Week 1 Lecture Notes Introduction to Physiology PDF

1 Introduction to Physiology, Chapter 1 Objectives. After studying this chapter you should be able to: 1. Define anatomy and physiology. 2. Explain why physiology today is considered a relative...

1 Introduction to Physiology, Chapter 1 Objectives. After studying this chapter you should be able to: 1. Define anatomy and physiology. 2. Explain why physiology today is considered a relatively broad science and discuss its various disciplines. 3. List and describe the 6 levels of structural organization. 4. Explain what emergent properties are and give an example. 5. List the 11 principal systems of the body, their functions, and representative organs. 6. Describe homeostasis, why this concept is important in medicine and physiology. Explain the how homeostasis is regulated – be sure to include the components of a feedback system and the characteristics of a negative and positive feedback loop with examples of both. 7. Explain how blood pressure is regulated to maintain homeostasis 8. Explain regulatory processes involved in the formation/dissipation of a fever that is caused by certain types of bacterial infections. How do antipyretics such as aspirin work? 9. Describe the four major body reference planes. 10. Describe the major body cavities, their representative organs and representative serous membranes. 11. Explain the following medical imaging procedures: X-Rays, CT, MRI, ultrasound, PET, DSA 12. Describe the components of experimental design, the difference between dependent and independent variables, and the importance of an experimental control. 13. Describe the difference between the following types of studies: Crossover study, blind study, double-blind study, double-blind crossover study. 14. Explain the difference between placebo and nocebo. Chapter 1 Overview Divisions of Physiology Structural and functional organization of the body – Levels of organization – Organ systems Organization of Body – Body planes and sections – Body cavities Homeostasis – Negative and positive feedback mechanisms Anatomy Defined Anatomy: Study of structure and the relationships among structures. – Structure refers to the shapes, sizes, and characteristics of the components of the human body. Anatomy is a Greek term that originates from 2 words: – Ana which means “up or apart” – Tomos which means “to cut” Physiology Defined Physiology: Study of how the body parts functions. – Explains the how and why Physiology is where we figure out how stuff works. – How muscles contract. – How neural impulses are formed. – How RBCs carry oxygen.  2 Divisions of Physiology Physiology is a relatively broad science because it can be divided into various disciplines. – Cell Physiology: Study of the functions of cells. Chemical process within cells and interactions between cells The cornerstone of physiology – Systemic Physiology: Study of the functioning of specific organ systems. Example: Cardiovascular physiology; reproductive physiology – Exercise Physiology: Study of the cell and organ functions during skeletal muscle activity. – Pathophysiology: Study of the effects of diseases on organ or system functions. Modern medicine depends on an understanding of both normal physiology and pathophysiology. Focus of clinical applications Organism Levels of Structural Organization The human body consists of several levels of structural organization, which interact to perform specific functions. 1. Chemical level: Atoms and molecules Atoms: Made of subatomic particles: protons (positive charge), neutrons (no charge) and electrons (negative charge). C, H, O, N, Ca, P make up 99% of our body weight Molecules: Two or more atoms held together by covalent bonds. Ex: water, DNA, proteins, carbohydrates, vitamins. Molecules are organized into organelles. How Much Are Your Ingredients Worth? Total worth: $4.50 Elements = ~ $1.00 Skin = ~ $3.50 Note: Skin is based on the selling price of cowhide, which is approximately $0.25 per square foot. 2. Cellular Level Organelles: Functional components of cells. Ex: nucleus, mitochondria Cells: Fundamental functional unit of life Cell theory – 2 parts – All organisms are made of cells Schleiden and Schwann (1839) – All cells come from pre-existing cells Virchow (1839)  3 3. Tissue Level Tissues: Groups of similar cells and their extracellular matrix joined together to perform the same general function. Four primary types of tissues: Muscle, epithelial, connective, nervous 4. Organ Level Organs: Combination of two or more different tissues that have specific functions Ex: stomach, heart, lungs, brain 5. Organ System Organ system: Two or more organs which function together for a common purpose – Ex: Digestive system includes the liver, stomach, intestines, pancreas, salivary glands, etc. 6. Organism: All the body systems functioning together Test Your Knowledge? 