CHARACTERISTICS OF LIFE



INTRODUCTION TO HUMAN PHYSIOLOGY

HUMAN PHYSIOLOGY is the study of the biological function of the human body all levels of organizations. It also considers what role man plays in the relation to the other organisms and world in which he lives.

1. It is the study of the anatomical structure and life processes that occur inside the body at all levels or organization: cells, tissues, organs, organ systems, and the interaction between each of these.

2. It is the study of “cause and effect” with an emphasis on the mechanisms of “how does this work.”

• A generalized example would be “what causes the heart to pump and what is its effect on the circulatory system.”

• Or more specifically we could say “what causes the pancreas to secrete insulin and what effect does this have on blood glucose levels.”

3. It is based upon careful observation and experimentation from which inferences are made. The data collected from these experiments and observations are always open to interpretation and change.

_ So, how is this study carried out? What general method do we apply to the study of the human body? How are ideas about the body verified? What is the scientific method, and what are its limits?

SCIENCE

So now that we know a little about human biology. How do we go about studying it? Well....we use science. But WHAT IS SCIENCE?

Before we can talk about human biology, we must first understand that it is a science. We also need to understand just how science operates.

_ This is important because usually the general public (you are separate from them now of course) does not understand how scientists operate. Usually one thinks of the proverbial bald guy in white lab coat, with taped glasses, and a bunch of test tubes and pens sticking out of his pocket…and of course this is a major misconception.

1. Science = is not easily defined, but here’s a try. a. It is the observation, identification, description, experimental investigation, and theoretical explanation of the natural world/phenomena. b. Such activities restricted to a class of natural phenomena. c. Such activities applied to an object of inquiry or study.

Methodological activity, discipline, or study. An activity that appears to require study and method.

Knowledge, especially that gained through experience.

Is the ongoing process of exploring and discovering the way nature works. We may never know everything there is to know about life and the universe, but we can continue to expand our understanding by making observations, asking questions, & seeking answers.

1. Science is our attempt to understand the objects and events we experience in nature and the means by which we do so. People develop understanding about things they experience by asking question and finding answers. What is life? Why does my heart beat? Why does it pump blood? What causes diseases such as Herpes, Diabetes, or AIDS? Why won’t my car start? In attempting to find answers to questions such as these, one is actually doing science. In biology most of the questions involve living things. Finding answers to them involves you in doing biology… the science of life. (adapted from Lawson, 1999).

Characteristics of Science:

1. It is guided by natural law

– The pursuit of scientific knowledge must be guided by the physical and chemical laws that govern the universe (state of existence).

2. It has to be explained by referencing these natural laws.

– Scientific knowledge must explain what is observed by reference in nature. We cannot invoke the explanations based on supernatural deities (ghosts, angels, gremlins, fairies, etc.) miracles, or magic.

– Science must only rely on observable, testable evidence which must either support or not support hypotheses. Extraordinary claims require extraordinary evidence.

3. Science is testable against the observable world.

– We must be able to make observations in the real world, directly or indirectly, ask questions, or form and test hypotheses = a tentative, causal explanation/answer for an observation or phenomenon.

_ We use observations and/or tests to answer questions about the natural world.

– Science relies on observable, testable evidence, which must either support or not support hypotheses.

4. Its conclusions are tentative, that is, are not necessarily the final word.

_ If we draw a conclusion based on some observation or test on some event, we must be ready always to discard or to modify our conclusion, if further observations falsify it.

_ Can’t be scientific if you start with a conclusion and refuse to change it regardless of the evidence developed during the course of the investigation.

5. It is falsifiable

4. You must be able to disprove any statement. If there is no possibility that the statement cannot be correct, then it isn’t science. What this means is that science will seek out errors and correct them. Unlike other philosophies, it’s a self-correcting system. We add to and take away information on a daily basis depending on new discoveries and new evidence.

6. It relies on evidence that is testable (from observations and experimentations). If we cannot make repeated observations or experiments to gather information, then it is outside the realm of science (e.g. UFO’s, haunted houses, etc.).

