The Inside and Outside the Body

Author(s): Murray Jensen*

University of Minnesota

Courses: Anatomy-PhysiologyAnatomy-Physiology

Keywords: structure Anatomy barriers

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The Inside and Outside the Body activity helps students develop a conceptual understanding of anatomical barriers such as skin and mucus membranes that separate internal cells and fluids from the external environment. This short exercise prepares students for lessons in both anatomy and physiology and reflects recommendations from policy documents that suggest teaching core concepts. Understanding processes such as absorption, gradients and flow, and body defenses relies on the core concept of anatomical barriers. Instructors can use the concepts taught in this activity in subsequent discussions of topics such as immune tolerance of the fetus, the devastating impact of burns, and the sites of gas exchange.


Jensen M. 2019. The Inside and Outside the Body. CourseSource. https://doi.org/10.24918/cs.2019.27

Lesson Learning Goals

  • Students will understand the role of anatomical barriers, such as skin and mucus membranes, in separating the inside and outside of the body. 
  • Students will be able to apply the concept of inside and outside the body to broader physiological concepts such as protection, gradients and flow, and absorption.
  • From Human Anatomy and Physiology Society (HAPS) Learning Objectives / Learning Goals (1): “Recognize and explain the interrelationships within and between anatomical and physiological systems of the human body (Fundamental Content & Process Goals: #5)   ‚Äč

Lesson Learning Objectives

Students will be able to:
  • correctly identify when a substance (e.g. fetus, bacteria, toxins) is inside or outside the body.
  • recognize the point at which a substance transitions from the inside to the outside of the body and vice versa.
  • apply the concept of inside and outside the body to both normal events, such as the movement of oxygen from the alveolus to the blood, and abnormal events, such as the presence of blood in the urine.

Article Context

Article Type
Course Level
Bloom's Cognitive Level
Vision and Change Core Competencies
Vision and Change Core Concepts
Class Type
Class Size
Key Scientific Process Skills
Pedagogical Approaches
Principles of How People Learn
Assessment Type


Textbooks in human anatomy and physiology are full of thousands of facts and details. For example, even the most introductory Anatomy and Physiology textbooks expect students to learn at least 150 bones (such as the occipital bone) and bone markings (such as the inferior nuchal line). The central question facing every anatomy and physiology educator is "What information should they know?" or, more specifically, "Just how important is the inferior nuchal line to a robust understanding of human anatomy?" Professional organizations such as the Human Anatomy and Physiology Society (HAPS) offer guidance by preparing endorsed collections of learning outcomes (1). One such outcome is "Identify bone markings (spines, processes, foramina, etc.) and describe their function (e.g., point of articulation, muscle tendon attachment, ligament attachment, passageway for nerves and vessels)" (Module F: Skeletal System & Articulations, Topic: Gross anatomy of bones, Learning Outcome #3). An anatomy and physiology educator could use this outcome to justify teaching the inferior nuchal line; indeed, learning outcomes documents can be used to justify "teaching everything" there is to be known. Unfortunately, "teach everything" is not useful advice for instructors faced with limited time.

Core concepts represent a different way to determine what to teach in the anatomy and physiology classroom. Core concepts, also known as cross-cutting themes, core principles, broad ideas, or even big ideas, are recommended by national policy documents such as Vision and Change, Next Generation Science Standards, and BIO2010 (2-4). Recommendations from these organizations represent a new and improved framework that can be used to organize course curriculum and make daily teaching decisions.

In human physiology, a research team has worked for over a decade to develop a validated list of core concepts (5). A sub-set of these concepts (most notably, homeostasis) have been fully "unpacked," and they have generated a concept inventory for homeostasis that can test student understanding and identify misconceptions (6). Their work, which they readily acknowledge is far from complete, is summarized in a recent monograph (7).

A validated list of core concepts in anatomy has not yet been developed, but a workshop at the 2015 HAPS Annual Meeting attempted to address this deficiency (8). In that one-hour session, 40 high school, college, and medical school educators collaboratively identified three potential core concepts: medical terminology, body spaces and cavities, and inside and outside the body. While much work remains to be done to develop a more extensive and validated list, these three preliminary core concepts can help guide curricular decisions. The third of these concepts serves as the foundation, as well as the name, of the classroom activity featured here. It might seem odd to traditional anatomy and physiology educators to exclude anatomical terms from an anatomy lesson, but this lesson is not traditional; it represents a shift away from learning anatomical details and towards developing a conceptual understanding of human anatomy.