1. The smallest living units in the body are: A. Elements B. Subatomic particles C. Cells D. Molecules 2. The level of organization that reflects the interactions between organ systems is the: A. Cellular Level B. Tissue Level C. Molecular Level D. Organism Emergent Properties Are properties that a complex system has, but the individual parts or members do not have. – An emergent property is not a property of any single component of a system, and it is greater than the simple sum of the system’s individual parts. Examples of Emergent Properties: – With each level of structural organization of humans emergent properties appear. For instance, a single heart cell is alive, but if you separate the macromolecules that combined to create the heart cell, these units are not alive. Heart is made of heart cells, heart cells on their own don't have the property of pumping blood. You will need the whole heart to be able to pump blood. Thus, the pumping property of the heart is an emergent property of the heart.  4 Overview of the 11 Organ Systems Integumentary System Structures: – Skin, hair, nails, sweat and oil glands Functions: – Provides a protective barrier for the body – Aids in vitamin D production – Helps in waste elimination – Prevents desiccation, heat loss, and pathogen entry – Contains sensory receptors for pain, touch, and temperature Skeletal System Structures: – Bones (206 total) and associated joints, cartilages, and ligaments Functions: – Protects and supports body organs – Provides a framework that muscles can use to create movement – Hemopoiesis (synthesis of blood cells) – Mineral storage Bone contains 99% of the body’s store of what mineral? (Hint → you can get this mineral from drinking milk) Muscular System Structures: – The 600+ skeletal muscles of the body – Attached to skeleton by tendons Functions: – Body movements – Maintains posture – Thermogenesis (generation of heat) Nervous System Structures: – Brain, spinal cord, peripheral nerves, and sense organs Functions: – Fast-acting control system of the body Controls cell function with electrical signals called action potentials. – Monitors the internal and external environment and responds (when necessary) by initiating muscular or glandular activity.  5 Endocrine System Structures: – All endocrine glands and hormone secreting cells. Endocrine glands: Pituitary, Thyroid, Parathyroid, Adrenal, and Pineal, Endocrine secreting cells are found in the Pancreas, Thymus, Small Intestine, Stomach, Testes, Ovaries, Kidneys, Heart, hypothalamus Functions: – Regulates body activities through hormones – Long-term control system of the body (slow acting) – Regulates growth, metabolism reproduction, and many other processes. Cardiovascular System Structures: – Heart, blood vessels, and blood Functions: – Transports nutrients (glucose, amino acids, lipids), gases (O2, CO2), wastes (urea, creatinine), and hormones. – Helps regulate body temperature and protect against disease Lymphatic System Structures: – Lymph, Lymphatic vessels, and organs containing lymphatic tissue such as lymph nodes, spleen, thymus, red bone marrow Functions: – Returns “leaked” fluid back to the bloodstream – Transports fats from GI tract – Filters (removes) foreign substances from blood and lymph – Combats disease (pathogens) Respiratory System Structures: – Lungs and associated passageways (Nasal cavity, pharynx, trachea, bronchi) Functions: – Supplies O2 and eliminates CO2 – Regulates blood pH – Produces vocal sounds Digestive System Structures: – Gastrointestinal tract (GI) and associated structures. GI tract consists of the oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus Associated organs include the teeth, salivary glands, pancreas, liver, gallbladder Functions: – Breaks down food into units that can be absorbed by the body by: Mechanical processes Chemical processes  6 Urinary System Structures: – Kidneys, ureters, urinary bladder, urethra Functions: – Removal of nitrogenous wastes – Maintains the body fluid volume, pH, and electrolyte levels. Reproductive System Structures: – Male: Testes, epididymis, vas deferens, associated glands and penis – Female: Ovaries, uterine (fallopian) tubes, uterus, cervix, vagina, mammary glands Functions: – Production of gametes (sperm and eggs) and ultimately the production of offspring. – Production of hormones that influence sexual function/behavior Organ Systems Interrelationships The integumentary system protects the body from the external environment Digestive and respiratory systems, in contact with the external environment, take in nutrients and oxygen Nutrients and oxygen are distributed by the cardiovascular system. Metabolic wastes are eliminated by the urinary and respiratory systems Test Your Knowledge? The two regulatory systems in the human body include the: A. Nervous and endocrine C. Muscular and skeletal B. Digestive and reproductive D. Cardiovascular and lymphatic Name the body system that functions in waste elimination, prevention of desiccation, heat loss, and pathogen entry, and is the site of pain and pressure receptors. A. Urinary system C. Reproductive system B. Skeletal system D. Integumentary system Major Requirements of Life: “Stayin’ Alive” Your body has about 100 trillion cells in it. For your life to NOT end abruptly, these cells need to have the correct amount of: Water; Oxygen; Nutrients (glucose, amino acids, etc) ; Waste removal; pH (7.35 – 7.45); Temperature; Electrolytes or Ions (sodium, calcium, etc.) Circulation – maintain right flow rate Let’s refer to all this stuff as “variables” because their value can change. Save your cell - group activity Homeostasis Homeostasis: Condition of dynamic constancy – the organism’s ability to maintain a relatively stable internal environment despite changes inside and outside the body. – Homeo means the same or unchanging and stasis means constant or standing still.  