7. One cannot ever prove things true or false in science. Probability plays a role, as do critical values.

8. Correlation does not imply Causation. Just because the price of beans in China goes up when the Dalllas Cowboys football team loses does NOT mean the loss caused the bean prices to go up (

Important Criteria for Determining… What is Science?: The following “rules” are also very important in determining what is and what isn’t science. If a claim/fact or study does not follow these “rules,” then it isn’t science.

1. Science is logical & rational

2. Science makes well-defined claims

3. Scientific hypotheses are falsifiable, as in testable.

4. Scientific experiments are repeatable

5. Science requires that claims be examined by peers in the same field

6. Science views unexplained gaps in theories with suspicion

7. Science requires evidence & caution in examining it

8. Science requires objectivity (open-mind)

9. Science does not accept coincidence as proof

10. Science doe not accept anecdotal evidence as proof

11. Science insists that extraordinary claims require extraordinary evidence

12. Absence of evidence is not evidence of absence

THE SCIENTIFIC METHOD

1. Everything we are going to study this semester from cells to reproduction is based on careful scientific investigation as produced by what is called the scientific method. It is not infallible, but is in fact, designed to be open to change and modification.

2. The Scientific Method is a method of collecting evidence through observation, questioning, hypothesis formation, and hypothesis testing (often through experimentation). One then examines the results and forms a conclusion and repeats the process, if necessary. It is therefore a step by step approach to investigating the natural world.

– All scientific investigation begins with an observation of the natural world. This also includes examining any previous info. that is published in the scientific literature.

– On the basis of this observation, the scientist asks a question.

– The scientist then proposes a causal explanation to the question (aka hypothesis). The hypothesis is tentative and may be changed based on the outcome of rigorous testing.

– Hypothesis testing is done by making further observations or conducting experiments.

– The results of such testing either confirm or contradict the hypothesis.

– Conclusions are then reached based on the results.

– If it is contradicted, the hypothesis is discarded and a new one is generated.

Example: One could use the scientific method to test the effects of exercise of the resting heart rate on teenagers.

Example: You use the scientific method in everyday life; (e.g. to figure out why your flashlight won’t work, car won't start etc.)

THE SCIENTIFIC METHOD AND EXPERIMENTAL DESIGN:

1. Observation: An artificial sweetener is known to cause some cells to divide rapidly?

2. Question: Will artificial sweetener, given to rats, cause them to have bladder cancer?

3. Hypothesis: Rats given artificial sweetener will develop bladder cancer (e.g. the sweetner is the cause)

4. Experiment: Two groups (one with sweetener = treatment group; one without = control group)

Define Dependent Variable:

Define the Independent Variable:

Define Controls:

Number of Replicates:

Sample Size:

Define Biases.

Results & Conclusions:

(Presentation/Publication/Peer-Review)

5. New hypothesis?

ALTERNATE ROUTES TO DISCOVERY:

Although many discoveries have followed just such a series of steps, many others have not. Most great scientific achievements are the result of creative genius, diligence, and many long hours of dedicated research. However, some revolutionary discoveries are simply the result of accident or flashes of insight, as in the following examples:

Some discoveries have been made by accident: Alexander Fleming in 1928, while trying to discover a cure for the flu left some open petri dishes by an open window. He discovered a green mold growing on them. Thinking his expt. was ruined he noticed the bacteria on the dish were killed by this green mold. Led to the discovery of penicillin (after the name of the mold Peniclliun notatum).

Some by pure observation. Behavior of hyenas and lions.

Flashes of Insight: Sir Isaac Newton had an apple fall on his head which sparked a connection that had never been made before---that the force, which pulled the apple to the ground, is also responsible for helping to hold the moon and planets together in their places = gravity. He eventually supported his supposition (hypothesis) mathematically. People used to think that the forces on heavenly bodies were different from those affecting earthly ones.

