DIGESTION

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Devin DeCarteret


Digestion is the process in which the body breaks down food. The food is both chemically and physically broke down. In humans, food is taken in by the oral cavity or mouth. In the mouth the food gets broken chemically by the saliva that is made up by enzymes. Saliva contains 90% water and the other 10% are chemicals. The physical process that happens in the mouth is called mastication. Mastication or chewing is the process by which food is crushed and ground by teeth. There are 32
teeth that are called adult teeth. During the mastication process, the food is positioned between the teeth for grinding by the cheek and tongue. As chewing continues, the food is made softer and warmer, and the enzymes in saliva begin to break down carbohydratesin the food. After chewing, the food (now called a bolus) is swallowed. It enters the esophagus and via peristalsis continues on to the stomach, where the next step of digestion occurs.
The esophagus is a narrow muscular tube about 20-30 centimeters long, which starts at the pharynx at the back of the mouth, passes through the thoracic diaphragm, and ends at the cardiac orifice of the stomach. The wall of the esophagus is made up of two layers of smooth muscles, which form a continuous layer from the esophagus to the colon and contract slowly, over long periods of time. The inner layer of muscles is arranged circularly in a series of descending rings, while the outer layer is arranged longitudinally. At the top of the esophagus, is a flap of tissue called the epiglottis that closes during swallowing to prevent food from entering the trachea (windpipe). The chewed food is pushed down the esophagus to the stomach through peristaltic contraction of these muscles. It takes only about seven seconds for food to pass through the esophagus and now digestion takes place. The next step is the small intestine, which has three parts: the Duodenum, Jejunum, and Ileum.
After being processed in the stomach, food is passed through via the pyloric sphincter. The majority of digestion and absorption occurs here after the milky chyme enters the duodenum. Bile neutralizes the chyme and is used to excrete waste products such as bilin and bile acids. Proteins and peptides are degraded into amino acids. Proteolytic enzymes, including trypsin and chymotrypsin, are secreted by the pancreas and cleave proteins into smaller peptides. The small intestine and remainder of the digestive tract undergoes peristalsis to transport food from the stomach to the rectum and allow food to be mixed with the digestive juices and absorbed. The circular muscles and longitudinal muscles are antagonistic muscles, with one contracting as the other relaxes. When the circular muscles contract, the lumen becomes narrower and longer and the food is squeezed and pushed forward. When the longitudinal muscles contract, the circular muscles relax and the gut dilates to become wider and shorter to allow food to enter. After the food has been passed through the small intestine, the food enters the large intestine. Within it, digestion is retained long enough to allow fermentation due to the action of gut bacteria, which breaks down some of the substances that remain after processing in the small intestine; some of the breakdown products are absorbed. In humans, these include most complex saccharides (at most three disaccharides are digestible in humans). In addition, in many vertebrates, the large intestine reabsorbs fluid; in a few, with desert lifestyles, this reabsorbtion makes continued existence possible.
Food products that cannot go through the villi, such as cellulose (dietary fiber), are mixed with other waste products from the body and become hard and concentrated feces. The feces is stored in the rectum for a certain period and then the stored feces is eliminated from the body due to the contraction and relaxation through the anus. The exit of this waste material is regulated by the anal sphincter.

The Endocrine System


The endocrine system is the system of glands, each of which secretes a type of hormone directly into the bloodstream to regulate the body. The endocrine system is in contrast to the exocrine system, which secretes its chemicals using ducts. It derives from the Greek words "endo" meaning inside, within, and "crinis" for
secrete. The endocrine system is an information signal system like the nervous system, yet its effects and mechanismare classifiably different.

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The endocrine system's effects are slow to initiate, and prolonged in their response, lasting for hours to weeks. The nervous system sends information very quickly, and responses are generally short lived. Hormones are substances (chemical mediators) released from endocrine tissue into the bloodstream where they travel to target tissue and generate a response. Hormones regulate various human functions, including metabolism, growth and development, tissue function, and mood. The field of study
dealing with the endocrine system and its disorders is endocrinology, a branch of internal medicine. Features of endocrine glands are, in general, their ductless nature, their vascularity, and usually the presence of intracellular vacuoles or granules storing their hormones. In contrast, exocrine glands, such as salivary glands, sweat glands, and glands within the gastrointestinal tract, tend to be much less vascular and have ducts or a hollow lumen. In addition to the specialised endocrine organs mentioned above, many other organs that are part of other body systems, such as the kidney, liver, heart and gonads, have secondary endocrine functions. For example the kidney secretes endocrine hormones such as erythropoietin and renin.


