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Chapter Three: Table of Contents

Levels of Organization 

Anatomical Position

Regional Terms

Directional Terms

Body Planes

Body Cavities and Serous Membranes

References

Image Descriptions

Levels of Organization

As you memorize the language components of medical terminology, it is important to support that learning within the context of anatomy and physiology. You will learn word parts, whole medical terms, and common abbreviations through the body system chapters. It is important to put into context where the medical term is referenced in the body and then consider how it works within the body.

Anatomy focuses on structure, and physiology focuses on function. Much of the study of physiology centers on the body’s tendency toward homeostasis.

• An atom is the smallest unit of any of these pure substances (elements).
  • Atoms comprise subatomic particles such as protons, electrons, and neutrons.
• Two or more atoms combine to form a molecule, such as the water molecules, proteins, and sugars in living things.
  • Molecules are the chemical building blocks of all body structures.
• A cell is the smallest independently functioning unit of a living organism.
  • Even bacteria, which are extremely small, independently-living organisms, have a cellular structure. Each bacterium is a single cell. All living structures of human anatomy contain cells, and almost all functions of human physiology are performed in cells or are initiated by cells
  • A human cell typically consists of flexible membranes that enclose cytoplasm, a water-based cellular fluid, and a variety of tiny functioning units called organelles. In humans, as in all organisms, cells perform all life functions.
• A tissue is a group of many similar cells (though sometimes composed of a few related types) that work together to perform a specific function.
• An organ is an anatomically distinct body structure of two or more tissue types. Each organ performs one or more specific physiological functions.

An organ system is a group of organs that work together to perform major functions or meet the body’s physiological needs.

Consider the breakdown into eleven distinct organ systems of the human body (Figure 3.2 and Figure 3.3). Assigning organs to organ systems can be imprecise since organs that “belong” to one system can also have functions integral to another system. Most organs contribute to more than one system.

 

Major Organ Systems

The organism level is the highest level of organization. An organism is a living being that has a cellular structure and that can independently perform all physiologic functions necessary for life. In multicellular organisms, including humans, all cells, tissues, organs, and organ systems of the body work together to maintain the life and health of the organism.

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Anatomical Position

Anatomists and healthcare providers use terminology for the purpose of precision and to reduce medical errors. For example, is a scar “above the wrist” located on the forearm two or three inches away from the hand? Or is it at the base of the hand? Is it on the palm side or back side? By using precise anatomical terminology, we eliminate ambiguity. Anatomical terms derive from ancient Greek and Latin words.

To further increase precision, anatomists standardize the way in which they view the body. Just as maps are normally oriented with north at the top, the standard body “map,” also known as the anatomical position, is that of the body standing upright with the feet at shoulder width and parallel, toes forward. The upper limbs are held out to each side, and the palms of the hands face forward, as illustrated in Figure 3.4.

Using this standard position reduces confusion. It does not matter how the body being described is oriented; the terms are used as if it is in an anatomical position. For example, a scar in the “anterior (front) carpal (wrist) region” would be present on the palm side of the wrist. The term “anterior” would be used even if the hand were palm down on a table.

A body that is lying down is described as either prone or supine. These terms are sometimes used to describe the position of the body during specific physical examinations or surgical procedures.

Anatomical Positions

Term	Word Parts	Description
prone prohn		Lying face down The word prone has an "o" in it, and so does the word down. People who are prone are facing down. They are lying on their stomach, which also has an "o." (https://www.yourdictionary.com/articles/prone-supine-difference)
supine su-pine		Lying face up. The term supine has a "u" in it, and so does the word up. People who are supine are facing up. They are lying on their back, so think about backing up. (https://www.yourdictionary.com/articles/prone-supine-difference)

Directional terms are essential for describing the relative locations of different body structures (Figure 3.5). For instance, an anatomist might describe one band of tissue as “inferior to” another, or a physician might describe a tumor as “superficial to” a deeper body structure. Commit these terms to memory to avoid confusion when studying or describing the locations of particular body parts.

