Marieb, E. (2008). Fundamentals of human anatomy and physiology, 8th ed.

The Circulatory System is the main transportation and cooling system for the body. The Red Blood Cells act like billions of little UPS trucks carrying all sorts of packages that are needed by all the cells in the body. Instead of UPS, I'll call them RBC's. RBC's carry oxygen and nutrients to the cells. Every cell in the body requires oxygen to remain alive. Besides RBC's, there are also White Blood Cells moving in the circulatory system traffic. White Blood Cells are the paramedics, police and street cleaners of the circulatory system. Anytime we have a cold, a cut, or an infection the WBC's go to work. The highway system of the Circulatory System consist a lot of one way streets. The superhighways of the circulatory system are the veins and arteries. Veins are used to carry blood to the heart. Arteries carry blood away from the heart. Most of the time, blood in the veins is blood where most of the oxygen and nutrients have already been delivered to the cells. This blood is called deoxygenated and is very dark red. Most of the time blood in the arteries is loaded with oxygen and nutrients and the color is very bright red. There is one artery that carries deoxygenated blood and there are some veins that carry oxygenated blood. To get to the bottom of this little mystery we need to talk about the Heart and Lungs.

The heart is a two sided, four-chambered pump. It is made up mostly of muscle. Heart muscle is very special. Unlike all the other muscles in the body, the heart muscle cannot afford to get tired. Imagine what would happen if every 15 minutes or so the pump got tired and decided to take a little nap! Not a pretty sight. So, heart muscle is always expanding and contracting, usually at between 60 and 100 beats per minute.

The right side of the heart is the low pressure side. Its main job is to push the RBC's, cargo bays mostly empty now, up to the lungs (loading docks and filling stations) so that they can get recharged with oxygen. Blood enters the right heart through a chamber called the Right Atrium. Atrium is another word for an 'entry room.' Since the right atrium is located above the Right Ventricle, a combination of gravity and an easy squeeze pushes the blood though the Tricuspid Valve into the right ventricle. The tricuspid valve is a valve made up of three 'leaflets' that allows blood to go from top to bottom in the heart but closes to prevent the blood from backing up into the right atrium when the right ventricle squeezes. After the blood is in the right ventricle, the right ventricle begins its contraction to push the blood out toward the lungs. Remember that this blood is deoxygenated. The blood leaves the right ventricle and enters the pulmonary artery. This artery and its two branches are the only arteries in the body to carry deoxygenated blood. Important: Arteries carry blood away from the heart. There is nothing in the definition that says blood has to be oxygenated.

When the blood leaves the pulmonary arteries it enters capillaries in the lungs. Capillaries are very, very small blood vessels that act as the connectors between veins and arteries. The capillaries in the lungs are very special because they are located against the alveoli or air sacks. When blood in the capillaries goes past the air sacks, the RBC's pick up oxygen. The alveoli are like the loading docks where trucks pick up their load. Capillaries are so small, in some places, which only one RBC at a time can get through!

When the blood has picked up its oxygen, it enters some blood vessels known as the cardiac veins. This is fully oxygenated blood and it is now in veins. Remember: Veins take blood to the heart. The cardiac veins empty into the left atrium. The left side of the heart is the high pressure side; its job is to push the blood out to the body.

The left atrium sits on top of the left ventricle and is separated from it by the mitral valve. The mitral valve is named this because it resembles, to some people, a Bishop's Mitered Hat. This valve has the same function as the tricuspid valve; it prevents blood from being pushed from the left ventricle back up to the left atrium.

The left ventricle is a very high pressure pump. Its main job is to produce enough pressure to push the blood out of the heart and into the body's circulation. When the blood leaves the left ventricle it enters the Aorta. There are valves located at the opening of the Aorta that prevent the blood from backing up into the ventricle. As soon as the blood is in the aorta, there are arteries called coronary arteries that take some of the blood and use it to nourish the heart muscle. Remember: the heart is like James Brown, it's the hardest working muscle in the body (in case you don't know, James Brown says he's the hardest working man in show business).

The aorta leaves the heart and heads toward, what else, the head. We have to keep our brains well nourished so we can make good grades in school. The arteries that take the blood to the head are located on something called the aortic arch. After the blood passes through the aortic arch it is then distributed to the rest of the body. The descending aorta goes behind the heart and down the center of the body.

Sometimes, if you are lying flat on your back, you can look down toward your feet and actually see your abdomen pulsate with each heart beat. This pulsation is really the aorta throbbing with each heart beat. Do not be alarmed, this is normal.

