The Digestive System
Digestion is the process in which the body breaks down the foods and liquids we consume physically and chemically. This process involves the breakdowns of everything we consume into various molecules that can be utilized by the body. The body doesn't simply intake the steak that you eat and use it as a whole to benefit the body, essentially. The process of digestion is broken down into the organs of which we breakdown and absorb food. Various organs have various enzymes and chemicals that help break down the food we ingest into smaller pieces and molecules that can be absorbed in various places.
Physical breakdown of the food we ingest begins in the mouth, where mastication, or chewing, begins. As we chew, salivary glands release saliva into the mouth via the parotid, submandibular, and sublingual glands. The salivary amylase in the saliva helps chemically breakdown carbohydrates, or starch into maltose. The maltose is absorbed in the tongue, while the rest of the food is swallowed in a process called deglutition, which is a voluntary movement, until the food mass, or bolus, reaches the esophagus. Next, involuntary muscle contractions help push the food down the esophagus in a process called peristalsis. This process is best demonstrated when taking a sleeve and squeezing out a mass through the other end. This brings the food to the stomach.
The stomach is located in the upper left side of the body. It contains hydrochloric acid, enzymes for protein breakdown, and mucus. The mucus covers the walls of the stomach, ensuring that the stomach's hydrochloric acid doesn't digest itself. Very few things are actually absorbed in the stomach, alcohol however, is one of them. The stomach contracts constantly, allowing all of the food inside to be exposed to the enzymes and hydrochloric acid
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inside of it. When a protein source enters the stomach, it is broken down into peptides with the addition of water and pepsin. These peptides are made of hundred of amino acids, and can be broken down into them to make even more protein molecules. Pepsin and trypsin, the enzymes responsible for breaking down protein, are created by pepsinogen when it is exposed to hydrochloric acid or water, respectively. Peptides are usually too large to be absorbed int he intestinal lining, but are absorbed in the small intestine once they are broken down into amino acids. Next, the food enters the small intestine via the duodenum.
The beginning of the small intestine is where a vital process of digestion begins. Secretions from the liver, galbladder, and pancreas are secreted into the small intestine via the common bile duct. Each secretion into the small intestine is responsible for the breakdown or chemical digestion of food for the digestive system. The small intestine contains slightly basic pH levels, which neutralizes the chyme that is passed from the stomach, and through the small intestine. Chyme is the material that is leftover from the stomach that has yet to be digested. Bile from the liver is responsible for the chemical digestion of fat. Once fats reach the small intestine, they are broken down my pancreatic enzymes and chemically broken further so that the small intestine may absorb the fats for energy. The small intestine is nearly twenty two feet long however, it's surface area is even larger than you would expect! The walls of the small intestine are lined with hair-like projections called villi, that increase the surface area exponentially. On these villi contain microvilli, which are essentially the same concept, for they are even smaller hair-like projections that allow the small intestine to absorb most of our foods and nutrients. The small intestine is the major organ involved in the digestion process. Capillaries run through each individual villi and microvilli in order to absorb the food's nutrients into the blood stream. This is true for water and some alcohol, where they will reach the liver and kidneys for filtration and secretion. Peristalsis occurs in the small intestine; the food is squeezed through all twenty two feet or so, until it reaches the large intestine.
The large intestine is responsible for what water, and other nutrients are left. Bacteria resides in the walls in the large intestine that helps break down the left over foods. These bacteria react with what nutrients are left and produces gases such as methane and hydrogen sulfate that contribute to the odor of feces. When the small intestine passes its food into the large intestine, it is almost the state of feces, yet the large intestine needs to absorb the water from it. When the water is absorbed from the material, it is mostly solid and does not contain anymore further nutrients. This is why at this point, that the feces is pooped out.