Term	Word Parts	Description
anterior (ventral) an-teer-ee-er	-al pertaining to later/o side	Describes the front or direction toward the front of the body. The toes are anterior to the foot.
posterior po-steer-ee-er	-ior pertaining to poster/o back (of body); behind	Describes the back or direction toward the back of the body. The popliteus (back of the knee) is posterior to the patella.
superior suh-peer-ee-er	-ior pertaining to superfic/o of or belonging to the surface	Describes a position above or higher than another part of the body proper. The orbits are superior to the oris.
inferior in-feer-ee-er	-ior pertaining to infer/o lower in situation or place	Describes a position below or lower than another part of the body proper; near or toward the tail (in humans, the coccyx, or lowest part of the spinal column). The pelvis is inferior to the abdomen.
lateral lat-er-al	-al pertaining to later/o side	Describes the side or direction toward the side of the body. The thumb (pollex) is lateral to the digits.
medial mee-dee-uh	-al pertaining to medi/o middle	Describes the middle or direction toward the middle of the body. The hallux (big toe) is the medial toe.
proximal prox-imal	-al pertaining to proxim/o near	Describes a position in a limb that is nearer to the point of attachment or the trunk of the body. The brachium is proximal to the antebrachium.
distal dis-tl	-al pertaining to dist/o far; distant	Describes a position in a limb that is farther from the point of attachment or the trunk of the body. The knee  is distal to the femur.
superficial su-per-fi-cial	-al pertaining to superfic/o of or belonging to the surface	Describes a position closer to the surface of the body. The skin is superficial to the bones
deep d-ee-p		Describes a position farther from the surface of the body. The brain is deep to the skull.

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Body Planes

Subdivisions of the Posterior (Dorsal) and Anterior (Ventral) Cavities

The posterior (dorsal) and anterior (ventral) cavities are each subdivided into smaller cavities.

The posterior (dorsal) cavity has two main subdivisions:

Dorsal Cavity

Cavity	Word Parts	Description
cranial cavity krey-nee-uh l	-al pertaining to crani/o skull	Houses the brain. Protected by the bones of the skulls and cerebrospinal fluid
spinal cavity (or vertebral cavity) spahyn-l	-al pertaining to spin/o spine (backbone)	Encloses the spinal cord

The anterior (ventral) cavity has two main subdivisions:

Anterior/Ventral Cavity

Cavity	Word Parts	Description
thoracic cavity thuhr-rAs-ik	-ic pertaining to 2 thorac/o chest	The more superior subdivision of the anterior cavity, and it is enclosed by the rib cage. The thoracic cavity contains the lungs and the heart, which are located in the mediastinum. The diaphragm forms the floor of the thoracic cavity and separates it from the more inferior abdominopelvic cavity.
abdominopelvic cavity ab-duh-muhn-OH-pEl-vik	-ic pertaining to abdomin/o abdomen pelv/o pelvis; hip region	The abdominopelvic cavity is the largest cavity in the body. The abdominal cavity houses the digestive organs, the pelvic cavity, and the reproductive organs.

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Test Yourself

References

CrashCourse. (2015, January 6). Introduction to anatomy & physiology: Crash Course A&P #1 [Video]. YouTube. https://youtu.be/uBGl2BujkPQ

Unless otherwise indicated, this chapter contains material adapted from Anatomy and Physiology (on OpenStax), by Betts et al. and is used under a CC BY 4.0 international license. Download and access this book for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction.

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Image Descriptions

Figure 3.1 image description: This illustration shows biological organization as a pyramid. The chemical level is at the pyramid’s apex, where atoms bond to form molecules with three-dimensional structures. An example shows two white hydrogen atoms bonding to a red oxygen atom to create water. The next level on the pyramid is cellular, as illustrated by a long, tapered, smooth muscle cell. At this level, various molecules combine to form the interior fluid and organelles of a body cell. The next level down is the tissue level. A community of similar cells forms body tissue. The example given here is a section of smooth muscle tissue containing many smooth muscle cells closely bound side by side. The next level down is the organ level, as illustrated with the bladder and urethra. The bladder contains smooth muscle, while the urethra contains skeletal muscle. These are both examples of muscle tissues. The next level down is the organ system level, as illustrated by the entire urinary system containing the kidney, ureters, bladder, and urethra. At this level, two or more organs work closely together to perform the functions of a body system. At the base of the pyramid is the organismal level illustrated with a woman drinking water. At this level, many organ systems work harmoniously together to perform the functions of an independent organism. [Return to Figure 3.1].

