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Body Compartments

A look at how we analyze what we are made of as we think about different levels of structure, function and composition in the human body.

Compartment Level

Elemental Composition


Interesting but has few practical uses

The simplest body components are those that are essentially indestructible: atoms themselves.

Molecular Composition


Tells us something of what is going on in the body---but not much.

Cells are molecular machines and bodies are collections of cells

Molecular Type (Organic)

Useful TYPES of Molecules

Gives a bit more information about body function than simple molecular composition.

Cellular function is a result of interactions between many types of molecules.

Molecular Function

Classification based on what chemicals actually do

Gives different information about body function than organic molecular composition.

Different molecules play different roles in human beings

Sub-Cellular Composition

Classification based upon the functional parts of cells

Has growing relevance to human health and especially to weight.

Smaller than cells and bigger than molecules: subcellular body composition

Cellular Types

Types of cells that compose the human body.

Has direct major significance to obesity but very hard to measure.

What types of cells is the body made from?

Tissue types


Has direct major significance to obesity but very hard to measure.

Cells can organize into functional groups that are smaller than organs.

Organ Systems

Actual organs: heart, lungs, live, etc...

At this level, we are looking at 'adipose tissue' itself. Highly relevant to obesity.

A look at body composition at the level of organs

Five Compartment Model

5 major 'compartments' of body mass

Far easier to measure and easy to interpret. Highly relevant to obesity

Now we look at body composition based on gross feature---features larger than organs.

Four Compartment Model

DXA Level

Vastly easier to measure and extremely simple to interpret. Most significant level of composition relating to obesity.

A simpler model of body composition, this is level at which DXA gives useful data.

Mass and Volume The One Compartment Model

Weight (mass) and Body Volume

Trivially easy to calculate from weight and height but far, far less relevant and useful and accurate than the 4-compartment model.

The concept behind 'BMI'


The human body can be divided into various compartments, ranging from the simplest atomic composition to more complex and abstract organizational schemes. These compartments allow for a better understanding of the body's structure and function. Here's a breakdown of the different levels of organization in the human body:

  1. Atomic composition: The human body is composed of atoms, which are the smallest units of chemical elements. Examples include hydrogen, oxygen, carbon, and nitrogen atoms.

  2. Molecular composition: Atoms combine to form molecules, which are the fundamental building blocks of the human body. Examples include water (H2O), carbohydrates, lipids, proteins, and nucleic acids (DNA and RNA).

  3. Cellular composition: Molecules make up cells, the basic structural and functional units of living organisms. Examples of cells include neurons, muscle cells, and red blood cells.

  4. Tissue level: A tissue is a group of similar cells and their extracellular matrix, working together to perform specific functions. There are four primary tissue types in the human body:

    a. Epithelial tissue: Covers and lines body surfaces and cavities, and forms glands. b. Connective tissue: Provides structural support, connects, and separates different tissues and organs. c. Muscle tissue: Facilitates movement through contraction and relaxation. d. Nervous tissue: Transmits and processes information to coordinate body functions.

  5. Organ level: An organ consists of two or more tissue types working together to perform specific functions. Examples include the heart, lungs, liver, and kidneys.

  6. Organ system level: Organ systems are groups of related organs that work together to carry out a specific set of functions. The human body has 11 major organ systems:

    a. Integumentary system: Protects the body and regulates temperature (skin, hair, nails). b. Skeletal system: Provides structural support and enables movement (bones, joints, cartilage). c. Muscular system: Facilitates movement and maintains posture (skeletal, smooth, and cardiac muscles). d. Nervous system: Controls and coordinates body functions (brain, spinal cord, nerves). e. Endocrine system: Regulates body functions through hormones (pituitary, thyroid, adrenal glands, etc.). f. Cardiovascular system: Transports nutrients and oxygen, and removes waste (heart, blood vessels). g. Respiratory system: Facilitates gas exchange (lungs, trachea, bronchi, alveoli). h. Digestive system: Processes food and absorbs nutrients (mouth, esophagus, stomach, intestines, liver). i. Urinary system: Eliminates waste and maintains fluid balance (kidneys, ureters, bladder, urethra). j. Reproductive system: Produces offspring (testes, ovaries, uterus, penis, vagina). k. Lymphatic and immune system: Defends the body against pathogens and maintains fluid balance (lymph nodes, spleen, thymus, bone marrow).

  7. Five Compartment Model

  8. Three Compartment Model

  9. Organism level: The highest level of organization, the organism is the complete living entity made up of all organ systems working together. In this case, the organism is the human body.

These organizational schemes help scientists and healthcare professionals understand the complex structure and function of the human body, allowing for more effective research, diagnosis, and treatment of various conditions.

Doing DEXA

If you want the world's most accurate body composition test, DEXA is the one. Below are the simple steps you can take to do your first DEXA Scan at Holland Clinic

  1. Making an appointment: To begin the process of obtaining a body composition DXA scan, you'll first need to make an appointment with a facility that offers the service. This can often be done online or over the phone. Ensure that the facility is reputable and employs trained professionals to perform the scan.

  2. Preparation: Before your appointment, there are a few things you should do to ensure accurate results:

    Dietary and exercise restrictions: Avoid heavy meals and vigorous exercise for at least two hours prior to the scan, as these can affect body composition measurements.

    Clothing: Wear comfortable, loose-fitting clothes without any metal components, such as zippers or buttons. Remove any jewelry, belts, or other metal accessories, as they can interfere with the scan.

  3. Doing the actual scan:

    a) Lying properly positioned in the scanner: Upon arrival, you'll be asked to lie down on a padded table with the scanning arm positioned above you. The technician will ensure that you are correctly aligned and that your body is straight and centered on the table.

    b) Ensuring comfort: The technician will make sure you are comfortable throughout the process. If you feel any discomfort, let the technician know immediately.

    c) The actual scan: i) The DXA scan typically takes about 10-15 minutes to complete. ii) It's important to remain still during the scan to ensure accurate results.

  4. Reviewing scan results: After the scan, the technician or a healthcare professional will review the results with you, explaining the various measurements and their significance for your overall body composition. They may also provide insights on areas for improvement or areas where you are excelling.

  5. Plan next scan (if wanted): If you wish to track your progress over time, you can schedule a follow-up scan in the future, typically three to six months after the initial scan.

  6. Use scan information to judge the quality of your fitness, athletic, or weight-loss plan: Based on the results of your DXA scan, you can assess the effectiveness of your current fitness or weight-loss regimen. If the results are favorable, continue with your current habits. If the results indicate that adjustments are needed, consider revising your nutrition, exercise, or lifestyle habits to better align with your goals. Remember that maintaining a healthy lifestyle is an ongoing process, and regular DXA scans can help you monitor your progress and make data-driven decisions.

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