7 Homeostasis is DYNAMIC! Homeostasis functions to maintain all physiological values within certain limits or at their set point. – Example: Keeps body temperature at 98.6 F (37 C) and maintains adequate nutrient and O2 levels for cells to flourish. Homeostatic variables are NOT kept rigidly fixed upon a single value; they are kept in a certain range. – Is your body temperature always exactly 98.6F? The Control of Body Temperature: Example of Homeostasis Homeostasis and Disease Body is healthy when homeostasis is maintained and thus is very important in the study of medicine. – Moderate homeostatic imbalance may result in a disorder or disease. – Severe imbalance may result in death. Watch Homeostasis Videos: In Canvas in Unit 1 you will see Videos on Homeostasis. Regulation of Homeostasis Regulatory mechanisms of homeostasis are categorized as intrinsic and extrinsic. Intrinsic or local control (autoregulation): Regulatory mechanisms (“built-in”) are within the organs – provide immediate response independent of nervous or endocrine system. – Example: Decline in O2 levels, CO2 buildup, decreased pH and increased wastes in a tissue stimulates the cells to release chemicals that dilate local blood vessels to increase blood flow and bring in more O2, and remove CO2, hydrogen ions and wastes. Extrinsic regulatory mechanisms: Mediated by the nervous and endocrine system which handle changes that are widespread throughout the body. – Example: Exercise results in the nervous system and endocrine system functioning to increase heart rate, broncho-dilation, increased muscle contraction, etc. Note: Extrinsic control permits coordinated regulation of several organs toward a common goal; in contrast, intrinsic control serve only the organ in which they occur.  8 Feedback Systems (Loops) Homeostasis is maintained by feedback systems (loops) – Feedback System (loop): Cycle of events where a condition is continually monitored, evaluated, changed if necessary to maintain consistency, and then monitored, reevaluated, and so on. Components of a Feedback System Feedback systems have three basic components: 1. Receptor (Sensor): Sensor detects changes (stimulus – input signal) in a condition (variable) Sends that information to a control center via an afferent nerve pathway or chemical signal. 2. Control or Integrating center: Structure such as the brain that receives and processes the information supplied by the receptor. Sets the range of values at which the condition should be maintained and determines an appropriate response based on the information it receives from the receptor. Output via an efferent nerve pathway or chemical signal 3. Effector: Cell or organ that receives output from the control center and produces a response that changes the condition by either depressing (negative feedback) or enhancing (positive feedback) the stimulus. Example: Skeletal muscles (effectors) cause you to shiver in response to cold conditions (stimulus) Classification of Feedback Systems Feedback systems can be classified as either negative feedback systems or positive feedback systems. Negative Feedback Negative feedback mechanisms: Process in which the body senses an internal change and activates mechanisms that reverse that change. – Mechanism reverses the direction of the initial change in condition – Examples: Blood pressure, glucose level, body temperature Example: Blood Glucose Levels – Understand the figure on blood glucose regulation.  9 When does a negative feedback process end? The answer is so cool! The process ends when that condition (variable) is back within its normal range. A negative feedback process begins when a particular variable leaves its homeostatic range. Negative feedback processes (or loops) are self-terminating. MAKE SURE YOU UNDERSTAND WHY! Example of Negative Feedback: Blood Pressure Blood Pressure to the head drops when a person goes from a lying to standing position – When you stand up, gravity pulls blood downward. Orthostatic hypotension, also called postural hypotension, is a form of low blood pressure that happens when you stand up from sitting or lying and your body has mechanisms to adjust for this. Blood pressure receptors known as baroreceptors (sensors) detect changes in blood pressure. – Baroreceptors are specialized sensory neurons in the walls of the aortic arch and the carotid sinuses that measure the degree of stretch in the vessel wall. Information is sent from the baroreceptors to the medulla oblongata via sensory