Life Sciences Glossary: Pharynx, Oesophagus, Stomach and Small Intestine

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Pharynx

Pharynx is a common passage in swallowing food and breathing. Glottis is the structure which allows air to enter into trachea. Epiglottis is the structure which prevents entry of food into windpipe during swallowing in mammals.

Oesophagus

Oesophagus is a long tube connecting pharynx to stomach. Oesophagus is involved in deglutition (swallowing) . In man, Oesophagus is about 10 inches long and does not secrete any digestive enzyme. Oesophagus secretes mucus and transport food to the stomach.

Stomach

Stomach is the most dilated part of alimentary canal. Food is stored in the stomach; mixed with acid, mucus, and pepsin; and released at a controlled, steady rate into the duodenum.

In mammals, it is divided into three regions:

  • Cardiac stomach-Anterior
  • Pyloric stomach- Posterior
  • Fundic stomach- Middle Stomach secretes gastric juice and HCI.

Gastric glands are of three types of cells.

  • Mucous cells- Secreting mucus
  • Chief or peptic or zymogen cells – Secreting pepsinogen and prorennin.
  • Oxyntic cells or parietal cells-Secreting HCI.

Intestine

  • The intestine is 22 feet long in man because such a length increases the scope of food absorption. The wall of investing is provided with only involuntary muscles.
  • The intestine is divisible into small intestine (proximal duodenum, middle jejunum and distal ileum and large intestine (caecum, colon and rectum) .

Small Intestine

  • The small intestine begins at the pyloric valve of the stomach. Duodenum is the smallest first part following the pyloric end of stomach. Duodenum forms the typical U-shaped loop containing the pancreas. In man, there is a common opening of bile duct and pancreatic duct opening in duodenum. The wall of duodenum contains intestinal glands (crypts of Lieberkuhn) and characteristic duodenal glands or Brunner՚s glands which produces alkaline mucus.
  • Behind the duodenum is jejunum, followed by ileum. Their internal lining is raised into innumerable minute finger-like processes called villi. In between the villi, the mucous membrane of small intestine is folded forming intestinal glands or crypts of Lieberkuhn. The intestinal juice or success entercus is secreted by crypts of Lieberkuhn. Intestine villi are more numerous and larger in the posterior part of small intestine than in anterior part because there is more digested food in the posterior part. Intestinal villi are mainly concerned with absorption. Villi are absent in stomach. The absorption of digested food mainly occurs in small intestine. Maximum absorption takes places in ileum. In the wall of small intestine, lymphatic tissues are present called payer՚s patches.

Large Intestine

  • Large intestine is much shorter and wider than the small investing. Large intestine of man is about 5 feet in length and average 2.5 inches in diameter. It has three parts: caecum, colon and rectum. Distally caecum terminates in a small, narrow, thick walled tube vermiform appendix. Inflammation of the vermiform appendix is called appendicitis.
  • Colon is thicker than small intestine and thinner than caecum. The colon of man is divided into ascending, transverse, descending and pelvic (sigmoid) portions. The pelvic colon continues into rectum. The rectum is the last part of alimentary canal, in man it is about 7 - 8 inches long. The terminal 1 inch of rectum is called anal canal and its exterior opening is called the anus.
  • The large intestine serves to store unabsorbed food remnants temporarily. The large intestine secretes no enzymes and plays only a minor role in the absorption of nutrients.

Digestive Glands and Their Functions

Salivary Glands

  • In the salivary glands, the secretary (zymogen) granules containing the salivary enzymes are discharged from the acinar cells into the ducts. About 1500 ml of saliva are secreted per day. The pH of saliva from resting glands is slightly less than 7.0, but during active secretion, it approaches 8.0. Saliva contains 2 digestive-enzymes: lingual lipase, secreted by glands on the tongue, and ptyalin (salivary amylase) , secreted by the salivary glands.
  • In man, 3 pairs of salivary glands are present. They pour salivary juices in the mouth. The process of digestion starts in mouth in presence of these juices.

The salivary glands of man are given below:

The Salivary Glands of Man Are Given Below
NameLocation
1. Sublingual (smallest)Beneath tongue
2. Parotid (largest)Beneath ears
3. Submaxillary (Submandibular)Jaw angles

Saliva performs a number of important functions. It facilitates swallowing, keeps the month moist, serves as a solvent for the molecules that stimulate the taste buds, aids speech by facilitating movements of the lips and tongue, and keeps the mouth and teeth clean. The saliva may also have some antibacterial action, and patients with deficient salivation (xerostomia) have a higher than normal incidence of dental caries. The buffers in saliva help maintain the oral pH at about 7.0. They also help neutralize gastric juice regurgitated into the Oesophagus.

Mumps

Is a viral disease by paramyxovirus causing painful inflammation of parotid glands?

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