Term
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Definition
| (also called the gastrointestinal tract, or alimentary canal); includes the mouth, pharynx, esophagus, stomach, small intestine and large intestine |
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Term
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Definition
| include the teeth, tongue, salivary glands, pancreas, liver, and gallbladder |
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Term
| Four categories of activity |
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Definition
Motility - movements of various parts of the digestive tract
Secretion - secretion into the digestive tract of various diestive juices and mucus
Digestion - the process of breaking up larger molecules into smaller ones
Absorption - the process whereby the products of digestion are transferred to the blood or lymph, for distribution to the cells of the body. |
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Term
| Saliva contains the following |
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Definition
- Calcium and phosphate, which prevent the enamel from the dissolving.
-Lysoyme, which destroys bacterial coats.
-A variety of antibacterial, antiviral, and antifungal peptides.
-Immunoglobulin A
-Amylase, an enzyme that carries out the preliminary digestion of polysaccharides; maltose is the is the major end product
-Mucin, a constituent mucus |
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Term
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Definition
a) food first enters the gastrointestinal tract via the mouth.
b) With the assistance of the teeth and tongue, it grinds it up and mixes it with saliva secreted into it by the salivary glands. THe process is called mastication.
c) Some preliminary digestion of carbohydrates occurs in the mouth, as a result of the action of the enzyme salivary amylase.
d) it is involved in swallowing. |
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Term
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Definition
| THe mouth is enclosed by the lips, cheeks, hard and soft palates, gums (gingivae), part of the tongue, and the mucous membrane that connects the sides and inferior (under) surface of the tongue to the gum on the inner surface o fhte mandible. The mouth also contains teeth. |
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Term
| The palate, or roof of the mouth, consists of the following |
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Definition
a) the hard palate, which is covered with keratinized, stratified squamos epithelium, and is formed from the palatine processes of the maxillae and the horizontal plates of the palatine bones. The upper part of the hard palate is the floor th nasal cavity.
b) The soft palate is a movable flap of tissue attached to the posterior border of the hard plate, Its posterior border hangs freely between the mouth and the pharynx. A median conical projection fro this posterior border is called uvula (you can easily see the uvula if you look into the mirror with your wide open) |
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Term
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Definition
| THe essential function of the pharynx in the digestive system is in swallowing |
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Term
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Definition
The pharynx has been described as a musculomembranous tube. It is lined with a mucous membrane, which is continuous wit the auditory tubes, nasal cavity, mouth, and larynx.
THe phary has a complicated striated muscle coat consisting of three constrictor muscles that pull the wall inwards during swallowing, acting partly like sphincters, and partly to promote peristaltic actions. THe contraction of the lower pharyngeal constrictor is coupled with relaxation of the cricopharyngeal muscle. THere are also other muscles that serve to control the pharynx and palate during swallowing and speech |
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Term
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Definition
the nasopharynx is behind the nose and above the soft palate. Air from the nasal cavity enters it through two posterior nasal apertures. The nasopharynx joins the oropharynx at a point called the pharyngeal isthmus, which is closed during swallowing, partly as a result of elevation of the soft palate.
THe phary ngeal tonsil (sometimes called the adenoid) is found in the roof and posterior wall of the nasopharynx. THis is a mass of lymphoid tissue that increases in size up to about 7 year of age, then usually begins to atrophy. |
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Term
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Definition
The oropharynx opens from the mouth, and runs from the soft plate to the epiglottis. It connects with the nasopharynx at the pharyngeal isthumus, which is closed when swallowing, so insuring that food and or drink do not go up into the nose.
The oropharynx contains the palatine tonsils, two masses of lymphoid tissue in its lateral walls. THese tonsils are variable in size and often get infected. |
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Term
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Definition
| THe laryngopharynx runs from the upper border of the epiglottis to the lower border of the cricoid cartilage, whire it becomes continuous with the esophagus. During swallowing, the larynx closes by contraction of the aryepiglottic folds. |
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Term
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Definition
| THe tonsils are components of the mucosa-associated lymphoid tissues (MALT). THey are not really part of the digestive system, but they play an important role in defending it against microbial intruders. All the tonsils make up a ring of lympoid tussue (Waldeyer’s ring) that guards the trachea and esophagus against invasion of infectious organanisms entering our bodies from the nose and mouth. THe ring of lymphoid tissues often becomes, infected, inflamed, and parts of it may increase in size as a result. In young children, increase in size of the lymphoid tissue found in the nose and nasopharynx, may interfere with respiration through the nose. |
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Term
| Weldeyer’s ring of lymphoid tissue consist of the following four components: |
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Definition
- Lingual tonsils: lymphoid nodules in the submucosa of the root of the tongue
- Platine tonsils (in the oropharynx)
- Pharyngeal tonsil (sometimes called the adenoid)
- Other lylmphoid masses between these major goups |
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Term
| Esophagus, function and anatomy |
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Definition
Function- helps in swallowing, connects the pharynx to the stomach
Anatomy - the esophagus is a 10-inch long, thick muscular tube lined with mucous membrane that passes behind the trachea, and connects the pharynx to the stomach. THe upper two-thirds of the esophagus contains skeletal (voluntary) muscle,but this gives way to smooth (invontary) muscle in the lower one-third. THere is a muscular mechanism (the lower esophageal sphincter) that prevents the stomach contents from being regurgitated into the esophagus. |
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Term
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Definition
a) to keep food until it is put into the duodenum
b) to mix food with gastric juice so that it forms a half-fluid mixture called chyme
c) to empty this chyme in little squirts into the small intestine
d) to start protein digestion |
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Term
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Definition
The stomach is essentially a bag with many folds (rugae) when it is empty. When the stomach is full, these folds disappear.