nerves. The Medulla oblongata (control center) of the brain analyzes the change in blood pressure and sends a nerve impulse to the heart and blood vessels (mainly arterioles), both of which are effectors, to correct the decrease in blood pressure. – Heart rate and amount of blood pumped are increased causing an increase in blood pressure – Vasoconstriction of arterioles increases blood pressure. Thus if BP is too high or too low, a reflex change in cardiac output is initiated in order to correct it. This example is negative feedback because the response (increased blood pressure) reverses the direction of the initial change (decreased blood pressure). Syncope Syncope ("sin-ko-pea") is the brief loss of consciousness (faint) caused by a temporary decrease in blood flow to the brain. Vasovagal syncope (Vaso = blood vessels; vagal = vagus nerve) is the most common (80%) type of syncope that occurs when your body overreacts to triggers, such as emotional stress, trauma, pain, the sight of blood, prolonged standing and straining (such as to have a bowel movement).  10 – The nervous system malfunctions causing your heart rate to slow and the blood vessels to vasodilate. This lowers your blood pressure resulting in diminished blood flow to your brain, and you faint Positive Feedback Positive feedback: Process in which the body senses a change and activates mechanisms that accelerates or increases that change in the condition (variable) even more in the same direction. Examples of Positive Feedback: Childbirth, ovulation, blood clotting. – Positive feedback mechanisms are less common than negative feedback mechanisms. Positive Feedback loops end with removal of the stimulus – baby delivered, egg ovulated, blood clotted. Example: Childbirth – When the baby is ready to be delivered, it drops lower in the uterus causing stretching of the uterus and cervix. Stretch receptors in the cervix and uterine wall are monitored by the hypothalamus of the brain. As the uterus stretches the hypothalamus releases oxytocin via the posterior pituitary gland, which Example: Blood clotting causes the uterus to contract. This contraction further distorts and open the cervix resulting in more oxytocin to be released which increase uterine contractions. The cycle continues until the baby is delivered and the stretching stimulation is eliminated stopping the positive feedback loop. Reviewing You Knowledge? In a homeostatic mechanism, what provides the control center’s response to the stimulus? A. Receptor B. Effector When the initial stimulus produces a response that exaggerates or amplifies the stimulus, the mechanism is called? A. Negative feedback B. Positive Feedback C. Autoregulation D. Homeostasis  11 Hypothalamus and Thermoregulation The hypothalamus regulates body temperature (the body’s thermostat) and functions by a negative feedback process. – Normal body temperature averages 37oC (98.6oF) taken with an oral thermometer and about 1oF higher when measured rectally. However, healthy adults can have resting body temperatures that range from less than 36oC (97oF) to over 37.5oC (99.5oF). These temperatures are perfectly normal for them and the variations have no clinical significance. – Temperature above homeostatic range can cause enzymatic proteins to denature and stop functioning. Absolute limit for human life is appears to be about 43oC (~109oF). Hypothalamus receives input from: – Peripheral thermoreceptors located in the skin. Less important in stimulating hypothalamic response as skin temperature can fluctuate dramatically with surrounding temperature. – Central thermoreceptors monitor blood temperature and are located in the body core (organs of thoracic and abdominal cavities) and the hypothalamus of the brain. More important in stimulating hypothalamic response as core body temperature normally fluctuates very little. When temperature increases above the hypothalamic set point the hypothalamus activates the following to cool the body: – Dilation of cutaneous (skin) blood vessels allowing more warm blood to radiate heat at the skin surface, – Sweat gland activation as temperature continues to increase. Perspiration is evaporated to increase heat loss.  12 When temperature decreases below the hypothalamic set point the hypothalamus activates the following to increase body heat. – Constriction of cutaneous (skin) blood vessels which diverts blood from skin capillaries to deeper tissues, minimizing heat loss from the skin surface. – Skeletal muscle activation as temperature continues to decrease. Shivering muscle produces a lot of heat to increase body temperature.  13 Homeostasis and Fever/Chills? Fever is an elevation of core temperature caused by a resetting of the hypothalamic thermostat. Common causes of fever are endogenous pyrogens released from phagocytes, viral or bacterial infections and bacterial toxins. A mild increase in temperature is thought to be beneficial because it increases the immune system’s response and inhibits bacterial growth. Steps involved with fever formation caused by bacterial infection. 