large quantities of plasma through the glomerular capillaries into the tubules then reabsorbing into the blood the substances needed by the body (as glucose, amino acids, water, and many of the ions) secretion excretion - especially metabolic waste products such as urea, drugs, toxins , pass through the renal tubules into the urine. Guyton and Hall Textbook of Medical Physiology, Chapter 26. Copyright © 2021 by Elsevier, Inc. All rights reserved.  PAGE 40 Homeostasis - Removal of Metabolic End Products Changes in concentrations of different substances in tubular fluid along the proximal convoluted tubule relative to the concentrations of these substances in the plasma and glomerular filtrate. Guyton and Hall Textbook of Medical Physiology, Chapter 28. Copyright © 2021 by Elsevier, Inc. All rights reserved.  PAGE 41 Homeostasis - Removal of Metabolic End Products Tegumentary System The skin and its various appendages (including the hair, nails, glands, and other structures) are important for: – excretion of wastes, – temperature regulation, – mechanical and thermal isolation (cover, cushion, and protect the deeper tissues and organs). The skin generally comprises about 12 to 15 percent of body weight. Guyton and Hall Textbook of Medical Physiology, Chapter 74. Copyright © 2021 by Elsevier, Inc. All rights reserved.  PAGE 42 Homeostasis - Removal of Metabolic End Products Gastrointestinal Tract. Undigested material that enters the gastrointestinal tract and some waste products of metabolism are eliminated in the feces. Liver. Among the functions of the liver is the detoxification or removal of many drugs and chemicals that are ingested. The liver secretes many of these wastes into the bile to be eventually eliminated in the feces. Homeostasis -Control Systems of the Body PAGE 43 The human body has thousands of control systems. Some of the most intricate of these systems are the genetic control systems - operate in all cells to help control intracellular and extracellular functions. The other two major systems evolved to communicate and coordinate body functions: – 1. The nervous system integrates tissue functions by a network of cells and cell processes. – 2. The endocrine system integrates organ function via chemicals that are secreted from endocrine tissues or “glands” into the extracellular fluid - hormones. Homeostasis - Regulation of Body Functions PAGE 44 The nervous system - composed of three major parts: the sensory input portion - detect the state of the body or the state of the surroundings (receptors – eye, ear, skin…) the central nervous system (or integrative portion ) - the brain and spinal cord. The brain can store information, generate thoughts, create ambition, and determine reactions that the body performs in response to the sensations. the motor output portion – carries out the response coming from the brain. Homeostasis - Regulation of Body Functions PAGE 45 The nervous system An important segment of the nervous system is called the autonomic system. It operates at a subconscious level and controls many functions of the internal organs: – the level of pumping activity by the heart, – movements of the gastrointestinal tract, – secretion by many of the body's glands. Homeostasis - Regulation of Body Functions PAGE 46 The autonomous nervous system The two divisions of the autonomic nervous system: the sympathetic nervous system (SNS) the parasympathetic nervous system (PNS). Netter's Essential Physiology, Chapter 7, 84-92 Copyright © 2016 by Elsevier, Inc. All rights reserved Homeostasis - Regulation of Body Functions PAGE 47 Hormone Systems The endocrine system is a network of glands that produce and secrete hormones, which are used by the body for a wide range of functions. Hormones control many different body functions, including: Metabolism Growth. Reproduction Sexual development Respiration Sensory perception Movement. Homeostasis - Regulation of Body Functions PAGE 48 Hormone Systems The endocrine system is part of the large chemical messenger systems, and includes: Endocrine hormones are released by glands or specialized cells into the circulating blood and influence the function of target cells (recognized by specific high-affinity receptors) at another location in the body. Neuroendocrine hormones are secreted by neurons into the circulating blood and influence the function of target cells at another location in the body. Paracrines