The supine position is a position of the body where the person is lying face up on their back In the prone position, the person is on their stomach and is face down, sometimes with the hands behind the head or neck. Lithotomy position is variation of the supine position with the legs separated, flexed, and supported in raised stirrups.

Anatomical terms are an easy way to talk about certain parts of the body without confusion. If the top of the head is the superior most portion of the body and the feet are the inferior most part of the body, then the femur is inferior to the hip, but superior to the knee joint.

The midsagittal plane or the median plane divides the body vertically into two symmetrical halves. It runs from the top of the head straight down the face, between the eyes, down the nose and through the naval. The horizontal or transverse plane divides the body into superior and inferior halves. The frontal plane divides the body in half between the anterior and posterior sides. It is sometimes called the coronal plane.

A sagittal plane divides the body into left and right portions, a frontal (or coronal) plane is perpendicular to a sagittal plane and divides the body into anterior and posterior portions. A vertical plane is not a term used in human anatomy.

"Proximal" is a way to describe locations in the extremities and appendages. A more proximal structure is located closer to the trunk, generally indicating closer to the shoulder or hip. In contrast, distal indicates a location that is farther from the trunk and closer to the end of the appendage. For example, there are three bones in each finger known as the phalanges. These bones are named according to orientation: proximal phalanx, intermediate phalanx, and distal phalanx. All of these, of course, are located distal to the metacarpals (wrist).

The terms "medial" and "lateral" are used to describe relative location toward the midline. A medial structure is closer to the midline (think nose and navel), while a lateral structure is farther from the midline. The term used to describe one structure that is next to another is "adjacent."

Terms used to describe the orientation of a structure commonly have a word that means the opposite so they can be related to one another. Proximal means that the structure is closer to a point of attachment, while lateral refers to a structure being away from the middle of the body. The opposing term for proximal is distal, meaning away from the point of attachment, and the opposing term for lateral is medial, meaning toward the center line.

Superior indicates above, while inferior indicates below. Anterior refers to the front, while posterior refers to the back. Superficial indicates that a structure is near the surface, while deep indicates that it is under other structures.

Anatomical position is the position with the body erect with arms at the sides and the palms forward. Distal is defined as situated away from the center of the body or from the point of attachment. Proximal describes a structure situated nearer to the center of the body or the point of attachment. Superior describes a structure situated nearer the vertex of the head in relation to the specific reference point; it is the opposite of inferior.

A transverse slice is the only view to section the body through the horizontal plane. The result is a superior region (above the cut) and an inferior region (below the cut). A transverse section of the brain is usually used to show the lentiform nucleus (consisting of the globus pallidus and putamen) and the caudate.

A coronal section runs from right to left across the body, dividing it into an anterior (ventral) portion and posterior (dorsal) portion.

A sagittal slice runs from anterior to posterior, dividing the body into left and right regions. A perfectly centered sagittal slice is called a medial sagittal section.

Lateral is a general directional that can be applied to objects farther from the midline of the body. The midline is defined as the medial sagittal plane, generally including the navel and nose. Structures such as the shoulders, ears, and hips are considered lateral. When used in relative terms, we can say that the lungs are lateral to the heart and the ovaries are lateral to the uterus. In contrast, the opposite term of lateral is medial; the heart is medial to the lungs and the uterus is medial to the ovaries.

The latissimus dorsi muscles are located on both sides of the spine, and their name is directionally descriptive. They have no bearing on directional terms, unless used as reference points. Anatomical structures attached to the midline could be described as lateral, but only if they deviate farther left or right from the midline. A structure can be attached to the midline, but run completely vertical in the medial sagittal plane.

Normal blood pH is about 7.4 in most tissues (it is a bit lower in veins since they carry waste products, which are acidic). To get back to the physiological set point of pH = 7.4, we want to remove the acid from the blood. The major blood buffer system is shown in the following equation:

As we know, carbon dioxide is one of the major byproducts of respiration, and is considered waste for our bodies. Combined with water and catalyzed by carbonic anhydrase, it is converted into carbonic acid. Carbonic acid is a weak acid and will partially dissociate into hydrogen ions and bicarbonate ions. Thus, overall, carbon dioxide and water yields acid (hydrogen ions). As a result, excess carbon dioxide in the blood will lower the pH.

In order to increase the pH, we must stop this equation from proceeding in the forward direction; thus, (remember Le Chatelier's principle) we must remove carbon dioxide from the left side. This will push the reaction in the reverse direction, quenching hydrogen ions (acid) and removing them from the blood, increasing blood pH back to normal.

Since we want to get rid of excess carbon dioxide, we breathe faster. Oxygen does not have any effect on blood pH. Furthermore, the atmospheric oxygen level (21%) is plenty for our bodies to utilize, as when we exhale there is about 15% oxygen left over, meaning we only use about 25% of the oxygen we breathe (this is why CPR works!).