1. Macrophages and other phagocytes ingest bacteria and can be stimulated to secrete various cytokines known as pyrogens (pyro=fire, -gen=produce) which are substances that produce a fever. One such pyrogen is interleukin - 1 (IL-1). 2. IL-1 circulates to the hypothalamus and induces hypothalamic neurons to secrete prostaglandins that reset the hypothalamic thermostat at a higher temperature, let’s say the hypothalamus thermostat is reset at 39oC (103oF). Prostaglandins are local chemical mediators which in this case, act directly on the hypothalamus. 3. Heat promoting mechanisms then act to bring the core body temperature up to this new setting. The heat-promoting mechanisms include vasoconstriction of blood vessels near the skin, increased metabolism, and shivering. Thus, even though core temperature is climbing higher than normal – say, 38oC (101oF) – the skin remains cold due to vasoconstriction of blood vessels, and shivering occurs. This condition, called a chill, is a definite sign that core temperature is rising. After several hours, core temperature  14 reaches the setting of the thermostat, and the chills disappear. But now the body will continue to regulate temperature at 39oC (103oF). 4. When the bacteria are gone pyrogens disappear, the thermostat is reset at normal – 37oC (98.6oF). Because core temperature is high in the beginning, the heat-losing mechanisms (vasodilation and sweating) kick in to decrease core temperature. The skin becomes warm, and the person begins to sweat. This phase of the fever indicates the core temperature is falling – commonly referred to as “the fever has broken”. Antipyretics and Fever Reduction – Antipyretics such as aspirin and ibuprofen are agents that relieve or reduce fever by inhibiting synthesis of certain prostaglandins within the hypothalamus and thus inhibit the effects of pyrogens to reset the hypothalamic thermostat. Nonsteroidal anti-inflammatory drugs (NSAIDs) are a class of drugs that reduce inflammation (pain, fever, and swelling). Examples: Aspirin and ibuprofen (Advil, Motrin) – Aspirin does not lower the temperature in a person without a fever because in the absence of pyrogens, prostaglandins that influence temperature are not produced in the hypothalamus in appreciable quantities. – We will discuss more on fever formation and its application when we cover the immune system. Body Planes and Sections Sagittal section passes vertically thru the body – Divides the body into right and left portions. – Midsagittal section divides the body into equal right and left sections – Parasagittal section divides the body into unequal right and left section Transverse section passes horizontally thru the body – Divides the body into superior and inferior portions. Frontal (coronal) section passes vertically thru the body – Divides the body into anterior and posterior sections. Oblique section passes thru the body at an angle  15 Body Cavities Body cavities are spaces within the body that house the internal organs (viscera); the body is divided into two major closed cavities: Dorsal and Ventral. – Note: Open cavities open to the exterior and include the oral cavity, nasal cavity, orbital (eye) cavities, and middle ear cavities. Dorsal Body Cavity Dorsal Body Cavity contains 2 subdivisions 1. Cranial cavity encases the brain 2. Vertebral cavity (canal) encloses the spinal cord. Ventral Body Cavity Ventral Body Cavity contains 2 subdivisions: Thoracic and Abdominopelvic cavities (separated by the diaphragm) 1. Thoracic cavity is subdivided into 2 pleural cavities and the pericardial cavity (located within the mediastinum) Each pleural cavity contains a lung Pericardial cavity surrounds the heart Mediastinum: region between the sternum, vertebrae and lungs. – Contains the esophagus, trachea, blood vessels, thymus and pericardial cavity 2. Abdominopelvic cavity contains 2 subdivisions separated by imaginary line running from symphysis pubis to sacral promontory 1. Abdominal cavity contains most of the viscera. Ex: stomach, small intestine, spleen, and liver etc.) 2. Pelvic cavity contains the urinary bladder, portions of the large intestine and internal reproductive organs. Dorsal cavity  16 Serous Membranes Serous membranes line the ventral cavities and organs. – Produce serous fluid (lubricant) to reduce friction. Serous membranes are classified based on their location – Visceral (organ) serous membranes cover the surfaces of organs – Parietal (wall) serous membranes line the cavity walls Serous Membranes of Thoracic Cavity Serous membranes of the thoracic cavity 1. Pericardial cavity surrounds the heart and contains pericardial fluid – Visceral pericardium covers the heart – Parietal pericardium lines the inner surface of the pericardial sac (pericardium) – Pericarditis is inflammation of the pericardium 2. Pleural cavity surrounds each lung and contains pleural fluid – Visceral pleura covers each lung – Parietal pleura lines the inner surface of the thoracic wall and diaphragm – Pleurisy is inflammation of the pleura. Serous Membranes of the Abdominal Cavity Peritoneum: Serous membrane that lines the wall and many organs of the abdominal cavity. – Parietal peritoneum: Lines the wall of the abdominal cavity – Visceral peritoneum: Covers the organs. – Peritoneal cavity: Space between the parietal and visceral peritoneum – Ascites: Distention of the peritoneal cavity due to accumulation of several liters of serous fluid. Retroperitoneal Retroperitoneal refers to abdominopelvic organs that lie outside of the parietal peritoneum – Includes: Kidneys, adrenal glands, pancreas, urinary bladder and parts of the intestine (duodenum, ascending and descending colon).  