Erin Odya

Cheat Sheet / Updated 03-08-2023

The human body is a beautiful and efficient system that everyone should know a little bit about. In order to study and talk about anatomy and physiology, though, you need to learn the language. You have to have a solid grasp on the directional terms, the body cavities, and the overall organization of the organs and their division of labor. A familiarity with common Latin and Greek word roots will go a long way too.

Article / Updated 12-20-2018

You’ve likely had your blood pressure taken before—the strap wrapped around your upper arm then inflated just to the point that you consider ripping it off from the pain. The purpose of this contraption is to block blood flow to your forearm. Then, as air is let out, blood begins to flow turbulently creating the audible sounds of Kortokoff (that’s why the stethoscope is positioned on your antecubital region, or inner elbow). When the pressure around your arm matches the systolic blood pressure, the maximum force that the blood puts on the walls of the arteries due to ventricular contraction, some blood gets through, hitting the walls which you can hear. Then, when the external pressure matches the diastolic blood pressure, the force applied to the walls between contractions, the sounds stop because the blood is now allowed to flow smoothly. So your blood pressure is recorded as the systolic pressure over the diastolic, or 120/80 mmHg on average. The importance of blood pressure is not only to keep the blood circulating; it is the driving force behind capillary exchange. Blood pressure that is too high (hypertension) damages the artery walls leading to a cascade of problems that can ultimately lead to heart failure. Unfortunately for us, the body doesn’t seem to care much about this issue, as plenty of resources are being exchanged at the capillaries. There is no built-in mechanism for homeostasis of blood pressure if it is chronically high. On the other hand, low blood pressure (hypotension) means the body’s tissues aren’t receiving enough oxygen and other nutrients—a problem that must be solved post haste. A series of hormones are released via the renin-angiotensin system, which leads to vasoconstriction (decreasing the diameter of the arteries) and water retention in the kidneys, both of which lead to an increase in blood pressure.

Article / Updated 10-21-2018

Innate, or non-specific, defenses are the tools our bodies use to attack foreign invaders regardless of their ilk. Adaptive, or specific, defense is part of the lymphatic system that protects our bodies from foreign invaders. How our innate defenses protect us Germs can be bacteria, viruses, fungi, or other microorganisms, and other foreign particles (pollen, toxins) can be problematic. Our innate defenses target all of these. First and foremost is our skin—the body’s largest organ and our first line of defense. Along with our other mechanical barriers, such as mucus and tears, most of the potential invaders are never even allowed entry. Should one make it into the body we have other innate strategies for our second line of defense: Chemical barriers Enzymes (in saliva, gastric juice) break down cell walls. Interferons block replication (especially of virus and tumor cells). Defensins poke large holes in cell membranes. Collectins group together pathogens for easier phagocytosis. Inflammation: Dilates blood vessels, sending more resources to the area where the pathogen was identified Fever: Weakens microorganisms and stimulates phagocytosis Natural killer cells (NKs): Secrete perforins to poke tiny holes in, or perforate, cell membranes Phagocytosis: Consumption of foreign invaders by specialized white blood cells Unfortunately, the occasional pathogen makes it past these defenses so our bodies mount a targeted attack. Furthermore, if we relied solely on our innate defenses, there would be massive amounts of collateral damage to our own cells (which is responsible for many of our symptoms of illness in the first place). How our adaptive defenses protect us The lymphatic system mounts a two-tiered attack—cell-mediated and humoral—that targets specific pathogens. An adaptive system minimizes collateral damage but takes time to get started. This process is dependent on molecules that stick off the surface of cells called antigens. All cells have them, unique to their variety, and that’s how our immune cells distinguish self versus non-self. A type of white blood cell called a macrophage destroys a pathogen by phagocytosis; however, it leaves the antigens intact and displays them on itself. This way, it’s one of our own cells that looks foreign searching for the matching lymphocytes to initiate our adaptive response. There are two varieties of lymphocyte that carry out this response: T cells which mature in the thymus and B cells which mature in the bone marrow (see the connection?). The action of T cells is called cell-mediated immunity and of B cells it is called humoral immunity. Cell-mediated immunity Once a macrophage finds a T cell with receptors that match its displayed antigens, they bind together. The lymphocyte, called a helper T cell, releases a chemical called interleukin-2, which activates another matching T cell. This stimulates the now cytotoxic T cell to begin proliferating (making copies of itself). These cytotoxic Ts (sometimes called killer Ts) will bind with antigens on the invader and release perforins, killing the pathogen. So only cells with this particular antigen will be targeted. When the battle has waned, suppressor T cells signal the adaptive immune process to stop. Some T cells will remain as memory T cells once the pathogen has been defeated. This way, if it invades again, it won’t take long for the macrophage to find a match and the pathogen will be destroyed before you even show any symptoms—thus providing you immunity. Humoral immunity B cells, with matching receptors, will bind to the pathogen or the antigen-presenting macrophage. When the helper T cell is activated it also releases cytokines which, in turn, activate the B cell. It begins to proliferate into plasma B cells and memory B cells. The memory Bs hang around with the memory T cells in the lymph nodes for protection later. The plasma Bs begin manufacturing antibodies, which are proteins that will bind to the antigens on the pathogens. When bound with antibodies, the pathogen is now neutralized. Since they have two binding sites, antibodies can also cause agglutination, clumping together the invaders for more efficient phagocytosis. They also can activate the complement cascade, a series of chemical reactions that can directly destroy the pathogen. The faster we can locate the matching B and T cells, the less damage the pathogen can cause. Lymphocytes are generated with random receptor shapes and researchers argue that we all have one cell in us somewhere to match any pathogen we could possibly encounter—the issue is, can we find it before the pathogen does irreversible damage.