The Endocrine System
The organs of the Endocrine System are not as major as the organs in the digestive system. The organs include the pineal gland, hypothalamus, pituitary gland, thyroid gland, parathyroid gland, thymus gland, adrenal glands, pancreas, and ovaries or testis. Although these organs are not large in size, the effect they have on the body is immeasurable. These glands and organs secrete chemical messengers called hormones that transport different signals to specific target cells. The major processes controlled by hormones are growth and development, mobilizing body defenses against stressors, maintaining homeostasis within the body, and regulating cellular metabolism and energy balance. Nearly all hormones can be classified as amino-based molecules or steroids. Steroid hormones include sex hormones made by the gonads and the hormones produced by the adrenal cortex. Hormones activate certain cells of the body, these cells being target cells or target organs. When a hormone is released, it is destined to reach a target cell. The target cell has a receptor protein and enzyme on the plasma membrane of the cell, and the hormone is specifically designed to bind to the receptor protein on the membrane for the activation on the cell. The enzyme stimulates a second messenger molecule (cAMP) that makes surrounding cells of the same function more susceptible to being activated by a hormone. When the surrounding cells continue to activate, the area that is activated by the hormone is immensely larger than just a singular cell. Hormones, of course act on an area or cell in numerous ways. The body has numerous counteractions that it takes upon itself to help maintain homeostasis or blood levels. Blood levels are sustained by nearly all hormones in various ways. These ways are described as negative feedback mechanisms. These mechanisms can be classified into three distinct categories; hormonal, humoral, and neural stimulus. In hormonal stimulus, endocrine organs are 'told' to secrete various hormones when acted upon by other hormones. In humoral stimulus, an endocrine organ is alerted by the contents of the blood to secrete it's hormone(s). In neural stimulus, nerve fibers stimulate hormone release, which is only in isolated cases.
The Pituitary Gland hangs by a stalk from the surface of the hypothalamus, and is responsible for the secretion of many hormones that trigger various important organs in the body. It secrets growth hormone, prolactin, follicle-stimulating hormone, luteinizing hormone, thyrotropic hormone, and adrenocorticotropic hormone. These all act upon the bones and muscles, mammary glands, testes or ovaries, thyroid, and adrenal cortex, respectively.
The Thyroid Gland is located at the base of the throat, and secretes two hormones; thyroid hormone and calcitonin. Thyroid hormone controls the rate at which glucose is oxidized, and converted into body heat and chemical energy. It is also important for normal tissue growth and development, especially in the reproductive and nervous systems. Calcitonin increases blood calcium levels by causing calcium to be deposited in the bones.
The Parathyroid glands are attached to the surface of the thyroid gland. They secrete parathyroid hormone or pth or parathormone, which is the most important regulator of calcium levels in the blood. When calcium levels drop to a certain level, pth is secreted which stimulates bone destruction cells to break down bone matrix and release calcium in the blood.
The adrenal glands curve over the top of the kidneys and secrete three major groups of steroid hormones called corticosteroids, mineralocorticoids, glucocorticoids, and sex hormones. Mineralocorticoids are produced by the outermost adrenal cortex cell layer. They regulate salt content in the blood, particularly potassium and sodium ions. This hormone targets the kidneys so they know how much salt to regulate out of the blood. Glucocorticoids promote normal cell metabolism and help the body to resist long-term stressors by increasing blood glucose levels. Sex hormones of males and females are secreted by the adrenal gland and help stimulate growth of pubic hair, change in pitch of voice, and other important factors of growing up.
The pancreatic islets, or islets of Langerhans produce and secreted are insulin and glucagon. High levels of glucose in the blood stimulate the release of insulin from the beta cells of the islets. Insulin speeds up the process of which a cell transports glucose across it's plasma membrane. When insulin is secreted in large amounts, the body is going to utilize glucose faster, and vice versa.
The Thymus Gland is located in the upper thorax, posterior to the sternum. It produces a hormone called thymosin which during childhood acts as an incubator for the maturation of a special group of white blood cells that are important in immune response.
The ovaries produce estrogens and progesterone. Estrogen stimulates the development of the secondary sex characteristics in females. These characteristics include maturation of the reproductive organs and the growth of pubic hair. It also works with progesterone to prepare the uterus to receive a fertilized egg, essentially assisting in the menstrual cycle. During pregnancy, progesterone quiets the muscles of the uterus so that an implanted embryo will not be aborted and prepares the breast tissue to produce milk.
The testes in males produce androgens or male sex hormones, including testosterone. Testosterone causes the development of male sex characteristics including maturation of reproductive system organs, growth of facial hair, development of heavy bones and muscles, and deepening of the voice. It is also responsible to stimulate a male's sex drive.

The Skeletal System
The skeletal system consists of the axial system and appendicular system. The axial system is composed of bones that form the longitudinal axis of the body. The appendicular system is composed of the bones of limbs and girdles. The systems are properly shown in the diagram to the right. The appendicular system includes joints, cartilages, and ligaments associated with the limbs.
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The skeletal system has many functions. These include support, protection, movement, storage, and blood cell formation. It is a support system because the legs act as pillars we stand, walk, and run. The ribs protect the internal digestive organs, as the skull protects the brain. The bones are used as levers so the body may move as needed. Also, blood cells are produced in the marrow cavities of certain bones. Bones can be classified into two different categories; compact and spongy. Compact bones are dense and have a smooth and homogeneous appearance. Spongy bone is composed of small needle-like pieces of bone and there is a lot of open space within the bone. The kinds of bones are long, short, flat, and irregular. Long bones include the humerous and the femur. The short bones, or sesamoid bones include bones such as the kneecap or the carpals of the wrist. Flat bones include the bones of the skull. The irregular bones include the pelvic girdle and the vertebrae.
