Donna Rae Siegfried

Cheat Sheet / Updated 04-20-2022

The human body is a beautiful and efficient system well worth study. In order to study and talk about anatomy and physiology, you need to start from an agreed-upon view of the human body. Anatomical position for the human form is the figure standing upright, eyes looking forward, upper extremities at the sides of the body with palms turned out. You also need to be familiar with standard anatomical terms, as well as the various planes, cavities, and organ systems that make up the physical form.

Article / Updated 04-23-2019

The polymerase chain reaction (PCR) is a process that can turn a single copy of a gene into more than a billion copies in just a few hours. It gives medical researchers the ability to make many copies of a gene whenever they want to genetically engineer something. For years, the very structure of DNA made studying it rather challenging. After all, DNA is incredibly long and very tiny. Fortunately, the advent of DNA technology, the tools and techniques used for reading and manipulating the DNA code, has made working with DNA much easier. In 1983, Kary Mullis discovered the PCR process, which allows scientists to make numerous copies of DNA molecules that they can then study. Today, PCR is used for Making lots of DNA for sequencing Finding and analyzing DNA from very small samples for use in forensics Detecting the presence of disease-causing microbes in human samples Producing numerous copies of genes for genetic engineering Scientists can even combine DNA from different organisms to artificially create materials such as human proteins or to give crop plants new characteristics. They can also compare different versions of the same gene to see exactly where disease-causing variations occur. PCR targets the gene to be copied with primers, single-stranded DNA sequences that are complementary to sequences next to the gene to be copied. To begin PCR, the DNA sample that contains the gene to be copied is combined with thousands of copies of primers that frame the gene on both sides. DNA polymerase uses the primers to begin DNA replication and copy the gene. The basic steps of PCR are repeated over and over until you have billions of copies of the DNA sequence between the two primers. The polymerase chain reaction. PCR works a little like chain e-mails. If you get a chain e-mail and send it on to two friends, who each send it on to two of their friends, and so on, pretty soon everyone has seen the same e-mail. In PCR, first a DNA molecule is copied, then the copies are copied, and so on, until you have 30 billion copies in just a few hours.

