THE HUMAN SKELETON

Gordon Dam

THE HUMAN HEARTH

The Human Heart

The heart is one of the most important organs in the entire human body. It is really nothing more than a pump, composed of muscle which pumps blood throughout the body, beating approximately 72 times per minute of our lives. The heart pumps the blood, which carries all the vital materials which help our bodies function and removes the waste products that we do not need. For example, the brain requires oxygen and glucose, which, if not received continuously, will cause it to loose consciousness. Muscles need oxygen, glucose and amino acids, as well as the proper ratio of sodium, calcium and potassium salts in order to contract normally. The glands need sufficient supplies of raw materials from which to manufacture the specific secretions. If the heart ever ceases to pump blood the body begins to shut down and after a very short period of time will die.

The heart is essentially a muscle(a little larger than the fist). Like any other muscle in the human body, it contracts and expands. Unlike skeletal muscles, however, the heart works on the "All -or-Nothing Law". That is, each time the heart contracts it does so with all its force. In skeletal muscles, the principle of "gradation" is present. The pumping of the heart is called the Cardiac Cycle, which occurs about 72 times per minute. This means that each cycle lasts about eight-tenths of a second. During this cycle the entire heart actually rests for about four-tenths of a second.

Make-up of the Heart.

The walls of the heart are made up of three layers, while the cavity is divided into four parts. There are two upper chambers, called the right and left atria, and two lower chambers, called the right and left ventricles. The Right Atrium, as it is called, receives blood from the upper and lower body through the superior vena cava and the inferior vena cava, respectively, and from the heart muscle itself through the coronary sinus. The right atrium is the larger of the two atria, having very thin walls. The right atrium opens into the right ventricle through the right atrioventicular valve(tricuspid), which only allows the blood to flow from the atria into the ventricle, but not in the reverse direction. The right ventricle pumps the blood to the lungs to be reoxygenated. The left atrium receives blood from the lungs via the four pulmonary veins. It is smaller than the right atrium, but has thicker walls. The valve between the left atrium and the left ventricle, the left atrioventicular valve(bicuspid), is smaller than the tricuspid. It opens into the left ventricle and again is a one way valve. The left ventricle pumps the blood throughout the body. It is the Aorta, the largest artery in the body, which originates from the left ventricle.

The Heart works as a pump moving blood around in our bodies to nourish every cell. Used blood, that is blood that has already been to the cells and has given up its nutrients to them, is drawn from the body by the right half of the heart, and then sent to the lungs to be reoxygenated. Blood that has been reoxygenated by the lungs is drawn into the left side of the heart and then pumped into the blood stream. It is the atria that draw the blood from the lungs and body, and the ventricles that pump it to the lungs and body. The output of each ventricle per beat is about 70 ml, or about 2 tablespoons. In a trained athlete this amount is about double. With the average heart rate of 72 beats per minute the heart will pump about 5 litres per ventricle, or about 10 litres total per minute. This is called the cardiac output. In a trained athlete the total cardiac output is about 20 litres. If we multiply the normal, non-athlete output by the average age of 70 years, we see that the cardiac output of the average human heart over a life time would be about 1 million litres, or about 250,000 gallons(US).

HIV/AIDS

Acquired immune deficiency syndrome or acquired immunodeficiency syndrome (AIDS) is a disease of the human immune system caused by the human immunodeficiency virus (HIV).^[1][2][3] This condition progressively reduces the effectiveness of the immune system and leaves individuals susceptible to opportunistic infections and tumors. HIV is transmitted through direct contact of a mucous membrane or the bloodstream with a bodily fluid containing HIV, such as blood, semen, vaginal fluid, preseminal fluid, and breast milk.^[4][5] This transmission can involve anal, vaginal or oral sex, blood transfusion, contaminated hypodermic needles, exchange between mother and baby during pregnancy, childbirth, breastfeeding or other exposure to one of the above bodily fluids.
AIDS is now a pandemic.^[6] As of 2009, the World Health Organization (WHO) estimated that there are 33.3 million people worldwide living with HIV/AIDS, with 2.6 million new HIV infections per year and 1.8 million annual deaths due to AIDS.^[7]In 2007, UNAIDS estimated: 33.2 million people worldwide had AIDS that year; AIDS killed 2.1 million people in the course of that year, including 330,000 children, and 76% of those deaths occurred in sub-Saharan Africa.^[8] According to UNAIDS 2009 report, worldwide some 60 million people have been infected, with some 25 million deaths, and 14 million orphaned children in southern Africa alone since the epidemic began.^[9]
Genetic research indicates that HIV originated in west-central Africa during the late nineteenth or early twentieth century.^[10][11] AIDS was first recognized by the U.S. Centers for Disease Control and Prevention in 1981 and its cause, HIV, identified in the early 1980s.^[12]