In accordance with the learning strategy recommended by the Process Oriented Guided Inquiry Learning (POGIL) organization (9), the Inside and Outside the Body activity uses questions following a three-step learning cycle (S1.Inside and Outside the Body - Handout). First, students answer questions that require simple inspection of the model (questions 1-3). Second, students engage in questions that promote the development of a simple conceptual understanding of the subject (questions 4-5). And third, students answer questions that require application of their new conceptual understanding (questions 6-13). A short set of POGIL activities covering topics such as levels of organization and blood glucose metabolism is available on the POGIL website (10).

The Inside and Outside the Body activity requires students to think of the words inside and outside in a different way from common, everyday language. In the discipline of anatomy and physiology, an item is inside the body if it is within the barrier created by the skin and mucous membranes (e.g., blood), and is considered outside the body if it has not crossed the barrier created by the skin and mucus membranes (e.g., food within the stomach). Compare this scientific definition to everyday language (e.g., water inside a glass) and instructors can begin to empathize with the challenge that this lesson poses to students.


The target audience for this activity is high school and college students taking an introductory anatomy and physiology course.


20 - 45 minutes


None required. This activity can be used on the first day of class in almost all anatomy and physiology courses.


Experience with cooperative group learning and guided inquiry is helpful, but not necessary. An excellent resource for instructors who are new to cooperative learning is Johnson, Johnson, and Smith's Active Learning: Cooperation in the College Classroom (11).

The activity relies on a very specific approach to the terms "inside the body" and "outside the body;" thus, instructors should thoroughly review the activity prior to using it with students.



Students work in groups of two or three to accurately trace a particle of food as it travels through the alimentary canal. Using information from this introductory task, students work as a team to develop a conceptual understanding of barriers and what is inside or outside the body.


Formative assessment: During the activity (Supporting File S1- Inside and outside the body-Handout) instructors should interrupt group work to review the answers for question 5, which requires students to determine if substances (e.g., air in the lungs) are inside or outside the body. Students will not be successful in the rest of the activity unless they understand the rationale behind the answer to question 5. It is important that the instructor carefully use the word "barrier" while engaging students in the class discussion, and it is also necessary for the instructor to help students use that term and concept correctly. Instructors may elect to give a summative assessment after the activity. Suggestions for question prompts are provided in the Lesson Plan section.


By working in groups of two or three, students practice working with others and navigating group dynamics. Inclusive learning and teaching can be promoted by implementing individual accountability and positive interdependence (11). Individual accountability is most often reinforced by giving assessments, such as quizzes and exams, on an individual basis. Positive interdependence is promoted by providing each group with a single worksheet, thus encouraging them to work together and share a common resource. Instructors can learn more about promoting inclusive teaching and learning through cooperative group learning in the monograph "Active Learning: Cooperation in the College Classroom" (11).


The activity introduces the core concept of barriers, explaining how skin and mucus membranes separate the "inside" of the body from the external environment. For most students, this concept is odd (for example, food in the stomach is considered outside the body) but learnable. Students should examine the model closely to see that the skin is continuous with mucus membranes lining the urinary, respiratory, digestive, and reproductive tracts. Thus, any molecule within these tracts is essentially outside the body.

Start the activity by arranging students into small groups of two or three students. Larger groups can result in individuals not participating in conversations and are thus not recommended. Group members should be able to make eye contact with each other. For example, situate students around the corner of a desk or table. (A phrase used to describe the ideal positioning of students within a group is "knee-to-knee and eye-to-eye.")

Instructions: Once students are arranged in their groups and before distributing the activity, the instructor must clearly communicate group work guidelines. The following paragraph shows sample language that might be used by an instructor who is new to group learning. Instructors who are more experienced with group learning can use the following text as a guide to introduce the lesson; it is not a required script.

"This activity is to be completed in groups of two or three, and each person in the group will take on a specific role or function. First, one person must be the reader. This person is required to read any words that are on the activity and must speak loudly so that all other students in the group can clearly hear. After reading a question in the activity the reader should stop and the group should engage in a discussion so as to determine an answer. Some questions are easy and quick, and others will require more time and thought. Another member of the group must be the recorder. This person writes down the answers to the questions on the worksheet. Do not write down any answer until there is agreement among group members. Be aware that some of questions might cause disagreements between group members and you must talk about your ideas and answers before writing down an answer. If no consensus can be found, write down two different answers and we will use that information for a group discussion at the end of class. The third role is combination of doubter and spokesperson. This person's primary job is to ask questions such as "Are we sure of that?" "Is this our final answer?" and "Are we ready to move on?" The secondary job for this individual is to be the group's spokesperson when we have a whole class discussion and I call on groups for answers. If you have only 2 members in your group, then one person must take on two roles. Now, before I hand out the activity, I need you to assign the three roles: reader, recorder, and doubter and spokesperson. Do that now."