Article / Updated 06-14-2017

Biology is a very special application of the laws of chemistry and physics. Biology follows and never violates the laws of the physical sciences, but this fact can sometimes be obscured in the complexity and other special characteristics of biological chemistry and physics. Following is a review of some of the principles of chemistry and physics that have special application in anatomy and physiology. Some of these principles overlap — for example, probability is one factor that drives the process of diffusion. Although what follows are oversimplified explanations of very profound and complex matters, they might help you better understand anatomy and physiology. Energy can neither be created nor destroyed The first law of thermodynamics is that energy can be neither created nor destroyed — it can only change form. Throughout any process, the total energy in the system remains the same. This law is one of the fundamental concepts in physics, chemistry, and biology. Energy is the ability to bring about change or to do work. It exists in many forms, such as heat, light, chemical energy, and electrical energy. Light energy can be captured in chemical bonds, such as in the process of photosynthesis. In physiological processes, the energy in the bonds of ATP is transformed into work when the chemical bonds are broken — to move things, for example, and to generate heat. (And where did the energy in ATP come from in the first place? Ultimately, the sun via photosynthesis.) Although the total energy in a system always remains the same, the energy available for biological processes does not. Cells can use energy only in certain specific forms. A physiological process that uses ATP doesn't use all the energy stored in those chemical bonds, but the leftover energy isn't in a form that can be used in another physiological process. It is "lost" to physiology, mostly as heat flowing out into the surrounding environment. Everything falls apart Energy is required to create "order" — for example, to build the atomic and molecular aggregations —"matter" or "stuff." Without continuous input of energy (maintenance), stuff falls apart. No news here for dwellers in the real world. As a physicist might put it, all systems tend toward increasing entropy (disorder). This is the second law of thermodynamics. Energy always moves from a point of higher concentration to a point of lower concentration, never the reverse. For example, where two adjacent objects are of different temperatures, heat flows only from the warmer object (higher energy) to the cooler object (lower energy). A state of order contains more energy than a state of disorder because of the energy that went into building the state of order. Energy flows outward into the relative chaos of disorder. Because living systems are highly ordered, the implications of the second law of thermodynamics are profound for physiology. The law means that physiological homeostasis (the maintenance of order) is an active process that requires energy. The energy that must be applied to drive any physiological process comes from releasing the chemical bonds in ATP. Everything's in motion Particles in a solution fly around constantly and collide with one another all the time. This kind of motion is called Brownian motion. The higher the temperature, the more frequent and harder the collisions. It's the reason why any reaction that can happen will happen, because (most of) the particles required for the reaction will collide sooner or later. This is especially important when considering all the molecules (such as glucose and ions) that move through membranes by simple or facilitated diffusion. Brownian motion is also a mechanism of entropy. Each of the molecular collisions converts energy in the molecules to heat, in which form the energy is transferred to the surroundings. Probability rules Everything that can happen will happen — some of the time. Other times, it won't. The proportion of times it does happen depends on a lot of factors. If a solution contains large numbers of each of two molecules required for a reaction, the different types will collide frequently. So, concentration affects the chances that a reaction will actually occur. The higher the solution's temperature, the more frequently molecules will collide and facilitate the reaction. But almost never will every possible reaction actually happen. Just by chance, some of these molecules won't meet up with their counterpart molecule. That's life. The chance, or randomness, can be quantified as probability. As with this hypothetical reaction, so with everything else related to biology and physiology: Probability, not certainty, rules. By the way, the existence of life itself is highly improbable. And the probability of the existence of the uniqueness that is you is more improbable still. Polarity charges life A molecule is said to be polar when the positive and negative electrical charges are separated between one side of the molecule and the other because of unequal electron sharing. For example, a molecule of water is polar because the oxygen hogs the electrons concentrating the negative charge on the oxygen atom. So the