Figure 3.2 image description: This illustration shows eight silhouettes of a human female, each showing the components of a different organ system. The integumentary system encloses internal body structures and is the site of many sensory receptors. The integumentary system includes the hair, skin, and nails. The skeletal system supports the body and, along with the muscular system, enables movement. The skeletal system includes cartilage, such as that at the tip of the nose and the bones and joints. The muscular system enables movement, along with the skeletal system, and helps maintain body temperature. The muscular system includes skeletal muscles and tendons that connect skeletal muscles to bones. The nervous system detects and processes sensory information and activates bodily responses. The nervous system includes the brain, spinal cord, and peripheral nerves, such as those in the limbs. The endocrine system secretes hormones and regulates bodily processes. The endocrine system includes the pituitary gland in the brain, the thyroid gland in the throat, the pancreas in the abdomen, the adrenal glands on top of the kidneys, and the testes in the scrotum of males, as well as the ovaries in the pelvic region of females. The cardiovascular system delivers oxygen and nutrients to the tissues as well as equalizes temperature in the body. The cardiovascular system includes the heart and blood vessels. [Return to Figure 3.2].

Figure 3.3 image description: The lymphatic system returns fluid to the blood and defends against pathogens. The lymphatic system includes the thymus in the chest, the spleen in the abdomen, the lymphatic vessels that spread throughout the body, and the lymph nodes distributed along the lymphatic vessels. The respiratory system removes carbon dioxide from the body and delivers oxygen to the blood. The respiratory system includes the nasal passages, the trachea, and the lungs. The digestive system processes food for use by the body and removes wastes from undigested food. The digestive system includes the stomach, the liver, the gallbladder (connected to the liver), the large intestine, and the small intestine. The urinary system controls water balance in the body and removes and excretes waste from the blood. The urinary system includes the kidneys and the urinary bladder. The reproductive system of males and females produces sex hormones and gametes. The male reproductive system delivers gametes to the female while the female reproductive system is specialized to support the embryo and fetus until birth and produce milk for the infant after birth. The male reproductive system includes the two testes within the scrotum and the epididymis, which wraps around each testis. The female reproductive system includes the mammary glands within the breasts, ovaries, and uterus within the pelvic cavity. [Return to Figure 3.3]

Figure 3.4 image description: This illustration shows an anterior and posterior view of the human body. The cranial region encompasses the upper part of the head, while the facial region encompasses the lower half of the head, beginning below the ears. The eyes are referred to as the ocular region. The cheeks are referred to as the buccal region. The ears are referred to as the auricle or otic region. The nose is referred to as the nasal region. The chin is referred to as the mental region. The neck is referred to as the cervical region. The trunk of the body contains, from superior to inferior, the thoracic region encompassing the chest, the mammary region encompassing each breast, the abdominal region encompassing the stomach area, the coxal region encompassing the beltline, and the pubic region encompassing the area above the genitals. The umbilicus, or navel, is located at the center of the abdomen. The pelvis and legs contain, from superior to inferior, the inguinal or groin region between the legs and the genitals, the pubic region surrounding the genitals, the femoral region encompassing the thighs, the patellar region encompassing the knee, the crural region encompassing the lower leg, the tarsal region encompassing the ankle, the pedal region encompassing the foot and the digital/phalangeal region encompassing the toes. The great toe is referred to as the hallux. The regions of the upper limbs, from superior to inferior, are the axillary region encompassing the armpit, the brachial region encompassing the upper arm, the antecubital region encompassing the front of the elbow, the antebrachial region encompassing the forearm, the carpal region encompassing the wrist, the palmar region encompassing the palm, and the digital/phalangeal region encompassing the fingers. The thumb is referred to as the pollux. The posterior view contains, from superior to inferior, the cervical region encompassing the neck, the dorsal region encompassing the upper back, and the lumbar region encompassing the lower back. The regions of the back of the arms, from superior to inferior, include the cervical region encompassing the neck, the acromial region encompassing the shoulder, the brachial region encompassing the upper arm, the olecranal region encompassing the back of the elbow, the antebrachial region encompasses the back of the arm, and the manual region encompassing the palm. The posterior regions of the legs, from superior to inferior, include the gluteal region encompassing the buttocks, the femoral region encompassing the thigh, the popliteal region encompassing the back of the knee, the sural region encompassing the back of the lower leg, and the plantar region encompassing the sole. Some regions are combined into larger regions. These include the trunk, a combination of the thoracic, mammary, abdominal, naval, and coxal regions. The cephalic region is a combination of all of the head regions. The upper limb region is a combination of all of the arm regions. The lower limb region is a combination of all of the leg regions. [Return to Figure 3.4].