The long bone is composed of the diaphysis and epiphyses. The diaphysis is the longer shaft of the bone, which is compo200px-Illu_long_bone.jpgsed of yellow marrow, compact bone, the periosteum, perforating fibers, and nutrient arteries. The epiphyses is composed mostly of spongy bone, but has a compact bone outer surface. Articular cartilage surrounds most of the epiphyses, for this is the part of the bone that makes up a joint. There is a thin line in the epiphyses that spans across as a layer of the bone, perpendicular to its surface. This line is called the epiphyseal line, and causes the growth of the bone, length-wise. At the end of puberty, the line calcifies and the period of growing for the patient.

Yellow Marrow makes up a majority of the diaphysis' cavity, also known as the medullary cavity. Red marrow is confined in the same area as the yellow marrow, but is mostly found in children to form blood cells. Red marrow is also found in adults however, it is found primarily in the spongy bone cavities of flat bones and the epiphyses of long bones.
Bone markings are where muscles, tendons, and ligaments attach to and blood vessels and nerves pass through. These markings include projections and processes, depressions and cavities.
Long bones are anatomically structured by a system called the Haversian system. This system surrounds the central canal and a blood vessel. Lamallae then further wrap around the central canal in layers, like an onion. The lamallae contain lamella, and the layers of lamellae are spaced by a matrix which is mostly made up of osteocytes. Perforating or Volkman's canals run perpendicularly or horizontally through the long bone. This system of blood flow in the bones allows quick healing and constant moisture.
The growth of bone, or ossification, is an elongated process that works wonders for the body's skeletal system. The first hyaline cartilage model is covered bone matrix of osteoblasts, or bone-forming cells. Next, the hyaline cartilage model is digested away, as most of the cartilage does in the diaphysis. The epiphyseal plates however do not calcify right away, for they are the origin of growth in the long bone. Bones widen by osteoblasts in periosteum adding bone tissue to the external face of the diaphysis. Red marrow is in the same area as yellow marrow, but is found in children to form blood cells. It is also found in adults in the cavities of spongy bone of flat bones and the epiphyses of long bones.
Long Bone Anatomy
Around the central or haversian canals, lamellae wrap around which contain lacunae, a matrix which contains osteocytes, or bone cells. A ring is formed by lamellae around canals and is called an osteon. Canaliculi branch out from the haversian canals and pass blood vessels and nerves through.
Growth and Formation of Bones (ossification)
First hyalione cartilage model is covered in bone matrix of osteoblasts, or bone forming cells. Then, hyaline cartilage model is digested away. Mostly all of this is digested, excluding articular cartilages and epiphyseal plates.
The widening of bones is thanks to the osteoblasts in the periosteum adding tissue to the external face of the diaphysis and the osteoclasts break down the inner layer of bone. Bones are constantly being remodeled due to calcium blood levels and pull of muscles and gravity on the skeleton. When calcium levels are low, PTH signals osteoclasts to break down the bone to deposit calcium into the blood.
There are two types of fractures, simple or clean, and open or compound. In a simple or clean break, the bone breaks internally, but does not penetrate the skin. In an open or compound break, the bone penetrates the skin. Both are treated by reduction, in which the bone ends are met either by the help of a physician or the pinning or wiring that can be provided during surgery.
The axial skeleton is made up of the skull, vertebrae, and bony thorax. The skull is made of the cranium and facial bones. The spinal column is made up of 26 bones, which are irregular shaped. These bones, or vertebrae, surround the spinal cord. There are exactly 24 vertebrae, and the other two bones are the sacrum and coccyx. The 24 vertebrae are made up of of seven cervical, twelve thoracic, and five lumbar vertebrae. The cervical vertebrae allow the neck to twist and bend. The thoracic vertebrae are the vertebrae that attach to the ribs, creating the torso. The lumbar vertebrae are massive compared to the other vertebrae, and they are the sturdiest. the sacrum is formed by the fusion of 5 vertebrae and formed the posterior wall of the pelvis. the coccyx is formed by three to five fused tiny vertebrae, this is the "tailbone".