From the aorta, blood is sent off to many other arteries and arterioles (very small arteries) where it gives oxygen and nutrition to every cell in the body. At the end of the arterioles are, guess what, capillaries. The blood gives up its cargo as it passes through the capillaries and enters the venous system.

The venous system carries the blood back to the heart. The blood flows from the capillaries, to venules (very small veins), to veins. The two largest veins in the body are the superior and inferior vena cavas. The superior vena cava carries the blood from the upper part of the body to the heart. The inferior vena cava carries the blood from the lower body to the heart. In medical terms, superior means above and inferior means under. Many people believe that the blood in the veins is blue; it is not. Venous blood is really dark red or maroon in color. Veins do have a bluish appearance and this may be why people think venous blood is blue. Both the superior and inferior vena cava end in the right atrium. The superior vena cava enters from the top and the inferior vena cava enters from the bottom.

The human brain is a mass of pinkish-gray tissue containing a neural network involving approximately 10 billion nerve cells, called neurons. Glial cells serve as the brain's support system, in addition to blood vessels and secretory organs. Weighing in at a mere three pounds, the brain operates as the central control system for movement, sleep, hunger, and thirst. It controls nearly every vital activity necessary for survival. Emotions are controlled by the brain: anger, fear, joy, love, elation, contentment, and happiness find their origin inside the brain. Furthermore, the brain receives and interprets the multitude of signals being sent by other parts of the body and the outside environment. There are three major divisions of the brain: the forebrain, midbrain, and hindbrain.

For anatomical study the forebrain is divided into two subdivisions: the telencephalon and the diencephalon. The primary structures of the telencephalon include the cerebral cortex, basal ganglia, and the limbic system. The diencephalon includes the thalamus and the hypothalamus.

Likened to the bark on a tree, the cerebral cortex surrounds the cerebral hemispheres. The cerebral cortex is the folded, convoluted tissue commonly imagined when an image/thought of the brain is recalled from memory. The folded, crumpled structure contains an enormous amount of small and large grooves (sulci and fissures) and bulges (gyri). This type of structure is beneficial for it greatly increases the overall surface are of the cortex. In fact, because of the convoluted design the area of the cerebral cortex is tripled!

The cerebral cortex is commonly referred to as gray matter. This is based upon the appearance of the cortex which, due to the predominance of cells appears grayish brown. The neurons of the cerebral cortex are connected to other neurons within the brain via millions of axons located beneath the cortex. This area is white in color due to the concentration of myelin; it is often called white matter.

One of the most apparent visible features of the brain is the division between the left and right hemispheres of the cerebral cortex. Through evolutionary advances the functions of each hemisphere have evolved. Mental and emotional differences between men and women are speculated to result from different modes of functioning between the two hemispheres. In most cases the left hemisphere is deemed the dominant half of the brain. This is due to its superior language abilities as well as its analytic, sequential.

In general terms it is well understood that the left hemisphere controls linguistic consciousness, the right half of the body, talking, reading, writing, spelling, speech communication, verbal intelligence and memories, and information processing in the areas of math, typing, grammar, logic, analytic reasoning, and perception of details. The right hemisphere is associated with 'unconscious' awareness (in the sense it is not linguistically based), perception of faces and patterns, comprehension of body language and social cues, creativity and insight, intuitive reasoning, visual-spatial processing, and holistic comprehension. Communication between the two hemispheres takes place through the corpus callosum, which, by the way, is more fully developed in women than men- likely giving rise to women's intuition.

The surface of the cerebral hemispheres is divided into four lobes corresponding to the names of the skull plates that protect them: the frontal lobe, parietal lobe, temporal lobe, and the occipital lobe. In addition to these four lobes, a fifth lobe exists called the insula. This lobe is internal and is not visible from the surface of the brain.

The frontal lobes went through a tremendous evolutionary expansion 50,000 years ago. Subsequently, the capacities for long-term planning, goal development, and the ability to override immediate gratification in favor for future goals greatly expanded. The frontal lobes are sometimes associated with what it means to be human. Absence of the frontal lobes typically results in a person who is deemed emotionally shallow, listless, apathetic, and insensitive to social norms. According to Candace Pert, "If God speaks to man, if man speaks to God, it would be through the frontal lobes, which is the part of the brain that has undergone the most recent evolutionary expansion." Furthermore, the frontal lobes exert a degree of control over the hypothalamus, which controls the autonomic nervous system and endocrine system, as well as organizes survival behavior. Control of movement is associated with the frontal lobes via the primary motor cortex located within this lobe.