The Skeletal System

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The human skeleton consists of both fused and individual bones supported and supplemented by ligaments, tendons, muscles and cartilage. It serves as a scaffold which supports organs, anchors muscles, and protects organs such as the brain, lungs and heart.
The biggest bone in the body is the bone in the thigh and the smallest is the stapes bone in the middle ear. Several factors contribute to the bone density and average mass of the human skeleton including; gender, race, hormonal factors, nutrition, physical activity and lifestyle behaviors. Because of these and other factors affecting an individual's weight the human skeleton may comprise between 12 and 20 percent of a person's total body weight with the average being 15 percent.
Besides contributing to body shape and form, our bones perform several important body function. The functions of the bones consist of support, protection, movement, storage, and blood cell formation.
  • Support. Bones form the internal framework that supports and anchors all soft organs. The bones of legs act as pillars to support the body trunk when we stand, and the rib cage supports the thoracic wall.
  • Protection. Bones protect soft body organs. The fused bones of the skull enclose the brain and the vertebrae surrounds the spinal cord.
  • Movement. Skeletal muscles, attached to bones by tendons, use the bones as levers to move the body and its parts.
  • Storage. Fat i stored in the internal cavities of bones. Bone itself serves as a storehouse for minerals, the most important being calcium and phosphorus, although others are stored. A small amount of calcium in its ion form must be present in the blood at all times for the nervous system to transmit messages for muscle contraction, and for the blood to clot.
  • Blood cell formation. Blood cell formation, or hematopoiesis, occurs within the marrow cavities of certain bones.
The adult skeleton is composed of 206 bones. There are two basic types of osseous, or bone, tissue: Compact bone is dense and looks smooth and homogeneous. Spongy bone is composed of small needle-like pieces of bone and lots of open space. The bones come in all different shapes and sizes. There are long bones, short bones, flat bones, and irregular bones.

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  • Long Bones. They are typically longer than they are wide. As a rule they have a shaft with heads at both ends. Long bones are mostly compact one. All the bones of the limb, except the wrist and ankle bones, are long bones.
  • Short Bones. They are
  • generally cube-shaped and contain mostly spongy bones. The bones of the wrist and ankle are short bones.
  • Flat Bones. They are thin, flattened, and usually curved. They have two thin layers of compact bone sandwiching a layer of spongy bone between them. Most of the bones of the skull, the ribs, and the sternum are flat bones.
  • Irregular Bones. The bones that don't fit into the previous categories are considered irregular. they consist of the vertebrae, and the hip bones.

Projection that are sites of muscle and ligament attachment
  • Tuberosity
    • Large, rounded projection; may be roughened
  • Crest
    • Narrow ridge of bone; usually prominent
  • Trochanter
    • Very large, blunt, irregularly shaped process
  • Line
    • Narrow ridge of bone; less prominent than a crest
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    • Small, rounded projection or process
  • Epicondyle
    • Raised area on or above a condyle
  • Spine
    • Sharp, slender, often pointed projection
  • Process
    • any bony prominence
Projections that help to form joints
  • Head
    • bony expansion carried on a narrow neck
  • Facet
    • smooth, nearly flat articular surface.
  • Condyle
    • Rounded articular projection
  • Ramus
    • armlike bar of bone
Depressions and openings allowing blood vessels and nerves to pass
  • Meatus
    • Canal-like passageway
  • Sinus
  • Fossa
    • shallow, basinlike depression in a bone, often serving as an articular surface
  • Groove
    • Furrow
  • Fissure
    • Narrow, slitlike opening
  • Foramen
    • round or oval opening through a bone

Common types of Fractures
  1. Comminuted
    1. Bone breaks into many fragments
  2. Compression
    1. Bone is crushed
  3. Depressed
    1. Broken bone portion is pressed inward
  4. Impacted
    1. Broken bone ends are forced into each other
  5. Spiral
    1. Ragged break occurs when excessive twisting forces are applied to a bone.
  6. Greenstick
    1. Bone breaks incompletely, much in the way a green twig breaks.0507_humanskull-latview_1.jpg