Curiosity for Systems of the Human Body

Those of us interested in the medical field aren't the only types of people who enjoy knowing a variety of medical facts. Personally, my intrigue with the human body began with a passion for the Saw films. As a lover of horror, you can often find reference to the human body in a variety of sub-genres that aren't restricted to so-called "torture porn". Perhaps I'm the only one who enjoys making these connections, but they are my two biggest passions. For this informal essay (really an informative stream of consciousness) I will point out a few facts I find fun, revolving around systems of the body I enjoy learning about the most.

I am currently in the process of receiving my Medical Assistant certification and have gathered these facts from my notes, and use of my class' textbook. We use the seventh edition of Medical Assisting: Administrative and Clinical Procedures with Anatomy and Physiology by Kathryn A. Booth, Lessa G. Whicker, and Terri D. Wyman.

Integumentary System facts:

Most cells in the stratum corneum, the superficial layer of the epidermis, are dead and very flat. Because they have accumulated keratin (a tough, hard protein), these cells stick together and form an impermeable layer that most bacteria, viruses, and water cannot penetrate.

All people have the same number of melanocytes. What varies in person to person is how active they are in producing melanin, a pigment which ultimately determines skin color. The amount of oxygenated blood in the dermis also helps in determining skin color.

When injured, the area of the injury site becomes inflamed. It gets its red appearance because nearby blood vessels dilate and swell, and because these then "leak", fluids seep into the spaces between cells in the area. This excess fluid activates pain receptors. At the same time, it promotes healing because more blood is traveling to the pain site, carrying more nutrients needed for skin repair and defensive cells to clear up the cause of inflammation.

Nervous System facts:

The tissues of the central nervous system (CNS) are so delicate they need a blood-brain barrier, plus layers of membrane, to protect them. The blood-brain barrier is formed by tight capillaries. Various waste products don't cross through the barrier well, but inflammation can make it more permeable.

The flight or fight instinct comes from the sympathetic branch of the automatic nervous system (ANS), and is triggered by nonepinephrine being released into organs and glands. This increases heart and breathing rates; slows down the activity of digestive glands, stomach muscles, and intestines; dilates the pupils; and constricts blood vessels to increase blood pressure. In the parasympathetic branch of the ANS, acetylcholine produces the opposite effect, although it has little effect on blood vessels because most blood vessels don't receive parasympathetic input.

Special Senses facts:

Lacrimal glands are found on the lateral edge of each eyeball. They are responsible for tear production. Tears are mostly water, but also contain lysozyme (an enzyme that can destroy bacteria and viruses), and they have an outer, oily layer that prevent them from evaporating. The nasolacrimal ducts drain tears into the nose and are located on the medial aspect of each eyeball.

When a person sees something, light enters the eye and passes through the cornea, pupil, lens, and fluids of the eye. The cornea, lens, and fluids help focus the light on to the retina by bending it - light patterns carry the image of whatever the person is seeing by projecting it upside-down on the retina. This is the refraction process. The retina then converts the light into nerve impulses that are transmitted along the optic nerve to the brain.

When a person moves their head, the perilymph and endolymph fluids in the semicircular canals and vestibule of the ears move. This activates a person's equilibrium and hearing receptors. The equilibrium receptors send information along the vestibular nerves for interpretation in the cerebrum.

In order for a person to hear their own voice, sound waves are conducted through the bones of the skull directly to the inner ear, bypassing the external and middle ear. This is known as bone conduction.

Cardiovascular System facts:

During one cardiac cycle, or heartbeat, you can hear two heart sounds called lubb and dubb. These sounds are generated by the valves of the heart when they snap shut. Lubb comes first, occurring when the ventricles contract, and tricuspid and bicuspid valves shut. Dubb follows, occurring when the atria contract, and aortic and pulmonary semilunar valves shut.

Veins have valves that prevent back flow and keep blood moving to the heart. This movement is helped by skeletal muscles - their contractions squeeze veins so blood is pushed through. Sympathetic nerves can also influence veins.

The average-sized adult body contains approximately four to six liters of blood, or approximately 8% of total body weight.

When a person is injured, there are four events that aid in stopping the flow of blood at the injured site: blood vessel spasm, platelet plug formation, blood clotting, and fibriolysis. Blood vessel spasm alone may stop bleeding if the blood vessel is small and the injury is limited - the vessel constricts to decrease the amount of blood flowing through it. If bleeding continues, platelets are called to clump together and form a plug. This process, primary hemostasis, occurs within seconds after an injury is received.

Skeletal System fact:

The rib cage is made of twelve pairs of ribs and the sternum. Ribs are classified based on their anterior attachment. First are the true ribs, the first seven pairs, which are attached directly to the sternum through costal cartilage. False ribs are pairs eight, nine, and ten, attached not to the sternum but to the costal cart of rib pair seven. Lastly are the floating ribs, pairs eleven and twelve. They do not attach to the sternum or any other structure, hence the name.

Respiratory System facts:

The paranasal sinuses are important because they reduce the weight of the skull and equalize pressure between the inside of the skull and the outside environment. They also give your voice its tone.

When a person inhales, their rib cage moves up and out; the diaphragm contracts and moves down; and pressure in the lungs decreases, bringing air in. When a person exhales, their rib cage moves down and in; the diaphragm relaxes and moves up; and pressure in the lungs increases, pushing air out.