Body Fluids

Body Water Content

Factors which determine the overall water weight of a human being include sex, age, mass and body fat percentage. Infants, with their low bone mass and low body fat, are 73% water! Due to the high concentration of water, an infants skin appears “dewy” and soft. Total body water declines after infancy, and by the team one reaches old age, total body water is only about 45%.

The average young man is around 60% water, while a healthy young woman is about 50%. This is because women typically have less skeletal muscle and more fat than males. Adipose (fat) tissue is the least hydrated tissue in the body (20% hydrated), even bone contains more water than fat. In contrast,  skeletal muscle contains 75% water. So, the more muscles one has, the higher the total body water % will be.

Fluid Compartments

There are two main fluid compartments water occupies in the body. About two-thirds is in the intracellular fluid compartment (ICF). The intracellular fluid is the fluid within the cells of the body.

The remaining one-third of body water is outside cells, in the extracellular fluid compartment (ECF). The ECF is the body’s internal environment and the cells external environment.

Exchange of gases, nutrients, water, and wastes between the three fluid compartments of the body.

In the image above, the ECF compartment is divisible in two compartments: (1) Plasma, the fluid portion of blood, and (2) interstitial fluid (IF), the fluid in the spaces between tissue cells.

Composition of body fluids

Electrolytes and Nonelectrolytes

Nonelectrolytes have bonds (usually covalent bonds) that prevent them from disassociating in a solution. Because of this, no electrically charged species are created when nonelectrolytes dissolve in water. Most nonelectrolytes are organic molecules — lipids, glucose, urea, creatinine, for example.

In contrast, electrolytes are chemical compounds that do disassociate into ions in water. Since ions are charged particles, they can conduct an electrical current — that’s why they’re called electrolytes! For the most part, electrolytes include organic salts, some proteins, and both organic and inorganic acids and bases.

Electrolytes have much greater osmotic power than nonelectrolytes because each electrolyte molecule disassociates into at least two ions. For instance, a molecule of sodium chloride (NaCl) contributes twice as many solute particles as glucose, and a molecule of magnesium chloride (MgCl2) contributes three times as many.

Regardless of the type of solute particle, water always moves according to osmotic gradients — from an area of lesser osmolarity to an area of greater osmolarity. For this reason, electrolytes have the greatest ability to cause fluid shifts.

The major fluid compartments of the body

Electrolyte concentrations of body fluids are usually expressed in milliequivalents per liter (mEq/L), a measure of the number of electrical charges in one liter of solution. We can compute the concentration of any solution using the following equation: mEq/L = ion concentration (mg/L) divided by the atomic weight of the ion (mg/mmol) X the number of electrical charges on the ion. For instance to calculate the mEq/L of sodium we would determine the normal concentration of the ion in plasma, look up its atomic weight in the periodic table and plug the values into the equation: Na+ (sodium) = 3300 mg/L divided by 23 mg/mmol X 1 = 143 mEq/L. We could do the same thing for calcium: Ca2+ = 100 mg/L divided by 40 mg/mmol X 2 = 5 mEq/L.

Comparison of Extracellular and Intracellular Fluids

If you look at the bar graph above you can see that each fluid compartment has a distinctive pattern of electrolytes. Beside the relatively high protein content in plasma, the extracellular fluids are very similar. The chief cation is sodium and the major anion is chloride. However, plasma contains fewer chloride molecules than interstitial fluid, because non-penetrating protein molecules are usually anions and plasma is electrically neutral. In contrast to extracellular fluid, intracellular fluid contains only small amounts of sodium and chloride. It’s most abundant cation is potassium, and its major anion is hydrogen phosphate. In the graph above, notice that sodium and potassium ion concentrations in ECF and ICF are nearly opposite. The distribution of these ions on the two sides of cellular membranes reflects the activity of cellular ATP-dependant sodium-potassium pumps, which keep intracellular sodium concentrations low and potassium concentrations high. Renal mechanisms can enforce ion distribution by secreting potassium into the filtrate as sodium is reabsorbed from the filtrate.

Electrolytes are the most abundant solutes in body fluids and determine most of their chemical and physical reactions, but they do not constitute the bulk of dissolved solutes in these fluids. Proteins and nonelectrolytes (phospholipids, cholesterol, and triglyceride) found in the ECF are large molecules. They account for around 90% of the mass of dissolved solutes in plasma and 60% in the IF, and 97% in the ICF.

