To prevent misunderstanding when reading and discussing anatomy, it is necessary to understand and use universally accepted terminology. You can begin building your anatomy vocabulary by learning the major surface regions of the body. We can identify these regions most effectively by looking at a body that is in anatomical position. In anatomical position, the person is standing erect with the head, palms, and feet facing forward, the feet slightly apart, and the arms by the sides. We will first highlight the basic layout of the body and the boundaries of selected regions. At the most basic level of gross anatomy, we can divide the body into two major regions: the axial and appendicular regions.
THE AXIAL REGION
The axial region (AK-sē-ul), so-named because it forms the body’s axis or central “core,” includes the head, neck, and trunk. Table 2-1 provides an alphabetized list of the axial regions and their sub-regions.
THE APPENDICULAR REGION
The appendicular region (ap-en-DIK-ū-lar), so-named because its parts append (attach) to different parts of the axial region, includes the upper limbs and lower limbs. Table 2-2 provides an alphabetized list of the appendicular regions and their sub-regions.
After learning the names and locations of the axial and appendicular regions, your expanded vocabulary will provide a basis for locating numerous structures inside the body. For instance, the femoral region, or thigh, contains the femur (thighbone), femoral artery, femoral vein, and femoral nerve. The fibular region contains the fibula, a long bone. Where would you expect to find the occipital artery and the popliteal vein? If you said the back of the head and the back of the knee then you are correct. Now that you have read about the major surface regions of the body, label those regions in Figure 2-1.
DIRECTIONAL TERMS
Now that you are familiar with the body’s surface landmarks, it’s time to learn the directional terms that relate the location of one body part to another. Using these directional terms can allow you to avoid prolonged explanations and misunderstanding when describing a particular location on or inside the body. Without this terminology, someone could interpret the statement, “The buccal region is next to the eye region,” to mean the forehead, nose, side of the head, or the cheek. However, saying, “The buccal region is inferior to the eye,” eliminates the fore- head, nose, and side of the head as possibilities.
To ensure consistency when using anatomy related directional terms, we always assume the body we are describing is in anatomical position. In this way, a given term can always relate the location of one body part relative to another, even when the body changes its position. For example, superior means “above,” so we can always say your cephalic region is superior to your trunk, even if you “stand on your head.” Also, keep in mind that in anatomy, right and left means the right and left sides of the body you are viewing, not your own right and left sides. Become familiar with the directional terms in Table 2-3 and then label them in Figure 2-2.
Table 2-1. Axial Regions
* Named for the coarse hairs, or pubes (PŪ-bēz), that appear in the pubic region when a person becomes sexually mature (reaches puberty).
**Some ancient cultures thought this part of the skeleton was sacred and would rise from the dead.
Table 2-2. Appendicular Regions
Figure 2-1. Anatomical position and the body’s major surface features
Figure 2-2. Directional Terms
Table 2-3. Directional Terms
PLANES AND SECTIONS
Now that you are familiar with the body’s surface anatomy, let’s take a look at some of the body’s internal features. To do this, we must consider the angles at which anatomists cut the body they want to study. This is important because many images in this text show flat cut surfaces within three dimensional body parts. In anatomy, a section is a cut that follows a straight path along an imaginary flat surface called a plane. Most anatomical studies utilize sections made along three planes that intersect the body at right angles; these include the sagittal, frontal, and transverse planes. A section made along a given plane has the same name as that plane; for example, to make a sagittal section, one cuts along a sagittal plane.
A sagittal (SAJ-i-tul) plane runs vertically and divides the body into right and left sides. We can be more specific when considering a sagittal plane’s location relative to the body’s midline (an imaginary vertical line running along the exact center of the body). A midsagittal plane lies on the midline to divide the body into two equal sides. A parasagittal plane runs alongside (para-, beside) the midline to divide the body into two unequal sides. Most images showing sagittal sections of the body or one of its parts are actually midsagittal sections.
A transverse, or horizontal, plane runs perpendicular (at right angles) to the sagittal and frontal planes and, for this reason, we sometimes call a transverse section a cross section. Any section made between the transverse plane and either a sagittal or a frontal plane is an oblique section (oblique, slanting).
A frontal, or coronal, plane (kō-RŌ-nul) runs vertically and divides the body into anterior and posterior parts. The word corona means “crown,” so imagine you are placing a crown on your head and look at the orientation of your thumbs. Since they point toward your head from each side, they can remind you of a coronal plane’s orientation. There are many frontal planes, but most images of frontal sections show the body or an organ divided into nearly equal anterior and posterior parts.
All of the sections just described can provide useful information about the anatomy of a particular body part, but each section produces a unique-looking image. Thus, to help you understand sectional views, we will provide small orientation diagrams that show the sectioned body part and the particular plane along which the cut occurred. You may have to make cuts along each of these planes on models provided in lab. Label the planes in Figure 2-3.
Figure 2-3. Planes of the body.