17 Body Tissues – Covered in great detail in Anatomy – Brief overview in Physiology Four types of primary tissues: Muscle, epithelial, connective, nervous Medical Imaging Procedures 1. Conventional Radiography (X-Rays) 2. Magnetic Resonance Imaging (MRI) 3. Computed Tomography (CT) 4. Ultrasound X-rays can locate metal objects your 5. Positron Emission Tomography (PET) child has swallowed, such as this jack. 6. Digital Subtraction Angiography (DSA). Conventional Radiology (CR, x-rays) Conventional Radiology (CR or x-rays): Beam of x-rays pass through the body and strike a photographic plate – image dependent on different absorption properties of tissues to the x- rays. – Resistance to x-ray penetration is called radiodensity and increases in the following sequence: air, fat, blood, liver, muscle, bone – At low doses, x-rays can be used to examine soft tissue such as the breast (mammography) and for determining bone density (bone densitometry). Use of a contrast medium – A contrast medium (ex: Barium) can be used to make hollow or fluid-filled structures visible in radiographs. Used to image blood vessels (angiography), the urinary system (intravenous urography), and the gastrointestinal tract (barium contrast x-rays)  18 Magnetic Resonance Imaging (MRI) Magnetic Resonance Imaging (MRI) Uses a magnetic field and radio waves to produce image – no radiation. – Protons line up along the magnetic field; pulse of radio waves are absorbed by protons and when released this pattern of energy is detected and used to construct images. – Shows fine details of soft tissues but is not so good for showing the fine details of bone. – Not to be used on patients with certain metals in their bodies (pace maker, defibrillator, cochlear implants, etc.) Key: #1 = Abdominal Aorta #2 = Inferior Vena Cava #3 = Left Crus of Diaphragm #4 = Liver #5 = Right Crus of Diaphragm #6 = Spleen #7 = Stomach Computed Tomography (CT) Computed Tomography or Computed Axial Tomography (CAT): X-ray beam traces an arc at multiple angles around a section of the body – Image shown on a video monitor – 3D images can be constructed – Visualizes soft tissues and organs with greater detail than conventional radiographs Used to screen for cancers and coronary artery disease. Ultrasound Scanning Ultrasound scanning: High-frequency sound waves reflect off body tissues and are detected by the same instrument. – An echogram (picture) is assembled from the pattern of echoes – Image which may be still or moving is called a sonogram – visualized on a video monitor – Safe, noninvasive, painless, and uses no dyes. Positron Emission Tomography (PET) Positron Emission Tomography (PET) – Radioactive isotopes are injected and later detected by gamma-ray cameras and interpreted by computers  19 – Provides information on structure and function (metabolism of brain, heart, etc). Digital Subtraction Angiography (DSA) Digital Subtraction Angiography (DSA) – A computer compared an x-ray image of a region of the body before and after a contrast dye has been introduced. Computer “subtracts” details common to both images. – Used to monitor blood blow through specific organs, such as the brain, heart, lungs or kidneys. Basic Steps of Scientific Method Scientific method is a way to ask and answer questions by making observations and doing experiments. 1. Observation: This can be what you see in nature, your experiences, Question? Question? thoughts, or from what you have read. 2. Question: Form a question about how a physiological event happens. 3. Hypothesis: Form a hypotheses which is an informed educated (logical) guess as to how that event happens based on observations Collect/Analyze Data and/or initial data collection. 4. Experiment: Design an experiment to test the hypothesis. Model Model 5. Collect and Analyze the Data: Collect data from experiment and critically analyze. 6. Conclusion: Based on the data, state whether the evidence supports or rejects the hypothesis. 7. Replicate: Repeat the experiment to ensure that the results were not an unusual one-time event. 8. Model: When the data support a hypothesis in multiple experiments, the hypothesis can become a working model. 