Chapter 1: Introduction; Directional Terms; Body Cavities


Human anatomy is primarily the scientific study of the morphology of the human body. Anatomy is subdivided
into gross anatomy and microscopic anatomy. Gross anatomy is the study of anatomical structures that can be seen by
unaided vision. Microscopic anatomy is the study of minute anatomical structures assisted with microscopes, which includes
histology (the study of the organization of tissues), and cytology (the study of cells). Anatomy, physiology (the study of
function) and biochemistry (the study of the chemistry of living structures) are complementary basic medical sciences when
applied to the human body. As such, these subjects are usually taught together (or in tandem) to students in the medical sciences.

In some of its facets human anatomy is closely related to embryology, comparative anatomy and comparative embryology, through common
roots in evolution; for example, much of the human body maintains the ancient segmental pattern that is present in all vertebrates with
basic units being repeated, which is particularly obvious in the vertebral column and in the ribcage, and can be traced from very early embryos.

The human body consists of biological systems, that consist of organs, that consist of tissues, that consist of cells and connective tissue.

Click here for the Levels of Body Organization

What you will be learning in this human anatomy course is the names of locations and structures of the human body.
It will be presented by organ systems. It will require a lot of memorization, visualization, imagination and time.


Anatomical Position

As a standard point or frame of reference, the human body is described as being in the anatomical position when it is standing erect, facing you, feet together flat on the floor, the arms slightly raised from the sides with the palms facing forward. Here is a list of useful directional terms. Know not only what they mean, but how to correctly use them.

Directional Terms

Supine................lying face up
Prone.................lying face down

Anterior (Ventral)............at the front
Posterior (Dorsal)............at the back

Cranial (Cephalic)...............toward the head
Caudal..............toward the tail

Medial..............nearer the midline of the body or a structure
Lateral..............Farther away from the midline of the body or a structure

Ipsilateral...............On the same side of the body or structure
Contralateral..............On the opposite side of the body or structure

Proximal...................Closer to a structure
Distal....................Further away from a structure

Superficial................Closer to the surface
Deep.....................Farther down below the surface


Planes of Sectioning

We will spend time studying not only the surface anatomy of many organs, but we will also have to look at the interior anatomy of many organs. For example, the brain has a lot of interesting internal anatomy. In order to see these internal structures we will have to cut, or section, the various organs or parts of the body. Now three dimensionally there would have to be three different directions, or planes, that we can cut something.

(1:Coronal Section; 2:Transverse (Horizontal) Section; 3:Ventral (Anterior); 4:Dorsal (Posterior);
5:Midsagittal; 6:Proximal; 7:Distal; 8:Superior; 9:Inferior; 10:Medial; 11:Lateral

The first direction, or sectional plane, that we may use to cut a specimen could be to cut it in a horizontal plane. This type of cut would leave you with a top piece and a bottom piece. This type of section is called a transverse section or plane.

A different type of cut would be to cut, or section, a specimen in a vertical direction so that you are left with a front piece and a back piece. This type of section is called a coronal section or plane. For example, if you wanted to look at the interior structures of the brain and how their shapes vary as you move from front to back inside the brain, you would need to make a series of coronal sections to follow the changes in the shape of the internal structures.

The third direction that you may wish to cut a specimen, or the entire body, is to cut it into a right piece and a left piece. This type of section is called a sagittal section or plane. Now be careful, I think we all automatically think to cut something equally in half right down the middle, but a sagittal section does not always have to be right down the middle. To cut a specimen right down the middle producing equal right and left halves is called a midsagittal section. To section a secimen into right and left pieces that are not necessarily equal (on off-center cut in the sagittal plane) is to make a parasagittal section.

Remember, we are cutting up a organ or part of the body in order to better visualize the internal structures of that organ or area of the body. You will have to then use your imagination to visualize in your mind how it looks uncut.


1:Cranial; 2:Vertebral Canal; 3:Thoracic; 4:Abdominal; 5:Pelvic

Before we start in detail naming many of the parts and structures of the human body, we must first step back and view the body as a series of hollow cavities or compartments that hold different organ systems. For example, we have a hollow skull for the brain. We also have a hollow chest, or thoracic cavity for the heart and lungs. We have a hollow abdominal cavity for the intestines and digestive organs. There is also the pelvic cavity housing primarily the reproductive organs in the female. So hopefully you can agree that we do consist of many hollow compartments. Speaking of the abdominal and pelvic cavities, as you well know, the two cavities are right next to each other. The pelvic cavity below outlined by the pelvic bones while the abdominal cavity is directly above outlined by the muscles of the abdominal wall. Since there is not natural boundary between the pelvic cavity and the abdominal cavity (they are continuous), they are commonly referred to together as the abdominopelvic cavity.
     