are secreted by cells into the extracellular fluid and affect neighboring target cells of a different type. Autocrines are secreted by cells into the extracellular fluid and affect the function of the same cells that produced them. Homeostasis - Regulation of Body Functions PAGE 49 The endocrine system is composed of : pituitary gland , thyroid gland , parathyroid glands , adrenal glands, pancreas, ovary, testis. Endocrine and Reproductive Physiology, 1, 1-24 Copyright © 2019, Elsevier Inc. All rights reserved. Homeostasis - Regulation of Body Functions PAGE 50 Hinson, Joy, Medical Sciences, 10, 441-482 Copyright © 2019, Elsevier Inc. All rights reserved. Homeostasis - Regulation of Body Functions PAGE 51 Hormone and Nervous Systems The nervous system regulates many muscular and secretory activities of the body, The hormonal system regulates many metabolic functions. The nervous and hormonal systems normally work together in a coordinated manner to control essentially all of the organ systems of the body. Homeostasis - Control Mechanism PAGE 52 Maintaining a nearly constant composition of the inner environment requires the action of control systems Examples of tightly controlled parameters that affect nearly the whole body are arterial pressure and blood volume. At the level of the milieu intérieur, tightly regulated parameters include: – body core temperature – plasma levels of oxygen, – plasma glucose, – potassium (K + ), sodium (Na +), calcium (Ca 2+ ) and hydrogen ions (H + ). Homeostasis PAGE 53 Constants The constituents of the body (various ions, nutrients, waste products, etc.) are normally regulated within a range of values, rather than at fixed values: normal value – the average value of a group of healthy individuals normal range (reference range) – the interval between which ~95% of values of a reference population fall into – mean ± 2 SD 5% of the “normal” population have test results outside the reference range some parameters vary between a very narrow range (e. g. pH, Na concentration), others a larger range (e. g. blood glucose level) Homeostasis PAGE 54 Constants Crash Course Medical Research, 45-60 Copyright © 2020, Elsevier Limited. All rights reserved. Homeostasis -Control Mechanism PAGE 55 Important Constituents and Physical Characteristics of Extracellular Fluid Approximate Normal Value Normal Range Short-Term Unit Nonlethal Limit Oxygen 40 35-45 10-1000 mm Hg (venous) Carbon dioxide 45 35-45 5-80 mm Hg (venous) Sodium ion 142 138-146 115-175 mmol/L Potassium ion 4.2 3.8-5.0 1.5-9.0 mmol/L Calcium ion 1.2 1.0-1.4 0.5-2.0 mmol/L Chloride ion 106 103-112 70-130 mmol/L Bicarbonate ion 24 24-32 8-45 mmol/L Glucose 90 75-95 20-1500 mg/dl Body 98.4 (37.0) 98-98.8 (37.0) 65-110 °F (°C) temperature Acid-base 7.4 7.3-7.5 6.9-8.0 pH Homeostasis -Control Mechanism PAGE 56 The negative-feedback mechanism is: one of the most common themes in physiology responsible for homeostasis (prevents large deviations from the normal value) a process in which the end results will inhibit the initial action from continuing to occur. Homeostasis -Control Mechanism PAGE 57 Negative feedback requires at least four elements: the system must be able to sense the vital parameter (e.g., glucose level) or something related to it. the system must be able to compare the input signal with some internal reference value called a set-point, thereby forming a difference signal. the system must produce some sort of output signal (e.g., release of insulin). the output signal must be able to activate an effector mechanism (e.g., glucose uptake and metabolism) that opposes the input signal and thereby brings the vital parameter closer to the set-point (e.g., decrease of blood glucose levels back to normal). Homeostasis -Control Mechanism PAGE 58 Naish, Medical Sciences, 1, 1-14 Davidson's Principles and Practice of Medicine, 18, Copyright © 2019, Elsevier Limited All rights reserved Copyright © 2018 Elsevier Ltd. All rights reserved. Homeostasis -Control Systems PAGE 59 Positive feedback is a process in which the end products of an action cause more of that action to occur in a feedback loop. it amplifies the original action. leads to instability rather than stability and, in some cases, can cause death. it is contrasted with negative feedback. In some instances, the body uses positive feedback to its advantage. Blood clotting Childbirth Ovulation Homeostasis -Control Systems PAGE 