Fluid Movement Among Compartments

Osmotic and Hydrostatic pressures regulate the continuous exchange and mixing of body fluids. Although water moves freely between the compartments along osmotic gradients, solutes are unequally distributed because of their size, electrical charge, or dependence on transport proteins. The image at the top of this article summarizes the exchanges of gases, solutes, and water between the three fluid compartments within the body. In general, substances must pass through both the plasma and interstitial fluid to reach the intracellular fluid. In the lungs, gastrointestinal tract, and kidneys, exchanges between the outside world and the plasma o

Electrolyte composition of blood plasma, interstitial fluid, and intracellular fluid.

ccur continuously. These exchanges alter plasma composition and volume, with plasma serving as the “highway” for delivering substances throughout the body. Compensating adjustments between the plasma and the other two fluid compartments follow quickly so that balance is restored.

Let’s review the movement of water and solutes across the boundaries between these compartments:

Exchanges between plasma and interstitial fluid occur across capillary walls. The hydrostatic pressure of blood forces nearly protein-free plasma out of the blood into the interstitial space. The filtered fluid is then almost completely reabsorbed into the bloodstream in response to the colloid osmotic pressure of plasma proteins. Under normal circumstances, lymphatic vessels pick up the small net leakage that remains behind in the interstitial space and return it to the blood.

Exchanges between the interstitial fluid and intracellular fluid occur across plasma membranes. Exchanges across the plasma membrane depend on its permeability properties. As a general rule, two-way osmotic flow of water is substantial. But ion fluxes are restricted and, in most cases, ions move selectively, by active transport or through channels. Movements of nutrients, respiratory gases, and wastes are typically unidirectional (both ways). For instance, glucose and oxygen move into the cells and metabolic wastes move out.

Many factors can change ECF and ICF volumes. Because water moves freely between compartments, however, the osmolarities of all body fluids are equal. Increasing the ECF solute content (mainly sodium chloride) causes osmotic and volume changes in the ICF — generally, a shift of water out of cells. Conversely, decreasing ECF osmolarity causes water to move into the cells. Thus, ECF solute concentration determines ICF volume.

Chemical Bonds

Chemical Bonds

When atoms combine with other atoms they are held together by chemical bonds(bonds formed between electrons of reacting atoms). These electrons occupy regions of space orbiting the nucleus called electron shells. Each electron contains one or more orbitals and each electron shell represents a different energy level (a general understanding of chemical bonds is necessary in anatomy and physiology).

A few key points to remember about electrons, orbitals, and electron shells include:

1. Electrons furthest from the nucleus have the greatest potential energy.
2. Electrons furthest from the nucleus are most likely to interact with other atoms.
3. The only electrons important in chemical bonding are those in the atoms outermost energy level.

   

The term valence shell indicates the atoms outermost electron shell or energy level (important).

When the valence shell is full (or has eight electrons), the atom is considered stable and non-reactive. If the outer shell is not full, electrons will compensate for it by gaining, losing, or sharing electrons with other atoms to achieve stability. This is when chemical bonds are formed.

Types of chemical bonds

There are three major types of chemical bonds: ionic, covalent, and hydrogen bonds.

Ionic bond– is a chemical bond between atoms formed by the transfer of one or more electrons from one atom to the other. The atom that gains an electrons is called the electron acceptor. Because electrons are electronegative, it acquires a net negative charge and is called an anion. The atom that loses electrons is called the electron donor. It acquires a net positive charge (because it loses electronegative electrons) and is called a cation. Anions and cations are formed whenever electron transfers between atoms occur. A good example of an ionic bond is table salt (NaCl). View the image above for a visual description.

Covalent bond– Electrons do not have to be completely transferred for atoms to achieve stability. Instead, they can be shared so each atom is able to fill it’s valence shell. When electrons occupy a single orbital shared by both atoms, it’s called a covalent bond. For instance, in the image above two fluorine atoms are sharing a pair of electrons on their valence shell.  They are covalently bonded. Typically there are single, double, and triple covalent bonds (atoms share one, two, or three pairs of electrons).

Polar and non-polar molecules

In the covalent bonds we have discussed, the shared electrons are shared equally between the atoms, but this is not always the case. Below is a brief list of terms describing how covalent bonds may differ.

Non-polar molecules– share electrons equally and are electrically balanced (do not have separate + and – poles of charge). Carbon dioxide molecules are non-polar.