water molecule has a positive charge at one end and a negative charge at the other, similar to a magnet. It attracts and holds other polar molecules. Methane is nonpolar because the carbon shares the electrons with the four hydrogen atoms uniformly. Polarity underlies a number of physical properties of a substance, including surface tension, solubility, and melting and boiling points. In physiology, polarity strongly determines which molecules form bonds and which don't — like how oil and water don't mix. More specifically for the study of physiology, lipids and water don't mix. Living cells use this principle to control the flow of substances into and out of the cell. Lipids are a large and varied group of organic compounds, including fats and oils. All lipids have hydrophobic portions to them — that is, they don't mix with water. Why not? Because a lipid is nonpolar, so it can't form bonds with water. Water molecules push nonpolar molecules aside to get closer to other polar molecules. Water is special Water is arguably the most important molecule in physiology. It accounts for around 60 percent of an adult's body weight. Water's strong polarity gives it characteristics that make it uniquely suited to providing its numerous functions. Water has a high specific heat. A substance's specific heat is the amount of heat required to raise the temperature of 1 gram of the substance 1 degree Celsius. Because water has a high specific heat, it can absorb heat from our active physiological process without increasing the body temperature. The polarity of water also separates molecules from each other; dissolving them. This makes it useful as a method of transport (like in blood). This also makes it an ideal environment for chemical reactions to occur. As such, nearly all our metabolic reactions take place in water. Fluids and solids Physiological processes, generally speaking, take place in fluids, and the properties of fluids are very important in these processes. In everyday conversation, "fluid" means "liquid," something that's usually water-based, like juice, broth, or tea. In physics and chemistry, though, a watery solution is one kind of fluid, whether it's one you'd care to drink or not. Air is another kind of fluid. Fats are fluids, even when they're solid: Butter is exactly the same substance whether cold or warm, and so is every other form of fat. Technically speaking, glass and pure metals are fluids! Salt, in contrast, is a solid. Salt (NaCl) crystals flow out of their containers in every kitchen and dining room, yes, but that doesn't make salt a fluid. It's got to do with the molecular structure. In solids, atoms are tightly packed together in a geometrically precise formation called a crystalline lattice. Sodium chloride is the model for this: Equal numbers of sodium and chlorine ions, each linked to six other ions, all pull each other in as tightly as the forces of polarity (electrical charge) require and allow. Solids are rigid at the molecular level; once bound together in a crystalline lattice, every atom in the molecule remains in place relative to its surrounding molecules. In fluids, things move around more. Components come together in various ways — carbon dioxide and molecular oxygen (O2) dissolve from air into water and back into air (in the lungs). Fluids take the shape of their container. Air flows into and fills your alveoli. A watery mass in your stomach changes shape with every churning contraction. Gaseous fluids can be easily compressed because the molecules are already so far apart. However, the compressibility of liquids is very limited because the water molecules are already held together just about as tightly as they can be made to go. Under pressure Boyle's law describes the inverse relationship between the volume and pressure of a gas. If nothing else changes, such as temperature, an increase in volume brings about a decrease in pressure. When the pressure drops in a fixed space, it creates a vacuum. The mechanisms of breathing utilize Boyle's law. When the diaphragm contracts, it increases the volume of the lungs, which decreases the pressure. The vacuum pulls air in through the upper respiratory tract. It's also a driving force for the cardiac cycle — opening and closing valves to move blood through the chambers of the heart. Redox reactions transfer electrons The concept of reduction-oxidation (or redox) reactions is basically this: An electron is transferred from one chemical entity (atom or molecule) to another. The entity that receives the electron is said to be REDuced. The entity that releases the electron is said to be OXidized. In a redox reaction, the reduction of one entity is always balanced by the oxidation of another. The entities are called a redox pair. The redox reaction changes the oxidation state of both entities. In some cases, the oxidized entity undergoes another reaction to acquire another electron. Note that this isn't a simple reversal of a redox reaction but a new reaction that involves another electron "donor" and frequently requires an enzyme catalyst. Here's a clever mnemonic to help with the terminology: OIL RIG — Oxidation Is Losing, Reduction Is Gaining (electrons, that is).

