DIGESTIVE-SYSTEM ANATOMY

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DIGESTIVE-SYSTEM ANATOMY

This comprises the Mouth, the Pharynx (which we refer to, under the Respiratory System), the ɶsophagus, the stomach, the Small Intestines, the large intestines, the Sigmoid, the Rectum, Liver, Gall-bladder and Pancreas, we take up one by one these items.

The mouth (oris) Its interior is lined by what is a modification of the skin, called mucous membrane. Unlike the skin, it is reddish in colour, studded with secreting glands and it has the power of absorbing things presented to it in solution. We shall learn of glands hereafter.

The Tongue (a muscular organ) Tonsils (glands); Palate (body and mucous-membrane-made) play their part in the digestive action which we will refer to later on. The tongue has specialized nerve-endings in it, which are raised in the form of papilla for the purpose of taste.

The Teeth are classified into

  • 4 Incissors or cutting teeth in each row
  • 2 Canine or piercing teeth
  • 3 Bicuspid or chewing teeth
  • 6 Molar or grinding teeth

They are placed in separate compartments in the jawbone, called sockets. They are richly supplied with blood-vessels and nerves, which run into their very core or pulp. That part of a tooth which is exposed to our view is bright, white and hard; the white coating is called enamel. This when broken or damaged, is never replaced. The part of the tooth which lies embedded in the gum is called its fang or cusp.

A child is born toothless; from the 6th month upto 1½ years the temporary set of milk-teeth erupt—twenty in all. By the age of six years, they all drop off and are replaced by the permanent teeth—thirty-two in all. These drop off in old age. But teeth kept clean ought not to decay.

ɶsophagus or gullet: It is a pipe through which food passes from the mouth into the stomach. As a rule, this pipe always contracts towards stomach. Hence a horse can send up its food and drink, although at the time of eating or drinking, its head is low. That part of the stomach, where the œsophagus joins it, is called the cardiac orifice of the stomach.

The Stomach ventriculus: It is a pear-shaped hollow bag, placed on the left upper side of abdomen, immediately below that part of diaphragm (or the muscular partition between the chest and belly) whereon sits the heart. It communicates with the mouth by means of the œsophagus and it is continuous with the intestines below. The region where the œsophagus enters the stomach is called the cardiac and the orifice, the cardiac orifice. The portion of the stomach which joins the small intestines is called the Pylorus and the orifice, the pyloric orifice. The stomach is covered on its outside by a serous layer, called the peritoneum. The peritoneum is by the way, a large continuous sheet of serous membrane which lines the inside of the abdominal walls, except where viscera are in direct contact, and is reflected on to the viscera. It passes directly over some viscera, binding them to the posterior abdominal wall. The peritoneum also forms ‘folds’ which receive different names, viz. omentum, mesentery or visceral ligaments. The potential, not real, space enclosed between the peritoneal layers is called the peritoneal cavity. It communicates with the lymphatic system.

The stomach has the following three principal systems:

  1. External or Peritoneum coat—Which help to bind it down again with the posterior wall of the abdomen and helps to carry on its lymphatic circulation.
  2. Middle or Muscular coat—Which enable it to contract upon the food-material that may reach inside. The muscles on its walls are so disposed as to enable the bag to contract in the form of a series of succeeding waves, passing in different directions.
  3. Internal or Mucous coat—which secretes.

We shall say here a few words regarding the mucous coat. The mucous coat or mucous membrane is described here in general terms, once for all. This is made up of a single layer of specialized cells and it is non-vascular, that is to say, no blood-vessels lie between their cells; blood vessels in abundance, however come up to their very base. The function of mucous membranes is to secrete ‘juices.’ Cells so modified as to yield, when aggregated, juices or secretions are called gland. We have seen elsewhere what a gland (in anatomical parlance) is—viz., a midway-station for filtering or arresting poisons or foreign bodies circulating in the lymph; these latter glands and naked-eye structures, nodular to the feel, and are generally spoken of as lymphatic glands—a term that explains their anatomy and physiology. But glands, as we understand them in the physiological sense of the term, are secreting structures. Any collection of specialized cells possessing the power to secrete fluids special to them, is called a gland. Thus, tear gland secretes tear; sweat-glands secrete sweat; testicular glands secrete semen and so on. While it is a fact that secreting glands (or, glands in the physiological sense of the term) are to be found chiefly on mucous surfaces, it will be wrong to assume that every bit of all mucous surfaces is made up of, or is studded with, such glands. In fact, glands are not so ubiquitous. Glands occur here and there on mucous or other specialized surfaces and are formed by certain groups of specialized cells dipping down into their substance. Glands are richly applied with blood-vessels, nerves and lymphatics. A secreting gland is a microscopic structure and it possesses a body, a neck or pipe or duct and an opening or mouth on the surface. Mucous membrane or mucous surface is such a lining as is studded with glands secreting an alkaline, lubricating sticky fluid, called mucus.