Yet, even though a great deal of scientific inquiry does not follow these steps, “the scientific method” forms the general ground rules that scientists use to formulate explanations (hypotheses) for how nature works, to test the accuracy of those explanations, and to report the finings so that others can benefit from the new information.

SOME COMMON MISCONCEPTIONS:

In general a fact in science can mean 2 things (1) an observation or (2) a statement concerning a direct observation of nature that is so consistently replicated (repeated) that virtually no doubt exists as to its validity.

4. for example. Mitochondria manufacture ATP; the heart pumps blood; red blood cells carry oxygen bound to hemoglobin.

There’s also a HUGE, I mean HUGE difference between a theory & hypothesis in scientific lingo vs. the general public.

There’s also a HUGE, I mean HUGE difference between a theory & hypothesis in scientific lingo vs. the general public.

Scientific theories are (1) collections of statements (tested hypotheses) about the natural world which can consistently explain naturally occurring phenomena and predict new events. (2) They are built up logically from testable observations and hypotheses. (3) They are based on numerous facts and experiments that have been tested large numbers of times and yielded statistically, consistent results (withstood the test of time). As such, they are very powerful scientific statements. (4) They serve as a logical framework by which these hypotheses can be interrelated and provide the basis for predictions that may as yet be untested. For example many theories have great predictive power, i.e., one can formulate new hypotheses for testing in a broad framework for investigating the natural world in a number of areas. (e.g cell theory, atomic theory, photosynthetic theory, gravitational theory, evolutionary theory, wave theory of light etc.). (5) Theories are the goals of science.

This is vastly different from what the public thinks when they hear the word “theory.” In general when most people hear this word they think of a “best guess” or “idea”. This is a valid definition, but very different from the scientific definition of the word. Because scientific theories are backed by repeated tests and numerous observations (literally thousands, even millions) they are not mere speculations or guesses, as the term is sometimes popularly used. Yet, in science even the most trusted theories must withstand the challenge of further experimentation and observation. This is how scientific progress is made, by correcting mistakes/ finding errors/ clarifying inconsistencies and adding to our collective body of knowledge. Cool huh!

When you hear on the TV show CSI: Las Vegas or Miami, “Can you prove your theory?” They are incorrect on two counts. Can you explain why?

Laws are generalizations that describe phenomena; whereas, theories explain phenomena. For example, the laws of thermodynamics describe what will happen under certain circumstances; thermodynamics theories explain why these events occur.  Laws, like facts and theories, can change with better data. But theories do not develop into laws with the accumulation of evidence. Rather, theories are the goal of science."

2. Example:

5. The first law of thermodynamics states that energy can neither be created nor destroyed. (Just changes form).

6. The second law of thermodynamics states that without the input of energy, entropy is ever increasing in the universe.

7. Thermodynamic theories explain how and why these occur.

CORRELATION VS. CAUSATION

LIMITS OF SCIENCE:

1. Neither the body of scientific information nor the methods of science can answer certain questions.

3. Science cannot determine whether God exists, what is moral or immoral, what is ethical or unethical. For example, science cannot say it is immoral to destroy vast rain forests or abort a human fetus. These are all areas that depend on personal experience and value judgment.

2. However, science can identify changes and predict consequences, and humans can form personal judgments about those consequences.

4. Example: What will happen if the rain forests are destroyed?

5. Example: What are the physiological and psychological consequences of an abortion?

3. Because science deals only with repeatable phenomena, brief, unpredictable, and unrepeated events (such as “miracles” and “ghosts”) cannot be investigated well by science. They exist in the realm of “pseudo-science.”

6. Fantastic claims like these (or UFO’s or even Bigfoot) are extraordinary, and as such they would require extraordinary evidence for their existence? (Are photographs and personal testimony enough for you)?