The Appendicular Skeleton is composed of 126 bones of the limbs or appendages. The shoulder girdle is composed of the clavicle and the scapulae. The clavicle or collar bone attaches to the manibrium and scapula, and helps avoid shoulder dislocation. It acts as a brace to hold the arm away from the top of the thorax. The scapulae are the shoulder blades. The scapula is not directly attached to the axial skeleton, but kept in place by ligaments and muscles. It only attaches to the axial skeleton at one point, and this is the sternoclavicular joint. The loose attachment of the scapula allows it to slide back and forth against the thorax. The arm is formeI110_L.JPGd by the humerus, the radius and the ulna. The humerus is what creates the joint of the shoulder, and the junction of the humerus and the radius and ulna create the elbow joint. The elbow is a hinge joint because of the ability to bend in one direction and pivot in that direction and it's opposing direction. The pelvic girdle is formed by two coxal bones, or ossa coxae or hip bones. Pelvic girdles differ in anatomy depending on the sex. Female pelvic girdles are wider and shorter, where as males have narrower and taller girdles. Where the sacrum meets the iliac part of the pelvic girdle is the sacroiliac joint. This is essentially where the spine meets the pelvis. The hip then connects to the femur at the hip to be square joint. This joint is a ball in socket joint, and moves freely for the most part. If it weren't for tissues, muscles, and ligaments, the leg would be able to move all the way around and twist 360 degrees. The femur meets with the tibia and fibula to create the knee joint. This joint, like the elbow, is a hinge joint. The four ligaments that keep the knee joint intact are the ACL, MCL, PCL, and LCL. These prevent the knee from pivoting, and bending laterally and medially. Finally, the tibia rests on top of the talus bone of the foot, to form the ankle joint. This joint moves more freely than the knee joint, but not as freely as the hip joint. The foot serves two purposes, it supports our body weight and allows us to propel our bodies forward when we walk and run.

The Muscular System
There are three types of muscles in the human body. These types are smooth muscle, cardiac muscle, and skeletal muscles. Smooth muscles are involuntary and include the intestinal tract and the processes that allow us to digest food. These fibers are spindle shaped, and form parallel lines to form sheets, there are no striations and the muscles themselves do not fatigue. Their constant function is necessary to live. Cardiac muscles are also involuntary and have striations. The fibers have one single nucleus and these muscles also do not fatigue. Skeletal muscles are the only voluntary muscles of the body. The help support the body, maintain body temperature, protect internal organs and stabilize joints. Each skeletal muscle has an origin and insertion, the origin is immovable and the insertion is movable.
There are three forms of potential energy storage within all skeleton muscle fibers. These are all possible places for muscles to retrieve energy and perform their functions. First, Adenosine Triphosphate or ATP provides short term energy supply for concentration and relaxation. There is only a small quantity of ATP molecules stored within the muscle fiber, however. Although there are not many ATP molecules within a muscle fiber, there are three to six times the amount of Creatine Phosphate stored. Creatine Phosphate serves as a longer term energy storage that helps quickly to produce more ATP. Creatine Phosphate cannot be used by the muscle for energy, it only helps to create ATP. Muscle fiber Glycogen is the "reserve tank" and has stored glucose in muscle and is a very long term storage mechanism.
There are two types of muscle fibers, red or dark fibers, and white or light fibers. The red or dark fibers owe their color to the high concentrations of myoglobin, which mainly functions as a temporary store for oxygen molecules witmuscle1.jpghin the muscle fiber. Each myoglobin molecule temporarily attaches and stores one oxygen molecule. These types of fibers are high oxidative fibers and are known as aerobic. This muscle type is abundant in the posterior muscles of the neck. They are the most fatigue resistant. Next are high oxidative fast twitch and contain large amounts of myoglobin and are aerobic. They are good for endurance by twitching rapidly, or long distances. The anatomy of a skeletal muscle is demonstrated in the diagram to the right. As shown, there are many myofibrils that make up a fascicle, which in turn make up a muscle. The ability of those myofibrils to utilize calcium, ATP, nitrogen, and potassium is what allows it to be more efficient in absorbing oxygen and utilizing it for longer or shorter periods of time in quick bursts. Within the myofibril, there are filaments myosin and actin. They pull together via means of cross bridges. When these filaments cross paths, the muscle contracts and allows movement. Actin filaments are thin and myosin are thick.
The body is capable of producing ten movements, along with their opposite motions. These motions include flexion, extension, rotation, abduction, adduction, circumduction, dorsiflexion and plantar flexion, inversion and eversion, supination and pronation, and opposition. These movements are used in everyday life. Flexion is the act of bringing a body part to it's origin. Extension is the act of elongating a body part. Inversion is moving the toes inward, eversion is moving them outwards.