At this time, group members should be talking to each other and assigning the three roles. Some groups might need the instructor to intervene and assign roles. However, most groups should be able to assign roles without teacher intervention.

Next, the instructor should provide some context for the activity. The following language might be used:

"This activity is titled 'Inside and Outside the Body.'" While the title of the activity makes it sound pretty easy, you will probably have moments of doubt; moments that make you say 'I don't get it!' In this lesson, doubt is good; it's an indication that you're learning. A key component to this exercise is that you are asked to 'think like an anatomist' or 'think like a physiologist.' After completing this activity, you should have a basic understanding of how a professional anatomist or physiologist views the concept of 'inside and outside the body.'"

At this time, the instructor should hand out one copy of the activity to each group (S1.Inside and Outside the Body - Handout). The instructor should walk around to ensure that the readers are speaking loudly and clearly. It is important that instructors do not tell students the answers to the questions; students will, and should, struggle with some questions in the activity. This struggle should promote conversation between students. For example, the second part of question 4, "Does this molecule ever enter the body?" should provoke student doubt . Many students erroneously believe that "food in the stomach is inside the body." If students are having trouble with this question, the instructor could ask students,"At what point does the food enter the body? Point to the place where the food passes from the outside to the inside of the body." In order for nutrients to pass into the body, they must cross the mucous membrane lining of the alimentary canal; they must cross an anatomical barrier.

After all groups have completed question 5, the instructor should conduct a whole-class discussion. Ideally, instructors should ask each spokesperson to stand and read their group's answer. For example, "Joe, what did your group say for food in the digestive tract? Inside or outside the body?" The item in question 5 that will likely generate the most doubt is "a fetus developing in the uterus." Many students believe that a developing fetus must be inside the female body, but the placenta and uterine wall provide an anatomical barrier between mother and fetus. The instructor might add to the discussion by noting that a fetus and the mother can have different blood types; their blood does not mix. Finally, at the end of the discussion for question 5, the instructor might say "Even if this is not making sense to you now, continue with the activity and we'll discuss it more in a few minutes." All groups may not agree on the answers to question 5. The whole class discussion for question 5 should take about two or three minutes. After the discussion the instructor should instruct students to work in groups to complete the activity.

After all groups are finished, the instructor should conduct a second whole class discussion by asking spokespersons to stand and provide answers. "Malik, how did your group answer question 9? Did the kid who swallowed a marble require emergency surgery?" Question 9 should be easy for students at this point in the activity; the marble was never absorbed into the body. Question 12 represents a move from the anatomy of barriers to their function. The tiny arrows in Model 1 represent movements into and out of the body, such as nutrient absorption from the alimentary canal into the blood and fluid filtration from the blood into the kidney tubules.

Question 11 involving a tattoo is difficult. Professional anatomists disagree on whether or not the ink from a tattoo is located inside or outside the body. Most instructors answer this question by explaining that the tattoo is located within the physical barrier (the skin) that separates the inside and outside the body.

After the class discussion the instructor should provide each student with a blank copy of the activity, and provide 5-10 minutes for students to transfer the answers from their group copy to their individual copies. The group copy can be handed in for marking. In almost all cases, marks on the activity are either "complete" or "incomplete." After marking, instructors can return the original activity to the groups.

After completing the activity students should know that air in the lungs is considered outside the body, urine in the bladder is outside the body, and even a fetus developing in a uterus is outside the body. The concept of what is inside and what is outside the body might still be confusing to some students at the end of the lesson, but might become clear as they engage in lessons covering the respiratory (ventilation and gas exchange), urinary (urine production), and reproductive systems (fetal development).


Two summative assessment questions which could also be used in a post-activity discussion are: (1) How can you have bacteria in your large intestine and still be healthy? and (2) How can it be possible for a developing fetus to have a different blood type from the mother? Don't different blood types cause problems? Another summative assessment question might involve students writing an essay to answer the following prompt: Your sister is eight months pregnant and very uncomfortable. Write a paragraph, using terms your sister can understand, that clearly explains that her fetus is not actually "inside" her body. (Important note, your sister has never had an anatomy and physiology course.)

A useful phrase to use in this lesson is "You're beginning to think like an anatomist." "Thinking like an anatomist" involves using concepts, such as barriers, to answer questions such as "what is inside and outside the body?"