1. A WORD about Believing vs. Knowing.

Critical Thinking Rules & Science

When analyzing an article, claim, advertisement, issue, or fact, you may find it useful to employ these rules:

1. Gather complete information about the claim/fact/observation. Is it plausible?

2. Understand and define all terms about the claim/fact/observation.

3. Question the methods by which data and information were derived?

8. Were the facts derived from experiments?

9. Were the experiments well executed?

10. Did the experiment include a control group and an experimental group?

11. Did the experiment include a sufficient number of subjects or replicates?

12. Has the experiment been repeated?

4. Question the conclusions:

13. Are the conclusions appropriate?

14. Was there enough information on which to base the conclusions?

5. Uncover assumptions and biases (= any influence or action that distorts the findings or slants them away from what is actually true or expected):

Are there any biases? If so what are they?

Was the experimental design biased? How so?

What could/should have been done differently?

Are there underlying assumptions that affect the conclusions?

6. Question the source of the information and/or the author:

Is the source reliable? Is he/she stating opinion or fact? Are the facts valid/verifiable?

Is the source an expert or supposed expert? How do you know?

What are the qualifications/experiences of the supposed expert? Do they have valid credentials from a recognized, accredited academic institution?

What questions would you have for the author? Did he/she have an agenda? Something to prove?

Is there anything you would consider unethical or dangerous?

7. Check the references/literature cited.

10. Are the references valid and verifiable? Are they from peer-reviewed journals?

If web resources are cited, are they accurate and credible?

8. Examine the big picture. Does it make sense in the grand scheme of things?

9. Look for multiple causes and effects. (Are there other things that could explain the results?)

10. Understand your own biases and values. How could your personal values affect your view of the issue, fact, statement, or conclusions?

PSEUDOSCIENCE

Pseudoscience fails to meet the criteria met by science generally (including the scientific method), and can be identified by a combination of these characteristics by:

* asserting claims, hypotheses, or theories without first verifying them in experiments.

* asserting claims which cannot be verified.

* asserting claims without supporting experimental evidence.

* asserting claims which contradict experimentally established results.

* failing to provide an experimental possibility of reproducible results.

* claiming a theory predicts something that it does not.

* claiming a theory predicts something that it has not been shown to predict.

* discrediting one theory based on rhetoric and no factual evidence.

* discrediting an established explanation with no factual evidence for the alternative or not having an alternative explanation

* asserting claims that violate falsifiability.

* violating Occam's Razor (the principle of choosing the explanation that requires the fewest additional assumptions when multiple viable explanations are possible); the more egregious the violation, the more likely.

Pseudoscience is distinguishable from revelation, theology or spirituality in that it claims to offer insight into the physical world by "scientific" means. Systems of thought that rely upon "divine" or "inspired" knowledge are not considered pseudoscience if they do not claim to be scientific or to overturn well-established science. There are also bodies of practical knowledge that are not claimed to be scientific. These are not pseudoscience.

Pseudoscience is also distinguishable from misleading statements in some Popular science, where commonly held beliefs are thought to meet the criteria of science, but often don't. The issue is muddled, however, because it is believed that "pop" science blurs the divide between science and pseudoscience among the general public.

Examples of fields of endeavor that many consider – to varying extents – pseudoscientific include Cold fusion, Götaland theory, pseudoarchaeology, Gene Ray's Time Cube, astrology, homeopathy, and creationism. Pseudoscientific science and medical practices are often quite popular. Medical pseudosciences even sometimes show notable therapeutic benefits, possibly due to the placebo effect or observer bias.

Many pseudosciences are associated with the New Age movement and there is a tendency to improperly associate all practices of the "New Age" with pseudoscience.

Certain "watchdog" groups, such as CSICOP, have released statements expressing concern about the apparent growing popularity of pseudoscience, especially when it applies to scientific fields that are intended to save people's lives. A number of self-proclaimed alternative medicine treatments have been designated pseudoscience by critics, largely because some of these methods inspire false hope in terminally ill patients, and end up costing large amounts of money without actually providing any real benefit, treatment, or cure for various ailments.