60 Positive feedback McGeown, Physiology, Chapter 9, Naish, Medical Sciences, 1, 1-14 Copyright © 2007, Elsevier Limited. All rights reserved. Copyright © 2019, Elsevier Limited All rights reserved Homeostasis -Control Mechanism Example PAGE 61 Regulation of Oxygen Concentrations in the Extracellular Fluid Because oxygen is one of the major substances required for chemical reactions in the cells - a special control mechanism to maintain an almost exact and constant oxygen concentration in the extracellular fluid. This mechanism depends essentially on the chemical characteristics of hemoglobin, which is present in all red blood cells. Homeostasis -Control Mechanism Example PAGE 62 Regulation of Oxygen Concentrations in the Extracellular Fluid Hemoglobin combines with oxygen as the blood passes through the lungs. In the the tissue capillaries, hemoglobin, – does not release oxygen into the tissue fluid if too much oxygen is already there. – release sufficient oxygen , if the oxygen concentration in the tissue fluid is too low. This regulation is called the oxygen-buffering function of hemoglobin. Homeostasis -Control Mechanism Example PAGE 63 Regulation of Carbon Dioxide Concentrations in the Extracellular Fluid Carbon dioxide is a major end product of the oxidative reactions in cells. A higher than normal carbon dioxide concentration in the blood excites the respiratory center, causing a person to breathe rapidly and deeply. This deep, rapid breathing removes excess carbon dioxide from the blood and tissue fluids. Guyton and Hall Textbook of Medical Physiology, Chapter 18, Copyright © 2021 by Elsevier, Inc. All rights reserved. Homeostasis -Control Systems PAGE 64 Regulation of Arterial Blood Pressure. Several systems contribute to the regulation of arterial blood pressure. The baroreceptor system - a rapidly acting control mechanism. Nerve receptors called baroreceptors (stimulated by stretch of the arterial wall) – arch of the aorta and bifurcation of the carotid arteries. Homeostasis -Control Systems PAGE 65 Regulation of Arterial Blood Pressure. Signals from the sensor → medulla of the brain → compared with a reference set point. The input signals are compared with the set point → generating an error signal that affects the sympathetic nervous system activity generating an action. Homeostasis -Control Systems PAGE 66 Regulation of Arterial Blood Pressure. High BP - the baroreceptors send barrages of nerve impulses to the medulla of the brain→ inhibit the vasomotor center → decreases the number of impulses transmitted from the vasomotor center through the sympathetic nervous system to the heart and blood vessels → diminished pumping activity by the heart and also dilation of the peripheral blood vessels → decrease the arterial pressure, moving it back toward normal. Low BP - relaxes the stretch receptors, allowing the vasomotor center to become more active → vasoconstriction and increased heart pumping. Homeostasis PAGE 67 Disturbed homeostasis Disease is often considered to be a state of disrupted homeostasis. in the presence of disease, homeostatic mechanisms continue to operate and maintain vital functions through multiple compensations. In many cases, these compensations mechanism return the body functions to normal: disease → state of health In other cases, these compensations may themselves lead to major deviations of the body's functions from the normal range, making it difficult to distinguish the primary cause of the disease from the compensatory responses. Homeostasis PAGE 68 Disturbed homeostasis Thus, homeostatic compensations that ensue after injury, disease, or major environmental challenges to the body may represent a “trade-off” that – is necessary to maintain vital body functions – but, in the long term, may contribute to additional abnormalities of body function. The discipline of pathophysiology – mechanisms that alter the various physiological processes in diseases or injury. References PAGE 69 1. Guyton and Hall, Textbook ot Medical Physiology thirteen edition, John E. Hall 2. Linda S. Constanzo, Physyology Sixth Edition 3. Boron, Walter F., MD, PhD; Boulpaep, Emile L., MD, Medical Physiology, Third Edition, 4. Berne and Levy Physiology, Koeppen, Bruce M., MD, PhD; Stanton, Bruce A., PhD. Published January 1, 2018. 5. Netter's Essential Physiology, Mulroney, Susan E., PhD; Myers, Adam K., PhD. Published January 1, 2016 References PAGE 70