Article / Updated 06-14-2017

One way to think of human development is as the unfolding in real time and space of a program for generating a unique biological organism. The program is launched when a new zygote comes into existence. All zygotes are created the same way and then proceed down the path of development encoded in their own species-specific and individual-specific DNA. The totality of the DNA of a zygote — that is, its genome — comes into existence at the time of fertilization. The DNA in the zygote's nucleus comprises genes (specific DNA sequences) from both its parents, 50-50, but this particular combination of genes has never been seen before and will never be again. Most genomes, including all human genomes, have aging and death built into the program. All die sooner or later. A few survive until their program has fully unfolded and reached its end. Stages of human development Development begins in the zygote and continues until death. There's no universally agreed-upon definition of the development stages (although two milestone events — birth and, for females, the onset of menstruation — are universally acknowledged), and the age range at which a person passes from one stage to the next is wide. Change is more or less continuous through life, and different organ systems undergo significant changes on their own development timetable. However, conventionally in human biology, the development milestones that mark the stages are based on developments in the nervous and reproductive systems. Dimensions of human development The structural and physiological changes that happen during human development include an increase in size, the acquisition of some specialized abilities, and the loss of some other specialized abilities continuously throughout life. When all goes well, senescence (aging) is the final stage of development. The following sections assume an organism for whom all is going well, biologically speaking: no fatal errors in the genome itself and adequate resources to sustain nutrition, thermoregulation, and all the rest of the life-maintaining physiological reactions. Growth in human development Part of human development involves an increase in size. Increased size is primarily accomplished by the growth of organs that exist in some form in the embryo: The heart grows larger, the brain grows larger, and the bones get longer and heavier. The organs grow by building more of their own tissues, and tissues get bigger by adding cells or increasing cell size. Everything (well, almost everything — there are always exceptions in biology!) grows together, mostly by adding cells. However, not everything grows equally. Different stages of development are characterized by different proportions of tissue types. For example, both the brain and the skeletal muscle increase in size from infancy to adulthood, but the proportion of muscle tissue to brain tissue is much higher in adulthood. When a three-dimensional object such as a living body increases in size, the surface-to-volume ratio decreases. (Or, to put it another way, the volume-to-surface ratio increases — more of your inside parts are dependent on fewer of your outside parts to interact directly with your environment.) The size of a human body strongly influences thermoregulation, fluid balance, and other key aspects of homeostasis. Differentiation during human development For humans, the acquisition of new abilities or improvements in existing abilities is part of development. New physiological abilities come about usually because of cell and tissue differentiation (function specialization). Tissue specialization begins in the pre-embryonic stage. A newborn has some version of more or less all the cell and tissue types, but many fully differentiated cells must be generated and integrated functionally into tissues at appropriate stages of development. Lots of human body functions aren't "learned" but "developed." The ability to digest starch, for example, is acquired during the first year of life, when the body starts producing the necessary enzymes — not when someone teaches a baby how. Toilet training is more about the maturity of the nervous system than the diligence of the parents. The acquisition of a new skill, structure, or process is sometimes accompanied by the loss of existing abilities. A young adult is better at planning than a teenager but has most likely lost some stamina for all-nighters, parties, and road trips. The stages of human development can be characterized by these abilities gained and lost. Among many aspects of development research, brain research has yielded very interesting data in recent years, aided by advanced imaging technology (see Chapter 1). In the late 1990s, the decades-old doctrine that humans don't generate any new brain cells after birth was definitively shown to be false. Data from many different kinds of studies since then have indicated that the human brain is plastic (capable of change and development) well into old age. Senescence during human development According to recent theories, age-related decline in specialized and even basic physiological functions is built into new genomes right at the start. Structures at the ends of the chromosomes called telomeres, which get shorter and shorter as a genome ages, control the number of times the genome can replicate. Gradually, cells lose the ability to divide. The number of aged and dying cells in a tissue eventually exceeds the number of new cells of their type being made to replace them. The tissue loses its ability to function, which impairs the organism's survival. The aging processes are an active area of research in anatomy and physiology. In recent decades, therapies and devices to counter aging's effects have dominated the medical products marketplace worldwide.