Polar molecules– Unequally share electrons and have two poles of opposite charge. Water is a good example of a polar molecule, it has a slightly negative oxygen end bonded to a slightly positive hydrogen end.

Hydrogen bonds– are the weakest bond of the three types. They are more like attractions than true bonds. They occur when a hydrogen atom, already covalently linked to an electronegative atom, is attracted by an atom looking for electrons (forming a bridge between them). Hydrogen bonding is responsible for the tenancy of water molecules to cling together and form films (referred to as surface tension). This is why water beads up into spheres when sitting on a flat surface. The best example of a hydrogen bond is the bonds formed between water molecules (refer to image above).

Molecules and Compounds

Molecules and Compounds

In a recent article we discussed the importance of atoms and elements, but most atoms do not exist in a free state. Instead, they combine with other atoms through chemical bonds forming molecules and compounds.

A molecule is a group of two or more atoms from the same element held together by a chemical bond. For instance, when two oxygen atoms combine, a molecule of oxygen gas forms.

When two (or more) different kinds of atoms combine, they form a compound. Compounds differ from molecules because they always contain atoms of at least two different elements. Since oxygen gas only contains one element, (oxygen) it’s considered a molecule. In contrast, water (H2O) is a compound because it contains two elements, hydrogen and oxygen. Properties of compounds are usually very different from the atoms they contain, this is an important concept to understand. For instance, water is very different from the atoms it contains (hydrogen and oxygen).

Mixtures

Mixtures are substances composed of two or more components (physically mixed together). Most matter in nature exists in the form of mixtures. There are three main types of mixtures: solutions, colloids, and suspensions.

• Solutions– are homogeneous mixtures of components (either gases, liquids, or solids). Homogeneous means the mixture has the same composition throughout.  For instance, if samples are taken from the mixture, they will have the same makeup and composition. Air and seawater are examples of homogeneous mixtures. The substance present in the greatest amount is called a solvent and is usually a liquid. Substances present in smaller amounts are called solutes. Solutes are usually dissolved by the solvent. Water is the human body’s main solvent. Most solutions in the body are true solutions (solutions containing gases, liquids, or solids dissolved in water). Saline solution is an example of a true solution.
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• Concentration of solutions– True solutions are described in terms of their concentration which can be indicated in several ways. Solutions in most colleges and hospitals are described by percentage (parts per 100). When using this method, the percentage is always based on the solute and the solvent is usually water. For instance, if the solution is 100 ml and the solute is 8 ml, the solution percentage would be 8.
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  Colloids (emulsions)– are heterogeneous mixtures (their composition differs in different areas of the mixture). Colloids have several unique properties, including the ability to undergo sol-gel transformations (to change reversibly from a fluid state to a solid gel). Jell-O is an example of a colloid that changes from a liquid to a gel when refrigerated. Sol-gel transformations underlie many important cell functions including cell division.
• Suspensions– are heterogeneous mixtures with large, visible solutes that tend to settle. An example of a suspension is a mixture of sand water (the sand settles to the bottom and completely separates until stirred again).
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Distinguishing mixtures from compounds

Mixtures differ from compounds in several important ways:

1. No chemical bonding occurs between the components of a mixture (chemical bonding does occur between compounds).
2. Some mixtures can be separated by physical means (straining, filtering). Compounds can only be separated by chemical means (breaking bonds).
3. All compounds are homogeneous. In contrast, some mixtures are homogeneous, while others are heterogeneous.

Atoms and Elements

Atoms and elements

All matter is composed of elements. An element is a structure that cannot be broken down into simpler substances (by ordinary methods). Some well known elements include oxygen, carbon, and iron. Currently, science recognizes 118 elements, 92 occur in nature and the other 26 are made artificially. 96% of the human body is made up of carbon, oxygen, hydrogen, and nitrogen. These are known as the four main elements of the human body. 20 other elements are also present in the body, some in trace amounts. The periodic table lists all known elements and explains the properties of each.

All elements are composed of smaller particles called atoms. Every elements atoms differ from those of other elements giving it unique physical and chemical properties.

• Physical properties– are properties we can detect with our senses (touch, smell) or measure (boiling point).
• Chemical properties– is how atoms interact with each other (bonding behavior).

Each element is designated with an atomic symbol. An atomic symbol is a one or two letter (usually the first letter/s of an elements name) shortened name. For instance, O stands for oxygen, C stands for carbon.