THree main regions can be distinguished. THese are the fundus, the body, and the antrum. THe plyoric end of the antrum empties into the duodenum o fthe small intestine.
THe cardiac orifice is where the esophagues opens into the stomach, and the pyloric orifice is where the stomach opens into the duodenum of the small intestine.
Circular arrangements of muscle fibers constitute the pyloric sphincter, controlling the exit of food out of the stomach and into the duodenum. A cardiac sphincter is sometimes described, and is assumed to control entry of food from the esophagus into the stomach. |
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Term
| The mucosa and epithelium of the stomach |
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Definition
TH emucosa of the stomach is thick, velvety and reddish-brown in color. its surface is pitted with the entrances to the gastric glands. the whole surface is convered with a columnar epithelium that secretes a thick and protective mucus
This epithelium is continually being renewed. THe older cells die by apoptosis, slough off into the lumen of the stomach, and new cells take their place. This renewal is fueled y multipotent stem cells. HTe turnover time is about 2-4 days, one of the fastest in the body. |
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Term
| Secretions of the stomach: Chief (peptic) cells - exocrine |
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Definition
| These cells secrete pepsinogen, the inactive precursor of the enzyme pepsin. HT econversion of pepsinogen to pepsin is facilitated by hydrocloric acid. Pepsin starts the breakdown of proteins. Therefore, it is called a proteolytic enzyme, or a protease. however, there are so many proteases in pancreatic juice, that pepsin is not indispensable to the process of protein digestion. |
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Term
| Secretions of the stomach: Paretal (oxyntic) cells - exocrine |
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Definition
Hydrocholoric acid
the main function of hydrochloric acid is that it activates the conversion of pepsinogen to pepsin, and it creates the highly acid enviroment (pH 1.0 or less) so that pepsin activity is optimal. Another function is that it denatures proteins, rendering them more susceptible to digestion by pepsin, and it also kills ingested bacteria (with the exception of Helicobacter pylori).
Ants dont secrete hydrochloric acid into their stomachs, instead they have formic acid. |
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| Secretions of the stomach: Parietal (oxyntic) cells - exocrine |
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Definition
intrinsic factor
a glycoprotein that binds to free vitamin B_12 (cyanocobalamin), the anti-pernicious anemia factor essential for normal erythropoiesis. Instrinsic factor is essential for the absorption of vitamin B_12 int he small intestine (actually, the the distal ileum). Gastrectomized individuals require monthly injections of vitamin B_12 to avoid pernicious anemia. |
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Term
| Secretions of the stomach: Globlet cells |
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Definition
Secrete viscid mucus, which coats the interior of the stomach with a thick layer. THis mucus layer serves to:
-lubricate
-form a layer that protects the gastric lining from the combined actions stomach acid and pepsin, so preventing the stomach from digesting itself. Part of the protective action is because the mucus traps the alkaline bicarbonate secreted by the epithelial cells |
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Term
| Secretions of the stomach: Epitheliacells and G-cells |
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Definition
Epithelial cells - secrete alkaline bicarbonate into the mucus layer, where it is trapped. THis may assist in protecting the gastric lining form the action of the acid.
G-cells (endocrine) - secrete the hormone gastrin |
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Term
| Small Intestine: Function |
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Definition
| The function of the small intestine is to absorb th eproducts of digestion of the various food stuffs eaten. Digestion also takes place in the small intestine, partly by enzymes in the pancreatic juice, partly by enzymes in the cells that line the small intestine. |
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Term
| Small Intestine - Anatomy |
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Definition
Ducts conveying pancreatic juice and bile open into the small intestine. The pancreatic juice is central to the digestive process, because it contains nearly all the enzymes needed for digesting carbohydrates, proteins, and fats. THe small intestine is divided into three segments.
a) Duodenum - a fixed, short, curved tube about 12 inches in length. THe duodenum contains duodenal glands of Brunner. THey have an alkaline, mucus secretion that helps to neutralize the acidity of the stomach fluid as it enters the duodenum. THese glands may secrete a trypsinogen-activating factor.