We shall now return to the consideration of stomach again. We have said that its interior is lined by a mucous membrane. While the stomach is empty, its mucous membrane is thrown into folds called ruge. While the greater portion of the mucous membrane secretes mucus to keep the inside of the stomach moist, portion of it are studded with secreting glands—that secrete pepsin and hydrochloric acid. Such glands are called peptic glands.

Intestines These are divided into the following portions—

  • Small intestines
    • Duodenum—10 inches long.
    • Jejunum-8 feet long.
    • Ileum—12 feet long
  • Large intestines
    • Caecum-2½ inches long.
    • Vermiform Appendix-3½ inches long.
    • Ascending Colon-6 inches long
    • Transverse Colon-20 inches long
    • Descending Colon-4 inches long
  • Pelvic colon
    • Pelvic colon (sigmoid)-4 inches long.
    • Rectum-5 inches long
    • Anus-1½ inches long.

Duodenum is the first part of the small intestines; it commences where the pyloric end of stomach terminates. It is arranged like the letter ‘c’ enclosing inside its curvature the head of the pancreas. Into it opens the common duct from gall-bladder and pancreas, called ductus communis choledochous.

Jejunum and Ileum are the middle and terminal parts respectively of the small intestines, it is difficult to say from freely movable cells, found in all part of the abdomen.

Like the stomach the small intestines possess (a) an external serous or peritoneal coat, two muscular coats, and (b) an inner mucous coat. The inner lining of the stomach is thrown into folds called rugae; the inner lining of the small intestines is thrown into permanent crescentic, circular and spiral folds, called valvuloe conniventes (or plicoe circular vel semilunares). They are thickly covered with minute projections called Villi, which give them a velvety appearance. Nodules of lymph tissue, called solitary glands, are scattered throughout the small intestines and aggravations of them are called Peyer’s patches.

Large Intestines: These begin in the right lower part of abdomen called (iliac region) as a blind head, called intestinal coecum, with which the useless appendage called vermiform appendix is connected. The ileum opens into the caecum and the opening is guarded by a valve, the colic valve. The colon is divided into three parts. The ascending colon proceeds upwards to under-surface of liver; thence it proceeds transversely (under the name of transverse colon) across the upper abdomen to under-surface of spleen; from here it bends downwards as the descending colon; its lowermost parts being called respectively iliac and pelvic colons. The points where the colon bends are called its flexures. The Vermiform Appendix is about 3½ inches long and it opens into the coecum, below the ileo-caecal orifice. It is a blind tube, the function of which is unknown.

The large intestines are distinguished from the small intestines by (a) its possessing appendices epiploicoe, i.e., pouch-like fatty projections of the peritoneum occurring on external surface of large intestines; (b) its having toenioe coli (for tape-like band) along the middle of the colon on its external surface; (c) its possessing sacculation (or pouchlike folds); and (d) by absence of vulvae conniventes and villi.

Regarding their structure, the large intestines have an intestinal mucous coat.

Liver: This is the largest gland (in the physiological sense) in the human body, weighing nearly 50 ounces. It lies immediately underneath the diaphragm, in the right upper part of the abdomen. In health, we can just feel its margin. It is divided, broadly speaking, into a right lobe and a left lobe, of which the right lobe forms the largest bulk. The hepatic artery and portal vein convey blood to the liver and the hepatic veins remove it. In connection with the liver, two things require attention (1) the Gall-bladder and (2) the Portal vein. Here we describe their organic constriction. Portal vein is formed by the union of the veins of pancreas, spleen, stomach and small intestines. It enters the under-surface of liver in two branches—one for each lobe. Inside the liver, it breaks up and ends in capillaries common to them and to branches of hepatic artery. Hepatic veins arise from these capillaries and carry blood to vena- cava inferior. The Gall-bladder is a pear-shaped hollow bag, lying on the under-surface of the liver, beyond whose margins its fundus or bigger end slightly projects. Its upper end or neck forms the systic duct, which runs backwards and medially and joints the hepatic duct to form the bile duct or ductus- choledochous.

Pancreas or Sweet-bread is an elongated gland, lying obliquely across the upper part of the posterior abdominal wall. It has a head, a neck, body and a tail. It possesses a duct, the Pancreatic Duct.

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