Article / Updated 09-24-2018

When different elements combine through chemical reactions, they form compounds. When compounds contain carbon, they’re called organic compounds. The four families of organic compounds with important biological functions—carbohydrates, lipids, proteins, and nucleic acids—are covered here. Carbohydrates These molecules consist of carbon, hydrogen, and oxygen in a ratio of roughly 1:2:1. If a test question involves identifying a compound as a carbohydrate, count the atoms and see if they fit that ratio. Carbohydrates are formed by the chemical reaction process of condensation, or dehydration synthesis, and broken apart by hydrolysis, the cleavage of a compound by a reaction that adds water. There are several subcategories of carbohydrates: Monosaccharides, or simple sugars, are the building blocks, or monomers, of larger carbohydrate molecules and are a source of stored energy (refer to the figure). Key monomers include glucose, fructose, and galactose. These three have the same numbers of carbon (6), hydrogen (12), and oxygen (6) atoms in each molecule—formally written as C6H12O6—but the bonding arrangements are different. Molecules with this kind of relationship are called isomers. Two important five-carbon monosaccharides (pentoses) are ribose, a component of ribonucleic acids (RNA), and deoxyribose, a component of deoxyribonucleic acids (DNA). Disaccharides are sugars formed by the bonding of two monosaccharides, including sucrose (table sugar), lactose, and maltose. Oligosaccharides (from the Greek oligo, a few, and sacchar, sugar) contain three to nine simple sugars that serve many functions. They are found on plasma membranes of cells where they function in cell-to-cell recognition. Polysaccharides are polymers, formed when many monomers bond into long, chainlike molecules. Glycogen is the primary polymer in the body; it breaks down into individual monomers of glucose, which cells use to generate usable energy. Lipids The most commonly known lipids are fats. These molecules consist of a 3-carbon glycerol linked to fatty acid chains. Insoluble in water because they contain an abundance of nonpolar bonds, lipid molecules have six times more stored energy than carbohydrate molecules. Upon hydrolysis, however, most fats form glycerol and fatty acids. A fatty acid is a long, straight chain of carbon atoms with hydrogen atoms attached, as shown here. If the carbon chain has its full number of hydrogen atoms, the fatty acid is saturated (examples include butter and lard). If the carbon chain has less than its full number of hydrogen atoms due to double bonds, the fatty acid is unsaturated (examples include margarine and vegetable oils). Phospholipids, as the name suggests, contain phosphorus and often nitrogen in place of one fatty acid chain. These are aligned side-by-side to form the cell membrane. Other lipids include cholesterol, vitamins A and D, and the steroid hormones. Proteins Among the largest molecules, proteins can reach molecular weights of some 40 million atomic units. Proteins always contain hydrogen, oxygen, nitrogen, and carbon, and sometimes contain phosphorus and sulfur. Examples of proteins in the body include antibodies, hemoglobin (the red pigment in red blood cells), and enzymes (catalysts that accelerate reactions in the body). The human body builds protein molecules using 20 different kinds of monomers called amino acids (refer to the figure). An amino acid is a carbon atom attached to a hydrogen atom, an amino group (-NH2), a carboxyl group (-COOH), and a unique side chain called the R group. Amino acids link together by peptide bonds to form long molecules called polypeptides, which then assemble into proteins. These bonds form when the carboxyl group of one molecule reacts with the amino group of another molecule, releasing a molecule of water (dehydration synthesis). A polypeptide, however, is not a functioning protein. It must then be folded, twisted, and often linked with other polypeptides to create a three-dimensional structure which allows it to carry out its function. Nucleic acids These long molecules, found primarily in the cell’s nucleus, act as the body’s genetic blueprint. They’re comprised of smaller building blocks called nucleotides. Each nucleotide, in turn, is composed of a five-carbon sugar (deoxyribose or ribose), a phosphate group, and a nitrogenous base. The sugar and phosphate groups link to form the backbone of the molecule. The base is attached to the sugar and aligns with its partner on the other strand, as shown in the figure. The nitrogenous bases in DNA are adenine, thymine, cytosine, and guanine; they always pair off A-T and C-G forming hydrogen bonds between the bases, creating the rungs of the DNA ladder. In RNA, which occurs in a single strand, thymine is replaced by uracil, so the nucleotides pair off A-U and C-G during transcription.