CHARACTERISTICS OF LIFE

In biology we study life and we use science to do so….But What is Life? What do we mean by life? What makes something alive? What makes something not alive? Can we distinguish the difference? What is the difference between something that is alive and something that is not alive?

Objective: determine the difference between life and non-life. How do you know if something is alive? Is there one single characteristic that distinguishes life from non-life? What are the characteristics that make something alive? Let’s begin our investigation here.

Introduction:

7. To study physiology, the function of cells, tissues, organs and organisms, they have to be alive.

8. We can't study the physiology of something if it's dead, right?

9. So tell me what makes something alive?

10. Ask a student to define "LIFE."

1. Rather than defining life, biologists describe it, usually as a list of activities and properties that characterize all living things.

Characteristics of Life:

Life is a collection of characteristics and no one single characteristic can separate life from non-life. Life exists on a continuum of non-living to living.

So rather than defining life, biologists describe it, usually as a list of activities and properties that characterize all living things.

Life is defined not by definition, but as a series of attributes seen in living things...

1. All living things follow the tenets of cell theory

14. All living things are made of 1 or more cells (and the products of cells).

15. All cells come from preexisting cells

16. Cell is the smallest unit of life that contains all its characteristics

17. Even the smallest, simplest cells are very complex.

2. Living things acquire and use energy & produce wastes = (respiration, digestion, & excretion)

18. Transform matter and energy to live.

19. Organisms maintain a high degree of organization with the input of energy

Eventually, what form of energy does all our food end up as?

3. Living things reproduce, grow, and develop

20. Organisms produce offspring similar to themselves that are capable of increasing in size and changing over time.

21. They transmit their characteristics to offspring by heredity/genetically = DNA.

4. Living things evolve

22. Inherited changes take place over many generations; permitting organisms to change as the environment changes

23. Natural Selection and Evolution

24. acclimatization vs. adaptation.

5. Living things respond to stimuli (react to light, pressure, temp, humidity, salinity, pH, etc.)

25. Living systems detect and respond to the internal and external environment

6. Living things maintain a state of homeostasis (maintain boundaries): stabilizing conditions inside the organism resist fluctuations in the environment

26. Example: T regulation

7. All living things are made of the same kinds of atoms & molecules.

27. Underlies the relatedness of all forms of life.

28. The same kinds of molecules (proteins, carbohydrates, lipids, & nucleic acids = DNA & RNA) are found in all forms of life from the smallest bacterium to the largest plant = sequoia tree, from the flea to the human

29. All composed of organic compounds = contain C (& H) as the basis for these molecules.

What can't we live without?

The ultimate goal of all body systems is to maintain life in order to reproduce. Yep, biology is nothing more than sex....getting those all important genes to the next generation. However, life is extraordinarily fragile & has several primary needs.

30. The following must be present in the correct amounts. Excesses or deficits may be equally harmful.

31. The following list illustrates what humans need to survive.

1. Osmoregulation and Water Balance (60-80% of body weight) — the universal solvent

32. serves as a medium for chemical reactions

33. serves as a fluid base for body secretions & excretions

2. Nutrient Acquistion/Aquirement and Waste Elimination.

34. provide fuel for cellular fxn (movement, making things, and tearing things down, transport, cell division & cell building (maintenance & growth)

3. Oxygen

35. The chemical reactions, that release energy from food, require oxygen as part of the reaction. Without it, we could not release the energy contained in food…we couldn’t make the energy currency molecule of cells…ATP.

4. Maintenance of Body Temperature/Thermoregulation.

36. If chemical reactions are to proceed at life-sustaining rates, Body Temp must be maintained at 37(C (98(C).

37. If too low, metabolic reactions stop. If too high, chemical reactions proceed so rapidly that proteins lose their shape and stop functioning.

38. At either extreme, death occurs.

5. Atmospheric Pressure

39. Breathing, namely exchanging oxygen & carbon dioxide in the lungs, depends on appropriate atmospheric pressure = the force exerted on the body by the weight of air.