Figure 3.5 image description: This illustration shows two diagrams: one of a side view of a female and the other of an anterior view of a female. Each diagram shows directional terms using double-sided arrows. The cranial-distal arrow runs vertically behind the torso and lower abdomen. The cranial arrow points toward the head, while the caudal arrow points toward the tail bone. The posterior/anterior arrow runs horizontally through the back and chest. The posterior or dorsal arrow points toward the back, while the anterior or ventral arrow points toward the abdomen. The proximal/distal arrow is on the right arm in the anterior view. The proximal arrow points up toward the shoulder, while the distal arrow points down toward the hand. The lateral-medial arrow is a horizontal arrow on the abdomen. The medial arrow points toward the navel, while the lateral arrow points away from the body to the right. Right refers to the right side of the woman’s body from her perspective, while left refers to the left side of the woman’s body from her perspective. [Return to Figure 3.5].

Figure 3.6 image description: This illustration shows a lateral and anterior view of the body and highlights the body cavities with different colors. The cranial cavity is a large, bean-shaped cavity filling most of the upper skull where the brain is located. The vertebral cavity is a very narrow, thread-like cavity running from the cranial cavity down the entire length of the spinal cord. Together, the cranial cavity and vertebral cavity can be referred to as the dorsal body cavity. The thoracic cavity consists of three cavities that fill the interior area of the chest. The two pleural cavities are situated on both sides of the body, anterior to the spine and lateral to the breastbone. The superior mediastinum is a wedge-shaped cavity located between the superior regions of the two thoracic cavities. The pericardial cavity within the mediastinum is located at the center of the chest below the superior mediastinum. The pericardial cavity roughly outlines the shape of the heart. The diaphragm divides the thoracic and abdominal cavities. The abdominal cavity occupies the entire lower half of the trunk, anterior to the spine. The pelvic cavity is just under the abdominal cavity, anterior to the buttocks. The pelvic cavity is funnel-shaped and located inferior and anterior to the abdominal cavity. Together, the abdominal and pelvic cavities can be referred to as the abdominopelvic cavity, while the thoracic, abdominal, and pelvic cavities together can be referred to as the ventral body cavity. [Return to Figure 3.6].

Figure 3.7 image description: This illustration shows the silhouette of a human female from an anterior view. Several organs are showing in her neck, thorax, abdomen, left arm, and right leg. Text boxes point out and describe the mucous membranes in several different organs. The topmost box points to the mouth and trachea. It states that mucous membranes line the digestive, respiratory, urinary, and reproductive tracts. They are coated with the secretions of mucous glands. The second box points to the outside edge of the lungs as well as the large intestine and states that serous membranes line body cavities that are closed to the exterior of the body, including the peritoneal, pleural, and pericardial cavities. The third box points to the skin of the hand. It states that the cutaneous membrane, also known as the skin, covers the body’s surface. The fourth box points to the right knee. It states that synovial membranes line joint cavities and produce the fluid within the joint.[Return to Figure 3.7]

Figure 3.8 image description: This diagram shows the pericardium on the left next to an analogy of a hand punching a balloon on the right. The pericardium is a two-layered sac that surrounds the entire heart except where the blood vessels emerge on the heart’s superior side. The pericardium has two layers because it folds over itself in the shape of the letter U. The inner layer that borders the heart is the visceral pericardium, while the outer layer is the parietal pericardium. The space between the two layers is called the pericardial cavity. The heart sits in the cavity like a fist punching into a balloon. The balloon surrounds the lower part of the fist with a two-layered sac, with the top of the balloon, where it contacts the fist, analogous to the visceral pericardium. The bottom of the balloon, where it is tied off, is analogous to the parietal pericardium. The air within the balloon is analogous to the pericardial cavity. [Return to Figure 3.8].

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