9. Theory: A model with substantial evidence from multiple investigators supporting it.  20 Independent vs Dependent Variables Experiments are designed to remove or alter a single variable at a time that the investigator thinks is an essential part of the phenomenon in order to test the hypothesis. A variable is any factor that can be changed or measured in an experiment. Independent variable: Controlled by the experimenter, it is the variable that is altered or removed. Dependent variable: The response to the change due to the independent variable. – Dependent variables are the measurements collected in the experiment. – The value of the dependent variable literally “depends upon” the value of the independent variable. Example: Increases in dietary intake of saturated fatty acids (independent variable) increases levels of serum cholesterol (dependent variable), while decreases in saturated fatty acid intake reduces serum cholesterol levels. Experimental Control Experimental control: A control group is a duplicate of the experimental group in every respect except that the independent variable is not changed. – The purpose of the control is to ensure that any observed changes are due to the manipulated variable and not to changes in some other variable. Example Experiment: A biologist notices (observation) that birds at a feeder seem to eat more in the winter than in the summer. She generates a hypothesis that cold temperatures cause birds to increase their food intake. To test her hypothesis, she designs an experiment in which she keeps birds at different temperatures and monitors how much food they eat. In her experiment, temperature, the manipulated element, is the independent variable. Food intake, which is hypothesized to be dependent on temperature, becomes the dependent variable. The control group would be a set of birds maintained at a warm summer temperature but otherwise treated exactly like the birds held at cold temperatures. The purpose of the control is to ensure that any observed changes are due to the manipulated variable and not to changes in some other variable. For example, suppose that in the bird-feeding experiment food intake increased after the investigator changed to a different food. Unless she had a control group that was also fed the new food, the investigator could not determine whether the increased food intake was due to temperature or to the fact that the new food was more palatable. During an experiment, the investigator carefully collects information, or data, about the effect that the manipulated (independent) variable has on the observed (dependent) variable. Variability and Types of Studies Variability: How spread out or closely clustered a set of data is. Human populations have a tremendous genetic and environmental variability. In order to show significant differences between experimental and control groups an investigator needs to include a large number of similar subjects.  21 Crossover Study: Each subject participates in both the experimental AND control groups. – Each individual’s response to the treatment can be compared with his or her own control values. – Effective when there is a wide variability within a population. – Note: Wash-out period is the time in the clinical study during which subjects receive no treatment for the indication understudy and the effects of a previous treatment are eliminated (or assumed to be eliminated) Examples of the flow of subjects through a Crossover Study Blind Study: Subjects do not know whether they are receiving the treatment or the placebo. – Problems can happen if the researchers assessing the subjects know which type of treatment each subject is receiving. This can be prevented by a double-blind study. Double-blind Studies: Both the subjects and researcher do not know who is receiving the treatment or placebo. A third party, not involved in the experiment, is the only one who knows which group is receiving the experimental treatment and which group is receiving the control treatment.  22 Double-blind crossover study: The control group is the first half of the experiment becomes the experimental group in the second half, and vice versa, but no one involved (except the third party) knows who is taking the active treatment. Psychological Aspects: Placebo vs. Nocebo Placebo (Latin for "I shall please"): An inactive or medically inert treatment or substance (such as a starch tablet) for a disease or other medical condition intended to deceive the recipient and have no medical effect. – Placebo Effect: Patient taking the placebo thinks they are taking the actual medication and due to the power of the mind, there is a positive change in health not attributable to medication or treatment. Nocebo (Latin for "I will harm"): An inert substance or form of therapy that should be ineffective but which causes symptoms of ill health. – Nocebo effect is where you warn recipient that a drug they are taking may have specific adverse side effects, those people will report a higher incidence of the side effects than a similar group of people who were not warned. – It is an ill effect caused by the suggestion or belief that something is harmful. It is the evil twin of the placebo and works the same way but depends on the perception of the patient. Scientific Method Videos: In our Canvas site you will find videos on various aspects of the scientific method including placebo and nocebo effects.