40. Altitude

Cell Theory: Smallest unit that has all the characteristics of life, all cells come from pre-existing cells, all organisms are composed of one or more cells...

Human Physiology also requires an extensive knowledge of other sciences, especially anatomy, chemistry, and physics.

41. Anatomy is the study of structure of organisms from the cellular level on up to the entire organism

42. Physiology: concerns the functioning of the body's structural machinery, that is, how the parts of the body work and carry out their life-sustaining activities. When all is said and done, physiology is explainable only in terms of the underlying anatomy.

43. Chemistry is the study of chemical reactions. We’ll go into more detail later.

44. Physic is the study of the physical laws that govern our universe, which humans are subject.

BIOLOGICAL ORGANIZATION:

The human body is formed from smaller structures and these smaller structures combine to make larger structures which allow the body to operate

1. Everything in the universe including living organisms is composed of matter. Matter is anything that occupies space, has mass, and can assume the form of either a solid, liquid, or a gas.

2. We currently organize the matter of the universe into elements. An element is a substance that cannot be broken down into simpler substances by chemical reactions.

• Each block in the periodic table represents an element which is a collection of atoms of the same kind

• There are 92 elements that occur naturally, although scientists have invented dozens more.

• Example: oxygen, silicon, aluminum, iron, nitrogen

• Referred to by their chemical symbols O, Al, Fe, N, etc.

3. Elements are composed of atoms of the same type. An atom is the smallest indivisible unit of matter composed of electrons, protons, neutrons.

• Lose or Gain electrons to obtain stability.

4. If two or more elements combine, it results in molecule of that substance:

• H2, O2, etc.

5. When 2 or more different elements bind together, they form molecules of a compound.

• H2O, CH4, NaCl.

• Organic compounds contain carbon (C6H12O6)

Texts define organic compounds as having C, except for CO, CO2, & CO3. (Diamond & graphite are classified as organic substances—they’re just carbon). I would think it’s better to define organic compounds as having C & H (“like pure cane sugar”), so there are no exceptions.

• Inorganic if it doesn't have C (NaCl)

• Body contains both organic & inorganic substances that are necessary for survival.

Molecules and Compounds combine to form cells:

1. The human body is a multicellular (multi, many; cellular, consisting of cells) system that consists of trillions of living cells.

45. Cells are the smallest living units that maintain most or all the characteristics of life. (We will examine these later).

46. There are hundreds of different types of cells in the human body. Many are highly specialized in structure and function: (neuron vs. sperm cell).

2. A group/association of specialized cells that carry out a specific function are called tissues: There are 4 basic tissue types:

47. connective tissue: blood (liquid tissue), bone, CT proper (hold organs together and forms tendons and ligaments), and cartilage

48. nervous tissue: contains cells specialized to conduct and carry impulses (info) throughout the body = neurons.

49. muscle tissue: smooth, cardiac, and skeletal.

50. epithelial tissue: covers and protects body surfaces, and cavities: (squamous, cuboidal, columnar) Buccal, Anal, Integumentary, etc.

3. Groups of 2 or more tissues working together to accomplish a specific function are called organs. (Usually larger structures)

51. Heart is a combination of the above tissues that performs a specific function: the pumping of the blood

52. Stomach serves as a temporary food holding tank, which also begins digestion. It, too, is a combination of the above tissues.

4. Several organs with closely coordinated functions form an organ system.

53. Example: the nervous system contains the brain, spinal cord, & neurons.

54. Example: the digestive system contains the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. The liver and pancreas are considered accessory organs.

5. Finally, groups of organ systems may combine to form an individual organism which represents the sum total of all structural levels working in unison to promote life.

Taxonomic Hierarchy of Humans: We are animals (specifically primates) and biologists classify us (along with all the other known organisms of our planet) in neat distinct categories, each of which shares common characteristics. For example, humans are classified as primates (and they with us), because we share many characteristics in common with our primate brothers (as we do with all of our mammal cousins). What follows is how biologists classify humans.