b) Jejunum - coiled tube two thirds of the length of the ileum
c) Ileum |
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Term
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Definition
| The small intesitne plays a very important role in aboroption of the products of digestion. Because of this, its inner surface covered by numerous intestinal villi, which give it a velvety texture. THey serve to increase the surface are of the of the small intestines, so increasing the effectiveness for absorption of the products of digestion. In fact, its available absoroptive surface is 300 times larger than an equivalent area of flat surface. |
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Term
| Epithelium covering the intestinal villi |
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Definition
| the intestinal villi are covered with a layer of simple columnar epithelium interspersed with mucus-secreting goblet cells. THe epithelium funtion both in digestion and absorption. THe surfaces of the epithelial cells, which are sometimes called enterocytes, consist of varety striking and regular arrangement of microvilli (distinguish these form the intestinal villi). Because of their appearance undr the microscope, the microvilli are said to form a brush border. |
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Term
| The brush has two important activities |
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Definition
- THe brush border is involved in absoroption of digested food molecules.
- THe brush border is rich in a variety of digestive enzymes that function to break up digested food molecules (eg peptides) into even smaller molecules (eg amino acids) once they have been absorbed into the brush border. NOte that these enzymes are NOT secreted. Digestion within the lumen of the small intesitne is carried out by enzymes in the pancreatic juice. |
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Term
| THe center of the intestinal villi |
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Definition
| consists of a nutrient arteriole supplying a capillary bed which empties into a venule. In the center of the villus is a blind-ended lymphatic channel called a lacteal. It gests its name form Lact-(milk). because the lymph in it becomes milky during fat digestion. |
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Term
Exocrine secretion of the small intestine
Paneth cells |
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Definition
| Between th eintestinal villi are small pores, representing the openings of tubular intestinal glands (crypts of Lieberkuhn). These glands secrete fluid. This fluid contrains antimicrobial proteins called defensins, lysozyme, phospolipase A2 secreted by cells called Paneth cells, which are found only at the bottom of the crypts of Lieberkuhn. THe Paneth cells keep the crypts sterile, and are important in defending against invasion of the epithelium by various pathogens. THe defensins are particularly important for survival. Mice that have been genetically engineered so that they do not produce active defensins succumb readily to infection with E.coli and Salmanella. Additionally, Paneth cells contain large amounts of zinc, which happens to be a cofactor for several of the proteases found in pancreatic juice. The fluid secreted by the crypts of Lieerkuhn does not contain any digestive enzymes. Digestion in the small intesine is largely the result of the enzymes in pancreatic juice, enzymes of the brush border, and intracellular peptidases. |
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Term
| Endocrine secretions of the small intestine |
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Definition
Cells lining various region of the small intestine secrete dmany hormones. THere are three main hormones that act on the stomach, pancreas, the gallbladder, and the bile duct.
a) Cholecystokinin (CCK) - Actually, the term “chlecystokinin” refers to a goup of peptides. Some are found in the gut, but at least one type of cholecystokinin is found in the brain
b) Secretin
c) Gastric inhibitory peptide (GIP) - Somatostatin is a hormone that mediates the action of GIP. |
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Term
| Stem cells in the small intestine |
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Definition
| At the base region of the cyrypts of Lieberkuh, just above the Pneth cells, there is a niche that contains a population of stem cells that generate new cells for the rapid and continual renewal of the intestinal epithelium. |
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Term
| Function of Large intestine |
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Definition
| in mainly to absorb fluid and salts (electrolytes). The function is important is important. THe average daily volume of water secreted into the gastrointestinal tract amounts to roughly seven liters! Most of this is absorbed in the large intestine, and only about 100 ml are lost via the feces. Various pathogens (cholera) can impair water reabsorption in the large intestine, and the rusult is diarrhoea |
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Term
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Definition
The large intestine extends from the distal end of the ileum of the small intestine to the anus. It is about 4 feet long. THere are no villi, as found in the small intestine. But in many areas the muncosa is incaginated to form numerous crypts. It is likely that colorectal cancer arise from the uncontrolled proliferation of these stem cells.
The epithelial cells bear many microvilli, appropriate for their function in absorbing fluid electrolytes.
- Caecum, which leads to the vermiform appendix and the colon
- Colon (ascending, transverse, descending, sigmoid)
- Rectum
- Anal canal |
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Term
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Definition
is a sphincter that controls the one-way passage of the contents of the small intestine into the large intesitine, and prevents the contents of the large intestine moving backwards into the small intestine.
THe internal and external sphincters of the anus are involved defecation. |
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Term
| Secretions of the Large intestine |
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Definition
| THe major secretory product is an alkaline mucus, produced by the numerous goblet cells that are found in the epithelium o fhte mucous membrane lining the large intestine. THis mucus protects the mucosa of the large intestine from chemical and mechanical damage. |
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