One possible pitfall to the Inside and Outside the Body activity is the lack of an obvious answer to the question 11 involving a tattoo. Some anatomists consider a tattoo inside the body because the ink in a tattoo can diffuse into human lymph fluid. Other anatomists claim tattoos to be outside the body because they are on the barrier (skin) that separates the inside and outside of the body. Instructors are encouraged to use question 11 to show that some questions do not have a clear answer. The point of the question is to help students to apply their knowledge of barriers to a novel situation. A possible follow-up question would be to ask students if they would ever consider getting a tattoo.

The Inside and Outside the Body activity has been used in many different types of classrooms, but has not been tested in large auditoriums. However, if an instructor has experience with active learning teaching techniques in large auditoriums, there is no reason that this activity could not be used in such an environment. Best practices in cooperative group learning are still germane to large auditoriums; organize students so that they are "knee-to-knee, and eye-to-eye" if possible, and be mindful of limiting group sizes to two or maybe three. Working in large auditoriums with fixed seating is especially difficult for group learning due to students sitting "shoulder-to-shoulder" which often limits the possibility for eye contact also makes listening to fellow group members difficult. Given this drawback, limiting group size to two is recommended when using the activity within a large auditorium. Additionally, the Inside and Outside the Body activity has not been used in an on-line learning course. The Inside and Outside the Body activity might be used for an asynchronous group discussion activity in an on-line course. However, hearing group members discuss and engage in the guided-inquiry process is central to developing an understanding of the learning objectives. Therefore, when working in an on-line environment, it is recommended that the Inside and Outside the Body activity involve a synchronous discussion with the discussion monitored and promoted by an anatomy and physiology educator.


  • S1. Inside and Outside the Body - Handout
  • S2. Inside and Outside the Body - Handout Instructor Key


This activity has been used and reviewed by over 50 college and high school instructors. The artwork was done by Lauren Jones. Dr. Kerry Hull proposed the addition of mucus membranes to the original model and also wrote question 13 in the activity.

This work has been previously published in the HAPS Educator and permission was granted by HAPS Educator Editor-in-Chief, Dr. Kerry Hull, to also publish in CourseSource).

Reference: Jensen, M. Inside and Outside of the Body. HAPS Educator. Vol 21, Suppl. 2, pp. 82-86. November 2017. doi: https://doi.org/10.21692/haps.2017.042


  1. Human Anatomy and Physiology Society. 2018. Learning Outcome Documents for Anatomy and Physiology I. Available from https://www.hapsweb.org/page/AP1 2018/11/01
  2. American Association for the Advancement of Science (AAAS) (2010). Vision and Change in Undergraduate Biology Education: A Call to Action. Washington, DC.
  3. Next Generation Science Standards: Lead States. 2013. Next Generation Science Standards: For States, by States. Washington, DC: National Academies Press.
  4. National Research Council. 2003. BIO 2010: Transforming Undergraduate Biology Education for Future Research Biologists. Washington, DC: National Academies Press.
  5. McFarland JL, Price RM, Wenderoth MP, Martinkov? P, Cliff W, Michael J, Modell H, Wright A. 2017. Development and Validation of the Homeostasis Concept Inventory. CBE Life Science Education 16(2). doi: 10.1187/cbe.16-10-0305
  6. Michael J, McFarland J. 2011. The Core Principles ("Big Ideas") of Physiology: Results of Faculty Surveys. Advances in Physiology Education 35:336-341. doi: 10.1152/advan.00004.2011
  7. Michael J, Cliff W, McFarland J, Modell H, Wright A. 2017. The Core Concepts of Physiology: A New Paradigm for Teaching Physiology. Springer.
  8. Jensen M., Barger, JB 2015. Identifying Core Concepts in Human Anatomy. Presentation. Human Anatomy and Physiology Society National Conference, San Antonio, TX.
  9. Brown, P. 2010. Process-Oriented Guided Inquiry Learning in an Introductory Anatomy and Physiology Course with a Diverse Student Population. Advances in Physiology Education. 34: 150-155. doi: 10.1152/advan.00055.2010
  10. Jensen, M. (2014). POGIL Activities for Introductory Anatomy and Physiology Courses. The POGIL Project. Accessed at: https://pogil.org/contact-us/the-pogil-team/activities-for-introductory-a-p-courses (12.20.2018).
  11. Johnson, D.W., Johnson, R.T., & Smith, K.A. (1991). Active Learning: Cooperation in the College Classroom. Edina, MN: Interaction.

Article Files

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Author(s): Murray Jensen*

University of Minnesota

About the Authors

*Correspondence to: Biology Teaching and Learning, College of Biological Sciences, University of Minnesota, 3-154 MCB, 420 Washington Ave SE, Minneapolis, MN 55455. Email: msjensen@umn.edu.

Competing Interests

The author does not have a financial, personal, or professional conflict of interest related to this work.



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