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Digestive System of Human Body

Updated on April 21, 2016

Digestive system can be defined as the system that consist of the alimentary canal which extends from the mouth to the anus, and several accessary organs which secretes substances being used in the process of digestion into the canal.

THE ALIMENTARY CANAL

Alimentary canal are the channel through which the food we consume passes through. The wall of the alimentary canal consist of four distinct layer, which are the mucous membrane, sub mucosa, muscular layer and serous layer. The alimentary canal includes
1) The mouth
2) Pharynx
3) Esophagus
4) Stomach
5) Small intestine
6) Large intestine
7) Rectum and
8) The anus

THE MOUTH: The mouth begins the digestion by receiving the food and mechanically breaking the size of solid particles and mixing them with saliva. The lips, cheek, tongue, palate, and the teeth helps in the process of chewing and swallowing the food.

The lip contains sensory receptors and skeletal muscles that determines the temperature and texture of food. The cheek contains outer layers of skin, pads of fat and muscles associated with expression and chewing. The tongue contains a mucous membrane that covers it and a membranous fold called the frenulum that connects the midline of the tongue to the floor of the mouth. The skeletal muscles that mostly make up the tongue mixes food with saliva during chewing and moves the food towards the pharynx during swallowing. The palate, which includes a hard and a soft portion, forms the roof of the mouth. The soft palate closes the opening of the nasal cavity during swallowing to prevent the food from entering the nasal cavity. The teeth helps reduce or breakdown food into smaller particles thus increasing the surface area of food particles in order to allow digestive enzymes react more effectively with the food molecules.

THE PHARYNX AND ESOPHAGUS: The pharynx is a cavity posterior to the mouth from which the tubular esophagus leads to the stomach. They are passageways whose muscular walls functions in swallowing.

THE STOMACH: The stomach is a J shaped organ located inferior to the diaphragm in the upper left part of the abdominal cavity. The stomach receives food from the esophagus, mixes the food with gastric juice, initiates protein digestion, carries on limited absorption, and moves food into the small intestine.

The stomach is divided into four regions, which includes:
1) The cardiac region
2) Fundic region
3) Body
4) Pyloric region

The cardiac region is an area near the esophagus opening. The fundic is a temporary storage area, i.e. where food is stored for the main time before moving them to the small intestine. The body of the stomach is the main part of the stomach; it lies between the fundic and the pyloric portion. The pyloric region narrows and becomes the pyloric canal as it approaches the small intestine. At the end of the pyloric canal is a muscular wall thickens and thereby forming a powerful circular muscle known as the pyloric sphincter, which is a valve between the stomach and the small intestine. It controls gastric emptying.

SMALL INTESTINE: The small intestine is a tubular organ that extends from the pyloric sphincter to the beginning of the large intestine. The small intestine with its coils fills much of the abdominal cavity.

The wall of the small intestine is lined with many tiny mucous membrane known as the intestinal villi; it increases the surface area and aid in mixing and in absorption. The intestinal glands are located between the villi. Intestinal glands at the base of the villi secretes large amount of a watery fluid, which brings digestive products into the villi. This fluids has a nearly neutral pH of 6.5- 7.5 and it lacks digestive enzymes.

The small intestine consist of three parts.
i) The duodenum
ii) The jejunum and
iii) The ileum

The duodenum is a C shaped part of the small intestine; it lies posterior to the parietal peritoneum and passes anterior to the right kidney and the upper three lumber vertebrae.

FUNCTION OF THE SMALL INTESTINE

1) The small intestine receives secretion from the pancreas and the liver.
2) Small intestine completes digestion of the nutrients in chyme.
3) It absorbs the products of digestion and transports the residues to the large intestine.

LARGE INTESTINE: The large intestine begins in the lower right side of the abdominal cavity where the ileum joins the cecum. The large intestine proceeds and ascends on the right side, crosses obliquely to the left and then descends into the pelvis. Moreover, at the distal end it opens as the anus on the outside of the body. The large intestine forms and stores feces.

Parts of the large intestine: the large intestine consists of four parts
i) The cecum
ii) Colon
iii) Rectum and
iv) The anal canal

The cecum begins the large intestine, it is a pouchlike structure hanging below the ileocecal opening and projects downward from its narrow tube with a closed end called the vermiform appendix, which does not have any digestive function rather it contains the lymphatic tissue. The colon is divided into four portions, the ascending colon, a transverse colon, descending colon and a sigmoid colon. The rectum lies next to the sacrum and are firmly attached with each other by the peritoneum. The rectum becomes the anal canal below the tip of the coccyx. The canal opens to the outside as the anus, which are guarded by two sphincter muscles, an internal anal sphincter muscle, and an external sphincter muscle.

FUNCTION OF THE LARGE INTESTINE

a) The large intestine has no digestive function
b) It secretes mucus
c) It absorbs water and electrolyte
d) It forms and stores feces.


THE ACCESSORY ORGANS OF THE DIGESTIVE SYSTEM

The accessory organs secretes substances used in the process of digestion into the alimentary canal. The accessary organs are:
a) Salivary gland
b) The liver
c) Gallbladder
d) Pancreas

  • Salivary glands: Salivary glands are glands that secretes saliva. This fluid (saliva) moistens food particles, help bind them together, and begins the chemical digestion of carbohydrates. The major salivary glandes are the parotid, submandibular and the sublingual glands. The parotid glands are the largest and are located anterior and inferior to the both ear. The submandibular glands are located in the floor of the mouth on the inside surface of the lower jaw. In addition, the sublingual glands, which are the smallest of the major salivary glands, are located on the floor of the mouth inferior to the tongue. When an individual sees, tastes or smells food parasympathetic nerve impulse elicit the secretion of the large volume of watery saliva.


LIVER: The liver is a reddish brown organ located in the upper right quadrant of the abdominal cavity, surrounded by the ribs, and well supplied with blood vessels.

FUNCTION OF THE LIVER
1) The liver secretes bile that directly affects digestion
2) The liver metabolizes carbohydrates, lipids, and proteins.
3) It stores some substances; it destroys toxins and filters blood.

GALL BLADDER: The gall bladder is a pear shaped sac located in a depression on the liver's inferior surface. It is lined with epithelial cells and has a strong muscular layer in its wall.

FUNCTION

1) The gall bladder stores bile between meals
2) It releases bile into the small intestine.

PANCREAS:The pancreas is an elongated flattened organ posterior to the stomach. It consist of two major types of secretory tissues, which are the exocrine gland, which secretes digestive juice and endocrine glandes, which releases hormones.
The pancreatic juice contains enzymes that carbohydrates, fats nucleic acids, and protein. The carbohydrates digestive enzymes is pancreatic amylase and the fat digestive enzyme is pancreatic lipase while the protein splitting enzymes are trypsin, chymotrypsin, and carboxypeptidase.

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