Atomic structure

Atoms are small, but atoms are made up of even smaller particles. These subatomic particles differ in mass, electrical charge and position. Below is a description of each.

Nucleus- each atom has a central nucleus. The central nucleus contains protons and neutrons bound together. The nucleus is surrounded by electrons (orbiting).

1. Proton– is a particle with a positive electrical charge.
2. Neutron– is a particle with a neutral charge. Because the nucleus is made up of protons and neutrons, it has an overall positive charge.
3. Electron– is a particle with a negative charge. Electrons are extremely small (1/2000 the mass of a proton).

All atoms are electrically neutral because the number of protons (+) is balanced out by the number of electrons (-). For example, iron has 26 protons and 26 electrons (making its electrical charge neutral). The number of electrons and protons is always equal in an atom.

Common elements in the human body

• Oxygen (O)- A major component of organic (carbon-containing) and inorganic (non-carbon containing) molecules. Oxygen is needed for the production of ATP during cellular respiration.
• Carbon (C)– Component of organic molecules (carbs, fats, proteins, molecules).
• Hydrogen (H)– Component of organic molecules. Influences pH of body fluids.
• Nitrogen (N)– A component of proteins and nucleic acids.
• Calcium (Ca)– found as salt in bones and teeth.
• Phosphorus (P)– Part of calcium phosphate salts in bones and teeth.
• Potassium (K)– Necessary for conduction of nerve impulses and muscle contraction. Major positive ion in cells
• Sulfur (S)– Component of proteins (especially muscle proteins).
• Sodium (Na)– Important in water balance, muscle contractions, and nerve impulses. Most abundant positive ion in extracellular fluid.
• Chlorine (Cl)– Most abundant negative ion in extracellular fluid.
• Magnesium (Mg)– Important in several metabolic reactions. Present in bone.
• Iodine (I)– Used to make functional thyroid hormones.
• Iron (Fe)– Component of hemoglobin (transports oxygen) and some enzymes.
There are trace elements in the body also. Trace elements are elements required in small (minute) amounts. A few examples include cobalt (Cr), flourine (F), copper (Cu), silicon (Se) and more.


Planetary model of the atom


The planetary model of an atom illustrated above depicts electrons moving around the central nucleus in a fixed circular orbit. But even though the orbits are fixed, the exact location of electrons isn’t known because they follow unknown trajectories around the nucleus. An orbital is defined as regions around the nucleus electrons are likely to be found most of the time. Using the orbital model is a useful tool in predicting the chemical behavior of atoms.
Atoms of different elements are composed of different numbers of protons, neutrons, and electrons. For instance, hydrogen has one proton, one electron, and no neutrons. Helium has two protons, two neutrons, and two electrons and the list goes on. So, how do we recognize and label these differences? Science uses atomic number, atomic weight, and mass number to do this. If you take a look at the periodic table, you can locate all of them.
• Atomic number– is equal to the number of protons int he nucleus of an atom. It is written as a subscript to the left of the atomic symbol. For instance, hydrogen’s atomic number would be 1 because it has one proton.
• Mass number– is the sum of the atoms protons and neutrons. For example, helium has two protons and two neutrons so its mass number is 4.
  
Isotopes– are structural variations of an element. Almost all known elements have two or more structural variations (isotopes). Isotopes have the same number of protons and electrons but differ in the number of neutrons they contain. Earlier, we said hydrogen has a mass number of 1 (which it does) but this is not always the case. Hydrogen has several isotopes, it’s most abundant contains a mass number of 1, but others contain mass numbers of 2 and 3.
Atomic weight– is an average of the relative weights (mass numbers) of all the isotopes of an element. In most cases, the atomic weight is equal to the mass number of its most abundant isotope.


Radioisotopes-the process of atomic decay is called radioactivity. This happens when an atom is unstable and decays spontaneously into a more stable form. Isotopes that cause radioactivity are called radioisotopes. Radioisotopes are valuable tools used in biology and medicine. For example, Iodine 131 is used to determine the size and activity of the thyroid gland. It’s also used to detect thyroid cancer, but radioisotopes can harm the body too. For instance, inhaled particles from decaying radon can cause lung cancer.

