Changes that occur in the alimentary canal

CHANGES THAT OCCUR IN THE ALIMENTARY CANAL

By: James Gerache

Mouth

The mouth is the beginning of the alimentary canal, it mechanically breaks down food and mixes it with saliva (1)

The mouth is made up of the tongue, palate, teeth, and salivary glands.

The tongue is composed of two parts:1. Body- made up of skeletal muscle fibers, and has a rough

surface which is composed of papillae or taste buds2. Root- attached to the hyoid bone, covered with lingual

tonsils(1) The palate is divided into 2 regions:

1. Hard palate- forms the roof of the mouth, and consist of stratified squamous epithelium tissue.

2. Soft palate- extends posteriorly to form the uvula, consist of stratified squamous epithelium tissue. (2)

Mouth cont.

Teeth are composed of a calcified material known as enamel.(2)

There are 4 types of teeth: 8 incisors, 4 canine, 8 premolars, and 12 molars. (1)

Salivary glands are scattered throughout the oral cavity. The glands are connected to the oral cavity by a system of ducts.(2)

Salivary glands are made up of two types of cells:

1. Serous glands- secrete salivary amylase a digestive enzyme

2. Mucous glands- secrete mucus for lubrication

Esophagus

The esophagus is a straight tube that begins at the base of the laryngopharynx and ends at the stomach. (1)

The esophagus has only one main function, which is to carry food, liquids, and salvia from the mouth to the stomach.(3)

The inner most lining of the esophagus is composed of stratified squamous epithelium for protection and at the base of this layer lies cuboidal epithelium for mitosis. (3)

To move food down the esophagus is done by peristalsis, this is done by muscle contractions around the esophagus to push the food to the stomach.(1,3)

Esophagus pictures

ESOPHAGEAL EPITHELIUM-10X MAG

ESOPHAGEAL EPITHELIUM- 4X MAG

Stomach The stomach’s main function is to receive ingesta

and to change them in such a way that they can be received by the small intestine. (4)

They stomach is split into 4 main compartments:1. fundus- balloons above the cardia, acts as short

term storage area, contains fundic glands that produce hydrochloric acid. (1,4)

2. Cardiac- small portion near the esophageal opening, it helps eliminate reflux of stomach content back into the esophagus. (5)

3. Body- main part of the stomach, aids in mechanically breaking down food by tonus and peristalsis, also contains fundic glands to chemically break down food. Mixes the food with gastric juices by tonus & peristalisis(1,4)

Stomach cont.4. Pyloric- separated into 2 portions: 1) the antrum- contains pyloric glands that produce juices that are alkaline and highly viscous. 2) canal- composed of circular muscle fibers that grind the chyme. (4)

The lining of the stomach is composed of 4 layers: the mucosa, the submucosa, muscular coat, & the serosa.(4)

The mucosa is the inner most lining of the stomach and is made up of columnar epithelium, mucous cells, chief cells, & parietal cells. The mucous, chief, and parietal cells release gastric juices.

The submucosa is composed of loose connective tissue and elastic tissue fibers, permits the mucosa to move freely with changes in contractility & tonus.(4)

The muscular coat is composed of smooth muscle to grind food.(4)

The serosa is composed entirely of peritoneum. (4)

Stomach: Cardiac Region- 40xmag.

Small intestine

The small intestine receives secretions from the pancreas and liver to aid in the digestion of nutrients and chyme, and also absorbs the products of digestion. (1)

The small intestine is composed of 3 segments:

1. Duodenum- shortest, widest, and most fixed part of the small intestine. (6)

2. Jejunum- 8- 10ft. In length, the diameter is greater than the Ileum.

3. Ileum- last segment of the small intestine, the walls are thinner & less vascular

Small intestine cont.

The inner lining of the walls of the small intestine are made up of circular folds called plicae circulares. These folds start about 1-2 in. past the pylorus and end in the lower ileum increasing the surface area for absorbtion.(6)

The inner lining also has finger like projections called intesinal villus. The villi are composed of a single layer of simple columnar epithelium. The epithelial cells have microvilli that project outward and increase the surface area by 24-fold. (1,6)

In the microvilli, digestive enzymes are embedded on the surface that helps break down any food molecules before absorption. (1,6,7)

Small intestine pictures

ILEUM- 10 X MAG ILEUM- 40X MAG.

Duodenum- 10 x mag.

Colon

The principal function of the colon is that of solidification of chyme and the storage and evacuation of waste. (1,7)

The colon can be split into two separate portions based on their function.

1. The right portion-which is composed of the cecum and the ascending colon has an absorptive function. (7)

a) the ascending colon mainly absorbs water and salt that the small intestine missed. (7)

2. The left portion- is composed of the transverse and descending colon and its main function is storage and evacuation of waste.

Colon cont.

The walls of the colon have the same tissue make up as other parts of the alimentary canal, which is the simple columnar epithelium. (1,7)

The columnar epithelium holds an abundant of goblet cells that secrete mucus for lubrication and the epithelium lacks the villi and microvilli due to not much absorption is done in the colon. (7)

Colon pictures

COLON- 10X MAG HUMAN COLON- 40X MAG

Anus

The anal canal is composed of the last 2.5-4 cm of the large intestine. (1)

Within the lining of the anal canal is the transition from the columnar epithelium so the intestine to the stratified squamous epithelium of the skin. (7)

At the distal end of the anal canal lies the anus, which is enclosed by two sphincter muscles: the internal and external sphincter. (7).

The internal sphincter is a continuation of the circular smooth muscle of the rectum which has involuntary control, and the external sphincter forms a collar around the anal canal which has voluntary control.(1,7)

Bibliography

1. 1) Shier, D., Butler, J.B., and R. Lewis. (2012). Hole’s Human Anatomy and Physiology. 13th Edition. McGraw-Hill Inc. Boston, MA.

2. Provenza, Dr. Vincent, and Werner Seibal. Oral Histology. Philadelphia, PA: Lea and Febiger, 1986

3. http://bio.rutgers.edu/~gb102/lab_9/904cm-esophagus.html 4. Bockus, Henry L. M.D.. Gastroenterology, vol. 1.

Philadelphia, P.A.: W.B. Saunders Company, 1963. 5. http://

alysculhane.com/horse_care/Vet_Anatomy_Physiology/digestive_system.htm

6. Sheehy, Thomas W. M.D., and Martin H. Floch M.D. The Small Intestine. Harper and Row, 1964.

7. Bockus, Henry L. M.D.. Gastroenterology, vol. 2. Philadelphia, P.A.: W.B. Saunders Company, 1963.