The parietal, temporal, and occipital lobes are specialized for perception. Within the parietal lobe is the primary somatosensory cortex which receives information pertaining to the senses of the body: touch, pressure, temperature, and pain. Visual information is received by the primary visual cortex located within the occipital lobe. Hearing is processed in the primary auditory cortex within the temporal lobe. The central sulcus (fissure of Rolando) divides the frontal lobe from the parietal lobe. The lateral fissure (fissure of Sylvius) separates the temporal lobe from the overlying frontal and parietal lobes. The parieto-occipital fissure separates the parietal and occipital lobes.

The corpus callosum is the primary connection between the left and right hemispheres of the cerebral cortex. Connection between the two halves takes place through axons that unite geographically similar regions of the two cerebral cortices.

Basal Ganglia: The basal ganglia are a collection of subcortical nuclei situated beneath the anterior portions of the lateral ventricles; they are involved with the control of movement. Parkinson's disease has an effect upon the basal ganglia resulting in poor balance, rigidity of the limbs, tremors, weakness, and difficulty with initiating movements. Some anatomists consider the amygdala (primary component of the limbic system) a part of the basal ganglia given its location. The Limbic System: The limbic system is a collection of brain structures involved with emotion, motivation, multifaceted behavior, and memory storage and recall. The hippocampus (sea horse) and the amygdala (almond), along with portions of the hypothalamus, thalamus, caudate nuclei, and septum function together to form the limbic system.

The diencephalon is the second major division of the forebrain. The principle structures include the thalamus and hypothalamus.

The thalamus is the relay station for incoming sensory signals and outgoing motor signals passing to and from the cerebral cortex. With the exception of the olfactory sense, all sensory input to the brain connected to nerve cell clusters (nuclei) of the thalamus. The thalamus consists of two large connected lobes. The massa intermedia serves as a bridge connecting the two lobes of the thalamus. It is comprised of gray matter and is deemed a non-critical part of the brain; absence of which is outwardly unnoticeable.

The hypothalamus is comprised of distinct areas and nuclei which control vital survival behaviors and activities; such as: eating, drinking, temperature regulation, sleep, emotional behavior, and sexual activity. It is located just beneath the thalamus and lies at the base of the brain. The autonomic nervous system and endocrine system are controlled by the hypothalamus. The anterior pituitary gland is directly connected to the hypothalamus via a special system of blood vessels. Neurosecretory cells released by the hypothalamus act upon the anterior pituitary gland which then secretes its hormones. Most hormones secreted by the anterior pituitary gland control other endocrine glands. Because of this the anterior pituitary gland is sometimes referred to as the Master Gland. Hormones of the posterior pituitary gland are also governed by the hypothalamus.

Two primary parts comprise the midbrain: the tectum and the tegmentum. The primary structure of the tectum includes the superior colliculi and the inferior colliculi. The superior colliculi form part of the visual system. The inferior colliculi are part of the auditory system. The structures appear as four small bumps located on the brain stem. Function in mammals relates to visual reflexes and reaction to moving stimuli.

The tegmentum is situated below the tectum. The reticular formation, periaqueductal gray matter, and the red nucleus and substantia nigra are part of the tegmentum. The reticular formation is comprised of more than 90 nuclei and an interconnected neural network located at the core of the brain stem. It receives sensory information and is involved with attention, sleep and arousal, muscle tonus, movement, and various vital reflexes.

The periaqueductal gray matter consists of neural circuits that control sequences of movements constituting species-typical behavior. The red nucleus and substantia nigra are parts of the motor system. The red nucleus serves as one of two major fiber systems bringing motor information from the brain to the spinal cord. The substantia nigra affects the caudate nucleus via dopamine-secreting neurons.

The cerebellum's primary function involves control of bodily movements. It serves as a reflex center for the coordination and precise maintenance of equilibrium. Voluntary and involuntary bodily movements are controlled by the cerebellum. Visual, auditory, vestibular, and somatosensory information is received by the cerebellum, as is information on the movements of individual muscles. Processing of this information results in the cerebellum's ability to guide bodily movements in a smooth and coordinated fashion. The pons appear as a large bulge in the brain stem between the mesencephalon and the medulla oblongata. The pons contain a portion of the reticular formation as well as nuclei believed important in the role of sleep and arousal.

The myelencephalon is comprised of one structure: the medulla oblongata (oblong marrow). It is the origin of the reticular formation and consists of nuclei which control vital bodily functions. The medulla oblongata is the control center for cardiac, vasoconstrictor, and respiratory functions. Reflex activities, including vomiting, are controlled by this structure of the hindbrain. Appearing as a pyramid-shaped enlargement of the spinal cord, damage to this area typically results in immediate death.