Basic Chemistry: Matter and Energy

Matter and energy

You may be asking yourself, what role does chemistry play in anatomy & physiology? Well, the answer is fairly simple. Your entire body is made up of 1000’s of chemicals that continuously interact with one another. Since chemical reactions are a part of all physiology processes within the body, a basic understanding of chemistry must be established to understand how physiological (digestion, pumping of blood, ect.) processes work. 

Furthermore, thanks to years of scientific studies and experiments using complex laboratory equipment such as stirrers for laboratory liquid and fluid, our understanding of chemistry and its role in anatomy and physiology has been enhanced.

Matter is defined as anything that occupies space and has mass. In many instances, matter can even be seen and felt.

States of matter

Matter can exist as a solid, liquid, or gas. Each state of matter is found in the human body. For example, bones and teeth are solid, they have a definite shape and volume. In contrast, blood is a liquid, it has a definite volume but its shape changes. The air we breath is considered a gas and has no definite shape or volume.

Energy

Energy is defined as the capacity to do work, or put matter into motion. Energy has no mass and can only be measured by the effects it has on matter. The greater work done, the more is needed to complete the task. For instance, a sprinter who just ran 100 meters uses more energy than someone who casually jogs 100 meters.

Kinetic versus Potential Energy

Energy exists as kinetic and potential energy. Each form can be transformed into the other.

• Kinetic energy– is energy in action. Kinetic energy is the opening of a door, or the pulling of a cart. It’s energy in motion (moving objects).
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• Potential energy– is stored energy. It is stored energy with the potential, or capability to do work. For instance, a battery is an example of potential energy. It’s stored energy that can be used in the future. Water behind a dam is a widely used example of potential energy.

When potential energy is released, it becomes kinetic energy allowing it to do work.

Forms of energy

• Chemical energy– is energy stored in bonds of chemical substances. When chemical reactions occur within the body, potential energy stored in bonds (atoms) is released and becomes kinetic energy. A good example of this would be energy from foods. When you eat food, the body does not use the food directly. Instead, energy from the food is captured in temporary bonds of ATP (adenosine triphospahte). Eventually, ATP’s bonds are broken and the stored energy is released. ATP is the most useful form of energy in living systems. It’s used to run almost every functional process of life.
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• Electrical energy– is formed when charged particles move. In the body, electrical currents are generated when ions (charged particles) move across cell membranes. The nervous system uses nerve impulses (electrical currents) to transmit messages throughout the body.
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• Mechanical energy– is energy that’s directly involved in moving matter. When you ride a bike, your legs provide the energy to move the pedals.
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• Radiant energy (electromagnetic energy)– is energy that travels in waves. This could be a topic all by itself but here’s a brief description. The waves vary in length and are collectively called the “electromagnetic spectrum”. They include radio waves, ultraviolet waves, infrared waves, visible light and more. An example would be ultraviolet waves from the sun causing sunburn (these same waves also stimulate the body to make vitamin D). Visible light stimulates the retina of our eyes and plays a role in vision. The list goes on.

Energy conversion

In most cases, energy is easily converted. For instance, chemical energy in gasoline can be used to power the motor of a car. By doing so, the energy is converted to mechanical energy (the tires move). During an energy conversion, some energy is always lost as heat. All energy conversions in the body give off heat. In turn, the heat helps us maintain our body temperature.

Body cavities and membranes

Body cavities and membranes

In most cases, the body is described as having two main cavities called the “dorsal and ventral body cavities”. Some anatomical references do not recognize the dorsal body cavity but we will use it in this example because it’s used by many professionals and colleges.

It also makes it easier to understand! If you would like to brush up on anatomical language and directional terms before moving on.

Dorsal body cavity

The dorsal body cavity protects organs of the nervous system and has two subdivisions. The cranial cavity is the area within the skull and encloses the brain. The spinal (vertebral) cavity encases the vertebral column and spinal cord.

Ventral Body cavity

Like the dorsal cavity, the ventral cavity has two subdivisions. The superior division is called the thoracic cavity. The thoracic cavity is surrounded by the ribs and muscles in the chest. It’s further su

divided into lateral pleural cavities (each pleural cavity envelopes a lung) and the mediastinum. Within The pericardial cavitylies within the mediastinum. It encloses the heart and remaining thoracic organs (trachea, esophagus, ect.).

The inferior division of the ventral body cavity is called the “abdominopelvic cavity” and is separated from the thoracic cavity by the diaphragm. The abdominopelvic cavity is also separated into two subdivisions, the “abdominal cavity” and “pelvic cavity“. The abdominal cavity contains the stomach, spleen, liver, intestines, and a few other organs. The pelvic cavity (inferior) contains the urinary bladder, rectum, and some reproductive organs.