1:Right Hypochondriac Region; 2:Right Lumbar Region; 3:Right Iliac (Inguinal) Region;
4:Epigastric Region; 5:Unbilical Region; 6:Hypogastric (Pubic) Region;
7:Left Hypochondriac Region; 8:Left Lumbar Region; 9:Left Iliac (Inguinal) Region.

This introduces a rule that we will come across over and over. When we wish to combine two anatomical terms, we simply put them together with the letter 'o' between them. To refer to the abdominal cavity and the pelvic cavity together, we say the 'abdominal' + 'o' + 'pelvic' = 'abdominopelvic' cavity.

So how do we place organs into these cavities and have them stay in place? Even trickier, how to we place an organ that is always moving, say the heart or the lungs or even your intestines, into one of these hollow cavities and keep it in place without firmly attaching it to the inside walls of the cavity since the organ needs to be able to move freely? Let's start with the heart as an example. If you imagine my closed fist as my heart, picture then a balloon right next to my 'fist/heart'. As I push my 'fist/heart' up against the balloon, one side of the balloon is in direct contact with my 'fist/heart' while the opposite side of the balloon is not touching my 'fist/heart'. As I continue to push my 'fist/heart' into the balloon, by 'fist/heart' will become completely surrounded by the balloon.

Yet the other side of the balloon is not touching my 'fist/heart', but is separated from it by the air in the balloon. Assume that the balloon is stick on the outside so that when I push my 'fist/heart' up against it farther and farther, the balloon sticks to my 'fist/heart'. If I hold the other side of the balloon with my other hand, my 'fist/heart' will not fall to the ground since it is stuck to the sticky surface of the balloon (remember, my 'fist/heart' is not suppost to be attached at the wrist). So now all I need to do is place this side of the balloon that is not in contact with the 'fist/heart' up inside my ribs and it will also stick. I've done it. My heart is free to beat and move, yet it won't fall down or wiggle loose since the other side of the balloon is attached to the insides of my ribs. Why this works so well is that it is just one single balloon. But one single balloon with two surfaces. One surface attached to the 'fist/heart' and the other surface attached to the insides of my ribs. This balloon is called the pericardium. Instead of the balloon being filled with air, it is filled with fluid, the pericardial fluid. Now the pericaridium can be named according to what surface you are talking about, the surface stuck to the heart or the surface stuck to the insides of the ribs. This is anatomy, so we give a name to each surface of the pericardium. The part of the pericardium that is stuck to the heart itself is called the visceral pericaridum while the other surface of the pericardium that is attached to the insides of the ribs is called the parietal pericardium. The pericardium has both the visceral portion and the parietal portion, but it is still one continuous balloon, one continuous membrane called the pericardium.


Now just to mention some very general, but important terms that relate to human anatomy. As you probably already know, the study of the creation and development of a new human, starting with the embryo is referred to as embryology, or sometimes referred to as developmental anatomy.

You will very quickly discover in this course that we will be spending a lot of time looking at the different human organs, tissues and cells with a microscope. To look at and learn the surface anatomy of the liver is useful, but to really understand what the liver does, we will need to look directly at liver cells under the microscope. The common term for microscopic anatomy is histology. In fact, you may want to look into some of the very nice internet histology sites to practice learning what the various human cells look like under the microscope. There are also some very nice histology atlases for sale that might be useful to you for a course like this. But check out the internet sites first, since they are free, and any type of atlas is going to be expensive.

In contrast to histology, when you study all the parts of the human body that you can see just with your eyes, with your 'naked eyes' as they say; this is referred to as gross anatomy. So, for example, a gross anatomical structure would just be something you can see without the need for a microscope.

In order to better examine certain organs and tissues, sometimes it is necessary to gently touch these structures. This is referred to as palpation. In order to feel your pulse, you would have to palpate the skin above a blood vessel.

If you listen to the heart, or the lungs inflating and deflating, this is referred to as auscultation. And when the doctor thumps or gently taps on your body, this is referred to as percussion.


And finally, just to warn you, you are hopefully very motivated and anxious to get started learning all the parts of the human body. But before we can do that, we must first start with the basics. We must talk about what the parts of the human body are made up of first, and those are cells. And if are going to talk about human cells and their components, we must get even more basic and talk about molecules and even atoms. But don't worry, this is not a chemistry class. However, you will be exposed to some 'biochemistry' (chemistry as it applies to biology), so do not be afraid.