BODY CAVITIES
Making either a midsagittal or a frontal section through the axial region reveals two major body cavities, the dorsal and ventral cavities. These cavities have no connections with the outside of the body and serve three major functions:
(1) to provide a location to hold vital organs;
(2) to protect vital organs from the external environment; and (3) to allow room for certain internal organs, such as the heart and lungs, to expand without compressing adjacent organs.
Dorsal Body Cavity
The dorsal body cavity is the more posterior of the body’s two major cavities and it contains a cranial cavity and a vertebral cavity. The cranial cavity, located inside the cranium of the cephalic region, is the more superior cavity and holds the brain. The vertebral (spinal) cavity is in the vertebral region and holds the spinal cord. The cranial and vertebral cavities are continuous with one another; that is, there is no barrier between them. Thick bones and tough connective tissue surround the dorsal cavity and protect the brain and spinal cord against external blows. In addition, the dorsal cavity contains a watery fluid that cushions the vital organs against the jarring effects of walking and running. The fluid also helps maintain a stable temperature within the cavity.
Ventral Body Cavity
The ventral body cavity is much larger than the dorsal cavity and is anterior to it. The ventral cavity has two major subdivisions: a thoracic cavity and the abdominopelvic cavity, separated from one another by a dome-shaped muscle called the diaphragm (DĪ-a-fram; “partition”). In general, anatomists refer to all organs within the ventral body cavity collectively as visceral organs (VIS-er-ul) or the viscera (VIS-er-a; “internal organ”).
The thoracic cavity is superior to the diaphragm and contains four smaller cavities. Two of these, the right and left pleural cavities (PLOO-rul), each hold a lung and are so-named because they occupy the lateral portions (pleura, side) of the thoracic cavity. Located intermediate to the right and left pleural cavities is the mediastinum (mē-dē-a-STĪ-num; “middle”). It contains the trachea (windpipe), esophagus, thymus gland, major blood vessels, and the pericardial cavity (per-i-KAR-dē-ul), which encloses the heart (peri, around; cardia-, heart). To review the organization of the thoracic cavity, you could say, “The heart is in the pericardial cavity, which is in the mediastinum, which is in the thoracic cavity, which is in the ventral cavity,” or “The ventral cavity contains the thoracic cavity, which contains the left pleural cavity, which contains the left lung.”
The abdominopelvic cavity is inferior to the diaphragm and has two major parts: the abdominal cavity and the pelvic cavity, although these cavities are continuous with one another. The abdominal cavity extends from the diaphragm to the pelvic region and contains the stomach, liver, pancreas, and other organs, including most of the intestines. The pelvic cavity is inferior and slightly posterior to the abdominal cavity. The pelvic cavity lies within the bony pelvis and contains the urinary bladder, internal reproductive organs, and the rectum (inferior part of the large intestine).
To reinforce your knowledge of different body cavities, practice describing the location of various internal organs, beginning with the most general cavity and ending with the most specific cavity and vice versa. For example, you could say, “The brain is within the cranial cavity, which is within the dorsal cavity,” or “The dorsal cavity contains the vertebral cavity, which contains the spinal cord. Use Table 2-4 to review the body’s major cavities and then label those cavities in Figure 2-4.
Table 2-4. Major cavities of the body
SEROUS MEMBRANES
A thin membrane, called a serous membrane (SĒR-us) protects the walls of the ventral cavity and the surfaces of visceral organs as these organs carry out their normal functions. Some visceral organs, such as the heart and lungs, change shape constantly, while other organs, including the stomach, intestines, and urinary bladder, change shape on a regular basis. These movements generate friction between adjacent visceral organs and between these organs and the walls of the ventral cavity. The serous membranes produce a slippery serous fluid that reduces this friction. The word serous relates to “whey,” or the watery part of curdled milk. (The “curd” is the solid part of curdled milk used to make cheese.)
There are several serous membranes in the ventral cavity, and each has two layers: the parietal (pa-RĪ-e-tul) layer attaches to the wall of the cavity (paries, wall), and the visceral layer surrounds individual visceral organs. Serous fluid is between the parietal and visceral layers of each serous membrane. You can make a model of a serous membrane by inserting your fist into a sealed balloon filled with water. The outer part of the balloon represents the parietal layer and the inner part represents the visceral layer. Your fist represents a visceral organ and the fluid in the balloon represents serous fluid.
Two serous membranes, the pleura and pericardium, lie within the thoracic cavity. The serous membrane associated with the lungs is the pleura (PLOO-ra). The two layers of the pleura include the parietal pleura, located on the walls of the thoracic cavity, and the visceral pleura on the surface of the lungs. The pleural cavity lies between the parietal and visceral pleura. The serous membrane associated with the heart is the pericardium (per-i-KAR-dē-um). The parietal pericardium lines the inner wall of the pericardial sac, a bag-like structure that encloses the heart. The visceral pericardium covers the surface of the heart. The pericardial cavity lies between the parietal and visceral pericardium.