Although treatments for AIDS and HIV can slow the course of the disease, there is no known cure or vaccine. Antiretroviral treatment reduces both the mortality and the morbidity of HIV infection, but these drugs are expensive and routine access to antiretroviral medication is not available in all countries.^[13] Due to the difficulty in treating HIV infection, preventing infection is a key aim in controlling the AIDS pandemic, with health organizations promoting safe sex and needle-exchange programmes in attempts to slow the spread of the virus.

Anatomy, Physiology & Pathology of the Human Eye

The human eye is the organ which gives us the sense of sight, allowing us to observe and learn more about the surrounding world than we do with any of the other four senses.  We use our eyes in almost every activity we perform, whether reading, working, watching television, writing a letter, driving a car, and in countless other ways.  Most people probably would agree that sight is the sense they value more than all the rest.
The eye allows us to see and interpret the shapes, colors, and dimensions of objects in the world by processing the light they reflect or emit.  The eye is able to detect bright light or dim light, but it cannot sense objects when light is absent.

process of vision

Light waves from an object (such as a tree) enter the eye first through the cornea, which is the clear dome at the front of the eye.  The light then progresses through the pupil, the circular opening in the center of the colored iris.
Fluctuations in incoming light change the size of the eye’s pupil.  When the light entering the eye is bright enough, the pupil will constrict (get smaller), due to the pupillary light response.
Initially, the light waves are bent or converged first by the cornea, and then further by the crystalline lens (located immediately behind the iris and the pupil), to a nodal point (N) located immediately behind the back surface of the lens.  At that point, the image becomes reversed (turned backwards) and inverted (turned upside-down).
The light continues through the vitreous humor, the clear gel that makes up about 80% of the eye’s volume, and then, ideally, back to a clear focus on the retina, behind the vitreous.  The small central area of the retina is the macula, which provides the best vision of any location in the retina.  If the eye is considered to be a type of camera (albeit, an extremely complex one), the retina is equivalent to the film inside of the camera, registering the tiny photons of light interacting with it.
Within the layers of the retina, light impulses are changed into electrical signals.  Then they are sent through the optic nerve, along the visual pathway, to the occipital cortex at the posterior (back) of the brain.  Here, the electrical signals are interpreted or “seen” by the brain as a visual image.
Actually, then, we do not “see” with our eyes but, rather, with our brains.  Our eyes merely are the beginnings of the visual process.

myopia, hyperopia, astigmatism

If the incoming light from a far away object focuses before it gets to the back of the eye, that eye’s refractive error is called “myopia” (nearsightedness).  If incoming light from something far away has not focused by the time it reaches the back of the eye, that eye’s refractive error is “hyperopia” (farsightedness).
In the case of “astigmatism,” one or more surfaces of the cornea or lens (the eye structures which focus incoming light) are not spherical (shaped like the side of a basketball) but, instead, are cylindrical or toric (shaped a bit like the side of a football).  As a result, there is no distinct point of focus inside the eye but, rather, a smeared or spread-out focus.  Astigmatism is the most common refractive error.

presbyopia (“after 40” vision)

