Digestion
Intake (How food enters)

Table of Contents


Intake starts in the mouth, where food is masticated, or chewed, and physically broken down. The tongue helps to move and mash the food against the hard palate. Saliva is added to the food to lubricate and further breakdown. Saliva is made in the salivary glands (paratid, sublingual, and submandibular) and is a substance made up from; water, mucus, and salivary amylase. Salivary amylase is an enzyme that chemically breaks down starches and polysaccharides into maltose and smaller polysaccharides. once the food is totally masticated and lubricated into one mass it is considered a bolus.
The bolus is then swallowed in a process called deglutition. This consists of two phases; the buccal phase and the pharyngeal-esophageal phase. The buccal phase occurs in the mouth, as the tongue pushes the bolus against the soft palate and into the pharynx. After this all digestion is invoulentary. The second phase, pharyngeal-esophageal phase, transports the food from the pharynx to the esophagus. Once the bolus is pushed back the soft palate rises to close of the nasal passages and the bolus enters the pharynxs. The larynx rises so that the epiglottis covers its opening as peristalsis carriers the bolus through the pharynx and into the esophagus. The upper esophageal sphincter contracts again as the larynx and epiglottis return to the former positions. From the esophagus, peristalsis squeezes the bolus down to the cardioesophageal sphincter. Once through the cardioesophageal sphincter the bolus enters the stomach.

Stomach (The storage tank)
Once the bolus of food enters the stomach, it is mechanically digested and chemically by gastric juices. Mechanically the bolus is turned by the muscles of the stomach. The stomach has a third muscular layer compared to other alimentary canal walls. This muscle is the oblique layer of muscle which is what allows for the churning and mixing of the bolus with the gastric juices. Gastric juices consist of pepsinogen and hydrochloric acid. Pepsinogen is an enzyme, activated by the acidity of hydrochloric acid, breaks down proteins into large polypeptides. The stomach also produces a sticky alkaline mucus to protect its walls from being damaged by the acid. Once the bolus is digested as much as i can be in the stomach its is resembles a heavy cream and is called chyme. The stomach then holds the chyme until further digestion is needed.

Small Intestine (Where all the magic happens)
The small intestine is where all the digestion occurs, after the small intestine very little is left to digestion. The small intestine consists of three parts; the duodenum, the jejunum, and the ilium. The lining of the small intestine consists of large circular folds in the sub mucosa which have millions of villi. This greatly increases the surface area to absorbed more nutrients. The villi consists of a lacteal and small blood capillaries which allow for absorption into the blood. The small intestine starts at the pyloric sphincter which separates the duodenum from the stomach. The stomach squirts amounts of chyme into the duodenum through the pyloric sphincter, depending on how much nutrients are needed. In the duodenum, food is chemically digested and throughout the small intestine the digested product is absorbed. To breakdown the chyme, the gallbladder releases bile through the cystic duct, into the bile duct, and through the duodenal papilla into the duodenum. Bile can also come straight from the liver if there is none stored in the gallbladder at the time. Bile is used to emulsify fat into smaller droplets so that there is more surface area to work on. The pancreas also releases pancreatic amylase and other pancreatic juices to digest chyme through the duodenal papilla. Pancreatic amylase digest sugar into smaller disaccharides and monosaccharides which are absorbed into the blood and used or filtered into the liver for further processing. Trypsin and other substances, produced by the pancreas, digest protein. Protein is digested to small polypeptides and amino acids and enter the blood capillaries and are transported to the liver. Pancreatic lipase digest the fats droplets into glycerol or monoglycerides, and fatty acids. The digested fat is then absorbed into the lacteals of the villi and are then transported through the blood stream and filtered through the liver. As the chyme digest it moves down the duodenum and through the other parts of the small intestine. As it reaches the end of the ilium the chyme is now harder and contains less liquid resembling more like fecal matter.

Large Intestine (Take out the trash)
The chyme enters the large intestine through the ileocecal valve. It is then called fecal matter. The large intestine consists of six separate segments; Cecum, Ascending colon, Transverse colon, Descending colon, Sigmoid colon, and Rectum. When the fecal matter first enters the large intestine it is in the cecum. It then moves through the large intestine in the order in which I listed the segments. Throughout the large intestine water is absorbed to harden the fecal matter and take up water needed for survival. Water and mucous are sometimes added to aid in lubrication for easy disposal. Once the fecal matter gets to the anal sphincter the involuntary sphincter opens which signals to your brain that fecal matter must be released. The voluntary sphincter opens on your own control which allows you to defecate at an appropriate time instead of whenever fecal matter is present.



Bone System

Bones are the most important component to body shape and form. The skeleton can be split into two divisions, Axial skeleton and Appendicular skeleton. Axial skeleton includes the the longitudinal axis of the body, whereas the Appendicular skeleton includes the bones of the limbs and girdles.

Bone provide:
  • support to hold the body and the basic framework in which muscles and organs can attach to.
  • protection for soft organs of the chest and the brain
  • movement is accomplished by the movement of bones by the skeletal muscles.
  • storage of calcium, fat, and minerals helps the body when food is not available.
There are two types of bone tissue, compact and spongy bone. Compact bone is dense, smooth, and homogeneous; this allows for a cavity inside the bone for marrow. Spongy bone is made up of a matrix of intertwining needle like bones with lots of open space. Bones overall can be classified as long bones, short bones, flat bones, and irregular bones. Long bones are usually longer than wider and are made up of mostly compact bone tissue. Short bones are generally cube shaped and are made up of mostly spongy bone tissue. Flat bones are thin bones that are made up of compact bone on two sides sandwiching a spongy bone layer, like skull or sternum. Irregular bone are any bones that don't fit any of these categories, like vertebrae and the hips.
Long bone structure is