Article / Updated 06-14-2017

Human birth is a commonplace miracle: from a single infinitesimal cell to a human baby in less than ten months. The following sections give a brief overview of how it happens. Free-floating zygote Following is a description of the events leading to the fertilization of a secondary oocyte and implantation of the blastocyst in the uterus from the point of view of the zygote, from the fusion of the haploid genomes of the parent gametes to implantation in the uterus. Fertilization, which takes about a day, begins when a sperm penetrates a secondary oocyte (an egg). After a sperm binds with the receptors in the zona pellucida, it uses enzymes in its acrosome to digest the egg's protective layer. When the sperm has finally reached the cell membrane of the oocyte, it attaches to receptors there. This triggers two important events: The zona pellucida will harden, preventing another sperm from fusing with the egg's actual cell membrane. The oocyte will restart meiosis II. As this happens, the sperm's nucleus is allowed into the cell. This way, when the nucleus is reforming in telophase II, the DNA contribution of the sperm is incorporated. The cell, now officially considered a zygote, has completed fertilization and ready to begin its journey. A dangerous journey The zygote undergoes cleavage (mitotic division) immediately. Over the next few days, the daughter cells (called blastomeres) divide twice more, to a total of 16 blastomeres, all within the rigid wall of the zona pellucida with no increase in overall size. The mass, now called a morula (mulberry-shaped), leaves the uterine tube and enters the uterine cavity. Cell division continues, still confined within the zona pellucida, and a cavity known as a blastocoel forms in the morula's center. Around the sixth day after fertilization, the hollow structure, now called a blastocyst, "hatches" from the slowly eroded zona pellucida within the uterine cavity. The outer layer of blastocyst cells secretes an enzyme that facilitates implantation in the endometrium. Angiogenesis (building of blood vessels) begins in the uterus, and diffusion between mother and blastocyst begins. When this diffusion is established, implantation is complete and the pregnancy is established. The new genome has survived a very dangerous stage of development. Biologists estimate that up to one-half of blastocysts fail to implant, and they die. But the new genome still has challenges ahead. The embryonic stage Weeks three through eight after implantation are called the embryonic stage. During these weeks, the embryo's cells begin to differentiate and specialize. The transition from blastocyst to embryo begins when the implanted blastocyst develops into a two-layer disc. The top layer of cells (epiblast) becomes the embryo and amniotic cavity; the lower layer of cells (hypoblast) becomes the yolk sac that nourishes the embryo. A narrow line of cells on the epiblast, called the primitive streak, signals gastrulation — cells migrate from the epiblast's outer edges into the primitive streak and downward, creating a new, middle layer. By 14 days or so after fertilization, the embryo, now called a gastrula, has ectoderm, mesoderm, and endoderm layers — the very beginning of tissue formation. The fetal stage Following week eight and lasting until birth is the fetal stage. Growth and development occur rapidly during this time. The primary germ layers continue their development as the fetus becomes more recognizable as a baby. The ectoderm develops into the skin and nervous tissues, while the endoderm forms your inner tubes — the alimentary canal and the respiratory tract. The mesoderm develops into everything in between, including the bones and muscles. See also "Dividing Fetal Development into Trimesters." Forming the placenta Immediately after implantation, the blastocyst initiates the formation of the placenta, a special organ that exists only during pregnancy that's made of the mother's cells in the outer layers and the fetus's cells in the inner layer. The placenta serves to support the sharing of physiological functions between the mother and the fetus: nourishment (provision of energy and nutrients), gas exchange (a fetus must take in oxygen and eliminate carbon dioxide before birth), and the elimination of metabolic waste. The placenta allows some substances to enter the fetal body and blocks others. It does a good job of delivering nutrients and maintaining fluid balance, but it's permeable to alcohol, many drugs, and some toxic substances. The placenta is a dark red disc of tissue about 9 inches (23 centimeters) in diameter and 1 inch (2.5 centimeters) thick in the center, and it weighs about a pound (roughly half a kilogram). It connects to the fetus by an umbilical cord of approximately 22 to 24 inches (56 to 61 centimeters) in length that contains two arteries and one vein. The placenta grows along with the fetus. Nutrients and oxygen diffuse through the placenta, and the fetal blood picks them up and carries them through the umbilical cord. Then, the wastes that result from the fetus metabolizing the nutrients and oxygen are carried back out through the umbilical cord and diffused into the placenta. The mother's blood picks up the wastes from the placenta, and her body excretes them. Geez, moms start cleaning up after their kids before they're even born! Both the fetus and the placenta are enclosed within the amniotic sac, a double-membrane structure filled with a fluid matrix called amniotic fluid. The fluid keeps the temperature constant for the developing fetus, allows for movement, and absorbs the shock from the mother's movements.