After age 40, and most noticeably after age 45, the human eye is affected by presbyopia.  This natural condition results in greater difficulty maintaining a clear focus at a near distance with an eye which sees clearly far away.
Presbyopia is caused by a lessening of flexibility of the crystalline lens, as well as to a weakening of the ciliary muscles which control lens focusing.  Both are attributable to the aging process.
An eye can see clearly at a far distance naturally, or it can be made to see clearly artificially, such as with the aid of eyeglasses or contact lenses, or else following a photorefractive procedure such as LASIK (laser-assisted in situ keratomileusis).  Nevertheless, presbyopia eventually will affect the near focusing of every human eye.

eye growth

The average newborn’s eyeball is about 18 millimeters in diameter, from front to back (axial length).  In an infant, the eye grows slightly to a length of approximately 19½ millimeters.
The eye continues to grow, gradually, to a length of about 24-25 millimeters, or about 1 inch, in adulthood.  A ping-pong ball is about 1½ inch in diameter, which makes the average adult eyeball about 2/3 the size of a ping-pong ball.
The eyeball is set in a protective cone-shaped cavity in the skull called the “orbit” or “socket.”  This bony orbit also enlarges as the eye grows.

extraocular muscles

The orbit is surrounded by layers of soft, fatty tissue.  These layers protect the eye and enable it to turn easily.
Traversing the fatty tissue are three pairs of extraocular muscles, which regulate the motion of each eye: the medial & lateral rectus muscles, the superior & inferior rectus muscles, and the superior & inferior oblique muscles.

eye structures

Several structures compose the human eye.  Among the most important anatomical components are the cornea, conjunctiva, iris, crystalline lens, vitreous humor, retina, macula, optic nerve, and extraocular muscles

ANATOMY OF THE BRAIN

The anatomy of the brain is complex due its intricate structure and function. This amazing organ acts as a control center by receiving, interpreting, and directing sensory information throughout the body. There are three major divisions of the brain. They are the forebrain, the midbrain, and the hindbrain.

Anatomy of the Brain: Brain Divisions

The forebrain is responsible for a variety of functions including receiving and processing sensory information, thinking, perceiving, producing and understanding language, and controlling motor function. There are two major divisions of forebrain: the diencephalon and the telencephalon. The diencephalon contains structures such as the thalamus and hypothalamus which are responsible for such functions as motor control, relaying sensory information, and controlling autonomic functions. The telencephalon contains the largest part of the brain, the cerebrum. Most of the actual information processing in the brain takes place in the cerebral cortex.

The midbrain and the hindbrain together make up the brainstem. The midbrain is the portion of the brainstem that connects the hindbrain and the forebrain. This region of the brain is involved in auditory and visual responses as well as motor function.

The hindbrain extends from the spinal cord and is composed of the metencephalon and myelencephalon. The metencephalon contains structures such as the pons and cerebellum. These regions assists in maintaining balance and equilibrium, movement coordination, and the conduction of sensory information. The myelencephalon is composed of the medulla oblongata which is responsible for controlling such autonomic functions as breathing, heart rate, and digestion.

ESTROGE NEW ROLE

Neuroscientists at the University of Massachusetts, Amherst (UMass), and the University of California, Los Angeles, have found that estrogen can act as a neurotransmitter, in addition to its usual role as a hormone in the bloodstream, according to a study published in the Journal of Neuroscience last month.
Estradiol—the type of estrogen that is most prevalent in the body during a female’s reproductive years—is produced by the ovaries and then enters the blood stream where it takes hours or days to bring about changes in the cortex region of the brain. But in of zebra finches, neurons also produced estradiol directly inside the presynaptic terminal. Within a matter of seconds, the hormone then crossed the synapses of the auditory forebrain—the area of the brain that responds to sound.

This is “similar to the way neurotransmitters are controlled,” Luke Remage-Healey, neuroscientist at UMass, said in a press release.
This is the first time that scientists have directly measured estrogen levels over a short period of time in the brain of a live animal to determine how estradiol is produced and transmitted between neurons. Because of the brain’s ability to produce it quickly and in a precise location, Remage-Healey and his colleagues believe that estradiol, which is known to play a role in memory, cognition, and neuroplasticity, may someday be a target to improve brain function.