Membranes in the Ventral body cavity

The walls of the ventral body cavity and outer covering of its organs contain a thin covering called the serosa (also called serous membrane). It is a double-layered membrane made up of two parts called the “parietal serosa” (lines the cavity walls) and “visceral serosa” (covers organs in the cavity). The serous membranes are separated by a thin layer of fluid called “serous fluid“. Serous fluid is secreted by both membranes and acts as a lubricant, allowing organs to slide in the cavity without causing friction.

Typically, the serous membranes are named according to the cavity and organ they associate with. For instance, the parietal pericardium lines the pericardial cavity.

Abdominopelvic regions and quadrants”

Because it’s so large, the abdominopelvic cavity is separated into regions and quadrants. The quadrants are self-explanatory and can be figured out fairly easily by looking at the abdominopelvic cavity. They consist of the:

• Right upper quadrant (RUQ)
• Left upper quadrant (LUQ)
• Right lower quadrant (RLQ)
• Left lower quadrant (LLQ)

Simply draw a cross over the cavity seperating it into four boxes, then use the directional terms accordingly.

Abdominopelvic Regions: Image by Mary Weis

The 9 regions of the abdominopelvic cavity are listed below (see image above also).

• Umbilical region– center-most region (belly button)
• Epigastric region– superior to the umbilical region (above belly)
• Hypogastric region– inferior to the umbilical region (pubic area)
• Right and left iliac (inguinal region)-located lateral to the hypogastric region
• Right and left lumbar regions– lateral to the umbilical region
• Right and left hypochondriac regions– lateral to the epigastric region

Other body cavities

• Nasal cavity– is part of the respiratory system. Located within the nose (and posterior).
• Orbital cavities– house the eyes
• Oral cavity– the mouth, contains the teeth and gums
• Synovial cavities–  surround freely movable joints and secrete a lubricating fluid like serous membranes.

The Language of Anatomy: anatomical position and directional terms

Anatomical position and directional terms

The healthcare industry has its own terminology, especially anatomy and physiology. In order to provide exquisite care and understand the inner workings of the human body, anatomical terminology is a necessity. We’ll begin by going over “anatomical position and directional terms”.

In order to describe body parts and positions correctly, the medical community has developed a set of anatomical positions and directional terms widely used in the healthcare industry. The anatomical reference point is a standard body position called the anatomical position. In the anatomical position, the body is erect, the palms of the hand face forward, the thumbs point away from the body, and the feet are slightly apart. It’s important to understand the anatomical position because most directional terms are based off it.

Orientation and directional terms

• Superior (cranial)– toward the head or upper part of the body; above
• Inferior (caudal)– away from the head or toward the lower part of the body; below
• Ventral (anterior)– toward or at the front of the body; in front of
• Dorsal (posterior)– toward or at the back of the body; behind
• Medial– toward or at the midline of the body
• Lateral– away from the midline of the body
• Intermediate– between a medial and lateral position
• Proximal– closer to the origin of the body part or point of attachment of a limb to the body trunk
• Distal– away from the origin of a body part or point of attachment of a limb to the body trunk
• Superficial (external)– toward or at the body surface
• Deep (internal)– Away from the body surface

Directional terms allow us to explain where one body part is when compared to another.

Regional Terms

The two main divisions of the body are its axial and appendicular parts. The axial part makes up the main axis of the body and includes the head, neck, and trunk. The appendicular part consists of the limbs (appendages) attached to the body’s axis. View the image above for an in depth look into all the regional terms used to designate specific areas within the human body. You will have to know them!

Body planes and sections

For anatomical purposes, the body is often sectioned into flat surfaces called planes. Thost frequently used body planes are the sagittal, transverse, and frontal planes. The image above shows how the body is cut into corresponding planes.

• Saggital plane– is a vertical plane that divides the body into right and left parts
• midsaggital plane- is the saggital plane that lies directly in the midline
• parasaggital planes– are saggital planes offset from the midline
• Frontal plane (coronal plane)– also lies vertically; divides the body into posterior and anterior sections
• Transverse plane (horizontal plane)– runs horizontally; divides the body into inferior and superior sections
• Oblique sections– are diagonal cuts made between the vertical and horizontal planes; seldom used