Article / Updated 06-14-2017

The 280 days, usually expressed as 40 weeks, are the human gestational period (length of pregnancy). This period is divided, again by convention, into three trimesters, though nothing specific marks the transition from one to the next. Officially, by convention, Day 1 of a pregnancy is the first day of the woman's previous menstrual period. Obviously, she wasn't pregnant on that day, nor for numerous days thereafter. But it's easier to be sure about the start date of a menstrual period than about the day of ovulation or fertilization or implantation, so that's the custom that doctors follow. Then, by convention, doctors count ahead 280 days to arrive at the due date, the date on which, if all pregnancies and all babies were alike, the birth would take place. Development during the first trimester All the body's organs begin development in the first trimester. The cardiovascular system forms from small vessels in the placenta three weeks after fertilization. The heart begins to beat at this time as well. During the second month, the organ systems continue to develop, and the limbs, fingers, and toes begin to form. The embryo starts to move at the end of the second month, although it's still too small for the mother to feel its movements. Also during the second month, ears, eyes, and genitalia appear, and the embryo loses its tail and begins to look less like a sea horse and more like a human. At the end of the first trimester, the fetus is about 4 inches long (10 centimeters) and weighs about an ounce (28 grams). The head is large, and hair has begun to grow. The intestines are inside the abdomen, and the urinary system (kidneys and bladder) starts to work. If you're counting weeks and feel you're losing track, remember that the trimesters of pregnancy are measured from Day 1 of the mother's last menstrual period. This date is around two weeks earlier than the date of fertilization. The embryonic stage is the second and third month of pregnancy. Development during the second trimester The fetus, with all its systems in place, continues programmed development in the second trimester. Ultrasound imaging shows the skeleton, head details, and external genitalia. Bone begins to replace the cartilage that formed during the embryonic stage. At the end of the second trimester, the fetus is about 12 to 14 inches (30 to 36 centimeters) long and weighs about 3 pounds (1.4 kilograms). Development during the third trimester The fetal development program speeds up in the third trimester. The fetus, with its systems developed, continues to grow in size. Subcutaneous fat is deposited, which serves as a critical energy reserve for brain and nervous system development. Near the end of the third trimester, the fetus positions itself for birth, turns its head down, and aims for the exit. When the fetus's head reaches the ischial spines of the pelvic bones, the fetus is said to be engaged for birth.

Article / Updated 06-14-2017

Taxonomy is the science that seeks to classify and organize living things, expressed as a series of mutually exclusive categories. The highest (most inclusive) category is domain, of which there are three: Archea, Eubacteria, Eukaryota. Each of these domains is split into kingdoms, which are further divided until each individual organism is its own unique species. Outside of bacteria, all living things fall under the Eukaryota domain; the kingdoms are: Protista, Fungi, Plantae, and Animalia. Within each kingdom, the system classifies each organism into the hierarchical subgroups (and sometimes sub-subgroups) of phylum, class, order, family, genus, and species. Here's the breakdown of humankind: Kingdom Animalia: All animals. Phylum Chordata: Animals that have a number of structures in common, particularly the notochord, a rodlike structure that forms the body's supporting axis. Subphylum Vertebrata: Animals with backbones. Superclass Tetrapoda: Four-footed vertebrates. Class Mammalia: Tetrapods with hair. Other classes of the vertebrata are Pisces (fish), Amphibia (frogs), Aves (birds), and Reptilia (scaly things). Order Primates: Mammals with more highly developed brains, flexible hips and shoulders, and prehensile hands and feet (able to grasp). Superfamily Hominoidea: Apes (chimpanzees, gorillas, orangutans, humans). Family Hominidae: Great apes, including humans. Genus Homo: The human species is the only surviving species of our genus, though this genus included several species in the evolutionary past. Species Sapiens: All species are given a two-part Latin name, in which the genus name comes first and a species epithet comes second. The biologists who name species sometimes try to use a descriptor in the epithet. For humans, they could have chosen "bipedal" or "talking" or "hairless," but they chose "thinker." Variety Sapiens: Some species get a "varietal" name, usually indicating a difference that's obvious but not necessarily important from an evolutionary point of view. The human species has one other variety, Homo sapiens neanderthalensis, which has been extinct for tens of thousands of years. All humans living since then are of one species variety, Homo sapiens sapiens. In the evolutionary classification of humans, there's no biologically valid category below species variety.