Article / Updated 09-24-2018

Lymph nodes are the site of filtration in the lymphatic system. Also sometimes incorrectly referred to as lymph glands—they don’t secrete anything, so technically they’re not glands—these bean-shaped sacs are surrounded by connective tissue (and therefore are tough to spot). Lymph nodes contain macrophages, which destroy bacteria, cancer cells, and other matter in the lymph fluid. Lymphocytes (a type of white blood cell), which produce an immune response to microorganisms, also are found in lymph nodes. The indented part of each node, called the hilum, is where the efferent vessels exit and where the blood vessels (that supply the node tissue) enter and exit. Afferent vessels bring the lymph in on the convex side. The stroma (body) of each node is surrounded by a fibrous capsule that dips into the node to form trabeculae, or septa (thin dividing walls) that divide the node into compartments. Reticular (netlike) fibers are attached to the trabeculae and form a framework for the lymphoid tissue and clusters of macrophages and B lymphocytes called lymphatic nodules. If you have trouble remembering your afferent from your efferent, think of the “a” as standing for “access” and the “e” as standing for “exit.” Although some lymph nodes are isolated from others, most nodes occur in groups, or clusters, particularly in the inguinal (groin), axillary (armpit), and mammary gland areas. (You can see some lymph nodes in the figure.) The following are the primary lymph node regions: Cervical: Found in the neck, filter lymph from the head Axillary: Found in armpits, filter lymph from arms and mammary region Supratrochlear: Found above inner elbow, filter lymph from hands Inguinal: Found in inguinal region, filter lymph from lower limbs and external genitalia Pelvic: Found in pelvic cavity, filter lymph from pelvic organs Abdominal: Found in abdominal cavity, filter lymph from abdominal organs Thoracic: Found in mediastinum, filter lymph from heart and lungs Each node acts like a filter bag filled with a network of thin, perforated sheets of tissue—a bit like cheesecloth—through which lymph must pass before moving on. White blood cells line the sheets of tissue, including several types that play critical roles in the body’s immune defenses. This filtering action explains why, when infection first starts, lymph nodes often swell with the cellular activity of the immune system launching into battle with the invading microorganisms.

Article / Updated 09-24-2018

Respiration, or the exchange of gases between an organism and its environment, occurs in three distinct processes: breathing, exchanging gases, and cellular respiration. Here’s a breakdown: Breathing: The technical term is pulmonary ventilation, or the movement of air into and out of the lungs. Breathing is comprised of two distinct actions: inspiration and expiration. Exchanging gases: This takes place between the lungs, the blood, and the body’s cells in two ways: Pulmonary, or external, respiration: The exchange in the lungs when blood gains oxygen and loses carbon dioxide Systemic, or internal, respiration: The exchange that takes place in and out of capillaries when the blood releases some of its oxygen and collects carbon dioxide from the tissues Cellular respiration: Oxygen is used in the catabolism of substances like glucose for the production of energy, creating CO2 as a byproduct. A single respiratory cycle consists of one inhalation followed by an expiration. The regular, restful breathing rate is controlled by the pons, while the medulla oblongata will signal any necessary changes to that pattern. To complete a normal inhalation, the diaphragm (the broad skeletal muscle that forms the bottom of the thoracic cavity) is triggered to contract. This pushes down on the contents of the abdominal cavity, thus increasing the volume of the lungs. An increase in volume causes a decrease in pressure (known as Boyle’s Law). So, as a result of the diaphragm contracting, the pressure of the air already inside the lungs drops below that of atmospheric pressure (the pressure of the air outside our bodies). Because gasses will naturally diffuse to areas of lower pressure, air flows into the lungs. Thus we do not need to “suck in” air with each normal breath. For a deeper inhalation, we contract the intercostal muscles (between the ribs), which pull the ribcage out, further increasing the volume and dropping the pressure inside the lungs even lower so more air can come in. Once inside the lungs, gasses can be exchanged between the air and the blood. Exhalation is a passive process; that is, we don’t tell the lungs to breathe out. We simply stop telling the diaphragm (and the intercostal muscles if they’re engaged) to contract. When they relax, volume decreases and pressure increases. Further, the lungs contain a great deal of elastic tissue. As the muscles relax, the elastic tissue snaps back. This elastic recoil briefly drops the pressure inside the lungs to below atmospheric pressure and air flows out.