Kingdom Animalia

Phylum Chordata

Subphylum Vertebrata

Class Mammalia

Order Primates

Suborder Anthropoidea

Infraorder Catarrhini

Superfamily Hominidae (The family of man, includes about 8-10 species of humans; all but us are extinct)

Subfamily Homininae

Genus Homo

Species Homo sapiens (Homo - man; sapiens - wise) Does irony define the human condition?

THEMES IN HUMAN PHYSIOLOGY

One key to understanding human biology and physiology is the ability to recognize patterns. The amount of information can seem overwhelming at times, but once you realize that many specific processes are variations on a few themes, learning physiology will be easier. Themes in human biology include homeostasis, integration of body systems, cell-to-cell communication, information transfer across the cell membrane, energy use, and the law of mass balance.

Integration: all of the body systems are coordinated to work with each other. It’s a cause and effect relationship. When something happens in one organ system it causes something else to happen in another organ system. Integration requires that the cells of the body communicate with one another rapidly and efficiently. Integration and coordination of responses take place in the brain and spinal cord and in endocrine and immune cells.

Cell-to-Cell Communication: A variety of sensing mechanisms monitor changes in the internal and external environments. These sensors which range from single cells to highly developed sense organs relay information to and from each other about environmental changes using two mechanisms.

55. chemical signals (endocrine system)

56. electrical signals (nervous system)

57. Information is sent between distant cells through the circulatory or lymphatic or nervous system.

Information transfer across the cell membrane: communication between the internal environment of the cells and the ECF requires information transfer across the cell membrane. Some molecules can pass through the membrane others remain outside and simply pass information through the membrane.

Energy Use: Living processes require continuous input of energy. Where does it come from? How is it used? In the body energy is used for synthesis and breakdown of molecules for cellular division, growth, & maintenance, to transport molecules, and to create movement.

Law of Mass Balance: This law says that if the amount of a substance in the body remains constant, then gain must be offset by an equal loss. For example, in order to maintain constant body temperature, heat gain from the external environment and from metabolism must be offset by heat loss to the external environment.

58. Most substances enter the body from the outside environment, although some, like heat, can be produced internally. The major routes of loss from the body are the urinary system, digestive system, respiratory system, & integumentary system.

59. Mass balance is monitored by sensors (receptors) that detect changes in the internal & external environments. When mass balance is disturbed, physiological & behavioral homeostatic reflexes bring the body back into balance.

60. Law of Mass Balance equation:

Total amount of substance “x” in the body = intake + production - output.

61. Mass balance is a fx of time. For example, a person is given an intravenous infusion of glucose containing 5 grams of glucose per liter. If the infusion is given at a rate of 2 milliliters per minute, the mass flow for glucose would be: 50 g GLU/1000 mL soln x 2 mL soln/min = 0.1 g GLU/min.

62. Substances, whose concentration, are maintained through mass balance include oxygen and carbon dioxide, water, salts, and hydrogen ions. In addition our bodies have regulatory mechanisms to keep temperature and energy stores within an acceptable range.

Homeostasis:

1. Although the human body as a whole is adapted to cope with a variable external environment, most of the individual cells of the body are much less tolerant of change. Only a small minority of cells in a multicellular organism are actually in direct contact with the external environment. The vast majority of the cells are sheltered from the outside world by the buffer zone of the extracellular fluid, the body fluid that surrounds the cells.

2. This internal environment serves as the interface between the external environment and the cells. When conditions outside the body change, the changes are reflected in the composition of the extracellular fluid, which in turn affects the cells. But our cells are not very tolerant of changes in their surroundings. As a result, a variety of mechanisms have evolved that maintain the composition of the ECF within a narrow range of values. Any change in the internal environment is met by a response that restores the normal condition.

3. The body’s coordinated response in order to maintain internal stability is the process known as homeostasis.

4. Homeostasis and the regulation of the internal environment are central precepts of physiology and create an underlying theme. Failure to maintain homeostasis disrupts normal function.

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