Article / Updated 06-14-2017

Jargon is a set of words and phrases that people who know a lot about a particular subject use to talk together. Anatomists and physiologists use jargon, much of which is shared with medicine and other fields of biology, especially human biology. Scientists try to create terminology that's precise and easy to understand by developing it systematically. That is, they create new words by putting together existing and known elements. They use certain syllables or word fragments over and over to build new terms. You'll soon start to recognize some of these fragments. Then you can put the meanings of different fragments together and accurately guess the meaning of a term you've never seen before, just as you can understand a sentence you've never read before. This table gets you started, listing some word fragments related to the organ systems. Body System Root or Word Fragment Meaning Technical Anatomical Word Fragments Skeletal system os-, oste-; arth- bone; joint Muscular system myo-, sarco- muscle, striated muscle Integument derm- skin Nervous system neur- nerve Endocrine system aden-, estr- gland, steroid Cardiovascular system card-, angi-, hema-, vaso- heart (muscle), vessel, blood vessels Respiratory system pulmon-, bronch- lung, windpipe Digestive system gastr-, enter-, dent-, hepat- stomach, intestine, teeth, liver Urinary system ren-, neph-; ur- kidney; urinary Lymphatic system lymph-, leuk-, -itis lymph, white, inflammation Reproductive system andr-, uter- male, uterine But why do these terms have to be Latin and Greek syllables and word fragments? Why should you have to dissect and put back together a term like iliohypogastric? Well, the terms that people use in common speech are understood slightly differently by different people, and the meanings are always undergoing change. Not so long ago, for example, no one speaking plain English used the term laptop to refer to a computer or hybrid to talk about a car. It's possible that, not many years from now, almost no one will understand what people mean by those words. Scientists, however, require consistency and preciseness to describe the things they talk about in a scientific context. The relative vagueness and changeability of terms in plain English makes this impossible. In contrast, Greek and Latin stopped changing centuries ago: ilio, hypo, and gastro have the same meaning now as they did 200 years ago. Every time you come across an anatomical or physiological term that's new to you, see if you recognize any parts of it. Using this knowledge, go as far as you can in guessing the meaning of the whole term.

Article / Updated 06-14-2017

Terms that indicate direction make no sense if you're looking at the body the wrong way. You likely know your right from your left, but ignoring perspective can get you all mixed up. Stand up straight. Look forward. Let your arms hang down at your sides and turn your palms so they're facing forward. You are now in anatomical position. Unless you are told otherwise, any reference to location (diagram or description) in the study of anatomy assumes this position. Using anatomical position as the standard removes confusion. The following list of common anatomical descriptive terms (direction words) may come in handy: Right: Toward the patient's right Left: Toward the patient's left Anterior/ventral: Front, or toward the front of the body Posterior/dorsal: Back, or toward the back of the body Medial: Toward the middle of the body Lateral: On the side or toward the side of the body Proximal: Nearer to the point of attachment or the trunk of the body Distal: Farther from the point of attachment or the trunk of the body (think "distance") Superficial: Nearer to the surface of the body Deep: Farther from the surface of the body Superior: Above or higher than another part Inferior: Below or lower than another part Notice that this list of terms is actually a series of pairs. Learning them as pairs is more effective and useful.

Article / Updated 06-14-2017

The anatomical regions (shown) compartmentalize the human body. Just like on a map, a region refers to a certain area. The body is divided into two major portions: axial and appendicular. The axial body runs right down the center (axis) and consists of everything except the limbs, meaning the head, neck, thorax (chest and back), abdomen, and pelvis. The appendicular body consists of appendages, otherwise known as upper and lower extremities (which you call arms and legs). Here's a list of the axial body's main regions: Head and neck Cephalic (head) Cervical (neck) Cranial (skull) Frontal (forehead) Nasal (nose) Occipital (base of skull) Oral (mouth) Orbital/ocular (eyes) Thorax Axillary (armpit) Costal (ribs) Deltoid (shoulder) Mammary (breast) Pectoral (chest) Scapular (shoulder blade) Sternal (breastbone) Vertebral (backbone) Abdomen Abdominal (abdomen) Gluteal (buttocks) Inguinal (bend of hip) Lumbar (lower back) Pelvic (area between hipbones) Perineal (area between anus and external genitalia) Pubic (genitals) Sacral (end of vertebral column) Here's a list of the appendicular body's main regions: Upper extremity Antebrachial (forearm) Antecubital (inner elbow) Brachial (upper arm) Carpal (wrist) Cubital (elbow) Digital (fingers/toes) Manual (hand) Palmar (palm) Lower extremity Crural (shin, front of lower leg) Femoral (thigh) Patellar (front of knee) Pedal (foot) Plantar (arch of foot) Popliteal (back of knee) Sural (calf, back of lower leg) Tarsal (ankle)