The most extensive serous membrane, the peritoneum (per-i-tō-NĒ-um; “stretched around”), lies within the abdominal cavity. The parietal peritoneum lines the walls of the abdominal cavity and the visceral peritoneum surrounds most of the visceral organs within the cavity. A few organs, such as the kidneys, adrenal glands, pancreas, and parts of the small and large intestine lie posterior to the parietal peritoneum. For this reason, we say these organs are retroperitoneal (retro, behind). The inferior portion of the parietal peritoneum extends into much of the pelvic cavity to cover portions of certain reproductive organs and the urinary bladder. The space between the parietal and visceral peritoneum is the peritoneal cavity. In much of the abdominopelvic cavity, the peritoneal cavity is only a “virtual” space because the peritoneal membranes lie next to one another. Review the body’s serous membranes and then label those membranes in Figure 2-4.
Figure 2-4. Major cavities and serous membranes of the body.
MUCOUS MEMBRANES
If an internal body cavity ultimately has connection with the outside of the body, the inner lining of that cavity is a mucous membrane (MŪ-kus). These membranes usually contain a thin coat of material called mucus (note the spelling). Mucus is a viscous (thick) material most often secreted by specialized goblet cells that are part of the mucous membrane. Mucous membranes include the inner linings of organs in the digestive, respiratory, urinary and reproductive systems.
ABDOMINOPELVIC QUADRANTS AND REGIONS
Just as a grid on a city map can help you locate a particular street, an imaginary grid on the abdominopelvic cavity can help you locate a particular visceral organ. The simplest grid, and the one used mostly by healthcare professionals, has one vertical line and one horizontal line intersecting at the umbilicus (navel). This simple grid forms four abdominopelvic quadrants (quad-, four). The names of the quadrants refer to their location relative to the subject’s right and left sides and include the upper right, upper left, lower right, and lower left.
Some anatomists may prefer a more elaborate grid to compartmentalize the abdominopelvic cavity. This grid resembles a tic-tac-toe grid with two parallel vertical lines intersecting two parallel horizontal lines, thereby dividing the abdominopelvic cavity into nine abdominopelvic regions.
- The two hypochondriac regions (hī-pō-KON-drē-ak; hypo, below; chondr-, cartilage) are the most superior, lateral Hypochondriac denotes a region below cartilage (a type of connective tissue) on the anterior, inferior portion of the rib cage.
- The epigastric region (ep-ē-GAS-trik) is inter- mediate to the right and left hypochondriac regions and is so-named because it contains most of the stomach (epi-, above; gastr-, stomach).
- The two lumbar regions are immediately inferior to the right and left hypochondriac regions.
- The umbilical region is in the center of the grid (in the vicinity of the umbilicus, or navel), which is immediately inferior to the epigastric region and medial to the right and left lumbar regions.
- The two inguinal (iliac) regions are the most inferior, lateral regions and are immediately inferior to the right and left lumbar regions.
- The hypogastric (pubic) region is intermediate to the inguinal regions.
Table 2-6 lists the abdominopelvic quad- rants and the nine abdominopelvic regions with their associated structures. After you become familiar with these items, label them in Figure 2-5.
Table 2-6. Divisions of the abdominopelvic cavity and their associated structures.
Figure 2-5. Abdominopelvic quadrants and regions
TOPICS TO KNOW FOR CHAPTER 2
(Body Organization)
abdominal cavity
abdominal region
abdominopelvic region
acromial region
anatomical position
antebrachial region
antecubital region
anterior
appendicular regions
axial regions
axillary region
brachial region
buccal region
calcaneal region
carpal region
caudal
cephalic
cervical region
contralateral
coronal plane
coxal region
cranial region
cross section
crural region
cubital region
deep
digital region
distal
dorsal
dorsal cavity
epigastric region
face
femoral region
fibular region
frontal region
frontal plane
gluteal region
hallux region
hypochondriac region
hypogastric region
iliac region
inferior
inguinal region
intermediate
ipsilateral
lateral
leg region
lower limb
lumbar region
mammary region
manual
medial
mediastinum
midsagittal plane
mucous membrane
mucus
natal cleft
neck
nuchal region
oblique section
occipital region
olecranal region
oral
orbital region
otic region
palmar region
parasagittal plane
parietal pericardium
parietal peritoneum
parietal pleura
patellar region
pedal
pelvic region
pericardial cavity
perineal region
peritoneal region
peroneal region
phalangeal
plantar region
pleura
pleural cavity
pollex region
popliteal region
posterior
proximal
pubic region
quadrant
sacral region
sagittal plane
scapular region
serous fluid
serous membrane
shoulder
skull
sole
spinal region
sternal region
superficial
superior
sural region
tarsal region
thigh
thoracic cavity
thoracic region
transverse plane
umbilical region
upper limb
ventral
ventral cavity
vertebral cavity
vertebral region
viscera
visceral pericardium
visceral peritoneum
visceral pleura
volar region
EOC Questions
